xfs_ialloc.c

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/*
 * 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_ialloc.h"
#include "xfs_alloc.h"
#include "xfs_rtalloc.h"
#include "xfs_error.h"
#include "xfs_bmap.h"


/*
 * Allocation group level functions.
 */
static inline int
xfs_ialloc_cluster_alignment(
    xfs_alloc_arg_t *args)
{
    if (xfs_sb_version_hasalign(&args->mp->m_sb) &&
        args->mp->m_sb.sb_inoalignmt >=
         XFS_B_TO_FSBT(args->mp, XFS_INODE_CLUSTER_SIZE(args->mp)))
        return args->mp->m_sb.sb_inoalignmt;
    return 1;
}

/*
 * Lookup a record by ino in the btree given by cur.
 */
int                 /* error */
xfs_inobt_lookup(
    struct xfs_btree_cur    *cur,   /* btree cursor */
    xfs_agino_t     ino,    /* starting inode of chunk */
    xfs_lookup_t        dir,    /* <=, >=, == */
    int         *stat)  /* success/failure */
{
    cur->bc_rec.i.ir_startino = ino;
    cur->bc_rec.i.ir_freecount = 0;
    cur->bc_rec.i.ir_free = 0;
    return xfs_btree_lookup(cur, dir, stat);
}

/*
 * Update the record referred to by cur to the value given.
 * This either works (return 0) or gets an EFSCORRUPTED error.
 */
STATIC int              /* error */
xfs_inobt_update(
    struct xfs_btree_cur    *cur,   /* btree cursor */
    xfs_inobt_rec_incore_t  *irec)  /* btree record */
{
    union xfs_btree_rec rec;

    rec.inobt.ir_startino = cpu_to_be32(irec->ir_startino);
    rec.inobt.ir_freecount = cpu_to_be32(irec->ir_freecount);
    rec.inobt.ir_free = cpu_to_be64(irec->ir_free);
    return xfs_btree_update(cur, &rec);
}

/*
 * Get the data from the pointed-to record.
 */
int                 /* error */
xfs_inobt_get_rec(
    struct xfs_btree_cur    *cur,   /* btree cursor */
    xfs_inobt_rec_incore_t  *irec,  /* btree record */
    int         *stat)  /* output: success/failure */
{
    union xfs_btree_rec *rec;
    int         error;

    error = xfs_btree_get_rec(cur, &rec, stat);
    if (!error && *stat == 1) {
        irec->ir_startino = be32_to_cpu(rec->inobt.ir_startino);
        irec->ir_freecount = be32_to_cpu(rec->inobt.ir_freecount);
        irec->ir_free = be64_to_cpu(rec->inobt.ir_free);
    }
    return error;
}

/*
 * Verify that the number of free inodes in the AGI is correct.
 */
#ifdef DEBUG
STATIC int
xfs_check_agi_freecount(
    struct xfs_btree_cur    *cur,
    struct xfs_agi      *agi)
{
    if (cur->bc_nlevels == 1) {
        xfs_inobt_rec_incore_t rec;
        int     freecount = 0;
        int     error;
        int     i;

        error = xfs_inobt_lookup(cur, 0, XFS_LOOKUP_GE, &i);
        if (error)
            return error;

        do {
            error = xfs_inobt_get_rec(cur, &rec, &i);
            if (error)
                return error;

            if (i) {
                freecount += rec.ir_freecount;
                error = xfs_btree_increment(cur, 0, &i);
                if (error)
                    return error;
            }
        } while (i == 1);

        if (!XFS_FORCED_SHUTDOWN(cur->bc_mp))
            ASSERT(freecount == be32_to_cpu(agi->agi_freecount));
    }
    return 0;
}
#else
#define xfs_check_agi_freecount(cur, agi)   0
#endif

/*
 * Initialise a new set of inodes.
 */
STATIC int
xfs_ialloc_inode_init(
    struct xfs_mount    *mp,
    struct xfs_trans    *tp,
    xfs_agnumber_t      agno,
    xfs_agblock_t       agbno,
    xfs_agblock_t       length,
    unsigned int        gen)
{
    struct xfs_buf      *fbuf;
    struct xfs_dinode   *free;
    int         blks_per_cluster, nbufs, ninodes;
    int         version;
    int         i, j;
    xfs_daddr_t     d;

    /*
     * Loop over the new block(s), filling in the inodes.
     * For small block sizes, manipulate the inodes in buffers
     * which are multiples of the blocks size.
     */
    if (mp->m_sb.sb_blocksize >= XFS_INODE_CLUSTER_SIZE(mp)) {
        blks_per_cluster = 1;
        nbufs = length;
        ninodes = mp->m_sb.sb_inopblock;
    } else {
        blks_per_cluster = XFS_INODE_CLUSTER_SIZE(mp) /
                   mp->m_sb.sb_blocksize;
        nbufs = length / blks_per_cluster;
        ninodes = blks_per_cluster * mp->m_sb.sb_inopblock;
    }

    /*
     * Figure out what version number to use in the inodes we create.
     * If the superblock version has caught up to the one that supports
     * the new inode format, then use the new inode version.  Otherwise
     * use the old version so that old kernels will continue to be
     * able to use the file system.
     */
    if (xfs_sb_version_hasnlink(&mp->m_sb))
        version = 2;
    else
        version = 1;

    for (j = 0; j < nbufs; j++) {
        /*
         * Get the block.
         */
        d = XFS_AGB_TO_DADDR(mp, agno, agbno + (j * blks_per_cluster));
        fbuf = xfs_trans_get_buf(tp, mp->m_ddev_targp, d,
                     mp->m_bsize * blks_per_cluster, 0);
        if (!fbuf)
            return ENOMEM;
        /*
         * Initialize all inodes in this buffer and then log them.
         *
         * XXX: It would be much better if we had just one transaction
         *  to log a whole cluster of inodes instead of all the
         *  individual transactions causing a lot of log traffic.
         */
        xfs_buf_zero(fbuf, 0, ninodes << mp->m_sb.sb_inodelog);
        for (i = 0; i < ninodes; i++) {
            int ioffset = i << mp->m_sb.sb_inodelog;
            uint    isize = sizeof(struct xfs_dinode);

            free = xfs_make_iptr(mp, fbuf, i);
            free->di_magic = cpu_to_be16(XFS_DINODE_MAGIC);
            free->di_version = version;
            free->di_gen = cpu_to_be32(gen);
            free->di_next_unlinked = cpu_to_be32(NULLAGINO);
            xfs_trans_log_buf(tp, fbuf, ioffset, ioffset + isize - 1);
        }
        xfs_trans_inode_alloc_buf(tp, fbuf);
    }
    return 0;
}

/*
 * Allocate new inodes in the allocation group specified by agbp.
 * Return 0 for success, else error code.
 */
STATIC int              /* error code or 0 */
xfs_ialloc_ag_alloc(
    xfs_trans_t *tp,        /* transaction pointer */
    xfs_buf_t   *agbp,      /* alloc group buffer */
    int     *alloc)
{
    xfs_agi_t   *agi;       /* allocation group header */
    xfs_alloc_arg_t args;       /* allocation argument structure */
    xfs_btree_cur_t *cur;       /* inode btree cursor */
    xfs_agnumber_t  agno;
    int     error;
    int     i;
    xfs_agino_t newino;     /* new first inode's number */
    xfs_agino_t newlen;     /* new number of inodes */
    xfs_agino_t thisino;    /* current inode number, for loop */
    int     isaligned = 0;  /* inode allocation at stripe unit */
                    /* boundary */
    struct xfs_perag *pag;

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

    /*
     * Locking will ensure that we don't have two callers in here
     * at one time.
     */
    newlen = XFS_IALLOC_INODES(args.mp);
    if (args.mp->m_maxicount &&
        args.mp->m_sb.sb_icount + newlen > args.mp->m_maxicount)
        return XFS_ERROR(ENOSPC);
    args.minlen = args.maxlen = XFS_IALLOC_BLOCKS(args.mp);
    /*
     * First try to allocate inodes contiguous with the last-allocated
     * chunk of inodes.  If the filesystem is striped, this will fill
     * an entire stripe unit with inodes.
     */
    agi = XFS_BUF_TO_AGI(agbp);
    newino = be32_to_cpu(agi->agi_newino);
    agno = be32_to_cpu(agi->agi_seqno);
    args.agbno = XFS_AGINO_TO_AGBNO(args.mp, newino) +
            XFS_IALLOC_BLOCKS(args.mp);
    if (likely(newino != NULLAGINO &&
          (args.agbno < be32_to_cpu(agi->agi_length)))) {
        args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);
        args.type = XFS_ALLOCTYPE_THIS_BNO;
        args.mod = args.total = args.wasdel = args.isfl =
            args.userdata = args.minalignslop = 0;
        args.prod = 1;

        /*
         * We need to take into account alignment here to ensure that
         * we don't modify the free list if we fail to have an exact
         * block. If we don't have an exact match, and every oher
         * attempt allocation attempt fails, we'll end up cancelling
         * a dirty transaction and shutting down.
         *
         * For an exact allocation, alignment must be 1,
         * however we need to take cluster alignment into account when
         * fixing up the freelist. Use the minalignslop field to
         * indicate that extra blocks might be required for alignment,
         * but not to use them in the actual exact allocation.
         */
        args.alignment = 1;
        args.minalignslop = xfs_ialloc_cluster_alignment(&args) - 1;

        /* Allow space for the inode btree to split. */
        args.minleft = args.mp->m_in_maxlevels - 1;
        if ((error = xfs_alloc_vextent(&args)))
            return error;
    } else
        args.fsbno = NULLFSBLOCK;

    if (unlikely(args.fsbno == NULLFSBLOCK)) {
        /*
         * Set the alignment for the allocation.
         * If stripe alignment is turned on then align at stripe unit
         * boundary.
         * If the cluster size is smaller than a filesystem block
         * then we're doing I/O for inodes in filesystem block size
         * pieces, so don't need alignment anyway.
         */
        isaligned = 0;
        if (args.mp->m_sinoalign) {
            ASSERT(!(args.mp->m_flags & XFS_MOUNT_NOALIGN));
            args.alignment = args.mp->m_dalign;
            isaligned = 1;
        } else
            args.alignment = xfs_ialloc_cluster_alignment(&args);
        /*
         * Need to figure out where to allocate the inode blocks.
         * Ideally they should be spaced out through the a.g.
         * For now, just allocate blocks up front.
         */
        args.agbno = be32_to_cpu(agi->agi_root);
        args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);
        /*
         * Allocate a fixed-size extent of inodes.
         */
        args.type = XFS_ALLOCTYPE_NEAR_BNO;
        args.mod = args.total = args.wasdel = args.isfl =
            args.userdata = args.minalignslop = 0;
        args.prod = 1;
        /*
         * Allow space for the inode btree to split.
         */
        args.minleft = args.mp->m_in_maxlevels - 1;
        if ((error = xfs_alloc_vextent(&args)))
            return error;
    }

    /*
     * If stripe alignment is turned on, then try again with cluster
     * alignment.
     */
    if (isaligned && args.fsbno == NULLFSBLOCK) {
        args.type = XFS_ALLOCTYPE_NEAR_BNO;
        args.agbno = be32_to_cpu(agi->agi_root);
        args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);
        args.alignment = xfs_ialloc_cluster_alignment(&args);
        if ((error = xfs_alloc_vextent(&args)))
            return error;
    }

    if (args.fsbno == NULLFSBLOCK) {
        *alloc = 0;
        return 0;
    }
    ASSERT(args.len == args.minlen);

    /*
     * Stamp and write the inode buffers.
     *
     * Seed the new inode cluster with a random generation number. This
     * prevents short-term reuse of generation numbers if a chunk is
     * freed and then immediately reallocated. We use random numbers
     * rather than a linear progression to prevent the next generation
     * number from being easily guessable.
     */
    error = xfs_ialloc_inode_init(args.mp, tp, agno, args.agbno,
            args.len, random32());

    if (error)
        return error;
    /*
     * Convert the results.
     */
    newino = XFS_OFFBNO_TO_AGINO(args.mp, args.agbno, 0);
    be32_add_cpu(&agi->agi_count, newlen);
    be32_add_cpu(&agi->agi_freecount, newlen);
    pag = xfs_perag_get(args.mp, agno);
    pag->pagi_freecount += newlen;
    xfs_perag_put(pag);
    agi->agi_newino = cpu_to_be32(newino);

    /*
     * Insert records describing the new inode chunk into the btree.
     */
    cur = xfs_inobt_init_cursor(args.mp, tp, agbp, agno);
    for (thisino = newino;
         thisino < newino + newlen;
         thisino += XFS_INODES_PER_CHUNK) {
        cur->bc_rec.i.ir_startino = thisino;
        cur->bc_rec.i.ir_freecount = XFS_INODES_PER_CHUNK;
        cur->bc_rec.i.ir_free = XFS_INOBT_ALL_FREE;
        error = xfs_btree_lookup(cur, XFS_LOOKUP_EQ, &i);
        if (error) {
            xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
            return error;
        }
        ASSERT(i == 0);
        error = xfs_btree_insert(cur, &i);
        if (error) {
            xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
            return error;
        }
        ASSERT(i == 1);
    }
    xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
    /*
     * Log allocation group header fields
     */
    xfs_ialloc_log_agi(tp, agbp,
        XFS_AGI_COUNT | XFS_AGI_FREECOUNT | XFS_AGI_NEWINO);
    /*
     * Modify/log superblock values for inode count and inode free count.
     */
    xfs_trans_mod_sb(tp, XFS_TRANS_SB_ICOUNT, (long)newlen);
    xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, (long)newlen);
    *alloc = 1;
    return 0;
}

STATIC xfs_agnumber_t
xfs_ialloc_next_ag(
    xfs_mount_t *mp)
{
    xfs_agnumber_t  agno;

    spin_lock(&mp->m_agirotor_lock);
    agno = mp->m_agirotor;
    if (++mp->m_agirotor >= mp->m_maxagi)
        mp->m_agirotor = 0;
    spin_unlock(&mp->m_agirotor_lock);

    return agno;
}

/*
 * Select an allocation group to look for a free inode in, based on the parent
 * inode and then mode.  Return the allocation group buffer.
 */
STATIC xfs_agnumber_t
xfs_ialloc_ag_select(
    xfs_trans_t *tp,        /* transaction pointer */
    xfs_ino_t   parent,     /* parent directory inode number */
    umode_t     mode,       /* bits set to indicate file type */
    int     okalloc)    /* ok to allocate more space */
{
    xfs_agnumber_t  agcount;    /* number of ag's in the filesystem */
    xfs_agnumber_t  agno;       /* current ag number */
    int     flags;      /* alloc buffer locking flags */
    xfs_extlen_t    ineed;      /* blocks needed for inode allocation */
    xfs_extlen_t    longest = 0;    /* longest extent available */
    xfs_mount_t *mp;        /* mount point structure */
    int     needspace;  /* file mode implies space allocated */
    xfs_perag_t *pag;       /* per allocation group data */
    xfs_agnumber_t  pagno;      /* parent (starting) ag number */
    int     error;

    /*
     * Files of these types need at least one block if length > 0
     * (and they won't fit in the inode, but that's hard to figure out).
     */
    needspace = S_ISDIR(mode) || S_ISREG(mode) || S_ISLNK(mode);
    mp = tp->t_mountp;
    agcount = mp->m_maxagi;
    if (S_ISDIR(mode))
        pagno = xfs_ialloc_next_ag(mp);
    else {
        pagno = XFS_INO_TO_AGNO(mp, parent);
        if (pagno >= agcount)
            pagno = 0;
    }

    ASSERT(pagno < agcount);

    /*
     * Loop through allocation groups, looking for one with a little
     * free space in it.  Note we don't look for free inodes, exactly.
     * Instead, we include whether there is a need to allocate inodes
     * to mean that blocks must be allocated for them,
     * if none are currently free.
     */
    agno = pagno;
    flags = XFS_ALLOC_FLAG_TRYLOCK;
    for (;;) {
        pag = xfs_perag_get(mp, agno);
        if (!pag->pagi_inodeok) {
            xfs_ialloc_next_ag(mp);
            goto nextag;
        }

        if (!pag->pagi_init) {
            error = xfs_ialloc_pagi_init(mp, tp, agno);
            if (error)
                goto nextag;
        }

        if (pag->pagi_freecount) {
            xfs_perag_put(pag);
            return agno;
        }

        if (!okalloc)
            goto nextag;

        if (!pag->pagf_init) {
            error = xfs_alloc_pagf_init(mp, tp, agno, flags);
            if (error)
                goto nextag;
        }

        /*
         * Is there enough free space for the file plus a block of
         * inodes? (if we need to allocate some)?
         */
        ineed = XFS_IALLOC_BLOCKS(mp);
        longest = pag->pagf_longest;
        if (!longest)
            longest = pag->pagf_flcount > 0;

        if (pag->pagf_freeblks >= needspace + ineed &&
            longest >= ineed) {
            xfs_perag_put(pag);
            return agno;
        }
nextag:
        xfs_perag_put(pag);
        /*
         * No point in iterating over the rest, if we're shutting
         * down.
         */
        if (XFS_FORCED_SHUTDOWN(mp))
            return NULLAGNUMBER;
        agno++;
        if (agno >= agcount)
            agno = 0;
        if (agno == pagno) {
            if (flags == 0)
                return NULLAGNUMBER;
            flags = 0;
        }
    }
}

/*
 * Try to retrieve the next record to the left/right from the current one.
 */
STATIC int
xfs_ialloc_next_rec(
    struct xfs_btree_cur    *cur,
    xfs_inobt_rec_incore_t  *rec,
    int         *done,
    int         left)
{
    int                     error;
    int         i;

    if (left)
        error = xfs_btree_decrement(cur, 0, &i);
    else
        error = xfs_btree_increment(cur, 0, &i);

    if (error)
        return error;
    *done = !i;
    if (i) {
        error = xfs_inobt_get_rec(cur, rec, &i);
        if (error)
            return error;
        XFS_WANT_CORRUPTED_RETURN(i == 1);
    }

    return 0;
}

STATIC int
xfs_ialloc_get_rec(
    struct xfs_btree_cur    *cur,
    xfs_agino_t     agino,
    xfs_inobt_rec_incore_t  *rec,
    int         *done,
    int         left)
{
    int                     error;
    int         i;

    error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_EQ, &i);
    if (error)
        return error;
    *done = !i;
    if (i) {
        error = xfs_inobt_get_rec(cur, rec, &i);
        if (error)
            return error;
        XFS_WANT_CORRUPTED_RETURN(i == 1);
    }

    return 0;
}

/*
 * Allocate an inode.
 *
 * The caller selected an AG for us, and made sure that free inodes are
 * available.
 */
STATIC int
xfs_dialloc_ag(
    struct xfs_trans    *tp,
    struct xfs_buf      *agbp,
    xfs_ino_t       parent,
    xfs_ino_t       *inop)
{
    struct xfs_mount    *mp = tp->t_mountp;
    struct xfs_agi      *agi = XFS_BUF_TO_AGI(agbp);
    xfs_agnumber_t      agno = be32_to_cpu(agi->agi_seqno);
    xfs_agnumber_t      pagno = XFS_INO_TO_AGNO(mp, parent);
    xfs_agino_t     pagino = XFS_INO_TO_AGINO(mp, parent);
    struct xfs_perag    *pag;
    struct xfs_btree_cur    *cur, *tcur;
    struct xfs_inobt_rec_incore rec, trec;
    xfs_ino_t       ino;
    int         error;
    int         offset;
    int         i, j;

    pag = xfs_perag_get(mp, agno);

    ASSERT(pag->pagi_init);
    ASSERT(pag->pagi_inodeok);
    ASSERT(pag->pagi_freecount > 0);

 restart_pagno:
    cur = xfs_inobt_init_cursor(mp, tp, agbp, agno);
    /*
     * If pagino is 0 (this is the root inode allocation) use newino.
     * This must work because we've just allocated some.
     */
    if (!pagino)
        pagino = be32_to_cpu(agi->agi_newino);

    error = xfs_check_agi_freecount(cur, agi);
    if (error)
        goto error0;

    /*
     * If in the same AG as the parent, try to get near the parent.
     */
    if (pagno == agno) {
        int     doneleft;   /* done, to the left */
        int     doneright;  /* done, to the right */
        int     searchdistance = 10;

        error = xfs_inobt_lookup(cur, pagino, XFS_LOOKUP_LE, &i);
        if (error)
            goto error0;
        XFS_WANT_CORRUPTED_GOTO(i == 1, error0);

        error = xfs_inobt_get_rec(cur, &rec, &j);
        if (error)
            goto error0;
        XFS_WANT_CORRUPTED_GOTO(i == 1, error0);

        if (rec.ir_freecount > 0) {
            /*
             * Found a free inode in the same chunk
             * as the parent, done.
             */
            goto alloc_inode;
        }


        /*
         * In the same AG as parent, but parent's chunk is full.
         */

        /* duplicate the cursor, search left & right simultaneously */
        error = xfs_btree_dup_cursor(cur, &tcur);
        if (error)
            goto error0;

        /*
         * Skip to last blocks looked up if same parent inode.
         */
        if (pagino != NULLAGINO &&
            pag->pagl_pagino == pagino &&
            pag->pagl_leftrec != NULLAGINO &&
            pag->pagl_rightrec != NULLAGINO) {
            error = xfs_ialloc_get_rec(tcur, pag->pagl_leftrec,
                           &trec, &doneleft, 1);
            if (error)
                goto error1;

            error = xfs_ialloc_get_rec(cur, pag->pagl_rightrec,
                           &rec, &doneright, 0);
            if (error)
                goto error1;
        } else {
            /* search left with tcur, back up 1 record */
            error = xfs_ialloc_next_rec(tcur, &trec, &doneleft, 1);
            if (error)
                goto error1;

            /* search right with cur, go forward 1 record. */
            error = xfs_ialloc_next_rec(cur, &rec, &doneright, 0);
            if (error)
                goto error1;
        }

        /*
         * Loop until we find an inode chunk with a free inode.
         */
        while (!doneleft || !doneright) {
            int useleft;  /* using left inode chunk this time */

            if (!--searchdistance) {
                /*
                 * Not in range - save last search
                 * location and allocate a new inode
                 */
                xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
                pag->pagl_leftrec = trec.ir_startino;
                pag->pagl_rightrec = rec.ir_startino;
                pag->pagl_pagino = pagino;
                goto newino;
            }

            /* figure out the closer block if both are valid. */
            if (!doneleft && !doneright) {
                useleft = pagino -
                 (trec.ir_startino + XFS_INODES_PER_CHUNK - 1) <
                  rec.ir_startino - pagino;
            } else {
                useleft = !doneleft;
            }

            /* free inodes to the left? */
            if (useleft && trec.ir_freecount) {
                rec = trec;
                xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
                cur = tcur;

                pag->pagl_leftrec = trec.ir_startino;
                pag->pagl_rightrec = rec.ir_startino;
                pag->pagl_pagino = pagino;
                goto alloc_inode;
            }

            /* free inodes to the right? */
            if (!useleft && rec.ir_freecount) {
                xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);

                pag->pagl_leftrec = trec.ir_startino;
                pag->pagl_rightrec = rec.ir_startino;
                pag->pagl_pagino = pagino;
                goto alloc_inode;
            }

            /* get next record to check */
            if (useleft) {
                error = xfs_ialloc_next_rec(tcur, &trec,
                                 &doneleft, 1);
            } else {
                error = xfs_ialloc_next_rec(cur, &rec,
                                 &doneright, 0);
            }
            if (error)
                goto error1;
        }

        /*
         * We've reached the end of the btree. because
         * we are only searching a small chunk of the
         * btree each search, there is obviously free
         * inodes closer to the parent inode than we
         * are now. restart the search again.
         */
        pag->pagl_pagino = NULLAGINO;
        pag->pagl_leftrec = NULLAGINO;
        pag->pagl_rightrec = NULLAGINO;
        xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
        xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
        goto restart_pagno;
    }

    /*
     * In a different AG from the parent.
     * See if the most recently allocated block has any free.
     */
newino:
    if (agi->agi_newino != cpu_to_be32(NULLAGINO)) {
        error = xfs_inobt_lookup(cur, be32_to_cpu(agi->agi_newino),
                     XFS_LOOKUP_EQ, &i);
        if (error)
            goto error0;

        if (i == 1) {
            error = xfs_inobt_get_rec(cur, &rec, &j);
            if (error)
                goto error0;

            if (j == 1 && rec.ir_freecount > 0) {
                /*
                 * The last chunk allocated in the group
                 * still has a free inode.
                 */
                goto alloc_inode;
            }
        }
    }

    /*
     * None left in the last group, search the whole AG
     */
    error = xfs_inobt_lookup(cur, 0, XFS_LOOKUP_GE, &i);
    if (error)
        goto error0;
    XFS_WANT_CORRUPTED_GOTO(i == 1, error0);

    for (;;) {
        error = xfs_inobt_get_rec(cur, &rec, &i);
        if (error)
            goto error0;
        XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
        if (rec.ir_freecount > 0)
            break;
        error = xfs_btree_increment(cur, 0, &i);
        if (error)
            goto error0;
        XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
    }

alloc_inode:
    offset = xfs_lowbit64(rec.ir_free);
    ASSERT(offset >= 0);
    ASSERT(offset < XFS_INODES_PER_CHUNK);
    ASSERT((XFS_AGINO_TO_OFFSET(mp, rec.ir_startino) %
                   XFS_INODES_PER_CHUNK) == 0);
    ino = XFS_AGINO_TO_INO(mp, agno, rec.ir_startino + offset);
    rec.ir_free &= ~XFS_INOBT_MASK(offset);
    rec.ir_freecount--;
    error = xfs_inobt_update(cur, &rec);
    if (error)
        goto error0;
    be32_add_cpu(&agi->agi_freecount, -1);
    xfs_ialloc_log_agi(tp, agbp, XFS_AGI_FREECOUNT);
    pag->pagi_freecount--;

    error = xfs_check_agi_freecount(cur, agi);
    if (error)
        goto error0;

    xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
    xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, -1);
    xfs_perag_put(pag);
    *inop = ino;
    return 0;
error1:
    xfs_btree_del_cursor(tcur, XFS_BTREE_ERROR);
error0:
    xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
    xfs_perag_put(pag);
    return error;
}

/*
 * Allocate an inode on disk.
 *
 * Mode is used to tell whether the new inode will need space, and whether it
 * is a directory.
 *
 * This function is designed to be called twice if it has to do an allocation
 * to make more free inodes.  On the first call, *IO_agbp should be set to NULL.
 * If an inode is available without having to performn an allocation, an inode
 * number is returned.  In this case, *IO_agbp would be NULL.  If an allocation
 * needes to be done, xfs_dialloc would return the current AGI buffer in
 * *IO_agbp.  The caller should then commit the current transaction, allocate a
 * new transaction, and call xfs_dialloc() again, passing in the previous value
 * of *IO_agbp.  IO_agbp should be held across the transactions. Since the AGI
 * buffer is locked across the two calls, the second call is guaranteed to have
 * a free inode available.
 *
 * Once we successfully pick an inode its number is returned and the on-disk
 * data structures are updated.  The inode itself is not read in, since doing so
 * would break ordering constraints with xfs_reclaim.
 */
int
xfs_dialloc(
    struct xfs_trans    *tp,
    xfs_ino_t       parent,
    umode_t         mode,
    int         okalloc,
    struct xfs_buf      **IO_agbp,
    xfs_ino_t       *inop)
{
    struct xfs_mount    *mp = tp->t_mountp;
    struct xfs_buf      *agbp;
    xfs_agnumber_t      agno;
    int         error;
    int         ialloced;
    int         noroom = 0;
    xfs_agnumber_t      start_agno;
    struct xfs_perag    *pag;

    if (*IO_agbp) {
        /*
         * If the caller passes in a pointer to the AGI buffer,
         * continue where we left off before.  In this case, we
         * know that the allocation group has free inodes.
         */
        agbp = *IO_agbp;
        goto out_alloc;
    }

    /*
     * We do not have an agbp, so select an initial allocation
     * group for inode allocation.
     */
    start_agno = xfs_ialloc_ag_select(tp, parent, mode, okalloc);
    if (start_agno == NULLAGNUMBER) {
        *inop = NULLFSINO;
        return 0;
    }

    /*
     * If we have already hit the ceiling of inode blocks then clear
     * okalloc so we scan all available agi structures for a free
     * inode.
     */
    if (mp->m_maxicount &&
        mp->m_sb.sb_icount + XFS_IALLOC_INODES(mp) > mp->m_maxicount) {
        noroom = 1;
        okalloc = 0;
    }

    /*
     * Loop until we find an allocation group that either has free inodes
     * or in which we can allocate some inodes.  Iterate through the
     * allocation groups upward, wrapping at the end.
     */
    agno = start_agno;
    for (;;) {
        pag = xfs_perag_get(mp, agno);
        if (!pag->pagi_inodeok) {
            xfs_ialloc_next_ag(mp);
            goto nextag;
        }

        if (!pag->pagi_init) {
            error = xfs_ialloc_pagi_init(mp, tp, agno);
            if (error)
                goto out_error;
        }

        /*
         * Do a first racy fast path check if this AG is usable.
         */
        if (!pag->pagi_freecount && !okalloc)
            goto nextag;

        /*
         * Then read in the AGI buffer and recheck with the AGI buffer
         * lock held.
         */
        error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
        if (error)
            goto out_error;

        if (pag->pagi_freecount) {
            xfs_perag_put(pag);
            goto out_alloc;
        }

        if (!okalloc)
            goto nextag_relse_buffer;


        error = xfs_ialloc_ag_alloc(tp, agbp, &ialloced);
        if (error) {
            xfs_trans_brelse(tp, agbp);

            if (error != ENOSPC)
                goto out_error;

            xfs_perag_put(pag);
            *inop = NULLFSINO;
            return 0;
        }

        if (ialloced) {
            /*
             * We successfully allocated some inodes, return
             * the current context to the caller so that it
             * can commit the current transaction and call
             * us again where we left off.
             */
            ASSERT(pag->pagi_freecount > 0);
            xfs_perag_put(pag);

            *IO_agbp = agbp;
            *inop = NULLFSINO;
            return 0;
        }

nextag_relse_buffer:
        xfs_trans_brelse(tp, agbp);
nextag:
        xfs_perag_put(pag);
        if (++agno == mp->m_sb.sb_agcount)
            agno = 0;
        if (agno == start_agno) {
            *inop = NULLFSINO;
            return noroom ? ENOSPC : 0;
        }
    }

out_alloc:
    *IO_agbp = NULL;
    return xfs_dialloc_ag(tp, agbp, parent, inop);
out_error:
    xfs_perag_put(pag);
    return XFS_ERROR(error);
}

/*
 * Free disk inode.  Carefully avoids touching the incore inode, all
 * manipulations incore are the caller's responsibility.
 * The on-disk inode is not changed by this operation, only the
 * btree (free inode mask) is changed.
 */
int
xfs_difree(
    xfs_trans_t *tp,        /* transaction pointer */
    xfs_ino_t   inode,      /* inode to be freed */
    xfs_bmap_free_t *flist,     /* extents to free */
    int     *delete,    /* set if inode cluster was deleted */
    xfs_ino_t   *first_ino) /* first inode in deleted cluster */
{
    /* REFERENCED */
    xfs_agblock_t   agbno;  /* block number containing inode */
    xfs_buf_t   *agbp;  /* buffer containing allocation group header */
    xfs_agino_t agino;  /* inode number relative to allocation group */
    xfs_agnumber_t  agno;   /* allocation group number */
    xfs_agi_t   *agi;   /* allocation group header */
    xfs_btree_cur_t *cur;   /* inode btree cursor */
    int     error;  /* error return value */
    int     i;  /* result code */
    int     ilen;   /* inodes in an inode cluster */
    xfs_mount_t *mp;    /* mount structure for filesystem */
    int     off;    /* offset of inode in inode chunk */
    xfs_inobt_rec_incore_t rec; /* btree record */
    struct xfs_perag *pag;

    mp = tp->t_mountp;

    /*
     * Break up inode number into its components.
     */
    agno = XFS_INO_TO_AGNO(mp, inode);
    if (agno >= mp->m_sb.sb_agcount)  {
        xfs_warn(mp, "%s: agno >= mp->m_sb.sb_agcount (%d >= %d).",
            __func__, agno, mp->m_sb.sb_agcount);
        ASSERT(0);
        return XFS_ERROR(EINVAL);
    }
    agino = XFS_INO_TO_AGINO(mp, inode);
    if (inode != XFS_AGINO_TO_INO(mp, agno, agino))  {
        xfs_warn(mp, "%s: inode != XFS_AGINO_TO_INO() (%llu != %llu).",
            __func__, (unsigned long long)inode,
            (unsigned long long)XFS_AGINO_TO_INO(mp, agno, agino));
        ASSERT(0);
        return XFS_ERROR(EINVAL);
    }
    agbno = XFS_AGINO_TO_AGBNO(mp, agino);
    if (agbno >= mp->m_sb.sb_agblocks)  {
        xfs_warn(mp, "%s: agbno >= mp->m_sb.sb_agblocks (%d >= %d).",
            __func__, agbno, mp->m_sb.sb_agblocks);
        ASSERT(0);
        return XFS_ERROR(EINVAL);
    }
    /*
     * Get the allocation group header.
     */
    error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
    if (error) {
        xfs_warn(mp, "%s: xfs_ialloc_read_agi() returned error %d.",
            __func__, error);
        return error;
    }
    agi = XFS_BUF_TO_AGI(agbp);
    ASSERT(agi->agi_magicnum == cpu_to_be32(XFS_AGI_MAGIC));
    ASSERT(agbno < be32_to_cpu(agi->agi_length));
    /*
     * Initialize the cursor.
     */
    cur = xfs_inobt_init_cursor(mp, tp, agbp, agno);

    error = xfs_check_agi_freecount(cur, agi);
    if (error)
        goto error0;

    /*
     * Look for the entry describing this inode.
     */
    if ((error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_LE, &i))) {
        xfs_warn(mp, "%s: xfs_inobt_lookup() returned error %d.",
            __func__, error);
        goto error0;
    }
    XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
    error = xfs_inobt_get_rec(cur, &rec, &i);
    if (error) {
        xfs_warn(mp, "%s: xfs_inobt_get_rec() returned error %d.",
            __func__, error);
        goto error0;
    }
    XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
    /*
     * Get the offset in the inode chunk.
     */
    off = agino - rec.ir_startino;
    ASSERT(off >= 0 && off < XFS_INODES_PER_CHUNK);
    ASSERT(!(rec.ir_free & XFS_INOBT_MASK(off)));
    /*
     * Mark the inode free & increment the count.
     */
    rec.ir_free |= XFS_INOBT_MASK(off);
    rec.ir_freecount++;

    /*
     * When an inode cluster is free, it becomes eligible for removal
     */
    if (!(mp->m_flags & XFS_MOUNT_IKEEP) &&
        (rec.ir_freecount == XFS_IALLOC_INODES(mp))) {

        *delete = 1;
        *first_ino = XFS_AGINO_TO_INO(mp, agno, rec.ir_startino);

        /*
         * Remove the inode cluster from the AGI B+Tree, adjust the
         * AGI and Superblock inode counts, and mark the disk space
         * to be freed when the transaction is committed.
         */
        ilen = XFS_IALLOC_INODES(mp);
        be32_add_cpu(&agi->agi_count, -ilen);
        be32_add_cpu(&agi->agi_freecount, -(ilen - 1));
        xfs_ialloc_log_agi(tp, agbp, XFS_AGI_COUNT | XFS_AGI_FREECOUNT);
        pag = xfs_perag_get(mp, agno);
        pag->pagi_freecount -= ilen - 1;
        xfs_perag_put(pag);
        xfs_trans_mod_sb(tp, XFS_TRANS_SB_ICOUNT, -ilen);
        xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, -(ilen - 1));

        if ((error = xfs_btree_delete(cur, &i))) {
            xfs_warn(mp, "%s: xfs_btree_delete returned error %d.",
                __func__, error);
            goto error0;
        }

        xfs_bmap_add_free(XFS_AGB_TO_FSB(mp,
                agno, XFS_INO_TO_AGBNO(mp,rec.ir_startino)),
                XFS_IALLOC_BLOCKS(mp), flist, mp);
    } else {
        *delete = 0;

        error = xfs_inobt_update(cur, &rec);
        if (error) {
            xfs_warn(mp, "%s: xfs_inobt_update returned error %d.",
                __func__, error);
            goto error0;
        }

        /* 
         * Change the inode free counts and log the ag/sb changes.
         */
        be32_add_cpu(&agi->agi_freecount, 1);
        xfs_ialloc_log_agi(tp, agbp, XFS_AGI_FREECOUNT);
        pag = xfs_perag_get(mp, agno);
        pag->pagi_freecount++;
        xfs_perag_put(pag);
        xfs_trans_mod_sb(tp, XFS_TRANS_SB_IFREE, 1);
    }

    error = xfs_check_agi_freecount(cur, agi);
    if (error)
        goto error0;

    xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
    return 0;

error0:
    xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
    return error;
}

STATIC int
xfs_imap_lookup(
    struct xfs_mount    *mp,
    struct xfs_trans    *tp,
    xfs_agnumber_t      agno,
    xfs_agino_t     agino,
    xfs_agblock_t       agbno,
    xfs_agblock_t       *chunk_agbno,
    xfs_agblock_t       *offset_agbno,
    int         flags)
{
    struct xfs_inobt_rec_incore rec;
    struct xfs_btree_cur    *cur;
    struct xfs_buf      *agbp;
    int         error;
    int         i;

    error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
    if (error) {
        xfs_alert(mp,
            "%s: xfs_ialloc_read_agi() returned error %d, agno %d",
            __func__, error, agno);
        return error;
    }

    /*
     * Lookup the inode record for the given agino. If the record cannot be
     * found, then it's an invalid inode number and we should abort. Once
     * we have a record, we need to ensure it contains the inode number
     * we are looking up.
     */
    cur = xfs_inobt_init_cursor(mp, tp, agbp, agno);
    error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_LE, &i);
    if (!error) {
        if (i)
            error = xfs_inobt_get_rec(cur, &rec, &i);
        if (!error && i == 0)
            error = EINVAL;
    }

    xfs_trans_brelse(tp, agbp);
    xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
    if (error)
        return error;

    /* check that the returned record contains the required inode */
    if (rec.ir_startino > agino ||
        rec.ir_startino + XFS_IALLOC_INODES(mp) <= agino)
        return EINVAL;

    /* for untrusted inodes check it is allocated first */
    if ((flags & XFS_IGET_UNTRUSTED) &&
        (rec.ir_free & XFS_INOBT_MASK(agino - rec.ir_startino)))
        return EINVAL;

    *chunk_agbno = XFS_AGINO_TO_AGBNO(mp, rec.ir_startino);
    *offset_agbno = agbno - *chunk_agbno;
    return 0;
}

/*
 * Return the location of the inode in imap, for mapping it into a buffer.
 */
int
xfs_imap(
    xfs_mount_t  *mp,   /* file system mount structure */
    xfs_trans_t  *tp,   /* transaction pointer */
    xfs_ino_t   ino,    /* inode to locate */
    struct xfs_imap *imap,  /* location map structure */
    uint        flags)  /* flags for inode btree lookup */
{
    xfs_agblock_t   agbno;  /* block number of inode in the alloc group */
    xfs_agino_t agino;  /* inode number within alloc group */
    xfs_agnumber_t  agno;   /* allocation group number */
    int     blks_per_cluster; /* num blocks per inode cluster */
    xfs_agblock_t   chunk_agbno;    /* first block in inode chunk */
    xfs_agblock_t   cluster_agbno;  /* first block in inode cluster */
    int     error;  /* error code */
    int     offset; /* index of inode in its buffer */
    int     offset_agbno;   /* blks from chunk start to inode */

    ASSERT(ino != NULLFSINO);

    /*
     * Split up the inode number into its parts.
     */
    agno = XFS_INO_TO_AGNO(mp, ino);
    agino = XFS_INO_TO_AGINO(mp, ino);
    agbno = XFS_AGINO_TO_AGBNO(mp, agino);
    if (agno >= mp->m_sb.sb_agcount || agbno >= mp->m_sb.sb_agblocks ||
        ino != XFS_AGINO_TO_INO(mp, agno, agino)) {
#ifdef DEBUG
        /*
         * Don't output diagnostic information for untrusted inodes
         * as they can be invalid without implying corruption.
         */
        if (flags & XFS_IGET_UNTRUSTED)
            return XFS_ERROR(EINVAL);
        if (agno >= mp->m_sb.sb_agcount) {
            xfs_alert(mp,
                "%s: agno (%d) >= mp->m_sb.sb_agcount (%d)",
                __func__, agno, mp->m_sb.sb_agcount);
        }
        if (agbno >= mp->m_sb.sb_agblocks) {
            xfs_alert(mp,
        "%s: agbno (0x%llx) >= mp->m_sb.sb_agblocks (0x%lx)",
                __func__, (unsigned long long)agbno,
                (unsigned long)mp->m_sb.sb_agblocks);
        }
        if (ino != XFS_AGINO_TO_INO(mp, agno, agino)) {
            xfs_alert(mp,
        "%s: ino (0x%llx) != XFS_AGINO_TO_INO() (0x%llx)",
                __func__, ino,
                XFS_AGINO_TO_INO(mp, agno, agino));
        }
        xfs_stack_trace();
#endif /* DEBUG */
        return XFS_ERROR(EINVAL);
    }

    blks_per_cluster = XFS_INODE_CLUSTER_SIZE(mp) >> mp->m_sb.sb_blocklog;

    /*
     * For bulkstat and handle lookups, we have an untrusted inode number
     * that we have to verify is valid. We cannot do this just by reading
     * the inode buffer as it may have been unlinked and removed leaving
     * inodes in stale state on disk. Hence we have to do a btree lookup
     * in all cases where an untrusted inode number is passed.
     */
    if (flags & XFS_IGET_UNTRUSTED) {
        error = xfs_imap_lookup(mp, tp, agno, agino, agbno,
                    &chunk_agbno, &offset_agbno, flags);
        if (error)
            return error;
        goto out_map;
    }

    /*
     * If the inode cluster size is the same as the blocksize or
     * smaller we get to the buffer by simple arithmetics.
     */
    if (XFS_INODE_CLUSTER_SIZE(mp) <= mp->m_sb.sb_blocksize) {
        offset = XFS_INO_TO_OFFSET(mp, ino);
        ASSERT(offset < mp->m_sb.sb_inopblock);

        imap->im_blkno = XFS_AGB_TO_DADDR(mp, agno, agbno);
        imap->im_len = XFS_FSB_TO_BB(mp, 1);
        imap->im_boffset = (ushort)(offset << mp->m_sb.sb_inodelog);
        return 0;
    }

    /*
     * If the inode chunks are aligned then use simple maths to
     * find the location. Otherwise we have to do a btree
     * lookup to find the location.
     */
    if (mp->m_inoalign_mask) {
        offset_agbno = agbno & mp->m_inoalign_mask;
        chunk_agbno = agbno - offset_agbno;
    } else {
        error = xfs_imap_lookup(mp, tp, agno, agino, agbno,
                    &chunk_agbno, &offset_agbno, flags);
        if (error)
            return error;
    }

out_map:
    ASSERT(agbno >= chunk_agbno);
    cluster_agbno = chunk_agbno +
        ((offset_agbno / blks_per_cluster) * blks_per_cluster);
    offset = ((agbno - cluster_agbno) * mp->m_sb.sb_inopblock) +
        XFS_INO_TO_OFFSET(mp, ino);

    imap->im_blkno = XFS_AGB_TO_DADDR(mp, agno, cluster_agbno);
    imap->im_len = XFS_FSB_TO_BB(mp, blks_per_cluster);
    imap->im_boffset = (ushort)(offset << mp->m_sb.sb_inodelog);

    /*
     * If the inode number maps to a block outside the bounds
     * of the file system then return NULL rather than calling
     * read_buf and panicing when we get an error from the
     * driver.
     */
    if ((imap->im_blkno + imap->im_len) >
        XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks)) {
        xfs_alert(mp,
    "%s: (im_blkno (0x%llx) + im_len (0x%llx)) > sb_dblocks (0x%llx)",
            __func__, (unsigned long long) imap->im_blkno,
            (unsigned long long) imap->im_len,
            XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks));
        return XFS_ERROR(EINVAL);
    }
    return 0;
}

/*
 * Compute and fill in value of m_in_maxlevels.
 */
void
xfs_ialloc_compute_maxlevels(
    xfs_mount_t *mp)        /* file system mount structure */
{
    int     level;
    uint        maxblocks;
    uint        maxleafents;
    int     minleafrecs;
    int     minnoderecs;

    maxleafents = (1LL << XFS_INO_AGINO_BITS(mp)) >>
        XFS_INODES_PER_CHUNK_LOG;
    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_in_maxlevels = level;
}

/*
 * Log specified fields for the ag hdr (inode section)
 */
void
xfs_ialloc_log_agi(
    xfs_trans_t *tp,        /* transaction pointer */
    xfs_buf_t   *bp,        /* allocation group header buffer */
    int     fields)     /* bitmask of fields to log */
{
    int         first;      /* first byte number */
    int         last;       /* last byte number */
    static const short  offsets[] = {   /* field starting offsets */
                    /* keep in sync with bit definitions */
        offsetof(xfs_agi_t, agi_magicnum),
        offsetof(xfs_agi_t, agi_versionnum),
        offsetof(xfs_agi_t, agi_seqno),
        offsetof(xfs_agi_t, agi_length),
        offsetof(xfs_agi_t, agi_count),
        offsetof(xfs_agi_t, agi_root),
        offsetof(xfs_agi_t, agi_level),
        offsetof(xfs_agi_t, agi_freecount),
        offsetof(xfs_agi_t, agi_newino),
        offsetof(xfs_agi_t, agi_dirino),
        offsetof(xfs_agi_t, agi_unlinked),
        sizeof(xfs_agi_t)
    };
#ifdef DEBUG
    xfs_agi_t       *agi;   /* allocation group header */

    agi = XFS_BUF_TO_AGI(bp);
    ASSERT(agi->agi_magicnum == cpu_to_be32(XFS_AGI_MAGIC));
#endif
    /*
     * Compute byte offsets for the first and last fields.
     */
    xfs_btree_offsets(fields, offsets, XFS_AGI_NUM_BITS, &first, &last);
    /*
     * Log the allocation group inode header buffer.
     */
    xfs_trans_log_buf(tp, bp, first, last);
}

#ifdef DEBUG
STATIC void
xfs_check_agi_unlinked(
    struct xfs_agi      *agi)
{
    int         i;

    for (i = 0; i < XFS_AGI_UNLINKED_BUCKETS; i++)
        ASSERT(agi->agi_unlinked[i]);
}
#else
#define xfs_check_agi_unlinked(agi)
#endif

/*
 * Read in the allocation group header (inode allocation section)
 */
int
xfs_read_agi(
    struct xfs_mount    *mp,    /* file system mount structure */
    struct xfs_trans    *tp,    /* transaction pointer */
    xfs_agnumber_t      agno,   /* allocation group number */
    struct xfs_buf      **bpp)  /* allocation group hdr buf */
{
    struct xfs_agi      *agi;   /* allocation group header */
    int         agi_ok; /* agi is consistent */
    int         error;

    ASSERT(agno != NULLAGNUMBER);

    error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp,
            XFS_AG_DADDR(mp, agno, XFS_AGI_DADDR(mp)),
            XFS_FSS_TO_BB(mp, 1), 0, bpp);
    if (error)
        return error;

    ASSERT(!xfs_buf_geterror(*bpp));
    agi = XFS_BUF_TO_AGI(*bpp);

    /*
     * Validate the magic number of the agi block.
     */
    agi_ok = agi->agi_magicnum == cpu_to_be32(XFS_AGI_MAGIC) &&
        XFS_AGI_GOOD_VERSION(be32_to_cpu(agi->agi_versionnum)) &&
        be32_to_cpu(agi->agi_seqno) == agno;
    if (unlikely(XFS_TEST_ERROR(!agi_ok, mp, XFS_ERRTAG_IALLOC_READ_AGI,
            XFS_RANDOM_IALLOC_READ_AGI))) {
        XFS_CORRUPTION_ERROR("xfs_read_agi", XFS_ERRLEVEL_LOW,
                     mp, agi);
        xfs_trans_brelse(tp, *bpp);
        return XFS_ERROR(EFSCORRUPTED);
    }

    xfs_buf_set_ref(*bpp, XFS_AGI_REF);

    xfs_check_agi_unlinked(agi);
    return 0;
}

int
xfs_ialloc_read_agi(
    struct xfs_mount    *mp,    /* file system mount structure */
    struct xfs_trans    *tp,    /* transaction pointer */
    xfs_agnumber_t      agno,   /* allocation group number */
    struct xfs_buf      **bpp)  /* allocation group hdr buf */
{
    struct xfs_agi      *agi;   /* allocation group header */
    struct xfs_perag    *pag;   /* per allocation group data */
    int         error;

    error = xfs_read_agi(mp, tp, agno, bpp);
    if (error)
        return error;

    agi = XFS_BUF_TO_AGI(*bpp);
    pag = xfs_perag_get(mp, agno);
    if (!pag->pagi_init) {
        pag->pagi_freecount = be32_to_cpu(agi->agi_freecount);
        pag->pagi_count = be32_to_cpu(agi->agi_count);
        pag->pagi_init = 1;
    }

    /*
     * It's possible for these to be out of sync if
     * we are in the middle of a forced shutdown.
     */
    ASSERT(pag->pagi_freecount == be32_to_cpu(agi->agi_freecount) ||
        XFS_FORCED_SHUTDOWN(mp));
    xfs_perag_put(pag);
    return 0;
}

/*
 * Read in the agi to initialise the per-ag data in the mount structure
 */
int
xfs_ialloc_pagi_init(
    xfs_mount_t *mp,        /* file system mount structure */
    xfs_trans_t *tp,        /* transaction pointer */
    xfs_agnumber_t  agno)       /* allocation group number */
{
    xfs_buf_t   *bp = NULL;
    int     error;

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