Merge branch 'pci/misc' into next

[karo-tx-linux.git] / fs / ext4 / indirect.c

/*
 *  linux/fs/ext4/indirect.c
 *
 *  from
 *
 *  linux/fs/ext4/inode.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/inode.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Goal-directed block allocation by Stephen Tweedie
 *      (sct@redhat.com), 1993, 1998
 */

#include <linux/aio.h>
#include "ext4_jbd2.h"
#include "truncate.h"

#include <trace/events/ext4.h>

typedef struct {
        __le32  *p;
        __le32  key;
        struct buffer_head *bh;
} Indirect;

static inline void add_chain(Indirect *p, struct buffer_head *bh, __le32 *v)
{
        p->key = *(p->p = v);
        p->bh = bh;
}

/**
 *      ext4_block_to_path - parse the block number into array of offsets
 *      @inode: inode in question (we are only interested in its superblock)
 *      @i_block: block number to be parsed
 *      @offsets: array to store the offsets in
 *      @boundary: set this non-zero if the referred-to block is likely to be
 *             followed (on disk) by an indirect block.
 *
 *      To store the locations of file's data ext4 uses a data structure common
 *      for UNIX filesystems - tree of pointers anchored in the inode, with
 *      data blocks at leaves and indirect blocks in intermediate nodes.
 *      This function translates the block number into path in that tree -
 *      return value is the path length and @offsets[n] is the offset of
 *      pointer to (n+1)th node in the nth one. If @block is out of range
 *      (negative or too large) warning is printed and zero returned.
 *
 *      Note: function doesn't find node addresses, so no IO is needed. All
 *      we need to know is the capacity of indirect blocks (taken from the
 *      inode->i_sb).
 */

/*
 * Portability note: the last comparison (check that we fit into triple
 * indirect block) is spelled differently, because otherwise on an
 * architecture with 32-bit longs and 8Kb pages we might get into trouble
 * if our filesystem had 8Kb blocks. We might use long long, but that would
 * kill us on x86. Oh, well, at least the sign propagation does not matter -
 * i_block would have to be negative in the very beginning, so we would not
 * get there at all.
 */

static int ext4_block_to_path(struct inode *inode,
                              ext4_lblk_t i_block,
                              ext4_lblk_t offsets[4], int *boundary)
{
        int ptrs = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        int ptrs_bits = EXT4_ADDR_PER_BLOCK_BITS(inode->i_sb);
        const long direct_blocks = EXT4_NDIR_BLOCKS,
                indirect_blocks = ptrs,
                double_blocks = (1 << (ptrs_bits * 2));
        int n = 0;
        int final = 0;

        if (i_block < direct_blocks) {
                offsets[n++] = i_block;
                final = direct_blocks;
        } else if ((i_block -= direct_blocks) < indirect_blocks) {
                offsets[n++] = EXT4_IND_BLOCK;
                offsets[n++] = i_block;
                final = ptrs;
        } else if ((i_block -= indirect_blocks) < double_blocks) {
                offsets[n++] = EXT4_DIND_BLOCK;
                offsets[n++] = i_block >> ptrs_bits;
                offsets[n++] = i_block & (ptrs - 1);
                final = ptrs;
        } else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
                offsets[n++] = EXT4_TIND_BLOCK;
                offsets[n++] = i_block >> (ptrs_bits * 2);
                offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
                offsets[n++] = i_block & (ptrs - 1);
                final = ptrs;
        } else {
                ext4_warning(inode->i_sb, "block %lu > max in inode %lu",
                             i_block + direct_blocks +
                             indirect_blocks + double_blocks, inode->i_ino);
        }
        if (boundary)
                *boundary = final - 1 - (i_block & (ptrs - 1));
        return n;
}

/**
 *      ext4_get_branch - read the chain of indirect blocks leading to data
 *      @inode: inode in question
 *      @depth: depth of the chain (1 - direct pointer, etc.)
 *      @offsets: offsets of pointers in inode/indirect blocks
 *      @chain: place to store the result
 *      @err: here we store the error value
 *
 *      Function fills the array of triples <key, p, bh> and returns %NULL
 *      if everything went OK or the pointer to the last filled triple
 *      (incomplete one) otherwise. Upon the return chain[i].key contains
 *      the number of (i+1)-th block in the chain (as it is stored in memory,
 *      i.e. little-endian 32-bit), chain[i].p contains the address of that
 *      number (it points into struct inode for i==0 and into the bh->b_data
 *      for i>0) and chain[i].bh points to the buffer_head of i-th indirect
 *      block for i>0 and NULL for i==0. In other words, it holds the block
 *      numbers of the chain, addresses they were taken from (and where we can
 *      verify that chain did not change) and buffer_heads hosting these
 *      numbers.
 *
 *      Function stops when it stumbles upon zero pointer (absent block)
 *              (pointer to last triple returned, *@err == 0)
 *      or when it gets an IO error reading an indirect block
 *              (ditto, *@err == -EIO)
 *      or when it reads all @depth-1 indirect blocks successfully and finds
 *      the whole chain, all way to the data (returns %NULL, *err == 0).
 *
 *      Need to be called with
 *      down_read(&EXT4_I(inode)->i_data_sem)
 */
static Indirect *ext4_get_branch(struct inode *inode, int depth,
                                 ext4_lblk_t  *offsets,
                                 Indirect chain[4], int *err)
{
        struct super_block *sb = inode->i_sb;
        Indirect *p = chain;
        struct buffer_head *bh;
        int ret = -EIO;

        *err = 0;
        /* i_data is not going away, no lock needed */
        add_chain(chain, NULL, EXT4_I(inode)->i_data + *offsets);
        if (!p->key)
                goto no_block;
        while (--depth) {
                bh = sb_getblk(sb, le32_to_cpu(p->key));
                if (unlikely(!bh)) {
                        ret = -ENOMEM;
                        goto failure;
                }

                if (!bh_uptodate_or_lock(bh)) {
                        if (bh_submit_read(bh) < 0) {
                                put_bh(bh);
                                goto failure;
                        }
                        /* validate block references */
                        if (ext4_check_indirect_blockref(inode, bh)) {
                                put_bh(bh);
                                goto failure;
                        }
                }

                add_chain(++p, bh, (__le32 *)bh->b_data + *++offsets);
                /* Reader: end */
                if (!p->key)
                        goto no_block;
        }
        return NULL;

failure:
        *err = ret;
no_block:
        return p;
}

/**
 *      ext4_find_near - find a place for allocation with sufficient locality
 *      @inode: owner
 *      @ind: descriptor of indirect block.
 *
 *      This function returns the preferred place for block allocation.
 *      It is used when heuristic for sequential allocation fails.
 *      Rules are:
 *        + if there is a block to the left of our position - allocate near it.
 *        + if pointer will live in indirect block - allocate near that block.
 *        + if pointer will live in inode - allocate in the same
 *          cylinder group.
 *
 * In the latter case we colour the starting block by the callers PID to
 * prevent it from clashing with concurrent allocations for a different inode
 * in the same block group.   The PID is used here so that functionally related
 * files will be close-by on-disk.
 *
 *      Caller must make sure that @ind is valid and will stay that way.
 */
static ext4_fsblk_t ext4_find_near(struct inode *inode, Indirect *ind)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        __le32 *start = ind->bh ? (__le32 *) ind->bh->b_data : ei->i_data;
        __le32 *p;

        /* Try to find previous block */
        for (p = ind->p - 1; p >= start; p--) {
                if (*p)
                        return le32_to_cpu(*p);
        }

        /* No such thing, so let's try location of indirect block */
        if (ind->bh)
                return ind->bh->b_blocknr;

        /*
         * It is going to be referred to from the inode itself? OK, just put it
         * into the same cylinder group then.
         */
        return ext4_inode_to_goal_block(inode);
}

/**
 *      ext4_find_goal - find a preferred place for allocation.
 *      @inode: owner
 *      @block:  block we want
 *      @partial: pointer to the last triple within a chain
 *
 *      Normally this function find the preferred place for block allocation,
 *      returns it.
 *      Because this is only used for non-extent files, we limit the block nr
 *      to 32 bits.
 */
static ext4_fsblk_t ext4_find_goal(struct inode *inode, ext4_lblk_t block,
                                   Indirect *partial)
{
        ext4_fsblk_t goal;

        /*
         * XXX need to get goal block from mballoc's data structures
         */

        goal = ext4_find_near(inode, partial);
        goal = goal & EXT4_MAX_BLOCK_FILE_PHYS;
        return goal;
}

/**
 *      ext4_blks_to_allocate - Look up the block map and count the number
 *      of direct blocks need to be allocated for the given branch.
 *
 *      @branch: chain of indirect blocks
 *      @k: number of blocks need for indirect blocks
 *      @blks: number of data blocks to be mapped.
 *      @blocks_to_boundary:  the offset in the indirect block
 *
 *      return the total number of blocks to be allocate, including the
 *      direct and indirect blocks.
 */
static int ext4_blks_to_allocate(Indirect *branch, int k, unsigned int blks,
                                 int blocks_to_boundary)
{
        unsigned int count = 0;

        /*
         * Simple case, [t,d]Indirect block(s) has not allocated yet
         * then it's clear blocks on that path have not allocated
         */
        if (k > 0) {
                /* right now we don't handle cross boundary allocation */
                if (blks < blocks_to_boundary + 1)
                        count += blks;
                else
                        count += blocks_to_boundary + 1;
                return count;
        }

        count++;
        while (count < blks && count <= blocks_to_boundary &&
                le32_to_cpu(*(branch[0].p + count)) == 0) {
                count++;
        }
        return count;
}

/**
 *      ext4_alloc_branch - allocate and set up a chain of blocks.
 *      @handle: handle for this transaction
 *      @inode: owner
 *      @indirect_blks: number of allocated indirect blocks
 *      @blks: number of allocated direct blocks
 *      @goal: preferred place for allocation
 *      @offsets: offsets (in the blocks) to store the pointers to next.
 *      @branch: place to store the chain in.
 *
 *      This function allocates blocks, zeroes out all but the last one,
 *      links them into chain and (if we are synchronous) writes them to disk.
 *      In other words, it prepares a branch that can be spliced onto the
 *      inode. It stores the information about that chain in the branch[], in
 *      the same format as ext4_get_branch() would do. We are calling it after
 *      we had read the existing part of chain and partial points to the last
 *      triple of that (one with zero ->key). Upon the exit we have the same
 *      picture as after the successful ext4_get_block(), except that in one
 *      place chain is disconnected - *branch->p is still zero (we did not
 *      set the last link), but branch->key contains the number that should
 *      be placed into *branch->p to fill that gap.
 *
 *      If allocation fails we free all blocks we've allocated (and forget
 *      their buffer_heads) and return the error value the from failed
 *      ext4_alloc_block() (normally -ENOSPC). Otherwise we set the chain
 *      as described above and return 0.
 */
static int ext4_alloc_branch(handle_t *handle, struct inode *inode,
                             ext4_lblk_t iblock, int indirect_blks,
                             int *blks, ext4_fsblk_t goal,
                             ext4_lblk_t *offsets, Indirect *branch)
{
        struct ext4_allocation_request  ar;
        struct buffer_head *            bh;
        ext4_fsblk_t                    b, new_blocks[4];
        __le32                          *p;
        int                             i, j, err, len = 1;

        /*
         * Set up for the direct block allocation
         */
        memset(&ar, 0, sizeof(ar));
        ar.inode = inode;
        ar.len = *blks;
        ar.logical = iblock;
        if (S_ISREG(inode->i_mode))
                ar.flags = EXT4_MB_HINT_DATA;

        for (i = 0; i <= indirect_blks; i++) {
                if (i == indirect_blks) {
                        ar.goal = goal;
                        new_blocks[i] = ext4_mb_new_blocks(handle, &ar, &err);
                } else
                        goal = new_blocks[i] = ext4_new_meta_blocks(handle, inode,
                                                        goal, 0, NULL, &err);
                if (err) {
                        i--;
                        goto failed;
                }
                branch[i].key = cpu_to_le32(new_blocks[i]);
                if (i == 0)
                        continue;

                bh = branch[i].bh = sb_getblk(inode->i_sb, new_blocks[i-1]);
                if (unlikely(!bh)) {
                        err = -ENOMEM;
                        goto failed;
                }
                lock_buffer(bh);
                BUFFER_TRACE(bh, "call get_create_access");
                err = ext4_journal_get_create_access(handle, bh);
                if (err) {
                        unlock_buffer(bh);
                        goto failed;
                }

                memset(bh->b_data, 0, bh->b_size);
                p = branch[i].p = (__le32 *) bh->b_data + offsets[i];
                b = new_blocks[i];

                if (i == indirect_blks)
                        len = ar.len;
                for (j = 0; j < len; j++)
                        *p++ = cpu_to_le32(b++);

                BUFFER_TRACE(bh, "marking uptodate");
                set_buffer_uptodate(bh);
                unlock_buffer(bh);

                BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
                err = ext4_handle_dirty_metadata(handle, inode, bh);
                if (err)
                        goto failed;
        }
        *blks = ar.len;
        return 0;
failed:
        for (; i >= 0; i--) {
                if (i != indirect_blks && branch[i].bh)
                        ext4_forget(handle, 1, inode, branch[i].bh,
                                    branch[i].bh->b_blocknr);
                ext4_free_blocks(handle, inode, NULL, new_blocks[i],
                                 (i == indirect_blks) ? ar.len : 1, 0);
        }
        return err;
}

/**
 * ext4_splice_branch - splice the allocated branch onto inode.
 * @handle: handle for this transaction
 * @inode: owner
 * @block: (logical) number of block we are adding
 * @chain: chain of indirect blocks (with a missing link - see
 *      ext4_alloc_branch)
 * @where: location of missing link
 * @num:   number of indirect blocks we are adding
 * @blks:  number of direct blocks we are adding
 *
 * This function fills the missing link and does all housekeeping needed in
 * inode (->i_blocks, etc.). In case of success we end up with the full
 * chain to new block and return 0.
 */
static int ext4_splice_branch(handle_t *handle, struct inode *inode,
                              ext4_lblk_t block, Indirect *where, int num,
                              int blks)
{
        int i;
        int err = 0;
        ext4_fsblk_t current_block;

        /*
         * If we're splicing into a [td]indirect block (as opposed to the
         * inode) then we need to get write access to the [td]indirect block
         * before the splice.
         */
        if (where->bh) {
                BUFFER_TRACE(where->bh, "get_write_access");
                err = ext4_journal_get_write_access(handle, where->bh);
                if (err)
                        goto err_out;
        }
        /* That's it */

        *where->p = where->key;

        /*
         * Update the host buffer_head or inode to point to more just allocated
         * direct blocks blocks
         */
        if (num == 0 && blks > 1) {
                current_block = le32_to_cpu(where->key) + 1;
                for (i = 1; i < blks; i++)
                        *(where->p + i) = cpu_to_le32(current_block++);
        }

        /* We are done with atomic stuff, now do the rest of housekeeping */
        /* had we spliced it onto indirect block? */
        if (where->bh) {
                /*
                 * If we spliced it onto an indirect block, we haven't
                 * altered the inode.  Note however that if it is being spliced
                 * onto an indirect block at the very end of the file (the
                 * file is growing) then we *will* alter the inode to reflect
                 * the new i_size.  But that is not done here - it is done in
                 * generic_commit_write->__mark_inode_dirty->ext4_dirty_inode.
                 */
                jbd_debug(5, "splicing indirect only\n");
                BUFFER_TRACE(where->bh, "call ext4_handle_dirty_metadata");
                err = ext4_handle_dirty_metadata(handle, inode, where->bh);
                if (err)
                        goto err_out;
        } else {
                /*
                 * OK, we spliced it into the inode itself on a direct block.
                 */
                ext4_mark_inode_dirty(handle, inode);
                jbd_debug(5, "splicing direct\n");
        }
        return err;

err_out:
        for (i = 1; i <= num; i++) {
                /*
                 * branch[i].bh is newly allocated, so there is no
                 * need to revoke the block, which is why we don't
                 * need to set EXT4_FREE_BLOCKS_METADATA.
                 */
                ext4_free_blocks(handle, inode, where[i].bh, 0, 1,
                                 EXT4_FREE_BLOCKS_FORGET);
        }
        ext4_free_blocks(handle, inode, NULL, le32_to_cpu(where[num].key),
                         blks, 0);

        return err;
}

/*
 * The ext4_ind_map_blocks() function handles non-extents inodes
 * (i.e., using the traditional indirect/double-indirect i_blocks
 * scheme) for ext4_map_blocks().
 *
 * Allocation strategy is simple: if we have to allocate something, we will
 * have to go the whole way to leaf. So let's do it before attaching anything
 * to tree, set linkage between the newborn blocks, write them if sync is
 * required, recheck the path, free and repeat if check fails, otherwise
 * set the last missing link (that will protect us from any truncate-generated
 * removals - all blocks on the path are immune now) and possibly force the
 * write on the parent block.
 * That has a nice additional property: no special recovery from the failed
 * allocations is needed - we simply release blocks and do not touch anything
 * reachable from inode.
 *
 * `handle' can be NULL if create == 0.
 *
 * return > 0, # of blocks mapped or allocated.
 * return = 0, if plain lookup failed.
 * return < 0, error case.
 *
 * The ext4_ind_get_blocks() function should be called with
 * down_write(&EXT4_I(inode)->i_data_sem) if allocating filesystem
 * blocks (i.e., flags has EXT4_GET_BLOCKS_CREATE set) or
 * down_read(&EXT4_I(inode)->i_data_sem) if not allocating file system
 * blocks.
 */
int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
                        struct ext4_map_blocks *map,
                        int flags)
{
        int err = -EIO;
        ext4_lblk_t offsets[4];
        Indirect chain[4];
        Indirect *partial;
        ext4_fsblk_t goal;
        int indirect_blks;
        int blocks_to_boundary = 0;
        int depth;
        int count = 0;
        ext4_fsblk_t first_block = 0;

        trace_ext4_ind_map_blocks_enter(inode, map->m_lblk, map->m_len, flags);
        J_ASSERT(!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)));
        J_ASSERT(handle != NULL || (flags & EXT4_GET_BLOCKS_CREATE) == 0);
        depth = ext4_block_to_path(inode, map->m_lblk, offsets,
                                   &blocks_to_boundary);

        if (depth == 0)
                goto out;

        partial = ext4_get_branch(inode, depth, offsets, chain, &err);

        /* Simplest case - block found, no allocation needed */
        if (!partial) {
                first_block = le32_to_cpu(chain[depth - 1].key);
                count++;
                /*map more blocks*/
                while (count < map->m_len && count <= blocks_to_boundary) {
                        ext4_fsblk_t blk;

                        blk = le32_to_cpu(*(chain[depth-1].p + count));

                        if (blk == first_block + count)
                                count++;
                        else
                                break;
                }
                goto got_it;
        }

        /* Next simple case - plain lookup or failed read of indirect block */
        if ((flags & EXT4_GET_BLOCKS_CREATE) == 0 || err == -EIO)
                goto cleanup;

        /*
         * Okay, we need to do block allocation.
        */
        if (EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
                                       EXT4_FEATURE_RO_COMPAT_BIGALLOC)) {
                EXT4_ERROR_INODE(inode, "Can't allocate blocks for "
                                 "non-extent mapped inodes with bigalloc");
                return -ENOSPC;
        }

        goal = ext4_find_goal(inode, map->m_lblk, partial);

        /* the number of blocks need to allocate for [d,t]indirect blocks */
        indirect_blks = (chain + depth) - partial - 1;

        /*
         * Next look up the indirect map to count the totoal number of
         * direct blocks to allocate for this branch.
         */
        count = ext4_blks_to_allocate(partial, indirect_blks,
                                      map->m_len, blocks_to_boundary);
        /*
         * Block out ext4_truncate while we alter the tree
         */
        err = ext4_alloc_branch(handle, inode, map->m_lblk, indirect_blks,
                                &count, goal,
                                offsets + (partial - chain), partial);

        /*
         * The ext4_splice_branch call will free and forget any buffers
         * on the new chain if there is a failure, but that risks using
         * up transaction credits, especially for bitmaps where the
         * credits cannot be returned.  Can we handle this somehow?  We
         * may need to return -EAGAIN upwards in the worst case.  --sct
         */
        if (!err)
                err = ext4_splice_branch(handle, inode, map->m_lblk,
                                         partial, indirect_blks, count);
        if (err)
                goto cleanup;

        map->m_flags |= EXT4_MAP_NEW;

        ext4_update_inode_fsync_trans(handle, inode, 1);
got_it:
        map->m_flags |= EXT4_MAP_MAPPED;
        map->m_pblk = le32_to_cpu(chain[depth-1].key);
        map->m_len = count;
        if (count > blocks_to_boundary)
                map->m_flags |= EXT4_MAP_BOUNDARY;
        err = count;
        /* Clean up and exit */
        partial = chain + depth - 1;    /* the whole chain */
cleanup:
        while (partial > chain) {
                BUFFER_TRACE(partial->bh, "call brelse");
                brelse(partial->bh);
                partial--;
        }
out:
        trace_ext4_ind_map_blocks_exit(inode, flags, map, err);
        return err;
}

/*
 * O_DIRECT for ext3 (or indirect map) based files
 *
 * If the O_DIRECT write will extend the file then add this inode to the
 * orphan list.  So recovery will truncate it back to the original size
 * if the machine crashes during the write.
 *
 * If the O_DIRECT write is intantiating holes inside i_size and the machine
 * crashes then stale disk data _may_ be exposed inside the file. But current
 * VFS code falls back into buffered path in that case so we are safe.
 */
ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
                           const struct iovec *iov, loff_t offset,
                           unsigned long nr_segs)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;
        struct ext4_inode_info *ei = EXT4_I(inode);
        handle_t *handle;
        ssize_t ret;
        int orphan = 0;
        size_t count = iov_length(iov, nr_segs);
        int retries = 0;

        if (rw == WRITE) {
                loff_t final_size = offset + count;

                if (final_size > inode->i_size) {
                        /* Credits for sb + inode write */
                        handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
                        if (IS_ERR(handle)) {
                                ret = PTR_ERR(handle);
                                goto out;
                        }
                        ret = ext4_orphan_add(handle, inode);
                        if (ret) {
                                ext4_journal_stop(handle);
                                goto out;
                        }
                        orphan = 1;
                        ei->i_disksize = inode->i_size;
                        ext4_journal_stop(handle);
                }
        }

retry:
        if (rw == READ && ext4_should_dioread_nolock(inode)) {
                /*
                 * Nolock dioread optimization may be dynamically disabled
                 * via ext4_inode_block_unlocked_dio(). Check inode's state
                 * while holding extra i_dio_count ref.
                 */
                atomic_inc(&inode->i_dio_count);
                smp_mb();
                if (unlikely(ext4_test_inode_state(inode,
                                                    EXT4_STATE_DIOREAD_LOCK))) {
                        inode_dio_done(inode);
                        goto locked;
                }
                ret = __blockdev_direct_IO(rw, iocb, inode,
                                 inode->i_sb->s_bdev, iov,
                                 offset, nr_segs,
                                 ext4_get_block, NULL, NULL, 0);
                inode_dio_done(inode);
        } else {
locked:
                ret = blockdev_direct_IO(rw, iocb, inode, iov,
                                 offset, nr_segs, ext4_get_block);

                if (unlikely((rw & WRITE) && ret < 0)) {
                        loff_t isize = i_size_read(inode);
                        loff_t end = offset + iov_length(iov, nr_segs);

                        if (end > isize)
                                ext4_truncate_failed_write(inode);
                }
        }
        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry;

        if (orphan) {
                int err;

                /* Credits for sb + inode write */
                handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
                if (IS_ERR(handle)) {
                        /* This is really bad luck. We've written the data
                         * but cannot extend i_size. Bail out and pretend
                         * the write failed... */
                        ret = PTR_ERR(handle);
                        if (inode->i_nlink)
                                ext4_orphan_del(NULL, inode);

                        goto out;
                }
                if (inode->i_nlink)
                        ext4_orphan_del(handle, inode);
                if (ret > 0) {
                        loff_t end = offset + ret;
                        if (end > inode->i_size) {
                                ei->i_disksize = end;
                                i_size_write(inode, end);
                                /*
                                 * We're going to return a positive `ret'
                                 * here due to non-zero-length I/O, so there's
                                 * no way of reporting error returns from
                                 * ext4_mark_inode_dirty() to userspace.  So
                                 * ignore it.
                                 */
                                ext4_mark_inode_dirty(handle, inode);
                        }
                }
                err = ext4_journal_stop(handle);
                if (ret == 0)
                        ret = err;
        }
out:
        return ret;
}

/*
 * Calculate the number of metadata blocks need to reserve
 * to allocate a new block at @lblocks for non extent file based file
 */
int ext4_ind_calc_metadata_amount(struct inode *inode, sector_t lblock)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        sector_t dind_mask = ~((sector_t)EXT4_ADDR_PER_BLOCK(inode->i_sb) - 1);
        int blk_bits;

        if (lblock < EXT4_NDIR_BLOCKS)
                return 0;

        lblock -= EXT4_NDIR_BLOCKS;

        if (ei->i_da_metadata_calc_len &&
            (lblock & dind_mask) == ei->i_da_metadata_calc_last_lblock) {
                ei->i_da_metadata_calc_len++;
                return 0;
        }
        ei->i_da_metadata_calc_last_lblock = lblock & dind_mask;
        ei->i_da_metadata_calc_len = 1;
        blk_bits = order_base_2(lblock);
        return (blk_bits / EXT4_ADDR_PER_BLOCK_BITS(inode->i_sb)) + 1;
}

/*
 * Calculate number of indirect blocks touched by mapping @nrblocks logically
 * contiguous blocks
 */
int ext4_ind_trans_blocks(struct inode *inode, int nrblocks)
{
        /*
         * With N contiguous data blocks, we need at most
         * N/EXT4_ADDR_PER_BLOCK(inode->i_sb) + 1 indirect blocks,
         * 2 dindirect blocks, and 1 tindirect block
         */
        return DIV_ROUND_UP(nrblocks, EXT4_ADDR_PER_BLOCK(inode->i_sb)) + 4;
}

/*
 * Truncate transactions can be complex and absolutely huge.  So we need to
 * be able to restart the transaction at a conventient checkpoint to make
 * sure we don't overflow the journal.
 *
 * Try to extend this transaction for the purposes of truncation.  If
 * extend fails, we need to propagate the failure up and restart the
 * transaction in the top-level truncate loop. --sct
 *
 * Returns 0 if we managed to create more room.  If we can't create more
 * room, and the transaction must be restarted we return 1.
 */
static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
{
        if (!ext4_handle_valid(handle))
                return 0;
        if (ext4_handle_has_enough_credits(handle, EXT4_RESERVE_TRANS_BLOCKS+1))
                return 0;
        if (!ext4_journal_extend(handle, ext4_blocks_for_truncate(inode)))
                return 0;
        return 1;
}

/*
 * Probably it should be a library function... search for first non-zero word
 * or memcmp with zero_page, whatever is better for particular architecture.
 * Linus?
 */
static inline int all_zeroes(__le32 *p, __le32 *q)
{
        while (p < q)
                if (*p++)
                        return 0;
        return 1;
}

/**
 *      ext4_find_shared - find the indirect blocks for partial truncation.
 *      @inode:   inode in question
 *      @depth:   depth of the affected branch
 *      @offsets: offsets of pointers in that branch (see ext4_block_to_path)
 *      @chain:   place to store the pointers to partial indirect blocks
 *      @top:     place to the (detached) top of branch
 *
 *      This is a helper function used by ext4_truncate().
 *
 *      When we do truncate() we may have to clean the ends of several
 *      indirect blocks but leave the blocks themselves alive. Block is
 *      partially truncated if some data below the new i_size is referred
 *      from it (and it is on the path to the first completely truncated
 *      data block, indeed).  We have to free the top of that path along
 *      with everything to the right of the path. Since no allocation
 *      past the truncation point is possible until ext4_truncate()
 *      finishes, we may safely do the latter, but top of branch may
 *      require special attention - pageout below the truncation point
 *      might try to populate it.
 *
 *      We atomically detach the top of branch from the tree, store the
 *      block number of its root in *@top, pointers to buffer_heads of
 *      partially truncated blocks - in @chain[].bh and pointers to
 *      their last elements that should not be removed - in
 *      @chain[].p. Return value is the pointer to last filled element
 *      of @chain.
 *
 *      The work left to caller to do the actual freeing of subtrees:
 *              a) free the subtree starting from *@top
 *              b) free the subtrees whose roots are stored in
 *                      (@chain[i].p+1 .. end of @chain[i].bh->b_data)
 *              c) free the subtrees growing from the inode past the @chain[0].
 *                      (no partially truncated stuff there).  */

static Indirect *ext4_find_shared(struct inode *inode, int depth,
                                  ext4_lblk_t offsets[4], Indirect chain[4],
                                  __le32 *top)
{
        Indirect *partial, *p;
        int k, err;

        *top = 0;
        /* Make k index the deepest non-null offset + 1 */
        for (k = depth; k > 1 && !offsets[k-1]; k--)
                ;
        partial = ext4_get_branch(inode, k, offsets, chain, &err);
        /* Writer: pointers */
        if (!partial)
                partial = chain + k-1;
        /*
         * If the branch acquired continuation since we've looked at it -
         * fine, it should all survive and (new) top doesn't belong to us.
         */
        if (!partial->key && *partial->p)
                /* Writer: end */
                goto no_top;
        for (p = partial; (p > chain) && all_zeroes((__le32 *) p->bh->b_data, p->p); p--)
                ;
        /*
         * OK, we've found the last block that must survive. The rest of our
         * branch should be detached before unlocking. However, if that rest
         * of branch is all ours and does not grow immediately from the inode
         * it's easier to cheat and just decrement partial->p.
         */
        if (p == chain + k - 1 && p > chain) {
                p->p--;
        } else {
                *top = *p->p;
                /* Nope, don't do this in ext4.  Must leave the tree intact */
#if 0
                *p->p = 0;
#endif
        }
        /* Writer: end */

        while (partial > p) {
                brelse(partial->bh);
                partial--;
        }
no_top:
        return partial;
}

/*
 * Zero a number of block pointers in either an inode or an indirect block.
 * If we restart the transaction we must again get write access to the
 * indirect block for further modification.
 *
 * We release `count' blocks on disk, but (last - first) may be greater
 * than `count' because there can be holes in there.
 *
 * Return 0 on success, 1 on invalid block range
 * and < 0 on fatal error.
 */
static int ext4_clear_blocks(handle_t *handle, struct inode *inode,
                             struct buffer_head *bh,
                             ext4_fsblk_t block_to_free,
                             unsigned long count, __le32 *first,
                             __le32 *last)
{
        __le32 *p;
        int     flags = EXT4_FREE_BLOCKS_VALIDATED;
        int     err;

        if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
                flags |= EXT4_FREE_BLOCKS_FORGET | EXT4_FREE_BLOCKS_METADATA;
        else if (ext4_should_journal_data(inode))
                flags |= EXT4_FREE_BLOCKS_FORGET;

        if (!ext4_data_block_valid(EXT4_SB(inode->i_sb), block_to_free,
                                   count)) {
                EXT4_ERROR_INODE(inode, "attempt to clear invalid "
                                 "blocks %llu len %lu",
                                 (unsigned long long) block_to_free, count);
                return 1;
        }

        if (try_to_extend_transaction(handle, inode)) {
                if (bh) {
                        BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
                        err = ext4_handle_dirty_metadata(handle, inode, bh);
                        if (unlikely(err))
                                goto out_err;
                }
                err = ext4_mark_inode_dirty(handle, inode);
                if (unlikely(err))
                        goto out_err;
                err = ext4_truncate_restart_trans(handle, inode,
                                        ext4_blocks_for_truncate(inode));
                if (unlikely(err))
                        goto out_err;
                if (bh) {
                        BUFFER_TRACE(bh, "retaking write access");
                        err = ext4_journal_get_write_access(handle, bh);
                        if (unlikely(err))
                                goto out_err;
                }
        }

        for (p = first; p < last; p++)
                *p = 0;

        ext4_free_blocks(handle, inode, NULL, block_to_free, count, flags);
        return 0;
out_err:
        ext4_std_error(inode->i_sb, err);
        return err;
}

/**
 * ext4_free_data - free a list of data blocks
 * @handle:     handle for this transaction
 * @inode:      inode we are dealing with
 * @this_bh:    indirect buffer_head which contains *@first and *@last
 * @first:      array of block numbers
 * @last:       points immediately past the end of array
 *
 * We are freeing all blocks referred from that array (numbers are stored as
 * little-endian 32-bit) and updating @inode->i_blocks appropriately.
 *
 * We accumulate contiguous runs of blocks to free.  Conveniently, if these
 * blocks are contiguous then releasing them at one time will only affect one
 * or two bitmap blocks (+ group descriptor(s) and superblock) and we won't
 * actually use a lot of journal space.
 *
 * @this_bh will be %NULL if @first and @last point into the inode's direct
 * block pointers.
 */
static void ext4_free_data(handle_t *handle, struct inode *inode,
                           struct buffer_head *this_bh,
                           __le32 *first, __le32 *last)
{
        ext4_fsblk_t block_to_free = 0;    /* Starting block # of a run */
        unsigned long count = 0;            /* Number of blocks in the run */
        __le32 *block_to_free_p = NULL;     /* Pointer into inode/ind
                                               corresponding to
                                               block_to_free */
        ext4_fsblk_t nr;                    /* Current block # */
        __le32 *p;                          /* Pointer into inode/ind
                                               for current block */
        int err = 0;

        if (this_bh) {                          /* For indirect block */
                BUFFER_TRACE(this_bh, "get_write_access");
                err = ext4_journal_get_write_access(handle, this_bh);
                /* Important: if we can't update the indirect pointers
                 * to the blocks, we can't free them. */
                if (err)
                        return;
        }

        for (p = first; p < last; p++) {
                nr = le32_to_cpu(*p);
                if (nr) {
                        /* accumulate blocks to free if they're contiguous */
                        if (count == 0) {
                                block_to_free = nr;
                                block_to_free_p = p;
                                count = 1;
                        } else if (nr == block_to_free + count) {
                                count++;
                        } else {
                                err = ext4_clear_blocks(handle, inode, this_bh,
                                                        block_to_free, count,
                                                        block_to_free_p, p);
                                if (err)
                                        break;
                                block_to_free = nr;
                                block_to_free_p = p;
                                count = 1;
                        }
                }
        }

        if (!err && count > 0)
                err = ext4_clear_blocks(handle, inode, this_bh, block_to_free,
                                        count, block_to_free_p, p);
        if (err < 0)
                /* fatal error */
                return;

        if (this_bh) {
                BUFFER_TRACE(this_bh, "call ext4_handle_dirty_metadata");

                /*
                 * The buffer head should have an attached journal head at this
                 * point. However, if the data is corrupted and an indirect
                 * block pointed to itself, it would have been detached when
                 * the block was cleared. Check for this instead of OOPSing.
                 */
                if ((EXT4_JOURNAL(inode) == NULL) || bh2jh(this_bh))
                        ext4_handle_dirty_metadata(handle, inode, this_bh);
                else
                        EXT4_ERROR_INODE(inode,
                                         "circular indirect block detected at "
                                         "block %llu",
                                (unsigned long long) this_bh->b_blocknr);
        }
}

/**
 *      ext4_free_branches - free an array of branches
 *      @handle: JBD handle for this transaction
 *      @inode: inode we are dealing with
 *      @parent_bh: the buffer_head which contains *@first and *@last
 *      @first: array of block numbers
 *      @last:  pointer immediately past the end of array
 *      @depth: depth of the branches to free
 *
 *      We are freeing all blocks referred from these branches (numbers are
 *      stored as little-endian 32-bit) and updating @inode->i_blocks
 *      appropriately.
 */
static void ext4_free_branches(handle_t *handle, struct inode *inode,
                               struct buffer_head *parent_bh,
                               __le32 *first, __le32 *last, int depth)
{
        ext4_fsblk_t nr;
        __le32 *p;

        if (ext4_handle_is_aborted(handle))
                return;

        if (depth--) {
                struct buffer_head *bh;
                int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
                p = last;
                while (--p >= first) {
                        nr = le32_to_cpu(*p);
                        if (!nr)
                                continue;               /* A hole */

                        if (!ext4_data_block_valid(EXT4_SB(inode->i_sb),
                                                   nr, 1)) {
                                EXT4_ERROR_INODE(inode,
                                                 "invalid indirect mapped "
                                                 "block %lu (level %d)",
                                                 (unsigned long) nr, depth);
                                break;
                        }

                        /* Go read the buffer for the next level down */
                        bh = sb_bread(inode->i_sb, nr);

                        /*
                         * A read failure? Report error and clear slot
                         * (should be rare).
                         */
                        if (!bh) {
                                EXT4_ERROR_INODE_BLOCK(inode, nr,
                                                       "Read failure");
                                continue;
                        }

                        /* This zaps the entire block.  Bottom up. */
                        BUFFER_TRACE(bh, "free child branches");
                        ext4_free_branches(handle, inode, bh,
                                        (__le32 *) bh->b_data,
                                        (__le32 *) bh->b_data + addr_per_block,
                                        depth);
                        brelse(bh);

                        /*
                         * Everything below this this pointer has been
                         * released.  Now let this top-of-subtree go.
                         *
                         * We want the freeing of this indirect block to be
                         * atomic in the journal with the updating of the
                         * bitmap block which owns it.  So make some room in
                         * the journal.
                         *
                         * We zero the parent pointer *after* freeing its
                         * pointee in the bitmaps, so if extend_transaction()
                         * for some reason fails to put the bitmap changes and
                         * the release into the same transaction, recovery
                         * will merely complain about releasing a free block,
                         * rather than leaking blocks.
                         */
                        if (ext4_handle_is_aborted(handle))
                                return;
                        if (try_to_extend_transaction(handle, inode)) {
                                ext4_mark_inode_dirty(handle, inode);
                                ext4_truncate_restart_trans(handle, inode,
                                            ext4_blocks_for_truncate(inode));
                        }

                        /*
                         * The forget flag here is critical because if
                         * we are journaling (and not doing data
                         * journaling), we have to make sure a revoke
                         * record is written to prevent the journal
                         * replay from overwriting the (former)
                         * indirect block if it gets reallocated as a
                         * data block.  This must happen in the same
                         * transaction where the data blocks are
                         * actually freed.
                         */
                        ext4_free_blocks(handle, inode, NULL, nr, 1,
                                         EXT4_FREE_BLOCKS_METADATA|
                                         EXT4_FREE_BLOCKS_FORGET);

                        if (parent_bh) {
                                /*
                                 * The block which we have just freed is
                                 * pointed to by an indirect block: journal it
                                 */
                                BUFFER_TRACE(parent_bh, "get_write_access");
                                if (!ext4_journal_get_write_access(handle,
                                                                   parent_bh)){
                                        *p = 0;
                                        BUFFER_TRACE(parent_bh,
                                        "call ext4_handle_dirty_metadata");
                                        ext4_handle_dirty_metadata(handle,
                                                                   inode,
                                                                   parent_bh);
                                }
                        }
                }
        } else {
                /* We have reached the bottom of the tree. */
                BUFFER_TRACE(parent_bh, "free data blocks");
                ext4_free_data(handle, inode, parent_bh, first, last);
        }
}

void ext4_ind_truncate(handle_t *handle, struct inode *inode)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        __le32 *i_data = ei->i_data;
        int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        ext4_lblk_t offsets[4];
        Indirect chain[4];
        Indirect *partial;
        __le32 nr = 0;
        int n = 0;
        ext4_lblk_t last_block, max_block;
        unsigned blocksize = inode->i_sb->s_blocksize;

        last_block = (inode->i_size + blocksize-1)
                                        >> EXT4_BLOCK_SIZE_BITS(inode->i_sb);
        max_block = (EXT4_SB(inode->i_sb)->s_bitmap_maxbytes + blocksize-1)
                                        >> EXT4_BLOCK_SIZE_BITS(inode->i_sb);

        if (last_block != max_block) {
                n = ext4_block_to_path(inode, last_block, offsets, NULL);
                if (n == 0)
                        return;
        }

        ext4_es_remove_extent(inode, last_block, EXT_MAX_BLOCKS - last_block);

        /*
         * The orphan list entry will now protect us from any crash which
         * occurs before the truncate completes, so it is now safe to propagate
         * the new, shorter inode size (held for now in i_size) into the
         * on-disk inode. We do this via i_disksize, which is the value which
         * ext4 *really* writes onto the disk inode.
         */
        ei->i_disksize = inode->i_size;

        if (last_block == max_block) {
                /*
                 * It is unnecessary to free any data blocks if last_block is
                 * equal to the indirect block limit.
                 */
                return;
        } else if (n == 1) {            /* direct blocks */
                ext4_free_data(handle, inode, NULL, i_data+offsets[0],
                               i_data + EXT4_NDIR_BLOCKS);
                goto do_indirects;
        }

        partial = ext4_find_shared(inode, n, offsets, chain, &nr);
        /* Kill the top of shared branch (not detached) */
        if (nr) {
                if (partial == chain) {
                        /* Shared branch grows from the inode */
                        ext4_free_branches(handle, inode, NULL,
                                           &nr, &nr+1, (chain+n-1) - partial);
                        *partial->p = 0;
                        /*
                         * We mark the inode dirty prior to restart,
                         * and prior to stop.  No need for it here.
                         */
                } else {
                        /* Shared branch grows from an indirect block */
                        BUFFER_TRACE(partial->bh, "get_write_access");
                        ext4_free_branches(handle, inode, partial->bh,
                                        partial->p,
                                        partial->p+1, (chain+n-1) - partial);
                }
        }
        /* Clear the ends of indirect blocks on the shared branch */
        while (partial > chain) {
                ext4_free_branches(handle, inode, partial->bh, partial->p + 1,
                                   (__le32*)partial->bh->b_data+addr_per_block,
                                   (chain+n-1) - partial);
                BUFFER_TRACE(partial->bh, "call brelse");
                brelse(partial->bh);
                partial--;
        }
do_indirects:
        /* Kill the remaining (whole) subtrees */
        switch (offsets[0]) {
        default:
                nr = i_data[EXT4_IND_BLOCK];
                if (nr) {
                        ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 1);
                        i_data[EXT4_IND_BLOCK] = 0;
                }
        case EXT4_IND_BLOCK:
                nr = i_data[EXT4_DIND_BLOCK];
                if (nr) {
                        ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 2);
                        i_data[EXT4_DIND_BLOCK] = 0;
                }
        case EXT4_DIND_BLOCK:
                nr = i_data[EXT4_TIND_BLOCK];
                if (nr) {
                        ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 3);
                        i_data[EXT4_TIND_BLOCK] = 0;
                }
        case EXT4_TIND_BLOCK:
                ;
        }
}

static int free_hole_blocks(handle_t *handle, struct inode *inode,
                            struct buffer_head *parent_bh, __le32 *i_data,
                            int level, ext4_lblk_t first,
                            ext4_lblk_t count, int max)
{
        struct buffer_head *bh = NULL;
        int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        int ret = 0;
        int i, inc;
        ext4_lblk_t offset;
        __le32 blk;

        inc = 1 << ((EXT4_BLOCK_SIZE_BITS(inode->i_sb) - 2) * level);
        for (i = 0, offset = 0; i < max; i++, i_data++, offset += inc) {
                if (offset >= count + first)
                        break;
                if (*i_data == 0 || (offset + inc) <= first)
                        continue;
                blk = *i_data;
                if (level > 0) {
                        ext4_lblk_t first2;
                        bh = sb_bread(inode->i_sb, le32_to_cpu(blk));
                        if (!bh) {
                                EXT4_ERROR_INODE_BLOCK(inode, le32_to_cpu(blk),
                                                       "Read failure");
                                return -EIO;
                        }
                        first2 = (first > offset) ? first - offset : 0;
                        ret = free_hole_blocks(handle, inode, bh,
                                               (__le32 *)bh->b_data, level - 1,
                                               first2, count - offset,
                                               inode->i_sb->s_blocksize >> 2);
                        if (ret) {
                                brelse(bh);
                                goto err;
                        }
                }
                if (level == 0 ||
                    (bh && all_zeroes((__le32 *)bh->b_data,
                                      (__le32 *)bh->b_data + addr_per_block))) {
                        ext4_free_data(handle, inode, parent_bh, &blk, &blk+1);
                        *i_data = 0;
                }
                brelse(bh);
                bh = NULL;
        }

err:
        return ret;
}

int ext4_free_hole_blocks(handle_t *handle, struct inode *inode,
                          ext4_lblk_t first, ext4_lblk_t stop)
{
        int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
        int level, ret = 0;
        int num = EXT4_NDIR_BLOCKS;
        ext4_lblk_t count, max = EXT4_NDIR_BLOCKS;
        __le32 *i_data = EXT4_I(inode)->i_data;

        count = stop - first;
        for (level = 0; level < 4; level++, max *= addr_per_block) {
                if (first < max) {
                        ret = free_hole_blocks(handle, inode, NULL, i_data,
                                               level, first, count, num);
                        if (ret)
                                goto err;
                        if (count > max - first)
                                count -= max - first;
                        else
                                break;
                        first = 0;
                } else {
                        first -= max;
                }
                i_data += num;
                if (level == 0) {
                        num = 1;
                        max = 1;
                }
        }

err:
        return ret;
}