WIP FPC-III support

[linux/fpc-iii.git] / fs / xfs / xfs_log_recover.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2000-2006 Silicon Graphics, Inc.
 * All Rights Reserved.
 */
#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_defer.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_trans_priv.h"
#include "xfs_alloc.h"
#include "xfs_ialloc.h"
#include "xfs_trace.h"
#include "xfs_icache.h"
#include "xfs_error.h"
#include "xfs_buf_item.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 *);

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

/*
 * Verify the log-relative block number and length in basic blocks are valid for
 * an operation involving the given XFS log buffer. Returns true if the fields
 * are valid, false otherwise.
 */
static inline bool
xlog_verify_bno(
        struct xlog     *log,
        xfs_daddr_t     blk_no,
        int             bbcount)
{
        if (blk_no < 0 || blk_no >= log->l_logBBsize)
                return false;
        if (bbcount <= 0 || (blk_no + bbcount) > log->l_logBBsize)
                return false;
        return true;
}

/*
 * 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 offset within the log.
 */
static char *
xlog_alloc_buffer(
        struct xlog     *log,
        int             nbblks)
{
        int align_mask = xfs_buftarg_dma_alignment(log->l_targ);

        /*
         * Pass log block 0 since we don't have an addr yet, buffer will be
         * verified on read.
         */
        if (XFS_IS_CORRUPT(log->l_mp, !xlog_verify_bno(log, 0, nbblks))) {
                xfs_warn(log->l_mp, "Invalid block length (0x%x) for buffer",
                        nbblks);
                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);
        return kmem_alloc_io(BBTOB(nbblks), align_mask, KM_MAYFAIL | KM_ZERO);
}

/*
 * 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 inline unsigned int
xlog_align(
        struct xlog     *log,
        xfs_daddr_t     blk_no)
{
        return BBTOB(blk_no & ((xfs_daddr_t)log->l_sectBBsize - 1));
}

static int
xlog_do_io(
        struct xlog             *log,
        xfs_daddr_t             blk_no,
        unsigned int            nbblks,
        char                    *data,
        unsigned int            op)
{
        int                     error;

        if (XFS_IS_CORRUPT(log->l_mp, !xlog_verify_bno(log, blk_no, nbblks))) {
                xfs_warn(log->l_mp,
                         "Invalid log block/length (0x%llx, 0x%x) for buffer",
                         blk_no, nbblks);
                return -EFSCORRUPTED;
        }

        blk_no = round_down(blk_no, log->l_sectBBsize);
        nbblks = round_up(nbblks, log->l_sectBBsize);
        ASSERT(nbblks > 0);

        error = xfs_rw_bdev(log->l_targ->bt_bdev, log->l_logBBstart + blk_no,
                        BBTOB(nbblks), data, op);
        if (error && !XFS_FORCED_SHUTDOWN(log->l_mp)) {
                xfs_alert(log->l_mp,
                          "log recovery %s I/O error at daddr 0x%llx len %d error %d",
                          op == REQ_OP_WRITE ? "write" : "read",
                          blk_no, nbblks, error);
        }
        return error;
}

STATIC int
xlog_bread_noalign(
        struct xlog     *log,
        xfs_daddr_t     blk_no,
        int             nbblks,
        char            *data)
{
        return xlog_do_io(log, blk_no, nbblks, data, REQ_OP_READ);
}

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

        error = xlog_do_io(log, blk_no, nbblks, data, REQ_OP_READ);
        if (!error)
                *offset = data + xlog_align(log, blk_no);
        return error;
}

STATIC int
xlog_bwrite(
        struct xlog     *log,
        xfs_daddr_t     blk_no,
        int             nbblks,
        char            *data)
{
        return xlog_do_io(log, blk_no, nbblks, data, REQ_OP_WRITE);
}

#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 (XFS_IS_CORRUPT(mp, 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);
                return -EFSCORRUPTED;
        }
        if (XFS_IS_CORRUPT(mp, !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);
                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_null(&head->h_fs_uuid)) {
                /*
                 * IRIX doesn't write the h_fs_uuid or h_fmt fields. If
                 * h_fs_uuid is null, we assume this log was last mounted
                 * by IRIX and continue.
                 */
                xfs_warn(mp, "null uuid in log - IRIX style log");
        } else if (XFS_IS_CORRUPT(mp, !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);
                return -EFSCORRUPTED;
        }
        return 0;
}

/*
 * 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,
        char            *buffer,
        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, buffer, &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;
        char            *buffer;
        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 (!(buffer = xlog_alloc_buffer(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, buffer, &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:
        kmem_free(buffer);
        return error;
}

static inline int
xlog_logrec_hblks(struct xlog *log, struct xlog_rec_header *rh)
{
        if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
                int     h_size = be32_to_cpu(rh->h_size);

                if ((be32_to_cpu(rh->h_version) & XLOG_VERSION_2) &&
                    h_size > XLOG_HEADER_CYCLE_SIZE)
                        return DIV_ROUND_UP(h_size, XLOG_HEADER_CYCLE_SIZE);
        }
        return 1;
}

/*
 * 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;
        char                    *buffer;
        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);

        buffer = xlog_alloc_buffer(log, num_blks);
        if (!buffer) {
                buffer = xlog_alloc_buffer(log, 1);
                if (!buffer)
                        return -ENOMEM;
                smallmem = 1;
        } else {
                error = xlog_bread(log, start_blk, num_blks, buffer, &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 = -EFSCORRUPTED;
                        goto out;
                }

                if (smallmem) {
                        error = xlog_bread(log, i, 1, buffer, &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.
         */
        xhdrs = xlog_logrec_hblks(log, head);

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

out:
        kmem_free(buffer);
        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)
{
        char            *buffer;
        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 */
        buffer = xlog_alloc_buffer(log, 1);
        if (!buffer)
                return -ENOMEM;

        error = xlog_bread(log, 0, 1, buffer, &offset);
        if (error)
                goto out_free_buffer;

        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, buffer, &offset);
        if (error)
                goto out_free_buffer;

        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;
                error = xlog_find_cycle_start(log, buffer, first_blk, &head_blk,
                                last_half_cycle);
                if (error)
                        goto out_free_buffer;
        }

        /*
         * 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 = min_t(int, log_bbnum, 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 out_free_buffer;
                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 out_free_buffer;
                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 out_free_buffer;
                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 out_free_buffer;
        } 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 out_free_buffer;
                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 out_free_buffer;
                        if (new_blk != log_bbnum)
                                head_blk = new_blk;
                } else if (error)
                        goto out_free_buffer;
        }

        kmem_free(buffer);
        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;

out_free_buffer:
        kmem_free(buffer);
        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,
        char                    *buffer,
        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, buffer, &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, buffer, &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,
        char                    *buffer,
        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, buffer, &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, buffer, &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;
}

/*
 * Calculate distance from head to tail (i.e., unused space in the log).
 */
static inline int
xlog_tail_distance(
        struct xlog     *log,
        xfs_daddr_t     head_blk,
        xfs_daddr_t     tail_blk)
{
        if (head_blk < tail_blk)
                return tail_blk - head_blk;

        return tail_blk + (log->l_logBBsize - head_blk);
}

/*
 * Verify the log tail. This is particularly important when torn or incomplete
 * writes have been detected near the front of the log and the head has been
 * walked back accordingly.
 *
 * We also have to handle the case where the tail was pinned and the head
 * blocked behind the tail right before a crash. If the tail had been pushed
 * immediately prior to the crash and the subsequent checkpoint was only
 * partially written, it's possible it overwrote the last referenced tail in the
 * log with garbage. This is not a coherency problem because the tail must have
 * been pushed before it can be overwritten, but appears as log corruption to
 * recovery because we have no way to know the tail was updated if the
 * subsequent checkpoint didn't write successfully.
 *
 * Therefore, CRC check the log from tail to head. If a failure occurs and the
 * offending record is within max iclog bufs from the head, walk the tail
 * forward and retry until a valid tail is found or corruption is detected out
 * of the range of a possible overwrite.
 */
STATIC int
xlog_verify_tail(
        struct xlog             *log,
        xfs_daddr_t             head_blk,
        xfs_daddr_t             *tail_blk,
        int                     hsize)
{
        struct xlog_rec_header  *thead;
        char                    *buffer;
        xfs_daddr_t             first_bad;
        int                     error = 0;
        bool                    wrapped;
        xfs_daddr_t             tmp_tail;
        xfs_daddr_t             orig_tail = *tail_blk;

        buffer = xlog_alloc_buffer(log, 1);
        if (!buffer)
                return -ENOMEM;

        /*
         * Make sure the tail points to a record (returns positive count on
         * success).
         */
        error = xlog_seek_logrec_hdr(log, head_blk, *tail_blk, 1, buffer,
                        &tmp_tail, &thead, &wrapped);
        if (error < 0)
                goto out;
        if (*tail_blk != tmp_tail)
                *tail_blk = tmp_tail;

        /*
         * Run a CRC check from the tail to the head. We can't just check
         * MAX_ICLOGS records past the tail because the tail may point to stale
         * blocks cleared during the search for the head/tail. These blocks are
         * overwritten with zero-length records and thus record count is not a
         * reliable indicator of the iclog state before a crash.
         */
        first_bad = 0;
        error = xlog_do_recovery_pass(log, head_blk, *tail_blk,
                                      XLOG_RECOVER_CRCPASS, &first_bad);
        while ((error == -EFSBADCRC || error == -EFSCORRUPTED) && first_bad) {
                int     tail_distance;

                /*
                 * Is corruption within range of the head? If so, retry from
                 * the next record. Otherwise return an error.
                 */
                tail_distance = xlog_tail_distance(log, head_blk, first_bad);
                if (tail_distance > BTOBB(XLOG_MAX_ICLOGS * hsize))
                        break;

                /* skip to the next record; returns positive count on success */
                error = xlog_seek_logrec_hdr(log, head_blk, first_bad, 2,
                                buffer, &tmp_tail, &thead, &wrapped);
                if (error < 0)
                        goto out;

                *tail_blk = tmp_tail;
                first_bad = 0;
                error = xlog_do_recovery_pass(log, head_blk, *tail_blk,
                                              XLOG_RECOVER_CRCPASS, &first_bad);
        }

        if (!error && *tail_blk != orig_tail)
                xfs_warn(log->l_mp,
                "Tail block (0x%llx) overwrite detected. Updated to 0x%llx",
                         orig_tail, *tail_blk);
out:
        kmem_free(buffer);
        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 */
        char                    *buffer,
        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;
        char                    *tmp_buffer;
        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/buffer pointers from the caller.
         */
        tmp_buffer = xlog_alloc_buffer(log, 1);
        if (!tmp_buffer)
                return -ENOMEM;
        error = xlog_rseek_logrec_hdr(log, *head_blk, *tail_blk,
                                      XLOG_MAX_ICLOGS, tmp_buffer,
                                      &tmp_rhead_blk, &tmp_rhead, &tmp_wrapped);
        kmem_free(tmp_buffer);
        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 || error == -EFSCORRUPTED) && first_bad) {
                /*
                 * 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 current cycle.
                 */
                found = xlog_rseek_logrec_hdr(log, first_bad, *tail_blk, 1,
                                buffer, 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;
                }
        }
        if (error)
                return error;

        return xlog_verify_tail(log, *head_blk, tail_blk,
                                be32_to_cpu((*rhead)->h_size));
}

/*
 * We need to make sure we handle log wrapping properly, so we can't use the
 * calculated logbno directly. Make sure it wraps to the correct bno inside the
 * log.
 *
 * The log is limited to 32 bit sizes, so we use the appropriate modulus
 * operation here and cast it back to a 64 bit daddr on return.
 */
static inline xfs_daddr_t
xlog_wrap_logbno(
        struct xlog             *log,
        xfs_daddr_t             bno)
{
        int                     mod;

        div_s64_rem(bno, log->l_logBBsize, &mod);
        return mod;
}

/*
 * 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,
        char                    *buffer,
        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.
         */
        hblks = xlog_logrec_hblks(log, rhead);
        after_umount_blk = xlog_wrap_logbno(log,
                        rhead_blk + hblks + BTOBB(be32_to_cpu(rhead->h_len)));

        if (*head_blk == after_umount_blk &&
            be32_to_cpu(rhead->h_num_logops) == 1) {
                umount_data_blk = xlog_wrap_logbno(log, rhead_blk + hblks);
                error = xlog_bread(log, umount_data_blk, 1, buffer, &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;
}

static void
xlog_set_state(
        struct xlog             *log,
        xfs_daddr_t             head_blk,
        struct xlog_rec_header  *rhead,
        xfs_daddr_t             rhead_blk,
        bool                    bump_cycle)
{
        /*
         * 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 (bump_cycle)
                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));
}

/*
 * 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;
        char                    *buffer;
        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);

        buffer = xlog_alloc_buffer(log, 1);
        if (!buffer)
                return -ENOMEM;
        if (*head_blk == 0) {                           /* special case */
                error = xlog_bread(log, 0, 1, buffer, &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, buffer,
                                      &rhead_blk, &rhead, &wrapped);
        if (error < 0)
                goto done;
        if (!error) {
                xfs_warn(log->l_mp, "%s: couldn't find sync record", __func__);
                error = -EFSCORRUPTED;
                goto done;
        }
        *tail_blk = BLOCK_LSN(be64_to_cpu(rhead->h_tail_lsn));

        /*
         * Set the log state based on the current head record.
         */
        xlog_set_state(log, *head_blk, rhead, rhead_blk, wrapped);
        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, buffer, &clean);
        if (error)
                goto done;

        /*
         * Verify the log head if the log is not clean (e.g., we have anything
         * but an unmount record at the head). This uses CRC verification to
         * detect and trim torn writes. If discovered, CRC failures are
         * considered torn writes and the log head is trimmed accordingly.
         *
         * Note that we can only run CRC verification when the log is dirty
         * because there's no guarantee that the log data behind an unmount
         * record is compatible with the current architecture.
         */
        if (!clean) {
                xfs_daddr_t     orig_head = *head_blk;

                error = xlog_verify_head(log, head_blk, tail_blk, buffer,
                                         &rhead_blk, &rhead, &wrapped);
                if (error)
                        goto done;

                /* update in-core state again if the head changed */
                if (*head_blk != orig_head) {
                        xlog_set_state(log, *head_blk, rhead, rhead_blk,
                                       wrapped);
                        tail_lsn = atomic64_read(&log->l_tail_lsn);
                        error = xlog_check_unmount_rec(log, head_blk, tail_blk,
                                                       rhead, rhead_blk, buffer,
                                                       &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_targ))
                error = xlog_clear_stale_blocks(log, tail_lsn);

done:
        kmem_free(buffer);

        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)
{
        char            *buffer;
        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 */
        buffer = xlog_alloc_buffer(log, 1);
        if (!buffer)
                return -ENOMEM;
        error = xlog_bread(log, 0, 1, buffer, &offset);
        if (error)
                goto out_free_buffer;

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

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

        last_cycle = xlog_get_cycle(offset);
        if (last_cycle != 0) {          /* log completely written to */
                kmem_free(buffer);
                return 0;
        }

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

        /*
         * 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 out_free_buffer;
        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 out_free_buffer;

        *blk_no = last_blk;
out_free_buffer:
        kmem_free(buffer);
        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;
        char            *buffer;
        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 (!(buffer = xlog_alloc_buffer(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, buffer);
                if (error)
                        goto out_free_buffer;

                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)) {
                        error = xlog_bread_noalign(log, ealign, sectbb,
                                        buffer + BBTOB(ealign - start_block));
                        if (error)
                                break;

                }

                offset = buffer + xlog_align(log, start_block);
                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, buffer);
                if (error)
                        break;
                start_block += endcount;
                j = 0;
        }

out_free_buffer:
        kmem_free(buffer);
        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 (XFS_IS_CORRUPT(log->l_mp,
                                   head_block < tail_block ||
                                   head_block >= log->l_logBBsize))
                        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 (XFS_IS_CORRUPT(log->l_mp,
                                   head_block >= tail_block ||
                                   head_cycle != tail_cycle + 1))
                        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;
}

/*
 * Release the recovered intent item in the AIL that matches the given intent
 * type and intent id.
 */
void
xlog_recover_release_intent(
        struct xlog             *log,
        unsigned short          intent_type,
        uint64_t                intent_id)
{
        struct xfs_ail_cursor   cur;
        struct xfs_log_item     *lip;
        struct xfs_ail          *ailp = log->l_ailp;

        spin_lock(&ailp->ail_lock);
        for (lip = xfs_trans_ail_cursor_first(ailp, &cur, 0); lip != NULL;
             lip = xfs_trans_ail_cursor_next(ailp, &cur)) {
                if (lip->li_type != intent_type)
                        continue;
                if (!lip->li_ops->iop_match(lip, intent_id))
                        continue;

                spin_unlock(&ailp->ail_lock);
                lip->li_ops->iop_release(lip);
                spin_lock(&ailp->ail_lock);
                break;
        }

        xfs_trans_ail_cursor_done(&cur);
        spin_unlock(&ailp->ail_lock);
}

/******************************************************************************
 *
 *              Log recover routines
 *
 ******************************************************************************
 */
static const struct xlog_recover_item_ops *xlog_recover_item_ops[] = {
        &xlog_buf_item_ops,
        &xlog_inode_item_ops,
        &xlog_dquot_item_ops,
        &xlog_quotaoff_item_ops,
        &xlog_icreate_item_ops,
        &xlog_efi_item_ops,
        &xlog_efd_item_ops,
        &xlog_rui_item_ops,
        &xlog_rud_item_ops,
        &xlog_cui_item_ops,
        &xlog_cud_item_ops,
        &xlog_bui_item_ops,
        &xlog_bud_item_ops,
};

static const struct xlog_recover_item_ops *
xlog_find_item_ops(
        struct xlog_recover_item                *item)
{
        unsigned int                            i;

        for (i = 0; i < ARRAY_SIZE(xlog_recover_item_ops); i++)
                if (ITEM_TYPE(item) == xlog_recover_item_ops[i]->item_type)
                        return xlog_recover_item_ops[i];

        return NULL;
}

/*
 * 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)
{
        struct xlog_recover_item *item, *n;
        int                     error = 0;
        LIST_HEAD(sort_list);
        LIST_HEAD(cancel_list);
        LIST_HEAD(buffer_list);
        LIST_HEAD(inode_buffer_list);
        LIST_HEAD(item_list);

        list_splice_init(&trans->r_itemq, &sort_list);
        list_for_each_entry_safe(item, n, &sort_list, ri_list) {
                enum xlog_recover_reorder       fate = XLOG_REORDER_ITEM_LIST;

                item->ri_ops = xlog_find_item_ops(item);
                if (!item->ri_ops) {
                        xfs_warn(log->l_mp,
                                "%s: unrecognized type of log operation (%d)",
                                __func__, ITEM_TYPE(item));
                        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 = -EFSCORRUPTED;
                        break;
                }

                if (item->ri_ops->reorder)
                        fate = item->ri_ops->reorder(item);

                switch (fate) {
                case XLOG_REORDER_BUFFER_LIST:
                        list_move_tail(&item->ri_list, &buffer_list);
                        break;
                case XLOG_REORDER_CANCEL_LIST:
                        trace_xfs_log_recover_item_reorder_head(log,
                                        trans, item, pass);
                        list_move(&item->ri_list, &cancel_list);
                        break;
                case XLOG_REORDER_INODE_BUFFER_LIST:
                        list_move(&item->ri_list, &inode_buffer_list);
                        break;
                case XLOG_REORDER_ITEM_LIST:
                        trace_xfs_log_recover_item_reorder_tail(log,
                                                        trans, item, pass);
                        list_move_tail(&item->ri_list, &item_list);
                        break;
                }
        }

        ASSERT(list_empty(&sort_list));
        if (!list_empty(&buffer_list))
                list_splice(&buffer_list, &trans->r_itemq);
        if (!list_empty(&item_list))
                list_splice_tail(&item_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;
}

void
xlog_buf_readahead(
        struct xlog             *log,
        xfs_daddr_t             blkno,
        uint                    len,
        const struct xfs_buf_ops *ops)
{
        if (!xlog_is_buffer_cancelled(log, blkno, len))
                xfs_buf_readahead(log->l_mp->m_ddev_targp, blkno, len, ops);
}

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) {
                trace_xfs_log_recover_item_recover(log, trans, item,
                                XLOG_RECOVER_PASS2);

                if (item->ri_ops->commit_pass2)
                        error = item->ri_ops->commit_pass2(log, buffer_list,
                                        item, trans->r_lsn);
                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,
        struct list_head        *buffer_list)
{
        int                             error = 0;
        int                             items_queued = 0;
        struct xlog_recover_item        *item;
        struct xlog_recover_item        *next;
        LIST_HEAD                       (ra_list);
        LIST_HEAD                       (done_list);

        #define XLOG_RECOVER_COMMIT_QUEUE_MAX 100

        hlist_del_init(&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) {
                trace_xfs_log_recover_item_recover(log, trans, item, pass);

                switch (pass) {
                case XLOG_RECOVER_PASS1:
                        if (item->ri_ops->commit_pass1)
                                error = item->ri_ops->commit_pass1(log, item);
                        break;
                case XLOG_RECOVER_PASS2:
                        if (item->ri_ops->ra_pass2)
                                item->ri_ops->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);

        return error;
}

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

        item = kmem_zalloc(sizeof(struct xlog_recover_item), 0);
        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)
{
        struct xlog_recover_item *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 -EFSCORRUPTED;
                }

                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, struct xlog_recover_item,
                          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 = krealloc(old_ptr, len + old_len, GFP_KERNEL | __GFP_NOFAIL);
        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)
{
        struct xfs_inode_log_format     *in_f;                  /* any will do */
        struct xlog_recover_item *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 -EFSCORRUPTED;
                }

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

                /*
                 * 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, 0);
        memcpy(ptr, dp, len);
        in_f = (struct xfs_inode_log_format *)ptr;

        /* take the tail entry */
        item = list_entry(trans->r_itemq.prev, struct xlog_recover_item,
                          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,
                                        struct xlog_recover_item, 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 -EFSCORRUPTED;
                }

                item->ri_total = in_f->ilf_size;
                item->ri_buf =
                        kmem_zalloc(item->ri_total * sizeof(xfs_log_iovec_t),
                                    0);
        }

        if (item->ri_total <= item->ri_cnt) {
                xfs_warn(log->l_mp,
        "log item region count (%d) overflowed size (%d)",
                                item->ri_cnt, item->ri_total);
                ASSERT(0);
                kmem_free(ptr);
                return -EFSCORRUPTED;
        }

        /* 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)
{
        struct xlog_recover_item *item, *n;
        int                     i;

        hlist_del_init(&trans->r_list);

        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,
        struct list_head        *buffer_list)
{
        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,
                                                  buffer_list);
                /* 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 = -EFSCORRUPTED;
                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), 0);
        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 list_head        *buffer_list)
{
        struct xlog_recover     *trans;
        unsigned int            len;
        int                     error;

        /* 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 -EFSCORRUPTED;
        }

        /*
         * 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 -EFSCORRUPTED;
        }

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

        /*
         * The recovered buffer queue is drained only once we know that all
         * recovery items for the current LSN have been processed. This is
         * required because:
         *
         * - Buffer write submission updates the metadata LSN of the buffer.
         * - Log recovery skips items with a metadata LSN >= the current LSN of
         *   the recovery item.
         * - Separate recovery items against the same metadata buffer can share
         *   a current LSN. I.e., consider that the LSN of a recovery item is
         *   defined as the starting LSN of the first record in which its
         *   transaction appears, that a record can hold multiple transactions,
         *   and/or that a transaction can span multiple records.
         *
         * In other words, we are allowed to submit a buffer from log recovery
         * once per current LSN. Otherwise, we may incorrectly skip recovery
         * items and cause corruption.
         *
         * We don't know up front whether buffers are updated multiple times per
         * LSN. Therefore, track the current LSN of each commit log record as it
         * is processed and drain the queue when it changes. Use commit records
         * because they are ordered correctly by the logging code.
         */
        if (log->l_recovery_lsn != trans->r_lsn &&
            ohead->oh_flags & XLOG_COMMIT_TRANS) {
                error = xfs_buf_delwri_submit(buffer_list);
                if (error)
                        return error;
                log->l_recovery_lsn = trans->r_lsn;
        }

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

/*
 * 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 list_head        *buffer_list)
{
        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;

        trace_xfs_log_recover_record(log, rhead, pass);
        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, buffer_list);
                if (error)
                        return error;

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

/* Take all the collected deferred ops and finish them in order. */
static int
xlog_finish_defer_ops(
        struct xfs_mount        *mp,
        struct list_head        *capture_list)
{
        struct xfs_defer_capture *dfc, *next;
        struct xfs_trans        *tp;
        struct xfs_inode        *ip;
        int                     error = 0;

        list_for_each_entry_safe(dfc, next, capture_list, dfc_list) {
                struct xfs_trans_res    resv;

                /*
                 * Create a new transaction reservation from the captured
                 * information.  Set logcount to 1 to force the new transaction
                 * to regrant every roll so that we can make forward progress
                 * in recovery no matter how full the log might be.
                 */
                resv.tr_logres = dfc->dfc_logres;
                resv.tr_logcount = 1;
                resv.tr_logflags = XFS_TRANS_PERM_LOG_RES;

                error = xfs_trans_alloc(mp, &resv, dfc->dfc_blkres,
                                dfc->dfc_rtxres, XFS_TRANS_RESERVE, &tp);
                if (error)
                        return error;

                /*
                 * Transfer to this new transaction all the dfops we captured
                 * from recovering a single intent item.
                 */
                list_del_init(&dfc->dfc_list);
                xfs_defer_ops_continue(dfc, tp, &ip);

                error = xfs_trans_commit(tp);
                if (ip) {
                        xfs_iunlock(ip, XFS_ILOCK_EXCL);
                        xfs_irele(ip);
                }
                if (error)
                        return error;
        }

        ASSERT(list_empty(capture_list));
        return 0;
}

/* Release all the captured defer ops and capture structures in this list. */
static void
xlog_abort_defer_ops(
        struct xfs_mount                *mp,
        struct list_head                *capture_list)
{
        struct xfs_defer_capture        *dfc;
        struct xfs_defer_capture        *next;

        list_for_each_entry_safe(dfc, next, capture_list, dfc_list) {
                list_del_init(&dfc->dfc_list);
                xfs_defer_ops_release(mp, dfc);
        }
}
/*
 * When this is called, all of the log intent items which did not have
 * corresponding log done items should be in the AIL.  What we do now
 * is update the data structures associated with each one.
 *
 * Since we process the log intent items 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 intent item 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 intents are the only things in the
 * AIL.  As we process them, however, other items are added to the
 * AIL.
 */
STATIC int
xlog_recover_process_intents(
        struct xlog             *log)
{
        LIST_HEAD(capture_list);
        struct xfs_ail_cursor   cur;
        struct xfs_log_item     *lip;
        struct xfs_ail          *ailp;
        int                     error = 0;
#if defined(DEBUG) || defined(XFS_WARN)
        xfs_lsn_t               last_lsn;
#endif

        ailp = log->l_ailp;
        spin_lock(&ailp->ail_lock);
#if defined(DEBUG) || defined(XFS_WARN)
        last_lsn = xlog_assign_lsn(log->l_curr_cycle, log->l_curr_block);
#endif
        for (lip = xfs_trans_ail_cursor_first(ailp, &cur, 0);
             lip != NULL;
             lip = xfs_trans_ail_cursor_next(ailp, &cur)) {
                /*
                 * We're done when we see something other than an intent.
                 * There should be no intents left in the AIL now.
                 */
                if (!xlog_item_is_intent(lip)) {
#ifdef DEBUG
                        for (; lip; lip = xfs_trans_ail_cursor_next(ailp, &cur))
                                ASSERT(!xlog_item_is_intent(lip));
#endif
                        break;
                }

                /*
                 * We should never see a redo item with a LSN higher than
                 * the last transaction we found in the log at the start
                 * of recovery.
                 */
                ASSERT(XFS_LSN_CMP(last_lsn, lip->li_lsn) >= 0);

                /*
                 * NOTE: If your intent processing routine can create more
                 * deferred ops, you /must/ attach them to the capture list in
                 * the recover routine or else those subsequent intents will be
                 * replayed in the wrong order!
                 */
                spin_unlock(&ailp->ail_lock);
                error = lip->li_ops->iop_recover(lip, &capture_list);
                spin_lock(&ailp->ail_lock);
                if (error) {
                        trace_xlog_intent_recovery_failed(log->l_mp, error,
                                        lip->li_ops->iop_recover);
                        break;
                }
        }

        xfs_trans_ail_cursor_done(&cur);
        spin_unlock(&ailp->ail_lock);
        if (error)
                goto err;

        error = xlog_finish_defer_ops(log->l_mp, &capture_list);
        if (error)
                goto err;

        return 0;
err:
        xlog_abort_defer_ops(log->l_mp, &capture_list);
        return error;
}

/*
 * A cancel occurs when the mount has failed and we're bailing out.
 * Release all pending log intent items so they don't pin the AIL.
 */
STATIC void
xlog_recover_cancel_intents(
        struct xlog             *log)
{
        struct xfs_log_item     *lip;
        struct xfs_ail_cursor   cur;
        struct xfs_ail          *ailp;

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

                spin_unlock(&ailp->ail_lock);
                lip->li_ops->iop_release(lip);
                spin_lock(&ailp->ail_lock);
                lip = xfs_trans_ail_cursor_next(ailp, &cur);
        }

        xfs_trans_ail_cursor_done(&cur);
        spin_unlock(&ailp->ail_lock);
}

/*
 * 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;
        struct xfs_buf  *agibp;
        int             offset;
        int             error;

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

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

        agi = agibp->b_addr;
        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);
        if (error)
                goto fail_iput;

        xfs_iflags_clear(ip, XFS_IRECOVERY);
        ASSERT(VFS_I(ip)->i_nlink == 0);
        ASSERT(VFS_I(ip)->i_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;

        xfs_irele(ip);
        return agino;

 fail_iput:
        xfs_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;
}

/*
 * Recover AGI unlinked lists
 *
 * 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.
 *
 * If everything we touch in the agi processing loop is already in memory, this
 * loop can hold the cpu for a long time. It runs without lock contention,
 * memory allocation contention, the need wait for IO, etc, and so will run
 * until we either run out of inodes to process, run low on memory or we run out
 * of log space.
 *
 * This behaviour is bad for latency on single CPU and non-preemptible kernels,
 * and can prevent other filesytem work (such as CIL pushes) from running. This
 * can lead to deadlocks if the recovery process runs out of log reservation
 * space. Hence we need to yield the CPU when there is other kernel work
 * scheduled on this CPU to ensure other scheduled work can run without undue
 * latency.
 */
STATIC void
xlog_recover_process_iunlinks(
        struct xlog     *log)
{
        xfs_mount_t     *mp;
        xfs_agnumber_t  agno;
        xfs_agi_t       *agi;
        struct xfs_buf  *agibp;
        xfs_agino_t     agino;
        int             bucket;
        int             error;

        mp = log->l_mp;

        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 = agibp->b_addr;
                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);
                                cond_resched();
                        }
                }
                xfs_buf_rele(agibp);
        }
}

STATIC void
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;
                }
        }
}

/*
 * 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,
        struct list_head        *buffer_list)
{
        __le32                  old_crc = rhead->h_crc;
        __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 old_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 (old_crc && crc != old_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 != old_crc) {
                if (old_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(old_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)) {
                        XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, log->l_mp);
                        return -EFSCORRUPTED;
                }
        }

        xlog_unpack_data(rhead, dp, log);

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

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

        if (XFS_IS_CORRUPT(log->l_mp,
                           rhead->h_magicno != cpu_to_be32(XLOG_HEADER_MAGIC_NUM)))
                return -EFSCORRUPTED;
        if (XFS_IS_CORRUPT(log->l_mp,
                           (!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 -EFSCORRUPTED;
        }

        /*
         * LR body must have data (or it wouldn't have been written)
         * and h_len must not be greater than LR buffer size.
         */
        hlen = be32_to_cpu(rhead->h_len);
        if (XFS_IS_CORRUPT(log->l_mp, hlen <= 0 || hlen > bufsize))
                return -EFSCORRUPTED;

        if (XFS_IS_CORRUPT(log->l_mp,
                           blkno > log->l_logBBsize || blkno > INT_MAX))
                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, rblk_no;
        xfs_daddr_t             rhead_blk;
        char                    *offset;
        char                    *hbp, *dbp;
        int                     error = 0, h_size, h_len;
        int                     error2 = 0;
        int                     bblks, split_bblks;
        int                     hblks, split_hblks, wrapped_hblks;
        int                     i;
        struct hlist_head       rhash[XLOG_RHASH_SIZE];
        LIST_HEAD               (buffer_list);

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

        for (i = 0; i < XLOG_RHASH_SIZE; i++)
                INIT_HLIST_HEAD(&rhash[i]);

        /*
         * 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_alloc_buffer(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;

                /*
                 * 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 && h_len <= log->l_mp->m_logbsize &&
                    rhead->h_num_logops == cpu_to_be32(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;
                }

                error = xlog_valid_rec_header(log, rhead, tail_blk, h_size);
                if (error)
                        goto bread_err1;

                hblks = xlog_logrec_hblks(log, rhead);
                if (hblks != 1) {
                        kmem_free(hbp);
                        hbp = xlog_alloc_buffer(log, hblks);
                }
        } else {
                ASSERT(log->l_sectBBsize == 1);
                hblks = 1;
                hbp = xlog_alloc_buffer(log, 1);
                h_size = XLOG_BIG_RECORD_BSIZE;
        }

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

        memset(rhash, 0, sizeof(rhash));
        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;
                        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_noalign(log, 0,
                                                wrapped_hblks,
                                                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, h_size);
                        if (error)
                                goto bread_err2;

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

                        /*
                         * Read the log record data in multiple reads if it
                         * wraps around the end of the log. Note that if the
                         * header already wrapped, blk_no could point past the
                         * end of the log. The record data is contiguous in
                         * that case.
                         */
                        if (blk_no + bblks <= log->l_logBBsize ||
                            blk_no >= log->l_logBBsize) {
                                rblk_no = xlog_wrap_logbno(log, blk_no);
                                error = xlog_bread(log, rblk_no, bblks, dbp,
                                                   &offset);
                                if (error)
                                        goto bread_err2;
                        } else {
                                /* This log record is split across the
                                 * physical end of log */
                                offset = dbp;
                                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_noalign(log, 0,
                                                bblks - split_bblks,
                                                offset + BBTOB(split_bblks));
                                if (error)
                                        goto bread_err2;
                        }

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

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

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

        /*
         * Submit buffers that have been added from the last record processed,
         * regardless of error status.
         */
        if (!list_empty(&buffer_list))
                error2 = xfs_buf_delwri_submit(&buffer_list);

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

        /*
         * Transactions are freed at commit time but transactions without commit
         * records on disk are never committed. Free any that may be left in the
         * hash table.
         */
        for (i = 0; i < XLOG_RHASH_SIZE; i++) {
                struct hlist_node       *tmp;
                struct xlog_recover     *trans;

                hlist_for_each_entry_safe(trans, tmp, &rhash[i], r_list)
                        xlog_recover_free_trans(trans);
        }

        return error ? error : error2;
}

/*
 * 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),
                                                 0);
        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)
{
        struct xfs_mount        *mp = log->l_mp;
        struct xfs_buf          *bp = mp->m_sb_bp;
        struct xfs_sb           *sbp = &mp->m_sb;
        int                     error;

        trace_xfs_log_recover(log, head_blk, tail_blk);

        /*
         * 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(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(mp);

        /*
         * Now that we've finished replaying all buffer and inode updates,
         * re-read the superblock and reverify it.
         */
        xfs_buf_lock(bp);
        xfs_buf_hold(bp);
        error = _xfs_buf_read(bp, XBF_READ);
        if (error) {
                if (!XFS_FORCED_SHUTDOWN(mp)) {
                        xfs_buf_ioerror_alert(bp, __this_address);
                        ASSERT(0);
                }
                xfs_buf_relse(bp);
                return error;
        }

        /* Convert superblock from on-disk format */
        xfs_sb_from_disk(sbp, bp->b_addr);
        xfs_buf_relse(bp);

        /* re-initialise in-core superblock and geometry structures */
        xfs_reinit_percpu_counters(mp);
        error = xfs_initialize_perag(mp, sbp->sb_agcount, &mp->m_maxagi);
        if (error) {
                xfs_warn(mp, "Failed post-recovery per-ag init: %d", error);
                return error;
        }
        mp->m_alloc_set_aside = xfs_alloc_set_aside(mp);

        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_intents(log);
                if (error) {
                        /*
                         * Cancel all the unprocessed intent items now so that
                         * we don't leave them pinned in the AIL.  This can
                         * cause the AIL to livelock on the pinned item if
                         * anyone tries to push the AIL (inode reclaim does
                         * this) before we get around to xfs_log_mount_cancel.
                         */
                        xlog_recover_cancel_intents(log);
                        xfs_alert(log->l_mp, "Failed to recover intents");
                        return error;
                }

                /*
                 * Sync the log to get all the intents out of the AIL.
                 * This isn't absolutely necessary, but it helps in
                 * case the unlink transactions would have problems
                 * pushing the intents 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;
}

void
xlog_recover_cancel(
        struct xlog     *log)
{
        if (log->l_flags & XLOG_RECOVERY_NEEDED)
                xlog_recover_cancel_intents(log);
}

#if defined(DEBUG)
/*
 * Read all of the agf and agi counters and check that they
 * are consistent with the superblock counters.
 */
STATIC void
xlog_recover_check_summary(
        struct xlog     *log)
{
        xfs_mount_t     *mp;
        struct xfs_buf  *agfbp;
        struct xfs_buf  *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 {
                        struct xfs_agf  *agfp = agfbp->b_addr;

                        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 = agibp->b_addr;

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