Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/cjb/mmc

[cris-mirror.git] / fs / xfs / 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_types.h"
#include "xfs_bit.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_btree.h"
#include "xfs_alloc.h"
#include "xfs_error.h"
#include "xfs_trace.h"


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

#define XFSA_FIXUP_BNO_OK       1
#define XFSA_FIXUP_CNT_OK       2

/*
 * Prototypes for per-ag allocation routines
 */

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 *);

/*
 * Internal functions.
 */

/*
 * 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.
 */
STATIC 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.
 */
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    diff;
        xfs_extlen_t    len;

        if (args->alignment > 1 && foundlen >= args->minlen) {
                bno = roundup(foundbno, args->alignment);
                diff = bno - foundbno;
                len = diff >= foundlen ? 0 : foundlen - diff;
        } else {
                bno = foundbno;
                len = foundlen;
        }
        *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 */
        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;
        if (freebno >= wantbno) {
                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) {
                if ((int)(rlen = rlen - k - args->mod) < (int)args->minlen)
                        return;
        } else {
                if ((int)(rlen = rlen - args->prod - (args->mod - k)) <
                    (int)args->minlen)
                        return;
        }
        ASSERT(rlen >= args->minlen);
        ASSERT(rlen <= args->maxlen);
        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)
                + be32_to_cpu(agf->agf_flcount)
                - args->len - args->minleft;
        if (diff >= 0)
                return 1;
        args->len += diff;              /* shrink the allocated space */
        if (args->len >= 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 */

        /*
         * 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(
                        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(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(
                        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(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(
                        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(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(i == 0);
                if ((error = xfs_btree_insert(cnt_cur, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(i == 1);
        }
        if (nfbno2 != NULLAGBLOCK) {
                if ((error = xfs_alloc_lookup_eq(cnt_cur, nfbno2, nflen2, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(i == 0);
                if ((error = xfs_btree_insert(cnt_cur, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(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(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(i == 0);
                if ((error = xfs_btree_insert(bno_cur, &i)))
                        return error;
                XFS_WANT_CORRUPTED_RETURN(i == 1);
        }
        return 0;
}

/*
 * 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);
        if (error)
                return error;
        ASSERT(bp);
        ASSERT(!XFS_BUF_GETERROR(bp));
        XFS_BUF_SET_VTYPE_REF(bp, B_FS_AGFL, 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;

                /*
                 * Search the busylist for these blocks and mark the
                 * transaction as synchronous if blocks are found. This
                 * avoids the need to block due to a synchronous log
                 * force to ensure correct ordering as the synchronous
                 * transaction will guarantee that for us.
                 */
                if (xfs_alloc_busy_search(args->mp, args->agno,
                                        args->agbno, args->len))
                        xfs_trans_set_sync(args->tp);
        }

        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(xs_allocx);
        XFS_STATS_ADD(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 */
        xfs_agblock_t   end;    /* end of allocated extent */
        int             error;
        xfs_agblock_t   fbno;   /* start block of found extent */
        xfs_agblock_t   fend;   /* end block of found extent */
        xfs_extlen_t    flen;   /* length of found extent */
        int             i;      /* success/failure of operation */
        xfs_agblock_t   maxend; /* end of maximal extent */
        xfs_agblock_t   minend; /* end of minimal extent */
        xfs_extlen_t    rlen;   /* length of returned extent */

        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(i == 1, error0);
        ASSERT(fbno <= args->agbno);
        minend = args->agbno + args->minlen;
        maxend = args->agbno + args->maxlen;
        fend = fbno + flen;

        /*
         * Give up if the freespace isn't long enough for the minimum request.
         */
        if (fend < minend)
                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.
         */
        end = XFS_AGBLOCK_MIN(fend, maxend);
        args->len = end - args->agbno;
        xfs_alloc_fix_len(args);
        if (!xfs_alloc_fix_minleft(args))
                goto not_found;

        rlen = args->len;
        ASSERT(args->agbno + rlen <= fend);
        end = args->agbno + rlen;

        /*
         * We are allocating agbno for rlen [agbno .. end]
         * 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,
        xfs_extlen_t            *slena, /* aligned length */
        int                     dir)    /* 0 = search right, 1 = search left */
{
        xfs_agblock_t           bno;
        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(i == 1, error0);
                xfs_alloc_compute_aligned(args, *sbno, *slen, &bno, slena);

                /*
                 * The good extent is closer than this one.
                 */
                if (!dir) {
                        if (bno >= args->agbno + gdiff)
                                goto out_use_good;
                } else {
                        if (bno <= 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, *sbno,
                                                       *slen, &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 = 0;     /* 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 = 0;     /* aligned ... */
        xfs_agblock_t   ltnew;          /* useful start bno of left side */
        xfs_extlen_t    rlen;           /* length of returned extent */
#if defined(DEBUG) && defined(__KERNEL__)
        /*
         * Randomly don't execute the first algorithm.
         */
        int             dofirst;        /* set to do first algorithm */

        dofirst = random32() & 1;
#endif
        /*
         * 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);
        ltlen = 0;
        bno_cur_lt = bno_cur_gt = NULL;
        /*
         * 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);
                        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;

#if defined(DEBUG) && defined(__KERNEL__)
                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(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(i == 1, error0);
                        xfs_alloc_compute_aligned(args, ltbno, ltlen,
                                                  &ltbnoa, &ltlena);
                        if (ltlena < args->minlen)
                                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, ltbno, ltlen, &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(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(i == 1, error0);
                        xfs_alloc_compute_aligned(args, ltbno, ltlen,
                                                  &ltbnoa, &ltlena);
                        if (ltlena >= args->minlen)
                                break;
                        if ((error = xfs_btree_decrement(bno_cur_lt, 0, &i)))
                                goto error0;
                        if (!i) {
                                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(i == 1, error0);
                        xfs_alloc_compute_aligned(args, gtbno, gtlen,
                                                  &gtbnoa, &gtlena);
                        if (gtlena >= args->minlen)
                                break;
                        if ((error = xfs_btree_increment(bno_cur_gt, 0, &i)))
                                goto error0;
                        if (!i) {
                                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, ltbno, ltlen, &ltnew);

                        error = xfs_alloc_find_best_extent(args,
                                                &bno_cur_lt, &bno_cur_gt,
                                                ltdiff, &gtbno, &gtlen, &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, gtbno, gtlen, &gtnew);

                        error = xfs_alloc_find_best_extent(args,
                                                &bno_cur_gt, &bno_cur_lt,
                                                gtdiff, &ltbno, &ltlen, &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) {
                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, ltbno,
                ltlen, &ltnew);
        ASSERT(ltnew >= ltbno);
        ASSERT(ltnew + rlen <= ltbno + ltlen);
        ASSERT(ltnew + rlen <= be32_to_cpu(XFS_BUF_TO_AGF(args->agbp)->agf_length));
        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 */

        /*
         * 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, 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, &fbno,
                                &flen, &i)))
                        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);
        }
        /*
         * There's a freespace as big as maxlen+alignment-1, get it.
         */
        else {
                if ((error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
        }
        /*
         * 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.
         */
        xfs_alloc_compute_aligned(args, fbno, flen, &rbno, &rlen);
        rlen = XFS_EXTLEN_MIN(args->maxlen, rlen);
        XFS_WANT_CORRUPTED_GOTO(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(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(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(i == 1, error0);
                rlen = bestrlen;
                rbno = bestrbno;
                flen = bestflen;
                fbno = bestfbno;
        }
        args->wasfromfl = 0;
        /*
         * Fix up the length.
         */
        args->len = rlen;
        xfs_alloc_fix_len(args);
        if (rlen < args->minlen || !xfs_alloc_fix_minleft(args)) {
                xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
                trace_xfs_alloc_size_nominleft(args);
                args->agbno = NULLAGBLOCK;
                return 0;
        }
        rlen = args->len;
        XFS_WANT_CORRUPTED_GOTO(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->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;
}

/*
 * 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(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) {
                        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->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(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(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(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(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(i == 1, error0);
                if ((error = xfs_btree_delete(cnt_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(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(i == 1, error0);
                if ((error = xfs_btree_delete(cnt_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(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(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(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(
                                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(i == 1, error0);
                if ((error = xfs_btree_delete(cnt_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(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(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(i == 1, error0);
                if ((error = xfs_btree_delete(cnt_cur, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(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(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(i == 0, error0);
        if ((error = xfs_btree_insert(cnt_cur, &i)))
                goto error0;
        XFS_WANT_CORRUPTED_GOTO(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(xs_freex);
        XFS_STATS_ADD(xs_freeb, len);

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

        /*
         * Since blocks move to the free list without the coordination
         * used in xfs_bmap_finish, we can't allow block to be available
         * for reallocation and non-transaction writing (user data)
         * until we know that the transaction that moved it to the free
         * list is permanently on disk.  We track the blocks by declaring
         * these blocks as "busy"; the busy list is maintained on a per-ag
         * basis and each transaction records which entries should be removed
         * when the iclog commits to disk.  If a busy block is allocated,
         * the iclog is pushed up to the LSN that freed the block.
         */
        xfs_alloc_busy_insert(tp, agno, bno, len);
        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 */
{
        int             level;
        uint            maxblocks;
        uint            maxleafents;
        int             minleafrecs;
        int             minnoderecs;

        maxleafents = (mp->m_sb.sb_agblocks + 1) / 2;
        minleafrecs = mp->m_alloc_mnr[0];
        minnoderecs = mp->m_alloc_mnr[1];
        maxblocks = (maxleafents + minleafrecs - 1) / minleafrecs;
        for (level = 1; maxblocks > 1; level++)
                maxblocks = (maxblocks + minnoderecs - 1) / minnoderecs;
        mp->m_ag_maxlevels = level;
}

/*
 * 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, delta = 0;

        need = XFS_MIN_FREELIST_PAG(pag, mp);
        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;
}

/*
 * Decide whether to use this allocation group for this allocation.
 * If so, fix up the btree freelist's size.
 */
STATIC int                      /* error */
xfs_alloc_fix_freelist(
        xfs_alloc_arg_t *args,  /* allocation argument structure */
        int             flags)  /* XFS_ALLOC_FLAG_... */
{
        xfs_buf_t       *agbp;  /* agf buffer pointer */
        xfs_agf_t       *agf;   /* a.g. freespace structure pointer */
        xfs_buf_t       *agflbp;/* agfl buffer pointer */
        xfs_agblock_t   bno;    /* freelist block */
        xfs_extlen_t    delta;  /* new blocks needed in freelist */
        int             error;  /* error result code */
        xfs_extlen_t    longest;/* longest extent in allocation group */
        xfs_mount_t     *mp;    /* file system mount point structure */
        xfs_extlen_t    need;   /* total blocks needed in freelist */
        xfs_perag_t     *pag;   /* per-ag information structure */
        xfs_alloc_arg_t targs;  /* local allocation arguments */
        xfs_trans_t     *tp;    /* transaction pointer */

        mp = args->mp;

        pag = args->pag;
        tp = args->tp;
        if (!pag->pagf_init) {
                if ((error = xfs_alloc_read_agf(mp, tp, args->agno, flags,
                                &agbp)))
                        return error;
                if (!pag->pagf_init) {
                        ASSERT(flags & XFS_ALLOC_FLAG_TRYLOCK);
                        ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING));
                        args->agbp = NULL;
                        return 0;
                }
        } else
                agbp = NULL;

        /*
         * 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));
                args->agbp = NULL;
                return 0;
        }

        if (!(flags & XFS_ALLOC_FLAG_FREEING)) {
                /*
                 * If it looks like there isn't a long enough extent, or enough
                 * total blocks, reject it.
                 */
                need = XFS_MIN_FREELIST_PAG(pag, mp);
                longest = xfs_alloc_longest_free_extent(mp, pag);
                if ((args->minlen + args->alignment + args->minalignslop - 1) >
                                longest ||
                    ((int)(pag->pagf_freeblks + pag->pagf_flcount -
                           need - args->total) < (int)args->minleft)) {
                        if (agbp)
                                xfs_trans_brelse(tp, agbp);
                        args->agbp = NULL;
                        return 0;
                }
        }

        /*
         * Get the a.g. freespace buffer.
         * Can fail if we're not blocking on locks, and it's held.
         */
        if (agbp == NULL) {
                if ((error = xfs_alloc_read_agf(mp, tp, args->agno, flags,
                                &agbp)))
                        return error;
                if (agbp == NULL) {
                        ASSERT(flags & XFS_ALLOC_FLAG_TRYLOCK);
                        ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING));
                        args->agbp = NULL;
                        return 0;
                }
        }
        /*
         * Figure out how many blocks we should have in the freelist.
         */
        agf = XFS_BUF_TO_AGF(agbp);
        need = XFS_MIN_FREELIST(agf, mp);
        /*
         * If there isn't enough total or single-extent, reject it.
         */
        if (!(flags & XFS_ALLOC_FLAG_FREEING)) {
                delta = need > be32_to_cpu(agf->agf_flcount) ?
                        (need - be32_to_cpu(agf->agf_flcount)) : 0;
                longest = be32_to_cpu(agf->agf_longest);
                longest = (longest > delta) ? (longest - delta) :
                        (be32_to_cpu(agf->agf_flcount) > 0 || longest > 0);
                if ((args->minlen + args->alignment + args->minalignslop - 1) >
                                longest ||
                    ((int)(be32_to_cpu(agf->agf_freeblks) +
                     be32_to_cpu(agf->agf_flcount) - need - args->total) <
                                (int)args->minleft)) {
                        xfs_trans_brelse(tp, agbp);
                        args->agbp = NULL;
                        return 0;
                }
        }
        /*
         * Make the freelist shorter if it's too long.
         */
        while (be32_to_cpu(agf->agf_flcount) > need) {
                xfs_buf_t       *bp;

                error = xfs_alloc_get_freelist(tp, agbp, &bno, 0);
                if (error)
                        return error;
                if ((error = xfs_free_ag_extent(tp, agbp, args->agno, bno, 1, 1)))
                        return error;
                bp = xfs_btree_get_bufs(mp, tp, args->agno, bno, 0);
                xfs_trans_binval(tp, bp);
        }
        /*
         * Initialize the args structure.
         */
        targs.tp = tp;
        targs.mp = mp;
        targs.agbp = agbp;
        targs.agno = args->agno;
        targs.mod = targs.minleft = targs.wasdel = targs.userdata =
                targs.minalignslop = 0;
        targs.alignment = targs.minlen = targs.prod = targs.isfl = 1;
        targs.type = XFS_ALLOCTYPE_THIS_AG;
        targs.pag = pag;
        if ((error = xfs_alloc_read_agfl(mp, tp, targs.agno, &agflbp)))
                return error;
        /*
         * Make the freelist longer if it's too short.
         */
        while (be32_to_cpu(agf->agf_flcount) < need) {
                targs.agbno = 0;
                targs.maxlen = need - be32_to_cpu(agf->agf_flcount);
                /*
                 * Allocate as many blocks as possible at once.
                 */
                if ((error = xfs_alloc_ag_vextent(&targs))) {
                        xfs_trans_brelse(tp, agflbp);
                        return error;
                }
                /*
                 * 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;
                        xfs_trans_brelse(tp, agflbp);
                        args->agbp = NULL;
                        return 0;
                }
                /*
                 * 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)
                                return error;
                }
        }
        xfs_trans_brelse(tp, agflbp);
        args->agbp = agbp;
        return 0;
}

/*
 * 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_agfl_t      *agfl;  /* a.g. freelist structure */
        xfs_buf_t       *agflbp;/* buffer for a.g. freelist structure */
        xfs_agblock_t   bno;    /* block number returned */
        int             error;
        int             logflags;
        xfs_mount_t     *mp;    /* mount structure */
        xfs_perag_t     *pag;   /* per allocation group data */

        agf = XFS_BUF_TO_AGF(agbp);
        /*
         * Freelist is empty, give up.
         */
        if (!agf->agf_flcount) {
                *bnop = NULLAGBLOCK;
                return 0;
        }
        /*
         * Read the array of free blocks.
         */
        mp = tp->t_mountp;
        if ((error = xfs_alloc_read_agfl(mp, tp,
                        be32_to_cpu(agf->agf_seqno), &agflbp)))
                return error;
        agfl = XFS_BUF_TO_AGFL(agflbp);
        /*
         * Get the block number and update the data structures.
         */
        bno = be32_to_cpu(agfl->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;

        /*
         * As blocks are freed, they are added to the per-ag busy list and
         * remain there until the freeing transaction is committed to disk.
         * Now that we have allocated blocks, this list must be searched to see
         * if a block is being reused.  If one is, then the freeing transaction
         * must be pushed to disk before this transaction.
         *
         * We do this by setting the current transaction to a sync transaction
         * which guarantees that the freeing transaction is on disk before this
         * transaction. This is done instead of a synchronous log force here so
         * that we don't sit and wait with the AGF locked in the transaction
         * during the log force.
         */
        if (xfs_alloc_busy_search(mp, be32_to_cpu(agf->agf_seqno), bno, 1))
                xfs_trans_set_sync(tp);
        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),
                sizeof(xfs_agf_t)
        };

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

        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 */
        xfs_agfl_t              *agfl;  /* a.g. free block array */
        __be32                  *blockp;/* pointer to array entry */
        int                     error;
        int                     logflags;
        xfs_mount_t             *mp;    /* mount structure */
        xfs_perag_t             *pag;   /* per allocation group data */

        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;
        agfl = XFS_BUF_TO_AGFL(agflbp);
        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));
        blockp = &agfl->agfl_bno[be32_to_cpu(agf->agf_fllast)];
        *blockp = cpu_to_be32(bno);
        xfs_alloc_log_agf(tp, agbp, logflags);
        xfs_trans_log_buf(tp, agflbp,
                (int)((xfs_caddr_t)blockp - (xfs_caddr_t)agfl),
                (int)((xfs_caddr_t)blockp - (xfs_caddr_t)agfl +
                        sizeof(xfs_agblock_t) - 1));
        return 0;
}

/*
 * 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 */
{
        struct xfs_agf  *agf;           /* ag freelist header */
        int             agf_ok;         /* set if agf is consistent */
        int             error;

        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);
        if (error)
                return error;
        if (!*bpp)
                return 0;

        ASSERT(!XFS_BUF_GETERROR(*bpp));
        agf = XFS_BUF_TO_AGF(*bpp);

        /*
         * Validate the magic number of the agf block.
         */
        agf_ok =
                be32_to_cpu(agf->agf_magicnum) == 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) &&
                be32_to_cpu(agf->agf_seqno) == agno;
        if (xfs_sb_version_haslazysbcount(&mp->m_sb))
                agf_ok = agf_ok && be32_to_cpu(agf->agf_btreeblks) <=
                                                be32_to_cpu(agf->agf_length);
        if (unlikely(XFS_TEST_ERROR(!agf_ok, mp, XFS_ERRTAG_ALLOC_READ_AGF,
                        XFS_RANDOM_ALLOC_READ_AGF))) {
                XFS_CORRUPTION_ERROR("xfs_alloc_read_agf",
                                     XFS_ERRLEVEL_LOW, mp, agf);
                xfs_trans_brelse(tp, *bpp);
                return XFS_ERROR(EFSCORRUPTED);
        }
        XFS_BUF_SET_VTYPE_REF(*bpp, B_FS_AGF, 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;

        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(!XFS_BUF_GETERROR(*bpp));

        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
        }
        xfs_perag_put(args->pag);
        return 0;
error0:
        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(
        xfs_trans_t     *tp,    /* transaction pointer */
        xfs_fsblock_t   bno,    /* starting block number of extent */
        xfs_extlen_t    len)    /* length of extent */
{
        xfs_alloc_arg_t args;
        int             error;

        ASSERT(len != 0);
        memset(&args, 0, sizeof(xfs_alloc_arg_t));
        args.tp = tp;
        args.mp = tp->t_mountp;
        args.agno = XFS_FSB_TO_AGNO(args.mp, bno);
        ASSERT(args.agno < args.mp->m_sb.sb_agcount);
        args.agbno = XFS_FSB_TO_AGBNO(args.mp, bno);
        args.pag = xfs_perag_get(args.mp, args.agno);
        if ((error = xfs_alloc_fix_freelist(&args, XFS_ALLOC_FLAG_FREEING)))
                goto error0;
#ifdef DEBUG
        ASSERT(args.agbp != NULL);
        ASSERT((args.agbno + len) <=
                be32_to_cpu(XFS_BUF_TO_AGF(args.agbp)->agf_length));
#endif
        error = xfs_free_ag_extent(tp, args.agbp, args.agno, args.agbno, len, 0);
error0:
        xfs_perag_put(args.pag);
        return error;
}


/*
 * AG Busy list management
 * The busy list contains block ranges that have been freed but whose
 * transactions have not yet hit disk.  If any block listed in a busy
 * list is reused, the transaction that freed it must be forced to disk
 * before continuing to use the block.
 *
 * xfs_alloc_busy_insert - add to the per-ag busy list
 * xfs_alloc_busy_clear - remove an item from the per-ag busy list
 * xfs_alloc_busy_search - search for a busy extent
 */

/*
 * Insert a new extent into the busy tree.
 *
 * The busy extent tree is indexed by the start block of the busy extent.
 * there can be multiple overlapping ranges in the busy extent tree but only
 * ever one entry at a given start block. The reason for this is that
 * multi-block extents can be freed, then smaller chunks of that extent
 * allocated and freed again before the first transaction commit is on disk.
 * If the exact same start block is freed a second time, we have to wait for
 * that busy extent to pass out of the tree before the new extent is inserted.
 * There are two main cases we have to handle here.
 *
 * The first case is a transaction that triggers a "free - allocate - free"
 * cycle. This can occur during btree manipulations as a btree block is freed
 * to the freelist, then allocated from the free list, then freed again. In
 * this case, the second extxpnet free is what triggers the duplicate and as
 * such the transaction IDs should match. Because the extent was allocated in
 * this transaction, the transaction must be marked as synchronous. This is
 * true for all cases where the free/alloc/free occurs in the one transaction,
 * hence the addition of the ASSERT(tp->t_flags & XFS_TRANS_SYNC) to this case.
 * This serves to catch violations of the second case quite effectively.
 *
 * The second case is where the free/alloc/free occur in different
 * transactions. In this case, the thread freeing the extent the second time
 * can't mark the extent busy immediately because it is already tracked in a
 * transaction that may be committing.  When the log commit for the existing
 * busy extent completes, the busy extent will be removed from the tree. If we
 * allow the second busy insert to continue using that busy extent structure,
 * it can be freed before this transaction is safely in the log.  Hence our
 * only option in this case is to force the log to remove the existing busy
 * extent from the list before we insert the new one with the current
 * transaction ID.
 *
 * The problem we are trying to avoid in the free-alloc-free in separate
 * transactions is most easily described with a timeline:
 *
 *      Thread 1        Thread 2        Thread 3        xfslogd
 *      xact alloc
 *      free X
 *      mark busy
 *      commit xact
 *      free xact
 *                      xact alloc
 *                      alloc X
 *                      busy search
 *                      mark xact sync
 *                      commit xact
 *                      free xact
 *                      force log
 *                      checkpoint starts
 *                      ....
 *                                      xact alloc
 *                                      free X
 *                                      mark busy
 *                                      finds match
 *                                      *** KABOOM! ***
 *                                      ....
 *                                                      log IO completes
 *                                                      unbusy X
 *                      checkpoint completes
 *
 * By issuing a log force in thread 3 @ "KABOOM", the thread will block until
 * the checkpoint completes, and the busy extent it matched will have been
 * removed from the tree when it is woken. Hence it can then continue safely.
 *
 * However, to ensure this matching process is robust, we need to use the
 * transaction ID for identifying transaction, as delayed logging results in
 * the busy extent and transaction lifecycles being different. i.e. the busy
 * extent is active for a lot longer than the transaction.  Hence the
 * transaction structure can be freed and reallocated, then mark the same
 * extent busy again in the new transaction. In this case the new transaction
 * will have a different tid but can have the same address, and hence we need
 * to check against the tid.
 *
 * Future: for delayed logging, we could avoid the log force if the extent was
 * first freed in the current checkpoint sequence. This, however, requires the
 * ability to pin the current checkpoint in memory until this transaction
 * commits to ensure that both the original free and the current one combine
 * logically into the one checkpoint. If the checkpoint sequences are
 * different, however, we still need to wait on a log force.
 */
void
xfs_alloc_busy_insert(
        struct xfs_trans        *tp,
        xfs_agnumber_t          agno,
        xfs_agblock_t           bno,
        xfs_extlen_t            len)
{
        struct xfs_busy_extent  *new;
        struct xfs_busy_extent  *busyp;
        struct xfs_perag        *pag;
        struct rb_node          **rbp;
        struct rb_node          *parent;
        int                     match;


        new = kmem_zalloc(sizeof(struct xfs_busy_extent), KM_MAYFAIL);
        if (!new) {
                /*
                 * No Memory!  Since it is now not possible to track the free
                 * block, make this a synchronous transaction to insure that
                 * the block is not reused before this transaction commits.
                 */
                trace_xfs_alloc_busy(tp, agno, bno, len, 1);
                xfs_trans_set_sync(tp);
                return;
        }

        new->agno = agno;
        new->bno = bno;
        new->length = len;
        new->tid = xfs_log_get_trans_ident(tp);

        INIT_LIST_HEAD(&new->list);

        /* trace before insert to be able to see failed inserts */
        trace_xfs_alloc_busy(tp, agno, bno, len, 0);

        pag = xfs_perag_get(tp->t_mountp, new->agno);
restart:
        spin_lock(&pag->pagb_lock);
        rbp = &pag->pagb_tree.rb_node;
        parent = NULL;
        busyp = NULL;
        match = 0;
        while (*rbp && match >= 0) {
                parent = *rbp;
                busyp = rb_entry(parent, struct xfs_busy_extent, rb_node);

                if (new->bno < busyp->bno) {
                        /* may overlap, but exact start block is lower */
                        rbp = &(*rbp)->rb_left;
                        if (new->bno + new->length > busyp->bno)
                                match = busyp->tid == new->tid ? 1 : -1;
                } else if (new->bno > busyp->bno) {
                        /* may overlap, but exact start block is higher */
                        rbp = &(*rbp)->rb_right;
                        if (bno < busyp->bno + busyp->length)
                                match = busyp->tid == new->tid ? 1 : -1;
                } else {
                        match = busyp->tid == new->tid ? 1 : -1;
                        break;
                }
        }
        if (match < 0) {
                /* overlap marked busy in different transaction */
                spin_unlock(&pag->pagb_lock);
                xfs_log_force(tp->t_mountp, XFS_LOG_SYNC);
                goto restart;
        }
        if (match > 0) {
                /*
                 * overlap marked busy in same transaction. Update if exact
                 * start block match, otherwise combine the busy extents into
                 * a single range.
                 */
                if (busyp->bno == new->bno) {
                        busyp->length = max(busyp->length, new->length);
                        spin_unlock(&pag->pagb_lock);
                        ASSERT(tp->t_flags & XFS_TRANS_SYNC);
                        xfs_perag_put(pag);
                        kmem_free(new);
                        return;
                }
                rb_erase(&busyp->rb_node, &pag->pagb_tree);
                new->length = max(busyp->bno + busyp->length,
                                        new->bno + new->length) -
                                min(busyp->bno, new->bno);
                new->bno = min(busyp->bno, new->bno);
        } else
                busyp = NULL;

        rb_link_node(&new->rb_node, parent, rbp);
        rb_insert_color(&new->rb_node, &pag->pagb_tree);

        list_add(&new->list, &tp->t_busy);
        spin_unlock(&pag->pagb_lock);
        xfs_perag_put(pag);
        kmem_free(busyp);
}

/*
 * Search for a busy extent within the range of the extent we are about to
 * allocate.  You need to be holding the busy extent tree lock when calling
 * xfs_alloc_busy_search(). This function returns 0 for no overlapping busy
 * extent, -1 for an overlapping but not exact busy extent, and 1 for an exact
 * match. This is done so that a non-zero return indicates an overlap that
 * will require a synchronous transaction, but it can still be
 * used to distinguish between a partial or exact match.
 */
int
xfs_alloc_busy_search(
        struct xfs_mount        *mp,
        xfs_agnumber_t          agno,
        xfs_agblock_t           bno,
        xfs_extlen_t            len)
{
        struct xfs_perag        *pag;
        struct rb_node          *rbp;
        struct xfs_busy_extent  *busyp;
        int                     match = 0;

        pag = xfs_perag_get(mp, agno);
        spin_lock(&pag->pagb_lock);

        rbp = pag->pagb_tree.rb_node;

        /* find closest start bno overlap */
        while (rbp) {
                busyp = rb_entry(rbp, struct xfs_busy_extent, rb_node);
                if (bno < busyp->bno) {
                        /* may overlap, but exact start block is lower */
                        if (bno + len > busyp->bno)
                                match = -1;
                        rbp = rbp->rb_left;
                } else if (bno > busyp->bno) {
                        /* may overlap, but exact start block is higher */
                        if (bno < busyp->bno + busyp->length)
                                match = -1;
                        rbp = rbp->rb_right;
                } else {
                        /* bno matches busyp, length determines exact match */
                        match = (busyp->length == len) ? 1 : -1;
                        break;
                }
        }
        spin_unlock(&pag->pagb_lock);
        trace_xfs_alloc_busysearch(mp, agno, bno, len, !!match);
        xfs_perag_put(pag);
        return match;
}

void
xfs_alloc_busy_clear(
        struct xfs_mount        *mp,
        struct xfs_busy_extent  *busyp)
{
        struct xfs_perag        *pag;

        trace_xfs_alloc_unbusy(mp, busyp->agno, busyp->bno,
                                                busyp->length);

        ASSERT(xfs_alloc_busy_search(mp, busyp->agno, busyp->bno,
                                                busyp->length) == 1);

        list_del_init(&busyp->list);

        pag = xfs_perag_get(mp, busyp->agno);
        spin_lock(&pag->pagb_lock);
        rb_erase(&busyp->rb_node, &pag->pagb_tree);
        spin_unlock(&pag->pagb_lock);
        xfs_perag_put(pag);

        kmem_free(busyp);
}