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xfs_alloc_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_ialloc.h"
#include "xfs_alloc.h"
#include "xfs_error.h"

/*
 * Prototypes for internal functions.
 */

STATIC void xfs_alloc_log_block(xfs_trans_t *, xfs_buf_t *, int);
STATIC void xfs_alloc_log_keys(xfs_btree_cur_t *, xfs_buf_t *, int, int);
STATIC void xfs_alloc_log_ptrs(xfs_btree_cur_t *, xfs_buf_t *, int, int);
STATIC void xfs_alloc_log_recs(xfs_btree_cur_t *, xfs_buf_t *, int, int);
STATIC int xfs_alloc_lshift(xfs_btree_cur_t *, int, int *);
STATIC int xfs_alloc_newroot(xfs_btree_cur_t *, int *);
STATIC int xfs_alloc_rshift(xfs_btree_cur_t *, int, int *);
STATIC int xfs_alloc_split(xfs_btree_cur_t *, int, xfs_agblock_t *,
            xfs_alloc_key_t *, xfs_btree_cur_t **, int *);
STATIC int xfs_alloc_updkey(xfs_btree_cur_t *, xfs_alloc_key_t *, int);

/*
 * Internal functions.
 */

/*
 * Single level of the xfs_alloc_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_alloc_delrec(
      xfs_btree_cur_t         *cur, /* btree cursor */
      int               level,      /* level removing record from */
      int               *stat)      /* fail/done/go-on */
{
      xfs_agf_t         *agf; /* allocation group freelist header */
      xfs_alloc_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_alloc_key_t         key;  /* kp points here if block is level 0 */
      xfs_agblock_t           lbno; /* left block's block number */
      xfs_buf_t         *lbp; /* left block's buffer pointer */
      xfs_alloc_block_t *left;      /* left btree block */
      xfs_alloc_key_t         *lkp=NULL;  /* left block key pointer */
      xfs_alloc_ptr_t         *lpp=NULL;  /* left block address pointer */
      int               lrecs=0;    /* number of records in left block */
      xfs_alloc_rec_t         *lrp; /* left block record pointer */
      xfs_mount_t       *mp;  /* mount structure */
      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_alloc_block_t *right;     /* right btree block */
      xfs_alloc_key_t         *rkp; /* right block key pointer */
      xfs_alloc_ptr_t         *rpp; /* right block address pointer */
      int               rrecs=0;    /* number of records in right block */
      int               numrecs;
      xfs_alloc_rec_t         *rrp; /* right block record pointer */
      xfs_btree_cur_t         *tcur;      /* temporary btree cursor */

      /*
       * 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_ALLOC_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;
      }
      XFS_STATS_INC(xs_abt_delrec);
      /*
       * 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) {
            lkp = XFS_ALLOC_KEY_ADDR(block, 1, cur);
            lpp = XFS_ALLOC_PTR_ADDR(block, 1, cur);
#ifdef DEBUG
            for (i = ptr; i < numrecs; i++) {
                  if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(lpp[i]), level)))
                        return error;
            }
#endif
            if (ptr < numrecs) {
                  memmove(&lkp[ptr - 1], &lkp[ptr],
                        (numrecs - ptr) * sizeof(*lkp));
                  memmove(&lpp[ptr - 1], &lpp[ptr],
                        (numrecs - ptr) * sizeof(*lpp));
                  xfs_alloc_log_ptrs(cur, bp, ptr, numrecs - 1);
                  xfs_alloc_log_keys(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 {
            lrp = XFS_ALLOC_REC_ADDR(block, 1, cur);
            if (ptr < numrecs) {
                  memmove(&lrp[ptr - 1], &lrp[ptr],
                        (numrecs - ptr) * sizeof(*lrp));
                  xfs_alloc_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.ar_startblock = lrp->ar_startblock;
                  key.ar_blockcount = lrp->ar_blockcount;
                  lkp = &key;
            }
      }
      /*
       * Decrement and log the number of entries in the block.
       */
      numrecs--;
      block->bb_numrecs = cpu_to_be16(numrecs);
      xfs_alloc_log_block(cur->bc_tp, bp, XFS_BB_NUMRECS);
      /*
       * See if the longest free extent in the allocation group was
       * changed by this operation.  True if it's the by-size btree, and
       * this is the leaf level, and there is no right sibling block,
       * and this was the last record.
       */
      agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);
      mp = cur->bc_mp;

      if (level == 0 &&
          cur->bc_btnum == XFS_BTNUM_CNT &&
          be32_to_cpu(block->bb_rightsib) == NULLAGBLOCK &&
          ptr > numrecs) {
            ASSERT(ptr == numrecs + 1);
            /*
             * There are still records in the block.  Grab the size
             * from the last one.
             */
            if (numrecs) {
                  rrp = XFS_ALLOC_REC_ADDR(block, numrecs, cur);
                  agf->agf_longest = rrp->ar_blockcount;
            }
            /*
             * No free extents left.
             */
            else
                  agf->agf_longest = 0;
            mp->m_perag[be32_to_cpu(agf->agf_seqno)].pagf_longest =
                  be32_to_cpu(agf->agf_longest);
            xfs_alloc_log_agf(cur->bc_tp, cur->bc_private.a.agbp,
                  XFS_AGF_LONGEST);
      }
      /*
       * 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) {
                  /*
                   * lpp is still set to the first pointer in the block.
                   * Make it the new root of the btree.
                   */
                  bno = be32_to_cpu(agf->agf_roots[cur->bc_btnum]);
                  agf->agf_roots[cur->bc_btnum] = *lpp;
                  be32_add(&agf->agf_levels[cur->bc_btnum], -1);
                  mp->m_perag[be32_to_cpu(agf->agf_seqno)].pagf_levels[cur->bc_btnum]--;
                  /*
                   * Put this buffer/block on the ag's freelist.
                   */
                  error = xfs_alloc_put_freelist(cur->bc_tp,
                              cur->bc_private.a.agbp, NULL, bno, 1);
                  if (error)
                        return error;
                  /*
                   * Since blocks move to the free list without the
                   * coordination used in xfs_bmap_finish, we can't allow
                   * block to be available for reallocation and
                   * non-transaction writing (user data) until we know
                   * that the transaction that moved it to the free list
                   * is permanently on disk. We track the blocks by
                   * declaring these blocks as "busy"; the busy list is
                   * maintained on a per-ag basis and each transaction
                   * records which entries should be removed when the
                   * iclog commits to disk. If a busy block is
                   * allocated, the iclog is pushed up to the LSN
                   * that freed the block.
                   */
                  xfs_alloc_mark_busy(cur->bc_tp,
                        be32_to_cpu(agf->agf_seqno), bno, 1);

                  xfs_trans_agbtree_delta(cur->bc_tp, -1);
                  xfs_alloc_log_agf(cur->bc_tp, cur->bc_private.a.agbp,
                        XFS_AGF_ROOTS | XFS_AGF_LEVELS);
                  /*
                   * Update the cursor so there's one fewer level.
                   */
                  xfs_btree_setbuf(cur, level, NULL);
                  cur->bc_nlevels--;
            } else if (level > 0 &&
                     (error = xfs_alloc_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_alloc_updkey(cur, lkp, level + 1)))
            return error;
      /*
       * If the number of records remaining in the block is at least
       * the minimum, we're done.
       */
      if (numrecs >= XFS_ALLOC_BLOCK_MINRECS(level, cur)) {
            if (level > 0 && (error = xfs_alloc_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_alloc_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_ALLOC_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_ALLOC_BLOCK_MINRECS(level, cur)) {
                  if ((error = xfs_alloc_lshift(tcur, level, &i)))
                        goto error0;
                  if (i) {
                        ASSERT(be16_to_cpu(block->bb_numrecs) >=
                               XFS_ALLOC_BLOCK_MINRECS(level, cur));
                        xfs_btree_del_cursor(tcur,
                                         XFS_BTREE_NOERROR);
                        if (level > 0 &&
                            (error = xfs_alloc_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) {
                  i = xfs_btree_firstrec(tcur, level);
                  XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
                  if ((error = xfs_alloc_decrement(tcur, level, &i)))
                        goto error0;
                  XFS_WANT_CORRUPTED_GOTO(i == 1, 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.
             */
            i = xfs_btree_firstrec(tcur, level);
            XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
            if ((error = xfs_alloc_decrement(tcur, level, &i)))
                  goto error0;
            XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
            xfs_btree_firstrec(tcur, level);
            /*
             * Grab a pointer to the block.
             */
            lbp = tcur->bc_bufs[level];
            left = XFS_BUF_TO_ALLOC_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_ALLOC_BLOCK_MINRECS(level, cur)) {
                  if ((error = xfs_alloc_rshift(tcur, level, &i)))
                        goto error0;
                  if (i) {
                        ASSERT(be16_to_cpu(block->bb_numrecs) >=
                               XFS_ALLOC_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_ALLOC_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_ALLOC_BTREE_REF)))
                  return error;
            left = XFS_BUF_TO_ALLOC_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_ALLOC_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_ALLOC_BTREE_REF)))
                  return error;
            right = XFS_BUF_TO_ALLOC_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_alloc_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_ALLOC_KEY_ADDR(left, lrecs + 1, cur);
            lpp = XFS_ALLOC_PTR_ADDR(left, lrecs + 1, cur);
            rkp = XFS_ALLOC_KEY_ADDR(right, 1, cur);
            rpp = XFS_ALLOC_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_alloc_log_keys(cur, lbp, lrecs + 1, lrecs + rrecs);
            xfs_alloc_log_ptrs(cur, lbp, lrecs + 1, lrecs + rrecs);
      } else {
            /*
             * It's a leaf.  Move records.
             */
            lrp = XFS_ALLOC_REC_ADDR(left, lrecs + 1, cur);
            rrp = XFS_ALLOC_REC_ADDR(right, 1, cur);
            memcpy(lrp, rrp, rrecs * sizeof(*lrp));
            xfs_alloc_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_alloc_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_alloc_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_alloc_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_ALLOC_BTREE_REF)))
                  return error;
            rrblock = XFS_BUF_TO_ALLOC_BLOCK(rrbp);
            if ((error = xfs_btree_check_sblock(cur, rrblock, level, rrbp)))
                  return error;
            rrblock->bb_leftsib = cpu_to_be32(lbno);
            xfs_alloc_log_block(cur->bc_tp, rrbp, XFS_BB_LEFTSIB);
      }
      /*
       * Free the deleting block by putting it on the freelist.
       */
      error = xfs_alloc_put_freelist(cur->bc_tp,
                               cur->bc_private.a.agbp, NULL, rbno, 1);
      if (error)
            return error;
      /*
       * Since blocks move to the free list without the coordination
       * used in xfs_bmap_finish, we can't allow block to be available
       * for reallocation and non-transaction writing (user data)
       * until we know that the transaction that moved it to the free
       * list is permanently on disk. We track the blocks by declaring
       * these blocks as "busy"; the busy list is maintained on a
       * per-ag basis and each transaction records which entries
       * should be removed when the iclog commits to disk. If a
       * busy block is allocated, the iclog is pushed up to the
       * LSN that freed the block.
       */
      xfs_alloc_mark_busy(cur->bc_tp, be32_to_cpu(agf->agf_seqno), bno, 1);
      xfs_trans_agbtree_delta(cur->bc_tp, -1);

      /*
       * Adjust the current level's cursor so that we're left referring
       * to the right node, after we're done.
       * If this leaves the ptr value 0 our caller will fix it 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_alloc_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_alloc_rec_t         *recp,      /* i/o: record data inserted */
      xfs_btree_cur_t         **curp,     /* output: new cursor replacing cur */
      int               *stat)      /* output: success/failure */
{
      xfs_agf_t         *agf; /* allocation group freelist header */
      xfs_alloc_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_alloc_key_t         key;  /* key value being inserted */
      xfs_alloc_key_t         *kp;  /* 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_alloc_key_t         nkey; /* new key value, from split */
      xfs_alloc_rec_t         nrec; /* new record value, for caller */
      int               numrecs;
      int               optr; /* old ptr value */
      xfs_alloc_ptr_t         *pp;  /* pointer to btree addresses */
      int               ptr;  /* index in btree block for this rec */
      xfs_alloc_rec_t         *rp;  /* pointer to btree records */

      ASSERT(be32_to_cpu(recp->ar_blockcount) > 0);

      /*
       * 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) {
            XFS_STATS_INC(xs_abt_insrec);
            if ((error = xfs_alloc_newroot(cur, &i)))
                  return error;
            *bnop = NULLAGBLOCK;
            *stat = i;
            return 0;
      }
      /*
       * Make a key out of the record data to be inserted, and save it.
       */
      key.ar_startblock = recp->ar_startblock;
      key.ar_blockcount = recp->ar_blockcount;
      optr = ptr = cur->bc_ptrs[level];
      /*
       * If we're off the left edge, return failure.
       */
      if (ptr == 0) {
            *stat = 0;
            return 0;
      }
      XFS_STATS_INC(xs_abt_insrec);
      /*
       * Get pointers to the btree buffer and block.
       */
      bp = cur->bc_bufs[level];
      block = XFS_BUF_TO_ALLOC_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_ALLOC_REC_ADDR(block, ptr, cur);
                  xfs_btree_check_rec(cur->bc_btnum, recp, rp);
            } else {
                  kp = XFS_ALLOC_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_ALLOC_BLOCK_MAXRECS(level, cur)) {
            /*
             * First, try shifting an entry to the right neighbor.
             */
            if ((error = xfs_alloc_rshift(cur, level, &i)))
                  return error;
            if (i) {
                  /* nothing */
            }
            /*
             * Next, try shifting an entry to the left neighbor.
             */
            else {
                  if ((error = xfs_alloc_lshift(cur, level, &i)))
                        return error;
                  if (i)
                        optr = ptr = cur->bc_ptrs[level];
                  else {
                        /*
                         * 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_alloc_split(cur, level, &nbno,
                                    &nkey, &ncur, &i)))
                              return error;
                        if (i) {
                              bp = cur->bc_bufs[level];
                              block = XFS_BUF_TO_ALLOC_BLOCK(bp);
#ifdef DEBUG
                              if ((error =
                                    xfs_btree_check_sblock(cur,
                                          block, level, bp)))
                                    return error;
#endif
                              ptr = cur->bc_ptrs[level];
                              nrec.ar_startblock = nkey.ar_startblock;
                              nrec.ar_blockcount = nkey.ar_blockcount;
                        }
                        /*
                         * Otherwise the insert fails.
                         */
                        else {
                              *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_ALLOC_KEY_ADDR(block, 1, cur);
            pp = XFS_ALLOC_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));
#ifdef DEBUG
            if ((error = xfs_btree_check_sptr(cur, *bnop, level)))
                  return error;
#endif
            /*
             * Now stuff the new data in, bump numrecs and log the new data.
             */
            kp[ptr - 1] = key;
            pp[ptr - 1] = cpu_to_be32(*bnop);
            numrecs++;
            block->bb_numrecs = cpu_to_be16(numrecs);
            xfs_alloc_log_keys(cur, bp, ptr, numrecs);
            xfs_alloc_log_ptrs(cur, bp, ptr, numrecs);
#ifdef DEBUG
            if (ptr < numrecs)
                  xfs_btree_check_key(cur->bc_btnum, kp + ptr - 1,
                        kp + ptr);
#endif
      } else {
            /*
             * It's a leaf entry.  Make a hole for the new record.
             */
            rp = XFS_ALLOC_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_alloc_log_recs(cur, bp, ptr, numrecs);
#ifdef DEBUG
            if (ptr < numrecs)
                  xfs_btree_check_rec(cur->bc_btnum, rp + ptr - 1,
                        rp + ptr);
#endif
      }
      /*
       * Log the new number of records in the btree header.
       */
      xfs_alloc_log_block(cur->bc_tp, bp, XFS_BB_NUMRECS);
      /*
       * If we inserted at the start of a block, update the parents' keys.
       */
      if (optr == 1 && (error = xfs_alloc_updkey(cur, &key, level + 1)))
            return error;
      /*
       * Look to see if the longest extent in the allocation group
       * needs to be updated.
       */

      agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);
      if (level == 0 &&
          cur->bc_btnum == XFS_BTNUM_CNT &&
          be32_to_cpu(block->bb_rightsib) == NULLAGBLOCK &&
          be32_to_cpu(recp->ar_blockcount) > be32_to_cpu(agf->agf_longest)) {
            /*
             * If this is a leaf in the by-size btree and there
             * is no right sibling block and this block is bigger
             * than the previous longest block, update it.
             */
            agf->agf_longest = recp->ar_blockcount;
            cur->bc_mp->m_perag[be32_to_cpu(agf->agf_seqno)].pagf_longest
                  = be32_to_cpu(recp->ar_blockcount);
            xfs_alloc_log_agf(cur->bc_tp, cur->bc_private.a.agbp,
                  XFS_AGF_LONGEST);
      }
      /*
       * 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_alloc_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_alloc_block_t, bb_magic),
            offsetof(xfs_alloc_block_t, bb_level),
            offsetof(xfs_alloc_block_t, bb_numrecs),
            offsetof(xfs_alloc_block_t, bb_leftsib),
            offsetof(xfs_alloc_block_t, bb_rightsib),
            sizeof(xfs_alloc_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_alloc_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_alloc_block_t *block;     /* btree block to log from */
      int               first;      /* first byte offset logged */
      xfs_alloc_key_t         *kp;  /* key pointer in btree block */
      int               last; /* last byte offset logged */

      block = XFS_BUF_TO_ALLOC_BLOCK(bp);
      kp = XFS_ALLOC_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_alloc_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_alloc_block_t *block;     /* btree block to log from */
      int               first;      /* first byte offset logged */
      int               last; /* last byte offset logged */
      xfs_alloc_ptr_t         *pp;  /* block-pointer pointer in btree blk */

      block = XFS_BUF_TO_ALLOC_BLOCK(bp);
      pp = XFS_ALLOC_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_alloc_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_alloc_block_t *block;     /* btree block to log from */
      int               first;      /* first byte offset logged */
      int               last; /* last byte offset logged */
      xfs_alloc_rec_t         *rp;  /* record pointer for btree block */


      block = XFS_BUF_TO_ALLOC_BLOCK(bp);
      rp = XFS_ALLOC_REC_ADDR(block, 1, cur);
#ifdef DEBUG
      {
            xfs_agf_t   *agf;
            xfs_alloc_rec_t   *p;

            agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);
            for (p = &rp[rfirst - 1]; p <= &rp[rlast - 1]; p++)
                  ASSERT(be32_to_cpu(p->ar_startblock) +
                         be32_to_cpu(p->ar_blockcount) <=
                         be32_to_cpu(agf->agf_length));
      }
#endif
      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);
}

/*
 * Lookup the record.  The cursor is made to point to it, based on dir.
 * Return 0 if can't find any such record, 1 for success.
 */
STATIC int                    /* error */
xfs_alloc_lookup(
      xfs_btree_cur_t         *cur, /* btree cursor */
      xfs_lookup_t            dir,  /* <=, ==, or >= */
      int               *stat)      /* success/failure */
{
      xfs_agblock_t           agbno;      /* a.g. relative btree block number */
      xfs_agnumber_t          agno; /* allocation group number */
      xfs_alloc_block_t *block=NULL;      /* current btree block */
      int               diff; /* difference for the current key */
      int               error;      /* error return value */
      int               keyno=0;    /* current key number */
      int               level;      /* level in the btree */
      xfs_mount_t       *mp;  /* file system mount point */

      XFS_STATS_INC(xs_abt_lookup);
      /*
       * Get the allocation group header, and the root block number.
       */
      mp = cur->bc_mp;

      {
            xfs_agf_t   *agf; /* a.g. freespace header */

            agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);
            agno = be32_to_cpu(agf->agf_seqno);
            agbno = be32_to_cpu(agf->agf_roots[cur->bc_btnum]);
      }
      /*
       * Iterate over each level in the btree, starting at the root.
       * For each level above the leaves, find the key we need, based
       * on the lookup record, then follow the corresponding block
       * pointer down to the next level.
       */
      for (level = cur->bc_nlevels - 1, diff = 1; level >= 0; level--) {
            xfs_buf_t   *bp;  /* buffer pointer for btree block */
            xfs_daddr_t d;    /* disk address of btree block */

            /*
             * Get the disk address we're looking for.
             */
            d = XFS_AGB_TO_DADDR(mp, agno, agbno);
            /*
             * If the old buffer at this level is for a different block,
             * throw it away, otherwise just use it.
             */
            bp = cur->bc_bufs[level];
            if (bp && XFS_BUF_ADDR(bp) != d)
                  bp = NULL;
            if (!bp) {
                  /*
                   * Need to get a new buffer.  Read it, then
                   * set it in the cursor, releasing the old one.
                   */
                  if ((error = xfs_btree_read_bufs(mp, cur->bc_tp, agno,
                              agbno, 0, &bp, XFS_ALLOC_BTREE_REF)))
                        return error;
                  xfs_btree_setbuf(cur, level, bp);
                  /*
                   * Point to the btree block, now that we have the buffer
                   */
                  block = XFS_BUF_TO_ALLOC_BLOCK(bp);
                  if ((error = xfs_btree_check_sblock(cur, block, level,
                              bp)))
                        return error;
            } else
                  block = XFS_BUF_TO_ALLOC_BLOCK(bp);
            /*
             * If we already had a key match at a higher level, we know
             * we need to use the first entry in this block.
             */
            if (diff == 0)
                  keyno = 1;
            /*
             * Otherwise we need to search this block.  Do a binary search.
             */
            else {
                  int         high; /* high entry number */
                  xfs_alloc_key_t   *kkbase=NULL;/* base of keys in block */
                  xfs_alloc_rec_t   *krbase=NULL;/* base of records in block */
                  int         low;  /* low entry number */

                  /*
                   * Get a pointer to keys or records.
                   */
                  if (level > 0)
                        kkbase = XFS_ALLOC_KEY_ADDR(block, 1, cur);
                  else
                        krbase = XFS_ALLOC_REC_ADDR(block, 1, cur);
                  /*
                   * Set low and high entry numbers, 1-based.
                   */
                  low = 1;
                  if (!(high = be16_to_cpu(block->bb_numrecs))) {
                        /*
                         * If the block is empty, the tree must
                         * be an empty leaf.
                         */
                        ASSERT(level == 0 && cur->bc_nlevels == 1);
                        cur->bc_ptrs[0] = dir != XFS_LOOKUP_LE;
                        *stat = 0;
                        return 0;
                  }
                  /*
                   * Binary search the block.
                   */
                  while (low <= high) {
                        xfs_extlen_t      blockcount; /* key value */
                        xfs_agblock_t     startblock; /* key value */

                        XFS_STATS_INC(xs_abt_compare);
                        /*
                         * keyno is average of low and high.
                         */
                        keyno = (low + high) >> 1;
                        /*
                         * Get startblock & blockcount.
                         */
                        if (level > 0) {
                              xfs_alloc_key_t   *kkp;

                              kkp = kkbase + keyno - 1;
                              startblock = be32_to_cpu(kkp->ar_startblock);
                              blockcount = be32_to_cpu(kkp->ar_blockcount);
                        } else {
                              xfs_alloc_rec_t   *krp;

                              krp = krbase + keyno - 1;
                              startblock = be32_to_cpu(krp->ar_startblock);
                              blockcount = be32_to_cpu(krp->ar_blockcount);
                        }
                        /*
                         * Compute difference to get next direction.
                         */
                        if (cur->bc_btnum == XFS_BTNUM_BNO)
                              diff = (int)startblock -
                                     (int)cur->bc_rec.a.ar_startblock;
                        else if (!(diff = (int)blockcount -
                                  (int)cur->bc_rec.a.ar_blockcount))
                              diff = (int)startblock -
                                  (int)cur->bc_rec.a.ar_startblock;
                        /*
                         * Less than, move right.
                         */
                        if (diff < 0)
                              low = keyno + 1;
                        /*
                         * Greater than, move left.
                         */
                        else if (diff > 0)
                              high = keyno - 1;
                        /*
                         * Equal, we're done.
                         */
                        else
                              break;
                  }
            }
            /*
             * If there are more levels, set up for the next level
             * by getting the block number and filling in the cursor.
             */
            if (level > 0) {
                  /*
                   * If we moved left, need the previous key number,
                   * unless there isn't one.
                   */
                  if (diff > 0 && --keyno < 1)
                        keyno = 1;
                  agbno = be32_to_cpu(*XFS_ALLOC_PTR_ADDR(block, keyno, cur));
#ifdef DEBUG
                  if ((error = xfs_btree_check_sptr(cur, agbno, level)))
                        return error;
#endif
                  cur->bc_ptrs[level] = keyno;
            }
      }
      /*
       * Done with the search.
       * See if we need to adjust the results.
       */
      if (dir != XFS_LOOKUP_LE && diff < 0) {
            keyno++;
            /*
             * If ge search and we went off the end of the block, but it's
             * not the last block, we're in the wrong block.
             */
            if (dir == XFS_LOOKUP_GE &&
                keyno > be16_to_cpu(block->bb_numrecs) &&
                be32_to_cpu(block->bb_rightsib) != NULLAGBLOCK) {
                  int   i;

                  cur->bc_ptrs[0] = keyno;
                  if ((error = xfs_alloc_increment(cur, 0, &i)))
                        return error;
                  XFS_WANT_CORRUPTED_RETURN(i == 1);
                  *stat = 1;
                  return 0;
            }
      }
      else if (dir == XFS_LOOKUP_LE && diff > 0)
            keyno--;
      cur->bc_ptrs[0] = keyno;
      /*
       * Return if we succeeded or not.
       */
      if (keyno == 0 || keyno > be16_to_cpu(block->bb_numrecs))
            *stat = 0;
      else
            *stat = ((dir != XFS_LOOKUP_EQ) || (diff == 0));
      return 0;
}

/*
 * Move 1 record left from cur/level if possible.
 * Update cur to reflect the new path.
 */
STATIC int                    /* error */
xfs_alloc_lshift(
      xfs_btree_cur_t         *cur, /* btree cursor */
      int               level,      /* level to shift record on */
      int               *stat)      /* success/failure */
{
      int               error;      /* error return value */
#ifdef DEBUG
      int               i;    /* loop index */
#endif
      xfs_alloc_key_t         key;  /* key value for leaf level upward */
      xfs_buf_t         *lbp; /* buffer for left neighbor block */
      xfs_alloc_block_t *left;      /* left neighbor btree block */
      int               nrec; /* new number of left block entries */
      xfs_buf_t         *rbp; /* buffer for right (current) block */
      xfs_alloc_block_t *right;     /* right (current) btree block */
      xfs_alloc_key_t         *rkp=NULL;  /* key pointer for right block */
      xfs_alloc_ptr_t         *rpp=NULL;  /* address pointer for right block */
      xfs_alloc_rec_t         *rrp=NULL;  /* record pointer for right block */

      /*
       * Set up variables for this block as "right".
       */
      rbp = cur->bc_bufs[level];
      right = XFS_BUF_TO_ALLOC_BLOCK(rbp);
#ifdef DEBUG
      if ((error = xfs_btree_check_sblock(cur, right, level, rbp)))
            return error;
#endif
      /*
       * If we've got no left sibling then we can't shift an entry left.
       */
      if (be32_to_cpu(right->bb_leftsib) == NULLAGBLOCK) {
            *stat = 0;
            return 0;
      }
      /*
       * If the cursor entry is the one that would be moved, don't
       * do it... it's too complicated.
       */
      if (cur->bc_ptrs[level] <= 1) {
            *stat = 0;
            return 0;
      }
      /*
       * Set up the left neighbor as "left".
       */
      if ((error = xfs_btree_read_bufs(cur->bc_mp, cur->bc_tp,
                  cur->bc_private.a.agno, be32_to_cpu(right->bb_leftsib),
                  0, &lbp, XFS_ALLOC_BTREE_REF)))
            return error;
      left = XFS_BUF_TO_ALLOC_BLOCK(lbp);
      if ((error = xfs_btree_check_sblock(cur, left, level, lbp)))
            return error;
      /*
       * If it's full, it can't take another entry.
       */
      if (be16_to_cpu(left->bb_numrecs) == XFS_ALLOC_BLOCK_MAXRECS(level, cur)) {
            *stat = 0;
            return 0;
      }
      nrec = be16_to_cpu(left->bb_numrecs) + 1;
      /*
       * If non-leaf, copy a key and a ptr to the left block.
       */
      if (level > 0) {
            xfs_alloc_key_t   *lkp; /* key pointer for left block */
            xfs_alloc_ptr_t   *lpp; /* address pointer for left block */

            lkp = XFS_ALLOC_KEY_ADDR(left, nrec, cur);
            rkp = XFS_ALLOC_KEY_ADDR(right, 1, cur);
            *lkp = *rkp;
            xfs_alloc_log_keys(cur, lbp, nrec, nrec);
            lpp = XFS_ALLOC_PTR_ADDR(left, nrec, cur);
            rpp = XFS_ALLOC_PTR_ADDR(right, 1, cur);
#ifdef DEBUG
            if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(*rpp), level)))
                  return error;
#endif
            *lpp = *rpp;
            xfs_alloc_log_ptrs(cur, lbp, nrec, nrec);
            xfs_btree_check_key(cur->bc_btnum, lkp - 1, lkp);
      }
      /*
       * If leaf, copy a record to the left block.
       */
      else {
            xfs_alloc_rec_t   *lrp; /* record pointer for left block */

            lrp = XFS_ALLOC_REC_ADDR(left, nrec, cur);
            rrp = XFS_ALLOC_REC_ADDR(right, 1, cur);
            *lrp = *rrp;
            xfs_alloc_log_recs(cur, lbp, nrec, nrec);
            xfs_btree_check_rec(cur->bc_btnum, lrp - 1, lrp);
      }
      /*
       * Bump and log left's numrecs, decrement and log right's numrecs.
       */
      be16_add(&left->bb_numrecs, 1);
      xfs_alloc_log_block(cur->bc_tp, lbp, XFS_BB_NUMRECS);
      be16_add(&right->bb_numrecs, -1);
      xfs_alloc_log_block(cur->bc_tp, rbp, XFS_BB_NUMRECS);
      /*
       * Slide the contents of right down one entry.
       */
      if (level > 0) {
#ifdef DEBUG
            for (i = 0; i < be16_to_cpu(right->bb_numrecs); i++) {
                  if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(rpp[i + 1]),
                              level)))
                        return error;
            }
#endif
            memmove(rkp, rkp + 1, be16_to_cpu(right->bb_numrecs) * sizeof(*rkp));
            memmove(rpp, rpp + 1, be16_to_cpu(right->bb_numrecs) * sizeof(*rpp));
            xfs_alloc_log_keys(cur, rbp, 1, be16_to_cpu(right->bb_numrecs));
            xfs_alloc_log_ptrs(cur, rbp, 1, be16_to_cpu(right->bb_numrecs));
      } else {
            memmove(rrp, rrp + 1, be16_to_cpu(right->bb_numrecs) * sizeof(*rrp));
            xfs_alloc_log_recs(cur, rbp, 1, be16_to_cpu(right->bb_numrecs));
            key.ar_startblock = rrp->ar_startblock;
            key.ar_blockcount = rrp->ar_blockcount;
            rkp = &key;
      }
      /*
       * Update the parent key values of right.
       */
      if ((error = xfs_alloc_updkey(cur, rkp, level + 1)))
            return error;
      /*
       * Slide the cursor value left one.
       */
      cur->bc_ptrs[level]--;
      *stat = 1;
      return 0;
}

/*
 * Allocate a new root block, fill it in.
 */
STATIC int                    /* error */
xfs_alloc_newroot(
      xfs_btree_cur_t         *cur, /* btree cursor */
      int               *stat)      /* success/failure */
{
      int               error;      /* error return value */
      xfs_agblock_t           lbno; /* left block number */
      xfs_buf_t         *lbp; /* left btree buffer */
      xfs_alloc_block_t *left;      /* left btree block */
      xfs_mount_t       *mp;  /* mount structure */
      xfs_agblock_t           nbno; /* new block number */
      xfs_buf_t         *nbp; /* new (root) buffer */
      xfs_alloc_block_t *new; /* new (root) btree block */
      int               nptr; /* new value for key index, 1 or 2 */
      xfs_agblock_t           rbno; /* right block number */
      xfs_buf_t         *rbp; /* right btree buffer */
      xfs_alloc_block_t *right;     /* right btree block */

      mp = cur->bc_mp;

      ASSERT(cur->bc_nlevels < XFS_AG_MAXLEVELS(mp));
      /*
       * Get a buffer from the freelist blocks, for the new root.
       */
      error = xfs_alloc_get_freelist(cur->bc_tp,
                              cur->bc_private.a.agbp, &nbno, 1);
      if (error)
            return error;
      /*
       * None available, we fail.
       */
      if (nbno == NULLAGBLOCK) {
            *stat = 0;
            return 0;
      }
      xfs_trans_agbtree_delta(cur->bc_tp, 1);
      nbp = xfs_btree_get_bufs(mp, cur->bc_tp, cur->bc_private.a.agno, nbno,
            0);
      new = XFS_BUF_TO_ALLOC_BLOCK(nbp);
      /*
       * Set the root data in the a.g. freespace structure.
       */
      {
            xfs_agf_t   *agf; /* a.g. freespace header */
            xfs_agnumber_t    seqno;

            agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);
            agf->agf_roots[cur->bc_btnum] = cpu_to_be32(nbno);
            be32_add(&agf->agf_levels[cur->bc_btnum], 1);
            seqno = be32_to_cpu(agf->agf_seqno);
            mp->m_perag[seqno].pagf_levels[cur->bc_btnum]++;
            xfs_alloc_log_agf(cur->bc_tp, cur->bc_private.a.agbp,
                  XFS_AGF_ROOTS | XFS_AGF_LEVELS);
      }
      /*
       * 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.
       */
      lbp = cur->bc_bufs[cur->bc_nlevels - 1];
      left = XFS_BUF_TO_ALLOC_BLOCK(lbp);
#ifdef DEBUG
      if ((error = xfs_btree_check_sblock(cur, left, cur->bc_nlevels - 1, lbp)))
            return error;
#endif
      if (be32_to_cpu(left->bb_rightsib) != NULLAGBLOCK) {
            /*
             * Our block is left, pick up the right block.
             */
            lbno = XFS_DADDR_TO_AGBNO(mp, XFS_BUF_ADDR(lbp));
            rbno = be32_to_cpu(left->bb_rightsib);
            if ((error = xfs_btree_read_bufs(mp, cur->bc_tp,
                        cur->bc_private.a.agno, rbno, 0, &rbp,
                        XFS_ALLOC_BTREE_REF)))
                  return error;
            right = XFS_BUF_TO_ALLOC_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 = lbp;
            right = left;
            rbno = XFS_DADDR_TO_AGBNO(mp, XFS_BUF_ADDR(rbp));
            lbno = be32_to_cpu(right->bb_leftsib);
            if ((error = xfs_btree_read_bufs(mp, cur->bc_tp,
                        cur->bc_private.a.agno, lbno, 0, &lbp,
                        XFS_ALLOC_BTREE_REF)))
                  return error;
            left = XFS_BUF_TO_ALLOC_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_alloc_log_block(cur->bc_tp, nbp, XFS_BB_ALL_BITS);
      ASSERT(lbno != NULLAGBLOCK && rbno != NULLAGBLOCK);
      /*
       * Fill in the key data in the new root.
       */
      {
            xfs_alloc_key_t         *kp;  /* btree key pointer */

            kp = XFS_ALLOC_KEY_ADDR(new, 1, cur);
            if (be16_to_cpu(left->bb_level) > 0) {
                  kp[0] = *XFS_ALLOC_KEY_ADDR(left, 1, cur);
                  kp[1] = *XFS_ALLOC_KEY_ADDR(right, 1, cur);
            } else {
                  xfs_alloc_rec_t   *rp;  /* btree record pointer */

                  rp = XFS_ALLOC_REC_ADDR(left, 1, cur);
                  kp[0].ar_startblock = rp->ar_startblock;
                  kp[0].ar_blockcount = rp->ar_blockcount;
                  rp = XFS_ALLOC_REC_ADDR(right, 1, cur);
                  kp[1].ar_startblock = rp->ar_startblock;
                  kp[1].ar_blockcount = rp->ar_blockcount;
            }
      }
      xfs_alloc_log_keys(cur, nbp, 1, 2);
      /*
       * Fill in the pointer data in the new root.
       */
      {
            xfs_alloc_ptr_t         *pp;  /* btree address pointer */

            pp = XFS_ALLOC_PTR_ADDR(new, 1, cur);
            pp[0] = cpu_to_be32(lbno);
            pp[1] = cpu_to_be32(rbno);
      }
      xfs_alloc_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;
}

/*
 * Move 1 record right from cur/level if possible.
 * Update cur to reflect the new path.
 */
STATIC int                    /* error */
xfs_alloc_rshift(
      xfs_btree_cur_t         *cur, /* btree cursor */
      int               level,      /* level to shift record on */
      int               *stat)      /* success/failure */
{
      int               error;      /* error return value */
      int               i;    /* loop index */
      xfs_alloc_key_t         key;  /* key value for leaf level upward */
      xfs_buf_t         *lbp; /* buffer for left (current) block */
      xfs_alloc_block_t *left;      /* left (current) btree block */
      xfs_buf_t         *rbp; /* buffer for right neighbor block */
      xfs_alloc_block_t *right;     /* right neighbor btree block */
      xfs_alloc_key_t         *rkp; /* key pointer for right block */
      xfs_btree_cur_t         *tcur;      /* temporary cursor */

      /*
       * Set up variables for this block as "left".
       */
      lbp = cur->bc_bufs[level];
      left = XFS_BUF_TO_ALLOC_BLOCK(lbp);
#ifdef DEBUG
      if ((error = xfs_btree_check_sblock(cur, left, level, lbp)))
            return error;
#endif
      /*
       * If we've got no right sibling then we can't shift an entry right.
       */
      if (be32_to_cpu(left->bb_rightsib) == NULLAGBLOCK) {
            *stat = 0;
            return 0;
      }
      /*
       * If the cursor entry is the one that would be moved, don't
       * do it... it's too complicated.
       */
      if (cur->bc_ptrs[level] >= be16_to_cpu(left->bb_numrecs)) {
            *stat = 0;
            return 0;
      }
      /*
       * Set up the right neighbor as "right".
       */
      if ((error = xfs_btree_read_bufs(cur->bc_mp, cur->bc_tp,
                  cur->bc_private.a.agno, be32_to_cpu(left->bb_rightsib),
                  0, &rbp, XFS_ALLOC_BTREE_REF)))
            return error;
      right = XFS_BUF_TO_ALLOC_BLOCK(rbp);
      if ((error = xfs_btree_check_sblock(cur, right, level, rbp)))
            return error;
      /*
       * If it's full, it can't take another entry.
       */
      if (be16_to_cpu(right->bb_numrecs) == XFS_ALLOC_BLOCK_MAXRECS(level, cur)) {
            *stat = 0;
            return 0;
      }
      /*
       * Make a hole at the start of the right neighbor block, then
       * copy the last left block entry to the hole.
       */
      if (level > 0) {
            xfs_alloc_key_t   *lkp; /* key pointer for left block */
            xfs_alloc_ptr_t   *lpp; /* address pointer for left block */
            xfs_alloc_ptr_t   *rpp; /* address pointer for right block */

            lkp = XFS_ALLOC_KEY_ADDR(left, be16_to_cpu(left->bb_numrecs), cur);
            lpp = XFS_ALLOC_PTR_ADDR(left, be16_to_cpu(left->bb_numrecs), cur);
            rkp = XFS_ALLOC_KEY_ADDR(right, 1, cur);
            rpp = XFS_ALLOC_PTR_ADDR(right, 1, cur);
#ifdef DEBUG
            for (i = be16_to_cpu(right->bb_numrecs) - 1; i >= 0; i--) {
                  if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(rpp[i]), level)))
                        return error;
            }
#endif
            memmove(rkp + 1, rkp, be16_to_cpu(right->bb_numrecs) * sizeof(*rkp));
            memmove(rpp + 1, rpp, be16_to_cpu(right->bb_numrecs) * sizeof(*rpp));
#ifdef DEBUG
            if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(*lpp), level)))
                  return error;
#endif
            *rkp = *lkp;
            *rpp = *lpp;
            xfs_alloc_log_keys(cur, rbp, 1, be16_to_cpu(right->bb_numrecs) + 1);
            xfs_alloc_log_ptrs(cur, rbp, 1, be16_to_cpu(right->bb_numrecs) + 1);
            xfs_btree_check_key(cur->bc_btnum, rkp, rkp + 1);
      } else {
            xfs_alloc_rec_t   *lrp; /* record pointer for left block */
            xfs_alloc_rec_t   *rrp; /* record pointer for right block */

            lrp = XFS_ALLOC_REC_ADDR(left, be16_to_cpu(left->bb_numrecs), cur);
            rrp = XFS_ALLOC_REC_ADDR(right, 1, cur);
            memmove(rrp + 1, rrp, be16_to_cpu(right->bb_numrecs) * sizeof(*rrp));
            *rrp = *lrp;
            xfs_alloc_log_recs(cur, rbp, 1, be16_to_cpu(right->bb_numrecs) + 1);
            key.ar_startblock = rrp->ar_startblock;
            key.ar_blockcount = rrp->ar_blockcount;
            rkp = &key;
            xfs_btree_check_rec(cur->bc_btnum, rrp, rrp + 1);
      }
      /*
       * Decrement and log left's numrecs, bump and log right's numrecs.
       */
      be16_add(&left->bb_numrecs, -1);
      xfs_alloc_log_block(cur->bc_tp, lbp, XFS_BB_NUMRECS);
      be16_add(&right->bb_numrecs, 1);
      xfs_alloc_log_block(cur->bc_tp, rbp, XFS_BB_NUMRECS);
      /*
       * Using a temporary cursor, update the parent key values of the
       * block on the right.
       */
      if ((error = xfs_btree_dup_cursor(cur, &tcur)))
            return error;
      i = xfs_btree_lastrec(tcur, level);
      XFS_WANT_CORRUPTED_GOTO(i == 1, error0);
      if ((error = xfs_alloc_increment(tcur, level, &i)) ||
          (error = xfs_alloc_updkey(tcur, rkp, level + 1)))
            goto error0;
      xfs_btree_del_cursor(tcur, XFS_BTREE_NOERROR);
      *stat = 1;
      return 0;
error0:
      xfs_btree_del_cursor(tcur, XFS_BTREE_ERROR);
      return error;
}

/*
 * Split cur/level block in half.
 * Return new block number and its first record (to be inserted into parent).
 */
STATIC int                    /* error */
xfs_alloc_split(
      xfs_btree_cur_t         *cur, /* btree cursor */
      int               level,      /* level to split */
      xfs_agblock_t           *bnop,      /* output: block number allocated */
      xfs_alloc_key_t         *keyp,      /* output: first key of new block */
      xfs_btree_cur_t         **curp,     /* output: new cursor */
      int               *stat)      /* success/failure */
{
      int               error;      /* error return value */
      int               i;    /* loop index/record number */
      xfs_agblock_t           lbno; /* left (current) block number */
      xfs_buf_t         *lbp; /* buffer for left block */
      xfs_alloc_block_t *left;      /* left (current) btree block */
      xfs_agblock_t           rbno; /* right (new) block number */
      xfs_buf_t         *rbp; /* buffer for right block */
      xfs_alloc_block_t *right;     /* right (new) btree block */

      /*
       * Allocate the new block from the freelist.
       * If we can't do it, we're toast.  Give up.
       */
      error = xfs_alloc_get_freelist(cur->bc_tp,
                               cur->bc_private.a.agbp, &rbno, 1);
      if (error)
            return error;
      if (rbno == NULLAGBLOCK) {
            *stat = 0;
            return 0;
      }
      xfs_trans_agbtree_delta(cur->bc_tp, 1);
      rbp = xfs_btree_get_bufs(cur->bc_mp, cur->bc_tp, cur->bc_private.a.agno,
            rbno, 0);
      /*
       * Set up the new block as "right".
       */
      right = XFS_BUF_TO_ALLOC_BLOCK(rbp);
      /*
       * "Left" is the current (according to the cursor) block.
       */
      lbp = cur->bc_bufs[level];
      left = XFS_BUF_TO_ALLOC_BLOCK(lbp);
#ifdef DEBUG
      if ((error = xfs_btree_check_sblock(cur, left, level, lbp)))
            return error;
#endif
      /*
       * Fill in the btree header for the new block.
       */
      right->bb_magic = cpu_to_be32(xfs_magics[cur->bc_btnum]);
      right->bb_level = left->bb_level;
      right->bb_numrecs = cpu_to_be16(be16_to_cpu(left->bb_numrecs) / 2);
      /*
       * Make sure that if there's an odd number of entries now, that
       * each new block will have the same number of entries.
       */
      if ((be16_to_cpu(left->bb_numrecs) & 1) &&
          cur->bc_ptrs[level] <= be16_to_cpu(right->bb_numrecs) + 1)
            be16_add(&right->bb_numrecs, 1);
      i = be16_to_cpu(left->bb_numrecs) - be16_to_cpu(right->bb_numrecs) + 1;
      /*
       * For non-leaf blocks, copy keys and addresses over to the new block.
       */
      if (level > 0) {
            xfs_alloc_key_t   *lkp; /* left btree key pointer */
            xfs_alloc_ptr_t   *lpp; /* left btree address pointer */
            xfs_alloc_key_t   *rkp; /* right btree key pointer */
            xfs_alloc_ptr_t   *rpp; /* right btree address pointer */

            lkp = XFS_ALLOC_KEY_ADDR(left, i, cur);
            lpp = XFS_ALLOC_PTR_ADDR(left, i, cur);
            rkp = XFS_ALLOC_KEY_ADDR(right, 1, cur);
            rpp = XFS_ALLOC_PTR_ADDR(right, 1, cur);
#ifdef DEBUG
            for (i = 0; i < be16_to_cpu(right->bb_numrecs); i++) {
                  if ((error = xfs_btree_check_sptr(cur, be32_to_cpu(lpp[i]), level)))
                        return error;
            }
#endif
            memcpy(rkp, lkp, be16_to_cpu(right->bb_numrecs) * sizeof(*rkp));
            memcpy(rpp, lpp, be16_to_cpu(right->bb_numrecs) * sizeof(*rpp));
            xfs_alloc_log_keys(cur, rbp, 1, be16_to_cpu(right->bb_numrecs));
            xfs_alloc_log_ptrs(cur, rbp, 1, be16_to_cpu(right->bb_numrecs));
            *keyp = *rkp;
      }
      /*
       * For leaf blocks, copy records over to the new block.
       */
      else {
            xfs_alloc_rec_t   *lrp; /* left btree record pointer */
            xfs_alloc_rec_t   *rrp; /* right btree record pointer */

            lrp = XFS_ALLOC_REC_ADDR(left, i, cur);
            rrp = XFS_ALLOC_REC_ADDR(right, 1, cur);
            memcpy(rrp, lrp, be16_to_cpu(right->bb_numrecs) * sizeof(*rrp));
            xfs_alloc_log_recs(cur, rbp, 1, be16_to_cpu(right->bb_numrecs));
            keyp->ar_startblock = rrp->ar_startblock;
            keyp->ar_blockcount = rrp->ar_blockcount;
      }
      /*
       * Find the left block number by looking in the buffer.
       * Adjust numrecs, sibling pointers.
       */
      lbno = XFS_DADDR_TO_AGBNO(cur->bc_mp, XFS_BUF_ADDR(lbp));
      be16_add(&left->bb_numrecs, -(be16_to_cpu(right->bb_numrecs)));
      right->bb_rightsib = left->bb_rightsib;
      left->bb_rightsib = cpu_to_be32(rbno);
      right->bb_leftsib = cpu_to_be32(lbno);
      xfs_alloc_log_block(cur->bc_tp, rbp, XFS_BB_ALL_BITS);
      xfs_alloc_log_block(cur->bc_tp, lbp, XFS_BB_NUMRECS | XFS_BB_RIGHTSIB);
      /*
       * If there's a block to the new block's right, make that block
       * point back to right instead of to left.
       */
      if (be32_to_cpu(right->bb_rightsib) != NULLAGBLOCK) {
            xfs_alloc_block_t *rrblock;   /* rr btree block */
            xfs_buf_t         *rrbp;            /* buffer for rrblock */

            if ((error = xfs_btree_read_bufs(cur->bc_mp, cur->bc_tp,
                        cur->bc_private.a.agno, be32_to_cpu(right->bb_rightsib), 0,
                        &rrbp, XFS_ALLOC_BTREE_REF)))
                  return error;
            rrblock = XFS_BUF_TO_ALLOC_BLOCK(rrbp);
            if ((error = xfs_btree_check_sblock(cur, rrblock, level, rrbp)))
                  return error;
            rrblock->bb_leftsib = cpu_to_be32(rbno);
            xfs_alloc_log_block(cur->bc_tp, rrbp, XFS_BB_LEFTSIB);
      }
      /*
       * If the cursor is really in the right block, move it there.
       * If it's just pointing past the last entry in left, then we'll
       * insert there, so don't change anything in that case.
       */
      if (cur->bc_ptrs[level] > be16_to_cpu(left->bb_numrecs) + 1) {
            xfs_btree_setbuf(cur, level, rbp);
            cur->bc_ptrs[level] -= be16_to_cpu(left->bb_numrecs);
      }
      /*
       * If there are more levels, we'll need another cursor which refers to
       * the right block, no matter where this cursor was.
       */
      if (level + 1 < cur->bc_nlevels) {
            if ((error = xfs_btree_dup_cursor(cur, curp)))
                  return error;
            (*curp)->bc_ptrs[level + 1]++;
      }
      *bnop = rbno;
      *stat = 1;
      return 0;
}

/*
 * Update keys at all levels from here to the root along the cursor's path.
 */
STATIC int                    /* error */
xfs_alloc_updkey(
      xfs_btree_cur_t         *cur, /* btree cursor */
      xfs_alloc_key_t         *keyp,      /* new key value to update to */
      int               level)      /* starting level for update */
{
      int               ptr;  /* index of key in block */

      /*
       * Go up the tree from this level toward the root.
       * At each level, update the key value to the value input.
       * Stop when we reach a level where the cursor isn't pointing
       * at the first entry in the block.
       */
      for (ptr = 1; ptr == 1 && level < cur->bc_nlevels; level++) {
            xfs_alloc_block_t *block;     /* btree block */
            xfs_buf_t         *bp;  /* buffer for block */
#ifdef DEBUG
            int               error;      /* error return value */
#endif
            xfs_alloc_key_t         *kp;  /* ptr to btree block keys */

            bp = cur->bc_bufs[level];
            block = XFS_BUF_TO_ALLOC_BLOCK(bp);
#ifdef DEBUG
            if ((error = xfs_btree_check_sblock(cur, block, level, bp)))
                  return error;
#endif
            ptr = cur->bc_ptrs[level];
            kp = XFS_ALLOC_KEY_ADDR(block, ptr, cur);
            *kp = *keyp;
            xfs_alloc_log_keys(cur, bp, ptr, ptr);
      }
      return 0;
}

/*
 * Externally visible routines.
 */

/*
 * Decrement cursor by one record at the level.
 * For nonzero levels the leaf-ward information is untouched.
 */
int                           /* error */
xfs_alloc_decrement(
      xfs_btree_cur_t         *cur, /* btree cursor */
      int               level,      /* level in btree, 0 is leaf */
      int               *stat)      /* success/failure */
{
      xfs_alloc_block_t *block;     /* btree block */
      int               error;      /* error return value */
      int               lev;  /* btree level */

      ASSERT(level < cur->bc_nlevels);
      /*
       * Read-ahead to the left at this level.
       */
      xfs_btree_readahead(cur, level, XFS_BTCUR_LEFTRA);
      /*
       * Decrement the ptr at this level.  If we're still in the block
       * then we're done.
       */
      if (--cur->bc_ptrs[level] > 0) {
            *stat = 1;
            return 0;
      }
      /*
       * Get a pointer to the btree block.
       */
      block = XFS_BUF_TO_ALLOC_BLOCK(cur->bc_bufs[level]);
#ifdef DEBUG
      if ((error = xfs_btree_check_sblock(cur, block, level,
                  cur->bc_bufs[level])))
            return error;
#endif
      /*
       * If we just went off the left edge of the tree, return failure.
       */
      if (be32_to_cpu(block->bb_leftsib) == NULLAGBLOCK) {
            *stat = 0;
            return 0;
      }
      /*
       * March up the tree decrementing pointers.
       * Stop when we don't go off the left edge of a block.
       */
      for (lev = level + 1; lev < cur->bc_nlevels; lev++) {
            if (--cur->bc_ptrs[lev] > 0)
                  break;
            /*
             * Read-ahead the left block, we're going to read it
             * in the next loop.
             */
            xfs_btree_readahead(cur, lev, XFS_BTCUR_LEFTRA);
      }
      /*
       * If we went off the root then we are seriously confused.
       */
      ASSERT(lev < cur->bc_nlevels);
      /*
       * Now walk back down the tree, fixing up the cursor's buffer
       * pointers and key numbers.
       */
      for (block = XFS_BUF_TO_ALLOC_BLOCK(cur->bc_bufs[lev]); lev > level; ) {
            xfs_agblock_t     agbno;      /* block number of btree block */
            xfs_buf_t   *bp;  /* buffer pointer for block */

            agbno = be32_to_cpu(*XFS_ALLOC_PTR_ADDR(block, cur->bc_ptrs[lev], cur));
            if ((error = xfs_btree_read_bufs(cur->bc_mp, cur->bc_tp,
                        cur->bc_private.a.agno, agbno, 0, &bp,
                        XFS_ALLOC_BTREE_REF)))
                  return error;
            lev--;
            xfs_btree_setbuf(cur, lev, bp);
            block = XFS_BUF_TO_ALLOC_BLOCK(bp);
            if ((error = xfs_btree_check_sblock(cur, block, lev, bp)))
                  return error;
            cur->bc_ptrs[lev] = be16_to_cpu(block->bb_numrecs);
      }
      *stat = 1;
      return 0;
}

/*
 * 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_alloc_delete(
      xfs_btree_cur_t   *cur,       /* btree cursor */
      int         *stat)            /* success/failure */
{
      int         error;            /* error return value */
      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_alloc_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_alloc_decrement(cur, level, &i)))
                              return error;
                        break;
                  }
            }
      }
      *stat = i;
      return 0;
}

/*
 * Get the data from the pointed-to record.
 */
int                           /* error */
xfs_alloc_get_rec(
      xfs_btree_cur_t         *cur, /* btree cursor */
      xfs_agblock_t           *bno, /* output: starting block of extent */
      xfs_extlen_t            *len, /* output: length of extent */
      int               *stat)      /* output: success/failure */
{
      xfs_alloc_block_t *block;     /* btree block */
#ifdef DEBUG
      int               error;      /* error return value */
#endif
      int               ptr;  /* record number */

      ptr = cur->bc_ptrs[0];
      block = XFS_BUF_TO_ALLOC_BLOCK(cur->bc_bufs[0]);
#ifdef DEBUG
      if ((error = xfs_btree_check_sblock(cur, block, 0, cur->bc_bufs[0])))
            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.
       */
      {
            xfs_alloc_rec_t         *rec; /* record data */

            rec = XFS_ALLOC_REC_ADDR(block, ptr, cur);
            *bno = be32_to_cpu(rec->ar_startblock);
            *len = be32_to_cpu(rec->ar_blockcount);
      }
      *stat = 1;
      return 0;
}

/*
 * Increment cursor by one record at the level.
 * For nonzero levels the leaf-ward information is untouched.
 */
int                           /* error */
xfs_alloc_increment(
      xfs_btree_cur_t         *cur, /* btree cursor */
      int               level,      /* level in btree, 0 is leaf */
      int               *stat)      /* success/failure */
{
      xfs_alloc_block_t *block;     /* btree block */
      xfs_buf_t         *bp;  /* tree block buffer */
      int               error;      /* error return value */
      int               lev;  /* btree level */

      ASSERT(level < cur->bc_nlevels);
      /*
       * Read-ahead to the right at this level.
       */
      xfs_btree_readahead(cur, level, XFS_BTCUR_RIGHTRA);
      /*
       * Get a pointer to the btree block.
       */
      bp = cur->bc_bufs[level];
      block = XFS_BUF_TO_ALLOC_BLOCK(bp);
#ifdef DEBUG
      if ((error = xfs_btree_check_sblock(cur, block, level, bp)))
            return error;
#endif
      /*
       * Increment the ptr at this level.  If we're still in the block
       * then we're done.
       */
      if (++cur->bc_ptrs[level] <= be16_to_cpu(block->bb_numrecs)) {
            *stat = 1;
            return 0;
      }
      /*
       * If we just went off the right edge of the tree, return failure.
       */
      if (be32_to_cpu(block->bb_rightsib) == NULLAGBLOCK) {
            *stat = 0;
            return 0;
      }
      /*
       * March up the tree incrementing pointers.
       * Stop when we don't go off the right edge of a block.
       */
      for (lev = level + 1; lev < cur->bc_nlevels; lev++) {
            bp = cur->bc_bufs[lev];
            block = XFS_BUF_TO_ALLOC_BLOCK(bp);
#ifdef DEBUG
            if ((error = xfs_btree_check_sblock(cur, block, lev, bp)))
                  return error;
#endif
            if (++cur->bc_ptrs[lev] <= be16_to_cpu(block->bb_numrecs))
                  break;
            /*
             * Read-ahead the right block, we're going to read it
             * in the next loop.
             */
            xfs_btree_readahead(cur, lev, XFS_BTCUR_RIGHTRA);
      }
      /*
       * If we went off the root then we are seriously confused.
       */
      ASSERT(lev < cur->bc_nlevels);
      /*
       * Now walk back down the tree, fixing up the cursor's buffer
       * pointers and key numbers.
       */
      for (bp = cur->bc_bufs[lev], block = XFS_BUF_TO_ALLOC_BLOCK(bp);
           lev > level; ) {
            xfs_agblock_t     agbno;      /* block number of btree block */

            agbno = be32_to_cpu(*XFS_ALLOC_PTR_ADDR(block, cur->bc_ptrs[lev], cur));
            if ((error = xfs_btree_read_bufs(cur->bc_mp, cur->bc_tp,
                        cur->bc_private.a.agno, agbno, 0, &bp,
                        XFS_ALLOC_BTREE_REF)))
                  return error;
            lev--;
            xfs_btree_setbuf(cur, lev, bp);
            block = XFS_BUF_TO_ALLOC_BLOCK(bp);
            if ((error = xfs_btree_check_sblock(cur, block, lev, bp)))
                  return error;
            cur->bc_ptrs[lev] = 1;
      }
      *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_alloc_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_alloc_rec_t   nrec;       /* record being inserted this level */
      xfs_btree_cur_t   *pcur;            /* previous level's cursor */

      level = 0;
      nbno = NULLAGBLOCK;
      nrec.ar_startblock = cpu_to_be32(cur->bc_rec.a.ar_startblock);
      nrec.ar_blockcount = cpu_to_be32(cur->bc_rec.a.ar_blockcount);
      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_alloc_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;
}

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

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

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

/*
 * Update the record referred to by cur, to the value given by [bno, len].
 * This either works (return 0) or gets an EFSCORRUPTED error.
 */
int                           /* error */
xfs_alloc_update(
      xfs_btree_cur_t         *cur, /* btree cursor */
      xfs_agblock_t           bno,  /* starting block of extent */
      xfs_extlen_t            len)  /* length of extent */
{
      xfs_alloc_block_t *block;     /* btree block to update */
      int               error;      /* error return value */
      int               ptr;  /* current record number (updating) */

      ASSERT(len > 0);
      /*
       * Pick up the a.g. freelist struct and the current block.
       */
      block = XFS_BUF_TO_ALLOC_BLOCK(cur->bc_bufs[0]);
#ifdef DEBUG
      if ((error = xfs_btree_check_sblock(cur, block, 0, cur->bc_bufs[0])))
            return error;
#endif
      /*
       * Get the address of the rec to be updated.
       */
      ptr = cur->bc_ptrs[0];
      {
            xfs_alloc_rec_t         *rp;  /* pointer to updated record */

            rp = XFS_ALLOC_REC_ADDR(block, ptr, cur);
            /*
             * Fill in the new contents and log them.
             */
            rp->ar_startblock = cpu_to_be32(bno);
            rp->ar_blockcount = cpu_to_be32(len);
            xfs_alloc_log_recs(cur, cur->bc_bufs[0], ptr, ptr);
      }
      /*
       * If it's the by-size btree and it's the last leaf block and
       * it's the last record... then update the size of the longest
       * extent in the a.g., which we cache in the a.g. freelist header.
       */
      if (cur->bc_btnum == XFS_BTNUM_CNT &&
          be32_to_cpu(block->bb_rightsib) == NULLAGBLOCK &&
          ptr == be16_to_cpu(block->bb_numrecs)) {
            xfs_agf_t   *agf; /* a.g. freespace header */
            xfs_agnumber_t    seqno;

            agf = XFS_BUF_TO_AGF(cur->bc_private.a.agbp);
            seqno = be32_to_cpu(agf->agf_seqno);
            cur->bc_mp->m_perag[seqno].pagf_longest = len;
            agf->agf_longest = cpu_to_be32(len);
            xfs_alloc_log_agf(cur->bc_tp, cur->bc_private.a.agbp,
                  XFS_AGF_LONGEST);
      }
      /*
       * Updating first record in leaf. Pass new key value up to our parent.
       */
      if (ptr == 1) {
            xfs_alloc_key_t   key;  /* key containing [bno, len] */

            key.ar_startblock = cpu_to_be32(bno);
            key.ar_blockcount = cpu_to_be32(len);
            if ((error = xfs_alloc_updkey(cur, &key, 1)))
                  return error;
      }
      return 0;
}

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