[XFS] implement generic xfs_btree_split

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / fs / xfs / xfs_ialloc_btree.c

/*
 * Copyright (c) 2000-2001,2005 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_btree_trace.h"
#include "xfs_ialloc.h"
#include "xfs_alloc.h"
#include "xfs_error.h"

STATIC void xfs_inobt_log_block(xfs_trans_t *, xfs_buf_t *, int);
STATIC void xfs_inobt_log_keys(xfs_btree_cur_t *, xfs_buf_t *, int, int);
STATIC void xfs_inobt_log_ptrs(xfs_btree_cur_t *, xfs_buf_t *, int, int);
STATIC void xfs_inobt_log_recs(xfs_btree_cur_t *, xfs_buf_t *, int, int);
STATIC int xfs_inobt_newroot(xfs_btree_cur_t *, int *);

/*
 * Single level of the xfs_inobt_delete record deletion routine.
 * Delete record pointed to by cur/level.
 * Remove the record from its block then rebalance the tree.
 * Return 0 for error, 1 for done, 2 to go on to the next level.
 */
STATIC int                              /* error */
xfs_inobt_delrec(
        xfs_btree_cur_t         *cur,   /* btree cursor */
        int                     level,  /* level removing record from */
        int                     *stat)  /* fail/done/go-on */
{
        xfs_buf_t               *agbp;  /* buffer for a.g. inode header */
        xfs_mount_t             *mp;    /* mount structure */
        xfs_agi_t               *agi;   /* allocation group inode header */
        xfs_inobt_block_t       *block; /* btree block record/key lives in */
        xfs_agblock_t           bno;    /* btree block number */
        xfs_buf_t               *bp;    /* buffer for block */
        int                     error;  /* error return value */
        int                     i;      /* loop index */
        xfs_inobt_key_t         key;    /* kp points here if block is level 0 */
        xfs_inobt_key_t         *kp = NULL;     /* pointer to btree keys */
        xfs_agblock_t           lbno;   /* left block's block number */
        xfs_buf_t               *lbp;   /* left block's buffer pointer */
        xfs_inobt_block_t       *left;  /* left btree block */
        xfs_inobt_key_t         *lkp;   /* left block key pointer */
        xfs_inobt_ptr_t         *lpp;   /* left block address pointer */
        int                     lrecs = 0;      /* number of records in left block */
        xfs_inobt_rec_t         *lrp;   /* left block record pointer */
        xfs_inobt_ptr_t         *pp = NULL;     /* pointer to btree addresses */
        int                     ptr;    /* index in btree block for this rec */
        xfs_agblock_t           rbno;   /* right block's block number */
        xfs_buf_t               *rbp;   /* right block's buffer pointer */
        xfs_inobt_block_t       *right; /* right btree block */
        xfs_inobt_key_t         *rkp;   /* right block key pointer */
        xfs_inobt_rec_t         *rp;    /* pointer to btree records */
        xfs_inobt_ptr_t         *rpp;   /* right block address pointer */
        int                     rrecs = 0;      /* number of records in right block */
        int                     numrecs;
        xfs_inobt_rec_t         *rrp;   /* right block record pointer */
        xfs_btree_cur_t         *tcur;  /* temporary btree cursor */

        mp = cur->bc_mp;

        /*
         * Get the index of the entry being deleted, check for nothing there.
         */
        ptr = cur->bc_ptrs[level];
        if (ptr == 0) {
                *stat = 0;
                return 0;
        }

        /*
         * Get the buffer & block containing the record or key/ptr.
         */
        bp = cur->bc_bufs[level];
        block = XFS_BUF_TO_INOBT_BLOCK(bp);
#ifdef DEBUG
        if ((error = xfs_btree_check_sblock(cur, block, level, bp)))
                return error;
#endif
        /*
         * Fail if we're off the end of the block.
         */

        numrecs = be16_to_cpu(block->bb_numrecs);
        if (ptr > numrecs) {
                *stat = 0;
                return 0;
        }
        /*
         * It's a nonleaf.  Excise the key and ptr being deleted, by
         * sliding the entries past them down one.
         * Log the changed areas of the block.
         */
        if (level > 0) {
                kp = XFS_INOBT_KEY_ADDR(block, 1, cur);
                pp = XFS_INOBT_PTR_ADDR(block, 1, cur);
#ifdef DEBUG
                for (i = ptr; i < numrecs; i++) {
                        if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(pp[i]), level)))
                                return error;
                }
#endif
                if (ptr < numrecs) {
                        memmove(&kp[ptr - 1], &kp[ptr],
                                (numrecs - ptr) * sizeof(*kp));
                        memmove(&pp[ptr - 1], &pp[ptr],
                                (numrecs - ptr) * sizeof(*kp));
                        xfs_inobt_log_keys(cur, bp, ptr, numrecs - 1);
                        xfs_inobt_log_ptrs(cur, bp, ptr, numrecs - 1);
                }
        }
        /*
         * It's a leaf.  Excise the record being deleted, by sliding the
         * entries past it down one.  Log the changed areas of the block.
         */
        else {
                rp = XFS_INOBT_REC_ADDR(block, 1, cur);
                if (ptr < numrecs) {
                        memmove(&rp[ptr - 1], &rp[ptr],
                                (numrecs - ptr) * sizeof(*rp));
                        xfs_inobt_log_recs(cur, bp, ptr, numrecs - 1);
                }
                /*
                 * If it's the first record in the block, we'll need a key
                 * structure to pass up to the next level (updkey).
                 */
                if (ptr == 1) {
                        key.ir_startino = rp->ir_startino;
                        kp = &key;
                }
        }
        /*
         * Decrement and log the number of entries in the block.
         */
        numrecs--;
        block->bb_numrecs = cpu_to_be16(numrecs);
        xfs_inobt_log_block(cur->bc_tp, bp, XFS_BB_NUMRECS);
        /*
         * Is this the root level?  If so, we're almost done.
         */
        if (level == cur->bc_nlevels - 1) {
                /*
                 * If this is the root level,
                 * and there's only one entry left,
                 * and it's NOT the leaf level,
                 * then we can get rid of this level.
                 */
                if (numrecs == 1 && level > 0) {
                        agbp = cur->bc_private.a.agbp;
                        agi = XFS_BUF_TO_AGI(agbp);
                        /*
                         * pp is still set to the first pointer in the block.
                         * Make it the new root of the btree.
                         */
                        bno = be32_to_cpu(agi->agi_root);
                        agi->agi_root = *pp;
                        be32_add_cpu(&agi->agi_level, -1);
                        /*
                         * Free the block.
                         */
                        if ((error = xfs_free_extent(cur->bc_tp,
                                XFS_AGB_TO_FSB(mp, cur->bc_private.a.agno, bno), 1)))
                                return error;
                        xfs_trans_binval(cur->bc_tp, bp);
                        xfs_ialloc_log_agi(cur->bc_tp, agbp,
                                XFS_AGI_ROOT | XFS_AGI_LEVEL);
                        /*
                         * Update the cursor so there's one fewer level.
                         */
                        cur->bc_bufs[level] = NULL;
                        cur->bc_nlevels--;
                } else if (level > 0 &&
                           (error = xfs_btree_decrement(cur, level, &i)))
                        return error;
                *stat = 1;
                return 0;
        }
        /*
         * If we deleted the leftmost entry in the block, update the
         * key values above us in the tree.
         */
        if (ptr == 1 && (error = xfs_btree_updkey(cur, (union xfs_btree_key *)kp, level + 1)))
                return error;
        /*
         * If the number of records remaining in the block is at least
         * the minimum, we're done.
         */
        if (numrecs >= XFS_INOBT_BLOCK_MINRECS(level, cur)) {
                if (level > 0 &&
                    (error = xfs_btree_decrement(cur, level, &i)))
                        return error;
                *stat = 1;
                return 0;
        }
        /*
         * Otherwise, we have to move some records around to keep the
         * tree balanced.  Look at the left and right sibling blocks to
         * see if we can re-balance by moving only one record.
         */
        rbno = be32_to_cpu(block->bb_rightsib);
        lbno = be32_to_cpu(block->bb_leftsib);
        bno = NULLAGBLOCK;
        ASSERT(rbno != NULLAGBLOCK || lbno != NULLAGBLOCK);
        /*
         * Duplicate the cursor so our btree manipulations here won't
         * disrupt the next level up.
         */
        if ((error = xfs_btree_dup_cursor(cur, &tcur)))
                return error;
        /*
         * If there's a right sibling, see if it's ok to shift an entry
         * out of it.
         */
        if (rbno != NULLAGBLOCK) {
                /*
                 * Move the temp cursor to the last entry in the next block.
                 * Actually any entry but the first would suffice.
                 */
                i = xfs_btree_lastrec(tcur, level);
                XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
                if ((error = xfs_btree_increment(tcur, level, &i)))
                        goto error0;
                XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
                i = xfs_btree_lastrec(tcur, level);
                XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
                /*
                 * Grab a pointer to the block.
                 */
                rbp = tcur->bc_bufs[level];
                right = XFS_BUF_TO_INOBT_BLOCK(rbp);
#ifdef DEBUG
                if ((error = xfs_btree_check_sblock(cur, right, level, rbp)))
                        goto error0;
#endif
                /*
                 * Grab the current block number, for future use.
                 */
                bno = be32_to_cpu(right->bb_leftsib);
                /*
                 * If right block is full enough so that removing one entry
                 * won't make it too empty, and left-shifting an entry out
                 * of right to us works, we're done.
                 */
                if (be16_to_cpu(right->bb_numrecs) - 1 >=
                     XFS_INOBT_BLOCK_MINRECS(level, cur)) {
                        if ((error = xfs_btree_lshift(tcur, level, &i)))
                                goto error0;
                        if (i) {
                                ASSERT(be16_to_cpu(block->bb_numrecs) >=
                                       XFS_INOBT_BLOCK_MINRECS(level, cur));
                                xfs_btree_del_cursor(tcur,
                                                     XFS_BTREE_NOERROR);
                                if (level > 0 &&
                                    (error = xfs_btree_decrement(cur, level,
                                                &i)))
                                        return error;
                                *stat = 1;
                                return 0;
                        }
                }
                /*
                 * Otherwise, grab the number of records in right for
                 * future reference, and fix up the temp cursor to point
                 * to our block again (last record).
                 */
                rrecs = be16_to_cpu(right->bb_numrecs);
                if (lbno != NULLAGBLOCK) {
                        xfs_btree_firstrec(tcur, level);
                        if ((error = xfs_btree_decrement(tcur, level, &i)))
                                goto error0;
                }
        }
        /*
         * If there's a left sibling, see if it's ok to shift an entry
         * out of it.
         */
        if (lbno != NULLAGBLOCK) {
                /*
                 * Move the temp cursor to the first entry in the
                 * previous block.
                 */
                xfs_btree_firstrec(tcur, level);
                if ((error = xfs_btree_decrement(tcur, level, &i)))
                        goto error0;
                xfs_btree_firstrec(tcur, level);
                /*
                 * Grab a pointer to the block.
                 */
                lbp = tcur->bc_bufs[level];
                left = XFS_BUF_TO_INOBT_BLOCK(lbp);
#ifdef DEBUG
                if ((error = xfs_btree_check_sblock(cur, left, level, lbp)))
                        goto error0;
#endif
                /*
                 * Grab the current block number, for future use.
                 */
                bno = be32_to_cpu(left->bb_rightsib);
                /*
                 * If left block is full enough so that removing one entry
                 * won't make it too empty, and right-shifting an entry out
                 * of left to us works, we're done.
                 */
                if (be16_to_cpu(left->bb_numrecs) - 1 >=
                     XFS_INOBT_BLOCK_MINRECS(level, cur)) {
                        if ((error = xfs_btree_rshift(tcur, level, &i)))
                                goto error0;
                        if (i) {
                                ASSERT(be16_to_cpu(block->bb_numrecs) >=
                                       XFS_INOBT_BLOCK_MINRECS(level, cur));
                                xfs_btree_del_cursor(tcur,
                                                     XFS_BTREE_NOERROR);
                                if (level == 0)
                                        cur->bc_ptrs[0]++;
                                *stat = 1;
                                return 0;
                        }
                }
                /*
                 * Otherwise, grab the number of records in right for
                 * future reference.
                 */
                lrecs = be16_to_cpu(left->bb_numrecs);
        }
        /*
         * Delete the temp cursor, we're done with it.
         */
        xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
        /*
         * If here, we need to do a join to keep the tree balanced.
         */
        ASSERT(bno != NULLAGBLOCK);
        /*
         * See if we can join with the left neighbor block.
         */
        if (lbno != NULLAGBLOCK &&
            lrecs + numrecs <= XFS_INOBT_BLOCK_MAXRECS(level, cur)) {
                /*
                 * Set "right" to be the starting block,
                 * "left" to be the left neighbor.
                 */
                rbno = bno;
                right = block;
                rrecs = be16_to_cpu(right->bb_numrecs);
                rbp = bp;
                if ((error = xfs_btree_read_bufs(mp, cur->bc_tp,
                                cur->bc_private.a.agno, lbno, 0, &lbp,
                                XFS_INO_BTREE_REF)))
                        return error;
                left = XFS_BUF_TO_INOBT_BLOCK(lbp);
                lrecs = be16_to_cpu(left->bb_numrecs);
                if ((error = xfs_btree_check_sblock(cur, left, level, lbp)))
                        return error;
        }
        /*
         * If that won't work, see if we can join with the right neighbor block.
         */
        else if (rbno != NULLAGBLOCK &&
                 rrecs + numrecs <= XFS_INOBT_BLOCK_MAXRECS(level, cur)) {
                /*
                 * Set "left" to be the starting block,
                 * "right" to be the right neighbor.
                 */
                lbno = bno;
                left = block;
                lrecs = be16_to_cpu(left->bb_numrecs);
                lbp = bp;
                if ((error = xfs_btree_read_bufs(mp, cur->bc_tp,
                                cur->bc_private.a.agno, rbno, 0, &rbp,
                                XFS_INO_BTREE_REF)))
                        return error;
                right = XFS_BUF_TO_INOBT_BLOCK(rbp);
                rrecs = be16_to_cpu(right->bb_numrecs);
                if ((error = xfs_btree_check_sblock(cur, right, level, rbp)))
                        return error;
        }
        /*
         * Otherwise, we can't fix the imbalance.
         * Just return.  This is probably a logic error, but it's not fatal.
         */
        else {
                if (level > 0 && (error = xfs_btree_decrement(cur, level, &i)))
                        return error;
                *stat = 1;
                return 0;
        }
        /*
         * We're now going to join "left" and "right" by moving all the stuff
         * in "right" to "left" and deleting "right".
         */
        if (level > 0) {
                /*
                 * It's a non-leaf.  Move keys and pointers.
                 */
                lkp = XFS_INOBT_KEY_ADDR(left, lrecs + 1, cur);
                lpp = XFS_INOBT_PTR_ADDR(left, lrecs + 1, cur);
                rkp = XFS_INOBT_KEY_ADDR(right, 1, cur);
                rpp = XFS_INOBT_PTR_ADDR(right, 1, cur);
#ifdef DEBUG
                for (i = 0; i < rrecs; i++) {
                        if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(rpp[i]), level)))
                                return error;
                }
#endif
                memcpy(lkp, rkp, rrecs * sizeof(*lkp));
                memcpy(lpp, rpp, rrecs * sizeof(*lpp));
                xfs_inobt_log_keys(cur, lbp, lrecs + 1, lrecs + rrecs);
                xfs_inobt_log_ptrs(cur, lbp, lrecs + 1, lrecs + rrecs);
        } else {
                /*
                 * It's a leaf.  Move records.
                 */
                lrp = XFS_INOBT_REC_ADDR(left, lrecs + 1, cur);
                rrp = XFS_INOBT_REC_ADDR(right, 1, cur);
                memcpy(lrp, rrp, rrecs * sizeof(*lrp));
                xfs_inobt_log_recs(cur, lbp, lrecs + 1, lrecs + rrecs);
        }
        /*
         * If we joined with the left neighbor, set the buffer in the
         * cursor to the left block, and fix up the index.
         */
        if (bp != lbp) {
                xfs_btree_setbuf(cur, level, lbp);
                cur->bc_ptrs[level] += lrecs;
        }
        /*
         * If we joined with the right neighbor and there's a level above
         * us, increment the cursor at that level.
         */
        else if (level + 1 < cur->bc_nlevels &&
                 (error = xfs_btree_increment(cur, level + 1, &i)))
                return error;
        /*
         * Fix up the number of records in the surviving block.
         */
        lrecs += rrecs;
        left->bb_numrecs = cpu_to_be16(lrecs);
        /*
         * Fix up the right block pointer in the surviving block, and log it.
         */
        left->bb_rightsib = right->bb_rightsib;
        xfs_inobt_log_block(cur->bc_tp, lbp, XFS_BB_NUMRECS | XFS_BB_RIGHTSIB);
        /*
         * If there is a right sibling now, make it point to the
         * remaining block.
         */
        if (be32_to_cpu(left->bb_rightsib) != NULLAGBLOCK) {
                xfs_inobt_block_t       *rrblock;
                xfs_buf_t               *rrbp;

                if ((error = xfs_btree_read_bufs(mp, cur->bc_tp,
                                cur->bc_private.a.agno, be32_to_cpu(left->bb_rightsib), 0,
                                &rrbp, XFS_INO_BTREE_REF)))
                        return error;
                rrblock = XFS_BUF_TO_INOBT_BLOCK(rrbp);
                if ((error = xfs_btree_check_sblock(cur, rrblock, level, rrbp)))
                        return error;
                rrblock->bb_leftsib = cpu_to_be32(lbno);
                xfs_inobt_log_block(cur->bc_tp, rrbp, XFS_BB_LEFTSIB);
        }
        /*
         * Free the deleting block.
         */
        if ((error = xfs_free_extent(cur->bc_tp, XFS_AGB_TO_FSB(mp,
                                     cur->bc_private.a.agno, rbno), 1)))
                return error;
        xfs_trans_binval(cur->bc_tp, rbp);
        /*
         * Readjust the ptr at this level if it's not a leaf, since it's
         * still pointing at the deletion point, which makes the cursor
         * inconsistent.  If this makes the ptr 0, the caller fixes it up.
         * We can't use decrement because it would change the next level up.
         */
        if (level > 0)
                cur->bc_ptrs[level]--;
        /*
         * Return value means the next level up has something to do.
         */
        *stat = 2;
        return 0;

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

/*
 * Insert one record/level.  Return information to the caller
 * allowing the next level up to proceed if necessary.
 */
STATIC int                              /* error */
xfs_inobt_insrec(
        xfs_btree_cur_t         *cur,   /* btree cursor */
        int                     level,  /* level to insert record at */
        xfs_agblock_t           *bnop,  /* i/o: block number inserted */
        xfs_inobt_rec_t         *recp,  /* i/o: record data inserted */
        xfs_btree_cur_t         **curp, /* output: new cursor replacing cur */
        int                     *stat)  /* success/failure */
{
        xfs_inobt_block_t       *block; /* btree block record/key lives in */
        xfs_buf_t               *bp;    /* buffer for block */
        int                     error;  /* error return value */
        int                     i;      /* loop index */
        xfs_inobt_key_t         key;    /* key value being inserted */
        xfs_inobt_key_t         *kp=NULL;       /* pointer to btree keys */
        xfs_agblock_t           nbno;   /* block number of allocated block */
        xfs_btree_cur_t         *ncur;  /* new cursor to be used at next lvl */
        xfs_inobt_key_t         nkey;   /* new key value, from split */
        xfs_inobt_rec_t         nrec;   /* new record value, for caller */
        int                     numrecs;
        int                     optr;   /* old ptr value */
        xfs_inobt_ptr_t         *pp;    /* pointer to btree addresses */
        int                     ptr;    /* index in btree block for this rec */
        xfs_inobt_rec_t         *rp=NULL;       /* pointer to btree records */

        /*
         * GCC doesn't understand the (arguably complex) control flow in
         * this function and complains about uninitialized structure fields
         * without this.
         */
        memset(&nrec, 0, sizeof(nrec));

        /*
         * If we made it to the root level, allocate a new root block
         * and we're done.
         */
        if (level >= cur->bc_nlevels) {
                error = xfs_inobt_newroot(cur, &i);
                *bnop = NULLAGBLOCK;
                *stat = i;
                return error;
        }
        /*
         * Make a key out of the record data to be inserted, and save it.
         */
        key.ir_startino = recp->ir_startino;
        optr = ptr = cur->bc_ptrs[level];
        /*
         * If we're off the left edge, return failure.
         */
        if (ptr == 0) {
                *stat = 0;
                return 0;
        }
        /*
         * Get pointers to the btree buffer and block.
         */
        bp = cur->bc_bufs[level];
        block = XFS_BUF_TO_INOBT_BLOCK(bp);
        numrecs = be16_to_cpu(block->bb_numrecs);
#ifdef DEBUG
        if ((error = xfs_btree_check_sblock(cur, block, level, bp)))
                return error;
        /*
         * Check that the new entry is being inserted in the right place.
         */
        if (ptr <= numrecs) {
                if (level == 0) {
                        rp = XFS_INOBT_REC_ADDR(block, ptr, cur);
                        xfs_btree_check_rec(cur->bc_btnum, recp, rp);
                } else {
                        kp = XFS_INOBT_KEY_ADDR(block, ptr, cur);
                        xfs_btree_check_key(cur->bc_btnum, &key, kp);
                }
        }
#endif
        nbno = NULLAGBLOCK;
        ncur = NULL;
        /*
         * If the block is full, we can't insert the new entry until we
         * make the block un-full.
         */
        if (numrecs == XFS_INOBT_BLOCK_MAXRECS(level, cur)) {
                /*
                 * First, try shifting an entry to the right neighbor.
                 */
                if ((error = xfs_btree_rshift(cur, level, &i)))
                        return error;
                if (i) {
                        /* nothing */
                }
                /*
                 * Next, try shifting an entry to the left neighbor.
                 */
                else {
                        if ((error = xfs_btree_lshift(cur, level, &i)))
                                return error;
                        if (i) {
                                optr = ptr = cur->bc_ptrs[level];
                        } else {
                                union xfs_btree_ptr bno = { .s = cpu_to_be32(nbno) };
                                /*
                                 * Next, try splitting the current block
                                 * in half. If this works we have to
                                 * re-set our variables because
                                 * we could be in a different block now.
                                 */
                                if ((error = xfs_btree_split(cur, level, &bno,
                                                (union xfs_btree_key *)&nkey,
                                                &ncur, &i)))
                                        return error;
                                nbno = be32_to_cpu(bno.s);
                                if (i) {
                                        bp = cur->bc_bufs[level];
                                        block = XFS_BUF_TO_INOBT_BLOCK(bp);
#ifdef DEBUG
                                        if ((error = xfs_btree_check_sblock(cur,
                                                        block, level, bp)))
                                                return error;
#endif
                                        ptr = cur->bc_ptrs[level];
                                        nrec.ir_startino = nkey.ir_startino;
                                } else {
                                        /*
                                         * Otherwise the insert fails.
                                         */
                                        *stat = 0;
                                        return 0;
                                }
                        }
                }
        }
        /*
         * At this point we know there's room for our new entry in the block
         * we're pointing at.
         */
        numrecs = be16_to_cpu(block->bb_numrecs);
        if (level > 0) {
                /*
                 * It's a non-leaf entry.  Make a hole for the new data
                 * in the key and ptr regions of the block.
                 */
                kp = XFS_INOBT_KEY_ADDR(block, 1, cur);
                pp = XFS_INOBT_PTR_ADDR(block, 1, cur);
#ifdef DEBUG
                for (i = numrecs; i >= ptr; i--) {
                        if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(pp[i - 1]), level)))
                                return error;
                }
#endif
                memmove(&kp[ptr], &kp[ptr - 1],
                        (numrecs - ptr + 1) * sizeof(*kp));
                memmove(&pp[ptr], &pp[ptr - 1],
                        (numrecs - ptr + 1) * sizeof(*pp));
                /*
                 * Now stuff the new data in, bump numrecs and log the new data.
                 */
#ifdef DEBUG
                if ((error = xfs_btree_check_sptr(cur, *bnop, level)))
                        return error;
#endif
                kp[ptr - 1] = key;
                pp[ptr - 1] = cpu_to_be32(*bnop);
                numrecs++;
                block->bb_numrecs = cpu_to_be16(numrecs);
                xfs_inobt_log_keys(cur, bp, ptr, numrecs);
                xfs_inobt_log_ptrs(cur, bp, ptr, numrecs);
        } else {
                /*
                 * It's a leaf entry.  Make a hole for the new record.
                 */
                rp = XFS_INOBT_REC_ADDR(block, 1, cur);
                memmove(&rp[ptr], &rp[ptr - 1],
                        (numrecs - ptr + 1) * sizeof(*rp));
                /*
                 * Now stuff the new record in, bump numrecs
                 * and log the new data.
                 */
                rp[ptr - 1] = *recp;
                numrecs++;
                block->bb_numrecs = cpu_to_be16(numrecs);
                xfs_inobt_log_recs(cur, bp, ptr, numrecs);
        }
        /*
         * Log the new number of records in the btree header.
         */
        xfs_inobt_log_block(cur->bc_tp, bp, XFS_BB_NUMRECS);
#ifdef DEBUG
        /*
         * Check that the key/record is in the right place, now.
         */
        if (ptr < numrecs) {
                if (level == 0)
                        xfs_btree_check_rec(cur->bc_btnum, rp + ptr - 1,
                                rp + ptr);
                else
                        xfs_btree_check_key(cur->bc_btnum, kp + ptr - 1,
                                kp + ptr);
        }
#endif
        /*
         * If we inserted at the start of a block, update the parents' keys.
         */
        if (optr == 1 && (error = xfs_btree_updkey(cur, (union xfs_btree_key *)&key, level + 1)))
                return error;
        /*
         * Return the new block number, if any.
         * If there is one, give back a record value and a cursor too.
         */
        *bnop = nbno;
        if (nbno != NULLAGBLOCK) {
                *recp = nrec;
                *curp = ncur;
        }
        *stat = 1;
        return 0;
}

/*
 * Log header fields from a btree block.
 */
STATIC void
xfs_inobt_log_block(
        xfs_trans_t             *tp,    /* transaction pointer */
        xfs_buf_t               *bp,    /* buffer containing btree block */
        int                     fields) /* mask of fields: XFS_BB_... */
{
        int                     first;  /* first byte offset logged */
        int                     last;   /* last byte offset logged */
        static const short      offsets[] = {   /* table of offsets */
                offsetof(xfs_inobt_block_t, bb_magic),
                offsetof(xfs_inobt_block_t, bb_level),
                offsetof(xfs_inobt_block_t, bb_numrecs),
                offsetof(xfs_inobt_block_t, bb_leftsib),
                offsetof(xfs_inobt_block_t, bb_rightsib),
                sizeof(xfs_inobt_block_t)
        };

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

/*
 * Log keys from a btree block (nonleaf).
 */
STATIC void
xfs_inobt_log_keys(
        xfs_btree_cur_t         *cur,   /* btree cursor */
        xfs_buf_t               *bp,    /* buffer containing btree block */
        int                     kfirst, /* index of first key to log */
        int                     klast)  /* index of last key to log */
{
        xfs_inobt_block_t       *block; /* btree block to log from */
        int                     first;  /* first byte offset logged */
        xfs_inobt_key_t         *kp;    /* key pointer in btree block */
        int                     last;   /* last byte offset logged */

        block = XFS_BUF_TO_INOBT_BLOCK(bp);
        kp = XFS_INOBT_KEY_ADDR(block, 1, cur);
        first = (int)((xfs_caddr_t)&kp[kfirst - 1] - (xfs_caddr_t)block);
        last = (int)(((xfs_caddr_t)&kp[klast] - 1) - (xfs_caddr_t)block);
        xfs_trans_log_buf(cur->bc_tp, bp, first, last);
}

/*
 * Log block pointer fields from a btree block (nonleaf).
 */
STATIC void
xfs_inobt_log_ptrs(
        xfs_btree_cur_t         *cur,   /* btree cursor */
        xfs_buf_t               *bp,    /* buffer containing btree block */
        int                     pfirst, /* index of first pointer to log */
        int                     plast)  /* index of last pointer to log */
{
        xfs_inobt_block_t       *block; /* btree block to log from */
        int                     first;  /* first byte offset logged */
        int                     last;   /* last byte offset logged */
        xfs_inobt_ptr_t         *pp;    /* block-pointer pointer in btree blk */

        block = XFS_BUF_TO_INOBT_BLOCK(bp);
        pp = XFS_INOBT_PTR_ADDR(block, 1, cur);
        first = (int)((xfs_caddr_t)&pp[pfirst - 1] - (xfs_caddr_t)block);
        last = (int)(((xfs_caddr_t)&pp[plast] - 1) - (xfs_caddr_t)block);
        xfs_trans_log_buf(cur->bc_tp, bp, first, last);
}

/*
 * Log records from a btree block (leaf).
 */
STATIC void
xfs_inobt_log_recs(
        xfs_btree_cur_t         *cur,   /* btree cursor */
        xfs_buf_t               *bp,    /* buffer containing btree block */
        int                     rfirst, /* index of first record to log */
        int                     rlast)  /* index of last record to log */
{
        xfs_inobt_block_t       *block; /* btree block to log from */
        int                     first;  /* first byte offset logged */
        int                     last;   /* last byte offset logged */
        xfs_inobt_rec_t         *rp;    /* record pointer for btree block */

        block = XFS_BUF_TO_INOBT_BLOCK(bp);
        rp = XFS_INOBT_REC_ADDR(block, 1, cur);
        first = (int)((xfs_caddr_t)&rp[rfirst - 1] - (xfs_caddr_t)block);
        last = (int)(((xfs_caddr_t)&rp[rlast] - 1) - (xfs_caddr_t)block);
        xfs_trans_log_buf(cur->bc_tp, bp, first, last);
}

/*
 * Allocate a new root block, fill it in.
 */
STATIC int                              /* error */
xfs_inobt_newroot(
        xfs_btree_cur_t         *cur,   /* btree cursor */
        int                     *stat)  /* success/failure */
{
        xfs_agi_t               *agi;   /* a.g. inode header */
        xfs_alloc_arg_t         args;   /* allocation argument structure */
        xfs_inobt_block_t       *block; /* one half of the old root block */
        xfs_buf_t               *bp;    /* buffer containing block */
        int                     error;  /* error return value */
        xfs_inobt_key_t         *kp;    /* btree key pointer */
        xfs_agblock_t           lbno;   /* left block number */
        xfs_buf_t               *lbp;   /* left buffer pointer */
        xfs_inobt_block_t       *left;  /* left btree block */
        xfs_buf_t               *nbp;   /* new (root) buffer */
        xfs_inobt_block_t       *new;   /* new (root) btree block */
        int                     nptr;   /* new value for key index, 1 or 2 */
        xfs_inobt_ptr_t         *pp;    /* btree address pointer */
        xfs_agblock_t           rbno;   /* right block number */
        xfs_buf_t               *rbp;   /* right buffer pointer */
        xfs_inobt_block_t       *right; /* right btree block */
        xfs_inobt_rec_t         *rp;    /* btree record pointer */

        ASSERT(cur->bc_nlevels < XFS_IN_MAXLEVELS(cur->bc_mp));

        /*
         * Get a block & a buffer.
         */
        agi = XFS_BUF_TO_AGI(cur->bc_private.a.agbp);
        args.tp = cur->bc_tp;
        args.mp = cur->bc_mp;
        args.fsbno = XFS_AGB_TO_FSB(args.mp, cur->bc_private.a.agno,
                be32_to_cpu(agi->agi_root));
        args.mod = args.minleft = args.alignment = args.total = args.wasdel =
                args.isfl = args.userdata = args.minalignslop = 0;
        args.minlen = args.maxlen = args.prod = 1;
        args.type = XFS_ALLOCTYPE_NEAR_BNO;
        if ((error = xfs_alloc_vextent(&args)))
                return error;
        /*
         * None available, we fail.
         */
        if (args.fsbno == NULLFSBLOCK) {
                *stat = 0;
                return 0;
        }
        ASSERT(args.len == 1);
        nbp = xfs_btree_get_bufs(args.mp, args.tp, args.agno, args.agbno, 0);
        new = XFS_BUF_TO_INOBT_BLOCK(nbp);
        /*
         * Set the root data in the a.g. inode structure.
         */
        agi->agi_root = cpu_to_be32(args.agbno);
        be32_add_cpu(&agi->agi_level, 1);
        xfs_ialloc_log_agi(args.tp, cur->bc_private.a.agbp,
                XFS_AGI_ROOT | XFS_AGI_LEVEL);
        /*
         * At the previous root level there are now two blocks: the old
         * root, and the new block generated when it was split.
         * We don't know which one the cursor is pointing at, so we
         * set up variables "left" and "right" for each case.
         */
        bp = cur->bc_bufs[cur->bc_nlevels - 1];
        block = XFS_BUF_TO_INOBT_BLOCK(bp);
#ifdef DEBUG
        if ((error = xfs_btree_check_sblock(cur, block, cur->bc_nlevels - 1, bp)))
                return error;
#endif
        if (be32_to_cpu(block->bb_rightsib) != NULLAGBLOCK) {
                /*
                 * Our block is left, pick up the right block.
                 */
                lbp = bp;
                lbno = XFS_DADDR_TO_AGBNO(args.mp, XFS_BUF_ADDR(lbp));
                left = block;
                rbno = be32_to_cpu(left->bb_rightsib);
                if ((error = xfs_btree_read_bufs(args.mp, args.tp, args.agno,
                                rbno, 0, &rbp, XFS_INO_BTREE_REF)))
                        return error;
                bp = rbp;
                right = XFS_BUF_TO_INOBT_BLOCK(rbp);
                if ((error = xfs_btree_check_sblock(cur, right,
                                cur->bc_nlevels - 1, rbp)))
                        return error;
                nptr = 1;
        } else {
                /*
                 * Our block is right, pick up the left block.
                 */
                rbp = bp;
                rbno = XFS_DADDR_TO_AGBNO(args.mp, XFS_BUF_ADDR(rbp));
                right = block;
                lbno = be32_to_cpu(right->bb_leftsib);
                if ((error = xfs_btree_read_bufs(args.mp, args.tp, args.agno,
                                lbno, 0, &lbp, XFS_INO_BTREE_REF)))
                        return error;
                bp = lbp;
                left = XFS_BUF_TO_INOBT_BLOCK(lbp);
                if ((error = xfs_btree_check_sblock(cur, left,
                                cur->bc_nlevels - 1, lbp)))
                        return error;
                nptr = 2;
        }
        /*
         * Fill in the new block's btree header and log it.
         */
        new->bb_magic = cpu_to_be32(xfs_magics[cur->bc_btnum]);
        new->bb_level = cpu_to_be16(cur->bc_nlevels);
        new->bb_numrecs = cpu_to_be16(2);
        new->bb_leftsib = cpu_to_be32(NULLAGBLOCK);
        new->bb_rightsib = cpu_to_be32(NULLAGBLOCK);
        xfs_inobt_log_block(args.tp, nbp, XFS_BB_ALL_BITS);
        ASSERT(lbno != NULLAGBLOCK && rbno != NULLAGBLOCK);
        /*
         * Fill in the key data in the new root.
         */
        kp = XFS_INOBT_KEY_ADDR(new, 1, cur);
        if (be16_to_cpu(left->bb_level) > 0) {
                kp[0] = *XFS_INOBT_KEY_ADDR(left, 1, cur);
                kp[1] = *XFS_INOBT_KEY_ADDR(right, 1, cur);
        } else {
                rp = XFS_INOBT_REC_ADDR(left, 1, cur);
                kp[0].ir_startino = rp->ir_startino;
                rp = XFS_INOBT_REC_ADDR(right, 1, cur);
                kp[1].ir_startino = rp->ir_startino;
        }
        xfs_inobt_log_keys(cur, nbp, 1, 2);
        /*
         * Fill in the pointer data in the new root.
         */
        pp = XFS_INOBT_PTR_ADDR(new, 1, cur);
        pp[0] = cpu_to_be32(lbno);
        pp[1] = cpu_to_be32(rbno);
        xfs_inobt_log_ptrs(cur, nbp, 1, 2);
        /*
         * Fix up the cursor.
         */
        xfs_btree_setbuf(cur, cur->bc_nlevels, nbp);
        cur->bc_ptrs[cur->bc_nlevels] = nptr;
        cur->bc_nlevels++;
        *stat = 1;
        return 0;
}

/*
 * Externally visible routines.
 */

/*
 * Delete the record pointed to by cur.
 * The cursor refers to the place where the record was (could be inserted)
 * when the operation returns.
 */
int                                     /* error */
xfs_inobt_delete(
        xfs_btree_cur_t *cur,           /* btree cursor */
        int             *stat)          /* success/failure */
{
        int             error;
        int             i;              /* result code */
        int             level;          /* btree level */

        /*
         * Go up the tree, starting at leaf level.
         * If 2 is returned then a join was done; go to the next level.
         * Otherwise we are done.
         */
        for (level = 0, i = 2; i == 2; level++) {
                if ((error = xfs_inobt_delrec(cur, level, &i)))
                        return error;
        }
        if (i == 0) {
                for (level = 1; level < cur->bc_nlevels; level++) {
                        if (cur->bc_ptrs[level] == 0) {
                                if ((error = xfs_btree_decrement(cur, level, &i)))
                                        return error;
                                break;
                        }
                }
        }
        *stat = i;
        return 0;
}


/*
 * Get the data from the pointed-to record.
 */
int                                     /* error */
xfs_inobt_get_rec(
        xfs_btree_cur_t         *cur,   /* btree cursor */
        xfs_agino_t             *ino,   /* output: starting inode of chunk */
        __int32_t               *fcnt,  /* output: number of free inodes */
        xfs_inofree_t           *free,  /* output: free inode mask */
        int                     *stat)  /* output: success/failure */
{
        xfs_inobt_block_t       *block; /* btree block */
        xfs_buf_t               *bp;    /* buffer containing btree block */
#ifdef DEBUG
        int                     error;  /* error return value */
#endif
        int                     ptr;    /* record number */
        xfs_inobt_rec_t         *rec;   /* record data */

        bp = cur->bc_bufs[0];
        ptr = cur->bc_ptrs[0];
        block = XFS_BUF_TO_INOBT_BLOCK(bp);
#ifdef DEBUG
        if ((error = xfs_btree_check_sblock(cur, block, 0, bp)))
                return error;
#endif
        /*
         * Off the right end or left end, return failure.
         */
        if (ptr > be16_to_cpu(block->bb_numrecs) || ptr <= 0) {
                *stat = 0;
                return 0;
        }
        /*
         * Point to the record and extract its data.
         */
        rec = XFS_INOBT_REC_ADDR(block, ptr, cur);
        *ino = be32_to_cpu(rec->ir_startino);
        *fcnt = be32_to_cpu(rec->ir_freecount);
        *free = be64_to_cpu(rec->ir_free);
        *stat = 1;
        return 0;
}

/*
 * Insert the current record at the point referenced by cur.
 * The cursor may be inconsistent on return if splits have been done.
 */
int                                     /* error */
xfs_inobt_insert(
        xfs_btree_cur_t *cur,           /* btree cursor */
        int             *stat)          /* success/failure */
{
        int             error;          /* error return value */
        int             i;              /* result value, 0 for failure */
        int             level;          /* current level number in btree */
        xfs_agblock_t   nbno;           /* new block number (split result) */
        xfs_btree_cur_t *ncur;          /* new cursor (split result) */
        xfs_inobt_rec_t nrec;           /* record being inserted this level */
        xfs_btree_cur_t *pcur;          /* previous level's cursor */

        level = 0;
        nbno = NULLAGBLOCK;
        nrec.ir_startino = cpu_to_be32(cur->bc_rec.i.ir_startino);
        nrec.ir_freecount = cpu_to_be32(cur->bc_rec.i.ir_freecount);
        nrec.ir_free = cpu_to_be64(cur->bc_rec.i.ir_free);
        ncur = NULL;
        pcur = cur;
        /*
         * Loop going up the tree, starting at the leaf level.
         * Stop when we don't get a split block, that must mean that
         * the insert is finished with this level.
         */
        do {
                /*
                 * Insert nrec/nbno into this level of the tree.
                 * Note if we fail, nbno will be null.
                 */
                if ((error = xfs_inobt_insrec(pcur, level++, &nbno, &nrec, &ncur,
                                &i))) {
                        if (pcur != cur)
                                xfs_btree_del_cursor(pcur, XFS_BTREE_ERROR);
                        return error;
                }
                /*
                 * See if the cursor we just used is trash.
                 * Can't trash the caller's cursor, but otherwise we should
                 * if ncur is a new cursor or we're about to be done.
                 */
                if (pcur != cur && (ncur || nbno == NULLAGBLOCK)) {
                        cur->bc_nlevels = pcur->bc_nlevels;
                        xfs_btree_del_cursor(pcur, XFS_BTREE_NOERROR);
                }
                /*
                 * If we got a new cursor, switch to it.
                 */
                if (ncur) {
                        pcur = ncur;
                        ncur = NULL;
                }
        } while (nbno != NULLAGBLOCK);
        *stat = i;
        return 0;
}

STATIC struct xfs_btree_cur *
xfs_inobt_dup_cursor(
        struct xfs_btree_cur    *cur)
{
        return xfs_inobt_init_cursor(cur->bc_mp, cur->bc_tp,
                        cur->bc_private.a.agbp, cur->bc_private.a.agno);
}

STATIC int
xfs_inobt_alloc_block(
        struct xfs_btree_cur    *cur,
        union xfs_btree_ptr     *start,
        union xfs_btree_ptr     *new,
        int                     length,
        int                     *stat)
{
        xfs_alloc_arg_t         args;           /* block allocation args */
        int                     error;          /* error return value */
        xfs_agblock_t           sbno = be32_to_cpu(start->s);

        XFS_BTREE_TRACE_CURSOR(cur, XBT_ENTRY);

        memset(&args, 0, sizeof(args));
        args.tp = cur->bc_tp;
        args.mp = cur->bc_mp;
        args.fsbno = XFS_AGB_TO_FSB(args.mp, cur->bc_private.a.agno, sbno);
        args.minlen = 1;
        args.maxlen = 1;
        args.prod = 1;
        args.type = XFS_ALLOCTYPE_NEAR_BNO;

        error = xfs_alloc_vextent(&args);
        if (error) {
                XFS_BTREE_TRACE_CURSOR(cur, XBT_ERROR);
                return error;
        }
        if (args.fsbno == NULLFSBLOCK) {
                XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);
                *stat = 0;
                return 0;
        }
        ASSERT(args.len == 1);
        XFS_BTREE_TRACE_CURSOR(cur, XBT_EXIT);

        new->s = cpu_to_be32(XFS_FSB_TO_AGBNO(args.mp, args.fsbno));
        *stat = 1;
        return 0;
}


STATIC int
xfs_inobt_get_maxrecs(
        struct xfs_btree_cur    *cur,
        int                     level)
{
        return cur->bc_mp->m_inobt_mxr[level != 0];
}

STATIC void
xfs_inobt_init_key_from_rec(
        union xfs_btree_key     *key,
        union xfs_btree_rec     *rec)
{
        key->inobt.ir_startino = rec->inobt.ir_startino;
}

/*
 * intial value of ptr for lookup
 */
STATIC void
xfs_inobt_init_ptr_from_cur(
        struct xfs_btree_cur    *cur,
        union xfs_btree_ptr     *ptr)
{
        struct xfs_agi          *agi = XFS_BUF_TO_AGI(cur->bc_private.a.agbp);

        ASSERT(cur->bc_private.a.agno == be32_to_cpu(agi->agi_seqno));

        ptr->s = agi->agi_root;
}

STATIC __int64_t
xfs_inobt_key_diff(
        struct xfs_btree_cur    *cur,
        union xfs_btree_key     *key)
{
        return (__int64_t)be32_to_cpu(key->inobt.ir_startino) -
                          cur->bc_rec.i.ir_startino;
}

#ifdef XFS_BTREE_TRACE
ktrace_t        *xfs_inobt_trace_buf;

STATIC void
xfs_inobt_trace_enter(
        struct xfs_btree_cur    *cur,
        const char              *func,
        char                    *s,
        int                     type,
        int                     line,
        __psunsigned_t          a0,
        __psunsigned_t          a1,
        __psunsigned_t          a2,
        __psunsigned_t          a3,
        __psunsigned_t          a4,
        __psunsigned_t          a5,
        __psunsigned_t          a6,
        __psunsigned_t          a7,
        __psunsigned_t          a8,
        __psunsigned_t          a9,
        __psunsigned_t          a10)
{
        ktrace_enter(xfs_inobt_trace_buf, (void *)(__psint_t)type,
                (void *)func, (void *)s, NULL, (void *)cur,
                (void *)a0, (void *)a1, (void *)a2, (void *)a3,
                (void *)a4, (void *)a5, (void *)a6, (void *)a7,
                (void *)a8, (void *)a9, (void *)a10);
}

STATIC void
xfs_inobt_trace_cursor(
        struct xfs_btree_cur    *cur,
        __uint32_t              *s0,
        __uint64_t              *l0,
        __uint64_t              *l1)
{
        *s0 = cur->bc_private.a.agno;
        *l0 = cur->bc_rec.i.ir_startino;
        *l1 = cur->bc_rec.i.ir_free;
}

STATIC void
xfs_inobt_trace_key(
        struct xfs_btree_cur    *cur,
        union xfs_btree_key     *key,
        __uint64_t              *l0,
        __uint64_t              *l1)
{
        *l0 = be32_to_cpu(key->inobt.ir_startino);
        *l1 = 0;
}

STATIC void
xfs_inobt_trace_record(
        struct xfs_btree_cur    *cur,
        union xfs_btree_rec     *rec,
        __uint64_t              *l0,
        __uint64_t              *l1,
        __uint64_t              *l2)
{
        *l0 = be32_to_cpu(rec->inobt.ir_startino);
        *l1 = be32_to_cpu(rec->inobt.ir_freecount);
        *l2 = be64_to_cpu(rec->inobt.ir_free);
}
#endif /* XFS_BTREE_TRACE */

static const struct xfs_btree_ops xfs_inobt_ops = {
        .rec_len                = sizeof(xfs_inobt_rec_t),
        .key_len                = sizeof(xfs_inobt_key_t),

        .dup_cursor             = xfs_inobt_dup_cursor,
        .alloc_block            = xfs_inobt_alloc_block,
        .get_maxrecs            = xfs_inobt_get_maxrecs,
        .init_key_from_rec      = xfs_inobt_init_key_from_rec,
        .init_ptr_from_cur      = xfs_inobt_init_ptr_from_cur,
        .key_diff               = xfs_inobt_key_diff,

#ifdef XFS_BTREE_TRACE
        .trace_enter            = xfs_inobt_trace_enter,
        .trace_cursor           = xfs_inobt_trace_cursor,
        .trace_key              = xfs_inobt_trace_key,
        .trace_record           = xfs_inobt_trace_record,
#endif
};

/*
 * Allocate a new inode btree cursor.
 */
struct xfs_btree_cur *                          /* new inode btree cursor */
xfs_inobt_init_cursor(
        struct xfs_mount        *mp,            /* file system mount point */
        struct xfs_trans        *tp,            /* transaction pointer */
        struct xfs_buf          *agbp,          /* buffer for agi structure */
        xfs_agnumber_t          agno)           /* allocation group number */
{
        struct xfs_agi          *agi = XFS_BUF_TO_AGI(agbp);
        struct xfs_btree_cur    *cur;

        cur = kmem_zone_zalloc(xfs_btree_cur_zone, KM_SLEEP);

        cur->bc_tp = tp;
        cur->bc_mp = mp;
        cur->bc_nlevels = be32_to_cpu(agi->agi_level);
        cur->bc_btnum = XFS_BTNUM_INO;
        cur->bc_blocklog = mp->m_sb.sb_blocklog;

        cur->bc_ops = &xfs_inobt_ops;

        cur->bc_private.a.agbp = agbp;
        cur->bc_private.a.agno = agno;

        return cur;
}