xfs: add tracepoints and error injection for deferred extent freeing

[cascardo/linux.git] / fs / xfs / libxfs / xfs_alloc.c

/*
 * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_shared.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_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_alloc.h"
#include "xfs_extent_busy.h"
#include "xfs_error.h"
#include "xfs_cksum.h"
#include "xfs_trace.h"
#include "xfs_trans.h"
#include "xfs_buf_item.h"
#include "xfs_log.h"

struct workqueue_struct *xfs_alloc_wq;

#define XFS_ABSDIFF(a,b)        (((a) <= (b)) ? ((b) - (a)) : ((a) - (b)))

#define XFSA_FIXUP_BNO_OK       1
#define XFSA_FIXUP_CNT_OK       2

STATIC int xfs_alloc_ag_vextent_exact(xfs_alloc_arg_t *);
STATIC int xfs_alloc_ag_vextent_near(xfs_alloc_arg_t *);
STATIC int xfs_alloc_ag_vextent_size(xfs_alloc_arg_t *);
STATIC int xfs_alloc_ag_vextent_small(xfs_alloc_arg_t *,
                xfs_btree_cur_t *, xfs_agblock_t *, xfs_extlen_t *, int *);

/*
 * Lookup the record equal to [bno, len] in the btree given by cur.
 */
STATIC int                              /* error */
xfs_alloc_lookup_eq(
        struct xfs_btree_cur    *cur,   /* btree cursor */
        xfs_agblock_t           bno,    /* starting block of extent */
        xfs_extlen_t            len,    /* length of extent */
        int                     *stat)  /* success/failure */
{
        cur->bc_rec.a.ar_startblock = bno;
        cur->bc_rec.a.ar_blockcount = len;
        return xfs_btree_lookup(cur, XFS_LOOKUP_EQ, stat);
}

/*
 * Lookup the first record greater than or equal to [bno, len]
 * in the btree given by cur.
 */
int                             /* error */
xfs_alloc_lookup_ge(
        struct xfs_btree_cur    *cur,   /* btree cursor */
        xfs_agblock_t           bno,    /* starting block of extent */
        xfs_extlen_t            len,    /* length of extent */
        int                     *stat)  /* success/failure */
{
        cur->bc_rec.a.ar_startblock = bno;
        cur->bc_rec.a.ar_blockcount = len;
        return xfs_btree_lookup(cur, XFS_LOOKUP_GE, stat);
}

/*
 * Lookup the first record less than or equal to [bno, len]
 * in the btree given by cur.
 */
static int                              /* error */
xfs_alloc_lookup_le(
        struct xfs_btree_cur    *cur,   /* btree cursor */
        xfs_agblock_t           bno,    /* starting block of extent */
        xfs_extlen_t            len,    /* length of extent */
        int                     *stat)  /* success/failure */
{
        cur->bc_rec.a.ar_startblock = bno;
        cur->bc_rec.a.ar_blockcount = len;
        return xfs_btree_lookup(cur, XFS_LOOKUP_LE, stat);
}

/*
 * Update the record referred to by cur to the value given
 * by [bno, len].
 * This either works (return 0) or gets an EFSCORRUPTED error.
 */
STATIC int                              /* error */
xfs_alloc_update(
        struct xfs_btree_cur    *cur,   /* btree cursor */
        xfs_agblock_t           bno,    /* starting block of extent */
        xfs_extlen_t            len)    /* length of extent */
{
        union xfs_btree_rec     rec;

        rec.alloc.ar_startblock = cpu_to_be32(bno);
        rec.alloc.ar_blockcount = cpu_to_be32(len);
        return xfs_btree_update(cur, &rec);
}

/*
 * Get the data from the pointed-to record.
 */
int                                     /* error */
xfs_alloc_get_rec(
        struct xfs_btree_cur    *cur,   /* btree cursor */
        xfs_agblock_t           *bno,   /* output: starting block of extent */
        xfs_extlen_t            *len,   /* output: length of extent */
        int                     *stat)  /* output: success/failure */
{
        union xfs_btree_rec     *rec;
        int                     error;

        error = xfs_btree_get_rec(cur, &rec, stat);
        if (!error && *stat == 1) {
                *bno = be32_to_cpu(rec->alloc.ar_startblock);
                *len = be32_to_cpu(rec->alloc.ar_blockcount);
        }
        return error;
}

/*
 * Compute aligned version of the found extent.
 * Takes alignment and min length into account.
 */
STATIC void
xfs_alloc_compute_aligned(
        xfs_alloc_arg_t *args,          /* allocation argument structure */
        xfs_agblock_t   foundbno,       /* starting block in found extent */
        xfs_extlen_t    foundlen,       /* length in found extent */
        xfs_agblock_t   *resbno,        /* result block number */
        xfs_extlen_t    *reslen)        /* result length */
{
        xfs_agblock_t   bno;
        xfs_extlen_t    len;
        xfs_extlen_t    diff;

        /* Trim busy sections out of found extent */
        xfs_extent_busy_trim(args, foundbno, foundlen, &bno, &len);

        /*
         * If we have a largish extent that happens to start before min_agbno,
         * see if we can shift it into range...
         */
        if (bno < args->min_agbno && bno + len > args->min_agbno) {
                diff = args->min_agbno - bno;
                if (len > diff) {
                        bno += diff;
                        len -= diff;
                }
        }

        if (args->alignment > 1 && len >= args->minlen) {
                xfs_agblock_t   aligned_bno = roundup(bno, args->alignment);

                diff = aligned_bno - bno;

                *resbno = aligned_bno;
                *reslen = diff >= len ? 0 : len - diff;
        } else {
                *resbno = bno;
                *reslen = len;
        }
}

/*
 * Compute best start block and diff for "near" allocations.
 * freelen >= wantlen already checked by caller.
 */
STATIC xfs_extlen_t                     /* difference value (absolute) */
xfs_alloc_compute_diff(
        xfs_agblock_t   wantbno,        /* target starting block */
        xfs_extlen_t    wantlen,        /* target length */
        xfs_extlen_t    alignment,      /* target alignment */
        char            userdata,       /* are we allocating data? */
        xfs_agblock_t   freebno,        /* freespace's starting block */
        xfs_extlen_t    freelen,        /* freespace's length */
        xfs_agblock_t   *newbnop)       /* result: best start block from free */
{
        xfs_agblock_t   freeend;        /* end of freespace extent */
        xfs_agblock_t   newbno1;        /* return block number */
        xfs_agblock_t   newbno2;        /* other new block number */
        xfs_extlen_t    newlen1=0;      /* length with newbno1 */
        xfs_extlen_t    newlen2=0;      /* length with newbno2 */
        xfs_agblock_t   wantend;        /* end of target extent */

        ASSERT(freelen >= wantlen);
        freeend = freebno + freelen;
        wantend = wantbno + wantlen;
        /*
         * We want to allocate from the start of a free extent if it is past
         * the desired block or if we are allocating user data and the free
         * extent is before desired block. The second case is there to allow
         * for contiguous allocation from the remaining free space if the file
         * grows in the short term.
         */
        if (freebno >= wantbno || (userdata && freeend < wantend)) {
                if ((newbno1 = roundup(freebno, alignment)) >= freeend)
                        newbno1 = NULLAGBLOCK;
        } else if (freeend >= wantend && alignment > 1) {
                newbno1 = roundup(wantbno, alignment);
                newbno2 = newbno1 - alignment;
                if (newbno1 >= freeend)
                        newbno1 = NULLAGBLOCK;
                else
                        newlen1 = XFS_EXTLEN_MIN(wantlen, freeend - newbno1);
                if (newbno2 < freebno)
                        newbno2 = NULLAGBLOCK;
                else
                        newlen2 = XFS_EXTLEN_MIN(wantlen, freeend - newbno2);
                if (newbno1 != NULLAGBLOCK && newbno2 != NULLAGBLOCK) {
                        if (newlen1 < newlen2 ||
                            (newlen1 == newlen2 &&
                             XFS_ABSDIFF(newbno1, wantbno) >
                             XFS_ABSDIFF(newbno2, wantbno)))
                                newbno1 = newbno2;
                } else if (newbno2 != NULLAGBLOCK)
                        newbno1 = newbno2;
        } else if (freeend >= wantend) {
                newbno1 = wantbno;
        } else if (alignment > 1) {
                newbno1 = roundup(freeend - wantlen, alignment);
                if (newbno1 > freeend - wantlen &&
                    newbno1 - alignment >= freebno)
                        newbno1 -= alignment;
                else if (newbno1 >= freeend)
                        newbno1 = NULLAGBLOCK;
        } else
                newbno1 = freeend - wantlen;
        *newbnop = newbno1;
        return newbno1 == NULLAGBLOCK ? 0 : XFS_ABSDIFF(newbno1, wantbno);
}

/*
 * Fix up the length, based on mod and prod.
 * len should be k * prod + mod for some k.
 * If len is too small it is returned unchanged.
 * If len hits maxlen it is left alone.
 */
STATIC void
xfs_alloc_fix_len(
        xfs_alloc_arg_t *args)          /* allocation argument structure */
{
        xfs_extlen_t    k;
        xfs_extlen_t    rlen;

        ASSERT(args->mod < args->prod);
        rlen = args->len;
        ASSERT(rlen >= args->minlen);
        ASSERT(rlen <= args->maxlen);
        if (args->prod <= 1 || rlen < args->mod || rlen == args->maxlen ||
            (args->mod == 0 && rlen < args->prod))
                return;
        k = rlen % args->prod;
        if (k == args->mod)
                return;
        if (k > args->mod)
                rlen = rlen - (k - args->mod);
        else
                rlen = rlen - args->prod + (args->mod - k);
        /* casts to (int) catch length underflows */
        if ((int)rlen < (int)args->minlen)
                return;
        ASSERT(rlen >= args->minlen && rlen <= args->maxlen);
        ASSERT(rlen % args->prod == args->mod);
        args->len = rlen;
}

/*
 * Fix up length if there is too little space left in the a.g.
 * Return 1 if ok, 0 if too little, should give up.
 */
STATIC int
xfs_alloc_fix_minleft(
        xfs_alloc_arg_t *args)          /* allocation argument structure */
{
        xfs_agf_t       *agf;           /* a.g. freelist header */
        int             diff;           /* free space difference */

        if (args->minleft == 0)
                return 1;
        agf = XFS_BUF_TO_AGF(args->agbp);
        diff = be32_to_cpu(agf->agf_freeblks)
                - args->len - args->minleft;
        if (diff >= 0)
                return 1;
        args->len += diff;              /* shrink the allocated space */
        /* casts to (int) catch length underflows */
        if ((int)args->len >= (int)args->minlen)
                return 1;
        args->agbno = NULLAGBLOCK;
        return 0;
}

/*
 * Update the two btrees, logically removing from freespace the extent
 * starting at rbno, rlen blocks.  The extent is contained within the
 * actual (current) free extent fbno for flen blocks.
 * Flags are passed in indicating whether the cursors are set to the
 * relevant records.
 */
STATIC int                              /* error code */
xfs_alloc_fixup_trees(
        xfs_btree_cur_t *cnt_cur,       /* cursor for by-size btree */
        xfs_btree_cur_t *bno_cur,       /* cursor for by-block btree */
        xfs_agblock_t   fbno,           /* starting block of free extent */
        xfs_extlen_t    flen,           /* length of free extent */
        xfs_agblock_t   rbno,           /* starting block of returned extent */
        xfs_extlen_t    rlen,           /* length of returned extent */
        int             flags)          /* flags, XFSA_FIXUP_... */
{
        int             error;          /* error code */
        int             i;              /* operation results */
        xfs_agblock_t   nfbno1;         /* first new free startblock */
        xfs_agblock_t   nfbno2;         /* second new free startblock */
        xfs_extlen_t    nflen1=0;       /* first new free length */
        xfs_extlen_t    nflen2=0;       /* second new free length */
        struct xfs_mount *mp;

        mp = cnt_cur->bc_mp;

        /*
         * Look up the record in the by-size tree if necessary.
         */
        if (flags & XFSA_FIXUP_CNT_OK) {
#ifdef DEBUG
                if ((error = xfs_alloc_get_rec(cnt_cur, &nfbno1, &nflen1, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp,
                        i == 1 && nfbno1 == fbno && nflen1 == flen);
#endif
        } else {
                if ((error = xfs_alloc_lookup_eq(cnt_cur, fbno, flen, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 1);
        }
        /*
         * Look up the record in the by-block tree if necessary.
         */
        if (flags & XFSA_FIXUP_BNO_OK) {
#ifdef DEBUG
                if ((error = xfs_alloc_get_rec(bno_cur, &nfbno1, &nflen1, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp,
                        i == 1 && nfbno1 == fbno && nflen1 == flen);
#endif
        } else {
                if ((error = xfs_alloc_lookup_eq(bno_cur, fbno, flen, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 1);
        }

#ifdef DEBUG
        if (bno_cur->bc_nlevels == 1 && cnt_cur->bc_nlevels == 1) {
                struct xfs_btree_block  *bnoblock;
                struct xfs_btree_block  *cntblock;

                bnoblock = XFS_BUF_TO_BLOCK(bno_cur->bc_bufs[0]);
                cntblock = XFS_BUF_TO_BLOCK(cnt_cur->bc_bufs[0]);

                XFS_WANT_CORRUPTED_RETURN(mp,
                        bnoblock->bb_numrecs == cntblock->bb_numrecs);
        }
#endif

        /*
         * Deal with all four cases: the allocated record is contained
         * within the freespace record, so we can have new freespace
         * at either (or both) end, or no freespace remaining.
         */
        if (rbno == fbno && rlen == flen)
                nfbno1 = nfbno2 = NULLAGBLOCK;
        else if (rbno == fbno) {
                nfbno1 = rbno + rlen;
                nflen1 = flen - rlen;
                nfbno2 = NULLAGBLOCK;
        } else if (rbno + rlen == fbno + flen) {
                nfbno1 = fbno;
                nflen1 = flen - rlen;
                nfbno2 = NULLAGBLOCK;
        } else {
                nfbno1 = fbno;
                nflen1 = rbno - fbno;
                nfbno2 = rbno + rlen;
                nflen2 = (fbno + flen) - nfbno2;
        }
        /*
         * Delete the entry from the by-size btree.
         */
        if ((error = xfs_btree_delete(cnt_cur, &i)))
                return error;
        XFS_WANT_CORRUPTED_RETURN(mp, i == 1);
        /*
         * Add new by-size btree entry(s).
         */
        if (nfbno1 != NULLAGBLOCK) {
                if ((error = xfs_alloc_lookup_eq(cnt_cur, nfbno1, nflen1, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 0);
                if ((error = xfs_btree_insert(cnt_cur, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 1);
        }
        if (nfbno2 != NULLAGBLOCK) {
                if ((error = xfs_alloc_lookup_eq(cnt_cur, nfbno2, nflen2, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 0);
                if ((error = xfs_btree_insert(cnt_cur, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 1);
        }
        /*
         * Fix up the by-block btree entry(s).
         */
        if (nfbno1 == NULLAGBLOCK) {
                /*
                 * No remaining freespace, just delete the by-block tree entry.
                 */
                if ((error = xfs_btree_delete(bno_cur, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 1);
        } else {
                /*
                 * Update the by-block entry to start later|be shorter.
                 */
                if ((error = xfs_alloc_update(bno_cur, nfbno1, nflen1)))
                        return error;
        }
        if (nfbno2 != NULLAGBLOCK) {
                /*
                 * 2 resulting free entries, need to add one.
                 */
                if ((error = xfs_alloc_lookup_eq(bno_cur, nfbno2, nflen2, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 0);
                if ((error = xfs_btree_insert(bno_cur, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(mp, i == 1);
        }
        return 0;
}

static bool
xfs_agfl_verify(
        struct xfs_buf  *bp)
{
        struct xfs_mount *mp = bp->b_target->bt_mount;
        struct xfs_agfl *agfl = XFS_BUF_TO_AGFL(bp);
        int             i;

        if (!uuid_equal(&agfl->agfl_uuid, &mp->m_sb.sb_meta_uuid))
                return false;
        if (be32_to_cpu(agfl->agfl_magicnum) != XFS_AGFL_MAGIC)
                return false;
        /*
         * during growfs operations, the perag is not fully initialised,
         * so we can't use it for any useful checking. growfs ensures we can't
         * use it by using uncached buffers that don't have the perag attached
         * so we can detect and avoid this problem.
         */
        if (bp->b_pag && be32_to_cpu(agfl->agfl_seqno) != bp->b_pag->pag_agno)
                return false;

        for (i = 0; i < XFS_AGFL_SIZE(mp); i++) {
                if (be32_to_cpu(agfl->agfl_bno[i]) != NULLAGBLOCK &&
                    be32_to_cpu(agfl->agfl_bno[i]) >= mp->m_sb.sb_agblocks)
                        return false;
        }

        return xfs_log_check_lsn(mp,
                                 be64_to_cpu(XFS_BUF_TO_AGFL(bp)->agfl_lsn));
}

static void
xfs_agfl_read_verify(
        struct xfs_buf  *bp)
{
        struct xfs_mount *mp = bp->b_target->bt_mount;

        /*
         * There is no verification of non-crc AGFLs because mkfs does not
         * initialise the AGFL to zero or NULL. Hence the only valid part of the
         * AGFL is what the AGF says is active. We can't get to the AGF, so we
         * can't verify just those entries are valid.
         */
        if (!xfs_sb_version_hascrc(&mp->m_sb))
                return;

        if (!xfs_buf_verify_cksum(bp, XFS_AGFL_CRC_OFF))
                xfs_buf_ioerror(bp, -EFSBADCRC);
        else if (!xfs_agfl_verify(bp))
                xfs_buf_ioerror(bp, -EFSCORRUPTED);

        if (bp->b_error)
                xfs_verifier_error(bp);
}

static void
xfs_agfl_write_verify(
        struct xfs_buf  *bp)
{
        struct xfs_mount *mp = bp->b_target->bt_mount;
        struct xfs_buf_log_item *bip = bp->b_fspriv;

        /* no verification of non-crc AGFLs */
        if (!xfs_sb_version_hascrc(&mp->m_sb))
                return;

        if (!xfs_agfl_verify(bp)) {
                xfs_buf_ioerror(bp, -EFSCORRUPTED);
                xfs_verifier_error(bp);
                return;
        }

        if (bip)
                XFS_BUF_TO_AGFL(bp)->agfl_lsn = cpu_to_be64(bip->bli_item.li_lsn);

        xfs_buf_update_cksum(bp, XFS_AGFL_CRC_OFF);
}

const struct xfs_buf_ops xfs_agfl_buf_ops = {
        .name = "xfs_agfl",
        .verify_read = xfs_agfl_read_verify,
        .verify_write = xfs_agfl_write_verify,
};

/*
 * Read in the allocation group free block array.
 */
STATIC int                              /* error */
xfs_alloc_read_agfl(
        xfs_mount_t     *mp,            /* mount point structure */
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_agnumber_t  agno,           /* allocation group number */
        xfs_buf_t       **bpp)          /* buffer for the ag free block array */
{
        xfs_buf_t       *bp;            /* return value */
        int             error;

        ASSERT(agno != NULLAGNUMBER);
        error = xfs_trans_read_buf(
                        mp, tp, mp->m_ddev_targp,
                        XFS_AG_DADDR(mp, agno, XFS_AGFL_DADDR(mp)),
                        XFS_FSS_TO_BB(mp, 1), 0, &bp, &xfs_agfl_buf_ops);
        if (error)
                return error;
        xfs_buf_set_ref(bp, XFS_AGFL_REF);
        *bpp = bp;
        return 0;
}

STATIC int
xfs_alloc_update_counters(
        struct xfs_trans        *tp,
        struct xfs_perag        *pag,
        struct xfs_buf          *agbp,
        long                    len)
{
        struct xfs_agf          *agf = XFS_BUF_TO_AGF(agbp);

        pag->pagf_freeblks += len;
        be32_add_cpu(&agf->agf_freeblks, len);

        xfs_trans_agblocks_delta(tp, len);
        if (unlikely(be32_to_cpu(agf->agf_freeblks) >
                     be32_to_cpu(agf->agf_length)))
                return -EFSCORRUPTED;

        xfs_alloc_log_agf(tp, agbp, XFS_AGF_FREEBLKS);
        return 0;
}

/*
 * Allocation group level functions.
 */

/*
 * Allocate a variable extent in the allocation group agno.
 * Type and bno are used to determine where in the allocation group the
 * extent will start.
 * Extent's length (returned in *len) will be between minlen and maxlen,
 * and of the form k * prod + mod unless there's nothing that large.
 * Return the starting a.g. block, or NULLAGBLOCK if we can't do it.
 */
STATIC int                      /* error */
xfs_alloc_ag_vextent(
        xfs_alloc_arg_t *args)  /* argument structure for allocation */
{
        int             error=0;

        ASSERT(args->minlen > 0);
        ASSERT(args->maxlen > 0);
        ASSERT(args->minlen <= args->maxlen);
        ASSERT(args->mod < args->prod);
        ASSERT(args->alignment > 0);
        /*
         * Branch to correct routine based on the type.
         */
        args->wasfromfl = 0;
        switch (args->type) {
        case XFS_ALLOCTYPE_THIS_AG:
                error = xfs_alloc_ag_vextent_size(args);
                break;
        case XFS_ALLOCTYPE_NEAR_BNO:
                error = xfs_alloc_ag_vextent_near(args);
                break;
        case XFS_ALLOCTYPE_THIS_BNO:
                error = xfs_alloc_ag_vextent_exact(args);
                break;
        default:
                ASSERT(0);
                /* NOTREACHED */
        }

        if (error || args->agbno == NULLAGBLOCK)
                return error;

        ASSERT(args->len >= args->minlen);
        ASSERT(args->len <= args->maxlen);
        ASSERT(!args->wasfromfl || !args->isfl);
        ASSERT(args->agbno % args->alignment == 0);

        if (!args->wasfromfl) {
                error = xfs_alloc_update_counters(args->tp, args->pag,
                                                  args->agbp,
                                                  -((long)(args->len)));
                if (error)
                        return error;

                ASSERT(!xfs_extent_busy_search(args->mp, args->agno,
                                              args->agbno, args->len));
        }

        if (!args->isfl) {
                xfs_trans_mod_sb(args->tp, args->wasdel ?
                                 XFS_TRANS_SB_RES_FDBLOCKS :
                                 XFS_TRANS_SB_FDBLOCKS,
                                 -((long)(args->len)));
        }

        XFS_STATS_INC(args->mp, xs_allocx);
        XFS_STATS_ADD(args->mp, xs_allocb, args->len);
        return error;
}

/*
 * Allocate a variable extent at exactly agno/bno.
 * Extent's length (returned in *len) will be between minlen and maxlen,
 * and of the form k * prod + mod unless there's nothing that large.
 * Return the starting a.g. block (bno), or NULLAGBLOCK if we can't do it.
 */
STATIC int                      /* error */
xfs_alloc_ag_vextent_exact(
        xfs_alloc_arg_t *args)  /* allocation argument structure */
{
        xfs_btree_cur_t *bno_cur;/* by block-number btree cursor */
        xfs_btree_cur_t *cnt_cur;/* by count btree cursor */
        int             error;
        xfs_agblock_t   fbno;   /* start block of found extent */
        xfs_extlen_t    flen;   /* length of found extent */
        xfs_agblock_t   tbno;   /* start block of trimmed extent */
        xfs_extlen_t    tlen;   /* length of trimmed extent */
        xfs_agblock_t   tend;   /* end block of trimmed extent */
        int             i;      /* success/failure of operation */

        ASSERT(args->alignment == 1);

        /*
         * Allocate/initialize a cursor for the by-number freespace btree.
         */
        bno_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
                                          args->agno, XFS_BTNUM_BNO);

        /*
         * Lookup bno and minlen in the btree (minlen is irrelevant, really).
         * Look for the closest free block <= bno, it must contain bno
         * if any free block does.
         */
        error = xfs_alloc_lookup_le(bno_cur, args->agbno, args->minlen, &i);
        if (error)
                goto error0;
        if (!i)
                goto not_found;

        /*
         * Grab the freespace record.
         */
        error = xfs_alloc_get_rec(bno_cur, &fbno, &flen, &i);
        if (error)
                goto error0;
        XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
        ASSERT(fbno <= args->agbno);

        /*
         * Check for overlapping busy extents.
         */
        xfs_extent_busy_trim(args, fbno, flen, &tbno, &tlen);

        /*
         * Give up if the start of the extent is busy, or the freespace isn't
         * long enough for the minimum request.
         */
        if (tbno > args->agbno)
                goto not_found;
        if (tlen < args->minlen)
                goto not_found;
        tend = tbno + tlen;
        if (tend < args->agbno + args->minlen)
                goto not_found;

        /*
         * End of extent will be smaller of the freespace end and the
         * maximal requested end.
         *
         * Fix the length according to mod and prod if given.
         */
        args->len = XFS_AGBLOCK_MIN(tend, args->agbno + args->maxlen)
                                                - args->agbno;
        xfs_alloc_fix_len(args);
        if (!xfs_alloc_fix_minleft(args))
                goto not_found;

        ASSERT(args->agbno + args->len <= tend);

        /*
         * We are allocating agbno for args->len
         * Allocate/initialize a cursor for the by-size btree.
         */
        cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
                args->agno, XFS_BTNUM_CNT);
        ASSERT(args->agbno + args->len <=
                be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
        error = xfs_alloc_fixup_trees(cnt_cur, bno_cur, fbno, flen, args->agbno,
                                      args->len, XFSA_FIXUP_BNO_OK);
        if (error) {
                xfs_btree_del_cursor(cnt_cur, XFS_BTREE_ERROR);
                goto error0;
        }

        xfs_btree_del_cursor(bno_cur, XFS_BTREE_NOERROR);
        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);

        args->wasfromfl = 0;
        trace_xfs_alloc_exact_done(args);
        return 0;

not_found:
        /* Didn't find it, return null. */
        xfs_btree_del_cursor(bno_cur, XFS_BTREE_NOERROR);
        args->agbno = NULLAGBLOCK;
        trace_xfs_alloc_exact_notfound(args);
        return 0;

error0:
        xfs_btree_del_cursor(bno_cur, XFS_BTREE_ERROR);
        trace_xfs_alloc_exact_error(args);
        return error;
}

/*
 * Search the btree in a given direction via the search cursor and compare
 * the records found against the good extent we've already found.
 */
STATIC int
xfs_alloc_find_best_extent(
        struct xfs_alloc_arg    *args,  /* allocation argument structure */
        struct xfs_btree_cur    **gcur, /* good cursor */
        struct xfs_btree_cur    **scur, /* searching cursor */
        xfs_agblock_t           gdiff,  /* difference for search comparison */
        xfs_agblock_t           *sbno,  /* extent found by search */
        xfs_extlen_t            *slen,  /* extent length */
        xfs_agblock_t           *sbnoa, /* aligned extent found by search */
        xfs_extlen_t            *slena, /* aligned extent length */
        int                     dir)    /* 0 = search right, 1 = search left */
{
        xfs_agblock_t           new;
        xfs_agblock_t           sdiff;
        int                     error;
        int                     i;

        /* The good extent is perfect, no need to  search. */
        if (!gdiff)
                goto out_use_good;

        /*
         * Look until we find a better one, run out of space or run off the end.
         */
        do {
                error = xfs_alloc_get_rec(*scur, sbno, slen, &i);
                if (error)
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
                xfs_alloc_compute_aligned(args, *sbno, *slen, sbnoa, slena);

                /*
                 * The good extent is closer than this one.
                 */
                if (!dir) {
                        if (*sbnoa > args->max_agbno)
                                goto out_use_good;
                        if (*sbnoa >= args->agbno + gdiff)
                                goto out_use_good;
                } else {
                        if (*sbnoa < args->min_agbno)
                                goto out_use_good;
                        if (*sbnoa <= args->agbno - gdiff)
                                goto out_use_good;
                }

                /*
                 * Same distance, compare length and pick the best.
                 */
                if (*slena >= args->minlen) {
                        args->len = XFS_EXTLEN_MIN(*slena, args->maxlen);
                        xfs_alloc_fix_len(args);

                        sdiff = xfs_alloc_compute_diff(args->agbno, args->len,
                                                       args->alignment,
                                                       args->userdata, *sbnoa,
                                                       *slena, &new);

                        /*
                         * Choose closer size and invalidate other cursor.
                         */
                        if (sdiff < gdiff)
                                goto out_use_search;
                        goto out_use_good;
                }

                if (!dir)
                        error = xfs_btree_increment(*scur, 0, &i);
                else
                        error = xfs_btree_decrement(*scur, 0, &i);
                if (error)
                        goto error0;
        } while (i);

out_use_good:
        xfs_btree_del_cursor(*scur, XFS_BTREE_NOERROR);
        *scur = NULL;
        return 0;

out_use_search:
        xfs_btree_del_cursor(*gcur, XFS_BTREE_NOERROR);
        *gcur = NULL;
        return 0;

error0:
        /* caller invalidates cursors */
        return error;
}

/*
 * Allocate a variable extent near bno in the allocation group agno.
 * Extent's length (returned in len) will be between minlen and maxlen,
 * and of the form k * prod + mod unless there's nothing that large.
 * Return the starting a.g. block, or NULLAGBLOCK if we can't do it.
 */
STATIC int                              /* error */
xfs_alloc_ag_vextent_near(
        xfs_alloc_arg_t *args)          /* allocation argument structure */
{
        xfs_btree_cur_t *bno_cur_gt;    /* cursor for bno btree, right side */
        xfs_btree_cur_t *bno_cur_lt;    /* cursor for bno btree, left side */
        xfs_btree_cur_t *cnt_cur;       /* cursor for count btree */
        xfs_agblock_t   gtbno;          /* start bno of right side entry */
        xfs_agblock_t   gtbnoa;         /* aligned ... */
        xfs_extlen_t    gtdiff;         /* difference to right side entry */
        xfs_extlen_t    gtlen;          /* length of right side entry */
        xfs_extlen_t    gtlena;         /* aligned ... */
        xfs_agblock_t   gtnew;          /* useful start bno of right side */
        int             error;          /* error code */
        int             i;              /* result code, temporary */
        int             j;              /* result code, temporary */
        xfs_agblock_t   ltbno;          /* start bno of left side entry */
        xfs_agblock_t   ltbnoa;         /* aligned ... */
        xfs_extlen_t    ltdiff;         /* difference to left side entry */
        xfs_extlen_t    ltlen;          /* length of left side entry */
        xfs_extlen_t    ltlena;         /* aligned ... */
        xfs_agblock_t   ltnew;          /* useful start bno of left side */
        xfs_extlen_t    rlen;           /* length of returned extent */
        int             forced = 0;
#ifdef DEBUG
        /*
         * Randomly don't execute the first algorithm.
         */
        int             dofirst;        /* set to do first algorithm */

        dofirst = prandom_u32() & 1;
#endif

        /* handle unitialized agbno range so caller doesn't have to */
        if (!args->min_agbno && !args->max_agbno)
                args->max_agbno = args->mp->m_sb.sb_agblocks - 1;
        ASSERT(args->min_agbno <= args->max_agbno);

        /* clamp agbno to the range if it's outside */
        if (args->agbno < args->min_agbno)
                args->agbno = args->min_agbno;
        if (args->agbno > args->max_agbno)
                args->agbno = args->max_agbno;

restart:
        bno_cur_lt = NULL;
        bno_cur_gt = NULL;
        ltlen = 0;
        gtlena = 0;
        ltlena = 0;

        /*
         * Get a cursor for the by-size btree.
         */
        cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
                args->agno, XFS_BTNUM_CNT);

        /*
         * See if there are any free extents as big as maxlen.
         */
        if ((error = xfs_alloc_lookup_ge(cnt_cur, 0, args->maxlen, &i)))
                goto error0;
        /*
         * If none, then pick up the last entry in the tree unless the
         * tree is empty.
         */
        if (!i) {
                if ((error = xfs_alloc_ag_vextent_small(args, cnt_cur, &ltbno,
                                &ltlen, &i)))
                        goto error0;
                if (i == 0 || ltlen == 0) {
                        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
                        trace_xfs_alloc_near_noentry(args);
                        return 0;
                }
                ASSERT(i == 1);
        }
        args->wasfromfl = 0;

        /*
         * First algorithm.
         * If the requested extent is large wrt the freespaces available
         * in this a.g., then the cursor will be pointing to a btree entry
         * near the right edge of the tree.  If it's in the last btree leaf
         * block, then we just examine all the entries in that block
         * that are big enough, and pick the best one.
         * This is written as a while loop so we can break out of it,
         * but we never loop back to the top.
         */
        while (xfs_btree_islastblock(cnt_cur, 0)) {
                xfs_extlen_t    bdiff;
                int             besti=0;
                xfs_extlen_t    blen=0;
                xfs_agblock_t   bnew=0;

#ifdef DEBUG
                if (dofirst)
                        break;
#endif
                /*
                 * Start from the entry that lookup found, sequence through
                 * all larger free blocks.  If we're actually pointing at a
                 * record smaller than maxlen, go to the start of this block,
                 * and skip all those smaller than minlen.
                 */
                if (ltlen || args->alignment > 1) {
                        cnt_cur->bc_ptrs[0] = 1;
                        do {
                                if ((error = xfs_alloc_get_rec(cnt_cur, &ltbno,
                                                &ltlen, &i)))
                                        goto error0;
                                XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
                                if (ltlen >= args->minlen)
                                        break;
                                if ((error = xfs_btree_increment(cnt_cur, 0, &i)))
                                        goto error0;
                        } while (i);
                        ASSERT(ltlen >= args->minlen);
                        if (!i)
                                break;
                }
                i = cnt_cur->bc_ptrs[0];
                for (j = 1, blen = 0, bdiff = 0;
                     !error && j && (blen < args->maxlen || bdiff > 0);
                     error = xfs_btree_increment(cnt_cur, 0, &j)) {
                        /*
                         * For each entry, decide if it's better than
                         * the previous best entry.
                         */
                        if ((error = xfs_alloc_get_rec(cnt_cur, &ltbno, &ltlen, &i)))
                                goto error0;
                        XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
                        xfs_alloc_compute_aligned(args, ltbno, ltlen,
                                                  &ltbnoa, &ltlena);
                        if (ltlena < args->minlen)
                                continue;
                        if (ltbnoa < args->min_agbno || ltbnoa > args->max_agbno)
                                continue;
                        args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
                        xfs_alloc_fix_len(args);
                        ASSERT(args->len >= args->minlen);
                        if (args->len < blen)
                                continue;
                        ltdiff = xfs_alloc_compute_diff(args->agbno, args->len,
                                args->alignment, args->userdata, ltbnoa,
                                ltlena, &ltnew);
                        if (ltnew != NULLAGBLOCK &&
                            (args->len > blen || ltdiff < bdiff)) {
                                bdiff = ltdiff;
                                bnew = ltnew;
                                blen = args->len;
                                besti = cnt_cur->bc_ptrs[0];
                        }
                }
                /*
                 * It didn't work.  We COULD be in a case where
                 * there's a good record somewhere, so try again.
                 */
                if (blen == 0)
                        break;
                /*
                 * Point at the best entry, and retrieve it again.
                 */
                cnt_cur->bc_ptrs[0] = besti;
                if ((error = xfs_alloc_get_rec(cnt_cur, &ltbno, &ltlen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
                ASSERT(ltbno + ltlen <= be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
                args->len = blen;
                if (!xfs_alloc_fix_minleft(args)) {
                        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
                        trace_xfs_alloc_near_nominleft(args);
                        return 0;
                }
                blen = args->len;
                /*
                 * We are allocating starting at bnew for blen blocks.
                 */
                args->agbno = bnew;
                ASSERT(bnew >= ltbno);
                ASSERT(bnew + blen <= ltbno + ltlen);
                /*
                 * Set up a cursor for the by-bno tree.
                 */
                bno_cur_lt = xfs_allocbt_init_cursor(args->mp, args->tp,
                        args->agbp, args->agno, XFS_BTNUM_BNO);
                /*
                 * Fix up the btree entries.
                 */
                if ((error = xfs_alloc_fixup_trees(cnt_cur, bno_cur_lt, ltbno,
                                ltlen, bnew, blen, XFSA_FIXUP_CNT_OK)))
                        goto error0;
                xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
                xfs_btree_del_cursor(bno_cur_lt, XFS_BTREE_NOERROR);

                trace_xfs_alloc_near_first(args);
                return 0;
        }
        /*
         * Second algorithm.
         * Search in the by-bno tree to the left and to the right
         * simultaneously, until in each case we find a space big enough,
         * or run into the edge of the tree.  When we run into the edge,
         * we deallocate that cursor.
         * If both searches succeed, we compare the two spaces and pick
         * the better one.
         * With alignment, it's possible for both to fail; the upper
         * level algorithm that picks allocation groups for allocations
         * is not supposed to do this.
         */
        /*
         * Allocate and initialize the cursor for the leftward search.
         */
        bno_cur_lt = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
                args->agno, XFS_BTNUM_BNO);
        /*
         * Lookup <= bno to find the leftward search's starting point.
         */
        if ((error = xfs_alloc_lookup_le(bno_cur_lt, args->agbno, args->maxlen, &i)))
                goto error0;
        if (!i) {
                /*
                 * Didn't find anything; use this cursor for the rightward
                 * search.
                 */
                bno_cur_gt = bno_cur_lt;
                bno_cur_lt = NULL;
        }
        /*
         * Found something.  Duplicate the cursor for the rightward search.
         */
        else if ((error = xfs_btree_dup_cursor(bno_cur_lt, &bno_cur_gt)))
                goto error0;
        /*
         * Increment the cursor, so we will point at the entry just right
         * of the leftward entry if any, or to the leftmost entry.
         */
        if ((error = xfs_btree_increment(bno_cur_gt, 0, &i)))
                goto error0;
        if (!i) {
                /*
                 * It failed, there are no rightward entries.
                 */
                xfs_btree_del_cursor(bno_cur_gt, XFS_BTREE_NOERROR);
                bno_cur_gt = NULL;
        }
        /*
         * Loop going left with the leftward cursor, right with the
         * rightward cursor, until either both directions give up or
         * we find an entry at least as big as minlen.
         */
        do {
                if (bno_cur_lt) {
                        if ((error = xfs_alloc_get_rec(bno_cur_lt, &ltbno, &ltlen, &i)))
                                goto error0;
                        XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
                        xfs_alloc_compute_aligned(args, ltbno, ltlen,
                                                  &ltbnoa, &ltlena);
                        if (ltlena >= args->minlen && ltbnoa >= args->min_agbno)
                                break;
                        if ((error = xfs_btree_decrement(bno_cur_lt, 0, &i)))
                                goto error0;
                        if (!i || ltbnoa < args->min_agbno) {
                                xfs_btree_del_cursor(bno_cur_lt,
                                                     XFS_BTREE_NOERROR);
                                bno_cur_lt = NULL;
                        }
                }
                if (bno_cur_gt) {
                        if ((error = xfs_alloc_get_rec(bno_cur_gt, &gtbno, &gtlen, &i)))
                                goto error0;
                        XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
                        xfs_alloc_compute_aligned(args, gtbno, gtlen,
                                                  &gtbnoa, &gtlena);
                        if (gtlena >= args->minlen && gtbnoa <= args->max_agbno)
                                break;
                        if ((error = xfs_btree_increment(bno_cur_gt, 0, &i)))
                                goto error0;
                        if (!i || gtbnoa > args->max_agbno) {
                                xfs_btree_del_cursor(bno_cur_gt,
                                                     XFS_BTREE_NOERROR);
                                bno_cur_gt = NULL;
                        }
                }
        } while (bno_cur_lt || bno_cur_gt);

        /*
         * Got both cursors still active, need to find better entry.
         */
        if (bno_cur_lt && bno_cur_gt) {
                if (ltlena >= args->minlen) {
                        /*
                         * Left side is good, look for a right side entry.
                         */
                        args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
                        xfs_alloc_fix_len(args);
                        ltdiff = xfs_alloc_compute_diff(args->agbno, args->len,
                                args->alignment, args->userdata, ltbnoa,
                                ltlena, &ltnew);

                        error = xfs_alloc_find_best_extent(args,
                                                &bno_cur_lt, &bno_cur_gt,
                                                ltdiff, &gtbno, &gtlen,
                                                &gtbnoa, &gtlena,
                                                0 /* search right */);
                } else {
                        ASSERT(gtlena >= args->minlen);

                        /*
                         * Right side is good, look for a left side entry.
                         */
                        args->len = XFS_EXTLEN_MIN(gtlena, args->maxlen);
                        xfs_alloc_fix_len(args);
                        gtdiff = xfs_alloc_compute_diff(args->agbno, args->len,
                                args->alignment, args->userdata, gtbnoa,
                                gtlena, &gtnew);

                        error = xfs_alloc_find_best_extent(args,
                                                &bno_cur_gt, &bno_cur_lt,
                                                gtdiff, &ltbno, &ltlen,
                                                &ltbnoa, &ltlena,
                                                1 /* search left */);
                }

                if (error)
                        goto error0;
        }

        /*
         * If we couldn't get anything, give up.
         */
        if (bno_cur_lt == NULL && bno_cur_gt == NULL) {
                xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);

                if (!forced++) {
                        trace_xfs_alloc_near_busy(args);
                        xfs_log_force(args->mp, XFS_LOG_SYNC);
                        goto restart;
                }
                trace_xfs_alloc_size_neither(args);
                args->agbno = NULLAGBLOCK;
                return 0;
        }

        /*
         * At this point we have selected a freespace entry, either to the
         * left or to the right.  If it's on the right, copy all the
         * useful variables to the "left" set so we only have one
         * copy of this code.
         */
        if (bno_cur_gt) {
                bno_cur_lt = bno_cur_gt;
                bno_cur_gt = NULL;
                ltbno = gtbno;
                ltbnoa = gtbnoa;
                ltlen = gtlen;
                ltlena = gtlena;
                j = 1;
        } else
                j = 0;

        /*
         * Fix up the length and compute the useful address.
         */
        args->len = XFS_EXTLEN_MIN(ltlena, args->maxlen);
        xfs_alloc_fix_len(args);
        if (!xfs_alloc_fix_minleft(args)) {
                trace_xfs_alloc_near_nominleft(args);
                xfs_btree_del_cursor(bno_cur_lt, XFS_BTREE_NOERROR);
                xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
                return 0;
        }
        rlen = args->len;
        (void)xfs_alloc_compute_diff(args->agbno, rlen, args->alignment,
                                     args->userdata, ltbnoa, ltlena, &ltnew);
        ASSERT(ltnew >= ltbno);
        ASSERT(ltnew + rlen <= ltbnoa + ltlena);
        ASSERT(ltnew + rlen <= be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
        ASSERT(ltnew >= args->min_agbno && ltnew <= args->max_agbno);
        args->agbno = ltnew;

        if ((error = xfs_alloc_fixup_trees(cnt_cur, bno_cur_lt, ltbno, ltlen,
                        ltnew, rlen, XFSA_FIXUP_BNO_OK)))
                goto error0;

        if (j)
                trace_xfs_alloc_near_greater(args);
        else
                trace_xfs_alloc_near_lesser(args);

        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
        xfs_btree_del_cursor(bno_cur_lt, XFS_BTREE_NOERROR);
        return 0;

 error0:
        trace_xfs_alloc_near_error(args);
        if (cnt_cur != NULL)
                xfs_btree_del_cursor(cnt_cur, XFS_BTREE_ERROR);
        if (bno_cur_lt != NULL)
                xfs_btree_del_cursor(bno_cur_lt, XFS_BTREE_ERROR);
        if (bno_cur_gt != NULL)
                xfs_btree_del_cursor(bno_cur_gt, XFS_BTREE_ERROR);
        return error;
}

/*
 * Allocate a variable extent anywhere in the allocation group agno.
 * Extent's length (returned in len) will be between minlen and maxlen,
 * and of the form k * prod + mod unless there's nothing that large.
 * Return the starting a.g. block, or NULLAGBLOCK if we can't do it.
 */
STATIC int                              /* error */
xfs_alloc_ag_vextent_size(
        xfs_alloc_arg_t *args)          /* allocation argument structure */
{
        xfs_btree_cur_t *bno_cur;       /* cursor for bno btree */
        xfs_btree_cur_t *cnt_cur;       /* cursor for cnt btree */
        int             error;          /* error result */
        xfs_agblock_t   fbno;           /* start of found freespace */
        xfs_extlen_t    flen;           /* length of found freespace */
        int             i;              /* temp status variable */
        xfs_agblock_t   rbno;           /* returned block number */
        xfs_extlen_t    rlen;           /* length of returned extent */
        int             forced = 0;

restart:
        /*
         * Allocate and initialize a cursor for the by-size btree.
         */
        cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
                args->agno, XFS_BTNUM_CNT);
        bno_cur = NULL;

        /*
         * Look for an entry >= maxlen+alignment-1 blocks.
         */
        if ((error = xfs_alloc_lookup_ge(cnt_cur, 0,
                        args->maxlen + args->alignment - 1, &i)))
                goto error0;

        /*
         * If none or we have busy extents that we cannot allocate from, then
         * we have to settle for a smaller extent. In the case that there are
         * no large extents, this will return the last entry in the tree unless
         * the tree is empty. In the case that there are only busy large
         * extents, this will return the largest small extent unless there
         * are no smaller extents available.
         */
        if (!i || forced > 1) {
                error = xfs_alloc_ag_vextent_small(args, cnt_cur,
                                                   &fbno, &flen, &i);
                if (error)
                        goto error0;
                if (i == 0 || flen == 0) {
                        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
                        trace_xfs_alloc_size_noentry(args);
                        return 0;
                }
                ASSERT(i == 1);
                xfs_alloc_compute_aligned(args, fbno, flen, &rbno, &rlen);
        } else {
                /*
                 * Search for a non-busy extent that is large enough.
                 * If we are at low space, don't check, or if we fall of
                 * the end of the btree, turn off the busy check and
                 * restart.
                 */
                for (;;) {
                        error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen, &i);
                        if (error)
                                goto error0;
                        XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);

                        xfs_alloc_compute_aligned(args, fbno, flen,
                                                  &rbno, &rlen);

                        if (rlen >= args->maxlen)
                                break;

                        error = xfs_btree_increment(cnt_cur, 0, &i);
                        if (error)
                                goto error0;
                        if (i == 0) {
                                /*
                                 * Our only valid extents must have been busy.
                                 * Make it unbusy by forcing the log out and
                                 * retrying. If we've been here before, forcing
                                 * the log isn't making the extents available,
                                 * which means they have probably been freed in
                                 * this transaction.  In that case, we have to
                                 * give up on them and we'll attempt a minlen
                                 * allocation the next time around.
                                 */
                                xfs_btree_del_cursor(cnt_cur,
                                                     XFS_BTREE_NOERROR);
                                trace_xfs_alloc_size_busy(args);
                                if (!forced++)
                                        xfs_log_force(args->mp, XFS_LOG_SYNC);
                                goto restart;
                        }
                }
        }

        /*
         * In the first case above, we got the last entry in the
         * by-size btree.  Now we check to see if the space hits maxlen
         * once aligned; if not, we search left for something better.
         * This can't happen in the second case above.
         */
        rlen = XFS_EXTLEN_MIN(args->maxlen, rlen);
        XFS_WANT_CORRUPTED_GOTO(args->mp, rlen == 0 ||
                        (rlen <= flen && rbno + rlen <= fbno + flen), error0);
        if (rlen < args->maxlen) {
                xfs_agblock_t   bestfbno;
                xfs_extlen_t    bestflen;
                xfs_agblock_t   bestrbno;
                xfs_extlen_t    bestrlen;

                bestrlen = rlen;
                bestrbno = rbno;
                bestflen = flen;
                bestfbno = fbno;
                for (;;) {
                        if ((error = xfs_btree_decrement(cnt_cur, 0, &i)))
                                goto error0;
                        if (i == 0)
                                break;
                        if ((error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen,
                                        &i)))
                                goto error0;
                        XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
                        if (flen < bestrlen)
                                break;
                        xfs_alloc_compute_aligned(args, fbno, flen,
                                                  &rbno, &rlen);
                        rlen = XFS_EXTLEN_MIN(args->maxlen, rlen);
                        XFS_WANT_CORRUPTED_GOTO(args->mp, rlen == 0 ||
                                (rlen <= flen && rbno + rlen <= fbno + flen),
                                error0);
                        if (rlen > bestrlen) {
                                bestrlen = rlen;
                                bestrbno = rbno;
                                bestflen = flen;
                                bestfbno = fbno;
                                if (rlen == args->maxlen)
                                        break;
                        }
                }
                if ((error = xfs_alloc_lookup_eq(cnt_cur, bestfbno, bestflen,
                                &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
                rlen = bestrlen;
                rbno = bestrbno;
                flen = bestflen;
                fbno = bestfbno;
        }
        args->wasfromfl = 0;
        /*
         * Fix up the length.
         */
        args->len = rlen;
        if (rlen < args->minlen) {
                if (!forced++) {
                        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
                        trace_xfs_alloc_size_busy(args);
                        xfs_log_force(args->mp, XFS_LOG_SYNC);
                        goto restart;
                }
                goto out_nominleft;
        }
        xfs_alloc_fix_len(args);

        if (!xfs_alloc_fix_minleft(args))
                goto out_nominleft;
        rlen = args->len;
        XFS_WANT_CORRUPTED_GOTO(args->mp, rlen <= flen, error0);
        /*
         * Allocate and initialize a cursor for the by-block tree.
         */
        bno_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
                args->agno, XFS_BTNUM_BNO);
        if ((error = xfs_alloc_fixup_trees(cnt_cur, bno_cur, fbno, flen,
                        rbno, rlen, XFSA_FIXUP_CNT_OK)))
                goto error0;
        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
        xfs_btree_del_cursor(bno_cur, XFS_BTREE_NOERROR);
        cnt_cur = bno_cur = NULL;
        args->len = rlen;
        args->agbno = rbno;
        XFS_WANT_CORRUPTED_GOTO(args->mp,
                args->agbno + args->len <=
                        be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length),
                error0);
        trace_xfs_alloc_size_done(args);
        return 0;

error0:
        trace_xfs_alloc_size_error(args);
        if (cnt_cur)
                xfs_btree_del_cursor(cnt_cur, XFS_BTREE_ERROR);
        if (bno_cur)
                xfs_btree_del_cursor(bno_cur, XFS_BTREE_ERROR);
        return error;

out_nominleft:
        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
        trace_xfs_alloc_size_nominleft(args);
        args->agbno = NULLAGBLOCK;
        return 0;
}

/*
 * Deal with the case where only small freespaces remain.
 * Either return the contents of the last freespace record,
 * or allocate space from the freelist if there is nothing in the tree.
 */
STATIC int                      /* error */
xfs_alloc_ag_vextent_small(
        xfs_alloc_arg_t *args,  /* allocation argument structure */
        xfs_btree_cur_t *ccur,  /* by-size cursor */
        xfs_agblock_t   *fbnop, /* result block number */
        xfs_extlen_t    *flenp, /* result length */
        int             *stat)  /* status: 0-freelist, 1-normal/none */
{
        int             error;
        xfs_agblock_t   fbno;
        xfs_extlen_t    flen;
        int             i;

        if ((error = xfs_btree_decrement(ccur, 0, &i)))
                goto error0;
        if (i) {
                if ((error = xfs_alloc_get_rec(ccur, &fbno, &flen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(args->mp, i == 1, error0);
        }
        /*
         * Nothing in the btree, try the freelist.  Make sure
         * to respect minleft even when pulling from the
         * freelist.
         */
        else if (args->minlen == 1 && args->alignment == 1 && !args->isfl &&
                 (be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_flcount)
                  > args->minleft)) {
                error = xfs_alloc_get_freelist(args->tp, args->agbp, &fbno, 0);
                if (error)
                        goto error0;
                if (fbno != NULLAGBLOCK) {
                        xfs_extent_busy_reuse(args->mp, args->agno, fbno, 1,
                                             args->userdata);

                        if (args->userdata) {
                                xfs_buf_t       *bp;

                                bp = xfs_btree_get_bufs(args->mp, args->tp,
                                        args->agno, fbno, 0);
                                xfs_trans_binval(args->tp, bp);
                        }
                        args->len = 1;
                        args->agbno = fbno;
                        XFS_WANT_CORRUPTED_GOTO(args->mp,
                                args->agbno + args->len <=
                                be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length),
                                error0);
                        args->wasfromfl = 1;
                        trace_xfs_alloc_small_freelist(args);
                        *stat = 0;
                        return 0;
                }
                /*
                 * Nothing in the freelist.
                 */
                else
                        flen = 0;
        }
        /*
         * Can't allocate from the freelist for some reason.
         */
        else {
                fbno = NULLAGBLOCK;
                flen = 0;
        }
        /*
         * Can't do the allocation, give up.
         */
        if (flen < args->minlen) {
                args->agbno = NULLAGBLOCK;
                trace_xfs_alloc_small_notenough(args);
                flen = 0;
        }
        *fbnop = fbno;
        *flenp = flen;
        *stat = 1;
        trace_xfs_alloc_small_done(args);
        return 0;

error0:
        trace_xfs_alloc_small_error(args);
        return error;
}

/*
 * Free the extent starting at agno/bno for length.
 */
STATIC int                      /* error */
xfs_free_ag_extent(
        xfs_trans_t     *tp,    /* transaction pointer */
        xfs_buf_t       *agbp,  /* buffer for a.g. freelist header */
        xfs_agnumber_t  agno,   /* allocation group number */
        xfs_agblock_t   bno,    /* starting block number */
        xfs_extlen_t    len,    /* length of extent */
        int             isfl)   /* set if is freelist blocks - no sb acctg */
{
        xfs_btree_cur_t *bno_cur;       /* cursor for by-block btree */
        xfs_btree_cur_t *cnt_cur;       /* cursor for by-size btree */
        int             error;          /* error return value */
        xfs_agblock_t   gtbno;          /* start of right neighbor block */
        xfs_extlen_t    gtlen;          /* length of right neighbor block */
        int             haveleft;       /* have a left neighbor block */
        int             haveright;      /* have a right neighbor block */
        int             i;              /* temp, result code */
        xfs_agblock_t   ltbno;          /* start of left neighbor block */
        xfs_extlen_t    ltlen;          /* length of left neighbor block */
        xfs_mount_t     *mp;            /* mount point struct for filesystem */
        xfs_agblock_t   nbno;           /* new starting block of freespace */
        xfs_extlen_t    nlen;           /* new length of freespace */
        xfs_perag_t     *pag;           /* per allocation group data */

        mp = tp->t_mountp;
        /*
         * Allocate and initialize a cursor for the by-block btree.
         */
        bno_cur = xfs_allocbt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_BNO);
        cnt_cur = NULL;
        /*
         * Look for a neighboring block on the left (lower block numbers)
         * that is contiguous with this space.
         */
        if ((error = xfs_alloc_lookup_le(bno_cur, bno, len, &haveleft)))
                goto error0;
        if (haveleft) {
                /*
                 * There is a block to our left.
                 */
                if ((error = xfs_alloc_get_rec(bno_cur, &ltbno, &ltlen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                /*
                 * It's not contiguous, though.
                 */
                if (ltbno + ltlen < bno)
                        haveleft = 0;
                else {
                        /*
                         * If this failure happens the request to free this
                         * space was invalid, it's (partly) already free.
                         * Very bad.
                         */
                        XFS_WANT_CORRUPTED_GOTO(mp,
                                                ltbno + ltlen <= bno, error0);
                }
        }
        /*
         * Look for a neighboring block on the right (higher block numbers)
         * that is contiguous with this space.
         */
        if ((error = xfs_btree_increment(bno_cur, 0, &haveright)))
                goto error0;
        if (haveright) {
                /*
                 * There is a block to our right.
                 */
                if ((error = xfs_alloc_get_rec(bno_cur, &gtbno, &gtlen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                /*
                 * It's not contiguous, though.
                 */
                if (bno + len < gtbno)
                        haveright = 0;
                else {
                        /*
                         * If this failure happens the request to free this
                         * space was invalid, it's (partly) already free.
                         * Very bad.
                         */
                        XFS_WANT_CORRUPTED_GOTO(mp, gtbno >= bno + len, error0);
                }
        }
        /*
         * Now allocate and initialize a cursor for the by-size tree.
         */
        cnt_cur = xfs_allocbt_init_cursor(mp, tp, agbp, agno, XFS_BTNUM_CNT);
        /*
         * Have both left and right contiguous neighbors.
         * Merge all three into a single free block.
         */
        if (haveleft && haveright) {
                /*
                 * Delete the old by-size entry on the left.
                 */
                if ((error = xfs_alloc_lookup_eq(cnt_cur, ltbno, ltlen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                if ((error = xfs_btree_delete(cnt_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                /*
                 * Delete the old by-size entry on the right.
                 */
                if ((error = xfs_alloc_lookup_eq(cnt_cur, gtbno, gtlen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                if ((error = xfs_btree_delete(cnt_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                /*
                 * Delete the old by-block entry for the right block.
                 */
                if ((error = xfs_btree_delete(bno_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                /*
                 * Move the by-block cursor back to the left neighbor.
                 */
                if ((error = xfs_btree_decrement(bno_cur, 0, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
#ifdef DEBUG
                /*
                 * Check that this is the right record: delete didn't
                 * mangle the cursor.
                 */
                {
                        xfs_agblock_t   xxbno;
                        xfs_extlen_t    xxlen;

                        if ((error = xfs_alloc_get_rec(bno_cur, &xxbno, &xxlen,
                                        &i)))
                                goto error0;
                        XFS_WANT_CORRUPTED_GOTO(mp,
                                i == 1 && xxbno == ltbno && xxlen == ltlen,
                                error0);
                }
#endif
                /*
                 * Update remaining by-block entry to the new, joined block.
                 */
                nbno = ltbno;
                nlen = len + ltlen + gtlen;
                if ((error = xfs_alloc_update(bno_cur, nbno, nlen)))
                        goto error0;
        }
        /*
         * Have only a left contiguous neighbor.
         * Merge it together with the new freespace.
         */
        else if (haveleft) {
                /*
                 * Delete the old by-size entry on the left.
                 */
                if ((error = xfs_alloc_lookup_eq(cnt_cur, ltbno, ltlen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                if ((error = xfs_btree_delete(cnt_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                /*
                 * Back up the by-block cursor to the left neighbor, and
                 * update its length.
                 */
                if ((error = xfs_btree_decrement(bno_cur, 0, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                nbno = ltbno;
                nlen = len + ltlen;
                if ((error = xfs_alloc_update(bno_cur, nbno, nlen)))
                        goto error0;
        }
        /*
         * Have only a right contiguous neighbor.
         * Merge it together with the new freespace.
         */
        else if (haveright) {
                /*
                 * Delete the old by-size entry on the right.
                 */
                if ((error = xfs_alloc_lookup_eq(cnt_cur, gtbno, gtlen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                if ((error = xfs_btree_delete(cnt_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
                /*
                 * Update the starting block and length of the right
                 * neighbor in the by-block tree.
                 */
                nbno = bno;
                nlen = len + gtlen;
                if ((error = xfs_alloc_update(bno_cur, nbno, nlen)))
                        goto error0;
        }
        /*
         * No contiguous neighbors.
         * Insert the new freespace into the by-block tree.
         */
        else {
                nbno = bno;
                nlen = len;
                if ((error = xfs_btree_insert(bno_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
        }
        xfs_btree_del_cursor(bno_cur, XFS_BTREE_NOERROR);
        bno_cur = NULL;
        /*
         * In all cases we need to insert the new freespace in the by-size tree.
         */
        if ((error = xfs_alloc_lookup_eq(cnt_cur, nbno, nlen, &i)))
                goto error0;
        XFS_WANT_CORRUPTED_GOTO(mp, i == 0, error0);
        if ((error = xfs_btree_insert(cnt_cur, &i)))
                goto error0;
        XFS_WANT_CORRUPTED_GOTO(mp, i == 1, error0);
        xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
        cnt_cur = NULL;

        /*
         * Update the freespace totals in the ag and superblock.
         */
        pag = xfs_perag_get(mp, agno);
        error = xfs_alloc_update_counters(tp, pag, agbp, len);
        xfs_perag_put(pag);
        if (error)
                goto error0;

        if (!isfl)
                xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, (long)len);
        XFS_STATS_INC(mp, xs_freex);
        XFS_STATS_ADD(mp, xs_freeb, len);

        trace_xfs_free_extent(mp, agno, bno, len, isfl, haveleft, haveright);

        return 0;

 error0:
        trace_xfs_free_extent(mp, agno, bno, len, isfl, -1, -1);
        if (bno_cur)
                xfs_btree_del_cursor(bno_cur, XFS_BTREE_ERROR);
        if (cnt_cur)
                xfs_btree_del_cursor(cnt_cur, XFS_BTREE_ERROR);
        return error;
}

/*
 * Visible (exported) allocation/free functions.
 * Some of these are used just by xfs_alloc_btree.c and this file.
 */

/*
 * Compute and fill in value of m_ag_maxlevels.
 */
void
xfs_alloc_compute_maxlevels(
        xfs_mount_t     *mp)    /* file system mount structure */
{
        mp->m_ag_maxlevels = xfs_btree_compute_maxlevels(mp, mp->m_alloc_mnr,
                        (mp->m_sb.sb_agblocks + 1) / 2);
}

/*
 * Find the length of the longest extent in an AG.
 */
xfs_extlen_t
xfs_alloc_longest_free_extent(
        struct xfs_mount        *mp,
        struct xfs_perag        *pag,
        xfs_extlen_t            need)
{
        xfs_extlen_t            delta = 0;

        if (need > pag->pagf_flcount)
                delta = need - pag->pagf_flcount;

        if (pag->pagf_longest > delta)
                return pag->pagf_longest - delta;
        return pag->pagf_flcount > 0 || pag->pagf_longest > 0;
}

unsigned int
xfs_alloc_min_freelist(
        struct xfs_mount        *mp,
        struct xfs_perag        *pag)
{
        unsigned int            min_free;

        /* space needed by-bno freespace btree */
        min_free = min_t(unsigned int, pag->pagf_levels[XFS_BTNUM_BNOi] + 1,
                                       mp->m_ag_maxlevels);
        /* space needed by-size freespace btree */
        min_free += min_t(unsigned int, pag->pagf_levels[XFS_BTNUM_CNTi] + 1,
                                       mp->m_ag_maxlevels);

        return min_free;
}

/*
 * Check if the operation we are fixing up the freelist for should go ahead or
 * not. If we are freeing blocks, we always allow it, otherwise the allocation
 * is dependent on whether the size and shape of free space available will
 * permit the requested allocation to take place.
 */
static bool
xfs_alloc_space_available(
        struct xfs_alloc_arg    *args,
        xfs_extlen_t            min_free,
        int                     flags)
{
        struct xfs_perag        *pag = args->pag;
        xfs_extlen_t            longest;
        int                     available;

        if (flags & XFS_ALLOC_FLAG_FREEING)
                return true;

        /* do we have enough contiguous free space for the allocation? */
        longest = xfs_alloc_longest_free_extent(args->mp, pag, min_free);
        if ((args->minlen + args->alignment + args->minalignslop - 1) > longest)
                return false;

        /* do have enough free space remaining for the allocation? */
        available = (int)(pag->pagf_freeblks + pag->pagf_flcount -
                          min_free - args->total);
        if (available < (int)args->minleft)
                return false;

        return true;
}

/*
 * Decide whether to use this allocation group for this allocation.
 * If so, fix up the btree freelist's size.
 */
int                     /* error */
xfs_alloc_fix_freelist(
        struct xfs_alloc_arg    *args,  /* allocation argument structure */
        int                     flags)  /* XFS_ALLOC_FLAG_... */
{
        struct xfs_mount        *mp = args->mp;
        struct xfs_perag        *pag = args->pag;
        struct xfs_trans        *tp = args->tp;
        struct xfs_buf          *agbp = NULL;
        struct xfs_buf          *agflbp = NULL;
        struct xfs_alloc_arg    targs;  /* local allocation arguments */
        xfs_agblock_t           bno;    /* freelist block */
        xfs_extlen_t            need;   /* total blocks needed in freelist */
        int                     error = 0;

        if (!pag->pagf_init) {
                error = xfs_alloc_read_agf(mp, tp, args->agno, flags, &agbp);
                if (error)
                        goto out_no_agbp;
                if (!pag->pagf_init) {
                        ASSERT(flags & XFS_ALLOC_FLAG_TRYLOCK);
                        ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING));
                        goto out_agbp_relse;
                }
        }

        /*
         * If this is a metadata preferred pag and we are user data then try
         * somewhere else if we are not being asked to try harder at this
         * point
         */
        if (pag->pagf_metadata && args->userdata &&
            (flags & XFS_ALLOC_FLAG_TRYLOCK)) {
                ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING));
                goto out_agbp_relse;
        }

        need = xfs_alloc_min_freelist(mp, pag);
        if (!xfs_alloc_space_available(args, need, flags))
                goto out_agbp_relse;

        /*
         * Get the a.g. freespace buffer.
         * Can fail if we're not blocking on locks, and it's held.
         */
        if (!agbp) {
                error = xfs_alloc_read_agf(mp, tp, args->agno, flags, &agbp);
                if (error)
                        goto out_no_agbp;
                if (!agbp) {
                        ASSERT(flags & XFS_ALLOC_FLAG_TRYLOCK);
                        ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING));
                        goto out_no_agbp;
                }
        }

        /* If there isn't enough total space or single-extent, reject it. */
        need = xfs_alloc_min_freelist(mp, pag);
        if (!xfs_alloc_space_available(args, need, flags))
                goto out_agbp_relse;

        /*
         * Make the freelist shorter if it's too long.
         *
         * Note that from this point onwards, we will always release the agf and
         * agfl buffers on error. This handles the case where we error out and
         * the buffers are clean or may not have been joined to the transaction
         * and hence need to be released manually. If they have been joined to
         * the transaction, then xfs_trans_brelse() will handle them
         * appropriately based on the recursion count and dirty state of the
         * buffer.
         *
         * XXX (dgc): When we have lots of free space, does this buy us
         * anything other than extra overhead when we need to put more blocks
         * back on the free list? Maybe we should only do this when space is
         * getting low or the AGFL is more than half full?
         */
        while (pag->pagf_flcount > need) {
                struct xfs_buf  *bp;

                error = xfs_alloc_get_freelist(tp, agbp, &bno, 0);
                if (error)
                        goto out_agbp_relse;
                error = xfs_free_ag_extent(tp, agbp, args->agno, bno, 1, 1);
                if (error)
                        goto out_agbp_relse;
                bp = xfs_btree_get_bufs(mp, tp, args->agno, bno, 0);
                xfs_trans_binval(tp, bp);
        }

        memset(&targs, 0, sizeof(targs));
        targs.tp = tp;
        targs.mp = mp;
        targs.agbp = agbp;
        targs.agno = args->agno;
        targs.alignment = targs.minlen = targs.prod = targs.isfl = 1;
        targs.type = XFS_ALLOCTYPE_THIS_AG;
        targs.pag = pag;
        error = xfs_alloc_read_agfl(mp, tp, targs.agno, &agflbp);
        if (error)
                goto out_agbp_relse;

        /* Make the freelist longer if it's too short. */
        while (pag->pagf_flcount < need) {
                targs.agbno = 0;
                targs.maxlen = need - pag->pagf_flcount;

                /* Allocate as many blocks as possible at once. */
                error = xfs_alloc_ag_vextent(&targs);
                if (error)
                        goto out_agflbp_relse;

                /*
                 * Stop if we run out.  Won't happen if callers are obeying
                 * the restrictions correctly.  Can happen for free calls
                 * on a completely full ag.
                 */
                if (targs.agbno == NULLAGBLOCK) {
                        if (flags & XFS_ALLOC_FLAG_FREEING)
                                break;
                        goto out_agflbp_relse;
                }
                /*
                 * Put each allocated block on the list.
                 */
                for (bno = targs.agbno; bno < targs.agbno + targs.len; bno++) {
                        error = xfs_alloc_put_freelist(tp, agbp,
                                                        agflbp, bno, 0);
                        if (error)
                                goto out_agflbp_relse;
                }
        }
        xfs_trans_brelse(tp, agflbp);
        args->agbp = agbp;
        return 0;

out_agflbp_relse:
        xfs_trans_brelse(tp, agflbp);
out_agbp_relse:
        if (agbp)
                xfs_trans_brelse(tp, agbp);
out_no_agbp:
        args->agbp = NULL;
        return error;
}

/*
 * Get a block from the freelist.
 * Returns with the buffer for the block gotten.
 */
int                             /* error */
xfs_alloc_get_freelist(
        xfs_trans_t     *tp,    /* transaction pointer */
        xfs_buf_t       *agbp,  /* buffer containing the agf structure */
        xfs_agblock_t   *bnop,  /* block address retrieved from freelist */
        int             btreeblk) /* destination is a AGF btree */
{
        xfs_agf_t       *agf;   /* a.g. freespace structure */
        xfs_buf_t       *agflbp;/* buffer for a.g. freelist structure */
        xfs_agblock_t   bno;    /* block number returned */
        __be32          *agfl_bno;
        int             error;
        int             logflags;
        xfs_mount_t     *mp = tp->t_mountp;
        xfs_perag_t     *pag;   /* per allocation group data */

        /*
         * Freelist is empty, give up.
         */
        agf = XFS_BUF_TO_AGF(agbp);
        if (!agf->agf_flcount) {
                *bnop = NULLAGBLOCK;
                return 0;
        }
        /*
         * Read the array of free blocks.
         */
        error = xfs_alloc_read_agfl(mp, tp, be32_to_cpu(agf->agf_seqno),
                                    &agflbp);
        if (error)
                return error;


        /*
         * Get the block number and update the data structures.
         */
        agfl_bno = XFS_BUF_TO_AGFL_BNO(mp, agflbp);
        bno = be32_to_cpu(agfl_bno[be32_to_cpu(agf->agf_flfirst)]);
        be32_add_cpu(&agf->agf_flfirst, 1);
        xfs_trans_brelse(tp, agflbp);
        if (be32_to_cpu(agf->agf_flfirst) == XFS_AGFL_SIZE(mp))
                agf->agf_flfirst = 0;

        pag = xfs_perag_get(mp, be32_to_cpu(agf->agf_seqno));
        be32_add_cpu(&agf->agf_flcount, -1);
        xfs_trans_agflist_delta(tp, -1);
        pag->pagf_flcount--;
        xfs_perag_put(pag);

        logflags = XFS_AGF_FLFIRST | XFS_AGF_FLCOUNT;
        if (btreeblk) {
                be32_add_cpu(&agf->agf_btreeblks, 1);
                pag->pagf_btreeblks++;
                logflags |= XFS_AGF_BTREEBLKS;
        }

        xfs_alloc_log_agf(tp, agbp, logflags);
        *bnop = bno;

        return 0;
}

/*
 * Log the given fields from the agf structure.
 */
void
xfs_alloc_log_agf(
        xfs_trans_t     *tp,    /* transaction pointer */
        xfs_buf_t       *bp,    /* buffer for a.g. freelist header */
        int             fields) /* mask of fields to be logged (XFS_AGF_...) */
{
        int     first;          /* first byte offset */
        int     last;           /* last byte offset */
        static const short      offsets[] = {
                offsetof(xfs_agf_t, agf_magicnum),
                offsetof(xfs_agf_t, agf_versionnum),
                offsetof(xfs_agf_t, agf_seqno),
                offsetof(xfs_agf_t, agf_length),
                offsetof(xfs_agf_t, agf_roots[0]),
                offsetof(xfs_agf_t, agf_levels[0]),
                offsetof(xfs_agf_t, agf_flfirst),
                offsetof(xfs_agf_t, agf_fllast),
                offsetof(xfs_agf_t, agf_flcount),
                offsetof(xfs_agf_t, agf_freeblks),
                offsetof(xfs_agf_t, agf_longest),
                offsetof(xfs_agf_t, agf_btreeblks),
                offsetof(xfs_agf_t, agf_uuid),
                sizeof(xfs_agf_t)
        };

        trace_xfs_agf(tp->t_mountp, XFS_BUF_TO_AGF(bp), fields, _RET_IP_);

        xfs_trans_buf_set_type(tp, bp, XFS_BLFT_AGF_BUF);

        xfs_btree_offsets(fields, offsets, XFS_AGF_NUM_BITS, &first, &last);
        xfs_trans_log_buf(tp, bp, (uint)first, (uint)last);
}

/*
 * Interface for inode allocation to force the pag data to be initialized.
 */
int                                     /* error */
xfs_alloc_pagf_init(
        xfs_mount_t             *mp,    /* file system mount structure */
        xfs_trans_t             *tp,    /* transaction pointer */
        xfs_agnumber_t          agno,   /* allocation group number */
        int                     flags)  /* XFS_ALLOC_FLAGS_... */
{
        xfs_buf_t               *bp;
        int                     error;

        if ((error = xfs_alloc_read_agf(mp, tp, agno, flags, &bp)))
                return error;
        if (bp)
                xfs_trans_brelse(tp, bp);
        return 0;
}

/*
 * Put the block on the freelist for the allocation group.
 */
int                                     /* error */
xfs_alloc_put_freelist(
        xfs_trans_t             *tp,    /* transaction pointer */
        xfs_buf_t               *agbp,  /* buffer for a.g. freelist header */
        xfs_buf_t               *agflbp,/* buffer for a.g. free block array */
        xfs_agblock_t           bno,    /* block being freed */
        int                     btreeblk) /* block came from a AGF btree */
{
        xfs_agf_t               *agf;   /* a.g. freespace structure */
        __be32                  *blockp;/* pointer to array entry */
        int                     error;
        int                     logflags;
        xfs_mount_t             *mp;    /* mount structure */
        xfs_perag_t             *pag;   /* per allocation group data */
        __be32                  *agfl_bno;
        int                     startoff;

        agf = XFS_BUF_TO_AGF(agbp);
        mp = tp->t_mountp;

        if (!agflbp && (error = xfs_alloc_read_agfl(mp, tp,
                        be32_to_cpu(agf->agf_seqno), &agflbp)))
                return error;
        be32_add_cpu(&agf->agf_fllast, 1);
        if (be32_to_cpu(agf->agf_fllast) == XFS_AGFL_SIZE(mp))
                agf->agf_fllast = 0;

        pag = xfs_perag_get(mp, be32_to_cpu(agf->agf_seqno));
        be32_add_cpu(&agf->agf_flcount, 1);
        xfs_trans_agflist_delta(tp, 1);
        pag->pagf_flcount++;

        logflags = XFS_AGF_FLLAST | XFS_AGF_FLCOUNT;
        if (btreeblk) {
                be32_add_cpu(&agf->agf_btreeblks, -1);
                pag->pagf_btreeblks--;
                logflags |= XFS_AGF_BTREEBLKS;
        }
        xfs_perag_put(pag);

        xfs_alloc_log_agf(tp, agbp, logflags);

        ASSERT(be32_to_cpu(agf->agf_flcount) <= XFS_AGFL_SIZE(mp));

        agfl_bno = XFS_BUF_TO_AGFL_BNO(mp, agflbp);
        blockp = &agfl_bno[be32_to_cpu(agf->agf_fllast)];
        *blockp = cpu_to_be32(bno);
        startoff = (char *)blockp - (char *)agflbp->b_addr;

        xfs_alloc_log_agf(tp, agbp, logflags);

        xfs_trans_buf_set_type(tp, agflbp, XFS_BLFT_AGFL_BUF);
        xfs_trans_log_buf(tp, agflbp, startoff,
                          startoff + sizeof(xfs_agblock_t) - 1);
        return 0;
}

static bool
xfs_agf_verify(
        struct xfs_mount *mp,
        struct xfs_buf  *bp)
 {
        struct xfs_agf  *agf = XFS_BUF_TO_AGF(bp);

        if (xfs_sb_version_hascrc(&mp->m_sb)) {
                if (!uuid_equal(&agf->agf_uuid, &mp->m_sb.sb_meta_uuid))
                        return false;
                if (!xfs_log_check_lsn(mp,
                                be64_to_cpu(XFS_BUF_TO_AGF(bp)->agf_lsn)))
                        return false;
        }

        if (!(agf->agf_magicnum == cpu_to_be32(XFS_AGF_MAGIC) &&
              XFS_AGF_GOOD_VERSION(be32_to_cpu(agf->agf_versionnum)) &&
              be32_to_cpu(agf->agf_freeblks) <= be32_to_cpu(agf->agf_length) &&
              be32_to_cpu(agf->agf_flfirst) < XFS_AGFL_SIZE(mp) &&
              be32_to_cpu(agf->agf_fllast) < XFS_AGFL_SIZE(mp) &&
              be32_to_cpu(agf->agf_flcount) <= XFS_AGFL_SIZE(mp)))
                return false;

        if (be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) > XFS_BTREE_MAXLEVELS ||
            be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]) > XFS_BTREE_MAXLEVELS)
                return false;

        /*
         * during growfs operations, the perag is not fully initialised,
         * so we can't use it for any useful checking. growfs ensures we can't
         * use it by using uncached buffers that don't have the perag attached
         * so we can detect and avoid this problem.
         */
        if (bp->b_pag && be32_to_cpu(agf->agf_seqno) != bp->b_pag->pag_agno)
                return false;

        if (xfs_sb_version_haslazysbcount(&mp->m_sb) &&
            be32_to_cpu(agf->agf_btreeblks) > be32_to_cpu(agf->agf_length))
                return false;

        return true;;

}

static void
xfs_agf_read_verify(
        struct xfs_buf  *bp)
{
        struct xfs_mount *mp = bp->b_target->bt_mount;

        if (xfs_sb_version_hascrc(&mp->m_sb) &&
            !xfs_buf_verify_cksum(bp, XFS_AGF_CRC_OFF))
                xfs_buf_ioerror(bp, -EFSBADCRC);
        else if (XFS_TEST_ERROR(!xfs_agf_verify(mp, bp), mp,
                                XFS_ERRTAG_ALLOC_READ_AGF,
                                XFS_RANDOM_ALLOC_READ_AGF))
                xfs_buf_ioerror(bp, -EFSCORRUPTED);

        if (bp->b_error)
                xfs_verifier_error(bp);
}

static void
xfs_agf_write_verify(
        struct xfs_buf  *bp)
{
        struct xfs_mount *mp = bp->b_target->bt_mount;
        struct xfs_buf_log_item *bip = bp->b_fspriv;

        if (!xfs_agf_verify(mp, bp)) {
                xfs_buf_ioerror(bp, -EFSCORRUPTED);
                xfs_verifier_error(bp);
                return;
        }

        if (!xfs_sb_version_hascrc(&mp->m_sb))
                return;

        if (bip)
                XFS_BUF_TO_AGF(bp)->agf_lsn = cpu_to_be64(bip->bli_item.li_lsn);

        xfs_buf_update_cksum(bp, XFS_AGF_CRC_OFF);
}

const struct xfs_buf_ops xfs_agf_buf_ops = {
        .name = "xfs_agf",
        .verify_read = xfs_agf_read_verify,
        .verify_write = xfs_agf_write_verify,
};

/*
 * Read in the allocation group header (free/alloc section).
 */
int                                     /* error */
xfs_read_agf(
        struct xfs_mount        *mp,    /* mount point structure */
        struct xfs_trans        *tp,    /* transaction pointer */
        xfs_agnumber_t          agno,   /* allocation group number */
        int                     flags,  /* XFS_BUF_ */
        struct xfs_buf          **bpp)  /* buffer for the ag freelist header */
{
        int             error;

        trace_xfs_read_agf(mp, agno);

        ASSERT(agno != NULLAGNUMBER);
        error = xfs_trans_read_buf(
                        mp, tp, mp->m_ddev_targp,
                        XFS_AG_DADDR(mp, agno, XFS_AGF_DADDR(mp)),
                        XFS_FSS_TO_BB(mp, 1), flags, bpp, &xfs_agf_buf_ops);
        if (error)
                return error;
        if (!*bpp)
                return 0;

        ASSERT(!(*bpp)->b_error);
        xfs_buf_set_ref(*bpp, XFS_AGF_REF);
        return 0;
}

/*
 * Read in the allocation group header (free/alloc section).
 */
int                                     /* error */
xfs_alloc_read_agf(
        struct xfs_mount        *mp,    /* mount point structure */
        struct xfs_trans        *tp,    /* transaction pointer */
        xfs_agnumber_t          agno,   /* allocation group number */
        int                     flags,  /* XFS_ALLOC_FLAG_... */
        struct xfs_buf          **bpp)  /* buffer for the ag freelist header */
{
        struct xfs_agf          *agf;           /* ag freelist header */
        struct xfs_perag        *pag;           /* per allocation group data */
        int                     error;

        trace_xfs_alloc_read_agf(mp, agno);

        ASSERT(agno != NULLAGNUMBER);
        error = xfs_read_agf(mp, tp, agno,
                        (flags & XFS_ALLOC_FLAG_TRYLOCK) ? XBF_TRYLOCK : 0,
                        bpp);
        if (error)
                return error;
        if (!*bpp)
                return 0;
        ASSERT(!(*bpp)->b_error);

        agf = XFS_BUF_TO_AGF(*bpp);
        pag = xfs_perag_get(mp, agno);
        if (!pag->pagf_init) {
                pag->pagf_freeblks = be32_to_cpu(agf->agf_freeblks);
                pag->pagf_btreeblks = be32_to_cpu(agf->agf_btreeblks);
                pag->pagf_flcount = be32_to_cpu(agf->agf_flcount);
                pag->pagf_longest = be32_to_cpu(agf->agf_longest);
                pag->pagf_levels[XFS_BTNUM_BNOi] =
                        be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNOi]);
                pag->pagf_levels[XFS_BTNUM_CNTi] =
                        be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNTi]);
                spin_lock_init(&pag->pagb_lock);
                pag->pagb_count = 0;
                pag->pagb_tree = RB_ROOT;
                pag->pagf_init = 1;
        }
#ifdef DEBUG
        else if (!XFS_FORCED_SHUTDOWN(mp)) {
                ASSERT(pag->pagf_freeblks == be32_to_cpu(agf->agf_freeblks));
                ASSERT(pag->pagf_btreeblks == be32_to_cpu(agf->agf_btreeblks));
                ASSERT(pag->pagf_flcount == be32_to_cpu(agf->agf_flcount));
                ASSERT(pag->pagf_longest == be32_to_cpu(agf->agf_longest));
                ASSERT(pag->pagf_levels[XFS_BTNUM_BNOi] ==
                       be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNOi]));
                ASSERT(pag->pagf_levels[XFS_BTNUM_CNTi] ==
                       be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNTi]));
        }
#endif
        xfs_perag_put(pag);
        return 0;
}

/*
 * Allocate an extent (variable-size).
 * Depending on the allocation type, we either look in a single allocation
 * group or loop over the allocation groups to find the result.
 */
int                             /* error */
xfs_alloc_vextent(
        xfs_alloc_arg_t *args)  /* allocation argument structure */
{
        xfs_agblock_t   agsize; /* allocation group size */
        int             error;
        int             flags;  /* XFS_ALLOC_FLAG_... locking flags */
        xfs_extlen_t    minleft;/* minimum left value, temp copy */
        xfs_mount_t     *mp;    /* mount structure pointer */
        xfs_agnumber_t  sagno;  /* starting allocation group number */
        xfs_alloctype_t type;   /* input allocation type */
        int             bump_rotor = 0;
        int             no_min = 0;
        xfs_agnumber_t  rotorstep = xfs_rotorstep; /* inode32 agf stepper */

        mp = args->mp;
        type = args->otype = args->type;
        args->agbno = NULLAGBLOCK;
        /*
         * Just fix this up, for the case where the last a.g. is shorter
         * (or there's only one a.g.) and the caller couldn't easily figure
         * that out (xfs_bmap_alloc).
         */
        agsize = mp->m_sb.sb_agblocks;
        if (args->maxlen > agsize)
                args->maxlen = agsize;
        if (args->alignment == 0)
                args->alignment = 1;
        ASSERT(XFS_FSB_TO_AGNO(mp, args->fsbno) < mp->m_sb.sb_agcount);
        ASSERT(XFS_FSB_TO_AGBNO(mp, args->fsbno) < agsize);
        ASSERT(args->minlen <= args->maxlen);
        ASSERT(args->minlen <= agsize);
        ASSERT(args->mod < args->prod);
        if (XFS_FSB_TO_AGNO(mp, args->fsbno) >= mp->m_sb.sb_agcount ||
            XFS_FSB_TO_AGBNO(mp, args->fsbno) >= agsize ||
            args->minlen > args->maxlen || args->minlen > agsize ||
            args->mod >= args->prod) {
                args->fsbno = NULLFSBLOCK;
                trace_xfs_alloc_vextent_badargs(args);
                return 0;
        }
        minleft = args->minleft;

        switch (type) {
        case XFS_ALLOCTYPE_THIS_AG:
        case XFS_ALLOCTYPE_NEAR_BNO:
        case XFS_ALLOCTYPE_THIS_BNO:
                /*
                 * These three force us into a single a.g.
                 */
                args->agno = XFS_FSB_TO_AGNO(mp, args->fsbno);
                args->pag = xfs_perag_get(mp, args->agno);
                args->minleft = 0;
                error = xfs_alloc_fix_freelist(args, 0);
                args->minleft = minleft;
                if (error) {
                        trace_xfs_alloc_vextent_nofix(args);
                        goto error0;
                }
                if (!args->agbp) {
                        trace_xfs_alloc_vextent_noagbp(args);
                        break;
                }
                args->agbno = XFS_FSB_TO_AGBNO(mp, args->fsbno);
                if ((error = xfs_alloc_ag_vextent(args)))
                        goto error0;
                break;
        case XFS_ALLOCTYPE_START_BNO:
                /*
                 * Try near allocation first, then anywhere-in-ag after
                 * the first a.g. fails.
                 */
                if ((args->userdata & XFS_ALLOC_INITIAL_USER_DATA) &&
                    (mp->m_flags & XFS_MOUNT_32BITINODES)) {
                        args->fsbno = XFS_AGB_TO_FSB(mp,
                                        ((mp->m_agfrotor / rotorstep) %
                                        mp->m_sb.sb_agcount), 0);
                        bump_rotor = 1;
                }
                args->agbno = XFS_FSB_TO_AGBNO(mp, args->fsbno);
                args->type = XFS_ALLOCTYPE_NEAR_BNO;
                /* FALLTHROUGH */
        case XFS_ALLOCTYPE_ANY_AG:
        case XFS_ALLOCTYPE_START_AG:
        case XFS_ALLOCTYPE_FIRST_AG:
                /*
                 * Rotate through the allocation groups looking for a winner.
                 */
                if (type == XFS_ALLOCTYPE_ANY_AG) {
                        /*
                         * Start with the last place we left off.
                         */
                        args->agno = sagno = (mp->m_agfrotor / rotorstep) %
                                        mp->m_sb.sb_agcount;
                        args->type = XFS_ALLOCTYPE_THIS_AG;
                        flags = XFS_ALLOC_FLAG_TRYLOCK;
                } else if (type == XFS_ALLOCTYPE_FIRST_AG) {
                        /*
                         * Start with allocation group given by bno.
                         */
                        args->agno = XFS_FSB_TO_AGNO(mp, args->fsbno);
                        args->type = XFS_ALLOCTYPE_THIS_AG;
                        sagno = 0;
                        flags = 0;
                } else {
                        if (type == XFS_ALLOCTYPE_START_AG)
                                args->type = XFS_ALLOCTYPE_THIS_AG;
                        /*
                         * Start with the given allocation group.
                         */
                        args->agno = sagno = XFS_FSB_TO_AGNO(mp, args->fsbno);
                        flags = XFS_ALLOC_FLAG_TRYLOCK;
                }
                /*
                 * Loop over allocation groups twice; first time with
                 * trylock set, second time without.
                 */
                for (;;) {
                        args->pag = xfs_perag_get(mp, args->agno);
                        if (no_min) args->minleft = 0;
                        error = xfs_alloc_fix_freelist(args, flags);
                        args->minleft = minleft;
                        if (error) {
                                trace_xfs_alloc_vextent_nofix(args);
                                goto error0;
                        }
                        /*
                         * If we get a buffer back then the allocation will fly.
                         */
                        if (args->agbp) {
                                if ((error = xfs_alloc_ag_vextent(args)))
                                        goto error0;
                                break;
                        }

                        trace_xfs_alloc_vextent_loopfailed(args);

                        /*
                         * Didn't work, figure out the next iteration.
                         */
                        if (args->agno == sagno &&
                            type == XFS_ALLOCTYPE_START_BNO)
                                args->type = XFS_ALLOCTYPE_THIS_AG;
                        /*
                        * For the first allocation, we can try any AG to get
                        * space.  However, if we already have allocated a
                        * block, we don't want to try AGs whose number is below
                        * sagno. Otherwise, we may end up with out-of-order
                        * locking of AGF, which might cause deadlock.
                        */
                        if (++(args->agno) == mp->m_sb.sb_agcount) {
                                if (args->firstblock != NULLFSBLOCK)
                                        args->agno = sagno;
                                else
                                        args->agno = 0;
                        }
                        /*
                         * Reached the starting a.g., must either be done
                         * or switch to non-trylock mode.
                         */
                        if (args->agno == sagno) {
                                if (no_min == 1) {
                                        args->agbno = NULLAGBLOCK;
                                        trace_xfs_alloc_vextent_allfailed(args);
                                        break;
                                }
                                if (flags == 0) {
                                        no_min = 1;
                                } else {
                                        flags = 0;
                                        if (type == XFS_ALLOCTYPE_START_BNO) {
                                                args->agbno = XFS_FSB_TO_AGBNO(mp,
                                                        args->fsbno);
                                                args->type = XFS_ALLOCTYPE_NEAR_BNO;
                                        }
                                }
                        }
                        xfs_perag_put(args->pag);
                }
                if (bump_rotor || (type == XFS_ALLOCTYPE_ANY_AG)) {
                        if (args->agno == sagno)
                                mp->m_agfrotor = (mp->m_agfrotor + 1) %
                                        (mp->m_sb.sb_agcount * rotorstep);
                        else
                                mp->m_agfrotor = (args->agno * rotorstep + 1) %
                                        (mp->m_sb.sb_agcount * rotorstep);
                }
                break;
        default:
                ASSERT(0);
                /* NOTREACHED */
        }
        if (args->agbno == NULLAGBLOCK)
                args->fsbno = NULLFSBLOCK;
        else {
                args->fsbno = XFS_AGB_TO_FSB(mp, args->agno, args->agbno);
#ifdef DEBUG
                ASSERT(args->len >= args->minlen);
                ASSERT(args->len <= args->maxlen);
                ASSERT(args->agbno % args->alignment == 0);
                XFS_AG_CHECK_DADDR(mp, XFS_FSB_TO_DADDR(mp, args->fsbno),
                        args->len);
#endif

                /* Zero the extent if we were asked to do so */
                if (args->userdata & XFS_ALLOC_USERDATA_ZERO) {
                        error = xfs_zero_extent(args->ip, args->fsbno, args->len);
                        if (error)
                                goto error0;
                }

        }
        xfs_perag_put(args->pag);
        return 0;
error0:
        xfs_perag_put(args->pag);
        return error;
}

/* Ensure that the freelist is at full capacity. */
int
xfs_free_extent_fix_freelist(
        struct xfs_trans        *tp,
        xfs_agnumber_t          agno,
        struct xfs_buf          **agbp)
{
        struct xfs_alloc_arg    args;
        int                     error;

        memset(&args, 0, sizeof(struct xfs_alloc_arg));
        args.tp = tp;
        args.mp = tp->t_mountp;
        args.agno = agno;

        /*
         * validate that the block number is legal - the enables us to detect
         * and handle a silent filesystem corruption rather than crashing.
         */
        if (args.agno >= args.mp->m_sb.sb_agcount)
                return -EFSCORRUPTED;

        args.pag = xfs_perag_get(args.mp, args.agno);
        ASSERT(args.pag);

        error = xfs_alloc_fix_freelist(&args, XFS_ALLOC_FLAG_FREEING);
        if (error)
                goto out;

        *agbp = args.agbp;
out:
        xfs_perag_put(args.pag);
        return error;
}

/*
 * Free an extent.
 * Just break up the extent address and hand off to xfs_free_ag_extent
 * after fixing up the freelist.
 */
int                             /* error */
xfs_free_extent(
        struct xfs_trans        *tp,    /* transaction pointer */
        xfs_fsblock_t           bno,    /* starting block number of extent */
        xfs_extlen_t            len)    /* length of extent */
{
        struct xfs_mount        *mp = tp->t_mountp;
        struct xfs_buf          *agbp;
        xfs_agnumber_t          agno = XFS_FSB_TO_AGNO(mp, bno);
        xfs_agblock_t           agbno = XFS_FSB_TO_AGBNO(mp, bno);
        int                     error;

        ASSERT(len != 0);

        trace_xfs_bmap_free_deferred(mp, agno, 0, agbno, len);

        if (XFS_TEST_ERROR(false, mp,
                        XFS_ERRTAG_FREE_EXTENT,
                        XFS_RANDOM_FREE_EXTENT))
                return -EIO;

        error = xfs_free_extent_fix_freelist(tp, agno, &agbp);
        if (error)
                return error;

        XFS_WANT_CORRUPTED_GOTO(mp, agbno < mp->m_sb.sb_agblocks, err);

        /* validate the extent size is legal now we have the agf locked */
        XFS_WANT_CORRUPTED_GOTO(mp,
                agbno + len <= be32_to_cpu(XFS_BUF_TO_AGF(agbp)->agf_length),
                                err);

        error = xfs_free_ag_extent(tp, agbp, agno, agbno, len, 0);
        if (error)
                goto err;

        xfs_extent_busy_insert(tp, agno, agbno, len, 0);
        return 0;

err:
        xfs_trans_brelse(tp, agbp);
        return error;
}