Btrfs: fix deadlock running delayed iputs at transaction commit time

[karo-tx-linux.git] / fs / btrfs / extent-tree.c

/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */
#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/sort.h>
#include <linux/rcupdate.h>
#include <linux/kthread.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include <linux/percpu_counter.h>
#include "hash.h"
#include "tree-log.h"
#include "disk-io.h"
#include "print-tree.h"
#include "volumes.h"
#include "raid56.h"
#include "locking.h"
#include "free-space-cache.h"
#include "math.h"
#include "sysfs.h"
#include "qgroup.h"

#undef SCRAMBLE_DELAYED_REFS

/*
 * control flags for do_chunk_alloc's force field
 * CHUNK_ALLOC_NO_FORCE means to only allocate a chunk
 * if we really need one.
 *
 * CHUNK_ALLOC_LIMITED means to only try and allocate one
 * if we have very few chunks already allocated.  This is
 * used as part of the clustering code to help make sure
 * we have a good pool of storage to cluster in, without
 * filling the FS with empty chunks
 *
 * CHUNK_ALLOC_FORCE means it must try to allocate one
 *
 */
enum {
        CHUNK_ALLOC_NO_FORCE = 0,
        CHUNK_ALLOC_LIMITED = 1,
        CHUNK_ALLOC_FORCE = 2,
};

/*
 * Control how reservations are dealt with.
 *
 * RESERVE_FREE - freeing a reservation.
 * RESERVE_ALLOC - allocating space and we need to update bytes_may_use for
 *   ENOSPC accounting
 * RESERVE_ALLOC_NO_ACCOUNT - allocating space and we should not update
 *   bytes_may_use as the ENOSPC accounting is done elsewhere
 */
enum {
        RESERVE_FREE = 0,
        RESERVE_ALLOC = 1,
        RESERVE_ALLOC_NO_ACCOUNT = 2,
};

static int update_block_group(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root, u64 bytenr,
                              u64 num_bytes, int alloc);
static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                struct btrfs_delayed_ref_node *node, u64 parent,
                                u64 root_objectid, u64 owner_objectid,
                                u64 owner_offset, int refs_to_drop,
                                struct btrfs_delayed_extent_op *extra_op);
static void __run_delayed_extent_op(struct btrfs_delayed_extent_op *extent_op,
                                    struct extent_buffer *leaf,
                                    struct btrfs_extent_item *ei);
static int alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root,
                                      u64 parent, u64 root_objectid,
                                      u64 flags, u64 owner, u64 offset,
                                      struct btrfs_key *ins, int ref_mod);
static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
                                     struct btrfs_root *root,
                                     u64 parent, u64 root_objectid,
                                     u64 flags, struct btrfs_disk_key *key,
                                     int level, struct btrfs_key *ins);
static int do_chunk_alloc(struct btrfs_trans_handle *trans,
                          struct btrfs_root *extent_root, u64 flags,
                          int force);
static int find_next_key(struct btrfs_path *path, int level,
                         struct btrfs_key *key);
static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
                            int dump_block_groups);
static int btrfs_update_reserved_bytes(struct btrfs_block_group_cache *cache,
                                       u64 num_bytes, int reserve,
                                       int delalloc);
static int block_rsv_use_bytes(struct btrfs_block_rsv *block_rsv,
                               u64 num_bytes);
int btrfs_pin_extent(struct btrfs_root *root,
                     u64 bytenr, u64 num_bytes, int reserved);

static noinline int
block_group_cache_done(struct btrfs_block_group_cache *cache)
{
        smp_mb();
        return cache->cached == BTRFS_CACHE_FINISHED ||
                cache->cached == BTRFS_CACHE_ERROR;
}

static int block_group_bits(struct btrfs_block_group_cache *cache, u64 bits)
{
        return (cache->flags & bits) == bits;
}

void btrfs_get_block_group(struct btrfs_block_group_cache *cache)
{
        atomic_inc(&cache->count);
}

void btrfs_put_block_group(struct btrfs_block_group_cache *cache)
{
        if (atomic_dec_and_test(&cache->count)) {
                WARN_ON(cache->pinned > 0);
                WARN_ON(cache->reserved > 0);
                kfree(cache->free_space_ctl);
                kfree(cache);
        }
}

/*
 * this adds the block group to the fs_info rb tree for the block group
 * cache
 */
static int btrfs_add_block_group_cache(struct btrfs_fs_info *info,
                                struct btrfs_block_group_cache *block_group)
{
        struct rb_node **p;
        struct rb_node *parent = NULL;
        struct btrfs_block_group_cache *cache;

        spin_lock(&info->block_group_cache_lock);
        p = &info->block_group_cache_tree.rb_node;

        while (*p) {
                parent = *p;
                cache = rb_entry(parent, struct btrfs_block_group_cache,
                                 cache_node);
                if (block_group->key.objectid < cache->key.objectid) {
                        p = &(*p)->rb_left;
                } else if (block_group->key.objectid > cache->key.objectid) {
                        p = &(*p)->rb_right;
                } else {
                        spin_unlock(&info->block_group_cache_lock);
                        return -EEXIST;
                }
        }

        rb_link_node(&block_group->cache_node, parent, p);
        rb_insert_color(&block_group->cache_node,
                        &info->block_group_cache_tree);

        if (info->first_logical_byte > block_group->key.objectid)
                info->first_logical_byte = block_group->key.objectid;

        spin_unlock(&info->block_group_cache_lock);

        return 0;
}

/*
 * This will return the block group at or after bytenr if contains is 0, else
 * it will return the block group that contains the bytenr
 */
static struct btrfs_block_group_cache *
block_group_cache_tree_search(struct btrfs_fs_info *info, u64 bytenr,
                              int contains)
{
        struct btrfs_block_group_cache *cache, *ret = NULL;
        struct rb_node *n;
        u64 end, start;

        spin_lock(&info->block_group_cache_lock);
        n = info->block_group_cache_tree.rb_node;

        while (n) {
                cache = rb_entry(n, struct btrfs_block_group_cache,
                                 cache_node);
                end = cache->key.objectid + cache->key.offset - 1;
                start = cache->key.objectid;

                if (bytenr < start) {
                        if (!contains && (!ret || start < ret->key.objectid))
                                ret = cache;
                        n = n->rb_left;
                } else if (bytenr > start) {
                        if (contains && bytenr <= end) {
                                ret = cache;
                                break;
                        }
                        n = n->rb_right;
                } else {
                        ret = cache;
                        break;
                }
        }
        if (ret) {
                btrfs_get_block_group(ret);
                if (bytenr == 0 && info->first_logical_byte > ret->key.objectid)
                        info->first_logical_byte = ret->key.objectid;
        }
        spin_unlock(&info->block_group_cache_lock);

        return ret;
}

static int add_excluded_extent(struct btrfs_root *root,
                               u64 start, u64 num_bytes)
{
        u64 end = start + num_bytes - 1;
        set_extent_bits(&root->fs_info->freed_extents[0],
                        start, end, EXTENT_UPTODATE, GFP_NOFS);
        set_extent_bits(&root->fs_info->freed_extents[1],
                        start, end, EXTENT_UPTODATE, GFP_NOFS);
        return 0;
}

static void free_excluded_extents(struct btrfs_root *root,
                                  struct btrfs_block_group_cache *cache)
{
        u64 start, end;

        start = cache->key.objectid;
        end = start + cache->key.offset - 1;

        clear_extent_bits(&root->fs_info->freed_extents[0],
                          start, end, EXTENT_UPTODATE, GFP_NOFS);
        clear_extent_bits(&root->fs_info->freed_extents[1],
                          start, end, EXTENT_UPTODATE, GFP_NOFS);
}

static int exclude_super_stripes(struct btrfs_root *root,
                                 struct btrfs_block_group_cache *cache)
{
        u64 bytenr;
        u64 *logical;
        int stripe_len;
        int i, nr, ret;

        if (cache->key.objectid < BTRFS_SUPER_INFO_OFFSET) {
                stripe_len = BTRFS_SUPER_INFO_OFFSET - cache->key.objectid;
                cache->bytes_super += stripe_len;
                ret = add_excluded_extent(root, cache->key.objectid,
                                          stripe_len);
                if (ret)
                        return ret;
        }

        for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
                bytenr = btrfs_sb_offset(i);
                ret = btrfs_rmap_block(&root->fs_info->mapping_tree,
                                       cache->key.objectid, bytenr,
                                       0, &logical, &nr, &stripe_len);
                if (ret)
                        return ret;

                while (nr--) {
                        u64 start, len;

                        if (logical[nr] > cache->key.objectid +
                            cache->key.offset)
                                continue;

                        if (logical[nr] + stripe_len <= cache->key.objectid)
                                continue;

                        start = logical[nr];
                        if (start < cache->key.objectid) {
                                start = cache->key.objectid;
                                len = (logical[nr] + stripe_len) - start;
                        } else {
                                len = min_t(u64, stripe_len,
                                            cache->key.objectid +
                                            cache->key.offset - start);
                        }

                        cache->bytes_super += len;
                        ret = add_excluded_extent(root, start, len);
                        if (ret) {
                                kfree(logical);
                                return ret;
                        }
                }

                kfree(logical);
        }
        return 0;
}

static struct btrfs_caching_control *
get_caching_control(struct btrfs_block_group_cache *cache)
{
        struct btrfs_caching_control *ctl;

        spin_lock(&cache->lock);
        if (!cache->caching_ctl) {
                spin_unlock(&cache->lock);
                return NULL;
        }

        ctl = cache->caching_ctl;
        atomic_inc(&ctl->count);
        spin_unlock(&cache->lock);
        return ctl;
}

static void put_caching_control(struct btrfs_caching_control *ctl)
{
        if (atomic_dec_and_test(&ctl->count))
                kfree(ctl);
}

#ifdef CONFIG_BTRFS_DEBUG
static void fragment_free_space(struct btrfs_root *root,
                                struct btrfs_block_group_cache *block_group)
{
        u64 start = block_group->key.objectid;
        u64 len = block_group->key.offset;
        u64 chunk = block_group->flags & BTRFS_BLOCK_GROUP_METADATA ?
                root->nodesize : root->sectorsize;
        u64 step = chunk << 1;

        while (len > chunk) {
                btrfs_remove_free_space(block_group, start, chunk);
                start += step;
                if (len < step)
                        len = 0;
                else
                        len -= step;
        }
}
#endif

/*
 * this is only called by cache_block_group, since we could have freed extents
 * we need to check the pinned_extents for any extents that can't be used yet
 * since their free space will be released as soon as the transaction commits.
 */
static u64 add_new_free_space(struct btrfs_block_group_cache *block_group,
                              struct btrfs_fs_info *info, u64 start, u64 end)
{
        u64 extent_start, extent_end, size, total_added = 0;
        int ret;

        while (start < end) {
                ret = find_first_extent_bit(info->pinned_extents, start,
                                            &extent_start, &extent_end,
                                            EXTENT_DIRTY | EXTENT_UPTODATE,
                                            NULL);
                if (ret)
                        break;

                if (extent_start <= start) {
                        start = extent_end + 1;
                } else if (extent_start > start && extent_start < end) {
                        size = extent_start - start;
                        total_added += size;
                        ret = btrfs_add_free_space(block_group, start,
                                                   size);
                        BUG_ON(ret); /* -ENOMEM or logic error */
                        start = extent_end + 1;
                } else {
                        break;
                }
        }

        if (start < end) {
                size = end - start;
                total_added += size;
                ret = btrfs_add_free_space(block_group, start, size);
                BUG_ON(ret); /* -ENOMEM or logic error */
        }

        return total_added;
}

static noinline void caching_thread(struct btrfs_work *work)
{
        struct btrfs_block_group_cache *block_group;
        struct btrfs_fs_info *fs_info;
        struct btrfs_caching_control *caching_ctl;
        struct btrfs_root *extent_root;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        u64 total_found = 0;
        u64 last = 0;
        u32 nritems;
        int ret = -ENOMEM;
        bool wakeup = true;

        caching_ctl = container_of(work, struct btrfs_caching_control, work);
        block_group = caching_ctl->block_group;
        fs_info = block_group->fs_info;
        extent_root = fs_info->extent_root;

        path = btrfs_alloc_path();
        if (!path)
                goto out;

        last = max_t(u64, block_group->key.objectid, BTRFS_SUPER_INFO_OFFSET);

#ifdef CONFIG_BTRFS_DEBUG
        /*
         * If we're fragmenting we don't want to make anybody think we can
         * allocate from this block group until we've had a chance to fragment
         * the free space.
         */
        if (btrfs_should_fragment_free_space(extent_root, block_group))
                wakeup = false;
#endif
        /*
         * We don't want to deadlock with somebody trying to allocate a new
         * extent for the extent root while also trying to search the extent
         * root to add free space.  So we skip locking and search the commit
         * root, since its read-only
         */
        path->skip_locking = 1;
        path->search_commit_root = 1;
        path->reada = 1;

        key.objectid = last;
        key.offset = 0;
        key.type = BTRFS_EXTENT_ITEM_KEY;
again:
        mutex_lock(&caching_ctl->mutex);
        /* need to make sure the commit_root doesn't disappear */
        down_read(&fs_info->commit_root_sem);

next:
        ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
        if (ret < 0)
                goto err;

        leaf = path->nodes[0];
        nritems = btrfs_header_nritems(leaf);

        while (1) {
                if (btrfs_fs_closing(fs_info) > 1) {
                        last = (u64)-1;
                        break;
                }

                if (path->slots[0] < nritems) {
                        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                } else {
                        ret = find_next_key(path, 0, &key);
                        if (ret)
                                break;

                        if (need_resched() ||
                            rwsem_is_contended(&fs_info->commit_root_sem)) {
                                if (wakeup)
                                        caching_ctl->progress = last;
                                btrfs_release_path(path);
                                up_read(&fs_info->commit_root_sem);
                                mutex_unlock(&caching_ctl->mutex);
                                cond_resched();
                                goto again;
                        }

                        ret = btrfs_next_leaf(extent_root, path);
                        if (ret < 0)
                                goto err;
                        if (ret)
                                break;
                        leaf = path->nodes[0];
                        nritems = btrfs_header_nritems(leaf);
                        continue;
                }

                if (key.objectid < last) {
                        key.objectid = last;
                        key.offset = 0;
                        key.type = BTRFS_EXTENT_ITEM_KEY;

                        if (wakeup)
                                caching_ctl->progress = last;
                        btrfs_release_path(path);
                        goto next;
                }

                if (key.objectid < block_group->key.objectid) {
                        path->slots[0]++;
                        continue;
                }

                if (key.objectid >= block_group->key.objectid +
                    block_group->key.offset)
                        break;

                if (key.type == BTRFS_EXTENT_ITEM_KEY ||
                    key.type == BTRFS_METADATA_ITEM_KEY) {
                        total_found += add_new_free_space(block_group,
                                                          fs_info, last,
                                                          key.objectid);
                        if (key.type == BTRFS_METADATA_ITEM_KEY)
                                last = key.objectid +
                                        fs_info->tree_root->nodesize;
                        else
                                last = key.objectid + key.offset;

                        if (total_found > (1024 * 1024 * 2)) {
                                total_found = 0;
                                if (wakeup)
                                        wake_up(&caching_ctl->wait);
                        }
                }
                path->slots[0]++;
        }
        ret = 0;

        total_found += add_new_free_space(block_group, fs_info, last,
                                          block_group->key.objectid +
                                          block_group->key.offset);
        spin_lock(&block_group->lock);
        block_group->caching_ctl = NULL;
        block_group->cached = BTRFS_CACHE_FINISHED;
        spin_unlock(&block_group->lock);

#ifdef CONFIG_BTRFS_DEBUG
        if (btrfs_should_fragment_free_space(extent_root, block_group)) {
                u64 bytes_used;

                spin_lock(&block_group->space_info->lock);
                spin_lock(&block_group->lock);
                bytes_used = block_group->key.offset -
                        btrfs_block_group_used(&block_group->item);
                block_group->space_info->bytes_used += bytes_used >> 1;
                spin_unlock(&block_group->lock);
                spin_unlock(&block_group->space_info->lock);
                fragment_free_space(extent_root, block_group);
        }
#endif

        caching_ctl->progress = (u64)-1;
err:
        btrfs_free_path(path);
        up_read(&fs_info->commit_root_sem);

        free_excluded_extents(extent_root, block_group);

        mutex_unlock(&caching_ctl->mutex);
out:
        if (ret) {
                spin_lock(&block_group->lock);
                block_group->caching_ctl = NULL;
                block_group->cached = BTRFS_CACHE_ERROR;
                spin_unlock(&block_group->lock);
        }
        wake_up(&caching_ctl->wait);

        put_caching_control(caching_ctl);
        btrfs_put_block_group(block_group);
}

static int cache_block_group(struct btrfs_block_group_cache *cache,
                             int load_cache_only)
{
        DEFINE_WAIT(wait);
        struct btrfs_fs_info *fs_info = cache->fs_info;
        struct btrfs_caching_control *caching_ctl;
        int ret = 0;

        caching_ctl = kzalloc(sizeof(*caching_ctl), GFP_NOFS);
        if (!caching_ctl)
                return -ENOMEM;

        INIT_LIST_HEAD(&caching_ctl->list);
        mutex_init(&caching_ctl->mutex);
        init_waitqueue_head(&caching_ctl->wait);
        caching_ctl->block_group = cache;
        caching_ctl->progress = cache->key.objectid;
        atomic_set(&caching_ctl->count, 1);
        btrfs_init_work(&caching_ctl->work, btrfs_cache_helper,
                        caching_thread, NULL, NULL);

        spin_lock(&cache->lock);
        /*
         * This should be a rare occasion, but this could happen I think in the
         * case where one thread starts to load the space cache info, and then
         * some other thread starts a transaction commit which tries to do an
         * allocation while the other thread is still loading the space cache
         * info.  The previous loop should have kept us from choosing this block
         * group, but if we've moved to the state where we will wait on caching
         * block groups we need to first check if we're doing a fast load here,
         * so we can wait for it to finish, otherwise we could end up allocating
         * from a block group who's cache gets evicted for one reason or
         * another.
         */
        while (cache->cached == BTRFS_CACHE_FAST) {
                struct btrfs_caching_control *ctl;

                ctl = cache->caching_ctl;
                atomic_inc(&ctl->count);
                prepare_to_wait(&ctl->wait, &wait, TASK_UNINTERRUPTIBLE);
                spin_unlock(&cache->lock);

                schedule();

                finish_wait(&ctl->wait, &wait);
                put_caching_control(ctl);
                spin_lock(&cache->lock);
        }

        if (cache->cached != BTRFS_CACHE_NO) {
                spin_unlock(&cache->lock);
                kfree(caching_ctl);
                return 0;
        }
        WARN_ON(cache->caching_ctl);
        cache->caching_ctl = caching_ctl;
        cache->cached = BTRFS_CACHE_FAST;
        spin_unlock(&cache->lock);

        if (fs_info->mount_opt & BTRFS_MOUNT_SPACE_CACHE) {
                mutex_lock(&caching_ctl->mutex);
                ret = load_free_space_cache(fs_info, cache);

                spin_lock(&cache->lock);
                if (ret == 1) {
                        cache->caching_ctl = NULL;
                        cache->cached = BTRFS_CACHE_FINISHED;
                        cache->last_byte_to_unpin = (u64)-1;
                        caching_ctl->progress = (u64)-1;
                } else {
                        if (load_cache_only) {
                                cache->caching_ctl = NULL;
                                cache->cached = BTRFS_CACHE_NO;
                        } else {
                                cache->cached = BTRFS_CACHE_STARTED;
                                cache->has_caching_ctl = 1;
                        }
                }
                spin_unlock(&cache->lock);
#ifdef CONFIG_BTRFS_DEBUG
                if (ret == 1 &&
                    btrfs_should_fragment_free_space(fs_info->extent_root,
                                                     cache)) {
                        u64 bytes_used;

                        spin_lock(&cache->space_info->lock);
                        spin_lock(&cache->lock);
                        bytes_used = cache->key.offset -
                                btrfs_block_group_used(&cache->item);
                        cache->space_info->bytes_used += bytes_used >> 1;
                        spin_unlock(&cache->lock);
                        spin_unlock(&cache->space_info->lock);
                        fragment_free_space(fs_info->extent_root, cache);
                }
#endif
                mutex_unlock(&caching_ctl->mutex);

                wake_up(&caching_ctl->wait);
                if (ret == 1) {
                        put_caching_control(caching_ctl);
                        free_excluded_extents(fs_info->extent_root, cache);
                        return 0;
                }
        } else {
                /*
                 * We are not going to do the fast caching, set cached to the
                 * appropriate value and wakeup any waiters.
                 */
                spin_lock(&cache->lock);
                if (load_cache_only) {
                        cache->caching_ctl = NULL;
                        cache->cached = BTRFS_CACHE_NO;
                } else {
                        cache->cached = BTRFS_CACHE_STARTED;
                        cache->has_caching_ctl = 1;
                }
                spin_unlock(&cache->lock);
                wake_up(&caching_ctl->wait);
        }

        if (load_cache_only) {
                put_caching_control(caching_ctl);
                return 0;
        }

        down_write(&fs_info->commit_root_sem);
        atomic_inc(&caching_ctl->count);
        list_add_tail(&caching_ctl->list, &fs_info->caching_block_groups);
        up_write(&fs_info->commit_root_sem);

        btrfs_get_block_group(cache);

        btrfs_queue_work(fs_info->caching_workers, &caching_ctl->work);

        return ret;
}

/*
 * return the block group that starts at or after bytenr
 */
static struct btrfs_block_group_cache *
btrfs_lookup_first_block_group(struct btrfs_fs_info *info, u64 bytenr)
{
        struct btrfs_block_group_cache *cache;

        cache = block_group_cache_tree_search(info, bytenr, 0);

        return cache;
}

/*
 * return the block group that contains the given bytenr
 */
struct btrfs_block_group_cache *btrfs_lookup_block_group(
                                                 struct btrfs_fs_info *info,
                                                 u64 bytenr)
{
        struct btrfs_block_group_cache *cache;

        cache = block_group_cache_tree_search(info, bytenr, 1);

        return cache;
}

static struct btrfs_space_info *__find_space_info(struct btrfs_fs_info *info,
                                                  u64 flags)
{
        struct list_head *head = &info->space_info;
        struct btrfs_space_info *found;

        flags &= BTRFS_BLOCK_GROUP_TYPE_MASK;

        rcu_read_lock();
        list_for_each_entry_rcu(found, head, list) {
                if (found->flags & flags) {
                        rcu_read_unlock();
                        return found;
                }
        }
        rcu_read_unlock();
        return NULL;
}

/*
 * after adding space to the filesystem, we need to clear the full flags
 * on all the space infos.
 */
void btrfs_clear_space_info_full(struct btrfs_fs_info *info)
{
        struct list_head *head = &info->space_info;
        struct btrfs_space_info *found;

        rcu_read_lock();
        list_for_each_entry_rcu(found, head, list)
                found->full = 0;
        rcu_read_unlock();
}

/* simple helper to search for an existing data extent at a given offset */
int btrfs_lookup_data_extent(struct btrfs_root *root, u64 start, u64 len)
{
        int ret;
        struct btrfs_key key;
        struct btrfs_path *path;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        key.objectid = start;
        key.offset = len;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        ret = btrfs_search_slot(NULL, root->fs_info->extent_root, &key, path,
                                0, 0);
        btrfs_free_path(path);
        return ret;
}

/*
 * helper function to lookup reference count and flags of a tree block.
 *
 * the head node for delayed ref is used to store the sum of all the
 * reference count modifications queued up in the rbtree. the head
 * node may also store the extent flags to set. This way you can check
 * to see what the reference count and extent flags would be if all of
 * the delayed refs are not processed.
 */
int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root, u64 bytenr,
                             u64 offset, int metadata, u64 *refs, u64 *flags)
{
        struct btrfs_delayed_ref_head *head;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_path *path;
        struct btrfs_extent_item *ei;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        u32 item_size;
        u64 num_refs;
        u64 extent_flags;
        int ret;

        /*
         * If we don't have skinny metadata, don't bother doing anything
         * different
         */
        if (metadata && !btrfs_fs_incompat(root->fs_info, SKINNY_METADATA)) {
                offset = root->nodesize;
                metadata = 0;
        }

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        if (!trans) {
                path->skip_locking = 1;
                path->search_commit_root = 1;
        }

search_again:
        key.objectid = bytenr;
        key.offset = offset;
        if (metadata)
                key.type = BTRFS_METADATA_ITEM_KEY;
        else
                key.type = BTRFS_EXTENT_ITEM_KEY;

        ret = btrfs_search_slot(trans, root->fs_info->extent_root,
                                &key, path, 0, 0);
        if (ret < 0)
                goto out_free;

        if (ret > 0 && metadata && key.type == BTRFS_METADATA_ITEM_KEY) {
                if (path->slots[0]) {
                        path->slots[0]--;
                        btrfs_item_key_to_cpu(path->nodes[0], &key,
                                              path->slots[0]);
                        if (key.objectid == bytenr &&
                            key.type == BTRFS_EXTENT_ITEM_KEY &&
                            key.offset == root->nodesize)
                                ret = 0;
                }
        }

        if (ret == 0) {
                leaf = path->nodes[0];
                item_size = btrfs_item_size_nr(leaf, path->slots[0]);
                if (item_size >= sizeof(*ei)) {
                        ei = btrfs_item_ptr(leaf, path->slots[0],
                                            struct btrfs_extent_item);
                        num_refs = btrfs_extent_refs(leaf, ei);
                        extent_flags = btrfs_extent_flags(leaf, ei);
                } else {
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
                        struct btrfs_extent_item_v0 *ei0;
                        BUG_ON(item_size != sizeof(*ei0));
                        ei0 = btrfs_item_ptr(leaf, path->slots[0],
                                             struct btrfs_extent_item_v0);
                        num_refs = btrfs_extent_refs_v0(leaf, ei0);
                        /* FIXME: this isn't correct for data */
                        extent_flags = BTRFS_BLOCK_FLAG_FULL_BACKREF;
#else
                        BUG();
#endif
                }
                BUG_ON(num_refs == 0);
        } else {
                num_refs = 0;
                extent_flags = 0;
                ret = 0;
        }

        if (!trans)
                goto out;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);
        head = btrfs_find_delayed_ref_head(trans, bytenr);
        if (head) {
                if (!mutex_trylock(&head->mutex)) {
                        atomic_inc(&head->node.refs);
                        spin_unlock(&delayed_refs->lock);

                        btrfs_release_path(path);

                        /*
                         * Mutex was contended, block until it's released and try
                         * again
                         */
                        mutex_lock(&head->mutex);
                        mutex_unlock(&head->mutex);
                        btrfs_put_delayed_ref(&head->node);
                        goto search_again;
                }
                spin_lock(&head->lock);
                if (head->extent_op && head->extent_op->update_flags)
                        extent_flags |= head->extent_op->flags_to_set;
                else
                        BUG_ON(num_refs == 0);

                num_refs += head->node.ref_mod;
                spin_unlock(&head->lock);
                mutex_unlock(&head->mutex);
        }
        spin_unlock(&delayed_refs->lock);
out:
        WARN_ON(num_refs == 0);
        if (refs)
                *refs = num_refs;
        if (flags)
                *flags = extent_flags;
out_free:
        btrfs_free_path(path);
        return ret;
}

/*
 * Back reference rules.  Back refs have three main goals:
 *
 * 1) differentiate between all holders of references to an extent so that
 *    when a reference is dropped we can make sure it was a valid reference
 *    before freeing the extent.
 *
 * 2) Provide enough information to quickly find the holders of an extent
 *    if we notice a given block is corrupted or bad.
 *
 * 3) Make it easy to migrate blocks for FS shrinking or storage pool
 *    maintenance.  This is actually the same as #2, but with a slightly
 *    different use case.
 *
 * There are two kinds of back refs. The implicit back refs is optimized
 * for pointers in non-shared tree blocks. For a given pointer in a block,
 * back refs of this kind provide information about the block's owner tree
 * and the pointer's key. These information allow us to find the block by
 * b-tree searching. The full back refs is for pointers in tree blocks not
 * referenced by their owner trees. The location of tree block is recorded
 * in the back refs. Actually the full back refs is generic, and can be
 * used in all cases the implicit back refs is used. The major shortcoming
 * of the full back refs is its overhead. Every time a tree block gets
 * COWed, we have to update back refs entry for all pointers in it.
 *
 * For a newly allocated tree block, we use implicit back refs for
 * pointers in it. This means most tree related operations only involve
 * implicit back refs. For a tree block created in old transaction, the
 * only way to drop a reference to it is COW it. So we can detect the
 * event that tree block loses its owner tree's reference and do the
 * back refs conversion.
 *
 * When a tree block is COW'd through a tree, there are four cases:
 *
 * The reference count of the block is one and the tree is the block's
 * owner tree. Nothing to do in this case.
 *
 * The reference count of the block is one and the tree is not the
 * block's owner tree. In this case, full back refs is used for pointers
 * in the block. Remove these full back refs, add implicit back refs for
 * every pointers in the new block.
 *
 * The reference count of the block is greater than one and the tree is
 * the block's owner tree. In this case, implicit back refs is used for
 * pointers in the block. Add full back refs for every pointers in the
 * block, increase lower level extents' reference counts. The original
 * implicit back refs are entailed to the new block.
 *
 * The reference count of the block is greater than one and the tree is
 * not the block's owner tree. Add implicit back refs for every pointer in
 * the new block, increase lower level extents' reference count.
 *
 * Back Reference Key composing:
 *
 * The key objectid corresponds to the first byte in the extent,
 * The key type is used to differentiate between types of back refs.
 * There are different meanings of the key offset for different types
 * of back refs.
 *
 * File extents can be referenced by:
 *
 * - multiple snapshots, subvolumes, or different generations in one subvol
 * - different files inside a single subvolume
 * - different offsets inside a file (bookend extents in file.c)
 *
 * The extent ref structure for the implicit back refs has fields for:
 *
 * - Objectid of the subvolume root
 * - objectid of the file holding the reference
 * - original offset in the file
 * - how many bookend extents
 *
 * The key offset for the implicit back refs is hash of the first
 * three fields.
 *
 * The extent ref structure for the full back refs has field for:
 *
 * - number of pointers in the tree leaf
 *
 * The key offset for the implicit back refs is the first byte of
 * the tree leaf
 *
 * When a file extent is allocated, The implicit back refs is used.
 * the fields are filled in:
 *
 *     (root_key.objectid, inode objectid, offset in file, 1)
 *
 * When a file extent is removed file truncation, we find the
 * corresponding implicit back refs and check the following fields:
 *
 *     (btrfs_header_owner(leaf), inode objectid, offset in file)
 *
 * Btree extents can be referenced by:
 *
 * - Different subvolumes
 *
 * Both the implicit back refs and the full back refs for tree blocks
 * only consist of key. The key offset for the implicit back refs is
 * objectid of block's owner tree. The key offset for the full back refs
 * is the first byte of parent block.
 *
 * When implicit back refs is used, information about the lowest key and
 * level of the tree block are required. These information are stored in
 * tree block info structure.
 */

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
static int convert_extent_item_v0(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,
                                  struct btrfs_path *path,
                                  u64 owner, u32 extra_size)
{
        struct btrfs_extent_item *item;
        struct btrfs_extent_item_v0 *ei0;
        struct btrfs_extent_ref_v0 *ref0;
        struct btrfs_tree_block_info *bi;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        struct btrfs_key found_key;
        u32 new_size = sizeof(*item);
        u64 refs;
        int ret;

        leaf = path->nodes[0];
        BUG_ON(btrfs_item_size_nr(leaf, path->slots[0]) != sizeof(*ei0));

        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        ei0 = btrfs_item_ptr(leaf, path->slots[0],
                             struct btrfs_extent_item_v0);
        refs = btrfs_extent_refs_v0(leaf, ei0);

        if (owner == (u64)-1) {
                while (1) {
                        if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                                ret = btrfs_next_leaf(root, path);
                                if (ret < 0)
                                        return ret;
                                BUG_ON(ret > 0); /* Corruption */
                                leaf = path->nodes[0];
                        }
                        btrfs_item_key_to_cpu(leaf, &found_key,
                                              path->slots[0]);
                        BUG_ON(key.objectid != found_key.objectid);
                        if (found_key.type != BTRFS_EXTENT_REF_V0_KEY) {
                                path->slots[0]++;
                                continue;
                        }
                        ref0 = btrfs_item_ptr(leaf, path->slots[0],
                                              struct btrfs_extent_ref_v0);
                        owner = btrfs_ref_objectid_v0(leaf, ref0);
                        break;
                }
        }
        btrfs_release_path(path);

        if (owner < BTRFS_FIRST_FREE_OBJECTID)
                new_size += sizeof(*bi);

        new_size -= sizeof(*ei0);
        ret = btrfs_search_slot(trans, root, &key, path,
                                new_size + extra_size, 1);
        if (ret < 0)
                return ret;
        BUG_ON(ret); /* Corruption */

        btrfs_extend_item(root, path, new_size);

        leaf = path->nodes[0];
        item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        btrfs_set_extent_refs(leaf, item, refs);
        /* FIXME: get real generation */
        btrfs_set_extent_generation(leaf, item, 0);
        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                btrfs_set_extent_flags(leaf, item,
                                       BTRFS_EXTENT_FLAG_TREE_BLOCK |
                                       BTRFS_BLOCK_FLAG_FULL_BACKREF);
                bi = (struct btrfs_tree_block_info *)(item + 1);
                /* FIXME: get first key of the block */
                memset_extent_buffer(leaf, 0, (unsigned long)bi, sizeof(*bi));
                btrfs_set_tree_block_level(leaf, bi, (int)owner);
        } else {
                btrfs_set_extent_flags(leaf, item, BTRFS_EXTENT_FLAG_DATA);
        }
        btrfs_mark_buffer_dirty(leaf);
        return 0;
}
#endif

static u64 hash_extent_data_ref(u64 root_objectid, u64 owner, u64 offset)
{
        u32 high_crc = ~(u32)0;
        u32 low_crc = ~(u32)0;
        __le64 lenum;

        lenum = cpu_to_le64(root_objectid);
        high_crc = btrfs_crc32c(high_crc, &lenum, sizeof(lenum));
        lenum = cpu_to_le64(owner);
        low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));
        lenum = cpu_to_le64(offset);
        low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));

        return ((u64)high_crc << 31) ^ (u64)low_crc;
}

static u64 hash_extent_data_ref_item(struct extent_buffer *leaf,
                                     struct btrfs_extent_data_ref *ref)
{
        return hash_extent_data_ref(btrfs_extent_data_ref_root(leaf, ref),
                                    btrfs_extent_data_ref_objectid(leaf, ref),
                                    btrfs_extent_data_ref_offset(leaf, ref));
}

static int match_extent_data_ref(struct extent_buffer *leaf,
                                 struct btrfs_extent_data_ref *ref,
                                 u64 root_objectid, u64 owner, u64 offset)
{
        if (btrfs_extent_data_ref_root(leaf, ref) != root_objectid ||
            btrfs_extent_data_ref_objectid(leaf, ref) != owner ||
            btrfs_extent_data_ref_offset(leaf, ref) != offset)
                return 0;
        return 1;
}

static noinline int lookup_extent_data_ref(struct btrfs_trans_handle *trans,
                                           struct btrfs_root *root,
                                           struct btrfs_path *path,
                                           u64 bytenr, u64 parent,
                                           u64 root_objectid,
                                           u64 owner, u64 offset)
{
        struct btrfs_key key;
        struct btrfs_extent_data_ref *ref;
        struct extent_buffer *leaf;
        u32 nritems;
        int ret;
        int recow;
        int err = -ENOENT;

        key.objectid = bytenr;
        if (parent) {
                key.type = BTRFS_SHARED_DATA_REF_KEY;
                key.offset = parent;
        } else {
                key.type = BTRFS_EXTENT_DATA_REF_KEY;
                key.offset = hash_extent_data_ref(root_objectid,
                                                  owner, offset);
        }
again:
        recow = 0;
        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret < 0) {
                err = ret;
                goto fail;
        }

        if (parent) {
                if (!ret)
                        return 0;
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
                key.type = BTRFS_EXTENT_REF_V0_KEY;
                btrfs_release_path(path);
                ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
                if (ret < 0) {
                        err = ret;
                        goto fail;
                }
                if (!ret)
                        return 0;
#endif
                goto fail;
        }

        leaf = path->nodes[0];
        nritems = btrfs_header_nritems(leaf);
        while (1) {
                if (path->slots[0] >= nritems) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                err = ret;
                        if (ret)
                                goto fail;

                        leaf = path->nodes[0];
                        nritems = btrfs_header_nritems(leaf);
                        recow = 1;
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.objectid != bytenr ||
                    key.type != BTRFS_EXTENT_DATA_REF_KEY)
                        goto fail;

                ref = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_extent_data_ref);

                if (match_extent_data_ref(leaf, ref, root_objectid,
                                          owner, offset)) {
                        if (recow) {
                                btrfs_release_path(path);
                                goto again;
                        }
                        err = 0;
                        break;
                }
                path->slots[0]++;
        }
fail:
        return err;
}

static noinline int insert_extent_data_ref(struct btrfs_trans_handle *trans,
                                           struct btrfs_root *root,
                                           struct btrfs_path *path,
                                           u64 bytenr, u64 parent,
                                           u64 root_objectid, u64 owner,
                                           u64 offset, int refs_to_add)
{
        struct btrfs_key key;
        struct extent_buffer *leaf;
        u32 size;
        u32 num_refs;
        int ret;

        key.objectid = bytenr;
        if (parent) {
                key.type = BTRFS_SHARED_DATA_REF_KEY;
                key.offset = parent;
                size = sizeof(struct btrfs_shared_data_ref);
        } else {
                key.type = BTRFS_EXTENT_DATA_REF_KEY;
                key.offset = hash_extent_data_ref(root_objectid,
                                                  owner, offset);
                size = sizeof(struct btrfs_extent_data_ref);
        }

        ret = btrfs_insert_empty_item(trans, root, path, &key, size);
        if (ret && ret != -EEXIST)
                goto fail;

        leaf = path->nodes[0];
        if (parent) {
                struct btrfs_shared_data_ref *ref;
                ref = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_shared_data_ref);
                if (ret == 0) {
                        btrfs_set_shared_data_ref_count(leaf, ref, refs_to_add);
                } else {
                        num_refs = btrfs_shared_data_ref_count(leaf, ref);
                        num_refs += refs_to_add;
                        btrfs_set_shared_data_ref_count(leaf, ref, num_refs);
                }
        } else {
                struct btrfs_extent_data_ref *ref;
                while (ret == -EEXIST) {
                        ref = btrfs_item_ptr(leaf, path->slots[0],
                                             struct btrfs_extent_data_ref);
                        if (match_extent_data_ref(leaf, ref, root_objectid,
                                                  owner, offset))
                                break;
                        btrfs_release_path(path);
                        key.offset++;
                        ret = btrfs_insert_empty_item(trans, root, path, &key,
                                                      size);
                        if (ret && ret != -EEXIST)
                                goto fail;

                        leaf = path->nodes[0];
                }
                ref = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_extent_data_ref);
                if (ret == 0) {
                        btrfs_set_extent_data_ref_root(leaf, ref,
                                                       root_objectid);
                        btrfs_set_extent_data_ref_objectid(leaf, ref, owner);
                        btrfs_set_extent_data_ref_offset(leaf, ref, offset);
                        btrfs_set_extent_data_ref_count(leaf, ref, refs_to_add);
                } else {
                        num_refs = btrfs_extent_data_ref_count(leaf, ref);
                        num_refs += refs_to_add;
                        btrfs_set_extent_data_ref_count(leaf, ref, num_refs);
                }
        }
        btrfs_mark_buffer_dirty(leaf);
        ret = 0;
fail:
        btrfs_release_path(path);
        return ret;
}

static noinline int remove_extent_data_ref(struct btrfs_trans_handle *trans,
                                           struct btrfs_root *root,
                                           struct btrfs_path *path,
                                           int refs_to_drop, int *last_ref)
{
        struct btrfs_key key;
        struct btrfs_extent_data_ref *ref1 = NULL;
        struct btrfs_shared_data_ref *ref2 = NULL;
        struct extent_buffer *leaf;
        u32 num_refs = 0;
        int ret = 0;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

        if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
                ref1 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_extent_data_ref);
                num_refs = btrfs_extent_data_ref_count(leaf, ref1);
        } else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
                ref2 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_shared_data_ref);
                num_refs = btrfs_shared_data_ref_count(leaf, ref2);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        } else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
                struct btrfs_extent_ref_v0 *ref0;
                ref0 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_extent_ref_v0);
                num_refs = btrfs_ref_count_v0(leaf, ref0);
#endif
        } else {
                BUG();
        }

        BUG_ON(num_refs < refs_to_drop);
        num_refs -= refs_to_drop;

        if (num_refs == 0) {
                ret = btrfs_del_item(trans, root, path);
                *last_ref = 1;
        } else {
                if (key.type == BTRFS_EXTENT_DATA_REF_KEY)
                        btrfs_set_extent_data_ref_count(leaf, ref1, num_refs);
                else if (key.type == BTRFS_SHARED_DATA_REF_KEY)
                        btrfs_set_shared_data_ref_count(leaf, ref2, num_refs);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
                else {
                        struct btrfs_extent_ref_v0 *ref0;
                        ref0 = btrfs_item_ptr(leaf, path->slots[0],
                                        struct btrfs_extent_ref_v0);
                        btrfs_set_ref_count_v0(leaf, ref0, num_refs);
                }
#endif
                btrfs_mark_buffer_dirty(leaf);
        }
        return ret;
}

static noinline u32 extent_data_ref_count(struct btrfs_path *path,
                                          struct btrfs_extent_inline_ref *iref)
{
        struct btrfs_key key;
        struct extent_buffer *leaf;
        struct btrfs_extent_data_ref *ref1;
        struct btrfs_shared_data_ref *ref2;
        u32 num_refs = 0;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (iref) {
                if (btrfs_extent_inline_ref_type(leaf, iref) ==
                    BTRFS_EXTENT_DATA_REF_KEY) {
                        ref1 = (struct btrfs_extent_data_ref *)(&iref->offset);
                        num_refs = btrfs_extent_data_ref_count(leaf, ref1);
                } else {
                        ref2 = (struct btrfs_shared_data_ref *)(iref + 1);
                        num_refs = btrfs_shared_data_ref_count(leaf, ref2);
                }
        } else if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
                ref1 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_extent_data_ref);
                num_refs = btrfs_extent_data_ref_count(leaf, ref1);
        } else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
                ref2 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_shared_data_ref);
                num_refs = btrfs_shared_data_ref_count(leaf, ref2);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        } else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
                struct btrfs_extent_ref_v0 *ref0;
                ref0 = btrfs_item_ptr(leaf, path->slots[0],
                                      struct btrfs_extent_ref_v0);
                num_refs = btrfs_ref_count_v0(leaf, ref0);
#endif
        } else {
                WARN_ON(1);
        }
        return num_refs;
}

static noinline int lookup_tree_block_ref(struct btrfs_trans_handle *trans,
                                          struct btrfs_root *root,
                                          struct btrfs_path *path,
                                          u64 bytenr, u64 parent,
                                          u64 root_objectid)
{
        struct btrfs_key key;
        int ret;

        key.objectid = bytenr;
        if (parent) {
                key.type = BTRFS_SHARED_BLOCK_REF_KEY;
                key.offset = parent;
        } else {
                key.type = BTRFS_TREE_BLOCK_REF_KEY;
                key.offset = root_objectid;
        }

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret > 0)
                ret = -ENOENT;
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        if (ret == -ENOENT && parent) {
                btrfs_release_path(path);
                key.type = BTRFS_EXTENT_REF_V0_KEY;
                ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
                if (ret > 0)
                        ret = -ENOENT;
        }
#endif
        return ret;
}

static noinline int insert_tree_block_ref(struct btrfs_trans_handle *trans,
                                          struct btrfs_root *root,
                                          struct btrfs_path *path,
                                          u64 bytenr, u64 parent,
                                          u64 root_objectid)
{
        struct btrfs_key key;
        int ret;

        key.objectid = bytenr;
        if (parent) {
                key.type = BTRFS_SHARED_BLOCK_REF_KEY;
                key.offset = parent;
        } else {
                key.type = BTRFS_TREE_BLOCK_REF_KEY;
                key.offset = root_objectid;
        }

        ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
        btrfs_release_path(path);
        return ret;
}

static inline int extent_ref_type(u64 parent, u64 owner)
{
        int type;
        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                if (parent > 0)
                        type = BTRFS_SHARED_BLOCK_REF_KEY;
                else
                        type = BTRFS_TREE_BLOCK_REF_KEY;
        } else {
                if (parent > 0)
                        type = BTRFS_SHARED_DATA_REF_KEY;
                else
                        type = BTRFS_EXTENT_DATA_REF_KEY;
        }
        return type;
}

static int find_next_key(struct btrfs_path *path, int level,
                         struct btrfs_key *key)

{
        for (; level < BTRFS_MAX_LEVEL; level++) {
                if (!path->nodes[level])
                        break;
                if (path->slots[level] + 1 >=
                    btrfs_header_nritems(path->nodes[level]))
                        continue;
                if (level == 0)
                        btrfs_item_key_to_cpu(path->nodes[level], key,
                                              path->slots[level] + 1);
                else
                        btrfs_node_key_to_cpu(path->nodes[level], key,
                                              path->slots[level] + 1);
                return 0;
        }
        return 1;
}

/*
 * look for inline back ref. if back ref is found, *ref_ret is set
 * to the address of inline back ref, and 0 is returned.
 *
 * if back ref isn't found, *ref_ret is set to the address where it
 * should be inserted, and -ENOENT is returned.
 *
 * if insert is true and there are too many inline back refs, the path
 * points to the extent item, and -EAGAIN is returned.
 *
 * NOTE: inline back refs are ordered in the same way that back ref
 *       items in the tree are ordered.
 */
static noinline_for_stack
int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref **ref_ret,
                                 u64 bytenr, u64 num_bytes,
                                 u64 parent, u64 root_objectid,
                                 u64 owner, u64 offset, int insert)
{
        struct btrfs_key key;
        struct extent_buffer *leaf;
        struct btrfs_extent_item *ei;
        struct btrfs_extent_inline_ref *iref;
        u64 flags;
        u64 item_size;
        unsigned long ptr;
        unsigned long end;
        int extra_size;
        int type;
        int want;
        int ret;
        int err = 0;
        bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
                                                 SKINNY_METADATA);

        key.objectid = bytenr;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        key.offset = num_bytes;

        want = extent_ref_type(parent, owner);
        if (insert) {
                extra_size = btrfs_extent_inline_ref_size(want);
                path->keep_locks = 1;
        } else
                extra_size = -1;

        /*
         * Owner is our parent level, so we can just add one to get the level
         * for the block we are interested in.
         */
        if (skinny_metadata && owner < BTRFS_FIRST_FREE_OBJECTID) {
                key.type = BTRFS_METADATA_ITEM_KEY;
                key.offset = owner;
        }

again:
        ret = btrfs_search_slot(trans, root, &key, path, extra_size, 1);
        if (ret < 0) {
                err = ret;
                goto out;
        }

        /*
         * We may be a newly converted file system which still has the old fat
         * extent entries for metadata, so try and see if we have one of those.
         */
        if (ret > 0 && skinny_metadata) {
                skinny_metadata = false;
                if (path->slots[0]) {
                        path->slots[0]--;
                        btrfs_item_key_to_cpu(path->nodes[0], &key,
                                              path->slots[0]);
                        if (key.objectid == bytenr &&
                            key.type == BTRFS_EXTENT_ITEM_KEY &&
                            key.offset == num_bytes)
                                ret = 0;
                }
                if (ret) {
                        key.objectid = bytenr;
                        key.type = BTRFS_EXTENT_ITEM_KEY;
                        key.offset = num_bytes;
                        btrfs_release_path(path);
                        goto again;
                }
        }

        if (ret && !insert) {
                err = -ENOENT;
                goto out;
        } else if (WARN_ON(ret)) {
                err = -EIO;
                goto out;
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        if (item_size < sizeof(*ei)) {
                if (!insert) {
                        err = -ENOENT;
                        goto out;
                }
                ret = convert_extent_item_v0(trans, root, path, owner,
                                             extra_size);
                if (ret < 0) {
                        err = ret;
                        goto out;
                }
                leaf = path->nodes[0];
                item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        }
#endif
        BUG_ON(item_size < sizeof(*ei));

        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        flags = btrfs_extent_flags(leaf, ei);

        ptr = (unsigned long)(ei + 1);
        end = (unsigned long)ei + item_size;

        if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK && !skinny_metadata) {
                ptr += sizeof(struct btrfs_tree_block_info);
                BUG_ON(ptr > end);
        }

        err = -ENOENT;
        while (1) {
                if (ptr >= end) {
                        WARN_ON(ptr > end);
                        break;
                }
                iref = (struct btrfs_extent_inline_ref *)ptr;
                type = btrfs_extent_inline_ref_type(leaf, iref);
                if (want < type)
                        break;
                if (want > type) {
                        ptr += btrfs_extent_inline_ref_size(type);
                        continue;
                }

                if (type == BTRFS_EXTENT_DATA_REF_KEY) {
                        struct btrfs_extent_data_ref *dref;
                        dref = (struct btrfs_extent_data_ref *)(&iref->offset);
                        if (match_extent_data_ref(leaf, dref, root_objectid,
                                                  owner, offset)) {
                                err = 0;
                                break;
                        }
                        if (hash_extent_data_ref_item(leaf, dref) <
                            hash_extent_data_ref(root_objectid, owner, offset))
                                break;
                } else {
                        u64 ref_offset;
                        ref_offset = btrfs_extent_inline_ref_offset(leaf, iref);
                        if (parent > 0) {
                                if (parent == ref_offset) {
                                        err = 0;
                                        break;
                                }
                                if (ref_offset < parent)
                                        break;
                        } else {
                                if (root_objectid == ref_offset) {
                                        err = 0;
                                        break;
                                }
                                if (ref_offset < root_objectid)
                                        break;
                        }
                }
                ptr += btrfs_extent_inline_ref_size(type);
        }
        if (err == -ENOENT && insert) {
                if (item_size + extra_size >=
                    BTRFS_MAX_EXTENT_ITEM_SIZE(root)) {
                        err = -EAGAIN;
                        goto out;
                }
                /*
                 * To add new inline back ref, we have to make sure
                 * there is no corresponding back ref item.
                 * For simplicity, we just do not add new inline back
                 * ref if there is any kind of item for this block
                 */
                if (find_next_key(path, 0, &key) == 0 &&
                    key.objectid == bytenr &&
                    key.type < BTRFS_BLOCK_GROUP_ITEM_KEY) {
                        err = -EAGAIN;
                        goto out;
                }
        }
        *ref_ret = (struct btrfs_extent_inline_ref *)ptr;
out:
        if (insert) {
                path->keep_locks = 0;
                btrfs_unlock_up_safe(path, 1);
        }
        return err;
}

/*
 * helper to add new inline back ref
 */
static noinline_for_stack
void setup_inline_extent_backref(struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref *iref,
                                 u64 parent, u64 root_objectid,
                                 u64 owner, u64 offset, int refs_to_add,
                                 struct btrfs_delayed_extent_op *extent_op)
{
        struct extent_buffer *leaf;
        struct btrfs_extent_item *ei;
        unsigned long ptr;
        unsigned long end;
        unsigned long item_offset;
        u64 refs;
        int size;
        int type;

        leaf = path->nodes[0];
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        item_offset = (unsigned long)iref - (unsigned long)ei;

        type = extent_ref_type(parent, owner);
        size = btrfs_extent_inline_ref_size(type);

        btrfs_extend_item(root, path, size);

        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        refs = btrfs_extent_refs(leaf, ei);
        refs += refs_to_add;
        btrfs_set_extent_refs(leaf, ei, refs);
        if (extent_op)
                __run_delayed_extent_op(extent_op, leaf, ei);

        ptr = (unsigned long)ei + item_offset;
        end = (unsigned long)ei + btrfs_item_size_nr(leaf, path->slots[0]);
        if (ptr < end - size)
                memmove_extent_buffer(leaf, ptr + size, ptr,
                                      end - size - ptr);

        iref = (struct btrfs_extent_inline_ref *)ptr;
        btrfs_set_extent_inline_ref_type(leaf, iref, type);
        if (type == BTRFS_EXTENT_DATA_REF_KEY) {
                struct btrfs_extent_data_ref *dref;
                dref = (struct btrfs_extent_data_ref *)(&iref->offset);
                btrfs_set_extent_data_ref_root(leaf, dref, root_objectid);
                btrfs_set_extent_data_ref_objectid(leaf, dref, owner);
                btrfs_set_extent_data_ref_offset(leaf, dref, offset);
                btrfs_set_extent_data_ref_count(leaf, dref, refs_to_add);
        } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
                struct btrfs_shared_data_ref *sref;
                sref = (struct btrfs_shared_data_ref *)(iref + 1);
                btrfs_set_shared_data_ref_count(leaf, sref, refs_to_add);
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
        } else if (type == BTRFS_SHARED_BLOCK_REF_KEY) {
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
        } else {
                btrfs_set_extent_inline_ref_offset(leaf, iref, root_objectid);
        }
        btrfs_mark_buffer_dirty(leaf);
}

static int lookup_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref **ref_ret,
                                 u64 bytenr, u64 num_bytes, u64 parent,
                                 u64 root_objectid, u64 owner, u64 offset)
{
        int ret;

        ret = lookup_inline_extent_backref(trans, root, path, ref_ret,
                                           bytenr, num_bytes, parent,
                                           root_objectid, owner, offset, 0);
        if (ret != -ENOENT)
                return ret;

        btrfs_release_path(path);
        *ref_ret = NULL;

        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                ret = lookup_tree_block_ref(trans, root, path, bytenr, parent,
                                            root_objectid);
        } else {
                ret = lookup_extent_data_ref(trans, root, path, bytenr, parent,
                                             root_objectid, owner, offset);
        }
        return ret;
}

/*
 * helper to update/remove inline back ref
 */
static noinline_for_stack
void update_inline_extent_backref(struct btrfs_root *root,
                                  struct btrfs_path *path,
                                  struct btrfs_extent_inline_ref *iref,
                                  int refs_to_mod,
                                  struct btrfs_delayed_extent_op *extent_op,
                                  int *last_ref)
{
        struct extent_buffer *leaf;
        struct btrfs_extent_item *ei;
        struct btrfs_extent_data_ref *dref = NULL;
        struct btrfs_shared_data_ref *sref = NULL;
        unsigned long ptr;
        unsigned long end;
        u32 item_size;
        int size;
        int type;
        u64 refs;

        leaf = path->nodes[0];
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        refs = btrfs_extent_refs(leaf, ei);
        WARN_ON(refs_to_mod < 0 && refs + refs_to_mod <= 0);
        refs += refs_to_mod;
        btrfs_set_extent_refs(leaf, ei, refs);
        if (extent_op)
                __run_delayed_extent_op(extent_op, leaf, ei);

        type = btrfs_extent_inline_ref_type(leaf, iref);

        if (type == BTRFS_EXTENT_DATA_REF_KEY) {
                dref = (struct btrfs_extent_data_ref *)(&iref->offset);
                refs = btrfs_extent_data_ref_count(leaf, dref);
        } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
                sref = (struct btrfs_shared_data_ref *)(iref + 1);
                refs = btrfs_shared_data_ref_count(leaf, sref);
        } else {
                refs = 1;
                BUG_ON(refs_to_mod != -1);
        }

        BUG_ON(refs_to_mod < 0 && refs < -refs_to_mod);
        refs += refs_to_mod;

        if (refs > 0) {
                if (type == BTRFS_EXTENT_DATA_REF_KEY)
                        btrfs_set_extent_data_ref_count(leaf, dref, refs);
                else
                        btrfs_set_shared_data_ref_count(leaf, sref, refs);
        } else {
                *last_ref = 1;
                size =  btrfs_extent_inline_ref_size(type);
                item_size = btrfs_item_size_nr(leaf, path->slots[0]);
                ptr = (unsigned long)iref;
                end = (unsigned long)ei + item_size;
                if (ptr + size < end)
                        memmove_extent_buffer(leaf, ptr, ptr + size,
                                              end - ptr - size);
                item_size -= size;
                btrfs_truncate_item(root, path, item_size, 1);
        }
        btrfs_mark_buffer_dirty(leaf);
}

static noinline_for_stack
int insert_inline_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 u64 bytenr, u64 num_bytes, u64 parent,
                                 u64 root_objectid, u64 owner,
                                 u64 offset, int refs_to_add,
                                 struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_extent_inline_ref *iref;
        int ret;

        ret = lookup_inline_extent_backref(trans, root, path, &iref,
                                           bytenr, num_bytes, parent,
                                           root_objectid, owner, offset, 1);
        if (ret == 0) {
                BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID);
                update_inline_extent_backref(root, path, iref,
                                             refs_to_add, extent_op, NULL);
        } else if (ret == -ENOENT) {
                setup_inline_extent_backref(root, path, iref, parent,
                                            root_objectid, owner, offset,
                                            refs_to_add, extent_op);
                ret = 0;
        }
        return ret;
}

static int insert_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 u64 bytenr, u64 parent, u64 root_objectid,
                                 u64 owner, u64 offset, int refs_to_add)
{
        int ret;
        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                BUG_ON(refs_to_add != 1);
                ret = insert_tree_block_ref(trans, root, path, bytenr,
                                            parent, root_objectid);
        } else {
                ret = insert_extent_data_ref(trans, root, path, bytenr,
                                             parent, root_objectid,
                                             owner, offset, refs_to_add);
        }
        return ret;
}

static int remove_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref *iref,
                                 int refs_to_drop, int is_data, int *last_ref)
{
        int ret = 0;

        BUG_ON(!is_data && refs_to_drop != 1);
        if (iref) {
                update_inline_extent_backref(root, path, iref,
                                             -refs_to_drop, NULL, last_ref);
        } else if (is_data) {
                ret = remove_extent_data_ref(trans, root, path, refs_to_drop,
                                             last_ref);
        } else {
                *last_ref = 1;
                ret = btrfs_del_item(trans, root, path);
        }
        return ret;
}

#define in_range(b, first, len)        ((b) >= (first) && (b) < (first) + (len))
static int btrfs_issue_discard(struct block_device *bdev, u64 start, u64 len,
                               u64 *discarded_bytes)
{
        int j, ret = 0;
        u64 bytes_left, end;
        u64 aligned_start = ALIGN(start, 1 << 9);

        if (WARN_ON(start != aligned_start)) {
                len -= aligned_start - start;
                len = round_down(len, 1 << 9);
                start = aligned_start;
        }

        *discarded_bytes = 0;

        if (!len)
                return 0;

        end = start + len;
        bytes_left = len;

        /* Skip any superblocks on this device. */
        for (j = 0; j < BTRFS_SUPER_MIRROR_MAX; j++) {
                u64 sb_start = btrfs_sb_offset(j);
                u64 sb_end = sb_start + BTRFS_SUPER_INFO_SIZE;
                u64 size = sb_start - start;

                if (!in_range(sb_start, start, bytes_left) &&
                    !in_range(sb_end, start, bytes_left) &&
                    !in_range(start, sb_start, BTRFS_SUPER_INFO_SIZE))
                        continue;

                /*
                 * Superblock spans beginning of range.  Adjust start and
                 * try again.
                 */
                if (sb_start <= start) {
                        start += sb_end - start;
                        if (start > end) {
                                bytes_left = 0;
                                break;
                        }
                        bytes_left = end - start;
                        continue;
                }

                if (size) {
                        ret = blkdev_issue_discard(bdev, start >> 9, size >> 9,
                                                   GFP_NOFS, 0);
                        if (!ret)
                                *discarded_bytes += size;
                        else if (ret != -EOPNOTSUPP)
                                return ret;
                }

                start = sb_end;
                if (start > end) {
                        bytes_left = 0;
                        break;
                }
                bytes_left = end - start;
        }

        if (bytes_left) {
                ret = blkdev_issue_discard(bdev, start >> 9, bytes_left >> 9,
                                           GFP_NOFS, 0);
                if (!ret)
                        *discarded_bytes += bytes_left;
        }
        return ret;
}

int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
                         u64 num_bytes, u64 *actual_bytes)
{
        int ret;
        u64 discarded_bytes = 0;
        struct btrfs_bio *bbio = NULL;


        /* Tell the block device(s) that the sectors can be discarded */
        ret = btrfs_map_block(root->fs_info, REQ_DISCARD,
                              bytenr, &num_bytes, &bbio, 0);
        /* Error condition is -ENOMEM */
        if (!ret) {
                struct btrfs_bio_stripe *stripe = bbio->stripes;
                int i;


                for (i = 0; i < bbio->num_stripes; i++, stripe++) {
                        u64 bytes;
                        if (!stripe->dev->can_discard)
                                continue;

                        ret = btrfs_issue_discard(stripe->dev->bdev,
                                                  stripe->physical,
                                                  stripe->length,
                                                  &bytes);
                        if (!ret)
                                discarded_bytes += bytes;
                        else if (ret != -EOPNOTSUPP)
                                break; /* Logic errors or -ENOMEM, or -EIO but I don't know how that could happen JDM */

                        /*
                         * Just in case we get back EOPNOTSUPP for some reason,
                         * just ignore the return value so we don't screw up
                         * people calling discard_extent.
                         */
                        ret = 0;
                }
                btrfs_put_bbio(bbio);
        }

        if (actual_bytes)
                *actual_bytes = discarded_bytes;


        if (ret == -EOPNOTSUPP)
                ret = 0;
        return ret;
}

/* Can return -ENOMEM */
int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root,
                         u64 bytenr, u64 num_bytes, u64 parent,
                         u64 root_objectid, u64 owner, u64 offset)
{
        int ret;
        struct btrfs_fs_info *fs_info = root->fs_info;

        BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID &&
               root_objectid == BTRFS_TREE_LOG_OBJECTID);

        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                ret = btrfs_add_delayed_tree_ref(fs_info, trans, bytenr,
                                        num_bytes,
                                        parent, root_objectid, (int)owner,
                                        BTRFS_ADD_DELAYED_REF, NULL);
        } else {
                ret = btrfs_add_delayed_data_ref(fs_info, trans, bytenr,
                                        num_bytes, parent, root_objectid,
                                        owner, offset, 0,
                                        BTRFS_ADD_DELAYED_REF, NULL);
        }
        return ret;
}

static int __btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,
                                  struct btrfs_delayed_ref_node *node,
                                  u64 parent, u64 root_objectid,
                                  u64 owner, u64 offset, int refs_to_add,
                                  struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_extent_item *item;
        struct btrfs_key key;
        u64 bytenr = node->bytenr;
        u64 num_bytes = node->num_bytes;
        u64 refs;
        int ret;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        path->reada = 1;
        path->leave_spinning = 1;
        /* this will setup the path even if it fails to insert the back ref */
        ret = insert_inline_extent_backref(trans, fs_info->extent_root, path,
                                           bytenr, num_bytes, parent,
                                           root_objectid, owner, offset,
                                           refs_to_add, extent_op);
        if ((ret < 0 && ret != -EAGAIN) || !ret)
                goto out;

        /*
         * Ok we had -EAGAIN which means we didn't have space to insert and
         * inline extent ref, so just update the reference count and add a
         * normal backref.
         */
        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        refs = btrfs_extent_refs(leaf, item);
        btrfs_set_extent_refs(leaf, item, refs + refs_to_add);
        if (extent_op)
                __run_delayed_extent_op(extent_op, leaf, item);

        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

        path->reada = 1;
        path->leave_spinning = 1;
        /* now insert the actual backref */
        ret = insert_extent_backref(trans, root->fs_info->extent_root,
                                    path, bytenr, parent, root_objectid,
                                    owner, offset, refs_to_add);
        if (ret)
                btrfs_abort_transaction(trans, root, ret);
out:
        btrfs_free_path(path);
        return ret;
}

static int run_delayed_data_ref(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                struct btrfs_delayed_ref_node *node,
                                struct btrfs_delayed_extent_op *extent_op,
                                int insert_reserved)
{
        int ret = 0;
        struct btrfs_delayed_data_ref *ref;
        struct btrfs_key ins;
        u64 parent = 0;
        u64 ref_root = 0;
        u64 flags = 0;

        ins.objectid = node->bytenr;
        ins.offset = node->num_bytes;
        ins.type = BTRFS_EXTENT_ITEM_KEY;

        ref = btrfs_delayed_node_to_data_ref(node);
        trace_run_delayed_data_ref(node, ref, node->action);

        if (node->type == BTRFS_SHARED_DATA_REF_KEY)
                parent = ref->parent;
        ref_root = ref->root;

        if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
                if (extent_op)
                        flags |= extent_op->flags_to_set;
                ret = alloc_reserved_file_extent(trans, root,
                                                 parent, ref_root, flags,
                                                 ref->objectid, ref->offset,
                                                 &ins, node->ref_mod);
        } else if (node->action == BTRFS_ADD_DELAYED_REF) {
                ret = __btrfs_inc_extent_ref(trans, root, node, parent,
                                             ref_root, ref->objectid,
                                             ref->offset, node->ref_mod,
                                             extent_op);
        } else if (node->action == BTRFS_DROP_DELAYED_REF) {
                ret = __btrfs_free_extent(trans, root, node, parent,
                                          ref_root, ref->objectid,
                                          ref->offset, node->ref_mod,
                                          extent_op);
        } else {
                BUG();
        }
        return ret;
}

static void __run_delayed_extent_op(struct btrfs_delayed_extent_op *extent_op,
                                    struct extent_buffer *leaf,
                                    struct btrfs_extent_item *ei)
{
        u64 flags = btrfs_extent_flags(leaf, ei);
        if (extent_op->update_flags) {
                flags |= extent_op->flags_to_set;
                btrfs_set_extent_flags(leaf, ei, flags);
        }

        if (extent_op->update_key) {
                struct btrfs_tree_block_info *bi;
                BUG_ON(!(flags & BTRFS_EXTENT_FLAG_TREE_BLOCK));
                bi = (struct btrfs_tree_block_info *)(ei + 1);
                btrfs_set_tree_block_key(leaf, bi, &extent_op->key);
        }
}

static int run_delayed_extent_op(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_delayed_ref_node *node,
                                 struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_key key;
        struct btrfs_path *path;
        struct btrfs_extent_item *ei;
        struct extent_buffer *leaf;
        u32 item_size;
        int ret;
        int err = 0;
        int metadata = !extent_op->is_data;

        if (trans->aborted)
                return 0;

        if (metadata && !btrfs_fs_incompat(root->fs_info, SKINNY_METADATA))
                metadata = 0;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        key.objectid = node->bytenr;

        if (metadata) {
                key.type = BTRFS_METADATA_ITEM_KEY;
                key.offset = extent_op->level;
        } else {
                key.type = BTRFS_EXTENT_ITEM_KEY;
                key.offset = node->num_bytes;
        }

again:
        path->reada = 1;
        path->leave_spinning = 1;
        ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key,
                                path, 0, 1);
        if (ret < 0) {
                err = ret;
                goto out;
        }
        if (ret > 0) {
                if (metadata) {
                        if (path->slots[0] > 0) {
                                path->slots[0]--;
                                btrfs_item_key_to_cpu(path->nodes[0], &key,
                                                      path->slots[0]);
                                if (key.objectid == node->bytenr &&
                                    key.type == BTRFS_EXTENT_ITEM_KEY &&
                                    key.offset == node->num_bytes)
                                        ret = 0;
                        }
                        if (ret > 0) {
                                btrfs_release_path(path);
                                metadata = 0;

                                key.objectid = node->bytenr;
                                key.offset = node->num_bytes;
                                key.type = BTRFS_EXTENT_ITEM_KEY;
                                goto again;
                        }
                } else {
                        err = -EIO;
                        goto out;
                }
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        if (item_size < sizeof(*ei)) {
                ret = convert_extent_item_v0(trans, root->fs_info->extent_root,
                                             path, (u64)-1, 0);
                if (ret < 0) {
                        err = ret;
                        goto out;
                }
                leaf = path->nodes[0];
                item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        }
#endif
        BUG_ON(item_size < sizeof(*ei));
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
        __run_delayed_extent_op(extent_op, leaf, ei);

        btrfs_mark_buffer_dirty(leaf);
out:
        btrfs_free_path(path);
        return err;
}

static int run_delayed_tree_ref(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                struct btrfs_delayed_ref_node *node,
                                struct btrfs_delayed_extent_op *extent_op,
                                int insert_reserved)
{
        int ret = 0;
        struct btrfs_delayed_tree_ref *ref;
        struct btrfs_key ins;
        u64 parent = 0;
        u64 ref_root = 0;
        bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
                                                 SKINNY_METADATA);

        ref = btrfs_delayed_node_to_tree_ref(node);
        trace_run_delayed_tree_ref(node, ref, node->action);

        if (node->type == BTRFS_SHARED_BLOCK_REF_KEY)
                parent = ref->parent;
        ref_root = ref->root;

        ins.objectid = node->bytenr;
        if (skinny_metadata) {
                ins.offset = ref->level;
                ins.type = BTRFS_METADATA_ITEM_KEY;
        } else {
                ins.offset = node->num_bytes;
                ins.type = BTRFS_EXTENT_ITEM_KEY;
        }

        BUG_ON(node->ref_mod != 1);
        if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
                BUG_ON(!extent_op || !extent_op->update_flags);
                ret = alloc_reserved_tree_block(trans, root,
                                                parent, ref_root,
                                                extent_op->flags_to_set,
                                                &extent_op->key,
                                                ref->level, &ins);
        } else if (node->action == BTRFS_ADD_DELAYED_REF) {
                ret = __btrfs_inc_extent_ref(trans, root, node,
                                             parent, ref_root,
                                             ref->level, 0, 1,
                                             extent_op);
        } else if (node->action == BTRFS_DROP_DELAYED_REF) {
                ret = __btrfs_free_extent(trans, root, node,
                                          parent, ref_root,
                                          ref->level, 0, 1, extent_op);
        } else {
                BUG();
        }
        return ret;
}

/* helper function to actually process a single delayed ref entry */
static int run_one_delayed_ref(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               struct btrfs_delayed_ref_node *node,
                               struct btrfs_delayed_extent_op *extent_op,
                               int insert_reserved)
{
        int ret = 0;

        if (trans->aborted) {
                if (insert_reserved)
                        btrfs_pin_extent(root, node->bytenr,
                                         node->num_bytes, 1);
                return 0;
        }

        if (btrfs_delayed_ref_is_head(node)) {
                struct btrfs_delayed_ref_head *head;
                /*
                 * we've hit the end of the chain and we were supposed
                 * to insert this extent into the tree.  But, it got
                 * deleted before we ever needed to insert it, so all
                 * we have to do is clean up the accounting
                 */
                BUG_ON(extent_op);
                head = btrfs_delayed_node_to_head(node);
                trace_run_delayed_ref_head(node, head, node->action);

                if (insert_reserved) {
                        btrfs_pin_extent(root, node->bytenr,
                                         node->num_bytes, 1);
                        if (head->is_data) {
                                ret = btrfs_del_csums(trans, root,
                                                      node->bytenr,
                                                      node->num_bytes);
                        }
                }

                /* Also free its reserved qgroup space */
                btrfs_qgroup_free_delayed_ref(root->fs_info,
                                              head->qgroup_ref_root,
                                              head->qgroup_reserved);
                return ret;
        }

        if (node->type == BTRFS_TREE_BLOCK_REF_KEY ||
            node->type == BTRFS_SHARED_BLOCK_REF_KEY)
                ret = run_delayed_tree_ref(trans, root, node, extent_op,
                                           insert_reserved);
        else if (node->type == BTRFS_EXTENT_DATA_REF_KEY ||
                 node->type == BTRFS_SHARED_DATA_REF_KEY)
                ret = run_delayed_data_ref(trans, root, node, extent_op,
                                           insert_reserved);
        else
                BUG();
        return ret;
}

static inline struct btrfs_delayed_ref_node *
select_delayed_ref(struct btrfs_delayed_ref_head *head)
{
        struct btrfs_delayed_ref_node *ref;

        if (list_empty(&head->ref_list))
                return NULL;

        /*
         * Select a delayed ref of type BTRFS_ADD_DELAYED_REF first.
         * This is to prevent a ref count from going down to zero, which deletes
         * the extent item from the extent tree, when there still are references
         * to add, which would fail because they would not find the extent item.
         */
        list_for_each_entry(ref, &head->ref_list, list) {
                if (ref->action == BTRFS_ADD_DELAYED_REF)
                        return ref;
        }

        return list_entry(head->ref_list.next, struct btrfs_delayed_ref_node,
                          list);
}

/*
 * Returns 0 on success or if called with an already aborted transaction.
 * Returns -ENOMEM or -EIO on failure and will abort the transaction.
 */
static noinline int __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                                             struct btrfs_root *root,
                                             unsigned long nr)
{
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_ref_node *ref;
        struct btrfs_delayed_ref_head *locked_ref = NULL;
        struct btrfs_delayed_extent_op *extent_op;
        struct btrfs_fs_info *fs_info = root->fs_info;
        ktime_t start = ktime_get();
        int ret;
        unsigned long count = 0;
        unsigned long actual_count = 0;
        int must_insert_reserved = 0;

        delayed_refs = &trans->transaction->delayed_refs;
        while (1) {
                if (!locked_ref) {
                        if (count >= nr)
                                break;

                        spin_lock(&delayed_refs->lock);
                        locked_ref = btrfs_select_ref_head(trans);
                        if (!locked_ref) {
                                spin_unlock(&delayed_refs->lock);
                                break;
                        }

                        /* grab the lock that says we are going to process
                         * all the refs for this head */
                        ret = btrfs_delayed_ref_lock(trans, locked_ref);
                        spin_unlock(&delayed_refs->lock);
                        /*
                         * we may have dropped the spin lock to get the head
                         * mutex lock, and that might have given someone else
                         * time to free the head.  If that's true, it has been
                         * removed from our list and we can move on.
                         */
                        if (ret == -EAGAIN) {
                                locked_ref = NULL;
                                count++;
                                continue;
                        }
                }

                /*
                 * We need to try and merge add/drops of the same ref since we
                 * can run into issues with relocate dropping the implicit ref
                 * and then it being added back again before the drop can
                 * finish.  If we merged anything we need to re-loop so we can
                 * get a good ref.
                 * Or we can get node references of the same type that weren't
                 * merged when created due to bumps in the tree mod seq, and
                 * we need to merge them to prevent adding an inline extent
                 * backref before dropping it (triggering a BUG_ON at
                 * insert_inline_extent_backref()).
                 */
                spin_lock(&locked_ref->lock);
                btrfs_merge_delayed_refs(trans, fs_info, delayed_refs,
                                         locked_ref);

                /*
                 * locked_ref is the head node, so we have to go one
                 * node back for any delayed ref updates
                 */
                ref = select_delayed_ref(locked_ref);

                if (ref && ref->seq &&
                    btrfs_check_delayed_seq(fs_info, delayed_refs, ref->seq)) {
                        spin_unlock(&locked_ref->lock);
                        btrfs_delayed_ref_unlock(locked_ref);
                        spin_lock(&delayed_refs->lock);
                        locked_ref->processing = 0;
                        delayed_refs->num_heads_ready++;
                        spin_unlock(&delayed_refs->lock);
                        locked_ref = NULL;
                        cond_resched();
                        count++;
                        continue;
                }

                /*
                 * record the must insert reserved flag before we
                 * drop the spin lock.
                 */
                must_insert_reserved = locked_ref->must_insert_reserved;
                locked_ref->must_insert_reserved = 0;

                extent_op = locked_ref->extent_op;
                locked_ref->extent_op = NULL;

                if (!ref) {


                        /* All delayed refs have been processed, Go ahead
                         * and send the head node to run_one_delayed_ref,
                         * so that any accounting fixes can happen
                         */
                        ref = &locked_ref->node;

                        if (extent_op && must_insert_reserved) {
                                btrfs_free_delayed_extent_op(extent_op);
                                extent_op = NULL;
                        }

                        if (extent_op) {
                                spin_unlock(&locked_ref->lock);
                                ret = run_delayed_extent_op(trans, root,
                                                            ref, extent_op);
                                btrfs_free_delayed_extent_op(extent_op);

                                if (ret) {
                                        /*
                                         * Need to reset must_insert_reserved if
                                         * there was an error so the abort stuff
                                         * can cleanup the reserved space
                                         * properly.
                                         */
                                        if (must_insert_reserved)
                                                locked_ref->must_insert_reserved = 1;
                                        locked_ref->processing = 0;
                                        btrfs_debug(fs_info, "run_delayed_extent_op returned %d", ret);
                                        btrfs_delayed_ref_unlock(locked_ref);
                                        return ret;
                                }
                                continue;
                        }

                        /*
                         * Need to drop our head ref lock and re-aqcuire the
                         * delayed ref lock and then re-check to make sure
                         * nobody got added.
                         */
                        spin_unlock(&locked_ref->lock);
                        spin_lock(&delayed_refs->lock);
                        spin_lock(&locked_ref->lock);
                        if (!list_empty(&locked_ref->ref_list) ||
                            locked_ref->extent_op) {
                                spin_unlock(&locked_ref->lock);
                                spin_unlock(&delayed_refs->lock);
                                continue;
                        }
                        ref->in_tree = 0;
                        delayed_refs->num_heads--;
                        rb_erase(&locked_ref->href_node,
                                 &delayed_refs->href_root);
                        spin_unlock(&delayed_refs->lock);
                } else {
                        actual_count++;
                        ref->in_tree = 0;
                        list_del(&ref->list);
                }
                atomic_dec(&delayed_refs->num_entries);

                if (!btrfs_delayed_ref_is_head(ref)) {
                        /*
                         * when we play the delayed ref, also correct the
                         * ref_mod on head
                         */
                        switch (ref->action) {
                        case BTRFS_ADD_DELAYED_REF:
                        case BTRFS_ADD_DELAYED_EXTENT:
                                locked_ref->node.ref_mod -= ref->ref_mod;
                                break;
                        case BTRFS_DROP_DELAYED_REF:
                                locked_ref->node.ref_mod += ref->ref_mod;
                                break;
                        default:
                                WARN_ON(1);
                        }
                }
                spin_unlock(&locked_ref->lock);

                ret = run_one_delayed_ref(trans, root, ref, extent_op,
                                          must_insert_reserved);

                btrfs_free_delayed_extent_op(extent_op);
                if (ret) {
                        locked_ref->processing = 0;
                        btrfs_delayed_ref_unlock(locked_ref);
                        btrfs_put_delayed_ref(ref);
                        btrfs_debug(fs_info, "run_one_delayed_ref returned %d", ret);
                        return ret;
                }

                /*
                 * If this node is a head, that means all the refs in this head
                 * have been dealt with, and we will pick the next head to deal
                 * with, so we must unlock the head and drop it from the cluster
                 * list before we release it.
                 */
                if (btrfs_delayed_ref_is_head(ref)) {
                        if (locked_ref->is_data &&
                            locked_ref->total_ref_mod < 0) {
                                spin_lock(&delayed_refs->lock);
                                delayed_refs->pending_csums -= ref->num_bytes;
                                spin_unlock(&delayed_refs->lock);
                        }
                        btrfs_delayed_ref_unlock(locked_ref);
                        locked_ref = NULL;
                }
                btrfs_put_delayed_ref(ref);
                count++;
                cond_resched();
        }

        /*
         * We don't want to include ref heads since we can have empty ref heads
         * and those will drastically skew our runtime down since we just do
         * accounting, no actual extent tree updates.
         */
        if (actual_count > 0) {
                u64 runtime = ktime_to_ns(ktime_sub(ktime_get(), start));
                u64 avg;

                /*
                 * We weigh the current average higher than our current runtime
                 * to avoid large swings in the average.
                 */
                spin_lock(&delayed_refs->lock);
                avg = fs_info->avg_delayed_ref_runtime * 3 + runtime;
                fs_info->avg_delayed_ref_runtime = avg >> 2;    /* div by 4 */
                spin_unlock(&delayed_refs->lock);
        }
        return 0;
}

#ifdef SCRAMBLE_DELAYED_REFS
/*
 * Normally delayed refs get processed in ascending bytenr order. This
 * correlates in most cases to the order added. To expose dependencies on this
 * order, we start to process the tree in the middle instead of the beginning
 */
static u64 find_middle(struct rb_root *root)
{
        struct rb_node *n = root->rb_node;
        struct btrfs_delayed_ref_node *entry;
        int alt = 1;
        u64 middle;
        u64 first = 0, last = 0;

        n = rb_first(root);
        if (n) {
                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
                first = entry->bytenr;
        }
        n = rb_last(root);
        if (n) {
                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
                last = entry->bytenr;
        }
        n = root->rb_node;

        while (n) {
                entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
                WARN_ON(!entry->in_tree);

                middle = entry->bytenr;

                if (alt)
                        n = n->rb_left;
                else
                        n = n->rb_right;

                alt = 1 - alt;
        }
        return middle;
}
#endif

static inline u64 heads_to_leaves(struct btrfs_root *root, u64 heads)
{
        u64 num_bytes;

        num_bytes = heads * (sizeof(struct btrfs_extent_item) +
                             sizeof(struct btrfs_extent_inline_ref));
        if (!btrfs_fs_incompat(root->fs_info, SKINNY_METADATA))
                num_bytes += heads * sizeof(struct btrfs_tree_block_info);

        /*
         * We don't ever fill up leaves all the way so multiply by 2 just to be
         * closer to what we're really going to want to ouse.
         */
        return div_u64(num_bytes, BTRFS_LEAF_DATA_SIZE(root));
}

/*
 * Takes the number of bytes to be csumm'ed and figures out how many leaves it
 * would require to store the csums for that many bytes.
 */
u64 btrfs_csum_bytes_to_leaves(struct btrfs_root *root, u64 csum_bytes)
{
        u64 csum_size;
        u64 num_csums_per_leaf;
        u64 num_csums;

        csum_size = BTRFS_LEAF_DATA_SIZE(root) - sizeof(struct btrfs_item);
        num_csums_per_leaf = div64_u64(csum_size,
                        (u64)btrfs_super_csum_size(root->fs_info->super_copy));
        num_csums = div64_u64(csum_bytes, root->sectorsize);
        num_csums += num_csums_per_leaf - 1;
        num_csums = div64_u64(num_csums, num_csums_per_leaf);
        return num_csums;
}

int btrfs_check_space_for_delayed_refs(struct btrfs_trans_handle *trans,
                                       struct btrfs_root *root)
{
        struct btrfs_block_rsv *global_rsv;
        u64 num_heads = trans->transaction->delayed_refs.num_heads_ready;
        u64 csum_bytes = trans->transaction->delayed_refs.pending_csums;
        u64 num_dirty_bgs = trans->transaction->num_dirty_bgs;
        u64 num_bytes, num_dirty_bgs_bytes;
        int ret = 0;

        num_bytes = btrfs_calc_trans_metadata_size(root, 1);
        num_heads = heads_to_leaves(root, num_heads);
        if (num_heads > 1)
                num_bytes += (num_heads - 1) * root->nodesize;
        num_bytes <<= 1;
        num_bytes += btrfs_csum_bytes_to_leaves(root, csum_bytes) * root->nodesize;
        num_dirty_bgs_bytes = btrfs_calc_trans_metadata_size(root,
                                                             num_dirty_bgs);
        global_rsv = &root->fs_info->global_block_rsv;

        /*
         * If we can't allocate any more chunks lets make sure we have _lots_ of
         * wiggle room since running delayed refs can create more delayed refs.
         */
        if (global_rsv->space_info->full) {
                num_dirty_bgs_bytes <<= 1;
                num_bytes <<= 1;
        }

        spin_lock(&global_rsv->lock);
        if (global_rsv->reserved <= num_bytes + num_dirty_bgs_bytes)
                ret = 1;
        spin_unlock(&global_rsv->lock);
        return ret;
}

int btrfs_should_throttle_delayed_refs(struct btrfs_trans_handle *trans,
                                       struct btrfs_root *root)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 num_entries =
                atomic_read(&trans->transaction->delayed_refs.num_entries);
        u64 avg_runtime;
        u64 val;

        smp_mb();
        avg_runtime = fs_info->avg_delayed_ref_runtime;
        val = num_entries * avg_runtime;
        if (num_entries * avg_runtime >= NSEC_PER_SEC)
                return 1;
        if (val >= NSEC_PER_SEC / 2)
                return 2;

        return btrfs_check_space_for_delayed_refs(trans, root);
}

struct async_delayed_refs {
        struct btrfs_root *root;
        int count;
        int error;
        int sync;
        struct completion wait;
        struct btrfs_work work;
};

static void delayed_ref_async_start(struct btrfs_work *work)
{
        struct async_delayed_refs *async;
        struct btrfs_trans_handle *trans;
        int ret;

        async = container_of(work, struct async_delayed_refs, work);

        trans = btrfs_join_transaction(async->root);
        if (IS_ERR(trans)) {
                async->error = PTR_ERR(trans);
                goto done;
        }

        /*
         * trans->sync means that when we call end_transaciton, we won't
         * wait on delayed refs
         */
        trans->sync = true;
        ret = btrfs_run_delayed_refs(trans, async->root, async->count);
        if (ret)
                async->error = ret;

        ret = btrfs_end_transaction(trans, async->root);
        if (ret && !async->error)
                async->error = ret;
done:
        if (async->sync)
                complete(&async->wait);
        else
                kfree(async);
}

int btrfs_async_run_delayed_refs(struct btrfs_root *root,
                                 unsigned long count, int wait)
{
        struct async_delayed_refs *async;
        int ret;

        async = kmalloc(sizeof(*async), GFP_NOFS);
        if (!async)
                return -ENOMEM;

        async->root = root->fs_info->tree_root;
        async->count = count;
        async->error = 0;
        if (wait)
                async->sync = 1;
        else
                async->sync = 0;
        init_completion(&async->wait);

        btrfs_init_work(&async->work, btrfs_extent_refs_helper,
                        delayed_ref_async_start, NULL, NULL);

        btrfs_queue_work(root->fs_info->extent_workers, &async->work);

        if (wait) {
                wait_for_completion(&async->wait);
                ret = async->error;
                kfree(async);
                return ret;
        }
        return 0;
}

/*
 * this starts processing the delayed reference count updates and
 * extent insertions we have queued up so far.  count can be
 * 0, which means to process everything in the tree at the start
 * of the run (but not newly added entries), or it can be some target
 * number you'd like to process.
 *
 * Returns 0 on success or if called with an aborted transaction
 * Returns <0 on error and aborts the transaction
 */
int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, unsigned long count)
{
        struct rb_node *node;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_ref_head *head;
        int ret;
        int run_all = count == (unsigned long)-1;
        bool can_flush_pending_bgs = trans->can_flush_pending_bgs;

        /* We'll clean this up in btrfs_cleanup_transaction */
        if (trans->aborted)
                return 0;

        if (root == root->fs_info->extent_root)
                root = root->fs_info->tree_root;

        delayed_refs = &trans->transaction->delayed_refs;
        if (count == 0)
                count = atomic_read(&delayed_refs->num_entries) * 2;

again:
#ifdef SCRAMBLE_DELAYED_REFS
        delayed_refs->run_delayed_start = find_middle(&delayed_refs->root);
#endif
        trans->can_flush_pending_bgs = false;
        ret = __btrfs_run_delayed_refs(trans, root, count);
        if (ret < 0) {
                btrfs_abort_transaction(trans, root, ret);
                return ret;
        }

        if (run_all) {
                if (!list_empty(&trans->new_bgs))
                        btrfs_create_pending_block_groups(trans, root);

                spin_lock(&delayed_refs->lock);
                node = rb_first(&delayed_refs->href_root);
                if (!node) {
                        spin_unlock(&delayed_refs->lock);
                        goto out;
                }
                count = (unsigned long)-1;

                while (node) {
                        head = rb_entry(node, struct btrfs_delayed_ref_head,
                                        href_node);
                        if (btrfs_delayed_ref_is_head(&head->node)) {
                                struct btrfs_delayed_ref_node *ref;

                                ref = &head->node;
                                atomic_inc(&ref->refs);

                                spin_unlock(&delayed_refs->lock);
                                /*
                                 * Mutex was contended, block until it's
                                 * released and try again
                                 */
                                mutex_lock(&head->mutex);
                                mutex_unlock(&head->mutex);

                                btrfs_put_delayed_ref(ref);
                                cond_resched();
                                goto again;
                        } else {
                                WARN_ON(1);
                        }
                        node = rb_next(node);
                }
                spin_unlock(&delayed_refs->lock);
                cond_resched();
                goto again;
        }
out:
        assert_qgroups_uptodate(trans);
        trans->can_flush_pending_bgs = can_flush_pending_bgs;
        return 0;
}

int btrfs_set_disk_extent_flags(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                u64 bytenr, u64 num_bytes, u64 flags,
                                int level, int is_data)
{
        struct btrfs_delayed_extent_op *extent_op;
        int ret;

        extent_op = btrfs_alloc_delayed_extent_op();
        if (!extent_op)
                return -ENOMEM;

        extent_op->flags_to_set = flags;
        extent_op->update_flags = 1;
        extent_op->update_key = 0;
        extent_op->is_data = is_data ? 1 : 0;
        extent_op->level = level;

        ret = btrfs_add_delayed_extent_op(root->fs_info, trans, bytenr,
                                          num_bytes, extent_op);
        if (ret)
                btrfs_free_delayed_extent_op(extent_op);
        return ret;
}

static noinline int check_delayed_ref(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root,
                                      struct btrfs_path *path,
                                      u64 objectid, u64 offset, u64 bytenr)
{
        struct btrfs_delayed_ref_head *head;
        struct btrfs_delayed_ref_node *ref;
        struct btrfs_delayed_data_ref *data_ref;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret = 0;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);
        head = btrfs_find_delayed_ref_head(trans, bytenr);
        if (!head) {
                spin_unlock(&delayed_refs->lock);
                return 0;
        }

        if (!mutex_trylock(&head->mutex)) {
                atomic_inc(&head->node.refs);
                spin_unlock(&delayed_refs->lock);

                btrfs_release_path(path);

                /*
                 * Mutex was contended, block until it's released and let
                 * caller try again
                 */
                mutex_lock(&head->mutex);
                mutex_unlock(&head->mutex);
                btrfs_put_delayed_ref(&head->node);
                return -EAGAIN;
        }
        spin_unlock(&delayed_refs->lock);

        spin_lock(&head->lock);
        list_for_each_entry(ref, &head->ref_list, list) {
                /* If it's a shared ref we know a cross reference exists */
                if (ref->type != BTRFS_EXTENT_DATA_REF_KEY) {
                        ret = 1;
                        break;
                }

                data_ref = btrfs_delayed_node_to_data_ref(ref);

                /*
                 * If our ref doesn't match the one we're currently looking at
                 * then we have a cross reference.
                 */
                if (data_ref->root != root->root_key.objectid ||
                    data_ref->objectid != objectid ||
                    data_ref->offset != offset) {
                        ret = 1;
                        break;
                }
        }
        spin_unlock(&head->lock);
        mutex_unlock(&head->mutex);
        return ret;
}

static noinline int check_committed_ref(struct btrfs_trans_handle *trans,
                                        struct btrfs_root *root,
                                        struct btrfs_path *path,
                                        u64 objectid, u64 offset, u64 bytenr)
{
        struct btrfs_root *extent_root = root->fs_info->extent_root;
        struct extent_buffer *leaf;
        struct btrfs_extent_data_ref *ref;
        struct btrfs_extent_inline_ref *iref;
        struct btrfs_extent_item *ei;
        struct btrfs_key key;
        u32 item_size;
        int ret;

        key.objectid = bytenr;
        key.offset = (u64)-1;
        key.type = BTRFS_EXTENT_ITEM_KEY;

        ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
        if (ret < 0)
                goto out;
        BUG_ON(ret == 0); /* Corruption */

        ret = -ENOENT;
        if (path->slots[0] == 0)
                goto out;

        path->slots[0]--;
        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

        if (key.objectid != bytenr || key.type != BTRFS_EXTENT_ITEM_KEY)
                goto out;

        ret = 1;
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        if (item_size < sizeof(*ei)) {
                WARN_ON(item_size != sizeof(struct btrfs_extent_item_v0));
                goto out;
        }
#endif
        ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);

        if (item_size != sizeof(*ei) +
            btrfs_extent_inline_ref_size(BTRFS_EXTENT_DATA_REF_KEY))
                goto out;

        if (btrfs_extent_generation(leaf, ei) <=
            btrfs_root_last_snapshot(&root->root_item))
                goto out;

        iref = (struct btrfs_extent_inline_ref *)(ei + 1);
        if (btrfs_extent_inline_ref_type(leaf, iref) !=
            BTRFS_EXTENT_DATA_REF_KEY)
                goto out;

        ref = (struct btrfs_extent_data_ref *)(&iref->offset);
        if (btrfs_extent_refs(leaf, ei) !=
            btrfs_extent_data_ref_count(leaf, ref) ||
            btrfs_extent_data_ref_root(leaf, ref) !=
            root->root_key.objectid ||
            btrfs_extent_data_ref_objectid(leaf, ref) != objectid ||
            btrfs_extent_data_ref_offset(leaf, ref) != offset)
                goto out;

        ret = 0;
out:
        return ret;
}

int btrfs_cross_ref_exist(struct btrfs_trans_handle *trans,
                          struct btrfs_root *root,
                          u64 objectid, u64 offset, u64 bytenr)
{
        struct btrfs_path *path;
        int ret;
        int ret2;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOENT;

        do {
                ret = check_committed_ref(trans, root, path, objectid,
                                          offset, bytenr);
                if (ret && ret != -ENOENT)
                        goto out;

                ret2 = check_delayed_ref(trans, root, path, objectid,
                                         offset, bytenr);
        } while (ret2 == -EAGAIN);

        if (ret2 && ret2 != -ENOENT) {
                ret = ret2;
                goto out;
        }

        if (ret != -ENOENT || ret2 != -ENOENT)
                ret = 0;
out:
        btrfs_free_path(path);
        if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID)
                WARN_ON(ret > 0);
        return ret;
}

static int __btrfs_mod_ref(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct extent_buffer *buf,
                           int full_backref, int inc)
{
        u64 bytenr;
        u64 num_bytes;
        u64 parent;
        u64 ref_root;
        u32 nritems;
        struct btrfs_key key;
        struct btrfs_file_extent_item *fi;
        int i;
        int level;
        int ret = 0;
        int (*process_func)(struct btrfs_trans_handle *, struct btrfs_root *,
                            u64, u64, u64, u64, u64, u64);


        if (btrfs_test_is_dummy_root(root))
                return 0;

        ref_root = btrfs_header_owner(buf);
        nritems = btrfs_header_nritems(buf);
        level = btrfs_header_level(buf);

        if (!test_bit(BTRFS_ROOT_REF_COWS, &root->state) && level == 0)
                return 0;

        if (inc)
                process_func = btrfs_inc_extent_ref;
        else
                process_func = btrfs_free_extent;

        if (full_backref)
                parent = buf->start;
        else
                parent = 0;

        for (i = 0; i < nritems; i++) {
                if (level == 0) {
                        btrfs_item_key_to_cpu(buf, &key, i);
                        if (key.type != BTRFS_EXTENT_DATA_KEY)
                                continue;
                        fi = btrfs_item_ptr(buf, i,
                                            struct btrfs_file_extent_item);
                        if (btrfs_file_extent_type(buf, fi) ==
                            BTRFS_FILE_EXTENT_INLINE)
                                continue;
                        bytenr = btrfs_file_extent_disk_bytenr(buf, fi);
                        if (bytenr == 0)
                                continue;

                        num_bytes = btrfs_file_extent_disk_num_bytes(buf, fi);
                        key.offset -= btrfs_file_extent_offset(buf, fi);
                        ret = process_func(trans, root, bytenr, num_bytes,
                                           parent, ref_root, key.objectid,
                                           key.offset);
                        if (ret)
                                goto fail;
                } else {
                        bytenr = btrfs_node_blockptr(buf, i);
                        num_bytes = root->nodesize;
                        ret = process_func(trans, root, bytenr, num_bytes,
                                           parent, ref_root, level - 1, 0);
                        if (ret)
                                goto fail;
                }
        }
        return 0;
fail:
        return ret;
}

int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                  struct extent_buffer *buf, int full_backref)
{
        return __btrfs_mod_ref(trans, root, buf, full_backref, 1);
}

int btrfs_dec_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                  struct extent_buffer *buf, int full_backref)
{
        return __btrfs_mod_ref(trans, root, buf, full_backref, 0);
}

static int write_one_cache_group(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct btrfs_block_group_cache *cache)
{
        int ret;
        struct btrfs_root *extent_root = root->fs_info->extent_root;
        unsigned long bi;
        struct extent_buffer *leaf;

        ret = btrfs_search_slot(trans, extent_root, &cache->key, path, 0, 1);
        if (ret) {
                if (ret > 0)
                        ret = -ENOENT;
                goto fail;
        }

        leaf = path->nodes[0];
        bi = btrfs_item_ptr_offset(leaf, path->slots[0]);
        write_extent_buffer(leaf, &cache->item, bi, sizeof(cache->item));
        btrfs_mark_buffer_dirty(leaf);
fail:
        btrfs_release_path(path);
        return ret;

}

static struct btrfs_block_group_cache *
next_block_group(struct btrfs_root *root,
                 struct btrfs_block_group_cache *cache)
{
        struct rb_node *node;

        spin_lock(&root->fs_info->block_group_cache_lock);

        /* If our block group was removed, we need a full search. */
        if (RB_EMPTY_NODE(&cache->cache_node)) {
                const u64 next_bytenr = cache->key.objectid + cache->key.offset;

                spin_unlock(&root->fs_info->block_group_cache_lock);
                btrfs_put_block_group(cache);
                cache = btrfs_lookup_first_block_group(root->fs_info,
                                                       next_bytenr);
                return cache;
        }
        node = rb_next(&cache->cache_node);
        btrfs_put_block_group(cache);
        if (node) {
                cache = rb_entry(node, struct btrfs_block_group_cache,
                                 cache_node);
                btrfs_get_block_group(cache);
        } else
                cache = NULL;
        spin_unlock(&root->fs_info->block_group_cache_lock);
        return cache;
}

static int cache_save_setup(struct btrfs_block_group_cache *block_group,
                            struct btrfs_trans_handle *trans,
                            struct btrfs_path *path)
{
        struct btrfs_root *root = block_group->fs_info->tree_root;
        struct inode *inode = NULL;
        u64 alloc_hint = 0;
        int dcs = BTRFS_DC_ERROR;
        u64 num_pages = 0;
        int retries = 0;
        int ret = 0;

        /*
         * If this block group is smaller than 100 megs don't bother caching the
         * block group.
         */
        if (block_group->key.offset < (100 * 1024 * 1024)) {
                spin_lock(&block_group->lock);
                block_group->disk_cache_state = BTRFS_DC_WRITTEN;
                spin_unlock(&block_group->lock);
                return 0;
        }

        if (trans->aborted)
                return 0;
again:
        inode = lookup_free_space_inode(root, block_group, path);
        if (IS_ERR(inode) && PTR_ERR(inode) != -ENOENT) {
                ret = PTR_ERR(inode);
                btrfs_release_path(path);
                goto out;
        }

        if (IS_ERR(inode)) {
                BUG_ON(retries);
                retries++;

                if (block_group->ro)
                        goto out_free;

                ret = create_free_space_inode(root, trans, block_group, path);
                if (ret)
                        goto out_free;
                goto again;
        }

        /* We've already setup this transaction, go ahead and exit */
        if (block_group->cache_generation == trans->transid &&
            i_size_read(inode)) {
                dcs = BTRFS_DC_SETUP;
                goto out_put;
        }

        /*
         * We want to set the generation to 0, that way if anything goes wrong
         * from here on out we know not to trust this cache when we load up next
         * time.
         */
        BTRFS_I(inode)->generation = 0;
        ret = btrfs_update_inode(trans, root, inode);
        if (ret) {
                /*
                 * So theoretically we could recover from this, simply set the
                 * super cache generation to 0 so we know to invalidate the
                 * cache, but then we'd have to keep track of the block groups
                 * that fail this way so we know we _have_ to reset this cache
                 * before the next commit or risk reading stale cache.  So to
                 * limit our exposure to horrible edge cases lets just abort the
                 * transaction, this only happens in really bad situations
                 * anyway.
                 */
                btrfs_abort_transaction(trans, root, ret);
                goto out_put;
        }
        WARN_ON(ret);

        if (i_size_read(inode) > 0) {
                ret = btrfs_check_trunc_cache_free_space(root,
                                        &root->fs_info->global_block_rsv);
                if (ret)
                        goto out_put;

                ret = btrfs_truncate_free_space_cache(root, trans, NULL, inode);
                if (ret)
                        goto out_put;
        }

        spin_lock(&block_group->lock);
        if (block_group->cached != BTRFS_CACHE_FINISHED ||
            !btrfs_test_opt(root, SPACE_CACHE)) {
                /*
                 * don't bother trying to write stuff out _if_
                 * a) we're not cached,
                 * b) we're with nospace_cache mount option.
                 */
                dcs = BTRFS_DC_WRITTEN;
                spin_unlock(&block_group->lock);
                goto out_put;
        }
        spin_unlock(&block_group->lock);

        /*
         * We hit an ENOSPC when setting up the cache in this transaction, just
         * skip doing the setup, we've already cleared the cache so we're safe.
         */
        if (test_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags)) {
                ret = -ENOSPC;
                goto out_put;
        }

        /*
         * Try to preallocate enough space based on how big the block group is.
         * Keep in mind this has to include any pinned space which could end up
         * taking up quite a bit since it's not folded into the other space
         * cache.
         */
        num_pages = div_u64(block_group->key.offset, 256 * 1024 * 1024);
        if (!num_pages)
                num_pages = 1;

        num_pages *= 16;
        num_pages *= PAGE_CACHE_SIZE;

        ret = btrfs_check_data_free_space(inode, 0, num_pages);
        if (ret)
                goto out_put;

        ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, num_pages,
                                              num_pages, num_pages,
                                              &alloc_hint);
        /*
         * Our cache requires contiguous chunks so that we don't modify a bunch
         * of metadata or split extents when writing the cache out, which means
         * we can enospc if we are heavily fragmented in addition to just normal
         * out of space conditions.  So if we hit this just skip setting up any
         * other block groups for this transaction, maybe we'll unpin enough
         * space the next time around.
         */
        if (!ret)
                dcs = BTRFS_DC_SETUP;
        else if (ret == -ENOSPC)
                set_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags);
        btrfs_free_reserved_data_space(inode, 0, num_pages);

out_put:
        iput(inode);
out_free:
        btrfs_release_path(path);
out:
        spin_lock(&block_group->lock);
        if (!ret && dcs == BTRFS_DC_SETUP)
                block_group->cache_generation = trans->transid;
        block_group->disk_cache_state = dcs;
        spin_unlock(&block_group->lock);

        return ret;
}

int btrfs_setup_space_cache(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root)
{
        struct btrfs_block_group_cache *cache, *tmp;
        struct btrfs_transaction *cur_trans = trans->transaction;
        struct btrfs_path *path;

        if (list_empty(&cur_trans->dirty_bgs) ||
            !btrfs_test_opt(root, SPACE_CACHE))
                return 0;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /* Could add new block groups, use _safe just in case */
        list_for_each_entry_safe(cache, tmp, &cur_trans->dirty_bgs,
                                 dirty_list) {
                if (cache->disk_cache_state == BTRFS_DC_CLEAR)
                        cache_save_setup(cache, trans, path);
        }

        btrfs_free_path(path);
        return 0;
}

/*
 * transaction commit does final block group cache writeback during a
 * critical section where nothing is allowed to change the FS.  This is
 * required in order for the cache to actually match the block group,
 * but can introduce a lot of latency into the commit.
 *
 * So, btrfs_start_dirty_block_groups is here to kick off block group
 * cache IO.  There's a chance we'll have to redo some of it if the
 * block group changes again during the commit, but it greatly reduces
 * the commit latency by getting rid of the easy block groups while
 * we're still allowing others to join the commit.
 */
int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root)
{
        struct btrfs_block_group_cache *cache;
        struct btrfs_transaction *cur_trans = trans->transaction;
        int ret = 0;
        int should_put;
        struct btrfs_path *path = NULL;
        LIST_HEAD(dirty);
        struct list_head *io = &cur_trans->io_bgs;
        int num_started = 0;
        int loops = 0;

        spin_lock(&cur_trans->dirty_bgs_lock);
        if (list_empty(&cur_trans->dirty_bgs)) {
                spin_unlock(&cur_trans->dirty_bgs_lock);
                return 0;
        }
        list_splice_init(&cur_trans->dirty_bgs, &dirty);
        spin_unlock(&cur_trans->dirty_bgs_lock);

again:
        /*
         * make sure all the block groups on our dirty list actually
         * exist
         */
        btrfs_create_pending_block_groups(trans, root);

        if (!path) {
                path = btrfs_alloc_path();
                if (!path)
                        return -ENOMEM;
        }

        /*
         * cache_write_mutex is here only to save us from balance or automatic
         * removal of empty block groups deleting this block group while we are
         * writing out the cache
         */
        mutex_lock(&trans->transaction->cache_write_mutex);
        while (!list_empty(&dirty)) {
                cache = list_first_entry(&dirty,
                                         struct btrfs_block_group_cache,
                                         dirty_list);
                /*
                 * this can happen if something re-dirties a block
                 * group that is already under IO.  Just wait for it to
                 * finish and then do it all again
                 */
                if (!list_empty(&cache->io_list)) {
                        list_del_init(&cache->io_list);
                        btrfs_wait_cache_io(root, trans, cache,
                                            &cache->io_ctl, path,
                                            cache->key.objectid);
                        btrfs_put_block_group(cache);
                }


                /*
                 * btrfs_wait_cache_io uses the cache->dirty_list to decide
                 * if it should update the cache_state.  Don't delete
                 * until after we wait.
                 *
                 * Since we're not running in the commit critical section
                 * we need the dirty_bgs_lock to protect from update_block_group
                 */
                spin_lock(&cur_trans->dirty_bgs_lock);
                list_del_init(&cache->dirty_list);
                spin_unlock(&cur_trans->dirty_bgs_lock);

                should_put = 1;

                cache_save_setup(cache, trans, path);

                if (cache->disk_cache_state == BTRFS_DC_SETUP) {
                        cache->io_ctl.inode = NULL;
                        ret = btrfs_write_out_cache(root, trans, cache, path);
                        if (ret == 0 && cache->io_ctl.inode) {
                                num_started++;
                                should_put = 0;

                                /*
                                 * the cache_write_mutex is protecting
                                 * the io_list
                                 */
                                list_add_tail(&cache->io_list, io);
                        } else {
                                /*
                                 * if we failed to write the cache, the
                                 * generation will be bad and life goes on
                                 */
                                ret = 0;
                        }
                }
                if (!ret) {
                        ret = write_one_cache_group(trans, root, path, cache);
                        /*
                         * Our block group might still be attached to the list
                         * of new block groups in the transaction handle of some
                         * other task (struct btrfs_trans_handle->new_bgs). This
                         * means its block group item isn't yet in the extent
                         * tree. If this happens ignore the error, as we will
                         * try again later in the critical section of the
                         * transaction commit.
                         */
                        if (ret == -ENOENT) {
                                ret = 0;
                                spin_lock(&cur_trans->dirty_bgs_lock);
                                if (list_empty(&cache->dirty_list)) {
                                        list_add_tail(&cache->dirty_list,
                                                      &cur_trans->dirty_bgs);
                                        btrfs_get_block_group(cache);
                                }
                                spin_unlock(&cur_trans->dirty_bgs_lock);
                        } else if (ret) {
                                btrfs_abort_transaction(trans, root, ret);
                        }
                }

                /* if its not on the io list, we need to put the block group */
                if (should_put)
                        btrfs_put_block_group(cache);

                if (ret)
                        break;

                /*
                 * Avoid blocking other tasks for too long. It might even save
                 * us from writing caches for block groups that are going to be
                 * removed.
                 */
                mutex_unlock(&trans->transaction->cache_write_mutex);
                mutex_lock(&trans->transaction->cache_write_mutex);
        }
        mutex_unlock(&trans->transaction->cache_write_mutex);

        /*
         * go through delayed refs for all the stuff we've just kicked off
         * and then loop back (just once)
         */
        ret = btrfs_run_delayed_refs(trans, root, 0);
        if (!ret && loops == 0) {
                loops++;
                spin_lock(&cur_trans->dirty_bgs_lock);
                list_splice_init(&cur_trans->dirty_bgs, &dirty);
                /*
                 * dirty_bgs_lock protects us from concurrent block group
                 * deletes too (not just cache_write_mutex).
                 */
                if (!list_empty(&dirty)) {
                        spin_unlock(&cur_trans->dirty_bgs_lock);
                        goto again;
                }
                spin_unlock(&cur_trans->dirty_bgs_lock);
        }

        btrfs_free_path(path);
        return ret;
}

int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root)
{
        struct btrfs_block_group_cache *cache;
        struct btrfs_transaction *cur_trans = trans->transaction;
        int ret = 0;
        int should_put;
        struct btrfs_path *path;
        struct list_head *io = &cur_trans->io_bgs;
        int num_started = 0;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /*
         * We don't need the lock here since we are protected by the transaction
         * commit.  We want to do the cache_save_setup first and then run the
         * delayed refs to make sure we have the best chance at doing this all
         * in one shot.
         */
        while (!list_empty(&cur_trans->dirty_bgs)) {
                cache = list_first_entry(&cur_trans->dirty_bgs,
                                         struct btrfs_block_group_cache,
                                         dirty_list);

                /*
                 * this can happen if cache_save_setup re-dirties a block
                 * group that is already under IO.  Just wait for it to
                 * finish and then do it all again
                 */
                if (!list_empty(&cache->io_list)) {
                        list_del_init(&cache->io_list);
                        btrfs_wait_cache_io(root, trans, cache,
                                            &cache->io_ctl, path,
                                            cache->key.objectid);
                        btrfs_put_block_group(cache);
                }

                /*
                 * don't remove from the dirty list until after we've waited
                 * on any pending IO
                 */
                list_del_init(&cache->dirty_list);
                should_put = 1;

                cache_save_setup(cache, trans, path);

                if (!ret)
                        ret = btrfs_run_delayed_refs(trans, root, (unsigned long) -1);

                if (!ret && cache->disk_cache_state == BTRFS_DC_SETUP) {
                        cache->io_ctl.inode = NULL;
                        ret = btrfs_write_out_cache(root, trans, cache, path);
                        if (ret == 0 && cache->io_ctl.inode) {
                                num_started++;
                                should_put = 0;
                                list_add_tail(&cache->io_list, io);
                        } else {
                                /*
                                 * if we failed to write the cache, the
                                 * generation will be bad and life goes on
                                 */
                                ret = 0;
                        }
                }
                if (!ret) {
                        ret = write_one_cache_group(trans, root, path, cache);
                        if (ret)
                                btrfs_abort_transaction(trans, root, ret);
                }

                /* if its not on the io list, we need to put the block group */
                if (should_put)
                        btrfs_put_block_group(cache);
        }

        while (!list_empty(io)) {
                cache = list_first_entry(io, struct btrfs_block_group_cache,
                                         io_list);
                list_del_init(&cache->io_list);
                btrfs_wait_cache_io(root, trans, cache,
                                    &cache->io_ctl, path, cache->key.objectid);
                btrfs_put_block_group(cache);
        }

        btrfs_free_path(path);
        return ret;
}

int btrfs_extent_readonly(struct btrfs_root *root, u64 bytenr)
{
        struct btrfs_block_group_cache *block_group;
        int readonly = 0;

        block_group = btrfs_lookup_block_group(root->fs_info, bytenr);
        if (!block_group || block_group->ro)
                readonly = 1;
        if (block_group)
                btrfs_put_block_group(block_group);
        return readonly;
}

static const char *alloc_name(u64 flags)
{
        switch (flags) {
        case BTRFS_BLOCK_GROUP_METADATA|BTRFS_BLOCK_GROUP_DATA:
                return "mixed";
        case BTRFS_BLOCK_GROUP_METADATA:
                return "metadata";
        case BTRFS_BLOCK_GROUP_DATA:
                return "data";
        case BTRFS_BLOCK_GROUP_SYSTEM:
                return "system";
        default:
                WARN_ON(1);
                return "invalid-combination";
        };
}

static int update_space_info(struct btrfs_fs_info *info, u64 flags,
                             u64 total_bytes, u64 bytes_used,
                             struct btrfs_space_info **space_info)
{
        struct btrfs_space_info *found;
        int i;
        int factor;
        int ret;

        if (flags & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1 |
                     BTRFS_BLOCK_GROUP_RAID10))
                factor = 2;
        else
                factor = 1;

        found = __find_space_info(info, flags);
        if (found) {
                spin_lock(&found->lock);
                found->total_bytes += total_bytes;
                found->disk_total += total_bytes * factor;
                found->bytes_used += bytes_used;
                found->disk_used += bytes_used * factor;
                if (total_bytes > 0)
                        found->full = 0;
                spin_unlock(&found->lock);
                *space_info = found;
                return 0;
        }
        found = kzalloc(sizeof(*found), GFP_NOFS);
        if (!found)
                return -ENOMEM;

        ret = percpu_counter_init(&found->total_bytes_pinned, 0, GFP_KERNEL);
        if (ret) {
                kfree(found);
                return ret;
        }

        for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
                INIT_LIST_HEAD(&found->block_groups[i]);
        init_rwsem(&found->groups_sem);
        spin_lock_init(&found->lock);
        found->flags = flags & BTRFS_BLOCK_GROUP_TYPE_MASK;
        found->total_bytes = total_bytes;
        found->disk_total = total_bytes * factor;
        found->bytes_used = bytes_used;
        found->disk_used = bytes_used * factor;
        found->bytes_pinned = 0;
        found->bytes_reserved = 0;
        found->bytes_readonly = 0;
        found->bytes_may_use = 0;
        found->full = 0;
        found->max_extent_size = 0;
        found->force_alloc = CHUNK_ALLOC_NO_FORCE;
        found->chunk_alloc = 0;
        found->flush = 0;
        init_waitqueue_head(&found->wait);
        INIT_LIST_HEAD(&found->ro_bgs);

        ret = kobject_init_and_add(&found->kobj, &space_info_ktype,
                                    info->space_info_kobj, "%s",
                                    alloc_name(found->flags));
        if (ret) {
                kfree(found);
                return ret;
        }

        *space_info = found;
        list_add_rcu(&found->list, &info->space_info);
        if (flags & BTRFS_BLOCK_GROUP_DATA)
                info->data_sinfo = found;

        return ret;
}

static void set_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
{
        u64 extra_flags = chunk_to_extended(flags) &
                                BTRFS_EXTENDED_PROFILE_MASK;

        write_seqlock(&fs_info->profiles_lock);
        if (flags & BTRFS_BLOCK_GROUP_DATA)
                fs_info->avail_data_alloc_bits |= extra_flags;
        if (flags & BTRFS_BLOCK_GROUP_METADATA)
                fs_info->avail_metadata_alloc_bits |= extra_flags;
        if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
                fs_info->avail_system_alloc_bits |= extra_flags;
        write_sequnlock(&fs_info->profiles_lock);
}

/*
 * returns target flags in extended format or 0 if restripe for this
 * chunk_type is not in progress
 *
 * should be called with either volume_mutex or balance_lock held
 */
static u64 get_restripe_target(struct btrfs_fs_info *fs_info, u64 flags)
{
        struct btrfs_balance_control *bctl = fs_info->balance_ctl;
        u64 target = 0;

        if (!bctl)
                return 0;

        if (flags & BTRFS_BLOCK_GROUP_DATA &&
            bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) {
                target = BTRFS_BLOCK_GROUP_DATA | bctl->data.target;
        } else if (flags & BTRFS_BLOCK_GROUP_SYSTEM &&
                   bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) {
                target = BTRFS_BLOCK_GROUP_SYSTEM | bctl->sys.target;
        } else if (flags & BTRFS_BLOCK_GROUP_METADATA &&
                   bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) {
                target = BTRFS_BLOCK_GROUP_METADATA | bctl->meta.target;
        }

        return target;
}

/*
 * @flags: available profiles in extended format (see ctree.h)
 *
 * Returns reduced profile in chunk format.  If profile changing is in
 * progress (either running or paused) picks the target profile (if it's
 * already available), otherwise falls back to plain reducing.
 */
static u64 btrfs_reduce_alloc_profile(struct btrfs_root *root, u64 flags)
{
        u64 num_devices = root->fs_info->fs_devices->rw_devices;
        u64 target;
        u64 raid_type;
        u64 allowed = 0;

        /*
         * see if restripe for this chunk_type is in progress, if so
         * try to reduce to the target profile
         */
        spin_lock(&root->fs_info->balance_lock);
        target = get_restripe_target(root->fs_info, flags);
        if (target) {
                /* pick target profile only if it's already available */
                if ((flags & target) & BTRFS_EXTENDED_PROFILE_MASK) {
                        spin_unlock(&root->fs_info->balance_lock);
                        return extended_to_chunk(target);
                }
        }
        spin_unlock(&root->fs_info->balance_lock);

        /* First, mask out the RAID levels which aren't possible */
        for (raid_type = 0; raid_type < BTRFS_NR_RAID_TYPES; raid_type++) {
                if (num_devices >= btrfs_raid_array[raid_type].devs_min)
                        allowed |= btrfs_raid_group[raid_type];
        }
        allowed &= flags;

        if (allowed & BTRFS_BLOCK_GROUP_RAID6)
                allowed = BTRFS_BLOCK_GROUP_RAID6;
        else if (allowed & BTRFS_BLOCK_GROUP_RAID5)
                allowed = BTRFS_BLOCK_GROUP_RAID5;
        else if (allowed & BTRFS_BLOCK_GROUP_RAID10)
                allowed = BTRFS_BLOCK_GROUP_RAID10;
        else if (allowed & BTRFS_BLOCK_GROUP_RAID1)
                allowed = BTRFS_BLOCK_GROUP_RAID1;
        else if (allowed & BTRFS_BLOCK_GROUP_RAID0)
                allowed = BTRFS_BLOCK_GROUP_RAID0;

        flags &= ~BTRFS_BLOCK_GROUP_PROFILE_MASK;

        return extended_to_chunk(flags | allowed);
}

static u64 get_alloc_profile(struct btrfs_root *root, u64 orig_flags)
{
        unsigned seq;
        u64 flags;

        do {
                flags = orig_flags;
                seq = read_seqbegin(&root->fs_info->profiles_lock);

                if (flags & BTRFS_BLOCK_GROUP_DATA)
                        flags |= root->fs_info->avail_data_alloc_bits;
                else if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
                        flags |= root->fs_info->avail_system_alloc_bits;
                else if (flags & BTRFS_BLOCK_GROUP_METADATA)
                        flags |= root->fs_info->avail_metadata_alloc_bits;
        } while (read_seqretry(&root->fs_info->profiles_lock, seq));

        return btrfs_reduce_alloc_profile(root, flags);
}

u64 btrfs_get_alloc_profile(struct btrfs_root *root, int data)
{
        u64 flags;
        u64 ret;

        if (data)
                flags = BTRFS_BLOCK_GROUP_DATA;
        else if (root == root->fs_info->chunk_root)
                flags = BTRFS_BLOCK_GROUP_SYSTEM;
        else
                flags = BTRFS_BLOCK_GROUP_METADATA;

        ret = get_alloc_profile(root, flags);
        return ret;
}

int btrfs_alloc_data_chunk_ondemand(struct inode *inode, u64 bytes)
{
        struct btrfs_space_info *data_sinfo;
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 used;
        int ret = 0;
        int need_commit = 2;
        int have_pinned_space;

        /* make sure bytes are sectorsize aligned */
        bytes = ALIGN(bytes, root->sectorsize);

        if (btrfs_is_free_space_inode(inode)) {
                need_commit = 0;
                ASSERT(current->journal_info);
        }

        data_sinfo = fs_info->data_sinfo;
        if (!data_sinfo)
                goto alloc;

again:
        /* make sure we have enough space to handle the data first */
        spin_lock(&data_sinfo->lock);
        used = data_sinfo->bytes_used + data_sinfo->bytes_reserved +
                data_sinfo->bytes_pinned + data_sinfo->bytes_readonly +
                data_sinfo->bytes_may_use;

        if (used + bytes > data_sinfo->total_bytes) {
                struct btrfs_trans_handle *trans;

                /*
                 * if we don't have enough free bytes in this space then we need
                 * to alloc a new chunk.
                 */
                if (!data_sinfo->full) {
                        u64 alloc_target;

                        data_sinfo->force_alloc = CHUNK_ALLOC_FORCE;
                        spin_unlock(&data_sinfo->lock);
alloc:
                        alloc_target = btrfs_get_alloc_profile(root, 1);
                        /*
                         * It is ugly that we don't call nolock join
                         * transaction for the free space inode case here.
                         * But it is safe because we only do the data space
                         * reservation for the free space cache in the
                         * transaction context, the common join transaction
                         * just increase the counter of the current transaction
                         * handler, doesn't try to acquire the trans_lock of
                         * the fs.
                         */
                        trans = btrfs_join_transaction(root);
                        if (IS_ERR(trans))
                                return PTR_ERR(trans);

                        ret = do_chunk_alloc(trans, root->fs_info->extent_root,
                                             alloc_target,
                                             CHUNK_ALLOC_NO_FORCE);
                        btrfs_end_transaction(trans, root);
                        if (ret < 0) {
                                if (ret != -ENOSPC)
                                        return ret;
                                else {
                                        have_pinned_space = 1;
                                        goto commit_trans;
                                }
                        }

                        if (!data_sinfo)
                                data_sinfo = fs_info->data_sinfo;

                        goto again;
                }

                /*
                 * If we don't have enough pinned space to deal with this
                 * allocation, and no removed chunk in current transaction,
                 * don't bother committing the transaction.
                 */
                have_pinned_space = percpu_counter_compare(
                        &data_sinfo->total_bytes_pinned,
                        used + bytes - data_sinfo->total_bytes);
                spin_unlock(&data_sinfo->lock);

                /* commit the current transaction and try again */
commit_trans:
                if (need_commit &&
                    !atomic_read(&root->fs_info->open_ioctl_trans)) {
                        need_commit--;

                        if (need_commit > 0)
                                btrfs_wait_ordered_roots(fs_info, -1);

                        trans = btrfs_join_transaction(root);
                        if (IS_ERR(trans))
                                return PTR_ERR(trans);
                        if (have_pinned_space >= 0 ||
                            test_bit(BTRFS_TRANS_HAVE_FREE_BGS,
                                     &trans->transaction->flags) ||
                            need_commit > 0) {
                                ret = btrfs_commit_transaction(trans, root);
                                if (ret)
                                        return ret;
                                /*
                                 * The cleaner kthread might still be doing iput
                                 * operations. Wait for it to finish so that
                                 * more space is released.
                                 */
                                mutex_lock(&root->fs_info->cleaner_delayed_iput_mutex);
                                mutex_unlock(&root->fs_info->cleaner_delayed_iput_mutex);
                                goto again;
                        } else {
                                btrfs_end_transaction(trans, root);
                        }
                }

                trace_btrfs_space_reservation(root->fs_info,
                                              "space_info:enospc",
                                              data_sinfo->flags, bytes, 1);
                return -ENOSPC;
        }
        data_sinfo->bytes_may_use += bytes;
        trace_btrfs_space_reservation(root->fs_info, "space_info",
                                      data_sinfo->flags, bytes, 1);
        spin_unlock(&data_sinfo->lock);

        return ret;
}

/*
 * New check_data_free_space() with ability for precious data reservation
 * Will replace old btrfs_check_data_free_space(), but for patch split,
 * add a new function first and then replace it.
 */
int btrfs_check_data_free_space(struct inode *inode, u64 start, u64 len)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        int ret;

        /* align the range */
        len = round_up(start + len, root->sectorsize) -
              round_down(start, root->sectorsize);
        start = round_down(start, root->sectorsize);

        ret = btrfs_alloc_data_chunk_ondemand(inode, len);
        if (ret < 0)
                return ret;

        /*
         * Use new btrfs_qgroup_reserve_data to reserve precious data space
         *
         * TODO: Find a good method to avoid reserve data space for NOCOW
         * range, but don't impact performance on quota disable case.
         */
        ret = btrfs_qgroup_reserve_data(inode, start, len);
        return ret;
}

/*
 * Called if we need to clear a data reservation for this inode
 * Normally in a error case.
 *
 * This one will *NOT* use accurate qgroup reserved space API, just for case
 * which we can't sleep and is sure it won't affect qgroup reserved space.
 * Like clear_bit_hook().
 */
void btrfs_free_reserved_data_space_noquota(struct inode *inode, u64 start,
                                            u64 len)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_space_info *data_sinfo;

        /* Make sure the range is aligned to sectorsize */
        len = round_up(start + len, root->sectorsize) -
              round_down(start, root->sectorsize);
        start = round_down(start, root->sectorsize);

        data_sinfo = root->fs_info->data_sinfo;
        spin_lock(&data_sinfo->lock);
        if (WARN_ON(data_sinfo->bytes_may_use < len))
                data_sinfo->bytes_may_use = 0;
        else
                data_sinfo->bytes_may_use -= len;
        trace_btrfs_space_reservation(root->fs_info, "space_info",
                                      data_sinfo->flags, len, 0);
        spin_unlock(&data_sinfo->lock);
}

/*
 * Called if we need to clear a data reservation for this inode
 * Normally in a error case.
 *
 * This one will handle the per-indoe data rsv map for accurate reserved
 * space framework.
 */
void btrfs_free_reserved_data_space(struct inode *inode, u64 start, u64 len)
{
        btrfs_free_reserved_data_space_noquota(inode, start, len);
        btrfs_qgroup_free_data(inode, start, len);
}

static void force_metadata_allocation(struct btrfs_fs_info *info)
{
        struct list_head *head = &info->space_info;
        struct btrfs_space_info *found;

        rcu_read_lock();
        list_for_each_entry_rcu(found, head, list) {
                if (found->flags & BTRFS_BLOCK_GROUP_METADATA)
                        found->force_alloc = CHUNK_ALLOC_FORCE;
        }
        rcu_read_unlock();
}

static inline u64 calc_global_rsv_need_space(struct btrfs_block_rsv *global)
{
        return (global->size << 1);
}

static int should_alloc_chunk(struct btrfs_root *root,
                              struct btrfs_space_info *sinfo, int force)
{
        struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
        u64 num_bytes = sinfo->total_bytes - sinfo->bytes_readonly;
        u64 num_allocated = sinfo->bytes_used + sinfo->bytes_reserved;
        u64 thresh;

        if (force == CHUNK_ALLOC_FORCE)
                return 1;

        /*
         * We need to take into account the global rsv because for all intents
         * and purposes it's used space.  Don't worry about locking the
         * global_rsv, it doesn't change except when the transaction commits.
         */
        if (sinfo->flags & BTRFS_BLOCK_GROUP_METADATA)
                num_allocated += calc_global_rsv_need_space(global_rsv);

        /*
         * in limited mode, we want to have some free space up to
         * about 1% of the FS size.
         */
        if (force == CHUNK_ALLOC_LIMITED) {
                thresh = btrfs_super_total_bytes(root->fs_info->super_copy);
                thresh = max_t(u64, 64 * 1024 * 1024,
                               div_factor_fine(thresh, 1));

                if (num_bytes - num_allocated < thresh)
                        return 1;
        }

        if (num_allocated + 2 * 1024 * 1024 < div_factor(num_bytes, 8))
                return 0;
        return 1;
}

static u64 get_profile_num_devs(struct btrfs_root *root, u64 type)
{
        u64 num_dev;

        if (type & (BTRFS_BLOCK_GROUP_RAID10 |
                    BTRFS_BLOCK_GROUP_RAID0 |
                    BTRFS_BLOCK_GROUP_RAID5 |
                    BTRFS_BLOCK_GROUP_RAID6))
                num_dev = root->fs_info->fs_devices->rw_devices;
        else if (type & BTRFS_BLOCK_GROUP_RAID1)
                num_dev = 2;
        else
                num_dev = 1;    /* DUP or single */

        return num_dev;
}

/*
 * If @is_allocation is true, reserve space in the system space info necessary
 * for allocating a chunk, otherwise if it's false, reserve space necessary for
 * removing a chunk.
 */
void check_system_chunk(struct btrfs_trans_handle *trans,
                        struct btrfs_root *root,
                        u64 type)
{
        struct btrfs_space_info *info;
        u64 left;
        u64 thresh;
        int ret = 0;
        u64 num_devs;

        /*
         * Needed because we can end up allocating a system chunk and for an
         * atomic and race free space reservation in the chunk block reserve.
         */
        ASSERT(mutex_is_locked(&root->fs_info->chunk_mutex));

        info = __find_space_info(root->fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
        spin_lock(&info->lock);
        left = info->total_bytes - info->bytes_used - info->bytes_pinned -
                info->bytes_reserved - info->bytes_readonly -
                info->bytes_may_use;
        spin_unlock(&info->lock);

        num_devs = get_profile_num_devs(root, type);

        /* num_devs device items to update and 1 chunk item to add or remove */
        thresh = btrfs_calc_trunc_metadata_size(root, num_devs) +
                btrfs_calc_trans_metadata_size(root, 1);

        if (left < thresh && btrfs_test_opt(root, ENOSPC_DEBUG)) {
                btrfs_info(root->fs_info, "left=%llu, need=%llu, flags=%llu",
                        left, thresh, type);
                dump_space_info(info, 0, 0);
        }

        if (left < thresh) {
                u64 flags;

                flags = btrfs_get_alloc_profile(root->fs_info->chunk_root, 0);
                /*
                 * Ignore failure to create system chunk. We might end up not
                 * needing it, as we might not need to COW all nodes/leafs from
                 * the paths we visit in the chunk tree (they were already COWed
                 * or created in the current transaction for example).
                 */
                ret = btrfs_alloc_chunk(trans, root, flags);
        }

        if (!ret) {
                ret = btrfs_block_rsv_add(root->fs_info->chunk_root,
                                          &root->fs_info->chunk_block_rsv,
                                          thresh, BTRFS_RESERVE_NO_FLUSH);
                if (!ret)
                        trans->chunk_bytes_reserved += thresh;
        }
}

static int do_chunk_alloc(struct btrfs_trans_handle *trans,
                          struct btrfs_root *extent_root, u64 flags, int force)
{
        struct btrfs_space_info *space_info;
        struct btrfs_fs_info *fs_info = extent_root->fs_info;
        int wait_for_alloc = 0;
        int ret = 0;

        /* Don't re-enter if we're already allocating a chunk */
        if (trans->allocating_chunk)
                return -ENOSPC;

        space_info = __find_space_info(extent_root->fs_info, flags);
        if (!space_info) {
                ret = update_space_info(extent_root->fs_info, flags,
                                        0, 0, &space_info);
                BUG_ON(ret); /* -ENOMEM */
        }
        BUG_ON(!space_info); /* Logic error */

again:
        spin_lock(&space_info->lock);
        if (force < space_info->force_alloc)
                force = space_info->force_alloc;
        if (space_info->full) {
                if (should_alloc_chunk(extent_root, space_info, force))
                        ret = -ENOSPC;
                else
                        ret = 0;
                spin_unlock(&space_info->lock);
                return ret;
        }

        if (!should_alloc_chunk(extent_root, space_info, force)) {
                spin_unlock(&space_info->lock);
                return 0;
        } else if (space_info->chunk_alloc) {
                wait_for_alloc = 1;
        } else {
                space_info->chunk_alloc = 1;
        }

        spin_unlock(&space_info->lock);

        mutex_lock(&fs_info->chunk_mutex);

        /*
         * The chunk_mutex is held throughout the entirety of a chunk
         * allocation, so once we've acquired the chunk_mutex we know that the
         * other guy is done and we need to recheck and see if we should
         * allocate.
         */
        if (wait_for_alloc) {
                mutex_unlock(&fs_info->chunk_mutex);
                wait_for_alloc = 0;
                goto again;
        }

        trans->allocating_chunk = true;

        /*
         * If we have mixed data/metadata chunks we want to make sure we keep
         * allocating mixed chunks instead of individual chunks.
         */
        if (btrfs_mixed_space_info(space_info))
                flags |= (BTRFS_BLOCK_GROUP_DATA | BTRFS_BLOCK_GROUP_METADATA);

        /*
         * if we're doing a data chunk, go ahead and make sure that
         * we keep a reasonable number of metadata chunks allocated in the
         * FS as well.
         */
        if (flags & BTRFS_BLOCK_GROUP_DATA && fs_info->metadata_ratio) {
                fs_info->data_chunk_allocations++;
                if (!(fs_info->data_chunk_allocations %
                      fs_info->metadata_ratio))
                        force_metadata_allocation(fs_info);
        }

        /*
         * Check if we have enough space in SYSTEM chunk because we may need
         * to update devices.
         */
        check_system_chunk(trans, extent_root, flags);

        ret = btrfs_alloc_chunk(trans, extent_root, flags);
        trans->allocating_chunk = false;

        spin_lock(&space_info->lock);
        if (ret < 0 && ret != -ENOSPC)
                goto out;
        if (ret)
                space_info->full = 1;
        else
                ret = 1;

        space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
out:
        space_info->chunk_alloc = 0;
        spin_unlock(&space_info->lock);
        mutex_unlock(&fs_info->chunk_mutex);
        /*
         * When we allocate a new chunk we reserve space in the chunk block
         * reserve to make sure we can COW nodes/leafs in the chunk tree or
         * add new nodes/leafs to it if we end up needing to do it when
         * inserting the chunk item and updating device items as part of the
         * second phase of chunk allocation, performed by
         * btrfs_finish_chunk_alloc(). So make sure we don't accumulate a
         * large number of new block groups to create in our transaction
         * handle's new_bgs list to avoid exhausting the chunk block reserve
         * in extreme cases - like having a single transaction create many new
         * block groups when starting to write out the free space caches of all
         * the block groups that were made dirty during the lifetime of the
         * transaction.
         */
        if (trans->can_flush_pending_bgs &&
            trans->chunk_bytes_reserved >= (2 * 1024 * 1024ull)) {
                btrfs_create_pending_block_groups(trans, trans->root);
                btrfs_trans_release_chunk_metadata(trans);
        }
        return ret;
}

static int can_overcommit(struct btrfs_root *root,
                          struct btrfs_space_info *space_info, u64 bytes,
                          enum btrfs_reserve_flush_enum flush)
{
        struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
        u64 profile = btrfs_get_alloc_profile(root, 0);
        u64 space_size;
        u64 avail;
        u64 used;

        used = space_info->bytes_used + space_info->bytes_reserved +
                space_info->bytes_pinned + space_info->bytes_readonly;

        /*
         * We only want to allow over committing if we have lots of actual space
         * free, but if we don't have enough space to handle the global reserve
         * space then we could end up having a real enospc problem when trying
         * to allocate a chunk or some other such important allocation.
         */
        spin_lock(&global_rsv->lock);
        space_size = calc_global_rsv_need_space(global_rsv);
        spin_unlock(&global_rsv->lock);
        if (used + space_size >= space_info->total_bytes)
                return 0;

        used += space_info->bytes_may_use;

        spin_lock(&root->fs_info->free_chunk_lock);
        avail = root->fs_info->free_chunk_space;
        spin_unlock(&root->fs_info->free_chunk_lock);

        /*
         * If we have dup, raid1 or raid10 then only half of the free
         * space is actually useable.  For raid56, the space info used
         * doesn't include the parity drive, so we don't have to
         * change the math
         */
        if (profile & (BTRFS_BLOCK_GROUP_DUP |
                       BTRFS_BLOCK_GROUP_RAID1 |
                       BTRFS_BLOCK_GROUP_RAID10))
                avail >>= 1;

        /*
         * If we aren't flushing all things, let us overcommit up to
         * 1/2th of the space. If we can flush, don't let us overcommit
         * too much, let it overcommit up to 1/8 of the space.
         */
        if (flush == BTRFS_RESERVE_FLUSH_ALL)
                avail >>= 3;
        else
                avail >>= 1;

        if (used + bytes < space_info->total_bytes + avail)
                return 1;
        return 0;
}

static void btrfs_writeback_inodes_sb_nr(struct btrfs_root *root,
                                         unsigned long nr_pages, int nr_items)
{
        struct super_block *sb = root->fs_info->sb;

        if (down_read_trylock(&sb->s_umount)) {
                writeback_inodes_sb_nr(sb, nr_pages, WB_REASON_FS_FREE_SPACE);
                up_read(&sb->s_umount);
        } else {
                /*
                 * We needn't worry the filesystem going from r/w to r/o though
                 * we don't acquire ->s_umount mutex, because the filesystem
                 * should guarantee the delalloc inodes list be empty after
                 * the filesystem is readonly(all dirty pages are written to
                 * the disk).
                 */
                btrfs_start_delalloc_roots(root->fs_info, 0, nr_items);
                if (!current->journal_info)
                        btrfs_wait_ordered_roots(root->fs_info, nr_items);
        }
}

static inline int calc_reclaim_items_nr(struct btrfs_root *root, u64 to_reclaim)
{
        u64 bytes;
        int nr;

        bytes = btrfs_calc_trans_metadata_size(root, 1);
        nr = (int)div64_u64(to_reclaim, bytes);
        if (!nr)
                nr = 1;
        return nr;
}

#define EXTENT_SIZE_PER_ITEM    (256 * 1024)

/*
 * shrink metadata reservation for delalloc
 */
static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
                            bool wait_ordered)
{
        struct btrfs_block_rsv *block_rsv;
        struct btrfs_space_info *space_info;
        struct btrfs_trans_handle *trans;
        u64 delalloc_bytes;
        u64 max_reclaim;
        long time_left;
        unsigned long nr_pages;
        int loops;
        int items;
        enum btrfs_reserve_flush_enum flush;

        /* Calc the number of the pages we need flush for space reservation */
        items = calc_reclaim_items_nr(root, to_reclaim);
        to_reclaim = items * EXTENT_SIZE_PER_ITEM;

        trans = (struct btrfs_trans_handle *)current->journal_info;
        block_rsv = &root->fs_info->delalloc_block_rsv;
        space_info = block_rsv->space_info;

        delalloc_bytes = percpu_counter_sum_positive(
                                                &root->fs_info->delalloc_bytes);
        if (delalloc_bytes == 0) {
                if (trans)
                        return;
                if (wait_ordered)
                        btrfs_wait_ordered_roots(root->fs_info, items);
                return;
        }

        loops = 0;
        while (delalloc_bytes && loops < 3) {
                max_reclaim = min(delalloc_bytes, to_reclaim);
                nr_pages = max_reclaim >> PAGE_CACHE_SHIFT;
                btrfs_writeback_inodes_sb_nr(root, nr_pages, items);
                /*
                 * We need to wait for the async pages to actually start before
                 * we do anything.
                 */
                max_reclaim = atomic_read(&root->fs_info->async_delalloc_pages);
                if (!max_reclaim)
                        goto skip_async;

                if (max_reclaim <= nr_pages)
                        max_reclaim = 0;
                else
                        max_reclaim -= nr_pages;

                wait_event(root->fs_info->async_submit_wait,
                           atomic_read(&root->fs_info->async_delalloc_pages) <=
                           (int)max_reclaim);
skip_async:
                if (!trans)
                        flush = BTRFS_RESERVE_FLUSH_ALL;
                else
                        flush = BTRFS_RESERVE_NO_FLUSH;
                spin_lock(&space_info->lock);
                if (can_overcommit(root, space_info, orig, flush)) {
                        spin_unlock(&space_info->lock);
                        break;
                }
                spin_unlock(&space_info->lock);

                loops++;
                if (wait_ordered && !trans) {
                        btrfs_wait_ordered_roots(root->fs_info, items);
                } else {
                        time_left = schedule_timeout_killable(1);
                        if (time_left)
                                break;
                }
                delalloc_bytes = percpu_counter_sum_positive(
                                                &root->fs_info->delalloc_bytes);
        }
}

/**
 * maybe_commit_transaction - possibly commit the transaction if its ok to
 * @root - the root we're allocating for
 * @bytes - the number of bytes we want to reserve
 * @force - force the commit
 *
 * This will check to make sure that committing the transaction will actually
 * get us somewhere and then commit the transaction if it does.  Otherwise it
 * will return -ENOSPC.
 */
static int may_commit_transaction(struct btrfs_root *root,
                                  struct btrfs_space_info *space_info,
                                  u64 bytes, int force)
{
        struct btrfs_block_rsv *delayed_rsv = &root->fs_info->delayed_block_rsv;
        struct btrfs_trans_handle *trans;

        trans = (struct btrfs_trans_handle *)current->journal_info;
        if (trans)
                return -EAGAIN;

        if (force)
                goto commit;

        /* See if there is enough pinned space to make this reservation */
        if (percpu_counter_compare(&space_info->total_bytes_pinned,
                                   bytes) >= 0)
                goto commit;

        /*
         * See if there is some space in the delayed insertion reservation for
         * this reservation.
         */
        if (space_info != delayed_rsv->space_info)
                return -ENOSPC;

        spin_lock(&delayed_rsv->lock);
        if (percpu_counter_compare(&space_info->total_bytes_pinned,
                                   bytes - delayed_rsv->size) >= 0) {
                spin_unlock(&delayed_rsv->lock);
                return -ENOSPC;
        }
        spin_unlock(&delayed_rsv->lock);

commit:
        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans))
                return -ENOSPC;

        return btrfs_commit_transaction(trans, root);
}

enum flush_state {
        FLUSH_DELAYED_ITEMS_NR  =       1,
        FLUSH_DELAYED_ITEMS     =       2,
        FLUSH_DELALLOC          =       3,
        FLUSH_DELALLOC_WAIT     =       4,
        ALLOC_CHUNK             =       5,
        COMMIT_TRANS            =       6,
};

static int flush_space(struct btrfs_root *root,
                       struct btrfs_space_info *space_info, u64 num_bytes,
                       u64 orig_bytes, int state)
{
        struct btrfs_trans_handle *trans;
        int nr;
        int ret = 0;

        switch (state) {
        case FLUSH_DELAYED_ITEMS_NR:
        case FLUSH_DELAYED_ITEMS:
                if (state == FLUSH_DELAYED_ITEMS_NR)
                        nr = calc_reclaim_items_nr(root, num_bytes) * 2;
                else
                        nr = -1;

                trans = btrfs_join_transaction(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        break;
                }
                ret = btrfs_run_delayed_items_nr(trans, root, nr);
                btrfs_end_transaction(trans, root);
                break;
        case FLUSH_DELALLOC:
        case FLUSH_DELALLOC_WAIT:
                shrink_delalloc(root, num_bytes * 2, orig_bytes,
                                state == FLUSH_DELALLOC_WAIT);
                break;
        case ALLOC_CHUNK:
                trans = btrfs_join_transaction(root);
                if (IS_ERR(trans)) {
                        ret = PTR_ERR(trans);
                        break;
                }
                ret = do_chunk_alloc(trans, root->fs_info->extent_root,
                                     btrfs_get_alloc_profile(root, 0),
                                     CHUNK_ALLOC_NO_FORCE);
                btrfs_end_transaction(trans, root);
                if (ret == -ENOSPC)
                        ret = 0;
                break;
        case COMMIT_TRANS:
                ret = may_commit_transaction(root, space_info, orig_bytes, 0);
                break;
        default:
                ret = -ENOSPC;
                break;
        }

        return ret;
}

static inline u64
btrfs_calc_reclaim_metadata_size(struct btrfs_root *root,
                                 struct btrfs_space_info *space_info)
{
        u64 used;
        u64 expected;
        u64 to_reclaim;

        to_reclaim = min_t(u64, num_online_cpus() * 1024 * 1024,
                                16 * 1024 * 1024);
        spin_lock(&space_info->lock);
        if (can_overcommit(root, space_info, to_reclaim,
                           BTRFS_RESERVE_FLUSH_ALL)) {
                to_reclaim = 0;
                goto out;
        }

        used = space_info->bytes_used + space_info->bytes_reserved +
               space_info->bytes_pinned + space_info->bytes_readonly +
               space_info->bytes_may_use;
        if (can_overcommit(root, space_info, 1024 * 1024,
                           BTRFS_RESERVE_FLUSH_ALL))
                expected = div_factor_fine(space_info->total_bytes, 95);
        else
                expected = div_factor_fine(space_info->total_bytes, 90);

        if (used > expected)
                to_reclaim = used - expected;
        else
                to_reclaim = 0;
        to_reclaim = min(to_reclaim, space_info->bytes_may_use +
                                     space_info->bytes_reserved);
out:
        spin_unlock(&space_info->lock);

        return to_reclaim;
}

static inline int need_do_async_reclaim(struct btrfs_space_info *space_info,
                                        struct btrfs_fs_info *fs_info, u64 used)
{
        u64 thresh = div_factor_fine(space_info->total_bytes, 98);

        /* If we're just plain full then async reclaim just slows us down. */
        if (space_info->bytes_used >= thresh)
                return 0;

        return (used >= thresh && !btrfs_fs_closing(fs_info) &&
                !test_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state));
}

static int btrfs_need_do_async_reclaim(struct btrfs_space_info *space_info,
                                       struct btrfs_fs_info *fs_info,
                                       int flush_state)
{
        u64 used;

        spin_lock(&space_info->lock);
        /*
         * We run out of space and have not got any free space via flush_space,
         * so don't bother doing async reclaim.
         */
        if (flush_state > COMMIT_TRANS && space_info->full) {
                spin_unlock(&space_info->lock);
                return 0;
        }

        used = space_info->bytes_used + space_info->bytes_reserved +
               space_info->bytes_pinned + space_info->bytes_readonly +
               space_info->bytes_may_use;
        if (need_do_async_reclaim(space_info, fs_info, used)) {
                spin_unlock(&space_info->lock);
                return 1;
        }
        spin_unlock(&space_info->lock);

        return 0;
}

static void btrfs_async_reclaim_metadata_space(struct work_struct *work)
{
        struct btrfs_fs_info *fs_info;
        struct btrfs_space_info *space_info;
        u64 to_reclaim;
        int flush_state;

        fs_info = container_of(work, struct btrfs_fs_info, async_reclaim_work);
        space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);

        to_reclaim = btrfs_calc_reclaim_metadata_size(fs_info->fs_root,
                                                      space_info);
        if (!to_reclaim)
                return;

        flush_state = FLUSH_DELAYED_ITEMS_NR;
        do {
                flush_space(fs_info->fs_root, space_info, to_reclaim,
                            to_reclaim, flush_state);
                flush_state++;
                if (!btrfs_need_do_async_reclaim(space_info, fs_info,
                                                 flush_state))
                        return;
        } while (flush_state < COMMIT_TRANS);
}

void btrfs_init_async_reclaim_work(struct work_struct *work)
{
        INIT_WORK(work, btrfs_async_reclaim_metadata_space);
}

/**
 * reserve_metadata_bytes - try to reserve bytes from the block_rsv's space
 * @root - the root we're allocating for
 * @block_rsv - the block_rsv we're allocating for
 * @orig_bytes - the number of bytes we want
 * @flush - whether or not we can flush to make our reservation
 *
 * This will reserve orgi_bytes number of bytes from the space info associated
 * with the block_rsv.  If there is not enough space it will make an attempt to
 * flush out space to make room.  It will do this by flushing delalloc if
 * possible or committing the transaction.  If flush is 0 then no attempts to
 * regain reservations will be made and this will fail if there is not enough
 * space already.
 */
static int reserve_metadata_bytes(struct btrfs_root *root,
                                  struct btrfs_block_rsv *block_rsv,
                                  u64 orig_bytes,
                                  enum btrfs_reserve_flush_enum flush)
{
        struct btrfs_space_info *space_info = block_rsv->space_info;
        u64 used;
        u64 num_bytes = orig_bytes;
        int flush_state = FLUSH_DELAYED_ITEMS_NR;
        int ret = 0;
        bool flushing = false;

again:
        ret = 0;
        spin_lock(&space_info->lock);
        /*
         * We only want to wait if somebody other than us is flushing and we
         * are actually allowed to flush all things.
         */
        while (flush == BTRFS_RESERVE_FLUSH_ALL && !flushing &&
               space_info->flush) {
                spin_unlock(&space_info->lock);
                /*
                 * If we have a trans handle we can't wait because the flusher
                 * may have to commit the transaction, which would mean we would
                 * deadlock since we are waiting for the flusher to finish, but
                 * hold the current transaction open.
                 */
                if (current->journal_info)
                        return -EAGAIN;
                ret = wait_event_killable(space_info->wait, !space_info->flush);
                /* Must have been killed, return */
                if (ret)
                        return -EINTR;

                spin_lock(&space_info->lock);
        }

        ret = -ENOSPC;
        used = space_info->bytes_used + space_info->bytes_reserved +
                space_info->bytes_pinned + space_info->bytes_readonly +
                space_info->bytes_may_use;

        /*
         * The idea here is that we've not already over-reserved the block group
         * then we can go ahead and save our reservation first and then start
         * flushing if we need to.  Otherwise if we've already overcommitted
         * lets start flushing stuff first and then come back and try to make
         * our reservation.
         */
        if (used <= space_info->total_bytes) {
                if (used + orig_bytes <= space_info->total_bytes) {
                        space_info->bytes_may_use += orig_bytes;
                        trace_btrfs_space_reservation(root->fs_info,
                                "space_info", space_info->flags, orig_bytes, 1);
                        ret = 0;
                } else {
                        /*
                         * Ok set num_bytes to orig_bytes since we aren't
                         * overocmmitted, this way we only try and reclaim what
                         * we need.
                         */
                        num_bytes = orig_bytes;
                }
        } else {
                /*
                 * Ok we're over committed, set num_bytes to the overcommitted
                 * amount plus the amount of bytes that we need for this
                 * reservation.
                 */
                num_bytes = used - space_info->total_bytes +
                        (orig_bytes * 2);
        }

        if (ret && can_overcommit(root, space_info, orig_bytes, flush)) {
                space_info->bytes_may_use += orig_bytes;
                trace_btrfs_space_reservation(root->fs_info, "space_info",
                                              space_info->flags, orig_bytes,
                                              1);
                ret = 0;
        }

        /*
         * Couldn't make our reservation, save our place so while we're trying
         * to reclaim space we can actually use it instead of somebody else
         * stealing it from us.
         *
         * We make the other tasks wait for the flush only when we can flush
         * all things.
         */
        if (ret && flush != BTRFS_RESERVE_NO_FLUSH) {
                flushing = true;
                space_info->flush = 1;
        } else if (!ret && space_info->flags & BTRFS_BLOCK_GROUP_METADATA) {
                used += orig_bytes;
                /*
                 * We will do the space reservation dance during log replay,
                 * which means we won't have fs_info->fs_root set, so don't do
                 * the async reclaim as we will panic.
                 */
                if (!root->fs_info->log_root_recovering &&
                    need_do_async_reclaim(space_info, root->fs_info, used) &&
                    !work_busy(&root->fs_info->async_reclaim_work))
                        queue_work(system_unbound_wq,
                                   &root->fs_info->async_reclaim_work);
        }
        spin_unlock(&space_info->lock);

        if (!ret || flush == BTRFS_RESERVE_NO_FLUSH)
                goto out;

        ret = flush_space(root, space_info, num_bytes, orig_bytes,
                          flush_state);
        flush_state++;

        /*
         * If we are FLUSH_LIMIT, we can not flush delalloc, or the deadlock
         * would happen. So skip delalloc flush.
         */
        if (flush == BTRFS_RESERVE_FLUSH_LIMIT &&
            (flush_state == FLUSH_DELALLOC ||
             flush_state == FLUSH_DELALLOC_WAIT))
                flush_state = ALLOC_CHUNK;

        if (!ret)
                goto again;
        else if (flush == BTRFS_RESERVE_FLUSH_LIMIT &&
                 flush_state < COMMIT_TRANS)
                goto again;
        else if (flush == BTRFS_RESERVE_FLUSH_ALL &&
                 flush_state <= COMMIT_TRANS)
                goto again;

out:
        if (ret == -ENOSPC &&
            unlikely(root->orphan_cleanup_state == ORPHAN_CLEANUP_STARTED)) {
                struct btrfs_block_rsv *global_rsv =
                        &root->fs_info->global_block_rsv;

                if (block_rsv != global_rsv &&
                    !block_rsv_use_bytes(global_rsv, orig_bytes))
                        ret = 0;
        }
        if (ret == -ENOSPC)
                trace_btrfs_space_reservation(root->fs_info,
                                              "space_info:enospc",
                                              space_info->flags, orig_bytes, 1);
        if (flushing) {
                spin_lock(&space_info->lock);
                space_info->flush = 0;
                wake_up_all(&space_info->wait);
                spin_unlock(&space_info->lock);
        }
        return ret;
}

static struct btrfs_block_rsv *get_block_rsv(
                                        const struct btrfs_trans_handle *trans,
                                        const struct btrfs_root *root)
{
        struct btrfs_block_rsv *block_rsv = NULL;

        if (test_bit(BTRFS_ROOT_REF_COWS, &root->state) ||
            (root == root->fs_info->csum_root && trans->adding_csums) ||
             (root == root->fs_info->uuid_root))
                block_rsv = trans->block_rsv;

        if (!block_rsv)
                block_rsv = root->block_rsv;

        if (!block_rsv)
                block_rsv = &root->fs_info->empty_block_rsv;

        return block_rsv;
}

static int block_rsv_use_bytes(struct btrfs_block_rsv *block_rsv,
                               u64 num_bytes)
{
        int ret = -ENOSPC;
        spin_lock(&block_rsv->lock);
        if (block_rsv->reserved >= num_bytes) {
                block_rsv->reserved -= num_bytes;
                if (block_rsv->reserved < block_rsv->size)
                        block_rsv->full = 0;
                ret = 0;
        }
        spin_unlock(&block_rsv->lock);
        return ret;
}

static void block_rsv_add_bytes(struct btrfs_block_rsv *block_rsv,
                                u64 num_bytes, int update_size)
{
        spin_lock(&block_rsv->lock);
        block_rsv->reserved += num_bytes;
        if (update_size)
                block_rsv->size += num_bytes;
        else if (block_rsv->reserved >= block_rsv->size)
                block_rsv->full = 1;
        spin_unlock(&block_rsv->lock);
}

int btrfs_cond_migrate_bytes(struct btrfs_fs_info *fs_info,
                             struct btrfs_block_rsv *dest, u64 num_bytes,
                             int min_factor)
{
        struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
        u64 min_bytes;

        if (global_rsv->space_info != dest->space_info)
                return -ENOSPC;

        spin_lock(&global_rsv->lock);
        min_bytes = div_factor(global_rsv->size, min_factor);
        if (global_rsv->reserved < min_bytes + num_bytes) {
                spin_unlock(&global_rsv->lock);
                return -ENOSPC;
        }
        global_rsv->reserved -= num_bytes;
        if (global_rsv->reserved < global_rsv->size)
                global_rsv->full = 0;
        spin_unlock(&global_rsv->lock);

        block_rsv_add_bytes(dest, num_bytes, 1);
        return 0;
}

static void block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
                                    struct btrfs_block_rsv *block_rsv,
                                    struct btrfs_block_rsv *dest, u64 num_bytes)
{
        struct btrfs_space_info *space_info = block_rsv->space_info;

        spin_lock(&block_rsv->lock);
        if (num_bytes == (u64)-1)
                num_bytes = block_rsv->size;
        block_rsv->size -= num_bytes;
        if (block_rsv->reserved >= block_rsv->size) {
                num_bytes = block_rsv->reserved - block_rsv->size;
                block_rsv->reserved = block_rsv->size;
                block_rsv->full = 1;
        } else {
                num_bytes = 0;
        }
        spin_unlock(&block_rsv->lock);

        if (num_bytes > 0) {
                if (dest) {
                        spin_lock(&dest->lock);
                        if (!dest->full) {
                                u64 bytes_to_add;

                                bytes_to_add = dest->size - dest->reserved;
                                bytes_to_add = min(num_bytes, bytes_to_add);
                                dest->reserved += bytes_to_add;
                                if (dest->reserved >= dest->size)
                                        dest->full = 1;
                                num_bytes -= bytes_to_add;
                        }
                        spin_unlock(&dest->lock);
                }
                if (num_bytes) {
                        spin_lock(&space_info->lock);
                        space_info->bytes_may_use -= num_bytes;
                        trace_btrfs_space_reservation(fs_info, "space_info",
                                        space_info->flags, num_bytes, 0);
                        spin_unlock(&space_info->lock);
                }
        }
}

static int block_rsv_migrate_bytes(struct btrfs_block_rsv *src,
                                   struct btrfs_block_rsv *dst, u64 num_bytes)
{
        int ret;

        ret = block_rsv_use_bytes(src, num_bytes);
        if (ret)
                return ret;

        block_rsv_add_bytes(dst, num_bytes, 1);
        return 0;
}

void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, unsigned short type)
{
        memset(rsv, 0, sizeof(*rsv));
        spin_lock_init(&rsv->lock);
        rsv->type = type;
}

struct btrfs_block_rsv *btrfs_alloc_block_rsv(struct btrfs_root *root,
                                              unsigned short type)
{
        struct btrfs_block_rsv *block_rsv;
        struct btrfs_fs_info *fs_info = root->fs_info;

        block_rsv = kmalloc(sizeof(*block_rsv), GFP_NOFS);
        if (!block_rsv)
                return NULL;

        btrfs_init_block_rsv(block_rsv, type);
        block_rsv->space_info = __find_space_info(fs_info,
                                                  BTRFS_BLOCK_GROUP_METADATA);
        return block_rsv;
}

void btrfs_free_block_rsv(struct btrfs_root *root,
                          struct btrfs_block_rsv *rsv)
{
        if (!rsv)
                return;
        btrfs_block_rsv_release(root, rsv, (u64)-1);
        kfree(rsv);
}

void __btrfs_free_block_rsv(struct btrfs_block_rsv *rsv)
{
        kfree(rsv);
}

int btrfs_block_rsv_add(struct btrfs_root *root,
                        struct btrfs_block_rsv *block_rsv, u64 num_bytes,
                        enum btrfs_reserve_flush_enum flush)
{
        int ret;

        if (num_bytes == 0)
                return 0;

        ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
        if (!ret) {
                block_rsv_add_bytes(block_rsv, num_bytes, 1);
                return 0;
        }

        return ret;
}

int btrfs_block_rsv_check(struct btrfs_root *root,
                          struct btrfs_block_rsv *block_rsv, int min_factor)
{
        u64 num_bytes = 0;
        int ret = -ENOSPC;

        if (!block_rsv)
                return 0;

        spin_lock(&block_rsv->lock);
        num_bytes = div_factor(block_rsv->size, min_factor);
        if (block_rsv->reserved >= num_bytes)
                ret = 0;
        spin_unlock(&block_rsv->lock);

        return ret;
}

int btrfs_block_rsv_refill(struct btrfs_root *root,
                           struct btrfs_block_rsv *block_rsv, u64 min_reserved,
                           enum btrfs_reserve_flush_enum flush)
{
        u64 num_bytes = 0;
        int ret = -ENOSPC;

        if (!block_rsv)
                return 0;

        spin_lock(&block_rsv->lock);
        num_bytes = min_reserved;
        if (block_rsv->reserved >= num_bytes)
                ret = 0;
        else
                num_bytes -= block_rsv->reserved;
        spin_unlock(&block_rsv->lock);

        if (!ret)
                return 0;

        ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
        if (!ret) {
                block_rsv_add_bytes(block_rsv, num_bytes, 0);
                return 0;
        }

        return ret;
}

int btrfs_block_rsv_migrate(struct btrfs_block_rsv *src_rsv,
                            struct btrfs_block_rsv *dst_rsv,
                            u64 num_bytes)
{
        return block_rsv_migrate_bytes(src_rsv, dst_rsv, num_bytes);
}

void btrfs_block_rsv_release(struct btrfs_root *root,
                             struct btrfs_block_rsv *block_rsv,
                             u64 num_bytes)
{
        struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
        if (global_rsv == block_rsv ||
            block_rsv->space_info != global_rsv->space_info)
                global_rsv = NULL;
        block_rsv_release_bytes(root->fs_info, block_rsv, global_rsv,
                                num_bytes);
}

/*
 * helper to calculate size of global block reservation.
 * the desired value is sum of space used by extent tree,
 * checksum tree and root tree
 */
static u64 calc_global_metadata_size(struct btrfs_fs_info *fs_info)
{
        struct btrfs_space_info *sinfo;
        u64 num_bytes;
        u64 meta_used;
        u64 data_used;
        int csum_size = btrfs_super_csum_size(fs_info->super_copy);

        sinfo = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_DATA);
        spin_lock(&sinfo->lock);
        data_used = sinfo->bytes_used;
        spin_unlock(&sinfo->lock);

        sinfo = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
        spin_lock(&sinfo->lock);
        if (sinfo->flags & BTRFS_BLOCK_GROUP_DATA)
                data_used = 0;
        meta_used = sinfo->bytes_used;
        spin_unlock(&sinfo->lock);

        num_bytes = (data_used >> fs_info->sb->s_blocksize_bits) *
                    csum_size * 2;
        num_bytes += div_u64(data_used + meta_used, 50);

        if (num_bytes * 3 > meta_used)
                num_bytes = div_u64(meta_used, 3);

        return ALIGN(num_bytes, fs_info->extent_root->nodesize << 10);
}

static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
{
        struct btrfs_block_rsv *block_rsv = &fs_info->global_block_rsv;
        struct btrfs_space_info *sinfo = block_rsv->space_info;
        u64 num_bytes;

        num_bytes = calc_global_metadata_size(fs_info);

        spin_lock(&sinfo->lock);
        spin_lock(&block_rsv->lock);

        block_rsv->size = min_t(u64, num_bytes, 512 * 1024 * 1024);

        num_bytes = sinfo->bytes_used + sinfo->bytes_pinned +
                    sinfo->bytes_reserved + sinfo->bytes_readonly +
                    sinfo->bytes_may_use;

        if (sinfo->total_bytes > num_bytes) {
                num_bytes = sinfo->total_bytes - num_bytes;
                block_rsv->reserved += num_bytes;
                sinfo->bytes_may_use += num_bytes;
                trace_btrfs_space_reservation(fs_info, "space_info",
                                      sinfo->flags, num_bytes, 1);
        }

        if (block_rsv->reserved >= block_rsv->size) {
                num_bytes = block_rsv->reserved - block_rsv->size;
                sinfo->bytes_may_use -= num_bytes;
                trace_btrfs_space_reservation(fs_info, "space_info",
                                      sinfo->flags, num_bytes, 0);
                block_rsv->reserved = block_rsv->size;
                block_rsv->full = 1;
        }

        spin_unlock(&block_rsv->lock);
        spin_unlock(&sinfo->lock);
}

static void init_global_block_rsv(struct btrfs_fs_info *fs_info)
{
        struct btrfs_space_info *space_info;

        space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
        fs_info->chunk_block_rsv.space_info = space_info;

        space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
        fs_info->global_block_rsv.space_info = space_info;
        fs_info->delalloc_block_rsv.space_info = space_info;
        fs_info->trans_block_rsv.space_info = space_info;
        fs_info->empty_block_rsv.space_info = space_info;
        fs_info->delayed_block_rsv.space_info = space_info;

        fs_info->extent_root->block_rsv = &fs_info->global_block_rsv;
        fs_info->csum_root->block_rsv = &fs_info->global_block_rsv;
        fs_info->dev_root->block_rsv = &fs_info->global_block_rsv;
        fs_info->tree_root->block_rsv = &fs_info->global_block_rsv;
        if (fs_info->quota_root)
                fs_info->quota_root->block_rsv = &fs_info->global_block_rsv;
        fs_info->chunk_root->block_rsv = &fs_info->chunk_block_rsv;

        update_global_block_rsv(fs_info);
}

static void release_global_block_rsv(struct btrfs_fs_info *fs_info)
{
        block_rsv_release_bytes(fs_info, &fs_info->global_block_rsv, NULL,
                                (u64)-1);
        WARN_ON(fs_info->delalloc_block_rsv.size > 0);
        WARN_ON(fs_info->delalloc_block_rsv.reserved > 0);
        WARN_ON(fs_info->trans_block_rsv.size > 0);
        WARN_ON(fs_info->trans_block_rsv.reserved > 0);
        WARN_ON(fs_info->chunk_block_rsv.size > 0);
        WARN_ON(fs_info->chunk_block_rsv.reserved > 0);
        WARN_ON(fs_info->delayed_block_rsv.size > 0);
        WARN_ON(fs_info->delayed_block_rsv.reserved > 0);
}

void btrfs_trans_release_metadata(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root)
{
        if (!trans->block_rsv)
                return;

        if (!trans->bytes_reserved)
                return;

        trace_btrfs_space_reservation(root->fs_info, "transaction",
                                      trans->transid, trans->bytes_reserved, 0);
        btrfs_block_rsv_release(root, trans->block_rsv, trans->bytes_reserved);
        trans->bytes_reserved = 0;
}

/*
 * To be called after all the new block groups attached to the transaction
 * handle have been created (btrfs_create_pending_block_groups()).
 */
void btrfs_trans_release_chunk_metadata(struct btrfs_trans_handle *trans)
{
        struct btrfs_fs_info *fs_info = trans->root->fs_info;

        if (!trans->chunk_bytes_reserved)
                return;

        WARN_ON_ONCE(!list_empty(&trans->new_bgs));

        block_rsv_release_bytes(fs_info, &fs_info->chunk_block_rsv, NULL,
                                trans->chunk_bytes_reserved);
        trans->chunk_bytes_reserved = 0;
}

/* Can only return 0 or -ENOSPC */
int btrfs_orphan_reserve_metadata(struct btrfs_trans_handle *trans,
                                  struct inode *inode)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_block_rsv *src_rsv = get_block_rsv(trans, root);
        struct btrfs_block_rsv *dst_rsv = root->orphan_block_rsv;

        /*
         * We need to hold space in order to delete our orphan item once we've
         * added it, so this takes the reservation so we can release it later
         * when we are truly done with the orphan item.
         */
        u64 num_bytes = btrfs_calc_trans_metadata_size(root, 1);
        trace_btrfs_space_reservation(root->fs_info, "orphan",
                                      btrfs_ino(inode), num_bytes, 1);
        return block_rsv_migrate_bytes(src_rsv, dst_rsv, num_bytes);
}

void btrfs_orphan_release_metadata(struct inode *inode)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        u64 num_bytes = btrfs_calc_trans_metadata_size(root, 1);
        trace_btrfs_space_reservation(root->fs_info, "orphan",
                                      btrfs_ino(inode), num_bytes, 0);
        btrfs_block_rsv_release(root, root->orphan_block_rsv, num_bytes);
}

/*
 * btrfs_subvolume_reserve_metadata() - reserve space for subvolume operation
 * root: the root of the parent directory
 * rsv: block reservation
 * items: the number of items that we need do reservation
 * qgroup_reserved: used to return the reserved size in qgroup
 *
 * This function is used to reserve the space for snapshot/subvolume
 * creation and deletion. Those operations are different with the
 * common file/directory operations, they change two fs/file trees
 * and root tree, the number of items that the qgroup reserves is
 * different with the free space reservation. So we can not use
 * the space reseravtion mechanism in start_transaction().
 */
int btrfs_subvolume_reserve_metadata(struct btrfs_root *root,
                                     struct btrfs_block_rsv *rsv,
                                     int items,
                                     u64 *qgroup_reserved,
                                     bool use_global_rsv)
{
        u64 num_bytes;
        int ret;
        struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;

        if (root->fs_info->quota_enabled) {
                /* One for parent inode, two for dir entries */
                num_bytes = 3 * root->nodesize;
                ret = btrfs_qgroup_reserve_meta(root, num_bytes);
                if (ret)
                        return ret;
        } else {
                num_bytes = 0;
        }

        *qgroup_reserved = num_bytes;

        num_bytes = btrfs_calc_trans_metadata_size(root, items);
        rsv->space_info = __find_space_info(root->fs_info,
                                            BTRFS_BLOCK_GROUP_METADATA);
        ret = btrfs_block_rsv_add(root, rsv, num_bytes,
                                  BTRFS_RESERVE_FLUSH_ALL);

        if (ret == -ENOSPC && use_global_rsv)
                ret = btrfs_block_rsv_migrate(global_rsv, rsv, num_bytes);

        if (ret && *qgroup_reserved)
                btrfs_qgroup_free_meta(root, *qgroup_reserved);

        return ret;
}

void btrfs_subvolume_release_metadata(struct btrfs_root *root,
                                      struct btrfs_block_rsv *rsv,
                                      u64 qgroup_reserved)
{
        btrfs_block_rsv_release(root, rsv, (u64)-1);
}

/**
 * drop_outstanding_extent - drop an outstanding extent
 * @inode: the inode we're dropping the extent for
 * @num_bytes: the number of bytes we're relaseing.
 *
 * This is called when we are freeing up an outstanding extent, either called
 * after an error or after an extent is written.  This will return the number of
 * reserved extents that need to be freed.  This must be called with
 * BTRFS_I(inode)->lock held.
 */
static unsigned drop_outstanding_extent(struct inode *inode, u64 num_bytes)
{
        unsigned drop_inode_space = 0;
        unsigned dropped_extents = 0;
        unsigned num_extents = 0;

        num_extents = (unsigned)div64_u64(num_bytes +
                                          BTRFS_MAX_EXTENT_SIZE - 1,
                                          BTRFS_MAX_EXTENT_SIZE);
        ASSERT(num_extents);
        ASSERT(BTRFS_I(inode)->outstanding_extents >= num_extents);
        BTRFS_I(inode)->outstanding_extents -= num_extents;

        if (BTRFS_I(inode)->outstanding_extents == 0 &&
            test_and_clear_bit(BTRFS_INODE_DELALLOC_META_RESERVED,
                               &BTRFS_I(inode)->runtime_flags))
                drop_inode_space = 1;

        /*
         * If we have more or the same amount of outsanding extents than we have
         * reserved then we need to leave the reserved extents count alone.
         */
        if (BTRFS_I(inode)->outstanding_extents >=
            BTRFS_I(inode)->reserved_extents)
                return drop_inode_space;

        dropped_extents = BTRFS_I(inode)->reserved_extents -
                BTRFS_I(inode)->outstanding_extents;
        BTRFS_I(inode)->reserved_extents -= dropped_extents;
        return dropped_extents + drop_inode_space;
}

/**
 * calc_csum_metadata_size - return the amount of metada space that must be
 *      reserved/free'd for the given bytes.
 * @inode: the inode we're manipulating
 * @num_bytes: the number of bytes in question
 * @reserve: 1 if we are reserving space, 0 if we are freeing space
 *
 * This adjusts the number of csum_bytes in the inode and then returns the
 * correct amount of metadata that must either be reserved or freed.  We
 * calculate how many checksums we can fit into one leaf and then divide the
 * number of bytes that will need to be checksumed by this value to figure out
 * how many checksums will be required.  If we are adding bytes then the number
 * may go up and we will return the number of additional bytes that must be
 * reserved.  If it is going down we will return the number of bytes that must
 * be freed.
 *
 * This must be called with BTRFS_I(inode)->lock held.
 */
static u64 calc_csum_metadata_size(struct inode *inode, u64 num_bytes,
                                   int reserve)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        u64 old_csums, num_csums;

        if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM &&
            BTRFS_I(inode)->csum_bytes == 0)
                return 0;

        old_csums = btrfs_csum_bytes_to_leaves(root, BTRFS_I(inode)->csum_bytes);
        if (reserve)
                BTRFS_I(inode)->csum_bytes += num_bytes;
        else
                BTRFS_I(inode)->csum_bytes -= num_bytes;
        num_csums = btrfs_csum_bytes_to_leaves(root, BTRFS_I(inode)->csum_bytes);

        /* No change, no need to reserve more */
        if (old_csums == num_csums)
                return 0;

        if (reserve)
                return btrfs_calc_trans_metadata_size(root,
                                                      num_csums - old_csums);

        return btrfs_calc_trans_metadata_size(root, old_csums - num_csums);
}

int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_block_rsv *block_rsv = &root->fs_info->delalloc_block_rsv;
        u64 to_reserve = 0;
        u64 csum_bytes;
        unsigned nr_extents = 0;
        int extra_reserve = 0;
        enum btrfs_reserve_flush_enum flush = BTRFS_RESERVE_FLUSH_ALL;
        int ret = 0;
        bool delalloc_lock = true;
        u64 to_free = 0;
        unsigned dropped;

        /* If we are a free space inode we need to not flush since we will be in
         * the middle of a transaction commit.  We also don't need the delalloc
         * mutex since we won't race with anybody.  We need this mostly to make
         * lockdep shut its filthy mouth.
         */
        if (btrfs_is_free_space_inode(inode)) {
                flush = BTRFS_RESERVE_NO_FLUSH;
                delalloc_lock = false;
        }

        if (flush != BTRFS_RESERVE_NO_FLUSH &&
            btrfs_transaction_in_commit(root->fs_info))
                schedule_timeout(1);

        if (delalloc_lock)
                mutex_lock(&BTRFS_I(inode)->delalloc_mutex);

        num_bytes = ALIGN(num_bytes, root->sectorsize);

        spin_lock(&BTRFS_I(inode)->lock);
        nr_extents = (unsigned)div64_u64(num_bytes +
                                         BTRFS_MAX_EXTENT_SIZE - 1,
                                         BTRFS_MAX_EXTENT_SIZE);
        BTRFS_I(inode)->outstanding_extents += nr_extents;
        nr_extents = 0;

        if (BTRFS_I(inode)->outstanding_extents >
            BTRFS_I(inode)->reserved_extents)
                nr_extents = BTRFS_I(inode)->outstanding_extents -
                        BTRFS_I(inode)->reserved_extents;

        /*
         * Add an item to reserve for updating the inode when we complete the
         * delalloc io.
         */
        if (!test_bit(BTRFS_INODE_DELALLOC_META_RESERVED,
                      &BTRFS_I(inode)->runtime_flags)) {
                nr_extents++;
                extra_reserve = 1;
        }

        to_reserve = btrfs_calc_trans_metadata_size(root, nr_extents);
        to_reserve += calc_csum_metadata_size(inode, num_bytes, 1);
        csum_bytes = BTRFS_I(inode)->csum_bytes;
        spin_unlock(&BTRFS_I(inode)->lock);

        if (root->fs_info->quota_enabled) {
                ret = btrfs_qgroup_reserve_meta(root,
                                nr_extents * root->nodesize);
                if (ret)
                        goto out_fail;
        }

        ret = reserve_metadata_bytes(root, block_rsv, to_reserve, flush);
        if (unlikely(ret)) {
                btrfs_qgroup_free_meta(root, nr_extents * root->nodesize);
                goto out_fail;
        }

        spin_lock(&BTRFS_I(inode)->lock);
        if (extra_reserve) {
                set_bit(BTRFS_INODE_DELALLOC_META_RESERVED,
                        &BTRFS_I(inode)->runtime_flags);
                nr_extents--;
        }
        BTRFS_I(inode)->reserved_extents += nr_extents;
        spin_unlock(&BTRFS_I(inode)->lock);

        if (delalloc_lock)
                mutex_unlock(&BTRFS_I(inode)->delalloc_mutex);

        if (to_reserve)
                trace_btrfs_space_reservation(root->fs_info, "delalloc",
                                              btrfs_ino(inode), to_reserve, 1);
        block_rsv_add_bytes(block_rsv, to_reserve, 1);

        return 0;

out_fail:
        spin_lock(&BTRFS_I(inode)->lock);
        dropped = drop_outstanding_extent(inode, num_bytes);
        /*
         * If the inodes csum_bytes is the same as the original
         * csum_bytes then we know we haven't raced with any free()ers
         * so we can just reduce our inodes csum bytes and carry on.
         */
        if (BTRFS_I(inode)->csum_bytes == csum_bytes) {
                calc_csum_metadata_size(inode, num_bytes, 0);
        } else {
                u64 orig_csum_bytes = BTRFS_I(inode)->csum_bytes;
                u64 bytes;

                /*
                 * This is tricky, but first we need to figure out how much we
                 * free'd from any free-ers that occured during this
                 * reservation, so we reset ->csum_bytes to the csum_bytes
                 * before we dropped our lock, and then call the free for the
                 * number of bytes that were freed while we were trying our
                 * reservation.
                 */
                bytes = csum_bytes - BTRFS_I(inode)->csum_bytes;
                BTRFS_I(inode)->csum_bytes = csum_bytes;
                to_free = calc_csum_metadata_size(inode, bytes, 0);


                /*
                 * Now we need to see how much we would have freed had we not
                 * been making this reservation and our ->csum_bytes were not
                 * artificially inflated.
                 */
                BTRFS_I(inode)->csum_bytes = csum_bytes - num_bytes;
                bytes = csum_bytes - orig_csum_bytes;
                bytes = calc_csum_metadata_size(inode, bytes, 0);

                /*
                 * Now reset ->csum_bytes to what it should be.  If bytes is
                 * more than to_free then we would have free'd more space had we
                 * not had an artificially high ->csum_bytes, so we need to free
                 * the remainder.  If bytes is the same or less then we don't
                 * need to do anything, the other free-ers did the correct
                 * thing.
                 */
                BTRFS_I(inode)->csum_bytes = orig_csum_bytes - num_bytes;
                if (bytes > to_free)
                        to_free = bytes - to_free;
                else
                        to_free = 0;
        }
        spin_unlock(&BTRFS_I(inode)->lock);
        if (dropped)
                to_free += btrfs_calc_trans_metadata_size(root, dropped);

        if (to_free) {
                btrfs_block_rsv_release(root, block_rsv, to_free);
                trace_btrfs_space_reservation(root->fs_info, "delalloc",
                                              btrfs_ino(inode), to_free, 0);
        }
        if (delalloc_lock)
                mutex_unlock(&BTRFS_I(inode)->delalloc_mutex);
        return ret;
}

/**
 * btrfs_delalloc_release_metadata - release a metadata reservation for an inode
 * @inode: the inode to release the reservation for
 * @num_bytes: the number of bytes we're releasing
 *
 * This will release the metadata reservation for an inode.  This can be called
 * once we complete IO for a given set of bytes to release their metadata
 * reservations.
 */
void btrfs_delalloc_release_metadata(struct inode *inode, u64 num_bytes)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        u64 to_free = 0;
        unsigned dropped;

        num_bytes = ALIGN(num_bytes, root->sectorsize);
        spin_lock(&BTRFS_I(inode)->lock);
        dropped = drop_outstanding_extent(inode, num_bytes);

        if (num_bytes)
                to_free = calc_csum_metadata_size(inode, num_bytes, 0);
        spin_unlock(&BTRFS_I(inode)->lock);
        if (dropped > 0)
                to_free += btrfs_calc_trans_metadata_size(root, dropped);

        if (btrfs_test_is_dummy_root(root))
                return;

        trace_btrfs_space_reservation(root->fs_info, "delalloc",
                                      btrfs_ino(inode), to_free, 0);

        btrfs_block_rsv_release(root, &root->fs_info->delalloc_block_rsv,
                                to_free);
}

/**
 * btrfs_delalloc_reserve_space - reserve data and metadata space for
 * delalloc
 * @inode: inode we're writing to
 * @start: start range we are writing to
 * @len: how long the range we are writing to
 *
 * TODO: This function will finally replace old btrfs_delalloc_reserve_space()
 *
 * This will do the following things
 *
 * o reserve space in data space info for num bytes
 *   and reserve precious corresponding qgroup space
 *   (Done in check_data_free_space)
 *
 * o reserve space for metadata space, based on the number of outstanding
 *   extents and how much csums will be needed
 *   also reserve metadata space in a per root over-reserve method.
 * o add to the inodes->delalloc_bytes
 * o add it to the fs_info's delalloc inodes list.
 *   (Above 3 all done in delalloc_reserve_metadata)
 *
 * Return 0 for success
 * Return <0 for error(-ENOSPC or -EQUOT)
 */
int btrfs_delalloc_reserve_space(struct inode *inode, u64 start, u64 len)
{
        int ret;

        ret = btrfs_check_data_free_space(inode, start, len);
        if (ret < 0)
                return ret;
        ret = btrfs_delalloc_reserve_metadata(inode, len);
        if (ret < 0)
                btrfs_free_reserved_data_space(inode, start, len);
        return ret;
}

/**
 * btrfs_delalloc_release_space - release data and metadata space for delalloc
 * @inode: inode we're releasing space for
 * @start: start position of the space already reserved
 * @len: the len of the space already reserved
 *
 * This must be matched with a call to btrfs_delalloc_reserve_space.  This is
 * called in the case that we don't need the metadata AND data reservations
 * anymore.  So if there is an error or we insert an inline extent.
 *
 * This function will release the metadata space that was not used and will
 * decrement ->delalloc_bytes and remove it from the fs_info delalloc_inodes
 * list if there are no delalloc bytes left.
 * Also it will handle the qgroup reserved space.
 */
void btrfs_delalloc_release_space(struct inode *inode, u64 start, u64 len)
{
        btrfs_delalloc_release_metadata(inode, len);
        btrfs_free_reserved_data_space(inode, start, len);
}

static int update_block_group(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root, u64 bytenr,
                              u64 num_bytes, int alloc)
{
        struct btrfs_block_group_cache *cache = NULL;
        struct btrfs_fs_info *info = root->fs_info;
        u64 total = num_bytes;
        u64 old_val;
        u64 byte_in_group;
        int factor;

        /* block accounting for super block */
        spin_lock(&info->delalloc_root_lock);
        old_val = btrfs_super_bytes_used(info->super_copy);
        if (alloc)
                old_val += num_bytes;
        else
                old_val -= num_bytes;
        btrfs_set_super_bytes_used(info->super_copy, old_val);
        spin_unlock(&info->delalloc_root_lock);

        while (total) {
                cache = btrfs_lookup_block_group(info, bytenr);
                if (!cache)
                        return -ENOENT;
                if (cache->flags & (BTRFS_BLOCK_GROUP_DUP |
                                    BTRFS_BLOCK_GROUP_RAID1 |
                                    BTRFS_BLOCK_GROUP_RAID10))
                        factor = 2;
                else
                        factor = 1;
                /*
                 * If this block group has free space cache written out, we
                 * need to make sure to load it if we are removing space.  This
                 * is because we need the unpinning stage to actually add the
                 * space back to the block group, otherwise we will leak space.
                 */
                if (!alloc && cache->cached == BTRFS_CACHE_NO)
                        cache_block_group(cache, 1);

                byte_in_group = bytenr - cache->key.objectid;
                WARN_ON(byte_in_group > cache->key.offset);

                spin_lock(&cache->space_info->lock);
                spin_lock(&cache->lock);

                if (btrfs_test_opt(root, SPACE_CACHE) &&
                    cache->disk_cache_state < BTRFS_DC_CLEAR)
                        cache->disk_cache_state = BTRFS_DC_CLEAR;

                old_val = btrfs_block_group_used(&cache->item);
                num_bytes = min(total, cache->key.offset - byte_in_group);
                if (alloc) {
                        old_val += num_bytes;
                        btrfs_set_block_group_used(&cache->item, old_val);
                        cache->reserved -= num_bytes;
                        cache->space_info->bytes_reserved -= num_bytes;
                        cache->space_info->bytes_used += num_bytes;
                        cache->space_info->disk_used += num_bytes * factor;
                        spin_unlock(&cache->lock);
                        spin_unlock(&cache->space_info->lock);
                } else {
                        old_val -= num_bytes;
                        btrfs_set_block_group_used(&cache->item, old_val);
                        cache->pinned += num_bytes;
                        cache->space_info->bytes_pinned += num_bytes;
                        cache->space_info->bytes_used -= num_bytes;
                        cache->space_info->disk_used -= num_bytes * factor;
                        spin_unlock(&cache->lock);
                        spin_unlock(&cache->space_info->lock);

                        set_extent_dirty(info->pinned_extents,
                                         bytenr, bytenr + num_bytes - 1,
                                         GFP_NOFS | __GFP_NOFAIL);
                }

                spin_lock(&trans->transaction->dirty_bgs_lock);
                if (list_empty(&cache->dirty_list)) {
                        list_add_tail(&cache->dirty_list,
                                      &trans->transaction->dirty_bgs);
                                trans->transaction->num_dirty_bgs++;
                        btrfs_get_block_group(cache);
                }
                spin_unlock(&trans->transaction->dirty_bgs_lock);

                /*
                 * No longer have used bytes in this block group, queue it for
                 * deletion. We do this after adding the block group to the
                 * dirty list to avoid races between cleaner kthread and space
                 * cache writeout.
                 */
                if (!alloc && old_val == 0) {
                        spin_lock(&info->unused_bgs_lock);
                        if (list_empty(&cache->bg_list)) {
                                btrfs_get_block_group(cache);
                                list_add_tail(&cache->bg_list,
                                              &info->unused_bgs);
                        }
                        spin_unlock(&info->unused_bgs_lock);
                }

                btrfs_put_block_group(cache);
                total -= num_bytes;
                bytenr += num_bytes;
        }
        return 0;
}

static u64 first_logical_byte(struct btrfs_root *root, u64 search_start)
{
        struct btrfs_block_group_cache *cache;
        u64 bytenr;

        spin_lock(&root->fs_info->block_group_cache_lock);
        bytenr = root->fs_info->first_logical_byte;
        spin_unlock(&root->fs_info->block_group_cache_lock);

        if (bytenr < (u64)-1)
                return bytenr;

        cache = btrfs_lookup_first_block_group(root->fs_info, search_start);
        if (!cache)
                return 0;

        bytenr = cache->key.objectid;
        btrfs_put_block_group(cache);

        return bytenr;
}

static int pin_down_extent(struct btrfs_root *root,
                           struct btrfs_block_group_cache *cache,
                           u64 bytenr, u64 num_bytes, int reserved)
{
        spin_lock(&cache->space_info->lock);
        spin_lock(&cache->lock);
        cache->pinned += num_bytes;
        cache->space_info->bytes_pinned += num_bytes;
        if (reserved) {
                cache->reserved -= num_bytes;
                cache->space_info->bytes_reserved -= num_bytes;
        }
        spin_unlock(&cache->lock);
        spin_unlock(&cache->space_info->lock);

        set_extent_dirty(root->fs_info->pinned_extents, bytenr,
                         bytenr + num_bytes - 1, GFP_NOFS | __GFP_NOFAIL);
        if (reserved)
                trace_btrfs_reserved_extent_free(root, bytenr, num_bytes);
        return 0;
}

/*
 * this function must be called within transaction
 */
int btrfs_pin_extent(struct btrfs_root *root,
                     u64 bytenr, u64 num_bytes, int reserved)
{
        struct btrfs_block_group_cache *cache;

        cache = btrfs_lookup_block_group(root->fs_info, bytenr);
        BUG_ON(!cache); /* Logic error */

        pin_down_extent(root, cache, bytenr, num_bytes, reserved);

        btrfs_put_block_group(cache);
        return 0;
}

/*
 * this function must be called within transaction
 */
int btrfs_pin_extent_for_log_replay(struct btrfs_root *root,
                                    u64 bytenr, u64 num_bytes)
{
        struct btrfs_block_group_cache *cache;
        int ret;

        cache = btrfs_lookup_block_group(root->fs_info, bytenr);
        if (!cache)
                return -EINVAL;

        /*
         * pull in the free space cache (if any) so that our pin
         * removes the free space from the cache.  We have load_only set
         * to one because the slow code to read in the free extents does check
         * the pinned extents.
         */
        cache_block_group(cache, 1);

        pin_down_extent(root, cache, bytenr, num_bytes, 0);

        /* remove us from the free space cache (if we're there at all) */
        ret = btrfs_remove_free_space(cache, bytenr, num_bytes);
        btrfs_put_block_group(cache);
        return ret;
}

static int __exclude_logged_extent(struct btrfs_root *root, u64 start, u64 num_bytes)
{
        int ret;
        struct btrfs_block_group_cache *block_group;
        struct btrfs_caching_control *caching_ctl;

        block_group = btrfs_lookup_block_group(root->fs_info, start);
        if (!block_group)
                return -EINVAL;

        cache_block_group(block_group, 0);
        caching_ctl = get_caching_control(block_group);

        if (!caching_ctl) {
                /* Logic error */
                BUG_ON(!block_group_cache_done(block_group));
                ret = btrfs_remove_free_space(block_group, start, num_bytes);
        } else {
                mutex_lock(&caching_ctl->mutex);

                if (start >= caching_ctl->progress) {
                        ret = add_excluded_extent(root, start, num_bytes);
                } else if (start + num_bytes <= caching_ctl->progress) {
                        ret = btrfs_remove_free_space(block_group,
                                                      start, num_bytes);
                } else {
                        num_bytes = caching_ctl->progress - start;
                        ret = btrfs_remove_free_space(block_group,
                                                      start, num_bytes);
                        if (ret)
                                goto out_lock;

                        num_bytes = (start + num_bytes) -
                                caching_ctl->progress;
                        start = caching_ctl->progress;
                        ret = add_excluded_extent(root, start, num_bytes);
                }
out_lock:
                mutex_unlock(&caching_ctl->mutex);
                put_caching_control(caching_ctl);
        }
        btrfs_put_block_group(block_group);
        return ret;
}

int btrfs_exclude_logged_extents(struct btrfs_root *log,
                                 struct extent_buffer *eb)
{
        struct btrfs_file_extent_item *item;
        struct btrfs_key key;
        int found_type;
        int i;

        if (!btrfs_fs_incompat(log->fs_info, MIXED_GROUPS))
                return 0;

        for (i = 0; i < btrfs_header_nritems(eb); i++) {
                btrfs_item_key_to_cpu(eb, &key, i);
                if (key.type != BTRFS_EXTENT_DATA_KEY)
                        continue;
                item = btrfs_item_ptr(eb, i, struct btrfs_file_extent_item);
                found_type = btrfs_file_extent_type(eb, item);
                if (found_type == BTRFS_FILE_EXTENT_INLINE)
                        continue;
                if (btrfs_file_extent_disk_bytenr(eb, item) == 0)
                        continue;
                key.objectid = btrfs_file_extent_disk_bytenr(eb, item);
                key.offset = btrfs_file_extent_disk_num_bytes(eb, item);
                __exclude_logged_extent(log, key.objectid, key.offset);
        }

        return 0;
}

/**
 * btrfs_update_reserved_bytes - update the block_group and space info counters
 * @cache:      The cache we are manipulating
 * @num_bytes:  The number of bytes in question
 * @reserve:    One of the reservation enums
 * @delalloc:   The blocks are allocated for the delalloc write
 *
 * This is called by the allocator when it reserves space, or by somebody who is
 * freeing space that was never actually used on disk.  For example if you
 * reserve some space for a new leaf in transaction A and before transaction A
 * commits you free that leaf, you call this with reserve set to 0 in order to
 * clear the reservation.
 *
 * Metadata reservations should be called with RESERVE_ALLOC so we do the proper
 * ENOSPC accounting.  For data we handle the reservation through clearing the
 * delalloc bits in the io_tree.  We have to do this since we could end up
 * allocating less disk space for the amount of data we have reserved in the
 * case of compression.
 *
 * If this is a reservation and the block group has become read only we cannot
 * make the reservation and return -EAGAIN, otherwise this function always
 * succeeds.
 */
static int btrfs_update_reserved_bytes(struct btrfs_block_group_cache *cache,
                                       u64 num_bytes, int reserve, int delalloc)
{
        struct btrfs_space_info *space_info = cache->space_info;
        int ret = 0;

        spin_lock(&space_info->lock);
        spin_lock(&cache->lock);
        if (reserve != RESERVE_FREE) {
                if (cache->ro) {
                        ret = -EAGAIN;
                } else {
                        cache->reserved += num_bytes;
                        space_info->bytes_reserved += num_bytes;
                        if (reserve == RESERVE_ALLOC) {
                                trace_btrfs_space_reservation(cache->fs_info,
                                                "space_info", space_info->flags,
                                                num_bytes, 0);
                                space_info->bytes_may_use -= num_bytes;
                        }

                        if (delalloc)
                                cache->delalloc_bytes += num_bytes;
                }
        } else {
                if (cache->ro)
                        space_info->bytes_readonly += num_bytes;
                cache->reserved -= num_bytes;
                space_info->bytes_reserved -= num_bytes;

                if (delalloc)
                        cache->delalloc_bytes -= num_bytes;
        }
        spin_unlock(&cache->lock);
        spin_unlock(&space_info->lock);
        return ret;
}

void btrfs_prepare_extent_commit(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_caching_control *next;
        struct btrfs_caching_control *caching_ctl;
        struct btrfs_block_group_cache *cache;

        down_write(&fs_info->commit_root_sem);

        list_for_each_entry_safe(caching_ctl, next,
                                 &fs_info->caching_block_groups, list) {
                cache = caching_ctl->block_group;
                if (block_group_cache_done(cache)) {
                        cache->last_byte_to_unpin = (u64)-1;
                        list_del_init(&caching_ctl->list);
                        put_caching_control(caching_ctl);
                } else {
                        cache->last_byte_to_unpin = caching_ctl->progress;
                }
        }

        if (fs_info->pinned_extents == &fs_info->freed_extents[0])
                fs_info->pinned_extents = &fs_info->freed_extents[1];
        else
                fs_info->pinned_extents = &fs_info->freed_extents[0];

        up_write(&fs_info->commit_root_sem);

        update_global_block_rsv(fs_info);
}

/*
 * Returns the free cluster for the given space info and sets empty_cluster to
 * what it should be based on the mount options.
 */
static struct btrfs_free_cluster *
fetch_cluster_info(struct btrfs_root *root, struct btrfs_space_info *space_info,
                   u64 *empty_cluster)
{
        struct btrfs_free_cluster *ret = NULL;
        bool ssd = btrfs_test_opt(root, SSD);

        *empty_cluster = 0;
        if (btrfs_mixed_space_info(space_info))
                return ret;

        if (ssd)
                *empty_cluster = 2 * 1024 * 1024;
        if (space_info->flags & BTRFS_BLOCK_GROUP_METADATA) {
                ret = &root->fs_info->meta_alloc_cluster;
                if (!ssd)
                        *empty_cluster = 64 * 1024;
        } else if ((space_info->flags & BTRFS_BLOCK_GROUP_DATA) && ssd) {
                ret = &root->fs_info->data_alloc_cluster;
        }

        return ret;
}

static int unpin_extent_range(struct btrfs_root *root, u64 start, u64 end,
                              const bool return_free_space)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_block_group_cache *cache = NULL;
        struct btrfs_space_info *space_info;
        struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
        struct btrfs_free_cluster *cluster = NULL;
        u64 len;
        u64 total_unpinned = 0;
        u64 empty_cluster = 0;
        bool readonly;

        while (start <= end) {
                readonly = false;
                if (!cache ||
                    start >= cache->key.objectid + cache->key.offset) {
                        if (cache)
                                btrfs_put_block_group(cache);
                        total_unpinned = 0;
                        cache = btrfs_lookup_block_group(fs_info, start);
                        BUG_ON(!cache); /* Logic error */

                        cluster = fetch_cluster_info(root,
                                                     cache->space_info,
                                                     &empty_cluster);
                        empty_cluster <<= 1;
                }

                len = cache->key.objectid + cache->key.offset - start;
                len = min(len, end + 1 - start);

                if (start < cache->last_byte_to_unpin) {
                        len = min(len, cache->last_byte_to_unpin - start);
                        if (return_free_space)
                                btrfs_add_free_space(cache, start, len);
                }

                start += len;
                total_unpinned += len;
                space_info = cache->space_info;

                /*
                 * If this space cluster has been marked as fragmented and we've
                 * unpinned enough in this block group to potentially allow a
                 * cluster to be created inside of it go ahead and clear the
                 * fragmented check.
                 */
                if (cluster && cluster->fragmented &&
                    total_unpinned > empty_cluster) {
                        spin_lock(&cluster->lock);
                        cluster->fragmented = 0;
                        spin_unlock(&cluster->lock);
                }

                spin_lock(&space_info->lock);
                spin_lock(&cache->lock);
                cache->pinned -= len;
                space_info->bytes_pinned -= len;
                space_info->max_extent_size = 0;
                percpu_counter_add(&space_info->total_bytes_pinned, -len);
                if (cache->ro) {
                        space_info->bytes_readonly += len;
                        readonly = true;
                }
                spin_unlock(&cache->lock);
                if (!readonly && global_rsv->space_info == space_info) {
                        spin_lock(&global_rsv->lock);
                        if (!global_rsv->full) {
                                len = min(len, global_rsv->size -
                                          global_rsv->reserved);
                                global_rsv->reserved += len;
                                space_info->bytes_may_use += len;
                                if (global_rsv->reserved >= global_rsv->size)
                                        global_rsv->full = 1;
                        }
                        spin_unlock(&global_rsv->lock);
                }
                spin_unlock(&space_info->lock);
        }

        if (cache)
                btrfs_put_block_group(cache);
        return 0;
}

int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_block_group_cache *block_group, *tmp;
        struct list_head *deleted_bgs;
        struct extent_io_tree *unpin;
        u64 start;
        u64 end;
        int ret;

        if (fs_info->pinned_extents == &fs_info->freed_extents[0])
                unpin = &fs_info->freed_extents[1];
        else
                unpin = &fs_info->freed_extents[0];

        while (!trans->aborted) {
                mutex_lock(&fs_info->unused_bg_unpin_mutex);
                ret = find_first_extent_bit(unpin, 0, &start, &end,
                                            EXTENT_DIRTY, NULL);
                if (ret) {
                        mutex_unlock(&fs_info->unused_bg_unpin_mutex);
                        break;
                }

                if (btrfs_test_opt(root, DISCARD))
                        ret = btrfs_discard_extent(root, start,
                                                   end + 1 - start, NULL);

                clear_extent_dirty(unpin, start, end, GFP_NOFS);
                unpin_extent_range(root, start, end, true);
                mutex_unlock(&fs_info->unused_bg_unpin_mutex);
                cond_resched();
        }

        /*
         * Transaction is finished.  We don't need the lock anymore.  We
         * do need to clean up the block groups in case of a transaction
         * abort.
         */
        deleted_bgs = &trans->transaction->deleted_bgs;
        list_for_each_entry_safe(block_group, tmp, deleted_bgs, bg_list) {
                u64 trimmed = 0;

                ret = -EROFS;
                if (!trans->aborted)
                        ret = btrfs_discard_extent(root,
                                                   block_group->key.objectid,
                                                   block_group->key.offset,
                                                   &trimmed);

                list_del_init(&block_group->bg_list);
                btrfs_put_block_group_trimming(block_group);
                btrfs_put_block_group(block_group);

                if (ret) {
                        const char *errstr = btrfs_decode_error(ret);
                        btrfs_warn(fs_info,
                                   "Discard failed while removing blockgroup: errno=%d %s\n",
                                   ret, errstr);
                }
        }

        return 0;
}

static void add_pinned_bytes(struct btrfs_fs_info *fs_info, u64 num_bytes,
                             u64 owner, u64 root_objectid)
{
        struct btrfs_space_info *space_info;
        u64 flags;

        if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                if (root_objectid == BTRFS_CHUNK_TREE_OBJECTID)
                        flags = BTRFS_BLOCK_GROUP_SYSTEM;
                else
                        flags = BTRFS_BLOCK_GROUP_METADATA;
        } else {
                flags = BTRFS_BLOCK_GROUP_DATA;
        }

        space_info = __find_space_info(fs_info, flags);
        BUG_ON(!space_info); /* Logic bug */
        percpu_counter_add(&space_info->total_bytes_pinned, num_bytes);
}


static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
                                struct btrfs_root *root,
                                struct btrfs_delayed_ref_node *node, u64 parent,
                                u64 root_objectid, u64 owner_objectid,
                                u64 owner_offset, int refs_to_drop,
                                struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_key key;
        struct btrfs_path *path;
        struct btrfs_fs_info *info = root->fs_info;
        struct btrfs_root *extent_root = info->extent_root;
        struct extent_buffer *leaf;
        struct btrfs_extent_item *ei;
        struct btrfs_extent_inline_ref *iref;
        int ret;
        int is_data;
        int extent_slot = 0;
        int found_extent = 0;
        int num_to_del = 1;
        u32 item_size;
        u64 refs;
        u64 bytenr = node->bytenr;
        u64 num_bytes = node->num_bytes;
        int last_ref = 0;
        bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
                                                 SKINNY_METADATA);

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        path->reada = 1;
        path->leave_spinning = 1;

        is_data = owner_objectid >= BTRFS_FIRST_FREE_OBJECTID;
        BUG_ON(!is_data && refs_to_drop != 1);

        if (is_data)
                skinny_metadata = 0;

        ret = lookup_extent_backref(trans, extent_root, path, &iref,
                                    bytenr, num_bytes, parent,
                                    root_objectid, owner_objectid,
                                    owner_offset);
        if (ret == 0) {
                extent_slot = path->slots[0];
                while (extent_slot >= 0) {
                        btrfs_item_key_to_cpu(path->nodes[0], &key,
                                              extent_slot);
                        if (key.objectid != bytenr)
                                break;
                        if (key.type == BTRFS_EXTENT_ITEM_KEY &&
                            key.offset == num_bytes) {
                                found_extent = 1;
                                break;
                        }
                        if (key.type == BTRFS_METADATA_ITEM_KEY &&
                            key.offset == owner_objectid) {
                                found_extent = 1;
                                break;
                        }
                        if (path->slots[0] - extent_slot > 5)
                                break;
                        extent_slot--;
                }
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
                item_size = btrfs_item_size_nr(path->nodes[0], extent_slot);
                if (found_extent && item_size < sizeof(*ei))
                        found_extent = 0;
#endif
                if (!found_extent) {
                        BUG_ON(iref);
                        ret = remove_extent_backref(trans, extent_root, path,
                                                    NULL, refs_to_drop,
                                                    is_data, &last_ref);
                        if (ret) {
                                btrfs_abort_transaction(trans, extent_root, ret);
                                goto out;
                        }
                        btrfs_release_path(path);
                        path->leave_spinning = 1;

                        key.objectid = bytenr;
                        key.type = BTRFS_EXTENT_ITEM_KEY;
                        key.offset = num_bytes;

                        if (!is_data && skinny_metadata) {
                                key.type = BTRFS_METADATA_ITEM_KEY;
                                key.offset = owner_objectid;
                        }

                        ret = btrfs_search_slot(trans, extent_root,
                                                &key, path, -1, 1);
                        if (ret > 0 && skinny_metadata && path->slots[0]) {
                                /*
                                 * Couldn't find our skinny metadata item,
                                 * see if we have ye olde extent item.
                                 */
                                path->slots[0]--;
                                btrfs_item_key_to_cpu(path->nodes[0], &key,
                                                      path->slots[0]);
                                if (key.objectid == bytenr &&
                                    key.type == BTRFS_EXTENT_ITEM_KEY &&
                                    key.offset == num_bytes)
                                        ret = 0;
                        }

                        if (ret > 0 && skinny_metadata) {
                                skinny_metadata = false;
                                key.objectid = bytenr;
                                key.type = BTRFS_EXTENT_ITEM_KEY;
                                key.offset = num_bytes;
                                btrfs_release_path(path);
                                ret = btrfs_search_slot(trans, extent_root,
                                                        &key, path, -1, 1);
                        }

                        if (ret) {
                                btrfs_err(info, "umm, got %d back from search, was looking for %llu",
                                        ret, bytenr);
                                if (ret > 0)
                                        btrfs_print_leaf(extent_root,
                                                         path->nodes[0]);
                        }
                        if (ret < 0) {
                                btrfs_abort_transaction(trans, extent_root, ret);
                                goto out;
                        }
                        extent_slot = path->slots[0];
                }
        } else if (WARN_ON(ret == -ENOENT)) {
                btrfs_print_leaf(extent_root, path->nodes[0]);
                btrfs_err(info,
                        "unable to find ref byte nr %llu parent %llu root %llu  owner %llu offset %llu",
                        bytenr, parent, root_objectid, owner_objectid,
                        owner_offset);
                btrfs_abort_transaction(trans, extent_root, ret);
                goto out;
        } else {
                btrfs_abort_transaction(trans, extent_root, ret);
                goto out;
        }

        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, extent_slot);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        if (item_size < sizeof(*ei)) {
                BUG_ON(found_extent || extent_slot != path->slots[0]);
                ret = convert_extent_item_v0(trans, extent_root, path,
                                             owner_objectid, 0);
                if (ret < 0) {
                        btrfs_abort_transaction(trans, extent_root, ret);
                        goto out;
                }

                btrfs_release_path(path);
                path->leave_spinning = 1;

                key.objectid = bytenr;
                key.type = BTRFS_EXTENT_ITEM_KEY;
                key.offset = num_bytes;

                ret = btrfs_search_slot(trans, extent_root, &key, path,
                                        -1, 1);
                if (ret) {
                        btrfs_err(info, "umm, got %d back from search, was looking for %llu",
                                ret, bytenr);
                        btrfs_print_leaf(extent_root, path->nodes[0]);
                }
                if (ret < 0) {
                        btrfs_abort_transaction(trans, extent_root, ret);
                        goto out;
                }

                extent_slot = path->slots[0];
                leaf = path->nodes[0];
                item_size = btrfs_item_size_nr(leaf, extent_slot);
        }
#endif
        BUG_ON(item_size < sizeof(*ei));
        ei = btrfs_item_ptr(leaf, extent_slot,
                            struct btrfs_extent_item);
        if (owner_objectid < BTRFS_FIRST_FREE_OBJECTID &&
            key.type == BTRFS_EXTENT_ITEM_KEY) {
                struct btrfs_tree_block_info *bi;
                BUG_ON(item_size < sizeof(*ei) + sizeof(*bi));
                bi = (struct btrfs_tree_block_info *)(ei + 1);
                WARN_ON(owner_objectid != btrfs_tree_block_level(leaf, bi));
        }

        refs = btrfs_extent_refs(leaf, ei);
        if (refs < refs_to_drop) {
                btrfs_err(info, "trying to drop %d refs but we only have %Lu "
                          "for bytenr %Lu", refs_to_drop, refs, bytenr);
                ret = -EINVAL;
                btrfs_abort_transaction(trans, extent_root, ret);
                goto out;
        }
        refs -= refs_to_drop;

        if (refs > 0) {
                if (extent_op)
                        __run_delayed_extent_op(extent_op, leaf, ei);
                /*
                 * In the case of inline back ref, reference count will
                 * be updated by remove_extent_backref
                 */
                if (iref) {
                        BUG_ON(!found_extent);
                } else {
                        btrfs_set_extent_refs(leaf, ei, refs);
                        btrfs_mark_buffer_dirty(leaf);
                }
                if (found_extent) {
                        ret = remove_extent_backref(trans, extent_root, path,
                                                    iref, refs_to_drop,
                                                    is_data, &last_ref);
                        if (ret) {
                                btrfs_abort_transaction(trans, extent_root, ret);
                                goto out;
                        }
                }
                add_pinned_bytes(root->fs_info, -num_bytes, owner_objectid,
                                 root_objectid);
        } else {
                if (found_extent) {
                        BUG_ON(is_data && refs_to_drop !=
                               extent_data_ref_count(path, iref));
                        if (iref) {
                                BUG_ON(path->slots[0] != extent_slot);
                        } else {
                                BUG_ON(path->slots[0] != extent_slot + 1);
                                path->slots[0] = extent_slot;
                                num_to_del = 2;
                        }
                }

                last_ref = 1;
                ret = btrfs_del_items(trans, extent_root, path, path->slots[0],
                                      num_to_del);
                if (ret) {
                        btrfs_abort_transaction(trans, extent_root, ret);
                        goto out;
                }
                btrfs_release_path(path);

                if (is_data) {
                        ret = btrfs_del_csums(trans, root, bytenr, num_bytes);
                        if (ret) {
                                btrfs_abort_transaction(trans, extent_root, ret);
                                goto out;
                        }
                }

                ret = update_block_group(trans, root, bytenr, num_bytes, 0);
                if (ret) {
                        btrfs_abort_transaction(trans, extent_root, ret);
                        goto out;
                }
        }
        btrfs_release_path(path);

out:
        btrfs_free_path(path);
        return ret;
}

/*
 * when we free an block, it is possible (and likely) that we free the last
 * delayed ref for that extent as well.  This searches the delayed ref tree for
 * a given extent, and if there are no other delayed refs to be processed, it
 * removes it from the tree.
 */
static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root, u64 bytenr)
{
        struct btrfs_delayed_ref_head *head;
        struct btrfs_delayed_ref_root *delayed_refs;
        int ret = 0;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);
        head = btrfs_find_delayed_ref_head(trans, bytenr);
        if (!head)
                goto out_delayed_unlock;

        spin_lock(&head->lock);
        if (!list_empty(&head->ref_list))
                goto out;

        if (head->extent_op) {
                if (!head->must_insert_reserved)
                        goto out;
                btrfs_free_delayed_extent_op(head->extent_op);
                head->extent_op = NULL;
        }

        /*
         * waiting for the lock here would deadlock.  If someone else has it
         * locked they are already in the process of dropping it anyway
         */
        if (!mutex_trylock(&head->mutex))
                goto out;

        /*
         * at this point we have a head with no other entries.  Go
         * ahead and process it.
         */
        head->node.in_tree = 0;
        rb_erase(&head->href_node, &delayed_refs->href_root);

        atomic_dec(&delayed_refs->num_entries);

        /*
         * we don't take a ref on the node because we're removing it from the
         * tree, so we just steal the ref the tree was holding.
         */
        delayed_refs->num_heads--;
        if (head->processing == 0)
                delayed_refs->num_heads_ready--;
        head->processing = 0;
        spin_unlock(&head->lock);
        spin_unlock(&delayed_refs->lock);

        BUG_ON(head->extent_op);
        if (head->must_insert_reserved)
                ret = 1;

        mutex_unlock(&head->mutex);
        btrfs_put_delayed_ref(&head->node);
        return ret;
out:
        spin_unlock(&head->lock);

out_delayed_unlock:
        spin_unlock(&delayed_refs->lock);
        return 0;
}

void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct extent_buffer *buf,
                           u64 parent, int last_ref)
{
        int pin = 1;
        int ret;

        if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) {
                ret = btrfs_add_delayed_tree_ref(root->fs_info, trans,
                                        buf->start, buf->len,
                                        parent, root->root_key.objectid,
                                        btrfs_header_level(buf),
                                        BTRFS_DROP_DELAYED_REF, NULL);
                BUG_ON(ret); /* -ENOMEM */
        }

        if (!last_ref)
                return;

        if (btrfs_header_generation(buf) == trans->transid) {
                struct btrfs_block_group_cache *cache;

                if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) {
                        ret = check_ref_cleanup(trans, root, buf->start);
                        if (!ret)
                                goto out;
                }

                cache = btrfs_lookup_block_group(root->fs_info, buf->start);

                if (btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
                        pin_down_extent(root, cache, buf->start, buf->len, 1);
                        btrfs_put_block_group(cache);
                        goto out;
                }

                WARN_ON(test_bit(EXTENT_BUFFER_DIRTY, &buf->bflags));

                btrfs_add_free_space(cache, buf->start, buf->len);
                btrfs_update_reserved_bytes(cache, buf->len, RESERVE_FREE, 0);
                btrfs_put_block_group(cache);
                trace_btrfs_reserved_extent_free(root, buf->start, buf->len);
                pin = 0;
        }
out:
        if (pin)
                add_pinned_bytes(root->fs_info, buf->len,
                                 btrfs_header_level(buf),
                                 root->root_key.objectid);

        /*
         * Deleting the buffer, clear the corrupt flag since it doesn't matter
         * anymore.
         */
        clear_bit(EXTENT_BUFFER_CORRUPT, &buf->bflags);
}

/* Can return -ENOMEM */
int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                      u64 bytenr, u64 num_bytes, u64 parent, u64 root_objectid,
                      u64 owner, u64 offset)
{
        int ret;
        struct btrfs_fs_info *fs_info = root->fs_info;

        if (btrfs_test_is_dummy_root(root))
                return 0;

        add_pinned_bytes(root->fs_info, num_bytes, owner, root_objectid);

        /*
         * tree log blocks never actually go into the extent allocation
         * tree, just update pinning info and exit early.
         */
        if (root_objectid == BTRFS_TREE_LOG_OBJECTID) {
                WARN_ON(owner >= BTRFS_FIRST_FREE_OBJECTID);
                /* unlocks the pinned mutex */
                btrfs_pin_extent(root, bytenr, num_bytes, 1);
                ret = 0;
        } else if (owner < BTRFS_FIRST_FREE_OBJECTID) {
                ret = btrfs_add_delayed_tree_ref(fs_info, trans, bytenr,
                                        num_bytes,
                                        parent, root_objectid, (int)owner,
                                        BTRFS_DROP_DELAYED_REF, NULL);
        } else {
                ret = btrfs_add_delayed_data_ref(fs_info, trans, bytenr,
                                                num_bytes,
                                                parent, root_objectid, owner,
                                                offset, 0,
                                                BTRFS_DROP_DELAYED_REF, NULL);
        }
        return ret;
}

/*
 * when we wait for progress in the block group caching, its because
 * our allocation attempt failed at least once.  So, we must sleep
 * and let some progress happen before we try again.
 *
 * This function will sleep at least once waiting for new free space to
 * show up, and then it will check the block group free space numbers
 * for our min num_bytes.  Another option is to have it go ahead
 * and look in the rbtree for a free extent of a given size, but this
 * is a good start.
 *
 * Callers of this must check if cache->cached == BTRFS_CACHE_ERROR before using
 * any of the information in this block group.
 */
static noinline void
wait_block_group_cache_progress(struct btrfs_block_group_cache *cache,
                                u64 num_bytes)
{
        struct btrfs_caching_control *caching_ctl;

        caching_ctl = get_caching_control(cache);
        if (!caching_ctl)
                return;

        wait_event(caching_ctl->wait, block_group_cache_done(cache) ||
                   (cache->free_space_ctl->free_space >= num_bytes));

        put_caching_control(caching_ctl);
}

static noinline int
wait_block_group_cache_done(struct btrfs_block_group_cache *cache)
{
        struct btrfs_caching_control *caching_ctl;
        int ret = 0;

        caching_ctl = get_caching_control(cache);
        if (!caching_ctl)
                return (cache->cached == BTRFS_CACHE_ERROR) ? -EIO : 0;

        wait_event(caching_ctl->wait, block_group_cache_done(cache));
        if (cache->cached == BTRFS_CACHE_ERROR)
                ret = -EIO;
        put_caching_control(caching_ctl);
        return ret;
}

int __get_raid_index(u64 flags)
{
        if (flags & BTRFS_BLOCK_GROUP_RAID10)
                return BTRFS_RAID_RAID10;
        else if (flags & BTRFS_BLOCK_GROUP_RAID1)
                return BTRFS_RAID_RAID1;
        else if (flags & BTRFS_BLOCK_GROUP_DUP)
                return BTRFS_RAID_DUP;
        else if (flags & BTRFS_BLOCK_GROUP_RAID0)
                return BTRFS_RAID_RAID0;
        else if (flags & BTRFS_BLOCK_GROUP_RAID5)
                return BTRFS_RAID_RAID5;
        else if (flags & BTRFS_BLOCK_GROUP_RAID6)
                return BTRFS_RAID_RAID6;

        return BTRFS_RAID_SINGLE; /* BTRFS_BLOCK_GROUP_SINGLE */
}

int get_block_group_index(struct btrfs_block_group_cache *cache)
{
        return __get_raid_index(cache->flags);
}

static const char *btrfs_raid_type_names[BTRFS_NR_RAID_TYPES] = {
        [BTRFS_RAID_RAID10]     = "raid10",
        [BTRFS_RAID_RAID1]      = "raid1",
        [BTRFS_RAID_DUP]        = "dup",
        [BTRFS_RAID_RAID0]      = "raid0",
        [BTRFS_RAID_SINGLE]     = "single",
        [BTRFS_RAID_RAID5]      = "raid5",
        [BTRFS_RAID_RAID6]      = "raid6",
};

static const char *get_raid_name(enum btrfs_raid_types type)
{
        if (type >= BTRFS_NR_RAID_TYPES)
                return NULL;

        return btrfs_raid_type_names[type];
}

enum btrfs_loop_type {
        LOOP_CACHING_NOWAIT = 0,
        LOOP_CACHING_WAIT = 1,
        LOOP_ALLOC_CHUNK = 2,
        LOOP_NO_EMPTY_SIZE = 3,
};

static inline void
btrfs_lock_block_group(struct btrfs_block_group_cache *cache,
                       int delalloc)
{
        if (delalloc)
                down_read(&cache->data_rwsem);
}

static inline void
btrfs_grab_block_group(struct btrfs_block_group_cache *cache,
                       int delalloc)
{
        btrfs_get_block_group(cache);
        if (delalloc)
                down_read(&cache->data_rwsem);
}

static struct btrfs_block_group_cache *
btrfs_lock_cluster(struct btrfs_block_group_cache *block_group,
                   struct btrfs_free_cluster *cluster,
                   int delalloc)
{
        struct btrfs_block_group_cache *used_bg;
        bool locked = false;
again:
        spin_lock(&cluster->refill_lock);
        if (locked) {
                if (used_bg == cluster->block_group)
                        return used_bg;

                up_read(&used_bg->data_rwsem);
                btrfs_put_block_group(used_bg);
        }

        used_bg = cluster->block_group;
        if (!used_bg)
                return NULL;

        if (used_bg == block_group)
                return used_bg;

        btrfs_get_block_group(used_bg);

        if (!delalloc)
                return used_bg;

        if (down_read_trylock(&used_bg->data_rwsem))
                return used_bg;

        spin_unlock(&cluster->refill_lock);
        down_read(&used_bg->data_rwsem);
        locked = true;
        goto again;
}

static inline void
btrfs_release_block_group(struct btrfs_block_group_cache *cache,
                         int delalloc)
{
        if (delalloc)
                up_read(&cache->data_rwsem);
        btrfs_put_block_group(cache);
}

/*
 * walks the btree of allocated extents and find a hole of a given size.
 * The key ins is changed to record the hole:
 * ins->objectid == start position
 * ins->flags = BTRFS_EXTENT_ITEM_KEY
 * ins->offset == the size of the hole.
 * Any available blocks before search_start are skipped.
 *
 * If there is no suitable free space, we will record the max size of
 * the free space extent currently.
 */
static noinline int find_free_extent(struct btrfs_root *orig_root,
                                     u64 num_bytes, u64 empty_size,
                                     u64 hint_byte, struct btrfs_key *ins,
                                     u64 flags, int delalloc)
{
        int ret = 0;
        struct btrfs_root *root = orig_root->fs_info->extent_root;
        struct btrfs_free_cluster *last_ptr = NULL;
        struct btrfs_block_group_cache *block_group = NULL;
        u64 search_start = 0;
        u64 max_extent_size = 0;
        u64 empty_cluster = 0;
        struct btrfs_space_info *space_info;
        int loop = 0;
        int index = __get_raid_index(flags);
        int alloc_type = (flags & BTRFS_BLOCK_GROUP_DATA) ?
                RESERVE_ALLOC_NO_ACCOUNT : RESERVE_ALLOC;
        bool failed_cluster_refill = false;
        bool failed_alloc = false;
        bool use_cluster = true;
        bool have_caching_bg = false;
        bool orig_have_caching_bg = false;
        bool full_search = false;

        WARN_ON(num_bytes < root->sectorsize);
        ins->type = BTRFS_EXTENT_ITEM_KEY;
        ins->objectid = 0;
        ins->offset = 0;

        trace_find_free_extent(orig_root, num_bytes, empty_size, flags);

        space_info = __find_space_info(root->fs_info, flags);
        if (!space_info) {
                btrfs_err(root->fs_info, "No space info for %llu", flags);
                return -ENOSPC;
        }

        /*
         * If our free space is heavily fragmented we may not be able to make
         * big contiguous allocations, so instead of doing the expensive search
         * for free space, simply return ENOSPC with our max_extent_size so we
         * can go ahead and search for a more manageable chunk.
         *
         * If our max_extent_size is large enough for our allocation simply
         * disable clustering since we will likely not be able to find enough
         * space to create a cluster and induce latency trying.
         */
        if (unlikely(space_info->max_extent_size)) {
                spin_lock(&space_info->lock);
                if (space_info->max_extent_size &&
                    num_bytes > space_info->max_extent_size) {
                        ins->offset = space_info->max_extent_size;
                        spin_unlock(&space_info->lock);
                        return -ENOSPC;
                } else if (space_info->max_extent_size) {
                        use_cluster = false;
                }
                spin_unlock(&space_info->lock);
        }

        last_ptr = fetch_cluster_info(orig_root, space_info, &empty_cluster);
        if (last_ptr) {
                spin_lock(&last_ptr->lock);
                if (last_ptr->block_group)
                        hint_byte = last_ptr->window_start;
                if (last_ptr->fragmented) {
                        /*
                         * We still set window_start so we can keep track of the
                         * last place we found an allocation to try and save
                         * some time.
                         */
                        hint_byte = last_ptr->window_start;
                        use_cluster = false;
                }
                spin_unlock(&last_ptr->lock);
        }

        search_start = max(search_start, first_logical_byte(root, 0));
        search_start = max(search_start, hint_byte);
        if (search_start == hint_byte) {
                block_group = btrfs_lookup_block_group(root->fs_info,
                                                       search_start);
                /*
                 * we don't want to use the block group if it doesn't match our
                 * allocation bits, or if its not cached.
                 *
                 * However if we are re-searching with an ideal block group
                 * picked out then we don't care that the block group is cached.
                 */
                if (block_group && block_group_bits(block_group, flags) &&
                    block_group->cached != BTRFS_CACHE_NO) {
                        down_read(&space_info->groups_sem);
                        if (list_empty(&block_group->list) ||
                            block_group->ro) {
                                /*
                                 * someone is removing this block group,
                                 * we can't jump into the have_block_group
                                 * target because our list pointers are not
                                 * valid
                                 */
                                btrfs_put_block_group(block_group);
                                up_read(&space_info->groups_sem);
                        } else {
                                index = get_block_group_index(block_group);
                                btrfs_lock_block_group(block_group, delalloc);
                                goto have_block_group;
                        }
                } else if (block_group) {
                        btrfs_put_block_group(block_group);
                }
        }
search:
        have_caching_bg = false;
        if (index == 0 || index == __get_raid_index(flags))
                full_search = true;
        down_read(&space_info->groups_sem);
        list_for_each_entry(block_group, &space_info->block_groups[index],
                            list) {
                u64 offset;
                int cached;

                btrfs_grab_block_group(block_group, delalloc);
                search_start = block_group->key.objectid;

                /*
                 * this can happen if we end up cycling through all the
                 * raid types, but we want to make sure we only allocate
                 * for the proper type.
                 */
                if (!block_group_bits(block_group, flags)) {
                    u64 extra = BTRFS_BLOCK_GROUP_DUP |
                                BTRFS_BLOCK_GROUP_RAID1 |
                                BTRFS_BLOCK_GROUP_RAID5 |
                                BTRFS_BLOCK_GROUP_RAID6 |
                                BTRFS_BLOCK_GROUP_RAID10;

                        /*
                         * if they asked for extra copies and this block group
                         * doesn't provide them, bail.  This does allow us to
                         * fill raid0 from raid1.
                         */
                        if ((flags & extra) && !(block_group->flags & extra))
                                goto loop;
                }

have_block_group:
                cached = block_group_cache_done(block_group);
                if (unlikely(!cached)) {
                        have_caching_bg = true;
                        ret = cache_block_group(block_group, 0);
                        BUG_ON(ret < 0);
                        ret = 0;
                }

                if (unlikely(block_group->cached == BTRFS_CACHE_ERROR))
                        goto loop;
                if (unlikely(block_group->ro))
                        goto loop;

                /*
                 * Ok we want to try and use the cluster allocator, so
                 * lets look there
                 */
                if (last_ptr && use_cluster) {
                        struct btrfs_block_group_cache *used_block_group;
                        unsigned long aligned_cluster;
                        /*
                         * the refill lock keeps out other
                         * people trying to start a new cluster
                         */
                        used_block_group = btrfs_lock_cluster(block_group,
                                                              last_ptr,
                                                              delalloc);
                        if (!used_block_group)
                                goto refill_cluster;

                        if (used_block_group != block_group &&
                            (used_block_group->ro ||
                             !block_group_bits(used_block_group, flags)))
                                goto release_cluster;

                        offset = btrfs_alloc_from_cluster(used_block_group,
                                                last_ptr,
                                                num_bytes,
                                                used_block_group->key.objectid,
                                                &max_extent_size);
                        if (offset) {
                                /* we have a block, we're done */
                                spin_unlock(&last_ptr->refill_lock);
                                trace_btrfs_reserve_extent_cluster(root,
                                                used_block_group,
                                                search_start, num_bytes);
                                if (used_block_group != block_group) {
                                        btrfs_release_block_group(block_group,
                                                                  delalloc);
                                        block_group = used_block_group;
                                }
                                goto checks;
                        }

                        WARN_ON(last_ptr->block_group != used_block_group);
release_cluster:
                        /* If we are on LOOP_NO_EMPTY_SIZE, we can't
                         * set up a new clusters, so lets just skip it
                         * and let the allocator find whatever block
                         * it can find.  If we reach this point, we
                         * will have tried the cluster allocator
                         * plenty of times and not have found
                         * anything, so we are likely way too
                         * fragmented for the clustering stuff to find
                         * anything.
                         *
                         * However, if the cluster is taken from the
                         * current block group, release the cluster
                         * first, so that we stand a better chance of
                         * succeeding in the unclustered
                         * allocation.  */
                        if (loop >= LOOP_NO_EMPTY_SIZE &&
                            used_block_group != block_group) {
                                spin_unlock(&last_ptr->refill_lock);
                                btrfs_release_block_group(used_block_group,
                                                          delalloc);
                                goto unclustered_alloc;
                        }

                        /*
                         * this cluster didn't work out, free it and
                         * start over
                         */
                        btrfs_return_cluster_to_free_space(NULL, last_ptr);

                        if (used_block_group != block_group)
                                btrfs_release_block_group(used_block_group,
                                                          delalloc);
refill_cluster:
                        if (loop >= LOOP_NO_EMPTY_SIZE) {
                                spin_unlock(&last_ptr->refill_lock);
                                goto unclustered_alloc;
                        }

                        aligned_cluster = max_t(unsigned long,
                                                empty_cluster + empty_size,
                                              block_group->full_stripe_len);

                        /* allocate a cluster in this block group */
                        ret = btrfs_find_space_cluster(root, block_group,
                                                       last_ptr, search_start,
                                                       num_bytes,
                                                       aligned_cluster);
                        if (ret == 0) {
                                /*
                                 * now pull our allocation out of this
                                 * cluster
                                 */
                                offset = btrfs_alloc_from_cluster(block_group,
                                                        last_ptr,
                                                        num_bytes,
                                                        search_start,
                                                        &max_extent_size);
                                if (offset) {
                                        /* we found one, proceed */
                                        spin_unlock(&last_ptr->refill_lock);
                                        trace_btrfs_reserve_extent_cluster(root,
                                                block_group, search_start,
                                                num_bytes);
                                        goto checks;
                                }
                        } else if (!cached && loop > LOOP_CACHING_NOWAIT
                                   && !failed_cluster_refill) {
                                spin_unlock(&last_ptr->refill_lock);

                                failed_cluster_refill = true;
                                wait_block_group_cache_progress(block_group,
                                       num_bytes + empty_cluster + empty_size);
                                goto have_block_group;
                        }

                        /*
                         * at this point we either didn't find a cluster
                         * or we weren't able to allocate a block from our
                         * cluster.  Free the cluster we've been trying
                         * to use, and go to the next block group
                         */
                        btrfs_return_cluster_to_free_space(NULL, last_ptr);
                        spin_unlock(&last_ptr->refill_lock);
                        goto loop;
                }

unclustered_alloc:
                /*
                 * We are doing an unclustered alloc, set the fragmented flag so
                 * we don't bother trying to setup a cluster again until we get
                 * more space.
                 */
                if (unlikely(last_ptr)) {
                        spin_lock(&last_ptr->lock);
                        last_ptr->fragmented = 1;
                        spin_unlock(&last_ptr->lock);
                }
                spin_lock(&block_group->free_space_ctl->tree_lock);
                if (cached &&
                    block_group->free_space_ctl->free_space <
                    num_bytes + empty_cluster + empty_size) {
                        if (block_group->free_space_ctl->free_space >
                            max_extent_size)
                                max_extent_size =
                                        block_group->free_space_ctl->free_space;
                        spin_unlock(&block_group->free_space_ctl->tree_lock);
                        goto loop;
                }
                spin_unlock(&block_group->free_space_ctl->tree_lock);

                offset = btrfs_find_space_for_alloc(block_group, search_start,
                                                    num_bytes, empty_size,
                                                    &max_extent_size);
                /*
                 * If we didn't find a chunk, and we haven't failed on this
                 * block group before, and this block group is in the middle of
                 * caching and we are ok with waiting, then go ahead and wait
                 * for progress to be made, and set failed_alloc to true.
                 *
                 * If failed_alloc is true then we've already waited on this
                 * block group once and should move on to the next block group.
                 */
                if (!offset && !failed_alloc && !cached &&
                    loop > LOOP_CACHING_NOWAIT) {
                        wait_block_group_cache_progress(block_group,
                                                num_bytes + empty_size);
                        failed_alloc = true;
                        goto have_block_group;
                } else if (!offset) {
                        goto loop;
                }
checks:
                search_start = ALIGN(offset, root->stripesize);

                /* move on to the next group */
                if (search_start + num_bytes >
                    block_group->key.objectid + block_group->key.offset) {
                        btrfs_add_free_space(block_group, offset, num_bytes);
                        goto loop;
                }

                if (offset < search_start)
                        btrfs_add_free_space(block_group, offset,
                                             search_start - offset);
                BUG_ON(offset > search_start);

                ret = btrfs_update_reserved_bytes(block_group, num_bytes,
                                                  alloc_type, delalloc);
                if (ret == -EAGAIN) {
                        btrfs_add_free_space(block_group, offset, num_bytes);
                        goto loop;
                }

                /* we are all good, lets return */
                ins->objectid = search_start;
                ins->offset = num_bytes;

                trace_btrfs_reserve_extent(orig_root, block_group,
                                           search_start, num_bytes);
                btrfs_release_block_group(block_group, delalloc);
                break;
loop:
                failed_cluster_refill = false;
                failed_alloc = false;
                BUG_ON(index != get_block_group_index(block_group));
                btrfs_release_block_group(block_group, delalloc);
        }
        up_read(&space_info->groups_sem);

        if ((loop == LOOP_CACHING_NOWAIT) && have_caching_bg
                && !orig_have_caching_bg)
                orig_have_caching_bg = true;

        if (!ins->objectid && loop >= LOOP_CACHING_WAIT && have_caching_bg)
                goto search;

        if (!ins->objectid && ++index < BTRFS_NR_RAID_TYPES)
                goto search;

        /*
         * LOOP_CACHING_NOWAIT, search partially cached block groups, kicking
         *                      caching kthreads as we move along
         * LOOP_CACHING_WAIT, search everything, and wait if our bg is caching
         * LOOP_ALLOC_CHUNK, force a chunk allocation and try again
         * LOOP_NO_EMPTY_SIZE, set empty_size and empty_cluster to 0 and try
         *                      again
         */
        if (!ins->objectid && loop < LOOP_NO_EMPTY_SIZE) {
                index = 0;
                if (loop == LOOP_CACHING_NOWAIT) {
                        /*
                         * We want to skip the LOOP_CACHING_WAIT step if we
                         * don't have any unached bgs and we've alrelady done a
                         * full search through.
                         */
                        if (orig_have_caching_bg || !full_search)
                                loop = LOOP_CACHING_WAIT;
                        else
                                loop = LOOP_ALLOC_CHUNK;
                } else {
                        loop++;
                }

                if (loop == LOOP_ALLOC_CHUNK) {
                        struct btrfs_trans_handle *trans;
                        int exist = 0;

                        trans = current->journal_info;
                        if (trans)
                                exist = 1;
                        else
                                trans = btrfs_join_transaction(root);

                        if (IS_ERR(trans)) {
                                ret = PTR_ERR(trans);
                                goto out;
                        }

                        ret = do_chunk_alloc(trans, root, flags,
                                             CHUNK_ALLOC_FORCE);

                        /*
                         * If we can't allocate a new chunk we've already looped
                         * through at least once, move on to the NO_EMPTY_SIZE
                         * case.
                         */
                        if (ret == -ENOSPC)
                                loop = LOOP_NO_EMPTY_SIZE;

                        /*
                         * Do not bail out on ENOSPC since we
                         * can do more things.
                         */
                        if (ret < 0 && ret != -ENOSPC)
                                btrfs_abort_transaction(trans,
                                                        root, ret);
                        else
                                ret = 0;
                        if (!exist)
                                btrfs_end_transaction(trans, root);
                        if (ret)
                                goto out;
                }

                if (loop == LOOP_NO_EMPTY_SIZE) {
                        /*
                         * Don't loop again if we already have no empty_size and
                         * no empty_cluster.
                         */
                        if (empty_size == 0 &&
                            empty_cluster == 0) {
                                ret = -ENOSPC;
                                goto out;
                        }
                        empty_size = 0;
                        empty_cluster = 0;
                }

                goto search;
        } else if (!ins->objectid) {
                ret = -ENOSPC;
        } else if (ins->objectid) {
                if (!use_cluster && last_ptr) {
                        spin_lock(&last_ptr->lock);
                        last_ptr->window_start = ins->objectid;
                        spin_unlock(&last_ptr->lock);
                }
                ret = 0;
        }
out:
        if (ret == -ENOSPC) {
                spin_lock(&space_info->lock);
                space_info->max_extent_size = max_extent_size;
                spin_unlock(&space_info->lock);
                ins->offset = max_extent_size;
        }
        return ret;
}

static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
                            int dump_block_groups)
{
        struct btrfs_block_group_cache *cache;
        int index = 0;

        spin_lock(&info->lock);
        printk(KERN_INFO "BTRFS: space_info %llu has %llu free, is %sfull\n",
               info->flags,
               info->total_bytes - info->bytes_used - info->bytes_pinned -
               info->bytes_reserved - info->bytes_readonly,
               (info->full) ? "" : "not ");
        printk(KERN_INFO "BTRFS: space_info total=%llu, used=%llu, pinned=%llu, "
               "reserved=%llu, may_use=%llu, readonly=%llu\n",
               info->total_bytes, info->bytes_used, info->bytes_pinned,
               info->bytes_reserved, info->bytes_may_use,
               info->bytes_readonly);
        spin_unlock(&info->lock);

        if (!dump_block_groups)
                return;

        down_read(&info->groups_sem);
again:
        list_for_each_entry(cache, &info->block_groups[index], list) {
                spin_lock(&cache->lock);
                printk(KERN_INFO "BTRFS: "
                           "block group %llu has %llu bytes, "
                           "%llu used %llu pinned %llu reserved %s\n",
                       cache->key.objectid, cache->key.offset,
                       btrfs_block_group_used(&cache->item), cache->pinned,
                       cache->reserved, cache->ro ? "[readonly]" : "");
                btrfs_dump_free_space(cache, bytes);
                spin_unlock(&cache->lock);
        }
        if (++index < BTRFS_NR_RAID_TYPES)
                goto again;
        up_read(&info->groups_sem);
}

int btrfs_reserve_extent(struct btrfs_root *root,
                         u64 num_bytes, u64 min_alloc_size,
                         u64 empty_size, u64 hint_byte,
                         struct btrfs_key *ins, int is_data, int delalloc)
{
        bool final_tried = num_bytes == min_alloc_size;
        u64 flags;
        int ret;

        flags = btrfs_get_alloc_profile(root, is_data);
again:
        WARN_ON(num_bytes < root->sectorsize);
        ret = find_free_extent(root, num_bytes, empty_size, hint_byte, ins,
                               flags, delalloc);

        if (ret == -ENOSPC) {
                if (!final_tried && ins->offset) {
                        num_bytes = min(num_bytes >> 1, ins->offset);
                        num_bytes = round_down(num_bytes, root->sectorsize);
                        num_bytes = max(num_bytes, min_alloc_size);
                        if (num_bytes == min_alloc_size)
                                final_tried = true;
                        goto again;
                } else if (btrfs_test_opt(root, ENOSPC_DEBUG)) {
                        struct btrfs_space_info *sinfo;

                        sinfo = __find_space_info(root->fs_info, flags);
                        btrfs_err(root->fs_info, "allocation failed flags %llu, wanted %llu",
                                flags, num_bytes);
                        if (sinfo)
                                dump_space_info(sinfo, num_bytes, 1);
                }
        }

        return ret;
}

static int __btrfs_free_reserved_extent(struct btrfs_root *root,
                                        u64 start, u64 len,
                                        int pin, int delalloc)
{
        struct btrfs_block_group_cache *cache;
        int ret = 0;

        cache = btrfs_lookup_block_group(root->fs_info, start);
        if (!cache) {
                btrfs_err(root->fs_info, "Unable to find block group for %llu",
                        start);
                return -ENOSPC;
        }

        if (pin)
                pin_down_extent(root, cache, start, len, 1);
        else {
                if (btrfs_test_opt(root, DISCARD))
                        ret = btrfs_discard_extent(root, start, len, NULL);
                btrfs_add_free_space(cache, start, len);
                btrfs_update_reserved_bytes(cache, len, RESERVE_FREE, delalloc);
        }

        btrfs_put_block_group(cache);

        trace_btrfs_reserved_extent_free(root, start, len);

        return ret;
}

int btrfs_free_reserved_extent(struct btrfs_root *root,
                               u64 start, u64 len, int delalloc)
{
        return __btrfs_free_reserved_extent(root, start, len, 0, delalloc);
}

int btrfs_free_and_pin_reserved_extent(struct btrfs_root *root,
                                       u64 start, u64 len)
{
        return __btrfs_free_reserved_extent(root, start, len, 1, 0);
}

static int alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root,
                                      u64 parent, u64 root_objectid,
                                      u64 flags, u64 owner, u64 offset,
                                      struct btrfs_key *ins, int ref_mod)
{
        int ret;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_extent_item *extent_item;
        struct btrfs_extent_inline_ref *iref;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        int type;
        u32 size;

        if (parent > 0)
                type = BTRFS_SHARED_DATA_REF_KEY;
        else
                type = BTRFS_EXTENT_DATA_REF_KEY;

        size = sizeof(*extent_item) + btrfs_extent_inline_ref_size(type);

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        path->leave_spinning = 1;
        ret = btrfs_insert_empty_item(trans, fs_info->extent_root, path,
                                      ins, size);
        if (ret) {
                btrfs_free_path(path);
                return ret;
        }

        leaf = path->nodes[0];
        extent_item = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_extent_item);
        btrfs_set_extent_refs(leaf, extent_item, ref_mod);
        btrfs_set_extent_generation(leaf, extent_item, trans->transid);
        btrfs_set_extent_flags(leaf, extent_item,
                               flags | BTRFS_EXTENT_FLAG_DATA);

        iref = (struct btrfs_extent_inline_ref *)(extent_item + 1);
        btrfs_set_extent_inline_ref_type(leaf, iref, type);
        if (parent > 0) {
                struct btrfs_shared_data_ref *ref;
                ref = (struct btrfs_shared_data_ref *)(iref + 1);
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
                btrfs_set_shared_data_ref_count(leaf, ref, ref_mod);
        } else {
                struct btrfs_extent_data_ref *ref;
                ref = (struct btrfs_extent_data_ref *)(&iref->offset);
                btrfs_set_extent_data_ref_root(leaf, ref, root_objectid);
                btrfs_set_extent_data_ref_objectid(leaf, ref, owner);
                btrfs_set_extent_data_ref_offset(leaf, ref, offset);
                btrfs_set_extent_data_ref_count(leaf, ref, ref_mod);
        }

        btrfs_mark_buffer_dirty(path->nodes[0]);
        btrfs_free_path(path);

        ret = update_block_group(trans, root, ins->objectid, ins->offset, 1);
        if (ret) { /* -ENOENT, logic error */
                btrfs_err(fs_info, "update block group failed for %llu %llu",
                        ins->objectid, ins->offset);
                BUG();
        }
        trace_btrfs_reserved_extent_alloc(root, ins->objectid, ins->offset);
        return ret;
}

static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
                                     struct btrfs_root *root,
                                     u64 parent, u64 root_objectid,
                                     u64 flags, struct btrfs_disk_key *key,
                                     int level, struct btrfs_key *ins)
{
        int ret;
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_extent_item *extent_item;
        struct btrfs_tree_block_info *block_info;
        struct btrfs_extent_inline_ref *iref;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        u32 size = sizeof(*extent_item) + sizeof(*iref);
        u64 num_bytes = ins->offset;
        bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
                                                 SKINNY_METADATA);

        if (!skinny_metadata)
                size += sizeof(*block_info);

        path = btrfs_alloc_path();
        if (!path) {
                btrfs_free_and_pin_reserved_extent(root, ins->objectid,
                                                   root->nodesize);
                return -ENOMEM;
        }

        path->leave_spinning = 1;
        ret = btrfs_insert_empty_item(trans, fs_info->extent_root, path,
                                      ins, size);
        if (ret) {
                btrfs_free_path(path);
                btrfs_free_and_pin_reserved_extent(root, ins->objectid,
                                                   root->nodesize);
                return ret;
        }

        leaf = path->nodes[0];
        extent_item = btrfs_item_ptr(leaf, path->slots[0],
                                     struct btrfs_extent_item);
        btrfs_set_extent_refs(leaf, extent_item, 1);
        btrfs_set_extent_generation(leaf, extent_item, trans->transid);
        btrfs_set_extent_flags(leaf, extent_item,
                               flags | BTRFS_EXTENT_FLAG_TREE_BLOCK);

        if (skinny_metadata) {
                iref = (struct btrfs_extent_inline_ref *)(extent_item + 1);
                num_bytes = root->nodesize;
        } else {
                block_info = (struct btrfs_tree_block_info *)(extent_item + 1);
                btrfs_set_tree_block_key(leaf, block_info, key);
                btrfs_set_tree_block_level(leaf, block_info, level);
                iref = (struct btrfs_extent_inline_ref *)(block_info + 1);
        }

        if (parent > 0) {
                BUG_ON(!(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF));
                btrfs_set_extent_inline_ref_type(leaf, iref,
                                                 BTRFS_SHARED_BLOCK_REF_KEY);
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
        } else {
                btrfs_set_extent_inline_ref_type(leaf, iref,
                                                 BTRFS_TREE_BLOCK_REF_KEY);
                btrfs_set_extent_inline_ref_offset(leaf, iref, root_objectid);
        }

        btrfs_mark_buffer_dirty(leaf);
        btrfs_free_path(path);

        ret = update_block_group(trans, root, ins->objectid, root->nodesize,
                                 1);
        if (ret) { /* -ENOENT, logic error */
                btrfs_err(fs_info, "update block group failed for %llu %llu",
                        ins->objectid, ins->offset);
                BUG();
        }

        trace_btrfs_reserved_extent_alloc(root, ins->objectid, root->nodesize);
        return ret;
}

int btrfs_alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                                     struct btrfs_root *root,
                                     u64 root_objectid, u64 owner,
                                     u64 offset, u64 ram_bytes,
                                     struct btrfs_key *ins)
{
        int ret;

        BUG_ON(root_objectid == BTRFS_TREE_LOG_OBJECTID);

        ret = btrfs_add_delayed_data_ref(root->fs_info, trans, ins->objectid,
                                         ins->offset, 0,
                                         root_objectid, owner, offset,
                                         ram_bytes, BTRFS_ADD_DELAYED_EXTENT,
                                         NULL);
        return ret;
}

/*
 * this is used by the tree logging recovery code.  It records that
 * an extent has been allocated and makes sure to clear the free
 * space cache bits as well
 */
int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   u64 root_objectid, u64 owner, u64 offset,
                                   struct btrfs_key *ins)
{
        int ret;
        struct btrfs_block_group_cache *block_group;

        /*
         * Mixed block groups will exclude before processing the log so we only
         * need to do the exlude dance if this fs isn't mixed.
         */
        if (!btrfs_fs_incompat(root->fs_info, MIXED_GROUPS)) {
                ret = __exclude_logged_extent(root, ins->objectid, ins->offset);
                if (ret)
                        return ret;
        }

        block_group = btrfs_lookup_block_group(root->fs_info, ins->objectid);
        if (!block_group)
                return -EINVAL;

        ret = btrfs_update_reserved_bytes(block_group, ins->offset,
                                          RESERVE_ALLOC_NO_ACCOUNT, 0);
        BUG_ON(ret); /* logic error */
        ret = alloc_reserved_file_extent(trans, root, 0, root_objectid,
                                         0, owner, offset, ins, 1);
        btrfs_put_block_group(block_group);
        return ret;
}

static struct extent_buffer *
btrfs_init_new_buffer(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                      u64 bytenr, int level)
{
        struct extent_buffer *buf;

        buf = btrfs_find_create_tree_block(root, bytenr);
        if (!buf)
                return ERR_PTR(-ENOMEM);
        btrfs_set_header_generation(buf, trans->transid);
        btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
        btrfs_tree_lock(buf);
        clean_tree_block(trans, root->fs_info, buf);
        clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);

        btrfs_set_lock_blocking(buf);
        btrfs_set_buffer_uptodate(buf);

        if (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID) {
                buf->log_index = root->log_transid % 2;
                /*
                 * we allow two log transactions at a time, use different
                 * EXENT bit to differentiate dirty pages.
                 */
                if (buf->log_index == 0)
                        set_extent_dirty(&root->dirty_log_pages, buf->start,
                                        buf->start + buf->len - 1, GFP_NOFS);
                else
                        set_extent_new(&root->dirty_log_pages, buf->start,
                                        buf->start + buf->len - 1, GFP_NOFS);
        } else {
                buf->log_index = -1;
                set_extent_dirty(&trans->transaction->dirty_pages, buf->start,
                         buf->start + buf->len - 1, GFP_NOFS);
        }
        trans->blocks_used++;
        /* this returns a buffer locked for blocking */
        return buf;
}

static struct btrfs_block_rsv *
use_block_rsv(struct btrfs_trans_handle *trans,
              struct btrfs_root *root, u32 blocksize)
{
        struct btrfs_block_rsv *block_rsv;
        struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
        int ret;
        bool global_updated = false;

        block_rsv = get_block_rsv(trans, root);

        if (unlikely(block_rsv->size == 0))
                goto try_reserve;
again:
        ret = block_rsv_use_bytes(block_rsv, blocksize);
        if (!ret)
                return block_rsv;

        if (block_rsv->failfast)
                return ERR_PTR(ret);

        if (block_rsv->type == BTRFS_BLOCK_RSV_GLOBAL && !global_updated) {
                global_updated = true;
                update_global_block_rsv(root->fs_info);
                goto again;
        }

        if (btrfs_test_opt(root, ENOSPC_DEBUG)) {
                static DEFINE_RATELIMIT_STATE(_rs,
                                DEFAULT_RATELIMIT_INTERVAL * 10,
                                /*DEFAULT_RATELIMIT_BURST*/ 1);
                if (__ratelimit(&_rs))
                        WARN(1, KERN_DEBUG
                                "BTRFS: block rsv returned %d\n", ret);
        }
try_reserve:
        ret = reserve_metadata_bytes(root, block_rsv, blocksize,
                                     BTRFS_RESERVE_NO_FLUSH);
        if (!ret)
                return block_rsv;
        /*
         * If we couldn't reserve metadata bytes try and use some from
         * the global reserve if its space type is the same as the global
         * reservation.
         */
        if (block_rsv->type != BTRFS_BLOCK_RSV_GLOBAL &&
            block_rsv->space_info == global_rsv->space_info) {
                ret = block_rsv_use_bytes(global_rsv, blocksize);
                if (!ret)
                        return global_rsv;
        }
        return ERR_PTR(ret);
}

static void unuse_block_rsv(struct btrfs_fs_info *fs_info,
                            struct btrfs_block_rsv *block_rsv, u32 blocksize)
{
        block_rsv_add_bytes(block_rsv, blocksize, 0);
        block_rsv_release_bytes(fs_info, block_rsv, NULL, 0);
}

/*
 * finds a free extent and does all the dirty work required for allocation
 * returns the tree buffer or an ERR_PTR on error.
 */
struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
                                        struct btrfs_root *root,
                                        u64 parent, u64 root_objectid,
                                        struct btrfs_disk_key *key, int level,
                                        u64 hint, u64 empty_size)
{
        struct btrfs_key ins;
        struct btrfs_block_rsv *block_rsv;
        struct extent_buffer *buf;
        struct btrfs_delayed_extent_op *extent_op;
        u64 flags = 0;
        int ret;
        u32 blocksize = root->nodesize;
        bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
                                                 SKINNY_METADATA);

        if (btrfs_test_is_dummy_root(root)) {
                buf = btrfs_init_new_buffer(trans, root, root->alloc_bytenr,
                                            level);
                if (!IS_ERR(buf))
                        root->alloc_bytenr += blocksize;
                return buf;
        }

        block_rsv = use_block_rsv(trans, root, blocksize);
        if (IS_ERR(block_rsv))
                return ERR_CAST(block_rsv);

        ret = btrfs_reserve_extent(root, blocksize, blocksize,
                                   empty_size, hint, &ins, 0, 0);
        if (ret)
                goto out_unuse;

        buf = btrfs_init_new_buffer(trans, root, ins.objectid, level);
        if (IS_ERR(buf)) {
                ret = PTR_ERR(buf);
                goto out_free_reserved;
        }

        if (root_objectid == BTRFS_TREE_RELOC_OBJECTID) {
                if (parent == 0)
                        parent = ins.objectid;
                flags |= BTRFS_BLOCK_FLAG_FULL_BACKREF;
        } else
                BUG_ON(parent > 0);

        if (root_objectid != BTRFS_TREE_LOG_OBJECTID) {
                extent_op = btrfs_alloc_delayed_extent_op();
                if (!extent_op) {
                        ret = -ENOMEM;
                        goto out_free_buf;
                }
                if (key)
                        memcpy(&extent_op->key, key, sizeof(extent_op->key));
                else
                        memset(&extent_op->key, 0, sizeof(extent_op->key));
                extent_op->flags_to_set = flags;
                if (skinny_metadata)
                        extent_op->update_key = 0;
                else
                        extent_op->update_key = 1;
                extent_op->update_flags = 1;
                extent_op->is_data = 0;
                extent_op->level = level;

                ret = btrfs_add_delayed_tree_ref(root->fs_info, trans,
                                                 ins.objectid, ins.offset,
                                                 parent, root_objectid, level,
                                                 BTRFS_ADD_DELAYED_EXTENT,
                                                 extent_op);
                if (ret)
                        goto out_free_delayed;
        }
        return buf;

out_free_delayed:
        btrfs_free_delayed_extent_op(extent_op);
out_free_buf:
        free_extent_buffer(buf);
out_free_reserved:
        btrfs_free_reserved_extent(root, ins.objectid, ins.offset, 0);
out_unuse:
        unuse_block_rsv(root->fs_info, block_rsv, blocksize);
        return ERR_PTR(ret);
}

struct walk_control {
        u64 refs[BTRFS_MAX_LEVEL];
        u64 flags[BTRFS_MAX_LEVEL];
        struct btrfs_key update_progress;
        int stage;
        int level;
        int shared_level;
        int update_ref;
        int keep_locks;
        int reada_slot;
        int reada_count;
        int for_reloc;
};

#define DROP_REFERENCE  1
#define UPDATE_BACKREF  2

static noinline void reada_walk_down(struct btrfs_trans_handle *trans,
                                     struct btrfs_root *root,
                                     struct walk_control *wc,
                                     struct btrfs_path *path)
{
        u64 bytenr;
        u64 generation;
        u64 refs;
        u64 flags;
        u32 nritems;
        u32 blocksize;
        struct btrfs_key key;
        struct extent_buffer *eb;
        int ret;
        int slot;
        int nread = 0;

        if (path->slots[wc->level] < wc->reada_slot) {
                wc->reada_count = wc->reada_count * 2 / 3;
                wc->reada_count = max(wc->reada_count, 2);
        } else {
                wc->reada_count = wc->reada_count * 3 / 2;
                wc->reada_count = min_t(int, wc->reada_count,
                                        BTRFS_NODEPTRS_PER_BLOCK(root));
        }

        eb = path->nodes[wc->level];
        nritems = btrfs_header_nritems(eb);
        blocksize = root->nodesize;

        for (slot = path->slots[wc->level]; slot < nritems; slot++) {
                if (nread >= wc->reada_count)
                        break;

                cond_resched();
                bytenr = btrfs_node_blockptr(eb, slot);
                generation = btrfs_node_ptr_generation(eb, slot);

                if (slot == path->slots[wc->level])
                        goto reada;

                if (wc->stage == UPDATE_BACKREF &&
                    generation <= root->root_key.offset)
                        continue;

                /* We don't lock the tree block, it's OK to be racy here */
                ret = btrfs_lookup_extent_info(trans, root, bytenr,
                                               wc->level - 1, 1, &refs,
                                               &flags);
                /* We don't care about errors in readahead. */
                if (ret < 0)
                        continue;
                BUG_ON(refs == 0);

                if (wc->stage == DROP_REFERENCE) {
                        if (refs == 1)
                                goto reada;

                        if (wc->level == 1 &&
                            (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                                continue;
                        if (!wc->update_ref ||
                            generation <= root->root_key.offset)
                                continue;
                        btrfs_node_key_to_cpu(eb, &key, slot);
                        ret = btrfs_comp_cpu_keys(&key,
                                                  &wc->update_progress);
                        if (ret < 0)
                                continue;
                } else {
                        if (wc->level == 1 &&
                            (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                                continue;
                }
reada:
                readahead_tree_block(root, bytenr);
                nread++;
        }
        wc->reada_slot = slot;
}

/*
 * These may not be seen by the usual inc/dec ref code so we have to
 * add them here.
 */
static int record_one_subtree_extent(struct btrfs_trans_handle *trans,
                                     struct btrfs_root *root, u64 bytenr,
                                     u64 num_bytes)
{
        struct btrfs_qgroup_extent_record *qrecord;
        struct btrfs_delayed_ref_root *delayed_refs;

        qrecord = kmalloc(sizeof(*qrecord), GFP_NOFS);
        if (!qrecord)
                return -ENOMEM;

        qrecord->bytenr = bytenr;
        qrecord->num_bytes = num_bytes;
        qrecord->old_roots = NULL;

        delayed_refs = &trans->transaction->delayed_refs;
        spin_lock(&delayed_refs->lock);
        if (btrfs_qgroup_insert_dirty_extent(delayed_refs, qrecord))
                kfree(qrecord);
        spin_unlock(&delayed_refs->lock);

        return 0;
}

static int account_leaf_items(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root,
                              struct extent_buffer *eb)
{
        int nr = btrfs_header_nritems(eb);
        int i, extent_type, ret;
        struct btrfs_key key;
        struct btrfs_file_extent_item *fi;
        u64 bytenr, num_bytes;

        /* We can be called directly from walk_up_proc() */
        if (!root->fs_info->quota_enabled)
                return 0;

        for (i = 0; i < nr; i++) {
                btrfs_item_key_to_cpu(eb, &key, i);

                if (key.type != BTRFS_EXTENT_DATA_KEY)
                        continue;

                fi = btrfs_item_ptr(eb, i, struct btrfs_file_extent_item);
                /* filter out non qgroup-accountable extents  */
                extent_type = btrfs_file_extent_type(eb, fi);

                if (extent_type == BTRFS_FILE_EXTENT_INLINE)
                        continue;

                bytenr = btrfs_file_extent_disk_bytenr(eb, fi);
                if (!bytenr)
                        continue;

                num_bytes = btrfs_file_extent_disk_num_bytes(eb, fi);

                ret = record_one_subtree_extent(trans, root, bytenr, num_bytes);
                if (ret)
                        return ret;
        }
        return 0;
}

/*
 * Walk up the tree from the bottom, freeing leaves and any interior
 * nodes which have had all slots visited. If a node (leaf or
 * interior) is freed, the node above it will have it's slot
 * incremented. The root node will never be freed.
 *
 * At the end of this function, we should have a path which has all
 * slots incremented to the next position for a search. If we need to
 * read a new node it will be NULL and the node above it will have the
 * correct slot selected for a later read.
 *
 * If we increment the root nodes slot counter past the number of
 * elements, 1 is returned to signal completion of the search.
 */
static int adjust_slots_upwards(struct btrfs_root *root,
                                struct btrfs_path *path, int root_level)
{
        int level = 0;
        int nr, slot;
        struct extent_buffer *eb;

        if (root_level == 0)
                return 1;

        while (level <= root_level) {
                eb = path->nodes[level];
                nr = btrfs_header_nritems(eb);
                path->slots[level]++;
                slot = path->slots[level];
                if (slot >= nr || level == 0) {
                        /*
                         * Don't free the root -  we will detect this
                         * condition after our loop and return a
                         * positive value for caller to stop walking the tree.
                         */
                        if (level != root_level) {
                                btrfs_tree_unlock_rw(eb, path->locks[level]);
                                path->locks[level] = 0;

                                free_extent_buffer(eb);
                                path->nodes[level] = NULL;
                                path->slots[level] = 0;
                        }
                } else {
                        /*
                         * We have a valid slot to walk back down
                         * from. Stop here so caller can process these
                         * new nodes.
                         */
                        break;
                }

                level++;
        }

        eb = path->nodes[root_level];
        if (path->slots[root_level] >= btrfs_header_nritems(eb))
                return 1;

        return 0;
}

/*
 * root_eb is the subtree root and is locked before this function is called.
 */
static int account_shared_subtree(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,
                                  struct extent_buffer *root_eb,
                                  u64 root_gen,
                                  int root_level)
{
        int ret = 0;
        int level;
        struct extent_buffer *eb = root_eb;
        struct btrfs_path *path = NULL;

        BUG_ON(root_level < 0 || root_level > BTRFS_MAX_LEVEL);
        BUG_ON(root_eb == NULL);

        if (!root->fs_info->quota_enabled)
                return 0;

        if (!extent_buffer_uptodate(root_eb)) {
                ret = btrfs_read_buffer(root_eb, root_gen);
                if (ret)
                        goto out;
        }

        if (root_level == 0) {
                ret = account_leaf_items(trans, root, root_eb);
                goto out;
        }

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /*
         * Walk down the tree.  Missing extent blocks are filled in as
         * we go. Metadata is accounted every time we read a new
         * extent block.
         *
         * When we reach a leaf, we account for file extent items in it,
         * walk back up the tree (adjusting slot pointers as we go)
         * and restart the search process.
         */
        extent_buffer_get(root_eb); /* For path */
        path->nodes[root_level] = root_eb;
        path->slots[root_level] = 0;
        path->locks[root_level] = 0; /* so release_path doesn't try to unlock */
walk_down:
        level = root_level;
        while (level >= 0) {
                if (path->nodes[level] == NULL) {
                        int parent_slot;
                        u64 child_gen;
                        u64 child_bytenr;

                        /* We need to get child blockptr/gen from
                         * parent before we can read it. */
                        eb = path->nodes[level + 1];
                        parent_slot = path->slots[level + 1];
                        child_bytenr = btrfs_node_blockptr(eb, parent_slot);
                        child_gen = btrfs_node_ptr_generation(eb, parent_slot);

                        eb = read_tree_block(root, child_bytenr, child_gen);
                        if (IS_ERR(eb)) {
                                ret = PTR_ERR(eb);
                                goto out;
                        } else if (!extent_buffer_uptodate(eb)) {
                                free_extent_buffer(eb);
                                ret = -EIO;
                                goto out;
                        }

                        path->nodes[level] = eb;
                        path->slots[level] = 0;

                        btrfs_tree_read_lock(eb);
                        btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
                        path->locks[level] = BTRFS_READ_LOCK_BLOCKING;

                        ret = record_one_subtree_extent(trans, root, child_bytenr,
                                                        root->nodesize);
                        if (ret)
                                goto out;
                }

                if (level == 0) {
                        ret = account_leaf_items(trans, root, path->nodes[level]);
                        if (ret)
                                goto out;

                        /* Nonzero return here means we completed our search */
                        ret = adjust_slots_upwards(root, path, root_level);
                        if (ret)
                                break;

                        /* Restart search with new slots */
                        goto walk_down;
                }

                level--;
        }

        ret = 0;
out:
        btrfs_free_path(path);

        return ret;
}

/*
 * helper to process tree block while walking down the tree.
 *
 * when wc->stage == UPDATE_BACKREF, this function updates
 * back refs for pointers in the block.
 *
 * NOTE: return value 1 means we should stop walking down.
 */
static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   struct btrfs_path *path,
                                   struct walk_control *wc, int lookup_info)
{
        int level = wc->level;
        struct extent_buffer *eb = path->nodes[level];
        u64 flag = BTRFS_BLOCK_FLAG_FULL_BACKREF;
        int ret;

        if (wc->stage == UPDATE_BACKREF &&
            btrfs_header_owner(eb) != root->root_key.objectid)
                return 1;

        /*
         * when reference count of tree block is 1, it won't increase
         * again. once full backref flag is set, we never clear it.
         */
        if (lookup_info &&
            ((wc->stage == DROP_REFERENCE && wc->refs[level] != 1) ||
             (wc->stage == UPDATE_BACKREF && !(wc->flags[level] & flag)))) {
                BUG_ON(!path->locks[level]);
                ret = btrfs_lookup_extent_info(trans, root,
                                               eb->start, level, 1,
                                               &wc->refs[level],
                                               &wc->flags[level]);
                BUG_ON(ret == -ENOMEM);
                if (ret)
                        return ret;
                BUG_ON(wc->refs[level] == 0);
        }

        if (wc->stage == DROP_REFERENCE) {
                if (wc->refs[level] > 1)
                        return 1;

                if (path->locks[level] && !wc->keep_locks) {
                        btrfs_tree_unlock_rw(eb, path->locks[level]);
                        path->locks[level] = 0;
                }
                return 0;
        }

        /* wc->stage == UPDATE_BACKREF */
        if (!(wc->flags[level] & flag)) {
                BUG_ON(!path->locks[level]);
                ret = btrfs_inc_ref(trans, root, eb, 1);
                BUG_ON(ret); /* -ENOMEM */
                ret = btrfs_dec_ref(trans, root, eb, 0);
                BUG_ON(ret); /* -ENOMEM */
                ret = btrfs_set_disk_extent_flags(trans, root, eb->start,
                                                  eb->len, flag,
                                                  btrfs_header_level(eb), 0);
                BUG_ON(ret); /* -ENOMEM */
                wc->flags[level] |= flag;
        }

        /*
         * the block is shared by multiple trees, so it's not good to
         * keep the tree lock
         */
        if (path->locks[level] && level > 0) {
                btrfs_tree_unlock_rw(eb, path->locks[level]);
                path->locks[level] = 0;
        }
        return 0;
}

/*
 * helper to process tree block pointer.
 *
 * when wc->stage == DROP_REFERENCE, this function checks
 * reference count of the block pointed to. if the block
 * is shared and we need update back refs for the subtree
 * rooted at the block, this function changes wc->stage to
 * UPDATE_BACKREF. if the block is shared and there is no
 * need to update back, this function drops the reference
 * to the block.
 *
 * NOTE: return value 1 means we should stop walking down.
 */
static noinline int do_walk_down(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct walk_control *wc, int *lookup_info)
{
        u64 bytenr;
        u64 generation;
        u64 parent;
        u32 blocksize;
        struct btrfs_key key;
        struct extent_buffer *next;
        int level = wc->level;
        int reada = 0;
        int ret = 0;
        bool need_account = false;

        generation = btrfs_node_ptr_generation(path->nodes[level],
                                               path->slots[level]);
        /*
         * if the lower level block was created before the snapshot
         * was created, we know there is no need to update back refs
         * for the subtree
         */
        if (wc->stage == UPDATE_BACKREF &&
            generation <= root->root_key.offset) {
                *lookup_info = 1;
                return 1;
        }

        bytenr = btrfs_node_blockptr(path->nodes[level], path->slots[level]);
        blocksize = root->nodesize;

        next = btrfs_find_tree_block(root->fs_info, bytenr);
        if (!next) {
                next = btrfs_find_create_tree_block(root, bytenr);
                if (!next)
                        return -ENOMEM;
                btrfs_set_buffer_lockdep_class(root->root_key.objectid, next,
                                               level - 1);
                reada = 1;
        }
        btrfs_tree_lock(next);
        btrfs_set_lock_blocking(next);

        ret = btrfs_lookup_extent_info(trans, root, bytenr, level - 1, 1,
                                       &wc->refs[level - 1],
                                       &wc->flags[level - 1]);
        if (ret < 0) {
                btrfs_tree_unlock(next);
                return ret;
        }

        if (unlikely(wc->refs[level - 1] == 0)) {
                btrfs_err(root->fs_info, "Missing references.");
                BUG();
        }
        *lookup_info = 0;

        if (wc->stage == DROP_REFERENCE) {
                if (wc->refs[level - 1] > 1) {
                        need_account = true;
                        if (level == 1 &&
                            (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                                goto skip;

                        if (!wc->update_ref ||
                            generation <= root->root_key.offset)
                                goto skip;

                        btrfs_node_key_to_cpu(path->nodes[level], &key,
                                              path->slots[level]);
                        ret = btrfs_comp_cpu_keys(&key, &wc->update_progress);
                        if (ret < 0)
                                goto skip;

                        wc->stage = UPDATE_BACKREF;
                        wc->shared_level = level - 1;
                }
        } else {
                if (level == 1 &&
                    (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                        goto skip;
        }

        if (!btrfs_buffer_uptodate(next, generation, 0)) {
                btrfs_tree_unlock(next);
                free_extent_buffer(next);
                next = NULL;
                *lookup_info = 1;
        }

        if (!next) {
                if (reada && level == 1)
                        reada_walk_down(trans, root, wc, path);
                next = read_tree_block(root, bytenr, generation);
                if (IS_ERR(next)) {
                        return PTR_ERR(next);
                } else if (!extent_buffer_uptodate(next)) {
                        free_extent_buffer(next);
                        return -EIO;
                }
                btrfs_tree_lock(next);
                btrfs_set_lock_blocking(next);
        }

        level--;
        BUG_ON(level != btrfs_header_level(next));
        path->nodes[level] = next;
        path->slots[level] = 0;
        path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
        wc->level = level;
        if (wc->level == 1)
                wc->reada_slot = 0;
        return 0;
skip:
        wc->refs[level - 1] = 0;
        wc->flags[level - 1] = 0;
        if (wc->stage == DROP_REFERENCE) {
                if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF) {
                        parent = path->nodes[level]->start;
                } else {
                        BUG_ON(root->root_key.objectid !=
                               btrfs_header_owner(path->nodes[level]));
                        parent = 0;
                }

                if (need_account) {
                        ret = account_shared_subtree(trans, root, next,
                                                     generation, level - 1);
                        if (ret) {
                                btrfs_err_rl(root->fs_info,
                                        "Error "
                                        "%d accounting shared subtree. Quota "
                                        "is out of sync, rescan required.",
                                        ret);
                        }
                }
                ret = btrfs_free_extent(trans, root, bytenr, blocksize, parent,
                                root->root_key.objectid, level - 1, 0);
                BUG_ON(ret); /* -ENOMEM */
        }
        btrfs_tree_unlock(next);
        free_extent_buffer(next);
        *lookup_info = 1;
        return 1;
}

/*
 * helper to process tree block while walking up the tree.
 *
 * when wc->stage == DROP_REFERENCE, this function drops
 * reference count on the block.
 *
 * when wc->stage == UPDATE_BACKREF, this function changes
 * wc->stage back to DROP_REFERENCE if we changed wc->stage
 * to UPDATE_BACKREF previously while processing the block.
 *
 * NOTE: return value 1 means we should stop walking up.
 */
static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct walk_control *wc)
{
        int ret;
        int level = wc->level;
        struct extent_buffer *eb = path->nodes[level];
        u64 parent = 0;

        if (wc->stage == UPDATE_BACKREF) {
                BUG_ON(wc->shared_level < level);
                if (level < wc->shared_level)
                        goto out;

                ret = find_next_key(path, level + 1, &wc->update_progress);
                if (ret > 0)
                        wc->update_ref = 0;

                wc->stage = DROP_REFERENCE;
                wc->shared_level = -1;
                path->slots[level] = 0;

                /*
                 * check reference count again if the block isn't locked.
                 * we should start walking down the tree again if reference
                 * count is one.
                 */
                if (!path->locks[level]) {
                        BUG_ON(level == 0);
                        btrfs_tree_lock(eb);
                        btrfs_set_lock_blocking(eb);
                        path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;

                        ret = btrfs_lookup_extent_info(trans, root,
                                                       eb->start, level, 1,
                                                       &wc->refs[level],
                                                       &wc->flags[level]);
                        if (ret < 0) {
                                btrfs_tree_unlock_rw(eb, path->locks[level]);
                                path->locks[level] = 0;
                                return ret;
                        }
                        BUG_ON(wc->refs[level] == 0);
                        if (wc->refs[level] == 1) {
                                btrfs_tree_unlock_rw(eb, path->locks[level]);
                                path->locks[level] = 0;
                                return 1;
                        }
                }
        }

        /* wc->stage == DROP_REFERENCE */
        BUG_ON(wc->refs[level] > 1 && !path->locks[level]);

        if (wc->refs[level] == 1) {
                if (level == 0) {
                        if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
                                ret = btrfs_dec_ref(trans, root, eb, 1);
                        else
                                ret = btrfs_dec_ref(trans, root, eb, 0);
                        BUG_ON(ret); /* -ENOMEM */
                        ret = account_leaf_items(trans, root, eb);
                        if (ret) {
                                btrfs_err_rl(root->fs_info,
                                        "error "
                                        "%d accounting leaf items. Quota "
                                        "is out of sync, rescan required.",
                                        ret);
                        }
                }
                /* make block locked assertion in clean_tree_block happy */
                if (!path->locks[level] &&
                    btrfs_header_generation(eb) == trans->transid) {
                        btrfs_tree_lock(eb);
                        btrfs_set_lock_blocking(eb);
                        path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
                }
                clean_tree_block(trans, root->fs_info, eb);
        }

        if (eb == root->node) {
                if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
                        parent = eb->start;
                else
                        BUG_ON(root->root_key.objectid !=
                               btrfs_header_owner(eb));
        } else {
                if (wc->flags[level + 1] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
                        parent = path->nodes[level + 1]->start;
                else
                        BUG_ON(root->root_key.objectid !=
                               btrfs_header_owner(path->nodes[level + 1]));
        }

        btrfs_free_tree_block(trans, root, eb, parent, wc->refs[level] == 1);
out:
        wc->refs[level] = 0;
        wc->flags[level] = 0;
        return 0;
}

static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
                                   struct btrfs_root *root,
                                   struct btrfs_path *path,
                                   struct walk_control *wc)
{
        int level = wc->level;
        int lookup_info = 1;
        int ret;

        while (level >= 0) {
                ret = walk_down_proc(trans, root, path, wc, lookup_info);
                if (ret > 0)
                        break;

                if (level == 0)
                        break;

                if (path->slots[level] >=
                    btrfs_header_nritems(path->nodes[level]))
                        break;

                ret = do_walk_down(trans, root, path, wc, &lookup_info);
                if (ret > 0) {
                        path->slots[level]++;
                        continue;
                } else if (ret < 0)
                        return ret;
                level = wc->level;
        }
        return 0;
}

static noinline int walk_up_tree(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct walk_control *wc, int max_level)
{
        int level = wc->level;
        int ret;

        path->slots[level] = btrfs_header_nritems(path->nodes[level]);
        while (level < max_level && path->nodes[level]) {
                wc->level = level;
                if (path->slots[level] + 1 <
                    btrfs_header_nritems(path->nodes[level])) {
                        path->slots[level]++;
                        return 0;
                } else {
                        ret = walk_up_proc(trans, root, path, wc);
                        if (ret > 0)
                                return 0;

                        if (path->locks[level]) {
                                btrfs_tree_unlock_rw(path->nodes[level],
                                                     path->locks[level]);
                                path->locks[level] = 0;
                        }
                        free_extent_buffer(path->nodes[level]);
                        path->nodes[level] = NULL;
                        level++;
                }
        }
        return 1;
}

/*
 * drop a subvolume tree.
 *
 * this function traverses the tree freeing any blocks that only
 * referenced by the tree.
 *
 * when a shared tree block is found. this function decreases its
 * reference count by one. if update_ref is true, this function
 * also make sure backrefs for the shared block and all lower level
 * blocks are properly updated.
 *
 * If called with for_reloc == 0, may exit early with -EAGAIN
 */
int btrfs_drop_snapshot(struct btrfs_root *root,
                         struct btrfs_block_rsv *block_rsv, int update_ref,
                         int for_reloc)
{
        struct btrfs_path *path;
        struct btrfs_trans_handle *trans;
        struct btrfs_root *tree_root = root->fs_info->tree_root;
        struct btrfs_root_item *root_item = &root->root_item;
        struct walk_control *wc;
        struct btrfs_key key;
        int err = 0;
        int ret;
        int level;
        bool root_dropped = false;

        btrfs_debug(root->fs_info, "Drop subvolume %llu", root->objectid);

        path = btrfs_alloc_path();
        if (!path) {
                err = -ENOMEM;
                goto out;
        }

        wc = kzalloc(sizeof(*wc), GFP_NOFS);
        if (!wc) {
                btrfs_free_path(path);
                err = -ENOMEM;
                goto out;
        }

        trans = btrfs_start_transaction(tree_root, 0);
        if (IS_ERR(trans)) {
                err = PTR_ERR(trans);
                goto out_free;
        }

        if (block_rsv)
                trans->block_rsv = block_rsv;

        if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
                level = btrfs_header_level(root->node);
                path->nodes[level] = btrfs_lock_root_node(root);
                btrfs_set_lock_blocking(path->nodes[level]);
                path->slots[level] = 0;
                path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
                memset(&wc->update_progress, 0,
                       sizeof(wc->update_progress));
        } else {
                btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);
                memcpy(&wc->update_progress, &key,
                       sizeof(wc->update_progress));

                level = root_item->drop_level;
                BUG_ON(level == 0);
                path->lowest_level = level;
                ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                path->lowest_level = 0;
                if (ret < 0) {
                        err = ret;
                        goto out_end_trans;
                }
                WARN_ON(ret > 0);

                /*
                 * unlock our path, this is safe because only this
                 * function is allowed to delete this snapshot
                 */
                btrfs_unlock_up_safe(path, 0);

                level = btrfs_header_level(root->node);
                while (1) {
                        btrfs_tree_lock(path->nodes[level]);
                        btrfs_set_lock_blocking(path->nodes[level]);
                        path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;

                        ret = btrfs_lookup_extent_info(trans, root,
                                                path->nodes[level]->start,
                                                level, 1, &wc->refs[level],
                                                &wc->flags[level]);
                        if (ret < 0) {
                                err = ret;
                                goto out_end_trans;
                        }
                        BUG_ON(wc->refs[level] == 0);

                        if (level == root_item->drop_level)
                                break;

                        btrfs_tree_unlock(path->nodes[level]);
                        path->locks[level] = 0;
                        WARN_ON(wc->refs[level] != 1);
                        level--;
                }
        }

        wc->level = level;
        wc->shared_level = -1;
        wc->stage = DROP_REFERENCE;
        wc->update_ref = update_ref;
        wc->keep_locks = 0;
        wc->for_reloc = for_reloc;
        wc->reada_count = BTRFS_NODEPTRS_PER_BLOCK(root);

        while (1) {

                ret = walk_down_tree(trans, root, path, wc);
                if (ret < 0) {
                        err = ret;
                        break;
                }

                ret = walk_up_tree(trans, root, path, wc, BTRFS_MAX_LEVEL);
                if (ret < 0) {
                        err = ret;
                        break;
                }

                if (ret > 0) {
                        BUG_ON(wc->stage != DROP_REFERENCE);
                        break;
                }

                if (wc->stage == DROP_REFERENCE) {
                        level = wc->level;
                        btrfs_node_key(path->nodes[level],
                                       &root_item->drop_progress,
                                       path->slots[level]);
                        root_item->drop_level = level;
                }

                BUG_ON(wc->level == 0);
                if (btrfs_should_end_transaction(trans, tree_root) ||
                    (!for_reloc && btrfs_need_cleaner_sleep(root))) {
                        ret = btrfs_update_root(trans, tree_root,
                                                &root->root_key,
                                                root_item);
                        if (ret) {
                                btrfs_abort_transaction(trans, tree_root, ret);
                                err = ret;
                                goto out_end_trans;
                        }

                        btrfs_end_transaction_throttle(trans, tree_root);
                        if (!for_reloc && btrfs_need_cleaner_sleep(root)) {
                                pr_debug("BTRFS: drop snapshot early exit\n");
                                err = -EAGAIN;
                                goto out_free;
                        }

                        trans = btrfs_start_transaction(tree_root, 0);
                        if (IS_ERR(trans)) {
                                err = PTR_ERR(trans);
                                goto out_free;
                        }
                        if (block_rsv)
                                trans->block_rsv = block_rsv;
                }
        }
        btrfs_release_path(path);
        if (err)
                goto out_end_trans;

        ret = btrfs_del_root(trans, tree_root, &root->root_key);
        if (ret) {
                btrfs_abort_transaction(trans, tree_root, ret);
                goto out_end_trans;
        }

        if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID) {
                ret = btrfs_find_root(tree_root, &root->root_key, path,
                                      NULL, NULL);
                if (ret < 0) {
                        btrfs_abort_transaction(trans, tree_root, ret);
                        err = ret;
                        goto out_end_trans;
                } else if (ret > 0) {
                        /* if we fail to delete the orphan item this time
                         * around, it'll get picked up the next time.
                         *
                         * The most common failure here is just -ENOENT.
                         */
                        btrfs_del_orphan_item(trans, tree_root,
                                              root->root_key.objectid);
                }
        }

        if (test_bit(BTRFS_ROOT_IN_RADIX, &root->state)) {
                btrfs_add_dropped_root(trans, root);
        } else {
                free_extent_buffer(root->node);
                free_extent_buffer(root->commit_root);
                btrfs_put_fs_root(root);
        }
        root_dropped = true;
out_end_trans:
        btrfs_end_transaction_throttle(trans, tree_root);
out_free:
        kfree(wc);
        btrfs_free_path(path);
out:
        /*
         * So if we need to stop dropping the snapshot for whatever reason we
         * need to make sure to add it back to the dead root list so that we
         * keep trying to do the work later.  This also cleans up roots if we
         * don't have it in the radix (like when we recover after a power fail
         * or unmount) so we don't leak memory.
         */
        if (!for_reloc && root_dropped == false)
                btrfs_add_dead_root(root);
        if (err && err != -EAGAIN)
                btrfs_std_error(root->fs_info, err, NULL);
        return err;
}

/*
 * drop subtree rooted at tree block 'node'.
 *
 * NOTE: this function will unlock and release tree block 'node'
 * only used by relocation code
 */
int btrfs_drop_subtree(struct btrfs_trans_handle *trans,
                        struct btrfs_root *root,
                        struct extent_buffer *node,
                        struct extent_buffer *parent)
{
        struct btrfs_path *path;
        struct walk_control *wc;
        int level;
        int parent_level;
        int ret = 0;
        int wret;

        BUG_ON(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID);

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        wc = kzalloc(sizeof(*wc), GFP_NOFS);
        if (!wc) {
                btrfs_free_path(path);
                return -ENOMEM;
        }

        btrfs_assert_tree_locked(parent);
        parent_level = btrfs_header_level(parent);
        extent_buffer_get(parent);
        path->nodes[parent_level] = parent;
        path->slots[parent_level] = btrfs_header_nritems(parent);

        btrfs_assert_tree_locked(node);
        level = btrfs_header_level(node);
        path->nodes[level] = node;
        path->slots[level] = 0;
        path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;

        wc->refs[parent_level] = 1;
        wc->flags[parent_level] = BTRFS_BLOCK_FLAG_FULL_BACKREF;
        wc->level = level;
        wc->shared_level = -1;
        wc->stage = DROP_REFERENCE;
        wc->update_ref = 0;
        wc->keep_locks = 1;
        wc->for_reloc = 1;
        wc->reada_count = BTRFS_NODEPTRS_PER_BLOCK(root);

        while (1) {
                wret = walk_down_tree(trans, root, path, wc);
                if (wret < 0) {
                        ret = wret;
                        break;
                }

                wret = walk_up_tree(trans, root, path, wc, parent_level);
                if (wret < 0)
                        ret = wret;
                if (wret != 0)
                        break;
        }

        kfree(wc);
        btrfs_free_path(path);
        return ret;
}

static u64 update_block_group_flags(struct btrfs_root *root, u64 flags)
{
        u64 num_devices;
        u64 stripped;

        /*
         * if restripe for this chunk_type is on pick target profile and
         * return, otherwise do the usual balance
         */
        stripped = get_restripe_target(root->fs_info, flags);
        if (stripped)
                return extended_to_chunk(stripped);

        num_devices = root->fs_info->fs_devices->rw_devices;

        stripped = BTRFS_BLOCK_GROUP_RAID0 |
                BTRFS_BLOCK_GROUP_RAID5 | BTRFS_BLOCK_GROUP_RAID6 |
                BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_RAID10;

        if (num_devices == 1) {
                stripped |= BTRFS_BLOCK_GROUP_DUP;
                stripped = flags & ~stripped;

                /* turn raid0 into single device chunks */
                if (flags & BTRFS_BLOCK_GROUP_RAID0)
                        return stripped;

                /* turn mirroring into duplication */
                if (flags & (BTRFS_BLOCK_GROUP_RAID1 |
                             BTRFS_BLOCK_GROUP_RAID10))
                        return stripped | BTRFS_BLOCK_GROUP_DUP;
        } else {
                /* they already had raid on here, just return */
                if (flags & stripped)
                        return flags;

                stripped |= BTRFS_BLOCK_GROUP_DUP;
                stripped = flags & ~stripped;

                /* switch duplicated blocks with raid1 */
                if (flags & BTRFS_BLOCK_GROUP_DUP)
                        return stripped | BTRFS_BLOCK_GROUP_RAID1;

                /* this is drive concat, leave it alone */
        }

        return flags;
}

static int inc_block_group_ro(struct btrfs_block_group_cache *cache, int force)
{
        struct btrfs_space_info *sinfo = cache->space_info;
        u64 num_bytes;
        u64 min_allocable_bytes;
        int ret = -ENOSPC;

        /*
         * We need some metadata space and system metadata space for
         * allocating chunks in some corner cases until we force to set
         * it to be readonly.
         */
        if ((sinfo->flags &
             (BTRFS_BLOCK_GROUP_SYSTEM | BTRFS_BLOCK_GROUP_METADATA)) &&
            !force)
                min_allocable_bytes = 1 * 1024 * 1024;
        else
                min_allocable_bytes = 0;

        spin_lock(&sinfo->lock);
        spin_lock(&cache->lock);

        if (cache->ro) {
                cache->ro++;
                ret = 0;
                goto out;
        }

        num_bytes = cache->key.offset - cache->reserved - cache->pinned -
                    cache->bytes_super - btrfs_block_group_used(&cache->item);

        if (sinfo->bytes_used + sinfo->bytes_reserved + sinfo->bytes_pinned +
            sinfo->bytes_may_use + sinfo->bytes_readonly + num_bytes +
            min_allocable_bytes <= sinfo->total_bytes) {
                sinfo->bytes_readonly += num_bytes;
                cache->ro++;
                list_add_tail(&cache->ro_list, &sinfo->ro_bgs);
                ret = 0;
        }
out:
        spin_unlock(&cache->lock);
        spin_unlock(&sinfo->lock);
        return ret;
}

int btrfs_inc_block_group_ro(struct btrfs_root *root,
                             struct btrfs_block_group_cache *cache)

{
        struct btrfs_trans_handle *trans;
        u64 alloc_flags;
        int ret;

again:
        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans))
                return PTR_ERR(trans);

        /*
         * we're not allowed to set block groups readonly after the dirty
         * block groups cache has started writing.  If it already started,
         * back off and let this transaction commit
         */
        mutex_lock(&root->fs_info->ro_block_group_mutex);
        if (test_bit(BTRFS_TRANS_DIRTY_BG_RUN, &trans->transaction->flags)) {
                u64 transid = trans->transid;

                mutex_unlock(&root->fs_info->ro_block_group_mutex);
                btrfs_end_transaction(trans, root);

                ret = btrfs_wait_for_commit(root, transid);
                if (ret)
                        return ret;
                goto again;
        }

        /*
         * if we are changing raid levels, try to allocate a corresponding
         * block group with the new raid level.
         */
        alloc_flags = update_block_group_flags(root, cache->flags);
        if (alloc_flags != cache->flags) {
                ret = do_chunk_alloc(trans, root, alloc_flags,
                                     CHUNK_ALLOC_FORCE);
                /*
                 * ENOSPC is allowed here, we may have enough space
                 * already allocated at the new raid level to
                 * carry on
                 */
                if (ret == -ENOSPC)
                        ret = 0;
                if (ret < 0)
                        goto out;
        }

        ret = inc_block_group_ro(cache, 0);
        if (!ret)
                goto out;
        alloc_flags = get_alloc_profile(root, cache->space_info->flags);
        ret = do_chunk_alloc(trans, root, alloc_flags,
                             CHUNK_ALLOC_FORCE);
        if (ret < 0)
                goto out;
        ret = inc_block_group_ro(cache, 0);
out:
        if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
                alloc_flags = update_block_group_flags(root, cache->flags);
                lock_chunks(root->fs_info->chunk_root);
                check_system_chunk(trans, root, alloc_flags);
                unlock_chunks(root->fs_info->chunk_root);
        }
        mutex_unlock(&root->fs_info->ro_block_group_mutex);

        btrfs_end_transaction(trans, root);
        return ret;
}

int btrfs_force_chunk_alloc(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root, u64 type)
{
        u64 alloc_flags = get_alloc_profile(root, type);
        return do_chunk_alloc(trans, root, alloc_flags,
                              CHUNK_ALLOC_FORCE);
}

/*
 * helper to account the unused space of all the readonly block group in the
 * space_info. takes mirrors into account.
 */
u64 btrfs_account_ro_block_groups_free_space(struct btrfs_space_info *sinfo)
{
        struct btrfs_block_group_cache *block_group;
        u64 free_bytes = 0;
        int factor;

        /* It's df, we don't care if it's racey */
        if (list_empty(&sinfo->ro_bgs))
                return 0;

        spin_lock(&sinfo->lock);
        list_for_each_entry(block_group, &sinfo->ro_bgs, ro_list) {
                spin_lock(&block_group->lock);

                if (!block_group->ro) {
                        spin_unlock(&block_group->lock);
                        continue;
                }

                if (block_group->flags & (BTRFS_BLOCK_GROUP_RAID1 |
                                          BTRFS_BLOCK_GROUP_RAID10 |
                                          BTRFS_BLOCK_GROUP_DUP))
                        factor = 2;
                else
                        factor = 1;

                free_bytes += (block_group->key.offset -
                               btrfs_block_group_used(&block_group->item)) *
                               factor;

                spin_unlock(&block_group->lock);
        }
        spin_unlock(&sinfo->lock);

        return free_bytes;
}

void btrfs_dec_block_group_ro(struct btrfs_root *root,
                              struct btrfs_block_group_cache *cache)
{
        struct btrfs_space_info *sinfo = cache->space_info;
        u64 num_bytes;

        BUG_ON(!cache->ro);

        spin_lock(&sinfo->lock);
        spin_lock(&cache->lock);
        if (!--cache->ro) {
                num_bytes = cache->key.offset - cache->reserved -
                            cache->pinned - cache->bytes_super -
                            btrfs_block_group_used(&cache->item);
                sinfo->bytes_readonly -= num_bytes;
                list_del_init(&cache->ro_list);
        }
        spin_unlock(&cache->lock);
        spin_unlock(&sinfo->lock);
}

/*
 * checks to see if its even possible to relocate this block group.
 *
 * @return - -1 if it's not a good idea to relocate this block group, 0 if its
 * ok to go ahead and try.
 */
int btrfs_can_relocate(struct btrfs_root *root, u64 bytenr)
{
        struct btrfs_block_group_cache *block_group;
        struct btrfs_space_info *space_info;
        struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
        struct btrfs_device *device;
        struct btrfs_trans_handle *trans;
        u64 min_free;
        u64 dev_min = 1;
        u64 dev_nr = 0;
        u64 target;
        int index;
        int full = 0;
        int ret = 0;

        block_group = btrfs_lookup_block_group(root->fs_info, bytenr);

        /* odd, couldn't find the block group, leave it alone */
        if (!block_group)
                return -1;

        min_free = btrfs_block_group_used(&block_group->item);

        /* no bytes used, we're good */
        if (!min_free)
                goto out;

        space_info = block_group->space_info;
        spin_lock(&space_info->lock);

        full = space_info->full;

        /*
         * if this is the last block group we have in this space, we can't
         * relocate it unless we're able to allocate a new chunk below.
         *
         * Otherwise, we need to make sure we have room in the space to handle
         * all of the extents from this block group.  If we can, we're good
         */
        if ((space_info->total_bytes != block_group->key.offset) &&
            (space_info->bytes_used + space_info->bytes_reserved +
             space_info->bytes_pinned + space_info->bytes_readonly +
             min_free < space_info->total_bytes)) {
                spin_unlock(&space_info->lock);
                goto out;
        }
        spin_unlock(&space_info->lock);

        /*
         * ok we don't have enough space, but maybe we have free space on our
         * devices to allocate new chunks for relocation, so loop through our
         * alloc devices and guess if we have enough space.  if this block
         * group is going to be restriped, run checks against the target
         * profile instead of the current one.
         */
        ret = -1;

        /*
         * index:
         *      0: raid10
         *      1: raid1
         *      2: dup
         *      3: raid0
         *      4: single
         */
        target = get_restripe_target(root->fs_info, block_group->flags);
        if (target) {
                index = __get_raid_index(extended_to_chunk(target));
        } else {
                /*
                 * this is just a balance, so if we were marked as full
                 * we know there is no space for a new chunk
                 */
                if (full)
                        goto out;

                index = get_block_group_index(block_group);
        }

        if (index == BTRFS_RAID_RAID10) {
                dev_min = 4;
                /* Divide by 2 */
                min_free >>= 1;
        } else if (index == BTRFS_RAID_RAID1) {
                dev_min = 2;
        } else if (index == BTRFS_RAID_DUP) {
                /* Multiply by 2 */
                min_free <<= 1;
        } else if (index == BTRFS_RAID_RAID0) {
                dev_min = fs_devices->rw_devices;
                min_free = div64_u64(min_free, dev_min);
        }

        /* We need to do this so that we can look at pending chunks */
        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                goto out;
        }

        mutex_lock(&root->fs_info->chunk_mutex);
        list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
                u64 dev_offset;

                /*
                 * check to make sure we can actually find a chunk with enough
                 * space to fit our block group in.
                 */
                if (device->total_bytes > device->bytes_used + min_free &&
                    !device->is_tgtdev_for_dev_replace) {
                        ret = find_free_dev_extent(trans, device, min_free,
                                                   &dev_offset, NULL);
                        if (!ret)
                                dev_nr++;

                        if (dev_nr >= dev_min)
                                break;

                        ret = -1;
                }
        }
        mutex_unlock(&root->fs_info->chunk_mutex);
        btrfs_end_transaction(trans, root);
out:
        btrfs_put_block_group(block_group);
        return ret;
}

static int find_first_block_group(struct btrfs_root *root,
                struct btrfs_path *path, struct btrfs_key *key)
{
        int ret = 0;
        struct btrfs_key found_key;
        struct extent_buffer *leaf;
        int slot;

        ret = btrfs_search_slot(NULL, root, key, path, 0, 0);
        if (ret < 0)
                goto out;

        while (1) {
                slot = path->slots[0];
                leaf = path->nodes[0];
                if (slot >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret == 0)
                                continue;
                        if (ret < 0)
                                goto out;
                        break;
                }
                btrfs_item_key_to_cpu(leaf, &found_key, slot);

                if (found_key.objectid >= key->objectid &&
                    found_key.type == BTRFS_BLOCK_GROUP_ITEM_KEY) {
                        ret = 0;
                        goto out;
                }
                path->slots[0]++;
        }
out:
        return ret;
}

void btrfs_put_block_group_cache(struct btrfs_fs_info *info)
{
        struct btrfs_block_group_cache *block_group;
        u64 last = 0;

        while (1) {
                struct inode *inode;

                block_group = btrfs_lookup_first_block_group(info, last);
                while (block_group) {
                        spin_lock(&block_group->lock);
                        if (block_group->iref)
                                break;
                        spin_unlock(&block_group->lock);
                        block_group = next_block_group(info->tree_root,
                                                       block_group);
                }
                if (!block_group) {
                        if (last == 0)
                                break;
                        last = 0;
                        continue;
                }

                inode = block_group->inode;
                block_group->iref = 0;
                block_group->inode = NULL;
                spin_unlock(&block_group->lock);
                iput(inode);
                last = block_group->key.objectid + block_group->key.offset;
                btrfs_put_block_group(block_group);
        }
}

int btrfs_free_block_groups(struct btrfs_fs_info *info)
{
        struct btrfs_block_group_cache *block_group;
        struct btrfs_space_info *space_info;
        struct btrfs_caching_control *caching_ctl;
        struct rb_node *n;

        down_write(&info->commit_root_sem);
        while (!list_empty(&info->caching_block_groups)) {
                caching_ctl = list_entry(info->caching_block_groups.next,
                                         struct btrfs_caching_control, list);
                list_del(&caching_ctl->list);
                put_caching_control(caching_ctl);
        }
        up_write(&info->commit_root_sem);

        spin_lock(&info->unused_bgs_lock);
        while (!list_empty(&info->unused_bgs)) {
                block_group = list_first_entry(&info->unused_bgs,
                                               struct btrfs_block_group_cache,
                                               bg_list);
                list_del_init(&block_group->bg_list);
                btrfs_put_block_group(block_group);
        }
        spin_unlock(&info->unused_bgs_lock);

        spin_lock(&info->block_group_cache_lock);
        while ((n = rb_last(&info->block_group_cache_tree)) != NULL) {
                block_group = rb_entry(n, struct btrfs_block_group_cache,
                                       cache_node);
                rb_erase(&block_group->cache_node,
                         &info->block_group_cache_tree);
                RB_CLEAR_NODE(&block_group->cache_node);
                spin_unlock(&info->block_group_cache_lock);

                down_write(&block_group->space_info->groups_sem);
                list_del(&block_group->list);
                up_write(&block_group->space_info->groups_sem);

                if (block_group->cached == BTRFS_CACHE_STARTED)
                        wait_block_group_cache_done(block_group);

                /*
                 * We haven't cached this block group, which means we could
                 * possibly have excluded extents on this block group.
                 */
                if (block_group->cached == BTRFS_CACHE_NO ||
                    block_group->cached == BTRFS_CACHE_ERROR)
                        free_excluded_extents(info->extent_root, block_group);

                btrfs_remove_free_space_cache(block_group);
                btrfs_put_block_group(block_group);

                spin_lock(&info->block_group_cache_lock);
        }
        spin_unlock(&info->block_group_cache_lock);

        /* now that all the block groups are freed, go through and
         * free all the space_info structs.  This is only called during
         * the final stages of unmount, and so we know nobody is
         * using them.  We call synchronize_rcu() once before we start,
         * just to be on the safe side.
         */
        synchronize_rcu();

        release_global_block_rsv(info);

        while (!list_empty(&info->space_info)) {
                int i;

                space_info = list_entry(info->space_info.next,
                                        struct btrfs_space_info,
                                        list);
                if (btrfs_test_opt(info->tree_root, ENOSPC_DEBUG)) {
                        if (WARN_ON(space_info->bytes_pinned > 0 ||
                            space_info->bytes_reserved > 0 ||
                            space_info->bytes_may_use > 0)) {
                                dump_space_info(space_info, 0, 0);
                        }
                }
                list_del(&space_info->list);
                for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
                        struct kobject *kobj;
                        kobj = space_info->block_group_kobjs[i];
                        space_info->block_group_kobjs[i] = NULL;
                        if (kobj) {
                                kobject_del(kobj);
                                kobject_put(kobj);
                        }
                }
                kobject_del(&space_info->kobj);
                kobject_put(&space_info->kobj);
        }
        return 0;
}

static void __link_block_group(struct btrfs_space_info *space_info,
                               struct btrfs_block_group_cache *cache)
{
        int index = get_block_group_index(cache);
        bool first = false;

        down_write(&space_info->groups_sem);
        if (list_empty(&space_info->block_groups[index]))
                first = true;
        list_add_tail(&cache->list, &space_info->block_groups[index]);
        up_write(&space_info->groups_sem);

        if (first) {
                struct raid_kobject *rkobj;
                int ret;

                rkobj = kzalloc(sizeof(*rkobj), GFP_NOFS);
                if (!rkobj)
                        goto out_err;
                rkobj->raid_type = index;
                kobject_init(&rkobj->kobj, &btrfs_raid_ktype);
                ret = kobject_add(&rkobj->kobj, &space_info->kobj,
                                  "%s", get_raid_name(index));
                if (ret) {
                        kobject_put(&rkobj->kobj);
                        goto out_err;
                }
                space_info->block_group_kobjs[index] = &rkobj->kobj;
        }

        return;
out_err:
        pr_warn("BTRFS: failed to add kobject for block cache. ignoring.\n");
}

static struct btrfs_block_group_cache *
btrfs_create_block_group_cache(struct btrfs_root *root, u64 start, u64 size)
{
        struct btrfs_block_group_cache *cache;

        cache = kzalloc(sizeof(*cache), GFP_NOFS);
        if (!cache)
                return NULL;

        cache->free_space_ctl = kzalloc(sizeof(*cache->free_space_ctl),
                                        GFP_NOFS);
        if (!cache->free_space_ctl) {
                kfree(cache);
                return NULL;
        }

        cache->key.objectid = start;
        cache->key.offset = size;
        cache->key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;

        cache->sectorsize = root->sectorsize;
        cache->fs_info = root->fs_info;
        cache->full_stripe_len = btrfs_full_stripe_len(root,
                                               &root->fs_info->mapping_tree,
                                               start);
        atomic_set(&cache->count, 1);
        spin_lock_init(&cache->lock);
        init_rwsem(&cache->data_rwsem);
        INIT_LIST_HEAD(&cache->list);
        INIT_LIST_HEAD(&cache->cluster_list);
        INIT_LIST_HEAD(&cache->bg_list);
        INIT_LIST_HEAD(&cache->ro_list);
        INIT_LIST_HEAD(&cache->dirty_list);
        INIT_LIST_HEAD(&cache->io_list);
        btrfs_init_free_space_ctl(cache);
        atomic_set(&cache->trimming, 0);

        return cache;
}

int btrfs_read_block_groups(struct btrfs_root *root)
{
        struct btrfs_path *path;
        int ret;
        struct btrfs_block_group_cache *cache;
        struct btrfs_fs_info *info = root->fs_info;
        struct btrfs_space_info *space_info;
        struct btrfs_key key;
        struct btrfs_key found_key;
        struct extent_buffer *leaf;
        int need_clear = 0;
        u64 cache_gen;

        root = info->extent_root;
        key.objectid = 0;
        key.offset = 0;
        key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        path->reada = 1;

        cache_gen = btrfs_super_cache_generation(root->fs_info->super_copy);
        if (btrfs_test_opt(root, SPACE_CACHE) &&
            btrfs_super_generation(root->fs_info->super_copy) != cache_gen)
                need_clear = 1;
        if (btrfs_test_opt(root, CLEAR_CACHE))
                need_clear = 1;

        while (1) {
                ret = find_first_block_group(root, path, &key);
                if (ret > 0)
                        break;
                if (ret != 0)
                        goto error;

                leaf = path->nodes[0];
                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);

                cache = btrfs_create_block_group_cache(root, found_key.objectid,
                                                       found_key.offset);
                if (!cache) {
                        ret = -ENOMEM;
                        goto error;
                }

                if (need_clear) {
                        /*
                         * When we mount with old space cache, we need to
                         * set BTRFS_DC_CLEAR and set dirty flag.
                         *
                         * a) Setting 'BTRFS_DC_CLEAR' makes sure that we
                         *    truncate the old free space cache inode and
                         *    setup a new one.
                         * b) Setting 'dirty flag' makes sure that we flush
                         *    the new space cache info onto disk.
                         */
                        if (btrfs_test_opt(root, SPACE_CACHE))
                                cache->disk_cache_state = BTRFS_DC_CLEAR;
                }

                read_extent_buffer(leaf, &cache->item,
                                   btrfs_item_ptr_offset(leaf, path->slots[0]),
                                   sizeof(cache->item));
                cache->flags = btrfs_block_group_flags(&cache->item);

                key.objectid = found_key.objectid + found_key.offset;
                btrfs_release_path(path);

                /*
                 * We need to exclude the super stripes now so that the space
                 * info has super bytes accounted for, otherwise we'll think
                 * we have more space than we actually do.
                 */
                ret = exclude_super_stripes(root, cache);
                if (ret) {
                        /*
                         * We may have excluded something, so call this just in
                         * case.
                         */
                        free_excluded_extents(root, cache);
                        btrfs_put_block_group(cache);
                        goto error;
                }

                /*
                 * check for two cases, either we are full, and therefore
                 * don't need to bother with the caching work since we won't
                 * find any space, or we are empty, and we can just add all
                 * the space in and be done with it.  This saves us _alot_ of
                 * time, particularly in the full case.
                 */
                if (found_key.offset == btrfs_block_group_used(&cache->item)) {
                        cache->last_byte_to_unpin = (u64)-1;
                        cache->cached = BTRFS_CACHE_FINISHED;
                        free_excluded_extents(root, cache);
                } else if (btrfs_block_group_used(&cache->item) == 0) {
                        cache->last_byte_to_unpin = (u64)-1;
                        cache->cached = BTRFS_CACHE_FINISHED;
                        add_new_free_space(cache, root->fs_info,
                                           found_key.objectid,
                                           found_key.objectid +
                                           found_key.offset);
                        free_excluded_extents(root, cache);
                }

                ret = btrfs_add_block_group_cache(root->fs_info, cache);
                if (ret) {
                        btrfs_remove_free_space_cache(cache);
                        btrfs_put_block_group(cache);
                        goto error;
                }

                ret = update_space_info(info, cache->flags, found_key.offset,
                                        btrfs_block_group_used(&cache->item),
                                        &space_info);
                if (ret) {
                        btrfs_remove_free_space_cache(cache);
                        spin_lock(&info->block_group_cache_lock);
                        rb_erase(&cache->cache_node,
                                 &info->block_group_cache_tree);
                        RB_CLEAR_NODE(&cache->cache_node);
                        spin_unlock(&info->block_group_cache_lock);
                        btrfs_put_block_group(cache);
                        goto error;
                }

                cache->space_info = space_info;
                spin_lock(&cache->space_info->lock);
                cache->space_info->bytes_readonly += cache->bytes_super;
                spin_unlock(&cache->space_info->lock);

                __link_block_group(space_info, cache);

                set_avail_alloc_bits(root->fs_info, cache->flags);
                if (btrfs_chunk_readonly(root, cache->key.objectid)) {
                        inc_block_group_ro(cache, 1);
                } else if (btrfs_block_group_used(&cache->item) == 0) {
                        spin_lock(&info->unused_bgs_lock);
                        /* Should always be true but just in case. */
                        if (list_empty(&cache->bg_list)) {
                                btrfs_get_block_group(cache);
                                list_add_tail(&cache->bg_list,
                                              &info->unused_bgs);
                        }
                        spin_unlock(&info->unused_bgs_lock);
                }
        }

        list_for_each_entry_rcu(space_info, &root->fs_info->space_info, list) {
                if (!(get_alloc_profile(root, space_info->flags) &
                      (BTRFS_BLOCK_GROUP_RAID10 |
                       BTRFS_BLOCK_GROUP_RAID1 |
                       BTRFS_BLOCK_GROUP_RAID5 |
                       BTRFS_BLOCK_GROUP_RAID6 |
                       BTRFS_BLOCK_GROUP_DUP)))
                        continue;
                /*
                 * avoid allocating from un-mirrored block group if there are
                 * mirrored block groups.
                 */
                list_for_each_entry(cache,
                                &space_info->block_groups[BTRFS_RAID_RAID0],
                                list)
                        inc_block_group_ro(cache, 1);
                list_for_each_entry(cache,
                                &space_info->block_groups[BTRFS_RAID_SINGLE],
                                list)
                        inc_block_group_ro(cache, 1);
        }

        init_global_block_rsv(info);
        ret = 0;
error:
        btrfs_free_path(path);
        return ret;
}

void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans,
                                       struct btrfs_root *root)
{
        struct btrfs_block_group_cache *block_group, *tmp;
        struct btrfs_root *extent_root = root->fs_info->extent_root;
        struct btrfs_block_group_item item;
        struct btrfs_key key;
        int ret = 0;
        bool can_flush_pending_bgs = trans->can_flush_pending_bgs;

        trans->can_flush_pending_bgs = false;
        list_for_each_entry_safe(block_group, tmp, &trans->new_bgs, bg_list) {
                if (ret)
                        goto next;

                spin_lock(&block_group->lock);
                memcpy(&item, &block_group->item, sizeof(item));
                memcpy(&key, &block_group->key, sizeof(key));
                spin_unlock(&block_group->lock);

                ret = btrfs_insert_item(trans, extent_root, &key, &item,
                                        sizeof(item));
                if (ret)
                        btrfs_abort_transaction(trans, extent_root, ret);
                ret = btrfs_finish_chunk_alloc(trans, extent_root,
                                               key.objectid, key.offset);
                if (ret)
                        btrfs_abort_transaction(trans, extent_root, ret);
next:
                list_del_init(&block_group->bg_list);
        }
        trans->can_flush_pending_bgs = can_flush_pending_bgs;
}

int btrfs_make_block_group(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, u64 bytes_used,
                           u64 type, u64 chunk_objectid, u64 chunk_offset,
                           u64 size)
{
        int ret;
        struct btrfs_root *extent_root;
        struct btrfs_block_group_cache *cache;

        extent_root = root->fs_info->extent_root;

        btrfs_set_log_full_commit(root->fs_info, trans);

        cache = btrfs_create_block_group_cache(root, chunk_offset, size);
        if (!cache)
                return -ENOMEM;

        btrfs_set_block_group_used(&cache->item, bytes_used);
        btrfs_set_block_group_chunk_objectid(&cache->item, chunk_objectid);
        btrfs_set_block_group_flags(&cache->item, type);

        cache->flags = type;
        cache->last_byte_to_unpin = (u64)-1;
        cache->cached = BTRFS_CACHE_FINISHED;
        ret = exclude_super_stripes(root, cache);
        if (ret) {
                /*
                 * We may have excluded something, so call this just in
                 * case.
                 */
                free_excluded_extents(root, cache);
                btrfs_put_block_group(cache);
                return ret;
        }

        add_new_free_space(cache, root->fs_info, chunk_offset,
                           chunk_offset + size);

        free_excluded_extents(root, cache);

#ifdef CONFIG_BTRFS_DEBUG
        if (btrfs_should_fragment_free_space(root, cache)) {
                u64 new_bytes_used = size - bytes_used;

                bytes_used += new_bytes_used >> 1;
                fragment_free_space(root, cache);
        }
#endif
        /*
         * Call to ensure the corresponding space_info object is created and
         * assigned to our block group, but don't update its counters just yet.
         * We want our bg to be added to the rbtree with its ->space_info set.
         */
        ret = update_space_info(root->fs_info, cache->flags, 0, 0,
                                &cache->space_info);
        if (ret) {
                btrfs_remove_free_space_cache(cache);
                btrfs_put_block_group(cache);
                return ret;
        }

        ret = btrfs_add_block_group_cache(root->fs_info, cache);
        if (ret) {
                btrfs_remove_free_space_cache(cache);
                btrfs_put_block_group(cache);
                return ret;
        }

        /*
         * Now that our block group has its ->space_info set and is inserted in
         * the rbtree, update the space info's counters.
         */
        ret = update_space_info(root->fs_info, cache->flags, size, bytes_used,
                                &cache->space_info);
        if (ret) {
                btrfs_remove_free_space_cache(cache);
                spin_lock(&root->fs_info->block_group_cache_lock);
                rb_erase(&cache->cache_node,
                         &root->fs_info->block_group_cache_tree);
                RB_CLEAR_NODE(&cache->cache_node);
                spin_unlock(&root->fs_info->block_group_cache_lock);
                btrfs_put_block_group(cache);
                return ret;
        }
        update_global_block_rsv(root->fs_info);

        spin_lock(&cache->space_info->lock);
        cache->space_info->bytes_readonly += cache->bytes_super;
        spin_unlock(&cache->space_info->lock);

        __link_block_group(cache->space_info, cache);

        list_add_tail(&cache->bg_list, &trans->new_bgs);

        set_avail_alloc_bits(extent_root->fs_info, type);

        return 0;
}

static void clear_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
{
        u64 extra_flags = chunk_to_extended(flags) &
                                BTRFS_EXTENDED_PROFILE_MASK;

        write_seqlock(&fs_info->profiles_lock);
        if (flags & BTRFS_BLOCK_GROUP_DATA)
                fs_info->avail_data_alloc_bits &= ~extra_flags;
        if (flags & BTRFS_BLOCK_GROUP_METADATA)
                fs_info->avail_metadata_alloc_bits &= ~extra_flags;
        if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
                fs_info->avail_system_alloc_bits &= ~extra_flags;
        write_sequnlock(&fs_info->profiles_lock);
}

int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root, u64 group_start,
                             struct extent_map *em)
{
        struct btrfs_path *path;
        struct btrfs_block_group_cache *block_group;
        struct btrfs_free_cluster *cluster;
        struct btrfs_root *tree_root = root->fs_info->tree_root;
        struct btrfs_key key;
        struct inode *inode;
        struct kobject *kobj = NULL;
        int ret;
        int index;
        int factor;
        struct btrfs_caching_control *caching_ctl = NULL;
        bool remove_em;

        root = root->fs_info->extent_root;

        block_group = btrfs_lookup_block_group(root->fs_info, group_start);
        BUG_ON(!block_group);
        BUG_ON(!block_group->ro);

        /*
         * Free the reserved super bytes from this block group before
         * remove it.
         */
        free_excluded_extents(root, block_group);

        memcpy(&key, &block_group->key, sizeof(key));
        index = get_block_group_index(block_group);
        if (block_group->flags & (BTRFS_BLOCK_GROUP_DUP |
                                  BTRFS_BLOCK_GROUP_RAID1 |
                                  BTRFS_BLOCK_GROUP_RAID10))
                factor = 2;
        else
                factor = 1;

        /* make sure this block group isn't part of an allocation cluster */
        cluster = &root->fs_info->data_alloc_cluster;
        spin_lock(&cluster->refill_lock);
        btrfs_return_cluster_to_free_space(block_group, cluster);
        spin_unlock(&cluster->refill_lock);

        /*
         * make sure this block group isn't part of a metadata
         * allocation cluster
         */
        cluster = &root->fs_info->meta_alloc_cluster;
        spin_lock(&cluster->refill_lock);
        btrfs_return_cluster_to_free_space(block_group, cluster);
        spin_unlock(&cluster->refill_lock);

        path = btrfs_alloc_path();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * get the inode first so any iput calls done for the io_list
         * aren't the final iput (no unlinks allowed now)
         */
        inode = lookup_free_space_inode(tree_root, block_group, path);

        mutex_lock(&trans->transaction->cache_write_mutex);
        /*
         * make sure our free spache cache IO is done before remove the
         * free space inode
         */
        spin_lock(&trans->transaction->dirty_bgs_lock);
        if (!list_empty(&block_group->io_list)) {
                list_del_init(&block_group->io_list);

                WARN_ON(!IS_ERR(inode) && inode != block_group->io_ctl.inode);

                spin_unlock(&trans->transaction->dirty_bgs_lock);
                btrfs_wait_cache_io(root, trans, block_group,
                                    &block_group->io_ctl, path,
                                    block_group->key.objectid);
                btrfs_put_block_group(block_group);
                spin_lock(&trans->transaction->dirty_bgs_lock);
        }

        if (!list_empty(&block_group->dirty_list)) {
                list_del_init(&block_group->dirty_list);
                btrfs_put_block_group(block_group);
        }
        spin_unlock(&trans->transaction->dirty_bgs_lock);
        mutex_unlock(&trans->transaction->cache_write_mutex);

        if (!IS_ERR(inode)) {
                ret = btrfs_orphan_add(trans, inode);
                if (ret) {
                        btrfs_add_delayed_iput(inode);
                        goto out;
                }
                clear_nlink(inode);
                /* One for the block groups ref */
                spin_lock(&block_group->lock);
                if (block_group->iref) {
                        block_group->iref = 0;
                        block_group->inode = NULL;
                        spin_unlock(&block_group->lock);
                        iput(inode);
                } else {
                        spin_unlock(&block_group->lock);
                }
                /* One for our lookup ref */
                btrfs_add_delayed_iput(inode);
        }

        key.objectid = BTRFS_FREE_SPACE_OBJECTID;
        key.offset = block_group->key.objectid;
        key.type = 0;

        ret = btrfs_search_slot(trans, tree_root, &key, path, -1, 1);
        if (ret < 0)
                goto out;
        if (ret > 0)
                btrfs_release_path(path);
        if (ret == 0) {
                ret = btrfs_del_item(trans, tree_root, path);
                if (ret)
                        goto out;
                btrfs_release_path(path);
        }

        spin_lock(&root->fs_info->block_group_cache_lock);
        rb_erase(&block_group->cache_node,
                 &root->fs_info->block_group_cache_tree);
        RB_CLEAR_NODE(&block_group->cache_node);

        if (root->fs_info->first_logical_byte == block_group->key.objectid)
                root->fs_info->first_logical_byte = (u64)-1;
        spin_unlock(&root->fs_info->block_group_cache_lock);

        down_write(&block_group->space_info->groups_sem);
        /*
         * we must use list_del_init so people can check to see if they
         * are still on the list after taking the semaphore
         */
        list_del_init(&block_group->list);
        if (list_empty(&block_group->space_info->block_groups[index])) {
                kobj = block_group->space_info->block_group_kobjs[index];
                block_group->space_info->block_group_kobjs[index] = NULL;
                clear_avail_alloc_bits(root->fs_info, block_group->flags);
        }
        up_write(&block_group->space_info->groups_sem);
        if (kobj) {
                kobject_del(kobj);
                kobject_put(kobj);
        }

        if (block_group->has_caching_ctl)
                caching_ctl = get_caching_control(block_group);
        if (block_group->cached == BTRFS_CACHE_STARTED)
                wait_block_group_cache_done(block_group);
        if (block_group->has_caching_ctl) {
                down_write(&root->fs_info->commit_root_sem);
                if (!caching_ctl) {
                        struct btrfs_caching_control *ctl;

                        list_for_each_entry(ctl,
                                    &root->fs_info->caching_block_groups, list)
                                if (ctl->block_group == block_group) {
                                        caching_ctl = ctl;
                                        atomic_inc(&caching_ctl->count);
                                        break;
                                }
                }
                if (caching_ctl)
                        list_del_init(&caching_ctl->list);
                up_write(&root->fs_info->commit_root_sem);
                if (caching_ctl) {
                        /* Once for the caching bgs list and once for us. */
                        put_caching_control(caching_ctl);
                        put_caching_control(caching_ctl);
                }
        }

        spin_lock(&trans->transaction->dirty_bgs_lock);
        if (!list_empty(&block_group->dirty_list)) {
                WARN_ON(1);
        }
        if (!list_empty(&block_group->io_list)) {
                WARN_ON(1);
        }
        spin_unlock(&trans->transaction->dirty_bgs_lock);
        btrfs_remove_free_space_cache(block_group);

        spin_lock(&block_group->space_info->lock);
        list_del_init(&block_group->ro_list);

        if (btrfs_test_opt(root, ENOSPC_DEBUG)) {
                WARN_ON(block_group->space_info->total_bytes
                        < block_group->key.offset);
                WARN_ON(block_group->space_info->bytes_readonly
                        < block_group->key.offset);
                WARN_ON(block_group->space_info->disk_total
                        < block_group->key.offset * factor);
        }
        block_group->space_info->total_bytes -= block_group->key.offset;
        block_group->space_info->bytes_readonly -= block_group->key.offset;
        block_group->space_info->disk_total -= block_group->key.offset * factor;

        spin_unlock(&block_group->space_info->lock);

        memcpy(&key, &block_group->key, sizeof(key));

        lock_chunks(root);
        if (!list_empty(&em->list)) {
                /* We're in the transaction->pending_chunks list. */
                free_extent_map(em);
        }
        spin_lock(&block_group->lock);
        block_group->removed = 1;
        /*
         * At this point trimming can't start on this block group, because we
         * removed the block group from the tree fs_info->block_group_cache_tree
         * so no one can't find it anymore and even if someone already got this
         * block group before we removed it from the rbtree, they have already
         * incremented block_group->trimming - if they didn't, they won't find
         * any free space entries because we already removed them all when we
         * called btrfs_remove_free_space_cache().
         *
         * And we must not remove the extent map from the fs_info->mapping_tree
         * to prevent the same logical address range and physical device space
         * ranges from being reused for a new block group. This is because our
         * fs trim operation (btrfs_trim_fs() / btrfs_ioctl_fitrim()) is
         * completely transactionless, so while it is trimming a range the
         * currently running transaction might finish and a new one start,
         * allowing for new block groups to be created that can reuse the same
         * physical device locations unless we take this special care.
         *
         * There may also be an implicit trim operation if the file system
         * is mounted with -odiscard. The same protections must remain
         * in place until the extents have been discarded completely when
         * the transaction commit has completed.
         */
        remove_em = (atomic_read(&block_group->trimming) == 0);
        /*
         * Make sure a trimmer task always sees the em in the pinned_chunks list
         * if it sees block_group->removed == 1 (needs to lock block_group->lock
         * before checking block_group->removed).
         */
        if (!remove_em) {
                /*
                 * Our em might be in trans->transaction->pending_chunks which
                 * is protected by fs_info->chunk_mutex ([lock|unlock]_chunks),
                 * and so is the fs_info->pinned_chunks list.
                 *
                 * So at this point we must be holding the chunk_mutex to avoid
                 * any races with chunk allocation (more specifically at
                 * volumes.c:contains_pending_extent()), to ensure it always
                 * sees the em, either in the pending_chunks list or in the
                 * pinned_chunks list.
                 */
                list_move_tail(&em->list, &root->fs_info->pinned_chunks);
        }
        spin_unlock(&block_group->lock);

        if (remove_em) {
                struct extent_map_tree *em_tree;

                em_tree = &root->fs_info->mapping_tree.map_tree;
                write_lock(&em_tree->lock);
                /*
                 * The em might be in the pending_chunks list, so make sure the
                 * chunk mutex is locked, since remove_extent_mapping() will
                 * delete us from that list.
                 */
                remove_extent_mapping(em_tree, em);
                write_unlock(&em_tree->lock);
                /* once for the tree */
                free_extent_map(em);
        }

        unlock_chunks(root);

        btrfs_put_block_group(block_group);
        btrfs_put_block_group(block_group);

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret > 0)
                ret = -EIO;
        if (ret < 0)
                goto out;

        ret = btrfs_del_item(trans, root, path);
out:
        btrfs_free_path(path);
        return ret;
}

struct btrfs_trans_handle *
btrfs_start_trans_remove_block_group(struct btrfs_fs_info *fs_info,
                                     const u64 chunk_offset)
{
        struct extent_map_tree *em_tree = &fs_info->mapping_tree.map_tree;
        struct extent_map *em;
        struct map_lookup *map;
        unsigned int num_items;

        read_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, chunk_offset, 1);
        read_unlock(&em_tree->lock);
        ASSERT(em && em->start == chunk_offset);

        /*
         * We need to reserve 3 + N units from the metadata space info in order
         * to remove a block group (done at btrfs_remove_chunk() and at
         * btrfs_remove_block_group()), which are used for:
         *
         * 1 unit for adding the free space inode's orphan (located in the tree
         * of tree roots).
         * 1 unit for deleting the block group item (located in the extent
         * tree).
         * 1 unit for deleting the free space item (located in tree of tree
         * roots).
         * N units for deleting N device extent items corresponding to each
         * stripe (located in the device tree).
         *
         * In order to remove a block group we also need to reserve units in the
         * system space info in order to update the chunk tree (update one or
         * more device items and remove one chunk item), but this is done at
         * btrfs_remove_chunk() through a call to check_system_chunk().
         */
        map = (struct map_lookup *)em->bdev;
        num_items = 3 + map->num_stripes;
        free_extent_map(em);

        return btrfs_start_transaction_fallback_global_rsv(fs_info->extent_root,
                                                           num_items, 1);
}

/*
 * Process the unused_bgs list and remove any that don't have any allocated
 * space inside of them.
 */
void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
{
        struct btrfs_block_group_cache *block_group;
        struct btrfs_space_info *space_info;
        struct btrfs_root *root = fs_info->extent_root;
        struct btrfs_trans_handle *trans;
        int ret = 0;

        if (!fs_info->open)
                return;

        spin_lock(&fs_info->unused_bgs_lock);
        while (!list_empty(&fs_info->unused_bgs)) {
                u64 start, end;
                int trimming;

                block_group = list_first_entry(&fs_info->unused_bgs,
                                               struct btrfs_block_group_cache,
                                               bg_list);
                list_del_init(&block_group->bg_list);

                space_info = block_group->space_info;

                if (ret || btrfs_mixed_space_info(space_info)) {
                        btrfs_put_block_group(block_group);
                        continue;
                }
                spin_unlock(&fs_info->unused_bgs_lock);

                mutex_lock(&fs_info->delete_unused_bgs_mutex);

                /* Don't want to race with allocators so take the groups_sem */
                down_write(&space_info->groups_sem);
                spin_lock(&block_group->lock);
                if (block_group->reserved ||
                    btrfs_block_group_used(&block_group->item) ||
                    block_group->ro ||
                    list_is_singular(&block_group->list)) {
                        /*
                         * We want to bail if we made new allocations or have
                         * outstanding allocations in this block group.  We do
                         * the ro check in case balance is currently acting on
                         * this block group.
                         */
                        spin_unlock(&block_group->lock);
                        up_write(&space_info->groups_sem);
                        goto next;
                }
                spin_unlock(&block_group->lock);

                /* We don't want to force the issue, only flip if it's ok. */
                ret = inc_block_group_ro(block_group, 0);
                up_write(&space_info->groups_sem);
                if (ret < 0) {
                        ret = 0;
                        goto next;
                }

                /*
                 * Want to do this before we do anything else so we can recover
                 * properly if we fail to join the transaction.
                 */
                trans = btrfs_start_trans_remove_block_group(fs_info,
                                                     block_group->key.objectid);
                if (IS_ERR(trans)) {
                        btrfs_dec_block_group_ro(root, block_group);
                        ret = PTR_ERR(trans);
                        goto next;
                }

                /*
                 * We could have pending pinned extents for this block group,
                 * just delete them, we don't care about them anymore.
                 */
                start = block_group->key.objectid;
                end = start + block_group->key.offset - 1;
                /*
                 * Hold the unused_bg_unpin_mutex lock to avoid racing with
                 * btrfs_finish_extent_commit(). If we are at transaction N,
                 * another task might be running finish_extent_commit() for the
                 * previous transaction N - 1, and have seen a range belonging
                 * to the block group in freed_extents[] before we were able to
                 * clear the whole block group range from freed_extents[]. This
                 * means that task can lookup for the block group after we
                 * unpinned it from freed_extents[] and removed it, leading to
                 * a BUG_ON() at btrfs_unpin_extent_range().
                 */
                mutex_lock(&fs_info->unused_bg_unpin_mutex);
                ret = clear_extent_bits(&fs_info->freed_extents[0], start, end,
                                  EXTENT_DIRTY, GFP_NOFS);
                if (ret) {
                        mutex_unlock(&fs_info->unused_bg_unpin_mutex);
                        btrfs_dec_block_group_ro(root, block_group);
                        goto end_trans;
                }
                ret = clear_extent_bits(&fs_info->freed_extents[1], start, end,
                                  EXTENT_DIRTY, GFP_NOFS);
                if (ret) {
                        mutex_unlock(&fs_info->unused_bg_unpin_mutex);
                        btrfs_dec_block_group_ro(root, block_group);
                        goto end_trans;
                }
                mutex_unlock(&fs_info->unused_bg_unpin_mutex);

                /* Reset pinned so btrfs_put_block_group doesn't complain */
                spin_lock(&space_info->lock);
                spin_lock(&block_group->lock);

                space_info->bytes_pinned -= block_group->pinned;
                space_info->bytes_readonly += block_group->pinned;
                percpu_counter_add(&space_info->total_bytes_pinned,
                                   -block_group->pinned);
                block_group->pinned = 0;

                spin_unlock(&block_group->lock);
                spin_unlock(&space_info->lock);

                /* DISCARD can flip during remount */
                trimming = btrfs_test_opt(root, DISCARD);

                /* Implicit trim during transaction commit. */
                if (trimming)
                        btrfs_get_block_group_trimming(block_group);

                /*
                 * Btrfs_remove_chunk will abort the transaction if things go
                 * horribly wrong.
                 */
                ret = btrfs_remove_chunk(trans, root,
                                         block_group->key.objectid);

                if (ret) {
                        if (trimming)
                                btrfs_put_block_group_trimming(block_group);
                        goto end_trans;
                }

                /*
                 * If we're not mounted with -odiscard, we can just forget
                 * about this block group. Otherwise we'll need to wait
                 * until transaction commit to do the actual discard.
                 */
                if (trimming) {
                        spin_lock(&fs_info->unused_bgs_lock);
                        /*
                         * A concurrent scrub might have added us to the list
                         * fs_info->unused_bgs, so use a list_move operation
                         * to add the block group to the deleted_bgs list.
                         */
                        list_move(&block_group->bg_list,
                                  &trans->transaction->deleted_bgs);
                        spin_unlock(&fs_info->unused_bgs_lock);
                        btrfs_get_block_group(block_group);
                }
end_trans:
                btrfs_end_transaction(trans, root);
next:
                mutex_unlock(&fs_info->delete_unused_bgs_mutex);
                btrfs_put_block_group(block_group);
                spin_lock(&fs_info->unused_bgs_lock);
        }
        spin_unlock(&fs_info->unused_bgs_lock);
}

int btrfs_init_space_info(struct btrfs_fs_info *fs_info)
{
        struct btrfs_space_info *space_info;
        struct btrfs_super_block *disk_super;
        u64 features;
        u64 flags;
        int mixed = 0;
        int ret;

        disk_super = fs_info->super_copy;
        if (!btrfs_super_root(disk_super))
                return 1;

        features = btrfs_super_incompat_flags(disk_super);
        if (features & BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS)
                mixed = 1;

        flags = BTRFS_BLOCK_GROUP_SYSTEM;
        ret = update_space_info(fs_info, flags, 0, 0, &space_info);
        if (ret)
                goto out;

        if (mixed) {
                flags = BTRFS_BLOCK_GROUP_METADATA | BTRFS_BLOCK_GROUP_DATA;
                ret = update_space_info(fs_info, flags, 0, 0, &space_info);
        } else {
                flags = BTRFS_BLOCK_GROUP_METADATA;
                ret = update_space_info(fs_info, flags, 0, 0, &space_info);
                if (ret)
                        goto out;

                flags = BTRFS_BLOCK_GROUP_DATA;
                ret = update_space_info(fs_info, flags, 0, 0, &space_info);
        }
out:
        return ret;
}

int btrfs_error_unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
{
        return unpin_extent_range(root, start, end, false);
}

/*
 * It used to be that old block groups would be left around forever.
 * Iterating over them would be enough to trim unused space.  Since we
 * now automatically remove them, we also need to iterate over unallocated
 * space.
 *
 * We don't want a transaction for this since the discard may take a
 * substantial amount of time.  We don't require that a transaction be
 * running, but we do need to take a running transaction into account
 * to ensure that we're not discarding chunks that were released in
 * the current transaction.
 *
 * Holding the chunks lock will prevent other threads from allocating
 * or releasing chunks, but it won't prevent a running transaction
 * from committing and releasing the memory that the pending chunks
 * list head uses.  For that, we need to take a reference to the
 * transaction.
 */
static int btrfs_trim_free_extents(struct btrfs_device *device,
                                   u64 minlen, u64 *trimmed)
{
        u64 start = 0, len = 0;
        int ret;

        *trimmed = 0;

        /* Not writeable = nothing to do. */
        if (!device->writeable)
                return 0;

        /* No free space = nothing to do. */
        if (device->total_bytes <= device->bytes_used)
                return 0;

        ret = 0;

        while (1) {
                struct btrfs_fs_info *fs_info = device->dev_root->fs_info;
                struct btrfs_transaction *trans;
                u64 bytes;

                ret = mutex_lock_interruptible(&fs_info->chunk_mutex);
                if (ret)
                        return ret;

                down_read(&fs_info->commit_root_sem);

                spin_lock(&fs_info->trans_lock);
                trans = fs_info->running_transaction;
                if (trans)
                        atomic_inc(&trans->use_count);
                spin_unlock(&fs_info->trans_lock);

                ret = find_free_dev_extent_start(trans, device, minlen, start,
                                                 &start, &len);
                if (trans)
                        btrfs_put_transaction(trans);

                if (ret) {
                        up_read(&fs_info->commit_root_sem);
                        mutex_unlock(&fs_info->chunk_mutex);
                        if (ret == -ENOSPC)
                                ret = 0;
                        break;
                }

                ret = btrfs_issue_discard(device->bdev, start, len, &bytes);
                up_read(&fs_info->commit_root_sem);
                mutex_unlock(&fs_info->chunk_mutex);

                if (ret)
                        break;

                start += len;
                *trimmed += bytes;

                if (fatal_signal_pending(current)) {
                        ret = -ERESTARTSYS;
                        break;
                }

                cond_resched();
        }

        return ret;
}

int btrfs_trim_fs(struct btrfs_root *root, struct fstrim_range *range)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_block_group_cache *cache = NULL;
        struct btrfs_device *device;
        struct list_head *devices;
        u64 group_trimmed;
        u64 start;
        u64 end;
        u64 trimmed = 0;
        u64 total_bytes = btrfs_super_total_bytes(fs_info->super_copy);
        int ret = 0;

        /*
         * try to trim all FS space, our block group may start from non-zero.
         */
        if (range->len == total_bytes)
                cache = btrfs_lookup_first_block_group(fs_info, range->start);
        else
                cache = btrfs_lookup_block_group(fs_info, range->start);

        while (cache) {
                if (cache->key.objectid >= (range->start + range->len)) {
                        btrfs_put_block_group(cache);
                        break;
                }

                start = max(range->start, cache->key.objectid);
                end = min(range->start + range->len,
                                cache->key.objectid + cache->key.offset);

                if (end - start >= range->minlen) {
                        if (!block_group_cache_done(cache)) {
                                ret = cache_block_group(cache, 0);
                                if (ret) {
                                        btrfs_put_block_group(cache);
                                        break;
                                }
                                ret = wait_block_group_cache_done(cache);
                                if (ret) {
                                        btrfs_put_block_group(cache);
                                        break;
                                }
                        }
                        ret = btrfs_trim_block_group(cache,
                                                     &group_trimmed,
                                                     start,
                                                     end,
                                                     range->minlen);

                        trimmed += group_trimmed;
                        if (ret) {
                                btrfs_put_block_group(cache);
                                break;
                        }
                }

                cache = next_block_group(fs_info->tree_root, cache);
        }

        mutex_lock(&root->fs_info->fs_devices->device_list_mutex);
        devices = &root->fs_info->fs_devices->alloc_list;
        list_for_each_entry(device, devices, dev_alloc_list) {
                ret = btrfs_trim_free_extents(device, range->minlen,
                                              &group_trimmed);
                if (ret)
                        break;

                trimmed += group_trimmed;
        }
        mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);

        range->len = trimmed;
        return ret;
}

/*
 * btrfs_{start,end}_write_no_snapshoting() are similar to
 * mnt_{want,drop}_write(), they are used to prevent some tasks from writing
 * data into the page cache through nocow before the subvolume is snapshoted,
 * but flush the data into disk after the snapshot creation, or to prevent
 * operations while snapshoting is ongoing and that cause the snapshot to be
 * inconsistent (writes followed by expanding truncates for example).
 */
void btrfs_end_write_no_snapshoting(struct btrfs_root *root)
{
        percpu_counter_dec(&root->subv_writers->counter);
        /*
         * Make sure counter is updated before we wake up waiters.
         */
        smp_mb();
        if (waitqueue_active(&root->subv_writers->wait))
                wake_up(&root->subv_writers->wait);
}

int btrfs_start_write_no_snapshoting(struct btrfs_root *root)
{
        if (atomic_read(&root->will_be_snapshoted))
                return 0;

        percpu_counter_inc(&root->subv_writers->counter);
        /*
         * Make sure counter is updated before we check for snapshot creation.
         */
        smp_mb();
        if (atomic_read(&root->will_be_snapshoted)) {
                btrfs_end_write_no_snapshoting(root);
                return 0;
        }
        return 1;
}