xfs: refactor unmount record detection into helper

[karo-tx-linux.git] / fs / xfs / xfs_log_recover.c

/*
 * Copyright (c) 2000-2006 Silicon Graphics, Inc.
 * 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 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would 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 the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_bit.h"
#include "xfs_sb.h"
#include "xfs_mount.h"
#include "xfs_da_format.h"
#include "xfs_da_btree.h"
#include "xfs_inode.h"
#include "xfs_trans.h"
#include "xfs_log.h"
#include "xfs_log_priv.h"
#include "xfs_log_recover.h"
#include "xfs_inode_item.h"
#include "xfs_extfree_item.h"
#include "xfs_trans_priv.h"
#include "xfs_alloc.h"
#include "xfs_ialloc.h"
#include "xfs_quota.h"
#include "xfs_cksum.h"
#include "xfs_trace.h"
#include "xfs_icache.h"
#include "xfs_bmap_btree.h"
#include "xfs_error.h"
#include "xfs_dir2.h"

#define BLK_AVG(blk1, blk2)     ((blk1+blk2) >> 1)

STATIC int
xlog_find_zeroed(
        struct xlog     *,
        xfs_daddr_t     *);
STATIC int
xlog_clear_stale_blocks(
        struct xlog     *,
        xfs_lsn_t);
#if defined(DEBUG)
STATIC void
xlog_recover_check_summary(
        struct xlog *);
#else
#define xlog_recover_check_summary(log)
#endif
STATIC int
xlog_do_recovery_pass(
        struct xlog *, xfs_daddr_t, xfs_daddr_t, int, xfs_daddr_t *);

/*
 * This structure is used during recovery to record the buf log items which
 * have been canceled and should not be replayed.
 */
struct xfs_buf_cancel {
        xfs_daddr_t             bc_blkno;
        uint                    bc_len;
        int                     bc_refcount;
        struct list_head        bc_list;
};

/*
 * Sector aligned buffer routines for buffer create/read/write/access
 */

/*
 * Verify the given count of basic blocks is valid number of blocks
 * to specify for an operation involving the given XFS log buffer.
 * Returns nonzero if the count is valid, 0 otherwise.
 */

static inline int
xlog_buf_bbcount_valid(
        struct xlog     *log,
        int             bbcount)
{
        return bbcount > 0 && bbcount <= log->l_logBBsize;
}

/*
 * Allocate a buffer to hold log data.  The buffer needs to be able
 * to map to a range of nbblks basic blocks at any valid (basic
 * block) offset within the log.
 */
STATIC xfs_buf_t *
xlog_get_bp(
        struct xlog     *log,
        int             nbblks)
{
        struct xfs_buf  *bp;

        if (!xlog_buf_bbcount_valid(log, nbblks)) {
                xfs_warn(log->l_mp, "Invalid block length (0x%x) for buffer",
                        nbblks);
                XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_HIGH, log->l_mp);
                return NULL;
        }

        /*
         * We do log I/O in units of log sectors (a power-of-2
         * multiple of the basic block size), so we round up the
         * requested size to accommodate the basic blocks required
         * for complete log sectors.
         *
         * In addition, the buffer may be used for a non-sector-
         * aligned block offset, in which case an I/O of the
         * requested size could extend beyond the end of the
         * buffer.  If the requested size is only 1 basic block it
         * will never straddle a sector boundary, so this won't be
         * an issue.  Nor will this be a problem if the log I/O is
         * done in basic blocks (sector size 1).  But otherwise we
         * extend the buffer by one extra log sector to ensure
         * there's space to accommodate this possibility.
         */
        if (nbblks > 1 && log->l_sectBBsize > 1)
                nbblks += log->l_sectBBsize;
        nbblks = round_up(nbblks, log->l_sectBBsize);

        bp = xfs_buf_get_uncached(log->l_mp->m_logdev_targp, nbblks, 0);
        if (bp)
                xfs_buf_unlock(bp);
        return bp;
}

STATIC void
xlog_put_bp(
        xfs_buf_t       *bp)
{
        xfs_buf_free(bp);
}

/*
 * Return the address of the start of the given block number's data
 * in a log buffer.  The buffer covers a log sector-aligned region.
 */
STATIC char *
xlog_align(
        struct xlog     *log,
        xfs_daddr_t     blk_no,
        int             nbblks,
        struct xfs_buf  *bp)
{
        xfs_daddr_t     offset = blk_no & ((xfs_daddr_t)log->l_sectBBsize - 1);

        ASSERT(offset + nbblks <= bp->b_length);
        return bp->b_addr + BBTOB(offset);
}


/*
 * nbblks should be uint, but oh well.  Just want to catch that 32-bit length.
 */
STATIC int
xlog_bread_noalign(
        struct xlog     *log,
        xfs_daddr_t     blk_no,
        int             nbblks,
        struct xfs_buf  *bp)
{
        int             error;

        if (!xlog_buf_bbcount_valid(log, nbblks)) {
                xfs_warn(log->l_mp, "Invalid block length (0x%x) for buffer",
                        nbblks);
                XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_HIGH, log->l_mp);
                return -EFSCORRUPTED;
        }

        blk_no = round_down(blk_no, log->l_sectBBsize);
        nbblks = round_up(nbblks, log->l_sectBBsize);

        ASSERT(nbblks > 0);
        ASSERT(nbblks <= bp->b_length);

        XFS_BUF_SET_ADDR(bp, log->l_logBBstart + blk_no);
        XFS_BUF_READ(bp);
        bp->b_io_length = nbblks;
        bp->b_error = 0;

        error = xfs_buf_submit_wait(bp);
        if (error && !XFS_FORCED_SHUTDOWN(log->l_mp))
                xfs_buf_ioerror_alert(bp, __func__);
        return error;
}

STATIC int
xlog_bread(
        struct xlog     *log,
        xfs_daddr_t     blk_no,
        int             nbblks,
        struct xfs_buf  *bp,
        char            **offset)
{
        int             error;

        error = xlog_bread_noalign(log, blk_no, nbblks, bp);
        if (error)
                return error;

        *offset = xlog_align(log, blk_no, nbblks, bp);
        return 0;
}

/*
 * Read at an offset into the buffer. Returns with the buffer in it's original
 * state regardless of the result of the read.
 */
STATIC int
xlog_bread_offset(
        struct xlog     *log,
        xfs_daddr_t     blk_no,         /* block to read from */
        int             nbblks,         /* blocks to read */
        struct xfs_buf  *bp,
        char            *offset)
{
        char            *orig_offset = bp->b_addr;
        int             orig_len = BBTOB(bp->b_length);
        int             error, error2;

        error = xfs_buf_associate_memory(bp, offset, BBTOB(nbblks));
        if (error)
                return error;

        error = xlog_bread_noalign(log, blk_no, nbblks, bp);

        /* must reset buffer pointer even on error */
        error2 = xfs_buf_associate_memory(bp, orig_offset, orig_len);
        if (error)
                return error;
        return error2;
}

/*
 * Write out the buffer at the given block for the given number of blocks.
 * The buffer is kept locked across the write and is returned locked.
 * This can only be used for synchronous log writes.
 */
STATIC int
xlog_bwrite(
        struct xlog     *log,
        xfs_daddr_t     blk_no,
        int             nbblks,
        struct xfs_buf  *bp)
{
        int             error;

        if (!xlog_buf_bbcount_valid(log, nbblks)) {
                xfs_warn(log->l_mp, "Invalid block length (0x%x) for buffer",
                        nbblks);
                XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_HIGH, log->l_mp);
                return -EFSCORRUPTED;
        }

        blk_no = round_down(blk_no, log->l_sectBBsize);
        nbblks = round_up(nbblks, log->l_sectBBsize);

        ASSERT(nbblks > 0);
        ASSERT(nbblks <= bp->b_length);

        XFS_BUF_SET_ADDR(bp, log->l_logBBstart + blk_no);
        XFS_BUF_ZEROFLAGS(bp);
        xfs_buf_hold(bp);
        xfs_buf_lock(bp);
        bp->b_io_length = nbblks;
        bp->b_error = 0;

        error = xfs_bwrite(bp);
        if (error)
                xfs_buf_ioerror_alert(bp, __func__);
        xfs_buf_relse(bp);
        return error;
}

#ifdef DEBUG
/*
 * dump debug superblock and log record information
 */
STATIC void
xlog_header_check_dump(
        xfs_mount_t             *mp,
        xlog_rec_header_t       *head)
{
        xfs_debug(mp, "%s:  SB : uuid = %pU, fmt = %d",
                __func__, &mp->m_sb.sb_uuid, XLOG_FMT);
        xfs_debug(mp, "    log : uuid = %pU, fmt = %d",
                &head->h_fs_uuid, be32_to_cpu(head->h_fmt));
}
#else
#define xlog_header_check_dump(mp, head)
#endif

/*
 * check log record header for recovery
 */
STATIC int
xlog_header_check_recover(
        xfs_mount_t             *mp,
        xlog_rec_header_t       *head)
{
        ASSERT(head->h_magicno == cpu_to_be32(XLOG_HEADER_MAGIC_NUM));

        /*
         * IRIX doesn't write the h_fmt field and leaves it zeroed
         * (XLOG_FMT_UNKNOWN). This stops us from trying to recover
         * a dirty log created in IRIX.
         */
        if (unlikely(head->h_fmt != cpu_to_be32(XLOG_FMT))) {
                xfs_warn(mp,
        "dirty log written in incompatible format - can't recover");
                xlog_header_check_dump(mp, head);
                XFS_ERROR_REPORT("xlog_header_check_recover(1)",
                                 XFS_ERRLEVEL_HIGH, mp);
                return -EFSCORRUPTED;
        } else if (unlikely(!uuid_equal(&mp->m_sb.sb_uuid, &head->h_fs_uuid))) {
                xfs_warn(mp,
        "dirty log entry has mismatched uuid - can't recover");
                xlog_header_check_dump(mp, head);
                XFS_ERROR_REPORT("xlog_header_check_recover(2)",
                                 XFS_ERRLEVEL_HIGH, mp);
                return -EFSCORRUPTED;
        }
        return 0;
}

/*
 * read the head block of the log and check the header
 */
STATIC int
xlog_header_check_mount(
        xfs_mount_t             *mp,
        xlog_rec_header_t       *head)
{
        ASSERT(head->h_magicno == cpu_to_be32(XLOG_HEADER_MAGIC_NUM));

        if (uuid_is_nil(&head->h_fs_uuid)) {
                /*
                 * IRIX doesn't write the h_fs_uuid or h_fmt fields. If
                 * h_fs_uuid is nil, we assume this log was last mounted
                 * by IRIX and continue.
                 */
                xfs_warn(mp, "nil uuid in log - IRIX style log");
        } else if (unlikely(!uuid_equal(&mp->m_sb.sb_uuid, &head->h_fs_uuid))) {
                xfs_warn(mp, "log has mismatched uuid - can't recover");
                xlog_header_check_dump(mp, head);
                XFS_ERROR_REPORT("xlog_header_check_mount",
                                 XFS_ERRLEVEL_HIGH, mp);
                return -EFSCORRUPTED;
        }
        return 0;
}

STATIC void
xlog_recover_iodone(
        struct xfs_buf  *bp)
{
        if (bp->b_error) {
                /*
                 * We're not going to bother about retrying
                 * this during recovery. One strike!
                 */
                if (!XFS_FORCED_SHUTDOWN(bp->b_target->bt_mount)) {
                        xfs_buf_ioerror_alert(bp, __func__);
                        xfs_force_shutdown(bp->b_target->bt_mount,
                                                SHUTDOWN_META_IO_ERROR);
                }
        }
        bp->b_iodone = NULL;
        xfs_buf_ioend(bp);
}

/*
 * This routine finds (to an approximation) the first block in the physical
 * log which contains the given cycle.  It uses a binary search algorithm.
 * Note that the algorithm can not be perfect because the disk will not
 * necessarily be perfect.
 */
STATIC int
xlog_find_cycle_start(
        struct xlog     *log,
        struct xfs_buf  *bp,
        xfs_daddr_t     first_blk,
        xfs_daddr_t     *last_blk,
        uint            cycle)
{
        char            *offset;
        xfs_daddr_t     mid_blk;
        xfs_daddr_t     end_blk;
        uint            mid_cycle;
        int             error;

        end_blk = *last_blk;
        mid_blk = BLK_AVG(first_blk, end_blk);
        while (mid_blk != first_blk && mid_blk != end_blk) {
                error = xlog_bread(log, mid_blk, 1, bp, &offset);
                if (error)
                        return error;
                mid_cycle = xlog_get_cycle(offset);
                if (mid_cycle == cycle)
                        end_blk = mid_blk;   /* last_half_cycle == mid_cycle */
                else
                        first_blk = mid_blk; /* first_half_cycle == mid_cycle */
                mid_blk = BLK_AVG(first_blk, end_blk);
        }
        ASSERT((mid_blk == first_blk && mid_blk+1 == end_blk) ||
               (mid_blk == end_blk && mid_blk-1 == first_blk));

        *last_blk = end_blk;

        return 0;
}

/*
 * Check that a range of blocks does not contain stop_on_cycle_no.
 * Fill in *new_blk with the block offset where such a block is
 * found, or with -1 (an invalid block number) if there is no such
 * block in the range.  The scan needs to occur from front to back
 * and the pointer into the region must be updated since a later
 * routine will need to perform another test.
 */
STATIC int
xlog_find_verify_cycle(
        struct xlog     *log,
        xfs_daddr_t     start_blk,
        int             nbblks,
        uint            stop_on_cycle_no,
        xfs_daddr_t     *new_blk)
{
        xfs_daddr_t     i, j;
        uint            cycle;
        xfs_buf_t       *bp;
        xfs_daddr_t     bufblks;
        char            *buf = NULL;
        int             error = 0;

        /*
         * Greedily allocate a buffer big enough to handle the full
         * range of basic blocks we'll be examining.  If that fails,
         * try a smaller size.  We need to be able to read at least
         * a log sector, or we're out of luck.
         */
        bufblks = 1 << ffs(nbblks);
        while (bufblks > log->l_logBBsize)
                bufblks >>= 1;
        while (!(bp = xlog_get_bp(log, bufblks))) {
                bufblks >>= 1;
                if (bufblks < log->l_sectBBsize)
                        return -ENOMEM;
        }

        for (i = start_blk; i < start_blk + nbblks; i += bufblks) {
                int     bcount;

                bcount = min(bufblks, (start_blk + nbblks - i));

                error = xlog_bread(log, i, bcount, bp, &buf);
                if (error)
                        goto out;

                for (j = 0; j < bcount; j++) {
                        cycle = xlog_get_cycle(buf);
                        if (cycle == stop_on_cycle_no) {
                                *new_blk = i+j;
                                goto out;
                        }

                        buf += BBSIZE;
                }
        }

        *new_blk = -1;

out:
        xlog_put_bp(bp);
        return error;
}

/*
 * Potentially backup over partial log record write.
 *
 * In the typical case, last_blk is the number of the block directly after
 * a good log record.  Therefore, we subtract one to get the block number
 * of the last block in the given buffer.  extra_bblks contains the number
 * of blocks we would have read on a previous read.  This happens when the
 * last log record is split over the end of the physical log.
 *
 * extra_bblks is the number of blocks potentially verified on a previous
 * call to this routine.
 */
STATIC int
xlog_find_verify_log_record(
        struct xlog             *log,
        xfs_daddr_t             start_blk,
        xfs_daddr_t             *last_blk,
        int                     extra_bblks)
{
        xfs_daddr_t             i;
        xfs_buf_t               *bp;
        char                    *offset = NULL;
        xlog_rec_header_t       *head = NULL;
        int                     error = 0;
        int                     smallmem = 0;
        int                     num_blks = *last_blk - start_blk;
        int                     xhdrs;

        ASSERT(start_blk != 0 || *last_blk != start_blk);

        if (!(bp = xlog_get_bp(log, num_blks))) {
                if (!(bp = xlog_get_bp(log, 1)))
                        return -ENOMEM;
                smallmem = 1;
        } else {
                error = xlog_bread(log, start_blk, num_blks, bp, &offset);
                if (error)
                        goto out;
                offset += ((num_blks - 1) << BBSHIFT);
        }

        for (i = (*last_blk) - 1; i >= 0; i--) {
                if (i < start_blk) {
                        /* valid log record not found */
                        xfs_warn(log->l_mp,
                "Log inconsistent (didn't find previous header)");
                        ASSERT(0);
                        error = -EIO;
                        goto out;
                }

                if (smallmem) {
                        error = xlog_bread(log, i, 1, bp, &offset);
                        if (error)
                                goto out;
                }

                head = (xlog_rec_header_t *)offset;

                if (head->h_magicno == cpu_to_be32(XLOG_HEADER_MAGIC_NUM))
                        break;

                if (!smallmem)
                        offset -= BBSIZE;
        }

        /*
         * We hit the beginning of the physical log & still no header.  Return
         * to caller.  If caller can handle a return of -1, then this routine
         * will be called again for the end of the physical log.
         */
        if (i == -1) {
                error = 1;
                goto out;
        }

        /*
         * We have the final block of the good log (the first block
         * of the log record _before_ the head. So we check the uuid.
         */
        if ((error = xlog_header_check_mount(log->l_mp, head)))
                goto out;

        /*
         * We may have found a log record header before we expected one.
         * last_blk will be the 1st block # with a given cycle #.  We may end
         * up reading an entire log record.  In this case, we don't want to
         * reset last_blk.  Only when last_blk points in the middle of a log
         * record do we update last_blk.
         */
        if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
                uint    h_size = be32_to_cpu(head->h_size);

                xhdrs = h_size / XLOG_HEADER_CYCLE_SIZE;
                if (h_size % XLOG_HEADER_CYCLE_SIZE)
                        xhdrs++;
        } else {
                xhdrs = 1;
        }

        if (*last_blk - i + extra_bblks !=
            BTOBB(be32_to_cpu(head->h_len)) + xhdrs)
                *last_blk = i;

out:
        xlog_put_bp(bp);
        return error;
}

/*
 * Head is defined to be the point of the log where the next log write
 * could go.  This means that incomplete LR writes at the end are
 * eliminated when calculating the head.  We aren't guaranteed that previous
 * LR have complete transactions.  We only know that a cycle number of
 * current cycle number -1 won't be present in the log if we start writing
 * from our current block number.
 *
 * last_blk contains the block number of the first block with a given
 * cycle number.
 *
 * Return: zero if normal, non-zero if error.
 */
STATIC int
xlog_find_head(
        struct xlog     *log,
        xfs_daddr_t     *return_head_blk)
{
        xfs_buf_t       *bp;
        char            *offset;
        xfs_daddr_t     new_blk, first_blk, start_blk, last_blk, head_blk;
        int             num_scan_bblks;
        uint            first_half_cycle, last_half_cycle;
        uint            stop_on_cycle;
        int             error, log_bbnum = log->l_logBBsize;

        /* Is the end of the log device zeroed? */
        error = xlog_find_zeroed(log, &first_blk);
        if (error < 0) {
                xfs_warn(log->l_mp, "empty log check failed");
                return error;
        }
        if (error == 1) {
                *return_head_blk = first_blk;

                /* Is the whole lot zeroed? */
                if (!first_blk) {
                        /* Linux XFS shouldn't generate totally zeroed logs -
                         * mkfs etc write a dummy unmount record to a fresh
                         * log so we can store the uuid in there
                         */
                        xfs_warn(log->l_mp, "totally zeroed log");
                }

                return 0;
        }

        first_blk = 0;                  /* get cycle # of 1st block */
        bp = xlog_get_bp(log, 1);
        if (!bp)
                return -ENOMEM;

        error = xlog_bread(log, 0, 1, bp, &offset);
        if (error)
                goto bp_err;

        first_half_cycle = xlog_get_cycle(offset);

        last_blk = head_blk = log_bbnum - 1;    /* get cycle # of last block */
        error = xlog_bread(log, last_blk, 1, bp, &offset);
        if (error)
                goto bp_err;

        last_half_cycle = xlog_get_cycle(offset);
        ASSERT(last_half_cycle != 0);

        /*
         * If the 1st half cycle number is equal to the last half cycle number,
         * then the entire log is stamped with the same cycle number.  In this
         * case, head_blk can't be set to zero (which makes sense).  The below
         * math doesn't work out properly with head_blk equal to zero.  Instead,
         * we set it to log_bbnum which is an invalid block number, but this
         * value makes the math correct.  If head_blk doesn't changed through
         * all the tests below, *head_blk is set to zero at the very end rather
         * than log_bbnum.  In a sense, log_bbnum and zero are the same block
         * in a circular file.
         */
        if (first_half_cycle == last_half_cycle) {
                /*
                 * In this case we believe that the entire log should have
                 * cycle number last_half_cycle.  We need to scan backwards
                 * from the end verifying that there are no holes still
                 * containing last_half_cycle - 1.  If we find such a hole,
                 * then the start of that hole will be the new head.  The
                 * simple case looks like
                 *        x | x ... | x - 1 | x
                 * Another case that fits this picture would be
                 *        x | x + 1 | x ... | x
                 * In this case the head really is somewhere at the end of the
                 * log, as one of the latest writes at the beginning was
                 * incomplete.
                 * One more case is
                 *        x | x + 1 | x ... | x - 1 | x
                 * This is really the combination of the above two cases, and
                 * the head has to end up at the start of the x-1 hole at the
                 * end of the log.
                 *
                 * In the 256k log case, we will read from the beginning to the
                 * end of the log and search for cycle numbers equal to x-1.
                 * We don't worry about the x+1 blocks that we encounter,
                 * because we know that they cannot be the head since the log
                 * started with x.
                 */
                head_blk = log_bbnum;
                stop_on_cycle = last_half_cycle - 1;
        } else {
                /*
                 * In this case we want to find the first block with cycle
                 * number matching last_half_cycle.  We expect the log to be
                 * some variation on
                 *        x + 1 ... | x ... | x
                 * The first block with cycle number x (last_half_cycle) will
                 * be where the new head belongs.  First we do a binary search
                 * for the first occurrence of last_half_cycle.  The binary
                 * search may not be totally accurate, so then we scan back
                 * from there looking for occurrences of last_half_cycle before
                 * us.  If that backwards scan wraps around the beginning of
                 * the log, then we look for occurrences of last_half_cycle - 1
                 * at the end of the log.  The cases we're looking for look
                 * like
                 *                               v binary search stopped here
                 *        x + 1 ... | x | x + 1 | x ... | x
                 *                   ^ but we want to locate this spot
                 * or
                 *        <---------> less than scan distance
                 *        x + 1 ... | x ... | x - 1 | x
                 *                           ^ we want to locate this spot
                 */
                stop_on_cycle = last_half_cycle;
                if ((error = xlog_find_cycle_start(log, bp, first_blk,
                                                &head_blk, last_half_cycle)))
                        goto bp_err;
        }

        /*
         * Now validate the answer.  Scan back some number of maximum possible
         * blocks and make sure each one has the expected cycle number.  The
         * maximum is determined by the total possible amount of buffering
         * in the in-core log.  The following number can be made tighter if
         * we actually look at the block size of the filesystem.
         */
        num_scan_bblks = XLOG_TOTAL_REC_SHIFT(log);
        if (head_blk >= num_scan_bblks) {
                /*
                 * We are guaranteed that the entire check can be performed
                 * in one buffer.
                 */
                start_blk = head_blk - num_scan_bblks;
                if ((error = xlog_find_verify_cycle(log,
                                                start_blk, num_scan_bblks,
                                                stop_on_cycle, &new_blk)))
                        goto bp_err;
                if (new_blk != -1)
                        head_blk = new_blk;
        } else {                /* need to read 2 parts of log */
                /*
                 * We are going to scan backwards in the log in two parts.
                 * First we scan the physical end of the log.  In this part
                 * of the log, we are looking for blocks with cycle number
                 * last_half_cycle - 1.
                 * If we find one, then we know that the log starts there, as
                 * we've found a hole that didn't get written in going around
                 * the end of the physical log.  The simple case for this is
                 *        x + 1 ... | x ... | x - 1 | x
                 *        <---------> less than scan distance
                 * If all of the blocks at the end of the log have cycle number
                 * last_half_cycle, then we check the blocks at the start of
                 * the log looking for occurrences of last_half_cycle.  If we
                 * find one, then our current estimate for the location of the
                 * first occurrence of last_half_cycle is wrong and we move
                 * back to the hole we've found.  This case looks like
                 *        x + 1 ... | x | x + 1 | x ...
                 *                               ^ binary search stopped here
                 * Another case we need to handle that only occurs in 256k
                 * logs is
                 *        x + 1 ... | x ... | x+1 | x ...
                 *                   ^ binary search stops here
                 * In a 256k log, the scan at the end of the log will see the
                 * x + 1 blocks.  We need to skip past those since that is
                 * certainly not the head of the log.  By searching for
                 * last_half_cycle-1 we accomplish that.
                 */
                ASSERT(head_blk <= INT_MAX &&
                        (xfs_daddr_t) num_scan_bblks >= head_blk);
                start_blk = log_bbnum - (num_scan_bblks - head_blk);
                if ((error = xlog_find_verify_cycle(log, start_blk,
                                        num_scan_bblks - (int)head_blk,
                                        (stop_on_cycle - 1), &new_blk)))
                        goto bp_err;
                if (new_blk != -1) {
                        head_blk = new_blk;
                        goto validate_head;
                }

                /*
                 * Scan beginning of log now.  The last part of the physical
                 * log is good.  This scan needs to verify that it doesn't find
                 * the last_half_cycle.
                 */
                start_blk = 0;
                ASSERT(head_blk <= INT_MAX);
                if ((error = xlog_find_verify_cycle(log,
                                        start_blk, (int)head_blk,
                                        stop_on_cycle, &new_blk)))
                        goto bp_err;
                if (new_blk != -1)
                        head_blk = new_blk;
        }

validate_head:
        /*
         * Now we need to make sure head_blk is not pointing to a block in
         * the middle of a log record.
         */
        num_scan_bblks = XLOG_REC_SHIFT(log);
        if (head_blk >= num_scan_bblks) {
                start_blk = head_blk - num_scan_bblks; /* don't read head_blk */

                /* start ptr at last block ptr before head_blk */
                error = xlog_find_verify_log_record(log, start_blk, &head_blk, 0);
                if (error == 1)
                        error = -EIO;
                if (error)
                        goto bp_err;
        } else {
                start_blk = 0;
                ASSERT(head_blk <= INT_MAX);
                error = xlog_find_verify_log_record(log, start_blk, &head_blk, 0);
                if (error < 0)
                        goto bp_err;
                if (error == 1) {
                        /* We hit the beginning of the log during our search */
                        start_blk = log_bbnum - (num_scan_bblks - head_blk);
                        new_blk = log_bbnum;
                        ASSERT(start_blk <= INT_MAX &&
                                (xfs_daddr_t) log_bbnum-start_blk >= 0);
                        ASSERT(head_blk <= INT_MAX);
                        error = xlog_find_verify_log_record(log, start_blk,
                                                        &new_blk, (int)head_blk);
                        if (error == 1)
                                error = -EIO;
                        if (error)
                                goto bp_err;
                        if (new_blk != log_bbnum)
                                head_blk = new_blk;
                } else if (error)
                        goto bp_err;
        }

        xlog_put_bp(bp);
        if (head_blk == log_bbnum)
                *return_head_blk = 0;
        else
                *return_head_blk = head_blk;
        /*
         * When returning here, we have a good block number.  Bad block
         * means that during a previous crash, we didn't have a clean break
         * from cycle number N to cycle number N-1.  In this case, we need
         * to find the first block with cycle number N-1.
         */
        return 0;

 bp_err:
        xlog_put_bp(bp);

        if (error)
                xfs_warn(log->l_mp, "failed to find log head");
        return error;
}

/*
 * Seek backwards in the log for log record headers.
 *
 * Given a starting log block, walk backwards until we find the provided number
 * of records or hit the provided tail block. The return value is the number of
 * records encountered or a negative error code. The log block and buffer
 * pointer of the last record seen are returned in rblk and rhead respectively.
 */
STATIC int
xlog_rseek_logrec_hdr(
        struct xlog             *log,
        xfs_daddr_t             head_blk,
        xfs_daddr_t             tail_blk,
        int                     count,
        struct xfs_buf          *bp,
        xfs_daddr_t             *rblk,
        struct xlog_rec_header  **rhead,
        bool                    *wrapped)
{
        int                     i;
        int                     error;
        int                     found = 0;
        char                    *offset = NULL;
        xfs_daddr_t             end_blk;

        *wrapped = false;

        /*
         * Walk backwards from the head block until we hit the tail or the first
         * block in the log.
         */
        end_blk = head_blk > tail_blk ? tail_blk : 0;
        for (i = (int) head_blk - 1; i >= end_blk; i--) {
                error = xlog_bread(log, i, 1, bp, &offset);
                if (error)
                        goto out_error;

                if (*(__be32 *) offset == cpu_to_be32(XLOG_HEADER_MAGIC_NUM)) {
                        *rblk = i;
                        *rhead = (struct xlog_rec_header *) offset;
                        if (++found == count)
                                break;
                }
        }

        /*
         * If we haven't hit the tail block or the log record header count,
         * start looking again from the end of the physical log. Note that
         * callers can pass head == tail if the tail is not yet known.
         */
        if (tail_blk >= head_blk && found != count) {
                for (i = log->l_logBBsize - 1; i >= (int) tail_blk; i--) {
                        error = xlog_bread(log, i, 1, bp, &offset);
                        if (error)
                                goto out_error;

                        if (*(__be32 *)offset ==
                            cpu_to_be32(XLOG_HEADER_MAGIC_NUM)) {
                                *wrapped = true;
                                *rblk = i;
                                *rhead = (struct xlog_rec_header *) offset;
                                if (++found == count)
                                        break;
                        }
                }
        }

        return found;

out_error:
        return error;
}

/*
 * Seek forward in the log for log record headers.
 *
 * Given head and tail blocks, walk forward from the tail block until we find
 * the provided number of records or hit the head block. The return value is the
 * number of records encountered or a negative error code. The log block and
 * buffer pointer of the last record seen are returned in rblk and rhead
 * respectively.
 */
STATIC int
xlog_seek_logrec_hdr(
        struct xlog             *log,
        xfs_daddr_t             head_blk,
        xfs_daddr_t             tail_blk,
        int                     count,
        struct xfs_buf          *bp,
        xfs_daddr_t             *rblk,
        struct xlog_rec_header  **rhead,
        bool                    *wrapped)
{
        int                     i;
        int                     error;
        int                     found = 0;
        char                    *offset = NULL;
        xfs_daddr_t             end_blk;

        *wrapped = false;

        /*
         * Walk forward from the tail block until we hit the head or the last
         * block in the log.
         */
        end_blk = head_blk > tail_blk ? head_blk : log->l_logBBsize - 1;
        for (i = (int) tail_blk; i <= end_blk; i++) {
                error = xlog_bread(log, i, 1, bp, &offset);
                if (error)
                        goto out_error;

                if (*(__be32 *) offset == cpu_to_be32(XLOG_HEADER_MAGIC_NUM)) {
                        *rblk = i;
                        *rhead = (struct xlog_rec_header *) offset;
                        if (++found == count)
                                break;
                }
        }

        /*
         * If we haven't hit the head block or the log record header count,
         * start looking again from the start of the physical log.
         */
        if (tail_blk > head_blk && found != count) {
                for (i = 0; i < (int) head_blk; i++) {
                        error = xlog_bread(log, i, 1, bp, &offset);
                        if (error)
                                goto out_error;

                        if (*(__be32 *)offset ==
                            cpu_to_be32(XLOG_HEADER_MAGIC_NUM)) {
                                *wrapped = true;
                                *rblk = i;
                                *rhead = (struct xlog_rec_header *) offset;
                                if (++found == count)
                                        break;
                        }
                }
        }

        return found;

out_error:
        return error;
}

/*
 * Check the log tail for torn writes. This is required when torn writes are
 * detected at the head and the head had to be walked back to a previous record.
 * The tail of the previous record must now be verified to ensure the torn
 * writes didn't corrupt the previous tail.
 *
 * Return an error if CRC verification fails as recovery cannot proceed.
 */
STATIC int
xlog_verify_tail(
        struct xlog             *log,
        xfs_daddr_t             head_blk,
        xfs_daddr_t             tail_blk)
{
        struct xlog_rec_header  *thead;
        struct xfs_buf          *bp;
        xfs_daddr_t             first_bad;
        int                     count;
        int                     error = 0;
        bool                    wrapped;
        xfs_daddr_t             tmp_head;

        bp = xlog_get_bp(log, 1);
        if (!bp)
                return -ENOMEM;

        /*
         * Seek XLOG_MAX_ICLOGS + 1 records past the current tail record to get
         * a temporary head block that points after the last possible
         * concurrently written record of the tail.
         */
        count = xlog_seek_logrec_hdr(log, head_blk, tail_blk,
                                     XLOG_MAX_ICLOGS + 1, bp, &tmp_head, &thead,
                                     &wrapped);
        if (count < 0) {
                error = count;
                goto out;
        }

        /*
         * If the call above didn't find XLOG_MAX_ICLOGS + 1 records, we ran
         * into the actual log head. tmp_head points to the start of the record
         * so update it to the actual head block.
         */
        if (count < XLOG_MAX_ICLOGS + 1)
                tmp_head = head_blk;

        /*
         * We now have a tail and temporary head block that covers at least
         * XLOG_MAX_ICLOGS records from the tail. We need to verify that these
         * records were completely written. Run a CRC verification pass from
         * tail to head and return the result.
         */
        error = xlog_do_recovery_pass(log, tmp_head, tail_blk,
                                      XLOG_RECOVER_CRCPASS, &first_bad);

out:
        xlog_put_bp(bp);
        return error;
}

/*
 * Detect and trim torn writes from the head of the log.
 *
 * Storage without sector atomicity guarantees can result in torn writes in the
 * log in the event of a crash. Our only means to detect this scenario is via
 * CRC verification. While we can't always be certain that CRC verification
 * failure is due to a torn write vs. an unrelated corruption, we do know that
 * only a certain number (XLOG_MAX_ICLOGS) of log records can be written out at
 * one time. Therefore, CRC verify up to XLOG_MAX_ICLOGS records at the head of
 * the log and treat failures in this range as torn writes as a matter of
 * policy. In the event of CRC failure, the head is walked back to the last good
 * record in the log and the tail is updated from that record and verified.
 */
STATIC int
xlog_verify_head(
        struct xlog             *log,
        xfs_daddr_t             *head_blk,      /* in/out: unverified head */
        xfs_daddr_t             *tail_blk,      /* out: tail block */
        struct xfs_buf          *bp,
        xfs_daddr_t             *rhead_blk,     /* start blk of last record */
        struct xlog_rec_header  **rhead,        /* ptr to last record */
        bool                    *wrapped)       /* last rec. wraps phys. log */
{
        struct xlog_rec_header  *tmp_rhead;
        struct xfs_buf          *tmp_bp;
        xfs_daddr_t             first_bad;
        xfs_daddr_t             tmp_rhead_blk;
        int                     found;
        int                     error;
        bool                    tmp_wrapped;

        /*
         * Check the head of the log for torn writes. Search backwards from the
         * head until we hit the tail or the maximum number of log record I/Os
         * that could have been in flight at one time. Use a temporary buffer so
         * we don't trash the rhead/bp pointers from the caller.
         */
        tmp_bp = xlog_get_bp(log, 1);
        if (!tmp_bp)
                return -ENOMEM;
        error = xlog_rseek_logrec_hdr(log, *head_blk, *tail_blk,
                                      XLOG_MAX_ICLOGS, tmp_bp, &tmp_rhead_blk,
                                      &tmp_rhead, &tmp_wrapped);
        xlog_put_bp(tmp_bp);
        if (error < 0)
                return error;

        /*
         * Now run a CRC verification pass over the records starting at the
         * block found above to the current head. If a CRC failure occurs, the
         * log block of the first bad record is saved in first_bad.
         */
        error = xlog_do_recovery_pass(log, *head_blk, tmp_rhead_blk,
                                      XLOG_RECOVER_CRCPASS, &first_bad);
        if (error == -EFSBADCRC) {
                /*
                 * We've hit a potential torn write. Reset the error and warn
                 * about it.
                 */
                error = 0;
                xfs_warn(log->l_mp,
"Torn write (CRC failure) detected at log block 0x%llx. Truncating head block from 0x%llx.",
                         first_bad, *head_blk);

                /*
                 * Get the header block and buffer pointer for the last good
                 * record before the bad record.
                 *
                 * Note that xlog_find_tail() clears the blocks at the new head
                 * (i.e., the records with invalid CRC) if the cycle number
                 * matches the the current cycle.
                 */
                found = xlog_rseek_logrec_hdr(log, first_bad, *tail_blk, 1, bp,
                                              rhead_blk, rhead, wrapped);
                if (found < 0)
                        return found;
                if (found == 0)         /* XXX: right thing to do here? */
                        return -EIO;

                /*
                 * Reset the head block to the starting block of the first bad
                 * log record and set the tail block based on the last good
                 * record.
                 *
                 * Bail out if the updated head/tail match as this indicates
                 * possible corruption outside of the acceptable
                 * (XLOG_MAX_ICLOGS) range. This is a job for xfs_repair...
                 */
                *head_blk = first_bad;
                *tail_blk = BLOCK_LSN(be64_to_cpu((*rhead)->h_tail_lsn));
                if (*head_blk == *tail_blk) {
                        ASSERT(0);
                        return 0;
                }

                /*
                 * Now verify the tail based on the updated head. This is
                 * required because the torn writes trimmed from the head could
                 * have been written over the tail of a previous record. Return
                 * any errors since recovery cannot proceed if the tail is
                 * corrupt.
                 *
                 * XXX: This leaves a gap in truly robust protection from torn
                 * writes in the log. If the head is behind the tail, the tail
                 * pushes forward to create some space and then a crash occurs
                 * causing the writes into the previous record's tail region to
                 * tear, log recovery isn't able to recover.
                 *
                 * How likely is this to occur? If possible, can we do something
                 * more intelligent here? Is it safe to push the tail forward if
                 * we can determine that the tail is within the range of the
                 * torn write (e.g., the kernel can only overwrite the tail if
                 * it has actually been pushed forward)? Alternatively, could we
                 * somehow prevent this condition at runtime?
                 */
                error = xlog_verify_tail(log, *head_blk, *tail_blk);
        }

        return error;
}

/*
 * Check whether the head of the log points to an unmount record. In other
 * words, determine whether the log is clean. If so, update the in-core state
 * appropriately.
 */
static int
xlog_check_unmount_rec(
        struct xlog             *log,
        xfs_daddr_t             *head_blk,
        xfs_daddr_t             *tail_blk,
        struct xlog_rec_header  *rhead,
        xfs_daddr_t             rhead_blk,
        struct xfs_buf          *bp,
        bool                    *clean)
{
        struct xlog_op_header   *op_head;
        xfs_daddr_t             umount_data_blk;
        xfs_daddr_t             after_umount_blk;
        int                     hblks;
        int                     error;
        char                    *offset;

        *clean = false;

        /*
         * Look for unmount record. If we find it, then we know there was a
         * clean unmount. Since 'i' could be the last block in the physical
         * log, we convert to a log block before comparing to the head_blk.
         *
         * Save the current tail lsn to use to pass to xlog_clear_stale_blocks()
         * below. We won't want to clear the unmount record if there is one, so
         * we pass the lsn of the unmount record rather than the block after it.
         */
        if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
                int     h_size = be32_to_cpu(rhead->h_size);
                int     h_version = be32_to_cpu(rhead->h_version);

                if ((h_version & XLOG_VERSION_2) &&
                    (h_size > XLOG_HEADER_CYCLE_SIZE)) {
                        hblks = h_size / XLOG_HEADER_CYCLE_SIZE;
                        if (h_size % XLOG_HEADER_CYCLE_SIZE)
                                hblks++;
                } else {
                        hblks = 1;
                }
        } else {
                hblks = 1;
        }
        after_umount_blk = rhead_blk + hblks + BTOBB(be32_to_cpu(rhead->h_len));
        after_umount_blk = do_mod(after_umount_blk, log->l_logBBsize);
        if (*head_blk == after_umount_blk &&
            be32_to_cpu(rhead->h_num_logops) == 1) {
                umount_data_blk = rhead_blk + hblks;
                umount_data_blk = do_mod(umount_data_blk, log->l_logBBsize);
                error = xlog_bread(log, umount_data_blk, 1, bp, &offset);
                if (error)
                        return error;

                op_head = (struct xlog_op_header *)offset;
                if (op_head->oh_flags & XLOG_UNMOUNT_TRANS) {
                        /*
                         * Set tail and last sync so that newly written log
                         * records will point recovery to after the current
                         * unmount record.
                         */
                        xlog_assign_atomic_lsn(&log->l_tail_lsn,
                                        log->l_curr_cycle, after_umount_blk);
                        xlog_assign_atomic_lsn(&log->l_last_sync_lsn,
                                        log->l_curr_cycle, after_umount_blk);
                        *tail_blk = after_umount_blk;

                        *clean = true;
                }
        }

        return 0;
}

/*
 * Find the sync block number or the tail of the log.
 *
 * This will be the block number of the last record to have its
 * associated buffers synced to disk.  Every log record header has
 * a sync lsn embedded in it.  LSNs hold block numbers, so it is easy
 * to get a sync block number.  The only concern is to figure out which
 * log record header to believe.
 *
 * The following algorithm uses the log record header with the largest
 * lsn.  The entire log record does not need to be valid.  We only care
 * that the header is valid.
 *
 * We could speed up search by using current head_blk buffer, but it is not
 * available.
 */
STATIC int
xlog_find_tail(
        struct xlog             *log,
        xfs_daddr_t             *head_blk,
        xfs_daddr_t             *tail_blk)
{
        xlog_rec_header_t       *rhead;
        char                    *offset = NULL;
        xfs_buf_t               *bp;
        int                     error;
        xfs_daddr_t             rhead_blk;
        xfs_lsn_t               tail_lsn;
        bool                    wrapped = false;
        bool                    clean = false;

        /*
         * Find previous log record
         */
        if ((error = xlog_find_head(log, head_blk)))
                return error;
        ASSERT(*head_blk < INT_MAX);

        bp = xlog_get_bp(log, 1);
        if (!bp)
                return -ENOMEM;
        if (*head_blk == 0) {                           /* special case */
                error = xlog_bread(log, 0, 1, bp, &offset);
                if (error)
                        goto done;

                if (xlog_get_cycle(offset) == 0) {
                        *tail_blk = 0;
                        /* leave all other log inited values alone */
                        goto done;
                }
        }

        /*
         * Search backwards through the log looking for the log record header
         * block. This wraps all the way back around to the head so something is
         * seriously wrong if we can't find it.
         */
        error = xlog_rseek_logrec_hdr(log, *head_blk, *head_blk, 1, bp,
                                      &rhead_blk, &rhead, &wrapped);
        if (error < 0)
                return error;
        if (!error) {
                xfs_warn(log->l_mp, "%s: couldn't find sync record", __func__);
                return -EIO;
        }
        *tail_blk = BLOCK_LSN(be64_to_cpu(rhead->h_tail_lsn));

        /*
         * Trim the head block back to skip over torn records. We can have
         * multiple log I/Os in flight at any time, so we assume CRC failures
         * back through the previous several records are torn writes and skip
         * them.
         */
        error = xlog_verify_head(log, head_blk, tail_blk, bp, &rhead_blk,
                                 &rhead, &wrapped);
        if (error)
                goto done;

        /*
         * Reset log values according to the state of the log when we
         * crashed.  In the case where head_blk == 0, we bump curr_cycle
         * one because the next write starts a new cycle rather than
         * continuing the cycle of the last good log record.  At this
         * point we have guaranteed that all partial log records have been
         * accounted for.  Therefore, we know that the last good log record
         * written was complete and ended exactly on the end boundary
         * of the physical log.
         */
        log->l_prev_block = rhead_blk;
        log->l_curr_block = (int)*head_blk;
        log->l_curr_cycle = be32_to_cpu(rhead->h_cycle);
        if (wrapped)
                log->l_curr_cycle++;
        atomic64_set(&log->l_tail_lsn, be64_to_cpu(rhead->h_tail_lsn));
        atomic64_set(&log->l_last_sync_lsn, be64_to_cpu(rhead->h_lsn));
        xlog_assign_grant_head(&log->l_reserve_head.grant, log->l_curr_cycle,
                                        BBTOB(log->l_curr_block));
        xlog_assign_grant_head(&log->l_write_head.grant, log->l_curr_cycle,
                                        BBTOB(log->l_curr_block));
        tail_lsn = atomic64_read(&log->l_tail_lsn);

        /*
         * Look for an unmount record at the head of the log. This sets the log
         * state to determine whether recovery is necessary.
         */
        error = xlog_check_unmount_rec(log, head_blk, tail_blk, rhead,
                                       rhead_blk, bp, &clean);
        if (error)
                goto done;

        /*
         * Note that the unmount was clean. If the unmount was not clean, we
         * need to know this to rebuild the superblock counters from the perag
         * headers if we have a filesystem using non-persistent counters.
         */
        if (clean)
                log->l_mp->m_flags |= XFS_MOUNT_WAS_CLEAN;

        /*
         * Make sure that there are no blocks in front of the head
         * with the same cycle number as the head.  This can happen
         * because we allow multiple outstanding log writes concurrently,
         * and the later writes might make it out before earlier ones.
         *
         * We use the lsn from before modifying it so that we'll never
         * overwrite the unmount record after a clean unmount.
         *
         * Do this only if we are going to recover the filesystem
         *
         * NOTE: This used to say "if (!readonly)"
         * However on Linux, we can & do recover a read-only filesystem.
         * We only skip recovery if NORECOVERY is specified on mount,
         * in which case we would not be here.
         *
         * But... if the -device- itself is readonly, just skip this.
         * We can't recover this device anyway, so it won't matter.
         */
        if (!xfs_readonly_buftarg(log->l_mp->m_logdev_targp))
                error = xlog_clear_stale_blocks(log, tail_lsn);

done:
        xlog_put_bp(bp);

        if (error)
                xfs_warn(log->l_mp, "failed to locate log tail");
        return error;
}

/*
 * Is the log zeroed at all?
 *
 * The last binary search should be changed to perform an X block read
 * once X becomes small enough.  You can then search linearly through
 * the X blocks.  This will cut down on the number of reads we need to do.
 *
 * If the log is partially zeroed, this routine will pass back the blkno
 * of the first block with cycle number 0.  It won't have a complete LR
 * preceding it.
 *
 * Return:
 *      0  => the log is completely written to
 *      1 => use *blk_no as the first block of the log
 *      <0 => error has occurred
 */
STATIC int
xlog_find_zeroed(
        struct xlog     *log,
        xfs_daddr_t     *blk_no)
{
        xfs_buf_t       *bp;
        char            *offset;
        uint            first_cycle, last_cycle;
        xfs_daddr_t     new_blk, last_blk, start_blk;
        xfs_daddr_t     num_scan_bblks;
        int             error, log_bbnum = log->l_logBBsize;

        *blk_no = 0;

        /* check totally zeroed log */
        bp = xlog_get_bp(log, 1);
        if (!bp)
                return -ENOMEM;
        error = xlog_bread(log, 0, 1, bp, &offset);
        if (error)
                goto bp_err;

        first_cycle = xlog_get_cycle(offset);
        if (first_cycle == 0) {         /* completely zeroed log */
                *blk_no = 0;
                xlog_put_bp(bp);
                return 1;
        }

        /* check partially zeroed log */
        error = xlog_bread(log, log_bbnum-1, 1, bp, &offset);
        if (error)
                goto bp_err;

        last_cycle = xlog_get_cycle(offset);
        if (last_cycle != 0) {          /* log completely written to */
                xlog_put_bp(bp);
                return 0;
        } else if (first_cycle != 1) {
                /*
                 * If the cycle of the last block is zero, the cycle of
                 * the first block must be 1. If it's not, maybe we're
                 * not looking at a log... Bail out.
                 */
                xfs_warn(log->l_mp,
                        "Log inconsistent or not a log (last==0, first!=1)");
                error = -EINVAL;
                goto bp_err;
        }

        /* we have a partially zeroed log */
        last_blk = log_bbnum-1;
        if ((error = xlog_find_cycle_start(log, bp, 0, &last_blk, 0)))
                goto bp_err;

        /*
         * Validate the answer.  Because there is no way to guarantee that
         * the entire log is made up of log records which are the same size,
         * we scan over the defined maximum blocks.  At this point, the maximum
         * is not chosen to mean anything special.   XXXmiken
         */
        num_scan_bblks = XLOG_TOTAL_REC_SHIFT(log);
        ASSERT(num_scan_bblks <= INT_MAX);

        if (last_blk < num_scan_bblks)
                num_scan_bblks = last_blk;
        start_blk = last_blk - num_scan_bblks;

        /*
         * We search for any instances of cycle number 0 that occur before
         * our current estimate of the head.  What we're trying to detect is
         *        1 ... | 0 | 1 | 0...
         *                       ^ binary search ends here
         */
        if ((error = xlog_find_verify_cycle(log, start_blk,
                                         (int)num_scan_bblks, 0, &new_blk)))
                goto bp_err;
        if (new_blk != -1)
                last_blk = new_blk;

        /*
         * Potentially backup over partial log record write.  We don't need
         * to search the end of the log because we know it is zero.
         */
        error = xlog_find_verify_log_record(log, start_blk, &last_blk, 0);
        if (error == 1)
                error = -EIO;
        if (error)
                goto bp_err;

        *blk_no = last_blk;
bp_err:
        xlog_put_bp(bp);
        if (error)
                return error;
        return 1;
}

/*
 * These are simple subroutines used by xlog_clear_stale_blocks() below
 * to initialize a buffer full of empty log record headers and write
 * them into the log.
 */
STATIC void
xlog_add_record(
        struct xlog             *log,
        char                    *buf,
        int                     cycle,
        int                     block,
        int                     tail_cycle,
        int                     tail_block)
{
        xlog_rec_header_t       *recp = (xlog_rec_header_t *)buf;

        memset(buf, 0, BBSIZE);
        recp->h_magicno = cpu_to_be32(XLOG_HEADER_MAGIC_NUM);
        recp->h_cycle = cpu_to_be32(cycle);
        recp->h_version = cpu_to_be32(
                        xfs_sb_version_haslogv2(&log->l_mp->m_sb) ? 2 : 1);
        recp->h_lsn = cpu_to_be64(xlog_assign_lsn(cycle, block));
        recp->h_tail_lsn = cpu_to_be64(xlog_assign_lsn(tail_cycle, tail_block));
        recp->h_fmt = cpu_to_be32(XLOG_FMT);
        memcpy(&recp->h_fs_uuid, &log->l_mp->m_sb.sb_uuid, sizeof(uuid_t));
}

STATIC int
xlog_write_log_records(
        struct xlog     *log,
        int             cycle,
        int             start_block,
        int             blocks,
        int             tail_cycle,
        int             tail_block)
{
        char            *offset;
        xfs_buf_t       *bp;
        int             balign, ealign;
        int             sectbb = log->l_sectBBsize;
        int             end_block = start_block + blocks;
        int             bufblks;
        int             error = 0;
        int             i, j = 0;

        /*
         * Greedily allocate a buffer big enough to handle the full
         * range of basic blocks to be written.  If that fails, try
         * a smaller size.  We need to be able to write at least a
         * log sector, or we're out of luck.
         */
        bufblks = 1 << ffs(blocks);
        while (bufblks > log->l_logBBsize)
                bufblks >>= 1;
        while (!(bp = xlog_get_bp(log, bufblks))) {
                bufblks >>= 1;
                if (bufblks < sectbb)
                        return -ENOMEM;
        }

        /* We may need to do a read at the start to fill in part of
         * the buffer in the starting sector not covered by the first
         * write below.
         */
        balign = round_down(start_block, sectbb);
        if (balign != start_block) {
                error = xlog_bread_noalign(log, start_block, 1, bp);
                if (error)
                        goto out_put_bp;

                j = start_block - balign;
        }

        for (i = start_block; i < end_block; i += bufblks) {
                int             bcount, endcount;

                bcount = min(bufblks, end_block - start_block);
                endcount = bcount - j;

                /* We may need to do a read at the end to fill in part of
                 * the buffer in the final sector not covered by the write.
                 * If this is the same sector as the above read, skip it.
                 */
                ealign = round_down(end_block, sectbb);
                if (j == 0 && (start_block + endcount > ealign)) {
                        offset = bp->b_addr + BBTOB(ealign - start_block);
                        error = xlog_bread_offset(log, ealign, sectbb,
                                                        bp, offset);
                        if (error)
                                break;

                }

                offset = xlog_align(log, start_block, endcount, bp);
                for (; j < endcount; j++) {
                        xlog_add_record(log, offset, cycle, i+j,
                                        tail_cycle, tail_block);
                        offset += BBSIZE;
                }
                error = xlog_bwrite(log, start_block, endcount, bp);
                if (error)
                        break;
                start_block += endcount;
                j = 0;
        }

 out_put_bp:
        xlog_put_bp(bp);
        return error;
}

/*
 * This routine is called to blow away any incomplete log writes out
 * in front of the log head.  We do this so that we won't become confused
 * if we come up, write only a little bit more, and then crash again.
 * If we leave the partial log records out there, this situation could
 * cause us to think those partial writes are valid blocks since they
 * have the current cycle number.  We get rid of them by overwriting them
 * with empty log records with the old cycle number rather than the
 * current one.
 *
 * The tail lsn is passed in rather than taken from
 * the log so that we will not write over the unmount record after a
 * clean unmount in a 512 block log.  Doing so would leave the log without
 * any valid log records in it until a new one was written.  If we crashed
 * during that time we would not be able to recover.
 */
STATIC int
xlog_clear_stale_blocks(
        struct xlog     *log,
        xfs_lsn_t       tail_lsn)
{
        int             tail_cycle, head_cycle;
        int             tail_block, head_block;
        int             tail_distance, max_distance;
        int             distance;
        int             error;

        tail_cycle = CYCLE_LSN(tail_lsn);
        tail_block = BLOCK_LSN(tail_lsn);
        head_cycle = log->l_curr_cycle;
        head_block = log->l_curr_block;

        /*
         * Figure out the distance between the new head of the log
         * and the tail.  We want to write over any blocks beyond the
         * head that we may have written just before the crash, but
         * we don't want to overwrite the tail of the log.
         */
        if (head_cycle == tail_cycle) {
                /*
                 * The tail is behind the head in the physical log,
                 * so the distance from the head to the tail is the
                 * distance from the head to the end of the log plus
                 * the distance from the beginning of the log to the
                 * tail.
                 */
                if (unlikely(head_block < tail_block || head_block >= log->l_logBBsize)) {
                        XFS_ERROR_REPORT("xlog_clear_stale_blocks(1)",
                                         XFS_ERRLEVEL_LOW, log->l_mp);
                        return -EFSCORRUPTED;
                }
                tail_distance = tail_block + (log->l_logBBsize - head_block);
        } else {
                /*
                 * The head is behind the tail in the physical log,
                 * so the distance from the head to the tail is just
                 * the tail block minus the head block.
                 */
                if (unlikely(head_block >= tail_block || head_cycle != (tail_cycle + 1))){
                        XFS_ERROR_REPORT("xlog_clear_stale_blocks(2)",
                                         XFS_ERRLEVEL_LOW, log->l_mp);
                        return -EFSCORRUPTED;
                }
                tail_distance = tail_block - head_block;
        }

        /*
         * If the head is right up against the tail, we can't clear
         * anything.
         */
        if (tail_distance <= 0) {
                ASSERT(tail_distance == 0);
                return 0;
        }

        max_distance = XLOG_TOTAL_REC_SHIFT(log);
        /*
         * Take the smaller of the maximum amount of outstanding I/O
         * we could have and the distance to the tail to clear out.
         * We take the smaller so that we don't overwrite the tail and
         * we don't waste all day writing from the head to the tail
         * for no reason.
         */
        max_distance = MIN(max_distance, tail_distance);

        if ((head_block + max_distance) <= log->l_logBBsize) {
                /*
                 * We can stomp all the blocks we need to without
                 * wrapping around the end of the log.  Just do it
                 * in a single write.  Use the cycle number of the
                 * current cycle minus one so that the log will look like:
                 *     n ... | n - 1 ...
                 */
                error = xlog_write_log_records(log, (head_cycle - 1),
                                head_block, max_distance, tail_cycle,
                                tail_block);
                if (error)
                        return error;
        } else {
                /*
                 * We need to wrap around the end of the physical log in
                 * order to clear all the blocks.  Do it in two separate
                 * I/Os.  The first write should be from the head to the
                 * end of the physical log, and it should use the current
                 * cycle number minus one just like above.
                 */
                distance = log->l_logBBsize - head_block;
                error = xlog_write_log_records(log, (head_cycle - 1),
                                head_block, distance, tail_cycle,
                                tail_block);

                if (error)
                        return error;

                /*
                 * Now write the blocks at the start of the physical log.
                 * This writes the remainder of the blocks we want to clear.
                 * It uses the current cycle number since we're now on the
                 * same cycle as the head so that we get:
                 *    n ... n ... | n - 1 ...
                 *    ^^^^^ blocks we're writing
                 */
                distance = max_distance - (log->l_logBBsize - head_block);
                error = xlog_write_log_records(log, head_cycle, 0, distance,
                                tail_cycle, tail_block);
                if (error)
                        return error;
        }

        return 0;
}

/******************************************************************************
 *
 *              Log recover routines
 *
 ******************************************************************************
 */

/*
 * Sort the log items in the transaction.
 *
 * The ordering constraints are defined by the inode allocation and unlink
 * behaviour. The rules are:
 *
 *      1. Every item is only logged once in a given transaction. Hence it
 *         represents the last logged state of the item. Hence ordering is
 *         dependent on the order in which operations need to be performed so
 *         required initial conditions are always met.
 *
 *      2. Cancelled buffers are recorded in pass 1 in a separate table and
 *         there's nothing to replay from them so we can simply cull them
 *         from the transaction. However, we can't do that until after we've
 *         replayed all the other items because they may be dependent on the
 *         cancelled buffer and replaying the cancelled buffer can remove it
 *         form the cancelled buffer table. Hence they have tobe done last.
 *
 *      3. Inode allocation buffers must be replayed before inode items that
 *         read the buffer and replay changes into it. For filesystems using the
 *         ICREATE transactions, this means XFS_LI_ICREATE objects need to get
 *         treated the same as inode allocation buffers as they create and
 *         initialise the buffers directly.
 *
 *      4. Inode unlink buffers must be replayed after inode items are replayed.
 *         This ensures that inodes are completely flushed to the inode buffer
 *         in a "free" state before we remove the unlinked inode list pointer.
 *
 * Hence the ordering needs to be inode allocation buffers first, inode items
 * second, inode unlink buffers third and cancelled buffers last.
 *
 * But there's a problem with that - we can't tell an inode allocation buffer
 * apart from a regular buffer, so we can't separate them. We can, however,
 * tell an inode unlink buffer from the others, and so we can separate them out
 * from all the other buffers and move them to last.
 *
 * Hence, 4 lists, in order from head to tail:
 *      - buffer_list for all buffers except cancelled/inode unlink buffers
 *      - item_list for all non-buffer items
 *      - inode_buffer_list for inode unlink buffers
 *      - cancel_list for the cancelled buffers
 *
 * Note that we add objects to the tail of the lists so that first-to-last
 * ordering is preserved within the lists. Adding objects to the head of the
 * list means when we traverse from the head we walk them in last-to-first
 * order. For cancelled buffers and inode unlink buffers this doesn't matter,
 * but for all other items there may be specific ordering that we need to
 * preserve.
 */
STATIC int
xlog_recover_reorder_trans(
        struct xlog             *log,
        struct xlog_recover     *trans,
        int                     pass)
{
        xlog_recover_item_t     *item, *n;
        int                     error = 0;
        LIST_HEAD(sort_list);
        LIST_HEAD(cancel_list);
        LIST_HEAD(buffer_list);
        LIST_HEAD(inode_buffer_list);
        LIST_HEAD(inode_list);

        list_splice_init(&trans->r_itemq, &sort_list);
        list_for_each_entry_safe(item, n, &sort_list, ri_list) {
                xfs_buf_log_format_t    *buf_f = item->ri_buf[0].i_addr;

                switch (ITEM_TYPE(item)) {
                case XFS_LI_ICREATE:
                        list_move_tail(&item->ri_list, &buffer_list);
                        break;
                case XFS_LI_BUF:
                        if (buf_f->blf_flags & XFS_BLF_CANCEL) {
                                trace_xfs_log_recover_item_reorder_head(log,
                                                        trans, item, pass);
                                list_move(&item->ri_list, &cancel_list);
                                break;
                        }
                        if (buf_f->blf_flags & XFS_BLF_INODE_BUF) {
                                list_move(&item->ri_list, &inode_buffer_list);
                                break;
                        }
                        list_move_tail(&item->ri_list, &buffer_list);
                        break;
                case XFS_LI_INODE:
                case XFS_LI_DQUOT:
                case XFS_LI_QUOTAOFF:
                case XFS_LI_EFD:
                case XFS_LI_EFI:
                        trace_xfs_log_recover_item_reorder_tail(log,
                                                        trans, item, pass);
                        list_move_tail(&item->ri_list, &inode_list);
                        break;
                default:
                        xfs_warn(log->l_mp,
                                "%s: unrecognized type of log operation",
                                __func__);
                        ASSERT(0);
                        /*
                         * return the remaining items back to the transaction
                         * item list so they can be freed in caller.
                         */
                        if (!list_empty(&sort_list))
                                list_splice_init(&sort_list, &trans->r_itemq);
                        error = -EIO;
                        goto out;
                }
        }
out:
        ASSERT(list_empty(&sort_list));
        if (!list_empty(&buffer_list))
                list_splice(&buffer_list, &trans->r_itemq);
        if (!list_empty(&inode_list))
                list_splice_tail(&inode_list, &trans->r_itemq);
        if (!list_empty(&inode_buffer_list))
                list_splice_tail(&inode_buffer_list, &trans->r_itemq);
        if (!list_empty(&cancel_list))
                list_splice_tail(&cancel_list, &trans->r_itemq);
        return error;
}

/*
 * Build up the table of buf cancel records so that we don't replay
 * cancelled data in the second pass.  For buffer records that are
 * not cancel records, there is nothing to do here so we just return.
 *
 * If we get a cancel record which is already in the table, this indicates
 * that the buffer was cancelled multiple times.  In order to ensure
 * that during pass 2 we keep the record in the table until we reach its
 * last occurrence in the log, we keep a reference count in the cancel
 * record in the table to tell us how many times we expect to see this
 * record during the second pass.
 */
STATIC int
xlog_recover_buffer_pass1(
        struct xlog                     *log,
        struct xlog_recover_item        *item)
{
        xfs_buf_log_format_t    *buf_f = item->ri_buf[0].i_addr;
        struct list_head        *bucket;
        struct xfs_buf_cancel   *bcp;

        /*
         * If this isn't a cancel buffer item, then just return.
         */
        if (!(buf_f->blf_flags & XFS_BLF_CANCEL)) {
                trace_xfs_log_recover_buf_not_cancel(log, buf_f);
                return 0;
        }

        /*
         * Insert an xfs_buf_cancel record into the hash table of them.
         * If there is already an identical record, bump its reference count.
         */
        bucket = XLOG_BUF_CANCEL_BUCKET(log, buf_f->blf_blkno);
        list_for_each_entry(bcp, bucket, bc_list) {
                if (bcp->bc_blkno == buf_f->blf_blkno &&
                    bcp->bc_len == buf_f->blf_len) {
                        bcp->bc_refcount++;
                        trace_xfs_log_recover_buf_cancel_ref_inc(log, buf_f);
                        return 0;
                }
        }

        bcp = kmem_alloc(sizeof(struct xfs_buf_cancel), KM_SLEEP);
        bcp->bc_blkno = buf_f->blf_blkno;
        bcp->bc_len = buf_f->blf_len;
        bcp->bc_refcount = 1;
        list_add_tail(&bcp->bc_list, bucket);

        trace_xfs_log_recover_buf_cancel_add(log, buf_f);
        return 0;
}

/*
 * Check to see whether the buffer being recovered has a corresponding
 * entry in the buffer cancel record table. If it is, return the cancel
 * buffer structure to the caller.
 */
STATIC struct xfs_buf_cancel *
xlog_peek_buffer_cancelled(
        struct xlog             *log,
        xfs_daddr_t             blkno,
        uint                    len,
        ushort                  flags)
{
        struct list_head        *bucket;
        struct xfs_buf_cancel   *bcp;

        if (!log->l_buf_cancel_table) {
                /* empty table means no cancelled buffers in the log */
                ASSERT(!(flags & XFS_BLF_CANCEL));
                return NULL;
        }

        bucket = XLOG_BUF_CANCEL_BUCKET(log, blkno);
        list_for_each_entry(bcp, bucket, bc_list) {
                if (bcp->bc_blkno == blkno && bcp->bc_len == len)
                        return bcp;
        }

        /*
         * We didn't find a corresponding entry in the table, so return 0 so
         * that the buffer is NOT cancelled.
         */
        ASSERT(!(flags & XFS_BLF_CANCEL));
        return NULL;
}

/*
 * If the buffer is being cancelled then return 1 so that it will be cancelled,
 * otherwise return 0.  If the buffer is actually a buffer cancel item
 * (XFS_BLF_CANCEL is set), then decrement the refcount on the entry in the
 * table and remove it from the table if this is the last reference.
 *
 * We remove the cancel record from the table when we encounter its last
 * occurrence in the log so that if the same buffer is re-used again after its
 * last cancellation we actually replay the changes made at that point.
 */
STATIC int
xlog_check_buffer_cancelled(
        struct xlog             *log,
        xfs_daddr_t             blkno,
        uint                    len,
        ushort                  flags)
{
        struct xfs_buf_cancel   *bcp;

        bcp = xlog_peek_buffer_cancelled(log, blkno, len, flags);
        if (!bcp)
                return 0;

        /*
         * We've go a match, so return 1 so that the recovery of this buffer
         * is cancelled.  If this buffer is actually a buffer cancel log
         * item, then decrement the refcount on the one in the table and
         * remove it if this is the last reference.
         */
        if (flags & XFS_BLF_CANCEL) {
                if (--bcp->bc_refcount == 0) {
                        list_del(&bcp->bc_list);
                        kmem_free(bcp);
                }
        }
        return 1;
}

/*
 * Perform recovery for a buffer full of inodes.  In these buffers, the only
 * data which should be recovered is that which corresponds to the
 * di_next_unlinked pointers in the on disk inode structures.  The rest of the
 * data for the inodes is always logged through the inodes themselves rather
 * than the inode buffer and is recovered in xlog_recover_inode_pass2().
 *
 * The only time when buffers full of inodes are fully recovered is when the
 * buffer is full of newly allocated inodes.  In this case the buffer will
 * not be marked as an inode buffer and so will be sent to
 * xlog_recover_do_reg_buffer() below during recovery.
 */
STATIC int
xlog_recover_do_inode_buffer(
        struct xfs_mount        *mp,
        xlog_recover_item_t     *item,
        struct xfs_buf          *bp,
        xfs_buf_log_format_t    *buf_f)
{
        int                     i;
        int                     item_index = 0;
        int                     bit = 0;
        int                     nbits = 0;
        int                     reg_buf_offset = 0;
        int                     reg_buf_bytes = 0;
        int                     next_unlinked_offset;
        int                     inodes_per_buf;
        xfs_agino_t             *logged_nextp;
        xfs_agino_t             *buffer_nextp;

        trace_xfs_log_recover_buf_inode_buf(mp->m_log, buf_f);

        /*
         * Post recovery validation only works properly on CRC enabled
         * filesystems.
         */
        if (xfs_sb_version_hascrc(&mp->m_sb))
                bp->b_ops = &xfs_inode_buf_ops;

        inodes_per_buf = BBTOB(bp->b_io_length) >> mp->m_sb.sb_inodelog;
        for (i = 0; i < inodes_per_buf; i++) {
                next_unlinked_offset = (i * mp->m_sb.sb_inodesize) +
                        offsetof(xfs_dinode_t, di_next_unlinked);

                while (next_unlinked_offset >=
                       (reg_buf_offset + reg_buf_bytes)) {
                        /*
                         * The next di_next_unlinked field is beyond
                         * the current logged region.  Find the next
                         * logged region that contains or is beyond
                         * the current di_next_unlinked field.
                         */
                        bit += nbits;
                        bit = xfs_next_bit(buf_f->blf_data_map,
                                           buf_f->blf_map_size, bit);

                        /*
                         * If there are no more logged regions in the
                         * buffer, then we're done.
                         */
                        if (bit == -1)
                                return 0;

                        nbits = xfs_contig_bits(buf_f->blf_data_map,
                                                buf_f->blf_map_size, bit);
                        ASSERT(nbits > 0);
                        reg_buf_offset = bit << XFS_BLF_SHIFT;
                        reg_buf_bytes = nbits << XFS_BLF_SHIFT;
                        item_index++;
                }

                /*
                 * If the current logged region starts after the current
                 * di_next_unlinked field, then move on to the next
                 * di_next_unlinked field.
                 */
                if (next_unlinked_offset < reg_buf_offset)
                        continue;

                ASSERT(item->ri_buf[item_index].i_addr != NULL);
                ASSERT((item->ri_buf[item_index].i_len % XFS_BLF_CHUNK) == 0);
                ASSERT((reg_buf_offset + reg_buf_bytes) <=
                                                        BBTOB(bp->b_io_length));

                /*
                 * The current logged region contains a copy of the
                 * current di_next_unlinked field.  Extract its value
                 * and copy it to the buffer copy.
                 */
                logged_nextp = item->ri_buf[item_index].i_addr +
                                next_unlinked_offset - reg_buf_offset;
                if (unlikely(*logged_nextp == 0)) {
                        xfs_alert(mp,
                "Bad inode buffer log record (ptr = 0x%p, bp = 0x%p). "
                "Trying to replay bad (0) inode di_next_unlinked field.",
                                item, bp);
                        XFS_ERROR_REPORT("xlog_recover_do_inode_buf",
                                         XFS_ERRLEVEL_LOW, mp);
                        return -EFSCORRUPTED;
                }

                buffer_nextp = xfs_buf_offset(bp, next_unlinked_offset);
                *buffer_nextp = *logged_nextp;

                /*
                 * If necessary, recalculate the CRC in the on-disk inode. We
                 * have to leave the inode in a consistent state for whoever
                 * reads it next....
                 */
                xfs_dinode_calc_crc(mp,
                                xfs_buf_offset(bp, i * mp->m_sb.sb_inodesize));

        }

        return 0;
}

/*
 * V5 filesystems know the age of the buffer on disk being recovered. We can
 * have newer objects on disk than we are replaying, and so for these cases we
 * don't want to replay the current change as that will make the buffer contents
 * temporarily invalid on disk.
 *
 * The magic number might not match the buffer type we are going to recover
 * (e.g. reallocated blocks), so we ignore the xfs_buf_log_format flags.  Hence
 * extract the LSN of the existing object in the buffer based on it's current
 * magic number.  If we don't recognise the magic number in the buffer, then
 * return a LSN of -1 so that the caller knows it was an unrecognised block and
 * so can recover the buffer.
 *
 * Note: we cannot rely solely on magic number matches to determine that the
 * buffer has a valid LSN - we also need to verify that it belongs to this
 * filesystem, so we need to extract the object's LSN and compare it to that
 * which we read from the superblock. If the UUIDs don't match, then we've got a
 * stale metadata block from an old filesystem instance that we need to recover
 * over the top of.
 */
static xfs_lsn_t
xlog_recover_get_buf_lsn(
        struct xfs_mount        *mp,
        struct xfs_buf          *bp)
{
        __uint32_t              magic32;
        __uint16_t              magic16;
        __uint16_t              magicda;
        void                    *blk = bp->b_addr;
        uuid_t                  *uuid;
        xfs_lsn_t               lsn = -1;

        /* v4 filesystems always recover immediately */
        if (!xfs_sb_version_hascrc(&mp->m_sb))
                goto recover_immediately;

        magic32 = be32_to_cpu(*(__be32 *)blk);
        switch (magic32) {
        case XFS_ABTB_CRC_MAGIC:
        case XFS_ABTC_CRC_MAGIC:
        case XFS_ABTB_MAGIC:
        case XFS_ABTC_MAGIC:
        case XFS_IBT_CRC_MAGIC:
        case XFS_IBT_MAGIC: {
                struct xfs_btree_block *btb = blk;

                lsn = be64_to_cpu(btb->bb_u.s.bb_lsn);
                uuid = &btb->bb_u.s.bb_uuid;
                break;
        }
        case XFS_BMAP_CRC_MAGIC:
        case XFS_BMAP_MAGIC: {
                struct xfs_btree_block *btb = blk;

                lsn = be64_to_cpu(btb->bb_u.l.bb_lsn);
                uuid = &btb->bb_u.l.bb_uuid;
                break;
        }
        case XFS_AGF_MAGIC:
                lsn = be64_to_cpu(((struct xfs_agf *)blk)->agf_lsn);
                uuid = &((struct xfs_agf *)blk)->agf_uuid;
                break;
        case XFS_AGFL_MAGIC:
                lsn = be64_to_cpu(((struct xfs_agfl *)blk)->agfl_lsn);
                uuid = &((struct xfs_agfl *)blk)->agfl_uuid;
                break;
        case XFS_AGI_MAGIC:
                lsn = be64_to_cpu(((struct xfs_agi *)blk)->agi_lsn);
                uuid = &((struct xfs_agi *)blk)->agi_uuid;
                break;
        case XFS_SYMLINK_MAGIC:
                lsn = be64_to_cpu(((struct xfs_dsymlink_hdr *)blk)->sl_lsn);
                uuid = &((struct xfs_dsymlink_hdr *)blk)->sl_uuid;
                break;
        case XFS_DIR3_BLOCK_MAGIC:
        case XFS_DIR3_DATA_MAGIC:
        case XFS_DIR3_FREE_MAGIC:
                lsn = be64_to_cpu(((struct xfs_dir3_blk_hdr *)blk)->lsn);
                uuid = &((struct xfs_dir3_blk_hdr *)blk)->uuid;
                break;
        case XFS_ATTR3_RMT_MAGIC:
                /*
                 * Remote attr blocks are written synchronously, rather than
                 * being logged. That means they do not contain a valid LSN
                 * (i.e. transactionally ordered) in them, and hence any time we
                 * see a buffer to replay over the top of a remote attribute
                 * block we should simply do so.
                 */
                goto recover_immediately;
        case XFS_SB_MAGIC:
                /*
                 * superblock uuids are magic. We may or may not have a
                 * sb_meta_uuid on disk, but it will be set in the in-core
                 * superblock. We set the uuid pointer for verification
                 * according to the superblock feature mask to ensure we check
                 * the relevant UUID in the superblock.
                 */
                lsn = be64_to_cpu(((struct xfs_dsb *)blk)->sb_lsn);
                if (xfs_sb_version_hasmetauuid(&mp->m_sb))
                        uuid = &((struct xfs_dsb *)blk)->sb_meta_uuid;
                else
                        uuid = &((struct xfs_dsb *)blk)->sb_uuid;
                break;
        default:
                break;
        }

        if (lsn != (xfs_lsn_t)-1) {
                if (!uuid_equal(&mp->m_sb.sb_meta_uuid, uuid))
                        goto recover_immediately;
                return lsn;
        }

        magicda = be16_to_cpu(((struct xfs_da_blkinfo *)blk)->magic);
        switch (magicda) {
        case XFS_DIR3_LEAF1_MAGIC:
        case XFS_DIR3_LEAFN_MAGIC:
        case XFS_DA3_NODE_MAGIC:
                lsn = be64_to_cpu(((struct xfs_da3_blkinfo *)blk)->lsn);
                uuid = &((struct xfs_da3_blkinfo *)blk)->uuid;
                break;
        default:
                break;
        }

        if (lsn != (xfs_lsn_t)-1) {
                if (!uuid_equal(&mp->m_sb.sb_uuid, uuid))
                        goto recover_immediately;
                return lsn;
        }

        /*
         * We do individual object checks on dquot and inode buffers as they
         * have their own individual LSN records. Also, we could have a stale
         * buffer here, so we have to at least recognise these buffer types.
         *
         * A notd complexity here is inode unlinked list processing - it logs
         * the inode directly in the buffer, but we don't know which inodes have
         * been modified, and there is no global buffer LSN. Hence we need to
         * recover all inode buffer types immediately. This problem will be
         * fixed by logical logging of the unlinked list modifications.
         */
        magic16 = be16_to_cpu(*(__be16 *)blk);
        switch (magic16) {
        case XFS_DQUOT_MAGIC:
        case XFS_DINODE_MAGIC:
                goto recover_immediately;
        default:
                break;
        }

        /* unknown buffer contents, recover immediately */

recover_immediately:
        return (xfs_lsn_t)-1;

}

/*
 * Validate the recovered buffer is of the correct type and attach the
 * appropriate buffer operations to them for writeback. Magic numbers are in a
 * few places:
 *      the first 16 bits of the buffer (inode buffer, dquot buffer),
 *      the first 32 bits of the buffer (most blocks),
 *      inside a struct xfs_da_blkinfo at the start of the buffer.
 */
static void
xlog_recover_validate_buf_type(
        struct xfs_mount        *mp,
        struct xfs_buf          *bp,
        xfs_buf_log_format_t    *buf_f)
{
        struct xfs_da_blkinfo   *info = bp->b_addr;
        __uint32_t              magic32;
        __uint16_t              magic16;
        __uint16_t              magicda;

        /*
         * We can only do post recovery validation on items on CRC enabled
         * fielsystems as we need to know when the buffer was written to be able
         * to determine if we should have replayed the item. If we replay old
         * metadata over a newer buffer, then it will enter a temporarily
         * inconsistent state resulting in verification failures. Hence for now
         * just avoid the verification stage for non-crc filesystems
         */
        if (!xfs_sb_version_hascrc(&mp->m_sb))
                return;

        magic32 = be32_to_cpu(*(__be32 *)bp->b_addr);
        magic16 = be16_to_cpu(*(__be16*)bp->b_addr);
        magicda = be16_to_cpu(info->magic);
        switch (xfs_blft_from_flags(buf_f)) {
        case XFS_BLFT_BTREE_BUF:
                switch (magic32) {
                case XFS_ABTB_CRC_MAGIC:
                case XFS_ABTC_CRC_MAGIC:
                case XFS_ABTB_MAGIC:
                case XFS_ABTC_MAGIC:
                        bp->b_ops = &xfs_allocbt_buf_ops;
                        break;
                case XFS_IBT_CRC_MAGIC:
                case XFS_FIBT_CRC_MAGIC:
                case XFS_IBT_MAGIC:
                case XFS_FIBT_MAGIC:
                        bp->b_ops = &xfs_inobt_buf_ops;
                        break;
                case XFS_BMAP_CRC_MAGIC:
                case XFS_BMAP_MAGIC:
                        bp->b_ops = &xfs_bmbt_buf_ops;
                        break;
                default:
                        xfs_warn(mp, "Bad btree block magic!");
                        ASSERT(0);
                        break;
                }
                break;
        case XFS_BLFT_AGF_BUF:
                if (magic32 != XFS_AGF_MAGIC) {
                        xfs_warn(mp, "Bad AGF block magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_agf_buf_ops;
                break;
        case XFS_BLFT_AGFL_BUF:
                if (magic32 != XFS_AGFL_MAGIC) {
                        xfs_warn(mp, "Bad AGFL block magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_agfl_buf_ops;
                break;
        case XFS_BLFT_AGI_BUF:
                if (magic32 != XFS_AGI_MAGIC) {
                        xfs_warn(mp, "Bad AGI block magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_agi_buf_ops;
                break;
        case XFS_BLFT_UDQUOT_BUF:
        case XFS_BLFT_PDQUOT_BUF:
        case XFS_BLFT_GDQUOT_BUF:
#ifdef CONFIG_XFS_QUOTA
                if (magic16 != XFS_DQUOT_MAGIC) {
                        xfs_warn(mp, "Bad DQUOT block magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_dquot_buf_ops;
#else
                xfs_alert(mp,
        "Trying to recover dquots without QUOTA support built in!");
                ASSERT(0);
#endif
                break;
        case XFS_BLFT_DINO_BUF:
                if (magic16 != XFS_DINODE_MAGIC) {
                        xfs_warn(mp, "Bad INODE block magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_inode_buf_ops;
                break;
        case XFS_BLFT_SYMLINK_BUF:
                if (magic32 != XFS_SYMLINK_MAGIC) {
                        xfs_warn(mp, "Bad symlink block magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_symlink_buf_ops;
                break;
        case XFS_BLFT_DIR_BLOCK_BUF:
                if (magic32 != XFS_DIR2_BLOCK_MAGIC &&
                    magic32 != XFS_DIR3_BLOCK_MAGIC) {
                        xfs_warn(mp, "Bad dir block magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_dir3_block_buf_ops;
                break;
        case XFS_BLFT_DIR_DATA_BUF:
                if (magic32 != XFS_DIR2_DATA_MAGIC &&
                    magic32 != XFS_DIR3_DATA_MAGIC) {
                        xfs_warn(mp, "Bad dir data magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_dir3_data_buf_ops;
                break;
        case XFS_BLFT_DIR_FREE_BUF:
                if (magic32 != XFS_DIR2_FREE_MAGIC &&
                    magic32 != XFS_DIR3_FREE_MAGIC) {
                        xfs_warn(mp, "Bad dir3 free magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_dir3_free_buf_ops;
                break;
        case XFS_BLFT_DIR_LEAF1_BUF:
                if (magicda != XFS_DIR2_LEAF1_MAGIC &&
                    magicda != XFS_DIR3_LEAF1_MAGIC) {
                        xfs_warn(mp, "Bad dir leaf1 magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_dir3_leaf1_buf_ops;
                break;
        case XFS_BLFT_DIR_LEAFN_BUF:
                if (magicda != XFS_DIR2_LEAFN_MAGIC &&
                    magicda != XFS_DIR3_LEAFN_MAGIC) {
                        xfs_warn(mp, "Bad dir leafn magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_dir3_leafn_buf_ops;
                break;
        case XFS_BLFT_DA_NODE_BUF:
                if (magicda != XFS_DA_NODE_MAGIC &&
                    magicda != XFS_DA3_NODE_MAGIC) {
                        xfs_warn(mp, "Bad da node magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_da3_node_buf_ops;
                break;
        case XFS_BLFT_ATTR_LEAF_BUF:
                if (magicda != XFS_ATTR_LEAF_MAGIC &&
                    magicda != XFS_ATTR3_LEAF_MAGIC) {
                        xfs_warn(mp, "Bad attr leaf magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_attr3_leaf_buf_ops;
                break;
        case XFS_BLFT_ATTR_RMT_BUF:
                if (magic32 != XFS_ATTR3_RMT_MAGIC) {
                        xfs_warn(mp, "Bad attr remote magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_attr3_rmt_buf_ops;
                break;
        case XFS_BLFT_SB_BUF:
                if (magic32 != XFS_SB_MAGIC) {
                        xfs_warn(mp, "Bad SB block magic!");
                        ASSERT(0);
                        break;
                }
                bp->b_ops = &xfs_sb_buf_ops;
                break;
        default:
                xfs_warn(mp, "Unknown buffer type %d!",
                         xfs_blft_from_flags(buf_f));
                break;
        }
}

/*
 * Perform a 'normal' buffer recovery.  Each logged region of the
 * buffer should be copied over the corresponding region in the
 * given buffer.  The bitmap in the buf log format structure indicates
 * where to place the logged data.
 */
STATIC void
xlog_recover_do_reg_buffer(
        struct xfs_mount        *mp,
        xlog_recover_item_t     *item,
        struct xfs_buf          *bp,
        xfs_buf_log_format_t    *buf_f)
{
        int                     i;
        int                     bit;
        int                     nbits;
        int                     error;

        trace_xfs_log_recover_buf_reg_buf(mp->m_log, buf_f);

        bit = 0;
        i = 1;  /* 0 is the buf format structure */
        while (1) {
                bit = xfs_next_bit(buf_f->blf_data_map,
                                   buf_f->blf_map_size, bit);
                if (bit == -1)
                        break;
                nbits = xfs_contig_bits(buf_f->blf_data_map,
                                        buf_f->blf_map_size, bit);
                ASSERT(nbits > 0);
                ASSERT(item->ri_buf[i].i_addr != NULL);
                ASSERT(item->ri_buf[i].i_len % XFS_BLF_CHUNK == 0);
                ASSERT(BBTOB(bp->b_io_length) >=
                       ((uint)bit << XFS_BLF_SHIFT) + (nbits << XFS_BLF_SHIFT));

                /*
                 * The dirty regions logged in the buffer, even though
                 * contiguous, may span multiple chunks. This is because the
                 * dirty region may span a physical page boundary in a buffer
                 * and hence be split into two separate vectors for writing into
                 * the log. Hence we need to trim nbits back to the length of
                 * the current region being copied out of the log.
                 */
                if (item->ri_buf[i].i_len < (nbits << XFS_BLF_SHIFT))
                        nbits = item->ri_buf[i].i_len >> XFS_BLF_SHIFT;

                /*
                 * Do a sanity check if this is a dquot buffer. Just checking
                 * the first dquot in the buffer should do. XXXThis is
                 * probably a good thing to do for other buf types also.
                 */
                error = 0;
                if (buf_f->blf_flags &
                   (XFS_BLF_UDQUOT_BUF|XFS_BLF_PDQUOT_BUF|XFS_BLF_GDQUOT_BUF)) {
                        if (item->ri_buf[i].i_addr == NULL) {
                                xfs_alert(mp,
                                        "XFS: NULL dquot in %s.", __func__);
                                goto next;
                        }
                        if (item->ri_buf[i].i_len < sizeof(xfs_disk_dquot_t)) {
                                xfs_alert(mp,
                                        "XFS: dquot too small (%d) in %s.",
                                        item->ri_buf[i].i_len, __func__);
                                goto next;
                        }
                        error = xfs_dqcheck(mp, item->ri_buf[i].i_addr,
                                               -1, 0, XFS_QMOPT_DOWARN,
                                               "dquot_buf_recover");
                        if (error)
                                goto next;
                }

                memcpy(xfs_buf_offset(bp,
                        (uint)bit << XFS_BLF_SHIFT),    /* dest */
                        item->ri_buf[i].i_addr,         /* source */
                        nbits<<XFS_BLF_SHIFT);          /* length */
 next:
                i++;
                bit += nbits;
        }

        /* Shouldn't be any more regions */
        ASSERT(i == item->ri_total);

        xlog_recover_validate_buf_type(mp, bp, buf_f);
}

/*
 * Perform a dquot buffer recovery.
 * Simple algorithm: if we have found a QUOTAOFF log item of the same type
 * (ie. USR or GRP), then just toss this buffer away; don't recover it.
 * Else, treat it as a regular buffer and do recovery.
 *
 * Return false if the buffer was tossed and true if we recovered the buffer to
 * indicate to the caller if the buffer needs writing.
 */
STATIC bool
xlog_recover_do_dquot_buffer(
        struct xfs_mount                *mp,
        struct xlog                     *log,
        struct xlog_recover_item        *item,
        struct xfs_buf                  *bp,
        struct xfs_buf_log_format       *buf_f)
{
        uint                    type;

        trace_xfs_log_recover_buf_dquot_buf(log, buf_f);

        /*
         * Filesystems are required to send in quota flags at mount time.
         */
        if (!mp->m_qflags)
                return false;

        type = 0;
        if (buf_f->blf_flags & XFS_BLF_UDQUOT_BUF)
                type |= XFS_DQ_USER;
        if (buf_f->blf_flags & XFS_BLF_PDQUOT_BUF)
                type |= XFS_DQ_PROJ;
        if (buf_f->blf_flags & XFS_BLF_GDQUOT_BUF)
                type |= XFS_DQ_GROUP;
        /*
         * This type of quotas was turned off, so ignore this buffer
         */
        if (log->l_quotaoffs_flag & type)
                return false;

        xlog_recover_do_reg_buffer(mp, item, bp, buf_f);
        return true;
}

/*
 * This routine replays a modification made to a buffer at runtime.
 * There are actually two types of buffer, regular and inode, which
 * are handled differently.  Inode buffers are handled differently
 * in that we only recover a specific set of data from them, namely
 * the inode di_next_unlinked fields.  This is because all other inode
 * data is actually logged via inode records and any data we replay
 * here which overlaps that may be stale.
 *
 * When meta-data buffers are freed at run time we log a buffer item
 * with the XFS_BLF_CANCEL bit set to indicate that previous copies
 * of the buffer in the log should not be replayed at recovery time.
 * This is so that if the blocks covered by the buffer are reused for
 * file data before we crash we don't end up replaying old, freed
 * meta-data into a user's file.
 *
 * To handle the cancellation of buffer log items, we make two passes
 * over the log during recovery.  During the first we build a table of
 * those buffers which have been cancelled, and during the second we
 * only replay those buffers which do not have corresponding cancel
 * records in the table.  See xlog_recover_buffer_pass[1,2] above
 * for more details on the implementation of the table of cancel records.
 */
STATIC int
xlog_recover_buffer_pass2(
        struct xlog                     *log,
        struct list_head                *buffer_list,
        struct xlog_recover_item        *item,
        xfs_lsn_t                       current_lsn)
{
        xfs_buf_log_format_t    *buf_f = item->ri_buf[0].i_addr;
        xfs_mount_t             *mp = log->l_mp;
        xfs_buf_t               *bp;
        int                     error;
        uint                    buf_flags;
        xfs_lsn_t               lsn;

        /*
         * In this pass we only want to recover all the buffers which have
         * not been cancelled and are not cancellation buffers themselves.
         */
        if (xlog_check_buffer_cancelled(log, buf_f->blf_blkno,
                        buf_f->blf_len, buf_f->blf_flags)) {
                trace_xfs_log_recover_buf_cancel(log, buf_f);
                return 0;
        }

        trace_xfs_log_recover_buf_recover(log, buf_f);

        buf_flags = 0;
        if (buf_f->blf_flags & XFS_BLF_INODE_BUF)
                buf_flags |= XBF_UNMAPPED;

        bp = xfs_buf_read(mp->m_ddev_targp, buf_f->blf_blkno, buf_f->blf_len,
                          buf_flags, NULL);
        if (!bp)
                return -ENOMEM;
        error = bp->b_error;
        if (error) {
                xfs_buf_ioerror_alert(bp, "xlog_recover_do..(read#1)");
                goto out_release;
        }

        /*
         * Recover the buffer only if we get an LSN from it and it's less than
         * the lsn of the transaction we are replaying.
         *
         * Note that we have to be extremely careful of readahead here.
         * Readahead does not attach verfiers to the buffers so if we don't
         * actually do any replay after readahead because of the LSN we found
         * in the buffer if more recent than that current transaction then we
         * need to attach the verifier directly. Failure to do so can lead to
         * future recovery actions (e.g. EFI and unlinked list recovery) can
         * operate on the buffers and they won't get the verifier attached. This
         * can lead to blocks on disk having the correct content but a stale
         * CRC.
         *
         * It is safe to assume these clean buffers are currently up to date.
         * If the buffer is dirtied by a later transaction being replayed, then
         * the verifier will be reset to match whatever recover turns that
         * buffer into.
         */
        lsn = xlog_recover_get_buf_lsn(mp, bp);
        if (lsn && lsn != -1 && XFS_LSN_CMP(lsn, current_lsn) >= 0) {
                xlog_recover_validate_buf_type(mp, bp, buf_f);
                goto out_release;
        }

        if (buf_f->blf_flags & XFS_BLF_INODE_BUF) {
                error = xlog_recover_do_inode_buffer(mp, item, bp, buf_f);
                if (error)
                        goto out_release;
        } else if (buf_f->blf_flags &
                  (XFS_BLF_UDQUOT_BUF|XFS_BLF_PDQUOT_BUF|XFS_BLF_GDQUOT_BUF)) {
                bool    dirty;

                dirty = xlog_recover_do_dquot_buffer(mp, log, item, bp, buf_f);
                if (!dirty)
                        goto out_release;
        } else {
                xlog_recover_do_reg_buffer(mp, item, bp, buf_f);
        }

        /*
         * Perform delayed write on the buffer.  Asynchronous writes will be
         * slower when taking into account all the buffers to be flushed.
         *
         * Also make sure that only inode buffers with good sizes stay in
         * the buffer cache.  The kernel moves inodes in buffers of 1 block
         * or mp->m_inode_cluster_size bytes, whichever is bigger.  The inode
         * buffers in the log can be a different size if the log was generated
         * by an older kernel using unclustered inode buffers or a newer kernel
         * running with a different inode cluster size.  Regardless, if the
         * the inode buffer size isn't MAX(blocksize, mp->m_inode_cluster_size)
         * for *our* value of mp->m_inode_cluster_size, then we need to keep
         * the buffer out of the buffer cache so that the buffer won't
         * overlap with future reads of those inodes.
         */
        if (XFS_DINODE_MAGIC ==
            be16_to_cpu(*((__be16 *)xfs_buf_offset(bp, 0))) &&
            (BBTOB(bp->b_io_length) != MAX(log->l_mp->m_sb.sb_blocksize,
                        (__uint32_t)log->l_mp->m_inode_cluster_size))) {
                xfs_buf_stale(bp);
                error = xfs_bwrite(bp);
        } else {
                ASSERT(bp->b_target->bt_mount == mp);
                bp->b_iodone = xlog_recover_iodone;
                xfs_buf_delwri_queue(bp, buffer_list);
        }

out_release:
        xfs_buf_relse(bp);
        return error;
}

/*
 * Inode fork owner changes
 *
 * If we have been told that we have to reparent the inode fork, it's because an
 * extent swap operation on a CRC enabled filesystem has been done and we are
 * replaying it. We need to walk the BMBT of the appropriate fork and change the
 * owners of it.
 *
 * The complexity here is that we don't have an inode context to work with, so
 * after we've replayed the inode we need to instantiate one.  This is where the
 * fun begins.
 *
 * We are in the middle of log recovery, so we can't run transactions. That
 * means we cannot use cache coherent inode instantiation via xfs_iget(), as
 * that will result in the corresponding iput() running the inode through
 * xfs_inactive(). If we've just replayed an inode core that changes the link
 * count to zero (i.e. it's been unlinked), then xfs_inactive() will run
 * transactions (bad!).
 *
 * So, to avoid this, we instantiate an inode directly from the inode core we've
 * just recovered. We have the buffer still locked, and all we really need to
 * instantiate is the inode core and the forks being modified. We can do this
 * manually, then run the inode btree owner change, and then tear down the
 * xfs_inode without having to run any transactions at all.
 *
 * Also, because we don't have a transaction context available here but need to
 * gather all the buffers we modify for writeback so we pass the buffer_list
 * instead for the operation to use.
 */

STATIC int
xfs_recover_inode_owner_change(
        struct xfs_mount        *mp,
        struct xfs_dinode       *dip,
        struct xfs_inode_log_format *in_f,
        struct list_head        *buffer_list)
{
        struct xfs_inode        *ip;
        int                     error;

        ASSERT(in_f->ilf_fields & (XFS_ILOG_DOWNER|XFS_ILOG_AOWNER));

        ip = xfs_inode_alloc(mp, in_f->ilf_ino);
        if (!ip)
                return -ENOMEM;

        /* instantiate the inode */
        xfs_dinode_from_disk(&ip->i_d, dip);
        ASSERT(ip->i_d.di_version >= 3);

        error = xfs_iformat_fork(ip, dip);
        if (error)
                goto out_free_ip;


        if (in_f->ilf_fields & XFS_ILOG_DOWNER) {
                ASSERT(in_f->ilf_fields & XFS_ILOG_DBROOT);
                error = xfs_bmbt_change_owner(NULL, ip, XFS_DATA_FORK,
                                              ip->i_ino, buffer_list);
                if (error)
                        goto out_free_ip;
        }

        if (in_f->ilf_fields & XFS_ILOG_AOWNER) {
                ASSERT(in_f->ilf_fields & XFS_ILOG_ABROOT);
                error = xfs_bmbt_change_owner(NULL, ip, XFS_ATTR_FORK,
                                              ip->i_ino, buffer_list);
                if (error)
                        goto out_free_ip;
        }

out_free_ip:
        xfs_inode_free(ip);
        return error;
}

STATIC int
xlog_recover_inode_pass2(
        struct xlog                     *log,
        struct list_head                *buffer_list,
        struct xlog_recover_item        *item,
        xfs_lsn_t                       current_lsn)
{
        xfs_inode_log_format_t  *in_f;
        xfs_mount_t             *mp = log->l_mp;
        xfs_buf_t               *bp;
        xfs_dinode_t            *dip;
        int                     len;
        char                    *src;
        char                    *dest;
        int                     error;
        int                     attr_index;
        uint                    fields;
        xfs_icdinode_t          *dicp;
        uint                    isize;
        int                     need_free = 0;

        if (item->ri_buf[0].i_len == sizeof(xfs_inode_log_format_t)) {
                in_f = item->ri_buf[0].i_addr;
        } else {
                in_f = kmem_alloc(sizeof(xfs_inode_log_format_t), KM_SLEEP);
                need_free = 1;
                error = xfs_inode_item_format_convert(&item->ri_buf[0], in_f);
                if (error)
                        goto error;
        }

        /*
         * Inode buffers can be freed, look out for it,
         * and do not replay the inode.
         */
        if (xlog_check_buffer_cancelled(log, in_f->ilf_blkno,
                                        in_f->ilf_len, 0)) {
                error = 0;
                trace_xfs_log_recover_inode_cancel(log, in_f);
                goto error;
        }
        trace_xfs_log_recover_inode_recover(log, in_f);

        bp = xfs_buf_read(mp->m_ddev_targp, in_f->ilf_blkno, in_f->ilf_len, 0,
                          &xfs_inode_buf_ops);
        if (!bp) {
                error = -ENOMEM;
                goto error;
        }
        error = bp->b_error;
        if (error) {
                xfs_buf_ioerror_alert(bp, "xlog_recover_do..(read#2)");
                goto out_release;
        }
        ASSERT(in_f->ilf_fields & XFS_ILOG_CORE);
        dip = xfs_buf_offset(bp, in_f->ilf_boffset);

        /*
         * Make sure the place we're flushing out to really looks
         * like an inode!
         */
        if (unlikely(dip->di_magic != cpu_to_be16(XFS_DINODE_MAGIC))) {
                xfs_alert(mp,
        "%s: Bad inode magic number, dip = 0x%p, dino bp = 0x%p, ino = %Ld",
                        __func__, dip, bp, in_f->ilf_ino);
                XFS_ERROR_REPORT("xlog_recover_inode_pass2(1)",
                                 XFS_ERRLEVEL_LOW, mp);
                error = -EFSCORRUPTED;
                goto out_release;
        }
        dicp = item->ri_buf[1].i_addr;
        if (unlikely(dicp->di_magic != XFS_DINODE_MAGIC)) {
                xfs_alert(mp,
                        "%s: Bad inode log record, rec ptr 0x%p, ino %Ld",
                        __func__, item, in_f->ilf_ino);
                XFS_ERROR_REPORT("xlog_recover_inode_pass2(2)",
                                 XFS_ERRLEVEL_LOW, mp);
                error = -EFSCORRUPTED;
                goto out_release;
        }

        /*
         * If the inode has an LSN in it, recover the inode only if it's less
         * than the lsn of the transaction we are replaying. Note: we still
         * need to replay an owner change even though the inode is more recent
         * than the transaction as there is no guarantee that all the btree
         * blocks are more recent than this transaction, too.
         */
        if (dip->di_version >= 3) {
                xfs_lsn_t       lsn = be64_to_cpu(dip->di_lsn);

                if (lsn && lsn != -1 && XFS_LSN_CMP(lsn, current_lsn) >= 0) {
                        trace_xfs_log_recover_inode_skip(log, in_f);
                        error = 0;
                        goto out_owner_change;
                }
        }

        /*
         * di_flushiter is only valid for v1/2 inodes. All changes for v3 inodes
         * are transactional and if ordering is necessary we can determine that
         * more accurately by the LSN field in the V3 inode core. Don't trust
         * the inode versions we might be changing them here - use the
         * superblock flag to determine whether we need to look at di_flushiter
         * to skip replay when the on disk inode is newer than the log one
         */
        if (!xfs_sb_version_hascrc(&mp->m_sb) &&
            dicp->di_flushiter < be16_to_cpu(dip->di_flushiter)) {
                /*
                 * Deal with the wrap case, DI_MAX_FLUSH is less
                 * than smaller numbers
                 */
                if (be16_to_cpu(dip->di_flushiter) == DI_MAX_FLUSH &&
                    dicp->di_flushiter < (DI_MAX_FLUSH >> 1)) {
                        /* do nothing */
                } else {
                        trace_xfs_log_recover_inode_skip(log, in_f);
                        error = 0;
                        goto out_release;
                }
        }

        /* Take the opportunity to reset the flush iteration count */
        dicp->di_flushiter = 0;

        if (unlikely(S_ISREG(dicp->di_mode))) {
                if ((dicp->di_format != XFS_DINODE_FMT_EXTENTS) &&
                    (dicp->di_format != XFS_DINODE_FMT_BTREE)) {
                        XFS_CORRUPTION_ERROR("xlog_recover_inode_pass2(3)",
                                         XFS_ERRLEVEL_LOW, mp, dicp);
                        xfs_alert(mp,
                "%s: Bad regular inode log record, rec ptr 0x%p, "
                "ino ptr = 0x%p, ino bp = 0x%p, ino %Ld",
                                __func__, item, dip, bp, in_f->ilf_ino);
                        error = -EFSCORRUPTED;
                        goto out_release;
                }
        } else if (unlikely(S_ISDIR(dicp->di_mode))) {
                if ((dicp->di_format != XFS_DINODE_FMT_EXTENTS) &&
                    (dicp->di_format != XFS_DINODE_FMT_BTREE) &&
                    (dicp->di_format != XFS_DINODE_FMT_LOCAL)) {
                        XFS_CORRUPTION_ERROR("xlog_recover_inode_pass2(4)",
                                             XFS_ERRLEVEL_LOW, mp, dicp);
                        xfs_alert(mp,
                "%s: Bad dir inode log record, rec ptr 0x%p, "
                "ino ptr = 0x%p, ino bp = 0x%p, ino %Ld",
                                __func__, item, dip, bp, in_f->ilf_ino);
                        error = -EFSCORRUPTED;
                        goto out_release;
                }
        }
        if (unlikely(dicp->di_nextents + dicp->di_anextents > dicp->di_nblocks)){
                XFS_CORRUPTION_ERROR("xlog_recover_inode_pass2(5)",
                                     XFS_ERRLEVEL_LOW, mp, dicp);
                xfs_alert(mp,
        "%s: Bad inode log record, rec ptr 0x%p, dino ptr 0x%p, "
        "dino bp 0x%p, ino %Ld, total extents = %d, nblocks = %Ld",
                        __func__, item, dip, bp, in_f->ilf_ino,
                        dicp->di_nextents + dicp->di_anextents,
                        dicp->di_nblocks);
                error = -EFSCORRUPTED;
                goto out_release;
        }
        if (unlikely(dicp->di_forkoff > mp->m_sb.sb_inodesize)) {
                XFS_CORRUPTION_ERROR("xlog_recover_inode_pass2(6)",
                                     XFS_ERRLEVEL_LOW, mp, dicp);
                xfs_alert(mp,
        "%s: Bad inode log record, rec ptr 0x%p, dino ptr 0x%p, "
        "dino bp 0x%p, ino %Ld, forkoff 0x%x", __func__,
                        item, dip, bp, in_f->ilf_ino, dicp->di_forkoff);
                error = -EFSCORRUPTED;
                goto out_release;
        }
        isize = xfs_icdinode_size(dicp->di_version);
        if (unlikely(item->ri_buf[1].i_len > isize)) {
                XFS_CORRUPTION_ERROR("xlog_recover_inode_pass2(7)",
                                     XFS_ERRLEVEL_LOW, mp, dicp);
                xfs_alert(mp,
                        "%s: Bad inode log record length %d, rec ptr 0x%p",
                        __func__, item->ri_buf[1].i_len, item);
                error = -EFSCORRUPTED;
                goto out_release;
        }

        /* The core is in in-core format */
        xfs_dinode_to_disk(dip, dicp);

        /* the rest is in on-disk format */
        if (item->ri_buf[1].i_len > isize) {
                memcpy((char *)dip + isize,
                        item->ri_buf[1].i_addr + isize,
                        item->ri_buf[1].i_len - isize);
        }

        fields = in_f->ilf_fields;
        switch (fields & (XFS_ILOG_DEV | XFS_ILOG_UUID)) {
        case XFS_ILOG_DEV:
                xfs_dinode_put_rdev(dip, in_f->ilf_u.ilfu_rdev);
                break;
        case XFS_ILOG_UUID:
                memcpy(XFS_DFORK_DPTR(dip),
                       &in_f->ilf_u.ilfu_uuid,
                       sizeof(uuid_t));
                break;
        }

        if (in_f->ilf_size == 2)
                goto out_owner_change;
        len = item->ri_buf[2].i_len;
        src = item->ri_buf[2].i_addr;
        ASSERT(in_f->ilf_size <= 4);
        ASSERT((in_f->ilf_size == 3) || (fields & XFS_ILOG_AFORK));
        ASSERT(!(fields & XFS_ILOG_DFORK) ||
               (len == in_f->ilf_dsize));

        switch (fields & XFS_ILOG_DFORK) {
        case XFS_ILOG_DDATA:
        case XFS_ILOG_DEXT:
                memcpy(XFS_DFORK_DPTR(dip), src, len);
                break;

        case XFS_ILOG_DBROOT:
                xfs_bmbt_to_bmdr(mp, (struct xfs_btree_block *)src, len,
                                 (xfs_bmdr_block_t *)XFS_DFORK_DPTR(dip),
                                 XFS_DFORK_DSIZE(dip, mp));
                break;

        default:
                /*
                 * There are no data fork flags set.
                 */
                ASSERT((fields & XFS_ILOG_DFORK) == 0);
                break;
        }

        /*
         * If we logged any attribute data, recover it.  There may or
         * may not have been any other non-core data logged in this
         * transaction.
         */
        if (in_f->ilf_fields & XFS_ILOG_AFORK) {
                if (in_f->ilf_fields & XFS_ILOG_DFORK) {
                        attr_index = 3;
                } else {
                        attr_index = 2;
                }
                len = item->ri_buf[attr_index].i_len;
                src = item->ri_buf[attr_index].i_addr;
                ASSERT(len == in_f->ilf_asize);

                switch (in_f->ilf_fields & XFS_ILOG_AFORK) {
                case XFS_ILOG_ADATA:
                case XFS_ILOG_AEXT:
                        dest = XFS_DFORK_APTR(dip);
                        ASSERT(len <= XFS_DFORK_ASIZE(dip, mp));
                        memcpy(dest, src, len);
                        break;

                case XFS_ILOG_ABROOT:
                        dest = XFS_DFORK_APTR(dip);
                        xfs_bmbt_to_bmdr(mp, (struct xfs_btree_block *)src,
                                         len, (xfs_bmdr_block_t*)dest,
                                         XFS_DFORK_ASIZE(dip, mp));
                        break;

                default:
                        xfs_warn(log->l_mp, "%s: Invalid flag", __func__);
                        ASSERT(0);
                        error = -EIO;
                        goto out_release;
                }
        }

out_owner_change:
        if (in_f->ilf_fields & (XFS_ILOG_DOWNER|XFS_ILOG_AOWNER))
                error = xfs_recover_inode_owner_change(mp, dip, in_f,
                                                       buffer_list);
        /* re-generate the checksum. */
        xfs_dinode_calc_crc(log->l_mp, dip);

        ASSERT(bp->b_target->bt_mount == mp);
        bp->b_iodone = xlog_recover_iodone;
        xfs_buf_delwri_queue(bp, buffer_list);

out_release:
        xfs_buf_relse(bp);
error:
        if (need_free)
                kmem_free(in_f);
        return error;
}

/*
 * Recover QUOTAOFF records. We simply make a note of it in the xlog
 * structure, so that we know not to do any dquot item or dquot buffer recovery,
 * of that type.
 */
STATIC int
xlog_recover_quotaoff_pass1(
        struct xlog                     *log,
        struct xlog_recover_item        *item)
{
        xfs_qoff_logformat_t    *qoff_f = item->ri_buf[0].i_addr;
        ASSERT(qoff_f);

        /*
         * The logitem format's flag tells us if this was user quotaoff,
         * group/project quotaoff or both.
         */
        if (qoff_f->qf_flags & XFS_UQUOTA_ACCT)
                log->l_quotaoffs_flag |= XFS_DQ_USER;
        if (qoff_f->qf_flags & XFS_PQUOTA_ACCT)
                log->l_quotaoffs_flag |= XFS_DQ_PROJ;
        if (qoff_f->qf_flags & XFS_GQUOTA_ACCT)
                log->l_quotaoffs_flag |= XFS_DQ_GROUP;

        return 0;
}

/*
 * Recover a dquot record
 */
STATIC int
xlog_recover_dquot_pass2(
        struct xlog                     *log,
        struct list_head                *buffer_list,
        struct xlog_recover_item        *item,
        xfs_lsn_t                       current_lsn)
{
        xfs_mount_t             *mp = log->l_mp;
        xfs_buf_t               *bp;
        struct xfs_disk_dquot   *ddq, *recddq;
        int                     error;
        xfs_dq_logformat_t      *dq_f;
        uint                    type;


        /*
         * Filesystems are required to send in quota flags at mount time.
         */
        if (mp->m_qflags == 0)
                return 0;

        recddq = item->ri_buf[1].i_addr;
        if (recddq == NULL) {
                xfs_alert(log->l_mp, "NULL dquot in %s.", __func__);
                return -EIO;
        }
        if (item->ri_buf[1].i_len < sizeof(xfs_disk_dquot_t)) {
                xfs_alert(log->l_mp, "dquot too small (%d) in %s.",
                        item->ri_buf[1].i_len, __func__);
                return -EIO;
        }

        /*
         * This type of quotas was turned off, so ignore this record.
         */
        type = recddq->d_flags & (XFS_DQ_USER | XFS_DQ_PROJ | XFS_DQ_GROUP);
        ASSERT(type);
        if (log->l_quotaoffs_flag & type)
                return 0;

        /*
         * At this point we know that quota was _not_ turned off.
         * Since the mount flags are not indicating to us otherwise, this
         * must mean that quota is on, and the dquot needs to be replayed.
         * Remember that we may not have fully recovered the superblock yet,
         * so we can't do the usual trick of looking at the SB quota bits.
         *
         * The other possibility, of course, is that the quota subsystem was
         * removed since the last mount - ENOSYS.
         */
        dq_f = item->ri_buf[0].i_addr;
        ASSERT(dq_f);
        error = xfs_dqcheck(mp, recddq, dq_f->qlf_id, 0, XFS_QMOPT_DOWARN,
                           "xlog_recover_dquot_pass2 (log copy)");
        if (error)
                return -EIO;
        ASSERT(dq_f->qlf_len == 1);

        /*
         * At this point we are assuming that the dquots have been allocated
         * and hence the buffer has valid dquots stamped in it. It should,
         * therefore, pass verifier validation. If the dquot is bad, then the
         * we'll return an error here, so we don't need to specifically check
         * the dquot in the buffer after the verifier has run.
         */
        error = xfs_trans_read_buf(mp, NULL, mp->m_ddev_targp, dq_f->qlf_blkno,
                                   XFS_FSB_TO_BB(mp, dq_f->qlf_len), 0, &bp,
                                   &xfs_dquot_buf_ops);
        if (error)
                return error;

        ASSERT(bp);
        ddq = xfs_buf_offset(bp, dq_f->qlf_boffset);

        /*
         * If the dquot has an LSN in it, recover the dquot only if it's less
         * than the lsn of the transaction we are replaying.
         */
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                struct xfs_dqblk *dqb = (struct xfs_dqblk *)ddq;
                xfs_lsn_t       lsn = be64_to_cpu(dqb->dd_lsn);

                if (lsn && lsn != -1 && XFS_LSN_CMP(lsn, current_lsn) >= 0) {
                        goto out_release;
                }
        }

        memcpy(ddq, recddq, item->ri_buf[1].i_len);
        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                xfs_update_cksum((char *)ddq, sizeof(struct xfs_dqblk),
                                 XFS_DQUOT_CRC_OFF);
        }

        ASSERT(dq_f->qlf_size == 2);
        ASSERT(bp->b_target->bt_mount == mp);
        bp->b_iodone = xlog_recover_iodone;
        xfs_buf_delwri_queue(bp, buffer_list);

out_release:
        xfs_buf_relse(bp);
        return 0;
}

/*
 * This routine is called to create an in-core extent free intent
 * item from the efi format structure which was logged on disk.
 * It allocates an in-core efi, copies the extents from the format
 * structure into it, and adds the efi to the AIL with the given
 * LSN.
 */
STATIC int
xlog_recover_efi_pass2(
        struct xlog                     *log,
        struct xlog_recover_item        *item,
        xfs_lsn_t                       lsn)
{
        int                             error;
        struct xfs_mount                *mp = log->l_mp;
        struct xfs_efi_log_item         *efip;
        struct xfs_efi_log_format       *efi_formatp;

        efi_formatp = item->ri_buf[0].i_addr;

        efip = xfs_efi_init(mp, efi_formatp->efi_nextents);
        error = xfs_efi_copy_format(&item->ri_buf[0], &efip->efi_format);
        if (error) {
                xfs_efi_item_free(efip);
                return error;
        }
        atomic_set(&efip->efi_next_extent, efi_formatp->efi_nextents);

        spin_lock(&log->l_ailp->xa_lock);
        /*
         * The EFI has two references. One for the EFD and one for EFI to ensure
         * it makes it into the AIL. Insert the EFI into the AIL directly and
         * drop the EFI reference. Note that xfs_trans_ail_update() drops the
         * AIL lock.
         */
        xfs_trans_ail_update(log->l_ailp, &efip->efi_item, lsn);
        xfs_efi_release(efip);
        return 0;
}


/*
 * This routine is called when an EFD format structure is found in a committed
 * transaction in the log. Its purpose is to cancel the corresponding EFI if it
 * was still in the log. To do this it searches the AIL for the EFI with an id
 * equal to that in the EFD format structure. If we find it we drop the EFD
 * reference, which removes the EFI from the AIL and frees it.
 */
STATIC int
xlog_recover_efd_pass2(
        struct xlog                     *log,
        struct xlog_recover_item        *item)
{
        xfs_efd_log_format_t    *efd_formatp;
        xfs_efi_log_item_t      *efip = NULL;
        xfs_log_item_t          *lip;
        __uint64_t              efi_id;
        struct xfs_ail_cursor   cur;
        struct xfs_ail          *ailp = log->l_ailp;

        efd_formatp = item->ri_buf[0].i_addr;
        ASSERT((item->ri_buf[0].i_len == (sizeof(xfs_efd_log_format_32_t) +
                ((efd_formatp->efd_nextents - 1) * sizeof(xfs_extent_32_t)))) ||
               (item->ri_buf[0].i_len == (sizeof(xfs_efd_log_format_64_t) +
                ((efd_formatp->efd_nextents - 1) * sizeof(xfs_extent_64_t)))));
        efi_id = efd_formatp->efd_efi_id;

        /*
         * Search for the EFI with the id in the EFD format structure in the
         * AIL.
         */
        spin_lock(&ailp->xa_lock);
        lip = xfs_trans_ail_cursor_first(ailp, &cur, 0);
        while (lip != NULL) {
                if (lip->li_type == XFS_LI_EFI) {
                        efip = (xfs_efi_log_item_t *)lip;
                        if (efip->efi_format.efi_id == efi_id) {
                                /*
                                 * Drop the EFD reference to the EFI. This
                                 * removes the EFI from the AIL and frees it.
                                 */
                                spin_unlock(&ailp->xa_lock);
                                xfs_efi_release(efip);
                                spin_lock(&ailp->xa_lock);
                                break;
                        }
                }
                lip = xfs_trans_ail_cursor_next(ailp, &cur);
        }

        xfs_trans_ail_cursor_done(&cur);
        spin_unlock(&ailp->xa_lock);

        return 0;
}

/*
 * This routine is called when an inode create format structure is found in a
 * committed transaction in the log.  It's purpose is to initialise the inodes
 * being allocated on disk. This requires us to get inode cluster buffers that
 * match the range to be intialised, stamped with inode templates and written
 * by delayed write so that subsequent modifications will hit the cached buffer
 * and only need writing out at the end of recovery.
 */
STATIC int
xlog_recover_do_icreate_pass2(
        struct xlog             *log,
        struct list_head        *buffer_list,
        xlog_recover_item_t     *item)
{
        struct xfs_mount        *mp = log->l_mp;
        struct xfs_icreate_log  *icl;
        xfs_agnumber_t          agno;
        xfs_agblock_t           agbno;
        unsigned int            count;
        unsigned int            isize;
        xfs_agblock_t           length;
        int                     blks_per_cluster;
        int                     bb_per_cluster;
        int                     cancel_count;
        int                     nbufs;
        int                     i;

        icl = (struct xfs_icreate_log *)item->ri_buf[0].i_addr;
        if (icl->icl_type != XFS_LI_ICREATE) {
                xfs_warn(log->l_mp, "xlog_recover_do_icreate_trans: bad type");
                return -EINVAL;
        }

        if (icl->icl_size != 1) {
                xfs_warn(log->l_mp, "xlog_recover_do_icreate_trans: bad icl size");
                return -EINVAL;
        }

        agno = be32_to_cpu(icl->icl_ag);
        if (agno >= mp->m_sb.sb_agcount) {
                xfs_warn(log->l_mp, "xlog_recover_do_icreate_trans: bad agno");
                return -EINVAL;
        }
        agbno = be32_to_cpu(icl->icl_agbno);
        if (!agbno || agbno == NULLAGBLOCK || agbno >= mp->m_sb.sb_agblocks) {
                xfs_warn(log->l_mp, "xlog_recover_do_icreate_trans: bad agbno");
                return -EINVAL;
        }
        isize = be32_to_cpu(icl->icl_isize);
        if (isize != mp->m_sb.sb_inodesize) {
                xfs_warn(log->l_mp, "xlog_recover_do_icreate_trans: bad isize");
                return -EINVAL;
        }
        count = be32_to_cpu(icl->icl_count);
        if (!count) {
                xfs_warn(log->l_mp, "xlog_recover_do_icreate_trans: bad count");
                return -EINVAL;
        }
        length = be32_to_cpu(icl->icl_length);
        if (!length || length >= mp->m_sb.sb_agblocks) {
                xfs_warn(log->l_mp, "xlog_recover_do_icreate_trans: bad length");
                return -EINVAL;
        }

        /*
         * The inode chunk is either full or sparse and we only support
         * m_ialloc_min_blks sized sparse allocations at this time.
         */
        if (length != mp->m_ialloc_blks &&
            length != mp->m_ialloc_min_blks) {
                xfs_warn(log->l_mp,
                         "%s: unsupported chunk length", __FUNCTION__);
                return -EINVAL;
        }

        /* verify inode count is consistent with extent length */
        if ((count >> mp->m_sb.sb_inopblog) != length) {
                xfs_warn(log->l_mp,
                         "%s: inconsistent inode count and chunk length",
                         __FUNCTION__);
                return -EINVAL;
        }

        /*
         * The icreate transaction can cover multiple cluster buffers and these
         * buffers could have been freed and reused. Check the individual
         * buffers for cancellation so we don't overwrite anything written after
         * a cancellation.
         */
        blks_per_cluster = xfs_icluster_size_fsb(mp);
        bb_per_cluster = XFS_FSB_TO_BB(mp, blks_per_cluster);
        nbufs = length / blks_per_cluster;
        for (i = 0, cancel_count = 0; i < nbufs; i++) {
                xfs_daddr_t     daddr;

                daddr = XFS_AGB_TO_DADDR(mp, agno,
                                         agbno + i * blks_per_cluster);
                if (xlog_check_buffer_cancelled(log, daddr, bb_per_cluster, 0))
                        cancel_count++;
        }

        /*
         * We currently only use icreate for a single allocation at a time. This
         * means we should expect either all or none of the buffers to be
         * cancelled. Be conservative and skip replay if at least one buffer is
         * cancelled, but warn the user that something is awry if the buffers
         * are not consistent.
         *
         * XXX: This must be refined to only skip cancelled clusters once we use
         * icreate for multiple chunk allocations.
         */
        ASSERT(!cancel_count || cancel_count == nbufs);
        if (cancel_count) {
                if (cancel_count != nbufs)
                        xfs_warn(mp,
        "WARNING: partial inode chunk cancellation, skipped icreate.");
                trace_xfs_log_recover_icreate_cancel(log, icl);
                return 0;
        }

        trace_xfs_log_recover_icreate_recover(log, icl);
        return xfs_ialloc_inode_init(mp, NULL, buffer_list, count, agno, agbno,
                                     length, be32_to_cpu(icl->icl_gen));
}

STATIC void
xlog_recover_buffer_ra_pass2(
        struct xlog                     *log,
        struct xlog_recover_item        *item)
{
        struct xfs_buf_log_format       *buf_f = item->ri_buf[0].i_addr;
        struct xfs_mount                *mp = log->l_mp;

        if (xlog_peek_buffer_cancelled(log, buf_f->blf_blkno,
                        buf_f->blf_len, buf_f->blf_flags)) {
                return;
        }

        xfs_buf_readahead(mp->m_ddev_targp, buf_f->blf_blkno,
                                buf_f->blf_len, NULL);
}

STATIC void
xlog_recover_inode_ra_pass2(
        struct xlog                     *log,
        struct xlog_recover_item        *item)
{
        struct xfs_inode_log_format     ilf_buf;
        struct xfs_inode_log_format     *ilfp;
        struct xfs_mount                *mp = log->l_mp;
        int                     error;

        if (item->ri_buf[0].i_len == sizeof(struct xfs_inode_log_format)) {
                ilfp = item->ri_buf[0].i_addr;
        } else {
                ilfp = &ilf_buf;
                memset(ilfp, 0, sizeof(*ilfp));
                error = xfs_inode_item_format_convert(&item->ri_buf[0], ilfp);
                if (error)
                        return;
        }

        if (xlog_peek_buffer_cancelled(log, ilfp->ilf_blkno, ilfp->ilf_len, 0))
                return;

        xfs_buf_readahead(mp->m_ddev_targp, ilfp->ilf_blkno,
                                ilfp->ilf_len, &xfs_inode_buf_ra_ops);
}

STATIC void
xlog_recover_dquot_ra_pass2(
        struct xlog                     *log,
        struct xlog_recover_item        *item)
{
        struct xfs_mount        *mp = log->l_mp;
        struct xfs_disk_dquot   *recddq;
        struct xfs_dq_logformat *dq_f;
        uint                    type;
        int                     len;


        if (mp->m_qflags == 0)
                return;

        recddq = item->ri_buf[1].i_addr;
        if (recddq == NULL)
                return;
        if (item->ri_buf[1].i_len < sizeof(struct xfs_disk_dquot))
                return;

        type = recddq->d_flags & (XFS_DQ_USER | XFS_DQ_PROJ | XFS_DQ_GROUP);
        ASSERT(type);
        if (log->l_quotaoffs_flag & type)
                return;

        dq_f = item->ri_buf[0].i_addr;
        ASSERT(dq_f);
        ASSERT(dq_f->qlf_len == 1);

        len = XFS_FSB_TO_BB(mp, dq_f->qlf_len);
        if (xlog_peek_buffer_cancelled(log, dq_f->qlf_blkno, len, 0))
                return;

        xfs_buf_readahead(mp->m_ddev_targp, dq_f->qlf_blkno, len,
                          &xfs_dquot_buf_ra_ops);
}

STATIC void
xlog_recover_ra_pass2(
        struct xlog                     *log,
        struct xlog_recover_item        *item)
{
        switch (ITEM_TYPE(item)) {
        case XFS_LI_BUF:
                xlog_recover_buffer_ra_pass2(log, item);
                break;
        case XFS_LI_INODE:
                xlog_recover_inode_ra_pass2(log, item);
                break;
        case XFS_LI_DQUOT:
                xlog_recover_dquot_ra_pass2(log, item);
                break;
        case XFS_LI_EFI:
        case XFS_LI_EFD:
        case XFS_LI_QUOTAOFF:
        default:
                break;
        }
}

STATIC int
xlog_recover_commit_pass1(
        struct xlog                     *log,
        struct xlog_recover             *trans,
        struct xlog_recover_item        *item)
{
        trace_xfs_log_recover_item_recover(log, trans, item, XLOG_RECOVER_PASS1);

        switch (ITEM_TYPE(item)) {
        case XFS_LI_BUF:
                return xlog_recover_buffer_pass1(log, item);
        case XFS_LI_QUOTAOFF:
                return xlog_recover_quotaoff_pass1(log, item);
        case XFS_LI_INODE:
        case XFS_LI_EFI:
        case XFS_LI_EFD:
        case XFS_LI_DQUOT:
        case XFS_LI_ICREATE:
                /* nothing to do in pass 1 */
                return 0;
        default:
                xfs_warn(log->l_mp, "%s: invalid item type (%d)",
                        __func__, ITEM_TYPE(item));
                ASSERT(0);
                return -EIO;
        }
}

STATIC int
xlog_recover_commit_pass2(
        struct xlog                     *log,
        struct xlog_recover             *trans,
        struct list_head                *buffer_list,
        struct xlog_recover_item        *item)
{
        trace_xfs_log_recover_item_recover(log, trans, item, XLOG_RECOVER_PASS2);

        switch (ITEM_TYPE(item)) {
        case XFS_LI_BUF:
                return xlog_recover_buffer_pass2(log, buffer_list, item,
                                                 trans->r_lsn);
        case XFS_LI_INODE:
                return xlog_recover_inode_pass2(log, buffer_list, item,
                                                 trans->r_lsn);
        case XFS_LI_EFI:
                return xlog_recover_efi_pass2(log, item, trans->r_lsn);
        case XFS_LI_EFD:
                return xlog_recover_efd_pass2(log, item);
        case XFS_LI_DQUOT:
                return xlog_recover_dquot_pass2(log, buffer_list, item,
                                                trans->r_lsn);
        case XFS_LI_ICREATE:
                return xlog_recover_do_icreate_pass2(log, buffer_list, item);
        case XFS_LI_QUOTAOFF:
                /* nothing to do in pass2 */
                return 0;
        default:
                xfs_warn(log->l_mp, "%s: invalid item type (%d)",
                        __func__, ITEM_TYPE(item));
                ASSERT(0);
                return -EIO;
        }
}

STATIC int
xlog_recover_items_pass2(
        struct xlog                     *log,
        struct xlog_recover             *trans,
        struct list_head                *buffer_list,
        struct list_head                *item_list)
{
        struct xlog_recover_item        *item;
        int                             error = 0;

        list_for_each_entry(item, item_list, ri_list) {
                error = xlog_recover_commit_pass2(log, trans,
                                          buffer_list, item);
                if (error)
                        return error;
        }

        return error;
}

/*
 * Perform the transaction.
 *
 * If the transaction modifies a buffer or inode, do it now.  Otherwise,
 * EFIs and EFDs get queued up by adding entries into the AIL for them.
 */
STATIC int
xlog_recover_commit_trans(
        struct xlog             *log,
        struct xlog_recover     *trans,
        int                     pass)
{
        int                             error = 0;
        int                             error2;
        int                             items_queued = 0;
        struct xlog_recover_item        *item;
        struct xlog_recover_item        *next;
        LIST_HEAD                       (buffer_list);
        LIST_HEAD                       (ra_list);
        LIST_HEAD                       (done_list);

        #define XLOG_RECOVER_COMMIT_QUEUE_MAX 100

        hlist_del(&trans->r_list);

        error = xlog_recover_reorder_trans(log, trans, pass);
        if (error)
                return error;

        list_for_each_entry_safe(item, next, &trans->r_itemq, ri_list) {
                switch (pass) {
                case XLOG_RECOVER_PASS1:
                        error = xlog_recover_commit_pass1(log, trans, item);
                        break;
                case XLOG_RECOVER_PASS2:
                        xlog_recover_ra_pass2(log, item);
                        list_move_tail(&item->ri_list, &ra_list);
                        items_queued++;
                        if (items_queued >= XLOG_RECOVER_COMMIT_QUEUE_MAX) {
                                error = xlog_recover_items_pass2(log, trans,
                                                &buffer_list, &ra_list);
                                list_splice_tail_init(&ra_list, &done_list);
                                items_queued = 0;
                        }

                        break;
                default:
                        ASSERT(0);
                }

                if (error)
                        goto out;
        }

out:
        if (!list_empty(&ra_list)) {
                if (!error)
                        error = xlog_recover_items_pass2(log, trans,
                                        &buffer_list, &ra_list);
                list_splice_tail_init(&ra_list, &done_list);
        }

        if (!list_empty(&done_list))
                list_splice_init(&done_list, &trans->r_itemq);

        error2 = xfs_buf_delwri_submit(&buffer_list);
        return error ? error : error2;
}

STATIC void
xlog_recover_add_item(
        struct list_head        *head)
{
        xlog_recover_item_t     *item;

        item = kmem_zalloc(sizeof(xlog_recover_item_t), KM_SLEEP);
        INIT_LIST_HEAD(&item->ri_list);
        list_add_tail(&item->ri_list, head);
}

STATIC int
xlog_recover_add_to_cont_trans(
        struct xlog             *log,
        struct xlog_recover     *trans,
        char                    *dp,
        int                     len)
{
        xlog_recover_item_t     *item;
        char                    *ptr, *old_ptr;
        int                     old_len;

        /*
         * If the transaction is empty, the header was split across this and the
         * previous record. Copy the rest of the header.
         */
        if (list_empty(&trans->r_itemq)) {
                ASSERT(len <= sizeof(struct xfs_trans_header));
                if (len > sizeof(struct xfs_trans_header)) {
                        xfs_warn(log->l_mp, "%s: bad header length", __func__);
                        return -EIO;
                }

                xlog_recover_add_item(&trans->r_itemq);
                ptr = (char *)&trans->r_theader +
                                sizeof(struct xfs_trans_header) - len;
                memcpy(ptr, dp, len);
                return 0;
        }

        /* take the tail entry */
        item = list_entry(trans->r_itemq.prev, xlog_recover_item_t, ri_list);

        old_ptr = item->ri_buf[item->ri_cnt-1].i_addr;
        old_len = item->ri_buf[item->ri_cnt-1].i_len;

        ptr = kmem_realloc(old_ptr, len+old_len, old_len, KM_SLEEP);
        memcpy(&ptr[old_len], dp, len);
        item->ri_buf[item->ri_cnt-1].i_len += len;
        item->ri_buf[item->ri_cnt-1].i_addr = ptr;
        trace_xfs_log_recover_item_add_cont(log, trans, item, 0);
        return 0;
}

/*
 * The next region to add is the start of a new region.  It could be
 * a whole region or it could be the first part of a new region.  Because
 * of this, the assumption here is that the type and size fields of all
 * format structures fit into the first 32 bits of the structure.
 *
 * This works because all regions must be 32 bit aligned.  Therefore, we
 * either have both fields or we have neither field.  In the case we have
 * neither field, the data part of the region is zero length.  We only have
 * a log_op_header and can throw away the header since a new one will appear
 * later.  If we have at least 4 bytes, then we can determine how many regions
 * will appear in the current log item.
 */
STATIC int
xlog_recover_add_to_trans(
        struct xlog             *log,
        struct xlog_recover     *trans,
        char                    *dp,
        int                     len)
{
        xfs_inode_log_format_t  *in_f;                  /* any will do */
        xlog_recover_item_t     *item;
        char                    *ptr;

        if (!len)
                return 0;
        if (list_empty(&trans->r_itemq)) {
                /* we need to catch log corruptions here */
                if (*(uint *)dp != XFS_TRANS_HEADER_MAGIC) {
                        xfs_warn(log->l_mp, "%s: bad header magic number",
                                __func__);
                        ASSERT(0);
                        return -EIO;
                }

                if (len > sizeof(struct xfs_trans_header)) {
                        xfs_warn(log->l_mp, "%s: bad header length", __func__);
                        ASSERT(0);
                        return -EIO;
                }

                /*
                 * The transaction header can be arbitrarily split across op
                 * records. If we don't have the whole thing here, copy what we
                 * do have and handle the rest in the next record.
                 */
                if (len == sizeof(struct xfs_trans_header))
                        xlog_recover_add_item(&trans->r_itemq);
                memcpy(&trans->r_theader, dp, len);
                return 0;
        }

        ptr = kmem_alloc(len, KM_SLEEP);
        memcpy(ptr, dp, len);
        in_f = (xfs_inode_log_format_t *)ptr;

        /* take the tail entry */
        item = list_entry(trans->r_itemq.prev, xlog_recover_item_t, ri_list);
        if (item->ri_total != 0 &&
             item->ri_total == item->ri_cnt) {
                /* tail item is in use, get a new one */
                xlog_recover_add_item(&trans->r_itemq);
                item = list_entry(trans->r_itemq.prev,
                                        xlog_recover_item_t, ri_list);
        }

        if (item->ri_total == 0) {              /* first region to be added */
                if (in_f->ilf_size == 0 ||
                    in_f->ilf_size > XLOG_MAX_REGIONS_IN_ITEM) {
                        xfs_warn(log->l_mp,
                "bad number of regions (%d) in inode log format",
                                  in_f->ilf_size);
                        ASSERT(0);
                        kmem_free(ptr);
                        return -EIO;
                }

                item->ri_total = in_f->ilf_size;
                item->ri_buf =
                        kmem_zalloc(item->ri_total * sizeof(xfs_log_iovec_t),
                                    KM_SLEEP);
        }
        ASSERT(item->ri_total > item->ri_cnt);
        /* Description region is ri_buf[0] */
        item->ri_buf[item->ri_cnt].i_addr = ptr;
        item->ri_buf[item->ri_cnt].i_len  = len;
        item->ri_cnt++;
        trace_xfs_log_recover_item_add(log, trans, item, 0);
        return 0;
}

/*
 * Free up any resources allocated by the transaction
 *
 * Remember that EFIs, EFDs, and IUNLINKs are handled later.
 */
STATIC void
xlog_recover_free_trans(
        struct xlog_recover     *trans)
{
        xlog_recover_item_t     *item, *n;
        int                     i;

        list_for_each_entry_safe(item, n, &trans->r_itemq, ri_list) {
                /* Free the regions in the item. */
                list_del(&item->ri_list);
                for (i = 0; i < item->ri_cnt; i++)
                        kmem_free(item->ri_buf[i].i_addr);
                /* Free the item itself */
                kmem_free(item->ri_buf);
                kmem_free(item);
        }
        /* Free the transaction recover structure */
        kmem_free(trans);
}

/*
 * On error or completion, trans is freed.
 */
STATIC int
xlog_recovery_process_trans(
        struct xlog             *log,
        struct xlog_recover     *trans,
        char                    *dp,
        unsigned int            len,
        unsigned int            flags,
        int                     pass)
{
        int                     error = 0;
        bool                    freeit = false;

        /* mask off ophdr transaction container flags */
        flags &= ~XLOG_END_TRANS;
        if (flags & XLOG_WAS_CONT_TRANS)
                flags &= ~XLOG_CONTINUE_TRANS;

        /*
         * Callees must not free the trans structure. We'll decide if we need to
         * free it or not based on the operation being done and it's result.
         */
        switch (flags) {
        /* expected flag values */
        case 0:
        case XLOG_CONTINUE_TRANS:
                error = xlog_recover_add_to_trans(log, trans, dp, len);
                break;
        case XLOG_WAS_CONT_TRANS:
                error = xlog_recover_add_to_cont_trans(log, trans, dp, len);
                break;
        case XLOG_COMMIT_TRANS:
                error = xlog_recover_commit_trans(log, trans, pass);
                /* success or fail, we are now done with this transaction. */
                freeit = true;
                break;

        /* unexpected flag values */
        case XLOG_UNMOUNT_TRANS:
                /* just skip trans */
                xfs_warn(log->l_mp, "%s: Unmount LR", __func__);
                freeit = true;
                break;
        case XLOG_START_TRANS:
        default:
                xfs_warn(log->l_mp, "%s: bad flag 0x%x", __func__, flags);
                ASSERT(0);
                error = -EIO;
                break;
        }
        if (error || freeit)
                xlog_recover_free_trans(trans);
        return error;
}

/*
 * Lookup the transaction recovery structure associated with the ID in the
 * current ophdr. If the transaction doesn't exist and the start flag is set in
 * the ophdr, then allocate a new transaction for future ID matches to find.
 * Either way, return what we found during the lookup - an existing transaction
 * or nothing.
 */
STATIC struct xlog_recover *
xlog_recover_ophdr_to_trans(
        struct hlist_head       rhash[],
        struct xlog_rec_header  *rhead,
        struct xlog_op_header   *ohead)
{
        struct xlog_recover     *trans;
        xlog_tid_t              tid;
        struct hlist_head       *rhp;

        tid = be32_to_cpu(ohead->oh_tid);
        rhp = &rhash[XLOG_RHASH(tid)];
        hlist_for_each_entry(trans, rhp, r_list) {
                if (trans->r_log_tid == tid)
                        return trans;
        }

        /*
         * skip over non-start transaction headers - we could be
         * processing slack space before the next transaction starts
         */
        if (!(ohead->oh_flags & XLOG_START_TRANS))
                return NULL;

        ASSERT(be32_to_cpu(ohead->oh_len) == 0);

        /*
         * This is a new transaction so allocate a new recovery container to
         * hold the recovery ops that will follow.
         */
        trans = kmem_zalloc(sizeof(struct xlog_recover), KM_SLEEP);
        trans->r_log_tid = tid;
        trans->r_lsn = be64_to_cpu(rhead->h_lsn);
        INIT_LIST_HEAD(&trans->r_itemq);
        INIT_HLIST_NODE(&trans->r_list);
        hlist_add_head(&trans->r_list, rhp);

        /*
         * Nothing more to do for this ophdr. Items to be added to this new
         * transaction will be in subsequent ophdr containers.
         */
        return NULL;
}

STATIC int
xlog_recover_process_ophdr(
        struct xlog             *log,
        struct hlist_head       rhash[],
        struct xlog_rec_header  *rhead,
        struct xlog_op_header   *ohead,
        char                    *dp,
        char                    *end,
        int                     pass)
{
        struct xlog_recover     *trans;
        unsigned int            len;

        /* Do we understand who wrote this op? */
        if (ohead->oh_clientid != XFS_TRANSACTION &&
            ohead->oh_clientid != XFS_LOG) {
                xfs_warn(log->l_mp, "%s: bad clientid 0x%x",
                        __func__, ohead->oh_clientid);
                ASSERT(0);
                return -EIO;
        }

        /*
         * Check the ophdr contains all the data it is supposed to contain.
         */
        len = be32_to_cpu(ohead->oh_len);
        if (dp + len > end) {
                xfs_warn(log->l_mp, "%s: bad length 0x%x", __func__, len);
                WARN_ON(1);
                return -EIO;
        }

        trans = xlog_recover_ophdr_to_trans(rhash, rhead, ohead);
        if (!trans) {
                /* nothing to do, so skip over this ophdr */
                return 0;
        }

        return xlog_recovery_process_trans(log, trans, dp, len,
                                           ohead->oh_flags, pass);
}

/*
 * There are two valid states of the r_state field.  0 indicates that the
 * transaction structure is in a normal state.  We have either seen the
 * start of the transaction or the last operation we added was not a partial
 * operation.  If the last operation we added to the transaction was a
 * partial operation, we need to mark r_state with XLOG_WAS_CONT_TRANS.
 *
 * NOTE: skip LRs with 0 data length.
 */
STATIC int
xlog_recover_process_data(
        struct xlog             *log,
        struct hlist_head       rhash[],
        struct xlog_rec_header  *rhead,
        char                    *dp,
        int                     pass)
{
        struct xlog_op_header   *ohead;
        char                    *end;
        int                     num_logops;
        int                     error;

        end = dp + be32_to_cpu(rhead->h_len);
        num_logops = be32_to_cpu(rhead->h_num_logops);

        /* check the log format matches our own - else we can't recover */
        if (xlog_header_check_recover(log->l_mp, rhead))
                return -EIO;

        while ((dp < end) && num_logops) {

                ohead = (struct xlog_op_header *)dp;
                dp += sizeof(*ohead);
                ASSERT(dp <= end);

                /* errors will abort recovery */
                error = xlog_recover_process_ophdr(log, rhash, rhead, ohead,
                                                    dp, end, pass);
                if (error)
                        return error;

                dp += be32_to_cpu(ohead->oh_len);
                num_logops--;
        }
        return 0;
}

/*
 * Process an extent free intent item that was recovered from
 * the log.  We need to free the extents that it describes.
 */
STATIC int
xlog_recover_process_efi(
        xfs_mount_t             *mp,
        xfs_efi_log_item_t      *efip)
{
        xfs_efd_log_item_t      *efdp;
        xfs_trans_t             *tp;
        int                     i;
        int                     error = 0;
        xfs_extent_t            *extp;
        xfs_fsblock_t           startblock_fsb;

        ASSERT(!test_bit(XFS_EFI_RECOVERED, &efip->efi_flags));

        /*
         * First check the validity of the extents described by the
         * EFI.  If any are bad, then assume that all are bad and
         * just toss the EFI.
         */
        for (i = 0; i < efip->efi_format.efi_nextents; i++) {
                extp = &(efip->efi_format.efi_extents[i]);
                startblock_fsb = XFS_BB_TO_FSB(mp,
                                   XFS_FSB_TO_DADDR(mp, extp->ext_start));
                if ((startblock_fsb == 0) ||
                    (extp->ext_len == 0) ||
                    (startblock_fsb >= mp->m_sb.sb_dblocks) ||
                    (extp->ext_len >= mp->m_sb.sb_agblocks)) {
                        /*
                         * This will pull the EFI from the AIL and
                         * free the memory associated with it.
                         */
                        set_bit(XFS_EFI_RECOVERED, &efip->efi_flags);
                        xfs_efi_release(efip);
                        return -EIO;
                }
        }

        tp = xfs_trans_alloc(mp, 0);
        error = xfs_trans_reserve(tp, &M_RES(mp)->tr_itruncate, 0, 0);
        if (error)
                goto abort_error;
        efdp = xfs_trans_get_efd(tp, efip, efip->efi_format.efi_nextents);

        for (i = 0; i < efip->efi_format.efi_nextents; i++) {
                extp = &(efip->efi_format.efi_extents[i]);
                error = xfs_trans_free_extent(tp, efdp, extp->ext_start,
                                              extp->ext_len);
                if (error)
                        goto abort_error;

        }

        set_bit(XFS_EFI_RECOVERED, &efip->efi_flags);
        error = xfs_trans_commit(tp);
        return error;

abort_error:
        xfs_trans_cancel(tp);
        return error;
}

/*
 * When this is called, all of the EFIs which did not have
 * corresponding EFDs should be in the AIL.  What we do now
 * is free the extents associated with each one.
 *
 * Since we process the EFIs in normal transactions, they
 * will be removed at some point after the commit.  This prevents
 * us from just walking down the list processing each one.
 * We'll use a flag in the EFI to skip those that we've already
 * processed and use the AIL iteration mechanism's generation
 * count to try to speed this up at least a bit.
 *
 * When we start, we know that the EFIs are the only things in
 * the AIL.  As we process them, however, other items are added
 * to the AIL.  Since everything added to the AIL must come after
 * everything already in the AIL, we stop processing as soon as
 * we see something other than an EFI in the AIL.
 */
STATIC int
xlog_recover_process_efis(
        struct xlog             *log)
{
        struct xfs_log_item     *lip;
        struct xfs_efi_log_item *efip;
        int                     error = 0;
        struct xfs_ail_cursor   cur;
        struct xfs_ail          *ailp;

        ailp = log->l_ailp;
        spin_lock(&ailp->xa_lock);
        lip = xfs_trans_ail_cursor_first(ailp, &cur, 0);
        while (lip != NULL) {
                /*
                 * We're done when we see something other than an EFI.
                 * There should be no EFIs left in the AIL now.
                 */
                if (lip->li_type != XFS_LI_EFI) {
#ifdef DEBUG
                        for (; lip; lip = xfs_trans_ail_cursor_next(ailp, &cur))
                                ASSERT(lip->li_type != XFS_LI_EFI);
#endif
                        break;
                }

                /*
                 * Skip EFIs that we've already processed.
                 */
                efip = container_of(lip, struct xfs_efi_log_item, efi_item);
                if (test_bit(XFS_EFI_RECOVERED, &efip->efi_flags)) {
                        lip = xfs_trans_ail_cursor_next(ailp, &cur);
                        continue;
                }

                spin_unlock(&ailp->xa_lock);
                error = xlog_recover_process_efi(log->l_mp, efip);
                spin_lock(&ailp->xa_lock);
                if (error)
                        goto out;
                lip = xfs_trans_ail_cursor_next(ailp, &cur);
        }
out:
        xfs_trans_ail_cursor_done(&cur);
        spin_unlock(&ailp->xa_lock);
        return error;
}

/*
 * A cancel occurs when the mount has failed and we're bailing out. Release all
 * pending EFIs so they don't pin the AIL.
 */
STATIC int
xlog_recover_cancel_efis(
        struct xlog             *log)
{
        struct xfs_log_item     *lip;
        struct xfs_efi_log_item *efip;
        int                     error = 0;
        struct xfs_ail_cursor   cur;
        struct xfs_ail          *ailp;

        ailp = log->l_ailp;
        spin_lock(&ailp->xa_lock);
        lip = xfs_trans_ail_cursor_first(ailp, &cur, 0);
        while (lip != NULL) {
                /*
                 * We're done when we see something other than an EFI.
                 * There should be no EFIs left in the AIL now.
                 */
                if (lip->li_type != XFS_LI_EFI) {
#ifdef DEBUG
                        for (; lip; lip = xfs_trans_ail_cursor_next(ailp, &cur))
                                ASSERT(lip->li_type != XFS_LI_EFI);
#endif
                        break;
                }

                efip = container_of(lip, struct xfs_efi_log_item, efi_item);

                spin_unlock(&ailp->xa_lock);
                xfs_efi_release(efip);
                spin_lock(&ailp->xa_lock);

                lip = xfs_trans_ail_cursor_next(ailp, &cur);
        }

        xfs_trans_ail_cursor_done(&cur);
        spin_unlock(&ailp->xa_lock);
        return error;
}

/*
 * This routine performs a transaction to null out a bad inode pointer
 * in an agi unlinked inode hash bucket.
 */
STATIC void
xlog_recover_clear_agi_bucket(
        xfs_mount_t     *mp,
        xfs_agnumber_t  agno,
        int             bucket)
{
        xfs_trans_t     *tp;
        xfs_agi_t       *agi;
        xfs_buf_t       *agibp;
        int             offset;
        int             error;

        tp = xfs_trans_alloc(mp, XFS_TRANS_CLEAR_AGI_BUCKET);
        error = xfs_trans_reserve(tp, &M_RES(mp)->tr_clearagi, 0, 0);
        if (error)
                goto out_abort;

        error = xfs_read_agi(mp, tp, agno, &agibp);
        if (error)
                goto out_abort;

        agi = XFS_BUF_TO_AGI(agibp);
        agi->agi_unlinked[bucket] = cpu_to_be32(NULLAGINO);
        offset = offsetof(xfs_agi_t, agi_unlinked) +
                 (sizeof(xfs_agino_t) * bucket);
        xfs_trans_log_buf(tp, agibp, offset,
                          (offset + sizeof(xfs_agino_t) - 1));

        error = xfs_trans_commit(tp);
        if (error)
                goto out_error;
        return;

out_abort:
        xfs_trans_cancel(tp);
out_error:
        xfs_warn(mp, "%s: failed to clear agi %d. Continuing.", __func__, agno);
        return;
}

STATIC xfs_agino_t
xlog_recover_process_one_iunlink(
        struct xfs_mount                *mp,
        xfs_agnumber_t                  agno,
        xfs_agino_t                     agino,
        int                             bucket)
{
        struct xfs_buf                  *ibp;
        struct xfs_dinode               *dip;
        struct xfs_inode                *ip;
        xfs_ino_t                       ino;
        int                             error;

        ino = XFS_AGINO_TO_INO(mp, agno, agino);
        error = xfs_iget(mp, NULL, ino, 0, 0, &ip);
        if (error)
                goto fail;

        /*
         * Get the on disk inode to find the next inode in the bucket.
         */
        error = xfs_imap_to_bp(mp, NULL, &ip->i_imap, &dip, &ibp, 0, 0);
        if (error)
                goto fail_iput;

        ASSERT(ip->i_d.di_nlink == 0);
        ASSERT(ip->i_d.di_mode != 0);

        /* setup for the next pass */
        agino = be32_to_cpu(dip->di_next_unlinked);
        xfs_buf_relse(ibp);

        /*
         * Prevent any DMAPI event from being sent when the reference on
         * the inode is dropped.
         */
        ip->i_d.di_dmevmask = 0;

        IRELE(ip);
        return agino;

 fail_iput:
        IRELE(ip);
 fail:
        /*
         * We can't read in the inode this bucket points to, or this inode
         * is messed up.  Just ditch this bucket of inodes.  We will lose
         * some inodes and space, but at least we won't hang.
         *
         * Call xlog_recover_clear_agi_bucket() to perform a transaction to
         * clear the inode pointer in the bucket.
         */
        xlog_recover_clear_agi_bucket(mp, agno, bucket);
        return NULLAGINO;
}

/*
 * xlog_iunlink_recover
 *
 * This is called during recovery to process any inodes which
 * we unlinked but not freed when the system crashed.  These
 * inodes will be on the lists in the AGI blocks.  What we do
 * here is scan all the AGIs and fully truncate and free any
 * inodes found on the lists.  Each inode is removed from the
 * lists when it has been fully truncated and is freed.  The
 * freeing of the inode and its removal from the list must be
 * atomic.
 */
STATIC void
xlog_recover_process_iunlinks(
        struct xlog     *log)
{
        xfs_mount_t     *mp;
        xfs_agnumber_t  agno;
        xfs_agi_t       *agi;
        xfs_buf_t       *agibp;
        xfs_agino_t     agino;
        int             bucket;
        int             error;
        uint            mp_dmevmask;

        mp = log->l_mp;

        /*
         * Prevent any DMAPI event from being sent while in this function.
         */
        mp_dmevmask = mp->m_dmevmask;
        mp->m_dmevmask = 0;

        for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
                /*
                 * Find the agi for this ag.
                 */
                error = xfs_read_agi(mp, NULL, agno, &agibp);
                if (error) {
                        /*
                         * AGI is b0rked. Don't process it.
                         *
                         * We should probably mark the filesystem as corrupt
                         * after we've recovered all the ag's we can....
                         */
                        continue;
                }
                /*
                 * Unlock the buffer so that it can be acquired in the normal
                 * course of the transaction to truncate and free each inode.
                 * Because we are not racing with anyone else here for the AGI
                 * buffer, we don't even need to hold it locked to read the
                 * initial unlinked bucket entries out of the buffer. We keep
                 * buffer reference though, so that it stays pinned in memory
                 * while we need the buffer.
                 */
                agi = XFS_BUF_TO_AGI(agibp);
                xfs_buf_unlock(agibp);

                for (bucket = 0; bucket < XFS_AGI_UNLINKED_BUCKETS; bucket++) {
                        agino = be32_to_cpu(agi->agi_unlinked[bucket]);
                        while (agino != NULLAGINO) {
                                agino = xlog_recover_process_one_iunlink(mp,
                                                        agno, agino, bucket);
                        }
                }
                xfs_buf_rele(agibp);
        }

        mp->m_dmevmask = mp_dmevmask;
}

STATIC int
xlog_unpack_data(
        struct xlog_rec_header  *rhead,
        char                    *dp,
        struct xlog             *log)
{
        int                     i, j, k;

        for (i = 0; i < BTOBB(be32_to_cpu(rhead->h_len)) &&
                  i < (XLOG_HEADER_CYCLE_SIZE / BBSIZE); i++) {
                *(__be32 *)dp = *(__be32 *)&rhead->h_cycle_data[i];
                dp += BBSIZE;
        }

        if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
                xlog_in_core_2_t *xhdr = (xlog_in_core_2_t *)rhead;
                for ( ; i < BTOBB(be32_to_cpu(rhead->h_len)); i++) {
                        j = i / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                        k = i % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
                        *(__be32 *)dp = xhdr[j].hic_xheader.xh_cycle_data[k];
                        dp += BBSIZE;
                }
        }

        return 0;
}

/*
 * CRC check, unpack and process a log record.
 */
STATIC int
xlog_recover_process(
        struct xlog             *log,
        struct hlist_head       rhash[],
        struct xlog_rec_header  *rhead,
        char                    *dp,
        int                     pass)
{
        int                     error;
        __le32                  crc;

        crc = xlog_cksum(log, rhead, dp, be32_to_cpu(rhead->h_len));

        /*
         * Nothing else to do if this is a CRC verification pass. Just return
         * if this a record with a non-zero crc. Unfortunately, mkfs always
         * sets h_crc to 0 so we must consider this valid even on v5 supers.
         * Otherwise, return EFSBADCRC on failure so the callers up the stack
         * know precisely what failed.
         */
        if (pass == XLOG_RECOVER_CRCPASS) {
                if (rhead->h_crc && crc != le32_to_cpu(rhead->h_crc))
                        return -EFSBADCRC;
                return 0;
        }

        /*
         * We're in the normal recovery path. Issue a warning if and only if the
         * CRC in the header is non-zero. This is an advisory warning and the
         * zero CRC check prevents warnings from being emitted when upgrading
         * the kernel from one that does not add CRCs by default.
         */
        if (crc != le32_to_cpu(rhead->h_crc)) {
                if (rhead->h_crc || xfs_sb_version_hascrc(&log->l_mp->m_sb)) {
                        xfs_alert(log->l_mp,
                "log record CRC mismatch: found 0x%x, expected 0x%x.",
                                        le32_to_cpu(rhead->h_crc),
                                        le32_to_cpu(crc));
                        xfs_hex_dump(dp, 32);
                }

                /*
                 * If the filesystem is CRC enabled, this mismatch becomes a
                 * fatal log corruption failure.
                 */
                if (xfs_sb_version_hascrc(&log->l_mp->m_sb))
                        return -EFSCORRUPTED;
        }

        error = xlog_unpack_data(rhead, dp, log);
        if (error)
                return error;

        return xlog_recover_process_data(log, rhash, rhead, dp, pass);
}

STATIC int
xlog_valid_rec_header(
        struct xlog             *log,
        struct xlog_rec_header  *rhead,
        xfs_daddr_t             blkno)
{
        int                     hlen;

        if (unlikely(rhead->h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM))) {
                XFS_ERROR_REPORT("xlog_valid_rec_header(1)",
                                XFS_ERRLEVEL_LOW, log->l_mp);
                return -EFSCORRUPTED;
        }
        if (unlikely(
            (!rhead->h_version ||
            (be32_to_cpu(rhead->h_version) & (~XLOG_VERSION_OKBITS))))) {
                xfs_warn(log->l_mp, "%s: unrecognised log version (%d).",
                        __func__, be32_to_cpu(rhead->h_version));
                return -EIO;
        }

        /* LR body must have data or it wouldn't have been written */
        hlen = be32_to_cpu(rhead->h_len);
        if (unlikely( hlen <= 0 || hlen > INT_MAX )) {
                XFS_ERROR_REPORT("xlog_valid_rec_header(2)",
                                XFS_ERRLEVEL_LOW, log->l_mp);
                return -EFSCORRUPTED;
        }
        if (unlikely( blkno > log->l_logBBsize || blkno > INT_MAX )) {
                XFS_ERROR_REPORT("xlog_valid_rec_header(3)",
                                XFS_ERRLEVEL_LOW, log->l_mp);
                return -EFSCORRUPTED;
        }
        return 0;
}

/*
 * Read the log from tail to head and process the log records found.
 * Handle the two cases where the tail and head are in the same cycle
 * and where the active portion of the log wraps around the end of
 * the physical log separately.  The pass parameter is passed through
 * to the routines called to process the data and is not looked at
 * here.
 */
STATIC int
xlog_do_recovery_pass(
        struct xlog             *log,
        xfs_daddr_t             head_blk,
        xfs_daddr_t             tail_blk,
        int                     pass,
        xfs_daddr_t             *first_bad)     /* out: first bad log rec */
{
        xlog_rec_header_t       *rhead;
        xfs_daddr_t             blk_no;
        xfs_daddr_t             rhead_blk;
        char                    *offset;
        xfs_buf_t               *hbp, *dbp;
        int                     error = 0, h_size, h_len;
        int                     bblks, split_bblks;
        int                     hblks, split_hblks, wrapped_hblks;
        struct hlist_head       rhash[XLOG_RHASH_SIZE];

        ASSERT(head_blk != tail_blk);
        rhead_blk = 0;

        /*
         * Read the header of the tail block and get the iclog buffer size from
         * h_size.  Use this to tell how many sectors make up the log header.
         */
        if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
                /*
                 * When using variable length iclogs, read first sector of
                 * iclog header and extract the header size from it.  Get a
                 * new hbp that is the correct size.
                 */
                hbp = xlog_get_bp(log, 1);
                if (!hbp)
                        return -ENOMEM;

                error = xlog_bread(log, tail_blk, 1, hbp, &offset);
                if (error)
                        goto bread_err1;

                rhead = (xlog_rec_header_t *)offset;
                error = xlog_valid_rec_header(log, rhead, tail_blk);
                if (error)
                        goto bread_err1;

                /*
                 * xfsprogs has a bug where record length is based on lsunit but
                 * h_size (iclog size) is hardcoded to 32k. Now that we
                 * unconditionally CRC verify the unmount record, this means the
                 * log buffer can be too small for the record and cause an
                 * overrun.
                 *
                 * Detect this condition here. Use lsunit for the buffer size as
                 * long as this looks like the mkfs case. Otherwise, return an
                 * error to avoid a buffer overrun.
                 */
                h_size = be32_to_cpu(rhead->h_size);
                h_len = be32_to_cpu(rhead->h_len);
                if (h_len > h_size) {
                        if (h_len <= log->l_mp->m_logbsize &&
                            be32_to_cpu(rhead->h_num_logops) == 1) {
                                xfs_warn(log->l_mp,
                "invalid iclog size (%d bytes), using lsunit (%d bytes)",
                                         h_size, log->l_mp->m_logbsize);
                                h_size = log->l_mp->m_logbsize;
                        } else
                                return -EFSCORRUPTED;
                }

                if ((be32_to_cpu(rhead->h_version) & XLOG_VERSION_2) &&
                    (h_size > XLOG_HEADER_CYCLE_SIZE)) {
                        hblks = h_size / XLOG_HEADER_CYCLE_SIZE;
                        if (h_size % XLOG_HEADER_CYCLE_SIZE)
                                hblks++;
                        xlog_put_bp(hbp);
                        hbp = xlog_get_bp(log, hblks);
                } else {
                        hblks = 1;
                }
        } else {
                ASSERT(log->l_sectBBsize == 1);
                hblks = 1;
                hbp = xlog_get_bp(log, 1);
                h_size = XLOG_BIG_RECORD_BSIZE;
        }

        if (!hbp)
                return -ENOMEM;
        dbp = xlog_get_bp(log, BTOBB(h_size));
        if (!dbp) {
                xlog_put_bp(hbp);
                return -ENOMEM;
        }

        memset(rhash, 0, sizeof(rhash));
        blk_no = rhead_blk = tail_blk;
        if (tail_blk > head_blk) {
                /*
                 * Perform recovery around the end of the physical log.
                 * When the head is not on the same cycle number as the tail,
                 * we can't do a sequential recovery.
                 */
                while (blk_no < log->l_logBBsize) {
                        /*
                         * Check for header wrapping around physical end-of-log
                         */
                        offset = hbp->b_addr;
                        split_hblks = 0;
                        wrapped_hblks = 0;
                        if (blk_no + hblks <= log->l_logBBsize) {
                                /* Read header in one read */
                                error = xlog_bread(log, blk_no, hblks, hbp,
                                                   &offset);
                                if (error)
                                        goto bread_err2;
                        } else {
                                /* This LR is split across physical log end */
                                if (blk_no != log->l_logBBsize) {
                                        /* some data before physical log end */
                                        ASSERT(blk_no <= INT_MAX);
                                        split_hblks = log->l_logBBsize - (int)blk_no;
                                        ASSERT(split_hblks > 0);
                                        error = xlog_bread(log, blk_no,
                                                           split_hblks, hbp,
                                                           &offset);
                                        if (error)
                                                goto bread_err2;
                                }

                                /*
                                 * Note: this black magic still works with
                                 * large sector sizes (non-512) only because:
                                 * - we increased the buffer size originally
                                 *   by 1 sector giving us enough extra space
                                 *   for the second read;
                                 * - the log start is guaranteed to be sector
                                 *   aligned;
                                 * - we read the log end (LR header start)
                                 *   _first_, then the log start (LR header end)
                                 *   - order is important.
                                 */
                                wrapped_hblks = hblks - split_hblks;
                                error = xlog_bread_offset(log, 0,
                                                wrapped_hblks, hbp,
                                                offset + BBTOB(split_hblks));
                                if (error)
                                        goto bread_err2;
                        }
                        rhead = (xlog_rec_header_t *)offset;
                        error = xlog_valid_rec_header(log, rhead,
                                                split_hblks ? blk_no : 0);
                        if (error)
                                goto bread_err2;

                        bblks = (int)BTOBB(be32_to_cpu(rhead->h_len));
                        blk_no += hblks;

                        /* Read in data for log record */
                        if (blk_no + bblks <= log->l_logBBsize) {
                                error = xlog_bread(log, blk_no, bblks, dbp,
                                                   &offset);
                                if (error)
                                        goto bread_err2;
                        } else {
                                /* This log record is split across the
                                 * physical end of log */
                                offset = dbp->b_addr;
                                split_bblks = 0;
                                if (blk_no != log->l_logBBsize) {
                                        /* some data is before the physical
                                         * end of log */
                                        ASSERT(!wrapped_hblks);
                                        ASSERT(blk_no <= INT_MAX);
                                        split_bblks =
                                                log->l_logBBsize - (int)blk_no;
                                        ASSERT(split_bblks > 0);
                                        error = xlog_bread(log, blk_no,
                                                        split_bblks, dbp,
                                                        &offset);
                                        if (error)
                                                goto bread_err2;
                                }

                                /*
                                 * Note: this black magic still works with
                                 * large sector sizes (non-512) only because:
                                 * - we increased the buffer size originally
                                 *   by 1 sector giving us enough extra space
                                 *   for the second read;
                                 * - the log start is guaranteed to be sector
                                 *   aligned;
                                 * - we read the log end (LR header start)
                                 *   _first_, then the log start (LR header end)
                                 *   - order is important.
                                 */
                                error = xlog_bread_offset(log, 0,
                                                bblks - split_bblks, dbp,
                                                offset + BBTOB(split_bblks));
                                if (error)
                                        goto bread_err2;
                        }

                        error = xlog_recover_process(log, rhash, rhead, offset,
                                                     pass);
                        if (error)
                                goto bread_err2;

                        blk_no += bblks;
                        rhead_blk = blk_no;
                }

                ASSERT(blk_no >= log->l_logBBsize);
                blk_no -= log->l_logBBsize;
                rhead_blk = blk_no;
        }

        /* read first part of physical log */
        while (blk_no < head_blk) {
                error = xlog_bread(log, blk_no, hblks, hbp, &offset);
                if (error)
                        goto bread_err2;

                rhead = (xlog_rec_header_t *)offset;
                error = xlog_valid_rec_header(log, rhead, blk_no);
                if (error)
                        goto bread_err2;

                /* blocks in data section */
                bblks = (int)BTOBB(be32_to_cpu(rhead->h_len));
                error = xlog_bread(log, blk_no+hblks, bblks, dbp,
                                   &offset);
                if (error)
                        goto bread_err2;

                error = xlog_recover_process(log, rhash, rhead, offset, pass);
                if (error)
                        goto bread_err2;

                blk_no += bblks + hblks;
                rhead_blk = blk_no;
        }

 bread_err2:
        xlog_put_bp(dbp);
 bread_err1:
        xlog_put_bp(hbp);

        if (error && first_bad)
                *first_bad = rhead_blk;

        return error;
}

/*
 * Do the recovery of the log.  We actually do this in two phases.
 * The two passes are necessary in order to implement the function
 * of cancelling a record written into the log.  The first pass
 * determines those things which have been cancelled, and the
 * second pass replays log items normally except for those which
 * have been cancelled.  The handling of the replay and cancellations
 * takes place in the log item type specific routines.
 *
 * The table of items which have cancel records in the log is allocated
 * and freed at this level, since only here do we know when all of
 * the log recovery has been completed.
 */
STATIC int
xlog_do_log_recovery(
        struct xlog     *log,
        xfs_daddr_t     head_blk,
        xfs_daddr_t     tail_blk)
{
        int             error, i;

        ASSERT(head_blk != tail_blk);

        /*
         * First do a pass to find all of the cancelled buf log items.
         * Store them in the buf_cancel_table for use in the second pass.
         */
        log->l_buf_cancel_table = kmem_zalloc(XLOG_BC_TABLE_SIZE *
                                                 sizeof(struct list_head),
                                                 KM_SLEEP);
        for (i = 0; i < XLOG_BC_TABLE_SIZE; i++)
                INIT_LIST_HEAD(&log->l_buf_cancel_table[i]);

        error = xlog_do_recovery_pass(log, head_blk, tail_blk,
                                      XLOG_RECOVER_PASS1, NULL);
        if (error != 0) {
                kmem_free(log->l_buf_cancel_table);
                log->l_buf_cancel_table = NULL;
                return error;
        }
        /*
         * Then do a second pass to actually recover the items in the log.
         * When it is complete free the table of buf cancel items.
         */
        error = xlog_do_recovery_pass(log, head_blk, tail_blk,
                                      XLOG_RECOVER_PASS2, NULL);
#ifdef DEBUG
        if (!error) {
                int     i;

                for (i = 0; i < XLOG_BC_TABLE_SIZE; i++)
                        ASSERT(list_empty(&log->l_buf_cancel_table[i]));
        }
#endif  /* DEBUG */

        kmem_free(log->l_buf_cancel_table);
        log->l_buf_cancel_table = NULL;

        return error;
}

/*
 * Do the actual recovery
 */
STATIC int
xlog_do_recover(
        struct xlog     *log,
        xfs_daddr_t     head_blk,
        xfs_daddr_t     tail_blk)
{
        int             error;
        xfs_buf_t       *bp;
        xfs_sb_t        *sbp;

        /*
         * First replay the images in the log.
         */
        error = xlog_do_log_recovery(log, head_blk, tail_blk);
        if (error)
                return error;

        /*
         * If IO errors happened during recovery, bail out.
         */
        if (XFS_FORCED_SHUTDOWN(log->l_mp)) {
                return -EIO;
        }

        /*
         * We now update the tail_lsn since much of the recovery has completed
         * and there may be space available to use.  If there were no extent
         * or iunlinks, we can free up the entire log and set the tail_lsn to
         * be the last_sync_lsn.  This was set in xlog_find_tail to be the
         * lsn of the last known good LR on disk.  If there are extent frees
         * or iunlinks they will have some entries in the AIL; so we look at
         * the AIL to determine how to set the tail_lsn.
         */
        xlog_assign_tail_lsn(log->l_mp);

        /*
         * Now that we've finished replaying all buffer and inode
         * updates, re-read in the superblock and reverify it.
         */
        bp = xfs_getsb(log->l_mp, 0);
        XFS_BUF_UNDONE(bp);
        ASSERT(!(XFS_BUF_ISWRITE(bp)));
        XFS_BUF_READ(bp);
        XFS_BUF_UNASYNC(bp);
        bp->b_ops = &xfs_sb_buf_ops;

        error = xfs_buf_submit_wait(bp);
        if (error) {
                if (!XFS_FORCED_SHUTDOWN(log->l_mp)) {
                        xfs_buf_ioerror_alert(bp, __func__);
                        ASSERT(0);
                }
                xfs_buf_relse(bp);
                return error;
        }

        /* Convert superblock from on-disk format */
        sbp = &log->l_mp->m_sb;
        xfs_sb_from_disk(sbp, XFS_BUF_TO_SBP(bp));
        ASSERT(sbp->sb_magicnum == XFS_SB_MAGIC);
        ASSERT(xfs_sb_good_version(sbp));
        xfs_reinit_percpu_counters(log->l_mp);

        xfs_buf_relse(bp);


        xlog_recover_check_summary(log);

        /* Normal transactions can now occur */
        log->l_flags &= ~XLOG_ACTIVE_RECOVERY;
        return 0;
}

/*
 * Perform recovery and re-initialize some log variables in xlog_find_tail.
 *
 * Return error or zero.
 */
int
xlog_recover(
        struct xlog     *log)
{
        xfs_daddr_t     head_blk, tail_blk;
        int             error;

        /* find the tail of the log */
        error = xlog_find_tail(log, &head_blk, &tail_blk);
        if (error)
                return error;

        /*
         * The superblock was read before the log was available and thus the LSN
         * could not be verified. Check the superblock LSN against the current
         * LSN now that it's known.
         */
        if (xfs_sb_version_hascrc(&log->l_mp->m_sb) &&
            !xfs_log_check_lsn(log->l_mp, log->l_mp->m_sb.sb_lsn))
                return -EINVAL;

        if (tail_blk != head_blk) {
                /* There used to be a comment here:
                 *
                 * disallow recovery on read-only mounts.  note -- mount
                 * checks for ENOSPC and turns it into an intelligent
                 * error message.
                 * ...but this is no longer true.  Now, unless you specify
                 * NORECOVERY (in which case this function would never be
                 * called), we just go ahead and recover.  We do this all
                 * under the vfs layer, so we can get away with it unless
                 * the device itself is read-only, in which case we fail.
                 */
                if ((error = xfs_dev_is_read_only(log->l_mp, "recovery"))) {
                        return error;
                }

                /*
                 * Version 5 superblock log feature mask validation. We know the
                 * log is dirty so check if there are any unknown log features
                 * in what we need to recover. If there are unknown features
                 * (e.g. unsupported transactions, then simply reject the
                 * attempt at recovery before touching anything.
                 */
                if (XFS_SB_VERSION_NUM(&log->l_mp->m_sb) == XFS_SB_VERSION_5 &&
                    xfs_sb_has_incompat_log_feature(&log->l_mp->m_sb,
                                        XFS_SB_FEAT_INCOMPAT_LOG_UNKNOWN)) {
                        xfs_warn(log->l_mp,
"Superblock has unknown incompatible log features (0x%x) enabled.",
                                (log->l_mp->m_sb.sb_features_log_incompat &
                                        XFS_SB_FEAT_INCOMPAT_LOG_UNKNOWN));
                        xfs_warn(log->l_mp,
"The log can not be fully and/or safely recovered by this kernel.");
                        xfs_warn(log->l_mp,
"Please recover the log on a kernel that supports the unknown features.");
                        return -EINVAL;
                }

                /*
                 * Delay log recovery if the debug hook is set. This is debug
                 * instrumention to coordinate simulation of I/O failures with
                 * log recovery.
                 */
                if (xfs_globals.log_recovery_delay) {
                        xfs_notice(log->l_mp,
                                "Delaying log recovery for %d seconds.",
                                xfs_globals.log_recovery_delay);
                        msleep(xfs_globals.log_recovery_delay * 1000);
                }

                xfs_notice(log->l_mp, "Starting recovery (logdev: %s)",
                                log->l_mp->m_logname ? log->l_mp->m_logname
                                                     : "internal");

                error = xlog_do_recover(log, head_blk, tail_blk);
                log->l_flags |= XLOG_RECOVERY_NEEDED;
        }
        return error;
}

/*
 * In the first part of recovery we replay inodes and buffers and build
 * up the list of extent free items which need to be processed.  Here
 * we process the extent free items and clean up the on disk unlinked
 * inode lists.  This is separated from the first part of recovery so
 * that the root and real-time bitmap inodes can be read in from disk in
 * between the two stages.  This is necessary so that we can free space
 * in the real-time portion of the file system.
 */
int
xlog_recover_finish(
        struct xlog     *log)
{
        /*
         * Now we're ready to do the transactions needed for the
         * rest of recovery.  Start with completing all the extent
         * free intent records and then process the unlinked inode
         * lists.  At this point, we essentially run in normal mode
         * except that we're still performing recovery actions
         * rather than accepting new requests.
         */
        if (log->l_flags & XLOG_RECOVERY_NEEDED) {
                int     error;
                error = xlog_recover_process_efis(log);
                if (error) {
                        xfs_alert(log->l_mp, "Failed to recover EFIs");
                        return error;
                }
                /*
                 * Sync the log to get all the EFIs out of the AIL.
                 * This isn't absolutely necessary, but it helps in
                 * case the unlink transactions would have problems
                 * pushing the EFIs out of the way.
                 */
                xfs_log_force(log->l_mp, XFS_LOG_SYNC);

                xlog_recover_process_iunlinks(log);

                xlog_recover_check_summary(log);

                xfs_notice(log->l_mp, "Ending recovery (logdev: %s)",
                                log->l_mp->m_logname ? log->l_mp->m_logname
                                                     : "internal");
                log->l_flags &= ~XLOG_RECOVERY_NEEDED;
        } else {
                xfs_info(log->l_mp, "Ending clean mount");
        }
        return 0;
}

int
xlog_recover_cancel(
        struct xlog     *log)
{
        int             error = 0;

        if (log->l_flags & XLOG_RECOVERY_NEEDED)
                error = xlog_recover_cancel_efis(log);

        return error;
}

#if defined(DEBUG)
/*
 * Read all of the agf and agi counters and check that they
 * are consistent with the superblock counters.
 */
void
xlog_recover_check_summary(
        struct xlog     *log)
{
        xfs_mount_t     *mp;
        xfs_agf_t       *agfp;
        xfs_buf_t       *agfbp;
        xfs_buf_t       *agibp;
        xfs_agnumber_t  agno;
        __uint64_t      freeblks;
        __uint64_t      itotal;
        __uint64_t      ifree;
        int             error;

        mp = log->l_mp;

        freeblks = 0LL;
        itotal = 0LL;
        ifree = 0LL;
        for (agno = 0; agno < mp->m_sb.sb_agcount; agno++) {
                error = xfs_read_agf(mp, NULL, agno, 0, &agfbp);
                if (error) {
                        xfs_alert(mp, "%s agf read failed agno %d error %d",
                                                __func__, agno, error);
                } else {
                        agfp = XFS_BUF_TO_AGF(agfbp);
                        freeblks += be32_to_cpu(agfp->agf_freeblks) +
                                    be32_to_cpu(agfp->agf_flcount);
                        xfs_buf_relse(agfbp);
                }

                error = xfs_read_agi(mp, NULL, agno, &agibp);
                if (error) {
                        xfs_alert(mp, "%s agi read failed agno %d error %d",
                                                __func__, agno, error);
                } else {
                        struct xfs_agi  *agi = XFS_BUF_TO_AGI(agibp);

                        itotal += be32_to_cpu(agi->agi_count);
                        ifree += be32_to_cpu(agi->agi_freecount);
                        xfs_buf_relse(agibp);
                }
        }
}
#endif /* DEBUG */