[thirdparty/xfsprogs-dev.git] / libxlog / xfs_log_recover.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2000-2006 Silicon Graphics, Inc.
 * All Rights Reserved.
 */
#include "libxfs.h"
#include "libxlog.h"

#define xfs_readonly_buftarg(buftarg)                   (0)

/* avoid set-but-unused var warning. gcc is not very bright. */
#define xlog_clear_stale_blocks(log, taillsn)           ({ \
        (taillsn) = (taillsn); \
        (0); \
})

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

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

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

/*
 * Allocate a buffer to hold log data.  The buffer needs to be able
 * to map to a range of nbblks basic blocks at any valid (basic
 * block) offset within the log.
 */
xfs_buf_t *
xlog_get_bp(
        struct xlog     *log,
        int             nbblks)
{
        if (!xlog_buf_bbcount_valid(log, nbblks)) {
                xfs_warn(log->l_mp, "Invalid block length (0x%x) for buffer",
                        nbblks);
                XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_HIGH, log->l_mp);
                return NULL;
        }

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

        return libxfs_getbufr(log->l_dev, (xfs_daddr_t)-1, nbblks);
}

void
xlog_put_bp(
        xfs_buf_t       *bp)
{
        libxfs_putbufr(bp);
}

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

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


/*
 * nbblks should be uint, but oh well.  Just want to catch that 32-bit length.
 */
int
xlog_bread_noalign(
        struct xlog     *log,
        xfs_daddr_t     blk_no,
        int             nbblks,
        struct xfs_buf  *bp)
{
        if (!xlog_buf_bbcount_valid(log, nbblks)) {
                xfs_warn(log->l_mp, "Invalid block length (0x%x) for buffer",
                        nbblks);
                XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_HIGH, log->l_mp);
                return EFSCORRUPTED;
        }

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

        ASSERT(nbblks > 0);
        ASSERT(BBTOB(nbblks) <= XFS_BUF_SIZE(bp));

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

        return libxfs_readbufr(log->l_dev, XFS_BUF_ADDR(bp), bp, nbblks, 0);
}

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

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

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

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

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

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

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

/*
 * 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.
 */
int
xlog_find_cycle_start(
        struct xlog     *log,
        struct xfs_buf  *bp,
        xfs_daddr_t     first_blk,
        xfs_daddr_t     *last_blk,
        uint            cycle)
{
        char            *offset;
        xfs_daddr_t     mid_blk;
        xfs_daddr_t     end_blk;
        uint            mid_cycle;
        int             error;

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

        *last_blk = end_blk;

        return 0;
}

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

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

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

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

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

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

                        buf += BBSIZE;
                }
        }

        *new_blk = -1;

out:
        xlog_put_bp(bp);
        return error;
}

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

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

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

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

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

                head = (xlog_rec_header_t *)offset;

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

                if (!smallmem)
                        offset -= BBSIZE;
        }

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

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

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

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

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

out:
        xlog_put_bp(bp);
        return error;
}

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

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

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

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

        first_half_cycle = xlog_get_cycle(offset);

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

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

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

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

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

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

                /* start ptr at last block ptr before head_blk */
                if ((error = xlog_find_verify_log_record(log, start_blk,
                                                        &head_blk, 0)) == -1) {
                        error = XFS_ERROR(EIO);
                        goto bp_err;
                } else if (error)
                        goto bp_err;
        } else {
                start_blk = 0;
                ASSERT(head_blk <= INT_MAX);
                if ((error = xlog_find_verify_log_record(log, start_blk,
                                                        &head_blk, 0)) == -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);
                        if ((error = xlog_find_verify_log_record(log,
                                                        start_blk, &new_blk,
                                                        (int)head_blk)) == -1) {
                                error = XFS_ERROR(EIO);
                                goto bp_err;
                        } else if (error)
                                goto bp_err;
                        if (new_blk != log_bbnum)
                                head_blk = new_blk;
                } else if (error)
                        goto bp_err;
        }

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

 bp_err:
        xlog_put_bp(bp);

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

/*
 * 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.
 */
int
xlog_find_tail(
        struct xlog             *log,
        xfs_daddr_t             *head_blk,
        xfs_daddr_t             *tail_blk)
{
        xlog_rec_header_t       *rhead;
        xlog_op_header_t        *op_head;
        char                    *offset = NULL;
        xfs_buf_t               *bp;
        int                     error, i, found;
        xfs_daddr_t             umount_data_blk;
        xfs_daddr_t             after_umount_blk;
        xfs_lsn_t               tail_lsn;
        int                     hblks;

        found = 0;

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

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

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

        /*
         * Search backwards looking for log record header block
         */
        ASSERT(*head_blk < INT_MAX);
        for (i = (int)(*head_blk) - 1; i >= 0; i--) {
                error = xlog_bread(log, i, 1, bp, &offset);
                if (error)
                        goto done;

                if (*(__be32 *)offset == cpu_to_be32(XLOG_HEADER_MAGIC_NUM)) {
                        found = 1;
                        break;
                }
        }
        /*
         * If we haven't found the log record header block, start looking
         * again from the end of the physical log.  XXXmiken: There should be
         * a check here to make sure we didn't search more than N blocks in
         * the previous code.
         */
        if (!found) {
                for (i = log->l_logBBsize - 1; i >= (int)(*head_blk); i--) {
                        error = xlog_bread(log, i, 1, bp, &offset);
                        if (error)
                                goto done;

                        if (*(__be32 *)offset ==
                            cpu_to_be32(XLOG_HEADER_MAGIC_NUM)) {
                                found = 2;
                                break;
                        }
                }
        }
        if (!found) {
                xfs_warn(log->l_mp, "%s: couldn't find sync record", __func__);
                xlog_put_bp(bp);
                ASSERT(0);
                return XFS_ERROR(EIO);
        }

        /* find blk_no of tail of log */
        rhead = (xlog_rec_header_t *)offset;
        *tail_blk = BLOCK_LSN(be64_to_cpu(rhead->h_tail_lsn));

        /*
         * 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 = i;
        log->l_curr_block = (int)*head_blk;
        log->l_curr_cycle = be32_to_cpu(rhead->h_cycle);
        if (found == 2)
                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));

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

                if ((h_version & XLOG_VERSION_2) &&
                    (h_size > XLOG_HEADER_CYCLE_SIZE)) {
                        hblks = h_size / XLOG_HEADER_CYCLE_SIZE;
                        if (h_size % XLOG_HEADER_CYCLE_SIZE)
                                hblks++;
                } else {
                        hblks = 1;
                }
        } else {
                hblks = 1;
        }
        after_umount_blk = (i + hblks + (int)
                BTOBB(be32_to_cpu(rhead->h_len))) % log->l_logBBsize;
        tail_lsn = atomic64_read(&log->l_tail_lsn);
        if (*head_blk == after_umount_blk &&
            be32_to_cpu(rhead->h_num_logops) == 1) {
                umount_data_blk = (i + hblks) % log->l_logBBsize;
                error = xlog_bread(log, umount_data_blk, 1, bp, &offset);
                if (error)
                        goto done;

                op_head = (xlog_op_header_t *)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;

                        /*
                         * 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.
                         */
                        log->l_mp->m_flags |= XFS_MOUNT_WAS_CLEAN;
                }
        }

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

done:
        xlog_put_bp(bp);

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

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

        *blk_no = 0;

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

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

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

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

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

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

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

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

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

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

STATIC xlog_recover_t *
xlog_recover_find_tid(
        struct hlist_head       *head,
        xlog_tid_t              tid)
{
        xlog_recover_t          *trans;
        struct hlist_node       *n;

        hlist_for_each_entry(trans, n, head, r_list) {
                if (trans->r_log_tid == tid)
                        return trans;
        }
        return NULL;
}

STATIC void
xlog_recover_new_tid(
        struct hlist_head       *head,
        xlog_tid_t              tid,
        xfs_lsn_t               lsn)
{
        xlog_recover_t          *trans;

        trans = kmem_zalloc(sizeof(xlog_recover_t), KM_SLEEP);
        trans->r_log_tid   = tid;
        trans->r_lsn       = lsn;
        INIT_LIST_HEAD(&trans->r_itemq);

        INIT_HLIST_NODE(&trans->r_list);
        hlist_add_head(&trans->r_list, head);
}

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

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

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

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

        if (list_empty(&trans->r_itemq)) {
                /* finish copying rest of trans header */
                xlog_recover_add_item(&trans->r_itemq);
                ptr = (char *) &trans->r_theader +
                                sizeof(xfs_trans_header_t) - len;
                memcpy(ptr, dp, len); /* d, s, l */
                return 0;
        }
        /* take the tail entry */
        item = list_entry(trans->r_itemq.prev, xlog_recover_item_t, ri_list);

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

        ptr = kmem_realloc(old_ptr, len+old_len, KM_SLEEP);
        memcpy(&ptr[old_len], dp, len); /* d, s, l */
        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 */
        xlog_recover_item_t     *item;
        char                    *ptr;

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

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

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

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

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

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

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

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

        hlist_del(&trans->r_list);
        if ((error = xlog_recover_do_trans(log, trans, pass)))
                return error;

        xlog_recover_free_trans(trans);
        return 0;
}

STATIC int
xlog_recover_unmount_trans(
        xlog_recover_t          *trans)
{
        /* Do nothing now */
        xfs_warn(log->l_mp, "%s: Unmount LR", __func__);
        return 0;
}

/*
 * 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)
{
        char                    *lp;
        int                     num_logops;
        xlog_op_header_t        *ohead;
        xlog_recover_t          *trans;
        xlog_tid_t              tid;
        int                     error;
        unsigned long           hash;
        uint                    flags;

        lp = 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 (XFS_ERROR(EIO));

        while ((dp < lp) && num_logops) {
                ASSERT(dp + sizeof(xlog_op_header_t) <= lp);
                ohead = (xlog_op_header_t *)dp;
                dp += sizeof(xlog_op_header_t);
                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 (XFS_ERROR(EIO));
                }
                tid = be32_to_cpu(ohead->oh_tid);
                hash = XLOG_RHASH(tid);
                trans = xlog_recover_find_tid(&rhash[hash], tid);
                if (trans == NULL) {               /* not found; add new tid */
                        if (ohead->oh_flags & XLOG_START_TRANS)
                                xlog_recover_new_tid(&rhash[hash], tid,
                                        be64_to_cpu(rhead->h_lsn));
                } else {
                        if (dp + be32_to_cpu(ohead->oh_len) > lp) {
                                xfs_warn(log->l_mp, "%s: bad length 0x%x",
                                        __func__, be32_to_cpu(ohead->oh_len));
                                return (XFS_ERROR(EIO));
                        }
                        flags = ohead->oh_flags & ~XLOG_END_TRANS;
                        if (flags & XLOG_WAS_CONT_TRANS)
                                flags &= ~XLOG_CONTINUE_TRANS;
                        switch (flags) {
                        case XLOG_COMMIT_TRANS:
                                error = xlog_recover_commit_trans(log,
                                                                trans, pass);
                                break;
                        case XLOG_UNMOUNT_TRANS:
                                error = xlog_recover_unmount_trans(trans);
                                break;
                        case XLOG_WAS_CONT_TRANS:
                                error = xlog_recover_add_to_cont_trans(log,
                                                trans, dp,
                                                be32_to_cpu(ohead->oh_len));
                                break;
                        case XLOG_START_TRANS:
                                xfs_warn(log->l_mp, "%s: bad transaction",
                                        __func__);
                                ASSERT(0);
                                error = XFS_ERROR(EIO);
                                break;
                        case 0:
                        case XLOG_CONTINUE_TRANS:
                                error = xlog_recover_add_to_trans(log, trans,
                                                dp, be32_to_cpu(ohead->oh_len));
                                break;
                        default:
                                xfs_warn(log->l_mp, "%s: bad flag 0x%x",
                                        __func__, flags);
                                ASSERT(0);
                                error = XFS_ERROR(EIO);
                                break;
                        }
                        if (error)
                                return error;
                }
                dp += be32_to_cpu(ohead->oh_len);
                num_logops--;
        }
        return 0;
}

/*
 * Upack the log buffer data and crc check it. If the check fails, issue a
 * warning if and only if the CRC in the header is non-zero. This makes the
 * check an advisory warning, and the zero CRC check will prevent failure
 * warnings from being emitted when upgrading the kernel from one that does not
 * add CRCs by default.
 *
 * When filesystems are CRC enabled, this CRC mismatch becomes a fatal log
 * corruption failure
 *
 * XXX: we do not calculate the CRC here yet. It's not clear what we should do
 * with CRC errors here in userspace, so we'll address that problem later on.
 */
#define xlog_cksum(l,r,dp,len)  ((r)->h_crc)
STATIC int
xlog_unpack_data_crc(
        struct xlog_rec_header  *rhead,
        char                    *dp,
        struct xlog             *log)
{
        __le32                  crc;

        crc = xlog_cksum(log, rhead, dp, be32_to_cpu(rhead->h_len));
        if (crc != rhead->h_crc) {
                if (rhead->h_crc || xfs_sb_version_hascrc(&log->l_mp->m_sb)) {
                        xfs_alert(log->l_mp,
                "log record CRC mismatch: found 0x%x, expected 0x%x.",
                                        le32_to_cpu(rhead->h_crc),
                                        le32_to_cpu(crc));
                        xfs_hex_dump(dp, 32);
                }

                /*
                 * If we've detected a log record corruption, then we can't
                 * recover past this point. Abort recovery if we are enforcing
                 * CRC protection by punting an error back up the stack.
                 */
                if (xfs_sb_version_hascrc(&log->l_mp->m_sb))
                        return EFSCORRUPTED;
        }

        return 0;
}

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

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

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

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

        return 0;
}

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

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

        /* LR body must have data or it wouldn't have been written */
        hlen = be32_to_cpu(rhead->h_len);
        if (unlikely( hlen <= 0 || hlen > INT_MAX )) {
                XFS_ERROR_REPORT("xlog_valid_rec_header(2)",
                                XFS_ERRLEVEL_LOW, log->l_mp);
                return XFS_ERROR(EFSCORRUPTED);
        }
        if (unlikely( blkno > log->l_logBBsize || blkno > INT_MAX )) {
                XFS_ERROR_REPORT("xlog_valid_rec_header(3)",
                                XFS_ERRLEVEL_LOW, log->l_mp);
                return XFS_ERROR(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.
 */
int
xlog_do_recovery_pass(
        struct xlog             *log,
        xfs_daddr_t             head_blk,
        xfs_daddr_t             tail_blk,
        int                     pass)
{
        xlog_rec_header_t       *rhead;
        xfs_daddr_t             blk_no;
        char                    *offset;
        xfs_buf_t               *hbp, *dbp;
        int                     error = 0, h_size;
        int                     bblks, split_bblks;
        int                     hblks, split_hblks, wrapped_hblks;
        struct hlist_head       rhash[XLOG_RHASH_SIZE];

        ASSERT(head_blk != tail_blk);

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

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

                rhead = (xlog_rec_header_t *)offset;
                error = xlog_valid_rec_header(log, rhead, tail_blk);
                if (error)
                        goto bread_err1;
                h_size = be32_to_cpu(rhead->h_size);
                if ((be32_to_cpu(rhead->h_version) & XLOG_VERSION_2) &&
                    (h_size > XLOG_HEADER_CYCLE_SIZE)) {
                        hblks = h_size / XLOG_HEADER_CYCLE_SIZE;
                        if (h_size % XLOG_HEADER_CYCLE_SIZE)
                                hblks++;
                        xlog_put_bp(hbp);
                        hbp = xlog_get_bp(log, hblks);
                } else {
                        hblks = 1;
                }
        } else {
                ASSERT(log->l_sectBBsize == 1);
                hblks = 1;
                hbp = xlog_get_bp(log, 1);
                h_size = XLOG_BIG_RECORD_BSIZE;
        }

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

        memset(rhash, 0, sizeof(rhash));
        if (tail_blk <= head_blk) {
                for (blk_no = tail_blk; blk_no < head_blk; ) {
                        error = xlog_bread(log, blk_no, hblks, hbp, &offset);
                        if (error)
                                goto bread_err2;

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

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

                        error = xlog_unpack_data(rhead, offset, log);
                        if (error)
                                goto bread_err2;

                        error = xlog_recover_process_data(log,
                                                rhash, rhead, offset, pass);
                        if (error)
                                goto bread_err2;
                        blk_no += bblks + hblks;
                }
        } else {
                /*
                 * 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 as above.
                 */
                blk_no = tail_blk;
                while (blk_no < log->l_logBBsize) {
                        /*
                         * Check for header wrapping around physical end-of-log
                         */
                        offset = hbp->b_addr;
                        split_hblks = 0;
                        wrapped_hblks = 0;
                        if (blk_no + hblks <= log->l_logBBsize) {
                                /* Read header in one read */
                                error = xlog_bread(log, blk_no, hblks, hbp,
                                                   &offset);
                                if (error)
                                        goto bread_err2;
                        } else {
                                /* This LR is split across physical log end */
                                if (blk_no != log->l_logBBsize) {
                                        /* some data before physical log end */
                                        ASSERT(blk_no <= INT_MAX);
                                        split_hblks = log->l_logBBsize - (int)blk_no;
                                        ASSERT(split_hblks > 0);
                                        error = xlog_bread(log, blk_no,
                                                           split_hblks, hbp,
                                                           &offset);
                                        if (error)
                                                goto bread_err2;
                                }

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

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

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

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

                        error = xlog_unpack_data(rhead, offset, log);
                        if (error)
                                goto bread_err2;

                        error = xlog_recover_process_data(log, rhash,
                                                        rhead, offset, pass);
                        if (error)
                                goto bread_err2;
                        blk_no += bblks;
                }

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

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

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

                        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_unpack_data(rhead, offset, log);
                        if (error)
                                goto bread_err2;

                        error = xlog_recover_process_data(log, rhash,
                                                        rhead, offset, pass);
                        if (error)
                                goto bread_err2;
                        blk_no += bblks + hblks;
                }
        }

 bread_err2:
        xlog_put_bp(dbp);
 bread_err1:
        xlog_put_bp(hbp);
        return error;
}