[safe/jmp/linux-2.6] / fs / xfs / xfs_ialloc.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_dir2.h"
#include "xfs_dmapi.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_dir2_sf.h"
#include "xfs_attr_sf.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.
 */
STATIC 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 void
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,
                                         XFS_BUF_LOCK);
                ASSERT(fbuf);
                ASSERT(!XFS_BUF_GETERROR(fbuf));

                /*
                 * 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_biozero(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);
        }
}

/*
 * 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 */

        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.
         */
        xfs_ialloc_inode_init(args.mp, tp, agno, args.agbno, args.len,
                              random32());

        /*
         * 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);
        down_read(&args.mp->m_peraglock);
        args.mp->m_perag[agno].pagi_freecount += newlen;
        up_read(&args.mp->m_peraglock);
        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_INLINE 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_buf_t *                      /* allocation group buffer */
xfs_ialloc_ag_select(
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_ino_t       parent,         /* parent directory inode number */
        mode_t          mode,           /* bits set to indicate file type */
        int             okalloc)        /* ok to allocate more space */
{
        xfs_buf_t       *agbp;          /* allocation group header buffer */
        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 */

        /*
         * 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;
        down_read(&mp->m_peraglock);
        for (;;) {
                pag = &mp->m_perag[agno];
                if (!pag->pagi_init) {
                        if (xfs_ialloc_read_agi(mp, tp, agno, &agbp)) {
                                agbp = NULL;
                                goto nextag;
                        }
                } else
                        agbp = NULL;

                if (!pag->pagi_inodeok) {
                        xfs_ialloc_next_ag(mp);
                        goto unlock_nextag;
                }

                /*
                 * Is there enough free space for the file plus a block
                 * of inodes (if we need to allocate some)?
                 */
                ineed = pag->pagi_freecount ? 0 : XFS_IALLOC_BLOCKS(mp);
                if (ineed && !pag->pagf_init) {
                        if (agbp == NULL &&
                            xfs_ialloc_read_agi(mp, tp, agno, &agbp)) {
                                agbp = NULL;
                                goto nextag;
                        }
                        (void)xfs_alloc_pagf_init(mp, tp, agno, flags);
                }
                if (!ineed || pag->pagf_init) {
                        if (ineed && !(longest = pag->pagf_longest))
                                longest = pag->pagf_flcount > 0;
                        if (!ineed ||
                            (pag->pagf_freeblks >= needspace + ineed &&
                             longest >= ineed &&
                             okalloc)) {
                                if (agbp == NULL &&
                                    xfs_ialloc_read_agi(mp, tp, agno, &agbp)) {
                                        agbp = NULL;
                                        goto nextag;
                                }
                                up_read(&mp->m_peraglock);
                                return agbp;
                        }
                }
unlock_nextag:
                if (agbp)
                        xfs_trans_brelse(tp, agbp);
nextag:
                /*
                 * No point in iterating over the rest, if we're shutting
                 * down.
                 */
                if (XFS_FORCED_SHUTDOWN(mp)) {
                        up_read(&mp->m_peraglock);
                        return NULL;
                }
                agno++;
                if (agno >= agcount)
                        agno = 0;
                if (agno == pagno) {
                        if (flags == 0) {
                                up_read(&mp->m_peraglock);
                                return NULL;
                        }
                        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;
}


/*
 * Visible inode allocation functions.
 */

/*
 * Allocate an inode on disk.
 * Mode is used to tell whether the new inode will need space, and whether
 * it is a directory.
 *
 * The arguments IO_agbp and alloc_done are defined to work within
 * the constraint of one allocation per transaction.
 * xfs_dialloc() 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,
 * i.e., xfs_dialloc() did not need to do an allocation, an inode
 * number is returned.  In this case, IO_agbp would be set to the
 * current ag_buf and alloc_done set to false.
 * If an allocation needed to be done, xfs_dialloc would return
 * the current ag_buf in IO_agbp and set alloc_done to true.
 * 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 agbp 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(
        xfs_trans_t     *tp,            /* transaction pointer */
        xfs_ino_t       parent,         /* parent inode (directory) */
        mode_t          mode,           /* mode bits for new inode */
        int             okalloc,        /* ok to allocate more space */
        xfs_buf_t       **IO_agbp,      /* in/out ag header's buffer */
        boolean_t       *alloc_done,    /* true if we needed to replenish
                                           inode freelist */
        xfs_ino_t       *inop)          /* inode number allocated */
{
        xfs_agnumber_t  agcount;        /* number of allocation groups */
        xfs_buf_t       *agbp;          /* allocation group header's buffer */
        xfs_agnumber_t  agno;           /* allocation group number */
        xfs_agi_t       *agi;           /* allocation group header structure */
        xfs_btree_cur_t *cur;           /* inode allocation btree cursor */
        int             error;          /* error return value */
        int             i;              /* result code */
        int             ialloced;       /* inode allocation status */
        int             noroom = 0;     /* no space for inode blk allocation */
        xfs_ino_t       ino;            /* fs-relative inode to be returned */
        /* REFERENCED */
        int             j;              /* result code */
        xfs_mount_t     *mp;            /* file system mount structure */
        int             offset;         /* index of inode in chunk */
        xfs_agino_t     pagino;         /* parent's AG relative inode # */
        xfs_agnumber_t  pagno;          /* parent's AG number */
        xfs_inobt_rec_incore_t rec;     /* inode allocation record */
        xfs_agnumber_t  tagno;          /* testing allocation group number */
        xfs_btree_cur_t *tcur;          /* temp cursor */
        xfs_inobt_rec_incore_t trec;    /* temp inode allocation record */


        if (*IO_agbp == NULL) {
                /*
                 * We do not have an agbp, so select an initial allocation
                 * group for inode allocation.
                 */
                agbp = xfs_ialloc_ag_select(tp, parent, mode, okalloc);
                /*
                 * Couldn't find an allocation group satisfying the
                 * criteria, give up.
                 */
                if (!agbp) {
                        *inop = NULLFSINO;
                        return 0;
                }
                agi = XFS_BUF_TO_AGI(agbp);
                ASSERT(be32_to_cpu(agi->agi_magicnum) == XFS_AGI_MAGIC);
        } else {
                /*
                 * Continue where we left off before.  In this case, we
                 * know that the allocation group has free inodes.
                 */
                agbp = *IO_agbp;
                agi = XFS_BUF_TO_AGI(agbp);
                ASSERT(be32_to_cpu(agi->agi_magicnum) == XFS_AGI_MAGIC);
                ASSERT(be32_to_cpu(agi->agi_freecount) > 0);
        }
        mp = tp->t_mountp;
        agcount = mp->m_sb.sb_agcount;
        agno = be32_to_cpu(agi->agi_seqno);
        tagno = agno;
        pagno = XFS_INO_TO_AGNO(mp, parent);
        pagino = XFS_INO_TO_AGINO(mp, parent);

        /*
         * 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.
         */
        *alloc_done = B_FALSE;
        while (!agi->agi_freecount) {
                /*
                 * Don't do anything if we're not supposed to allocate
                 * any blocks, just go on to the next ag.
                 */
                if (okalloc) {
                        /*
                         * Try to allocate some new inodes in the allocation
                         * group.
                         */
                        if ((error = xfs_ialloc_ag_alloc(tp, agbp, &ialloced))) {
                                xfs_trans_brelse(tp, agbp);
                                if (error == ENOSPC) {
                                        *inop = NULLFSINO;
                                        return 0;
                                } else
                                        return error;
                        }
                        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(be32_to_cpu(agi->agi_freecount) > 0);
                                *alloc_done = B_TRUE;
                                *IO_agbp = agbp;
                                *inop = NULLFSINO;
                                return 0;
                        }
                }
                /*
                 * If it failed, give up on this ag.
                 */
                xfs_trans_brelse(tp, agbp);
                /*
                 * Go on to the next ag: get its ag header.
                 */
nextag:
                if (++tagno == agcount)
                        tagno = 0;
                if (tagno == agno) {
                        *inop = NULLFSINO;
                        return noroom ? ENOSPC : 0;
                }
                down_read(&mp->m_peraglock);
                if (mp->m_perag[tagno].pagi_inodeok == 0) {
                        up_read(&mp->m_peraglock);
                        goto nextag;
                }
                error = xfs_ialloc_read_agi(mp, tp, tagno, &agbp);
                up_read(&mp->m_peraglock);
                if (error)
                        goto nextag;
                agi = XFS_BUF_TO_AGI(agbp);
                ASSERT(be32_to_cpu(agi->agi_magicnum) == XFS_AGI_MAGIC);
        }
        /*
         * Here with an allocation group that has a free inode.
         * Reset agno since we may have chosen a new ag in the
         * loop above.
         */
        agno = tagno;
        *IO_agbp = NULL;
        cur = xfs_inobt_init_cursor(mp, tp, agbp, be32_to_cpu(agi->agi_seqno));
        /*
         * 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 */

                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;

                /* 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 */

                        /* 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;
                                goto alloc_inode;
                        }

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

        /*
         * In a different AG from the parent.
         * See if the most recently allocated block has any free.
         */
        else if (be32_to_cpu(agi->agi_newino) != 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_ialloc_find_free(&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);
        down_read(&mp->m_peraglock);
        mp->m_perag[tagno].pagi_freecount--;
        up_read(&mp->m_peraglock);

        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);
        *inop = ino;
        return 0;
error1:
        xfs_btree_del_cursor(tcur, XFS_BTREE_ERROR);
error0:
        xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
        return 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 */

        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)  {
                cmn_err(CE_WARN,
                        "xfs_difree: agno >= mp->m_sb.sb_agcount (%d >= %d) on %s.  Returning EINVAL.",
                        agno, mp->m_sb.sb_agcount, mp->m_fsname);
                ASSERT(0);
                return XFS_ERROR(EINVAL);
        }
        agino = XFS_INO_TO_AGINO(mp, inode);
        if (inode != XFS_AGINO_TO_INO(mp, agno, agino))  {
                cmn_err(CE_WARN,
                        "xfs_difree: inode != XFS_AGINO_TO_INO() "
                        "(%llu != %llu) on %s.  Returning EINVAL.",
                        (unsigned long long)inode,
                        (unsigned long long)XFS_AGINO_TO_INO(mp, agno, agino),
                        mp->m_fsname);
                ASSERT(0);
                return XFS_ERROR(EINVAL);
        }
        agbno = XFS_AGINO_TO_AGBNO(mp, agino);
        if (agbno >= mp->m_sb.sb_agblocks)  {
                cmn_err(CE_WARN,
                        "xfs_difree: agbno >= mp->m_sb.sb_agblocks (%d >= %d) on %s.  Returning EINVAL.",
                        agbno, mp->m_sb.sb_agblocks, mp->m_fsname);
                ASSERT(0);
                return XFS_ERROR(EINVAL);
        }
        /*
         * Get the allocation group header.
         */
        down_read(&mp->m_peraglock);
        error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
        up_read(&mp->m_peraglock);
        if (error) {
                cmn_err(CE_WARN,
                        "xfs_difree: xfs_ialloc_read_agi() returned an error %d on %s.  Returning error.",
                        error, mp->m_fsname);
                return error;
        }
        agi = XFS_BUF_TO_AGI(agbp);
        ASSERT(be32_to_cpu(agi->agi_magicnum) == 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))) {
                cmn_err(CE_WARN,
                        "xfs_difree: xfs_inobt_lookup returned()  an error %d on %s.  Returning error.",
                        error, mp->m_fsname);
                goto error0;
        }
        XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
        error = xfs_inobt_get_rec(cur, &rec, &i);
        if (error) {
                cmn_err(CE_WARN,
                        "xfs_difree: xfs_inobt_get_rec()  returned an error %d on %s.  Returning error.",
                        error, mp->m_fsname);
                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);
                down_read(&mp->m_peraglock);
                mp->m_perag[agno].pagi_freecount -= ilen - 1;
                up_read(&mp->m_peraglock);
                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))) {
                        cmn_err(CE_WARN, "xfs_difree: xfs_btree_delete returned an error %d on %s.\n",
                                error, mp->m_fsname);
                        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) {
                        cmn_err(CE_WARN,
        "xfs_difree: xfs_inobt_update returned an error %d on %s.",
                                error, mp->m_fsname);
                        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);
                down_read(&mp->m_peraglock);
                mp->m_perag[agno].pagi_freecount++;
                up_read(&mp->m_peraglock);
                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;
}

/*
 * 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
                /* no diagnostics for bulkstat, ino comes from userspace */
                if (flags & XFS_IGET_BULKSTAT)
                        return XFS_ERROR(EINVAL);
                if (agno >= mp->m_sb.sb_agcount) {
                        xfs_fs_cmn_err(CE_ALERT, mp,
                                        "xfs_imap: agno (%d) >= "
                                        "mp->m_sb.sb_agcount (%d)",
                                        agno,  mp->m_sb.sb_agcount);
                }
                if (agbno >= mp->m_sb.sb_agblocks) {
                        xfs_fs_cmn_err(CE_ALERT, mp,
                                        "xfs_imap: agbno (0x%llx) >= "
                                        "mp->m_sb.sb_agblocks (0x%lx)",
                                        (unsigned long long) agbno,
                                        (unsigned long) mp->m_sb.sb_agblocks);
                }
                if (ino != XFS_AGINO_TO_INO(mp, agno, agino)) {
                        xfs_fs_cmn_err(CE_ALERT, mp,
                                        "xfs_imap: ino (0x%llx) != "
                                        "XFS_AGINO_TO_INO(mp, agno, agino) "
                                        "(0x%llx)",
                                        ino, XFS_AGINO_TO_INO(mp, agno, agino));
                }
                xfs_stack_trace();
#endif /* DEBUG */
                return XFS_ERROR(EINVAL);
        }

        /*
         * 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;
        }

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

        /*
         * If we get a block number passed from bulkstat we can use it to
         * find the buffer easily.
         */
        if (imap->im_blkno) {
                offset = XFS_INO_TO_OFFSET(mp, ino);
                ASSERT(offset < mp->m_sb.sb_inopblock);

                cluster_agbno = xfs_daddr_to_agbno(mp, imap->im_blkno);
                offset += (agbno - cluster_agbno) * mp->m_sb.sb_inopblock;

                imap->im_len = XFS_FSB_TO_BB(mp, blks_per_cluster);
                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 {
                xfs_btree_cur_t *cur;   /* inode btree cursor */
                xfs_inobt_rec_incore_t chunk_rec;
                xfs_buf_t       *agbp;  /* agi buffer */
                int             i;      /* temp state */

                down_read(&mp->m_peraglock);
                error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
                up_read(&mp->m_peraglock);
                if (error) {
                        xfs_fs_cmn_err(CE_ALERT, mp, "xfs_imap: "
                                        "xfs_ialloc_read_agi() returned "
                                        "error %d, agno %d",
                                        error, agno);
                        return error;
                }

                cur = xfs_inobt_init_cursor(mp, tp, agbp, agno);
                error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_LE, &i);
                if (error) {
                        xfs_fs_cmn_err(CE_ALERT, mp, "xfs_imap: "
                                        "xfs_inobt_lookup() failed");
                        goto error0;
                }

                error = xfs_inobt_get_rec(cur, &chunk_rec, &i);
                if (error) {
                        xfs_fs_cmn_err(CE_ALERT, mp, "xfs_imap: "
                                        "xfs_inobt_get_rec() failed");
                        goto error0;
                }
                if (i == 0) {
#ifdef DEBUG
                        xfs_fs_cmn_err(CE_ALERT, mp, "xfs_imap: "
                                        "xfs_inobt_get_rec() failed");
#endif /* DEBUG */
                        error = XFS_ERROR(EINVAL);
                }
 error0:
                xfs_trans_brelse(tp, agbp);
                xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
                if (error)
                        return error;
                chunk_agbno = XFS_AGINO_TO_AGBNO(mp, chunk_rec.ir_startino);
                offset_agbno = agbno - chunk_agbno;
        }

        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_fs_cmn_err(CE_ALERT, mp, "xfs_imap: "
                        "(imap->im_blkno (0x%llx) + imap->im_len (0x%llx)) > "
                        " XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks) (0x%llx)",
                        (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(be32_to_cpu(agi->agi_magicnum) == 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(*bpp && !XFS_BUF_GETERROR(*bpp));
        agi = XFS_BUF_TO_AGI(*bpp);

        /*
         * Validate the magic number of the agi block.
         */
        agi_ok = be32_to_cpu(agi->agi_magicnum) == 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_VTYPE_REF(*bpp, B_FS_AGI, 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 = &mp->m_perag[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));
        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;
}