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jfs_dmap.c

/*
 *   Copyright (C) International Business Machines Corp., 2000-2004
 *
 *   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; either version 2 of the License, or 
 *   (at your option) any later version.
 * 
 *   This program is distributed in the hope that it will 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 to the Free Software 
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include <linux/fs.h>
#include "jfs_incore.h"
#include "jfs_superblock.h"
#include "jfs_dmap.h"
#include "jfs_imap.h"
#include "jfs_lock.h"
#include "jfs_metapage.h"
#include "jfs_debug.h"

/*
 *    SERIALIZATION of the Block Allocation Map.
 *
 *    the working state of the block allocation map is accessed in
 *    two directions:
 *    
 *    1) allocation and free requests that start at the dmap
 *       level and move up through the dmap control pages (i.e.
 *       the vast majority of requests).
 * 
 *    2) allocation requests that start at dmap control page
 *       level and work down towards the dmaps.
 *    
 *    the serialization scheme used here is as follows. 
 *
 *    requests which start at the bottom are serialized against each 
 *    other through buffers and each requests holds onto its buffers 
 *    as it works it way up from a single dmap to the required level 
 *    of dmap control page.
 *    requests that start at the top are serialized against each other
 *    and request that start from the bottom by the multiple read/single
 *    write inode lock of the bmap inode. requests starting at the top
 *    take this lock in write mode while request starting at the bottom
 *    take the lock in read mode.  a single top-down request may proceed
 *    exclusively while multiple bottoms-up requests may proceed 
 *    simultaneously (under the protection of busy buffers).
 *    
 *    in addition to information found in dmaps and dmap control pages,
 *    the working state of the block allocation map also includes read/
 *    write information maintained in the bmap descriptor (i.e. total
 *    free block count, allocation group level free block counts).
 *    a single exclusive lock (BMAP_LOCK) is used to guard this information
 *    in the face of multiple-bottoms up requests.
 *    (lock ordering: IREAD_LOCK, BMAP_LOCK);
 *    
 *    accesses to the persistent state of the block allocation map (limited
 *    to the persistent bitmaps in dmaps) is guarded by (busy) buffers.
 */

#define BMAP_LOCK_INIT(bmp)   mutex_init(&bmp->db_bmaplock)
#define BMAP_LOCK(bmp)        mutex_lock(&bmp->db_bmaplock)
#define BMAP_UNLOCK(bmp)      mutex_unlock(&bmp->db_bmaplock)

/*
 * forward references
 */
static void dbAllocBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
                  int nblocks);
static void dbSplit(dmtree_t * tp, int leafno, int splitsz, int newval);
static int dbBackSplit(dmtree_t * tp, int leafno);
static int dbJoin(dmtree_t * tp, int leafno, int newval);
static void dbAdjTree(dmtree_t * tp, int leafno, int newval);
static int dbAdjCtl(struct bmap * bmp, s64 blkno, int newval, int alloc,
                int level);
static int dbAllocAny(struct bmap * bmp, s64 nblocks, int l2nb, s64 * results);
static int dbAllocNext(struct bmap * bmp, struct dmap * dp, s64 blkno,
                   int nblocks);
static int dbAllocNear(struct bmap * bmp, struct dmap * dp, s64 blkno,
                   int nblocks,
                   int l2nb, s64 * results);
static int dbAllocDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
                   int nblocks);
static int dbAllocDmapLev(struct bmap * bmp, struct dmap * dp, int nblocks,
                    int l2nb,
                    s64 * results);
static int dbAllocAG(struct bmap * bmp, int agno, s64 nblocks, int l2nb,
                 s64 * results);
static int dbAllocCtl(struct bmap * bmp, s64 nblocks, int l2nb, s64 blkno,
                  s64 * results);
static int dbExtend(struct inode *ip, s64 blkno, s64 nblocks, s64 addnblocks);
static int dbFindBits(u32 word, int l2nb);
static int dbFindCtl(struct bmap * bmp, int l2nb, int level, s64 * blkno);
static int dbFindLeaf(dmtree_t * tp, int l2nb, int *leafidx);
static int dbFreeBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
                  int nblocks);
static int dbFreeDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
                  int nblocks);
static int dbMaxBud(u8 * cp);
s64 dbMapFileSizeToMapSize(struct inode *ipbmap);
static int blkstol2(s64 nb);

static int cntlz(u32 value);
static int cnttz(u32 word);

static int dbAllocDmapBU(struct bmap * bmp, struct dmap * dp, s64 blkno,
                   int nblocks);
static int dbInitDmap(struct dmap * dp, s64 blkno, int nblocks);
static int dbInitDmapTree(struct dmap * dp);
static int dbInitTree(struct dmaptree * dtp);
static int dbInitDmapCtl(struct dmapctl * dcp, int level, int i);
static int dbGetL2AGSize(s64 nblocks);

/*
 *    buddy table
 *
 * table used for determining buddy sizes within characters of 
 * dmap bitmap words.  the characters themselves serve as indexes
 * into the table, with the table elements yielding the maximum
 * binary buddy of free bits within the character.
 */
static const s8 budtab[256] = {
      3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
      2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
      2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
      2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
      2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
      2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
      2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
      2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, -1
};


/*
 * NAME:          dbMount()
 *
 * FUNCTION:      initializate the block allocation map.
 *
 *          memory is allocated for the in-core bmap descriptor and
 *          the in-core descriptor is initialized from disk.
 *
 * PARAMETERS:
 *      ipbmap    -  pointer to in-core inode for the block map.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOMEM   - insufficient memory
 *      -EIO      - i/o error
 */
int dbMount(struct inode *ipbmap)
{
      struct bmap *bmp;
      struct dbmap_disk *dbmp_le;
      struct metapage *mp;
      int i;

      /*
       * allocate/initialize the in-memory bmap descriptor
       */
      /* allocate memory for the in-memory bmap descriptor */
      bmp = kmalloc(sizeof(struct bmap), GFP_KERNEL);
      if (bmp == NULL)
            return -ENOMEM;

      /* read the on-disk bmap descriptor. */
      mp = read_metapage(ipbmap,
                     BMAPBLKNO << JFS_SBI(ipbmap->i_sb)->l2nbperpage,
                     PSIZE, 0);
      if (mp == NULL) {
            kfree(bmp);
            return -EIO;
      }

      /* copy the on-disk bmap descriptor to its in-memory version. */
      dbmp_le = (struct dbmap_disk *) mp->data;
      bmp->db_mapsize = le64_to_cpu(dbmp_le->dn_mapsize);
      bmp->db_nfree = le64_to_cpu(dbmp_le->dn_nfree);
      bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
      bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
      bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
      bmp->db_maxag = le32_to_cpu(dbmp_le->dn_maxag);
      bmp->db_agpref = le32_to_cpu(dbmp_le->dn_agpref);
      bmp->db_aglevel = le32_to_cpu(dbmp_le->dn_aglevel);
      bmp->db_agheigth = le32_to_cpu(dbmp_le->dn_agheigth);
      bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);
      bmp->db_agstart = le32_to_cpu(dbmp_le->dn_agstart);
      bmp->db_agl2size = le32_to_cpu(dbmp_le->dn_agl2size);
      for (i = 0; i < MAXAG; i++)
            bmp->db_agfree[i] = le64_to_cpu(dbmp_le->dn_agfree[i]);
      bmp->db_agsize = le64_to_cpu(dbmp_le->dn_agsize);
      bmp->db_maxfreebud = dbmp_le->dn_maxfreebud;

      /* release the buffer. */
      release_metapage(mp);

      /* bind the bmap inode and the bmap descriptor to each other. */
      bmp->db_ipbmap = ipbmap;
      JFS_SBI(ipbmap->i_sb)->bmap = bmp;

      memset(bmp->db_active, 0, sizeof(bmp->db_active));

      /*
       * allocate/initialize the bmap lock
       */
      BMAP_LOCK_INIT(bmp);

      return (0);
}


/*
 * NAME:          dbUnmount()
 *
 * FUNCTION:      terminate the block allocation map in preparation for
 *          file system unmount.
 *
 *          the in-core bmap descriptor is written to disk and
 *          the memory for this descriptor is freed.
 *
 * PARAMETERS:
 *      ipbmap    -  pointer to in-core inode for the block map.
 *
 * RETURN VALUES:
 *      0   - success
 *      -EIO      - i/o error
 */
int dbUnmount(struct inode *ipbmap, int mounterror)
{
      struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;

      if (!(mounterror || isReadOnly(ipbmap)))
            dbSync(ipbmap);

      /*
       * Invalidate the page cache buffers
       */
      truncate_inode_pages(ipbmap->i_mapping, 0);

      /* free the memory for the in-memory bmap. */
      kfree(bmp);

      return (0);
}

/*
 *    dbSync()
 */
int dbSync(struct inode *ipbmap)
{
      struct dbmap_disk *dbmp_le;
      struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;
      struct metapage *mp;
      int i;

      /*
       * write bmap global control page
       */
      /* get the buffer for the on-disk bmap descriptor. */
      mp = read_metapage(ipbmap,
                     BMAPBLKNO << JFS_SBI(ipbmap->i_sb)->l2nbperpage,
                     PSIZE, 0);
      if (mp == NULL) {
            jfs_err("dbSync: read_metapage failed!");
            return -EIO;
      }
      /* copy the in-memory version of the bmap to the on-disk version */
      dbmp_le = (struct dbmap_disk *) mp->data;
      dbmp_le->dn_mapsize = cpu_to_le64(bmp->db_mapsize);
      dbmp_le->dn_nfree = cpu_to_le64(bmp->db_nfree);
      dbmp_le->dn_l2nbperpage = cpu_to_le32(bmp->db_l2nbperpage);
      dbmp_le->dn_numag = cpu_to_le32(bmp->db_numag);
      dbmp_le->dn_maxlevel = cpu_to_le32(bmp->db_maxlevel);
      dbmp_le->dn_maxag = cpu_to_le32(bmp->db_maxag);
      dbmp_le->dn_agpref = cpu_to_le32(bmp->db_agpref);
      dbmp_le->dn_aglevel = cpu_to_le32(bmp->db_aglevel);
      dbmp_le->dn_agheigth = cpu_to_le32(bmp->db_agheigth);
      dbmp_le->dn_agwidth = cpu_to_le32(bmp->db_agwidth);
      dbmp_le->dn_agstart = cpu_to_le32(bmp->db_agstart);
      dbmp_le->dn_agl2size = cpu_to_le32(bmp->db_agl2size);
      for (i = 0; i < MAXAG; i++)
            dbmp_le->dn_agfree[i] = cpu_to_le64(bmp->db_agfree[i]);
      dbmp_le->dn_agsize = cpu_to_le64(bmp->db_agsize);
      dbmp_le->dn_maxfreebud = bmp->db_maxfreebud;

      /* write the buffer */
      write_metapage(mp);

      /*
       * write out dirty pages of bmap
       */
      filemap_write_and_wait(ipbmap->i_mapping);

      diWriteSpecial(ipbmap, 0);

      return (0);
}


/*
 * NAME:          dbFree()
 *
 * FUNCTION:      free the specified block range from the working block
 *          allocation map.
 *
 *          the blocks will be free from the working map one dmap
 *          at a time.
 *
 * PARAMETERS:
 *      ip  -  pointer to in-core inode;
 *      blkno     -  starting block number to be freed.
 *      nblocks   -  number of blocks to be freed.
 *
 * RETURN VALUES:
 *      0   - success
 *      -EIO      - i/o error
 */
int dbFree(struct inode *ip, s64 blkno, s64 nblocks)
{
      struct metapage *mp;
      struct dmap *dp;
      int nb, rc;
      s64 lblkno, rem;
      struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
      struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;

      IREAD_LOCK(ipbmap);

      /* block to be freed better be within the mapsize. */
      if (unlikely((blkno == 0) || (blkno + nblocks > bmp->db_mapsize))) {
            IREAD_UNLOCK(ipbmap);
            printk(KERN_ERR "blkno = %Lx, nblocks = %Lx\n",
                   (unsigned long long) blkno,
                   (unsigned long long) nblocks);
            jfs_error(ip->i_sb,
                    "dbFree: block to be freed is outside the map");
            return -EIO;
      }

      /*
       * free the blocks a dmap at a time.
       */
      mp = NULL;
      for (rem = nblocks; rem > 0; rem -= nb, blkno += nb) {
            /* release previous dmap if any */
            if (mp) {
                  write_metapage(mp);
            }

            /* get the buffer for the current dmap. */
            lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
            mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
            if (mp == NULL) {
                  IREAD_UNLOCK(ipbmap);
                  return -EIO;
            }
            dp = (struct dmap *) mp->data;

            /* determine the number of blocks to be freed from
             * this dmap.
             */
            nb = min(rem, BPERDMAP - (blkno & (BPERDMAP - 1)));

            /* free the blocks. */
            if ((rc = dbFreeDmap(bmp, dp, blkno, nb))) {
                  jfs_error(ip->i_sb, "dbFree: error in block map\n");
                  release_metapage(mp);
                  IREAD_UNLOCK(ipbmap);
                  return (rc);
            }
      }

      /* write the last buffer. */
      write_metapage(mp);

      IREAD_UNLOCK(ipbmap);

      return (0);
}


/*
 * NAME:    dbUpdatePMap()
 *
 * FUNCTION:    update the allocation state (free or allocate) of the
 *          specified block range in the persistent block allocation map.
 *          
 *          the blocks will be updated in the persistent map one
 *          dmap at a time.
 *
 * PARAMETERS:
 *      ipbmap    -  pointer to in-core inode for the block map.
 *      free      - TRUE if block range is to be freed from the persistent
 *            map; FALSE if it is to   be allocated.
 *      blkno     -  starting block number of the range.
 *      nblocks   -  number of contiguous blocks in the range.
 *      tblk      -  transaction block;
 *
 * RETURN VALUES:
 *      0   - success
 *      -EIO      - i/o error
 */
int
dbUpdatePMap(struct inode *ipbmap,
           int free, s64 blkno, s64 nblocks, struct tblock * tblk)
{
      int nblks, dbitno, wbitno, rbits;
      int word, nbits, nwords;
      struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;
      s64 lblkno, rem, lastlblkno;
      u32 mask;
      struct dmap *dp;
      struct metapage *mp;
      struct jfs_log *log;
      int lsn, difft, diffp;
      unsigned long flags;

      /* the blocks better be within the mapsize. */
      if (blkno + nblocks > bmp->db_mapsize) {
            printk(KERN_ERR "blkno = %Lx, nblocks = %Lx\n",
                   (unsigned long long) blkno,
                   (unsigned long long) nblocks);
            jfs_error(ipbmap->i_sb,
                    "dbUpdatePMap: blocks are outside the map");
            return -EIO;
      }

      /* compute delta of transaction lsn from log syncpt */
      lsn = tblk->lsn;
      log = (struct jfs_log *) JFS_SBI(tblk->sb)->log;
      logdiff(difft, lsn, log);

      /*
       * update the block state a dmap at a time.
       */
      mp = NULL;
      lastlblkno = 0;
      for (rem = nblocks; rem > 0; rem -= nblks, blkno += nblks) {
            /* get the buffer for the current dmap. */
            lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
            if (lblkno != lastlblkno) {
                  if (mp) {
                        write_metapage(mp);
                  }

                  mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE,
                                 0);
                  if (mp == NULL)
                        return -EIO;
                  metapage_wait_for_io(mp);
            }
            dp = (struct dmap *) mp->data;

            /* determine the bit number and word within the dmap of
             * the starting block.  also determine how many blocks
             * are to be updated within this dmap.
             */
            dbitno = blkno & (BPERDMAP - 1);
            word = dbitno >> L2DBWORD;
            nblks = min(rem, (s64)BPERDMAP - dbitno);

            /* update the bits of the dmap words. the first and last
             * words may only have a subset of their bits updated. if
             * this is the case, we'll work against that word (i.e.
             * partial first and/or last) only in a single pass.  a 
             * single pass will also be used to update all words that
             * are to have all their bits updated.
             */
            for (rbits = nblks; rbits > 0;
                 rbits -= nbits, dbitno += nbits) {
                  /* determine the bit number within the word and
                   * the number of bits within the word.
                   */
                  wbitno = dbitno & (DBWORD - 1);
                  nbits = min(rbits, DBWORD - wbitno);

                  /* check if only part of the word is to be updated. */
                  if (nbits < DBWORD) {
                        /* update (free or allocate) the bits
                         * in this word.
                         */
                        mask =
                            (ONES << (DBWORD - nbits) >> wbitno);
                        if (free)
                              dp->pmap[word] &=
                                  cpu_to_le32(~mask);
                        else
                              dp->pmap[word] |=
                                  cpu_to_le32(mask);

                        word += 1;
                  } else {
                        /* one or more words are to have all
                         * their bits updated.  determine how
                         * many words and how many bits.
                         */
                        nwords = rbits >> L2DBWORD;
                        nbits = nwords << L2DBWORD;

                        /* update (free or allocate) the bits
                         * in these words.
                         */
                        if (free)
                              memset(&dp->pmap[word], 0,
                                     nwords * 4);
                        else
                              memset(&dp->pmap[word], (int) ONES,
                                     nwords * 4);

                        word += nwords;
                  }
            }

            /*
             * update dmap lsn
             */
            if (lblkno == lastlblkno)
                  continue;

            lastlblkno = lblkno;

            LOGSYNC_LOCK(log, flags);
            if (mp->lsn != 0) {
                  /* inherit older/smaller lsn */
                  logdiff(diffp, mp->lsn, log);
                  if (difft < diffp) {
                        mp->lsn = lsn;

                        /* move bp after tblock in logsync list */
                        list_move(&mp->synclist, &tblk->synclist);
                  }

                  /* inherit younger/larger clsn */
                  logdiff(difft, tblk->clsn, log);
                  logdiff(diffp, mp->clsn, log);
                  if (difft > diffp)
                        mp->clsn = tblk->clsn;
            } else {
                  mp->log = log;
                  mp->lsn = lsn;

                  /* insert bp after tblock in logsync list */
                  log->count++;
                  list_add(&mp->synclist, &tblk->synclist);

                  mp->clsn = tblk->clsn;
            }
            LOGSYNC_UNLOCK(log, flags);
      }

      /* write the last buffer. */
      if (mp) {
            write_metapage(mp);
      }

      return (0);
}


/*
 * NAME:    dbNextAG()
 *
 * FUNCTION:    find the preferred allocation group for new allocations.
 *
 *          Within the allocation groups, we maintain a preferred
 *          allocation group which consists of a group with at least
 *          average free space.  It is the preferred group that we target
 *          new inode allocation towards.  The tie-in between inode
 *          allocation and block allocation occurs as we allocate the
 *          first (data) block of an inode and specify the inode (block)
 *          as the allocation hint for this block.
 *
 *          We try to avoid having more than one open file growing in
 *          an allocation group, as this will lead to fragmentation.
 *          This differs from the old OS/2 method of trying to keep
 *          empty ags around for large allocations.
 *
 * PARAMETERS:
 *      ipbmap    -  pointer to in-core inode for the block map.
 *
 * RETURN VALUES:
 *      the preferred allocation group number.
 */
int dbNextAG(struct inode *ipbmap)
{
      s64 avgfree;
      int agpref;
      s64 hwm = 0;
      int i;
      int next_best = -1;
      struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;

      BMAP_LOCK(bmp);

      /* determine the average number of free blocks within the ags. */
      avgfree = (u32)bmp->db_nfree / bmp->db_numag;

      /*
       * if the current preferred ag does not have an active allocator
       * and has at least average freespace, return it
       */
      agpref = bmp->db_agpref;
      if ((atomic_read(&bmp->db_active[agpref]) == 0) &&
          (bmp->db_agfree[agpref] >= avgfree))
            goto unlock;

      /* From the last preferred ag, find the next one with at least
       * average free space.
       */
      for (i = 0 ; i < bmp->db_numag; i++, agpref++) {
            if (agpref == bmp->db_numag)
                  agpref = 0;

            if (atomic_read(&bmp->db_active[agpref]))
                  /* open file is currently growing in this ag */
                  continue;
            if (bmp->db_agfree[agpref] >= avgfree) {
                  /* Return this one */
                  bmp->db_agpref = agpref;
                  goto unlock;
            } else if (bmp->db_agfree[agpref] > hwm) {
                  /* Less than avg. freespace, but best so far */
                  hwm = bmp->db_agfree[agpref];
                  next_best = agpref;
            }
      }

      /*
       * If no inactive ag was found with average freespace, use the
       * next best
       */
      if (next_best != -1)
            bmp->db_agpref = next_best;
      /* else leave db_agpref unchanged */
unlock:
      BMAP_UNLOCK(bmp);

      /* return the preferred group.
       */
      return (bmp->db_agpref);
}

/*
 * NAME:    dbAlloc()
 *
 * FUNCTION:    attempt to allocate a specified number of contiguous free
 *          blocks from the working allocation block map.
 *
 *          the block allocation policy uses hints and a multi-step
 *          approach.
 *
 *          for allocation requests smaller than the number of blocks
 *          per dmap, we first try to allocate the new blocks
 *          immediately following the hint.  if these blocks are not
 *          available, we try to allocate blocks near the hint.  if
 *          no blocks near the hint are available, we next try to 
 *          allocate within the same dmap as contains the hint.
 *
 *          if no blocks are available in the dmap or the allocation
 *          request is larger than the dmap size, we try to allocate
 *          within the same allocation group as contains the hint. if
 *          this does not succeed, we finally try to allocate anywhere
 *          within the aggregate.
 *
 *          we also try to allocate anywhere within the aggregate for
 *          for allocation requests larger than the allocation group
 *          size or requests that specify no hint value.
 *
 * PARAMETERS:
 *      ip  -  pointer to in-core inode;
 *      hint      - allocation hint.
 *      nblocks   - number of contiguous blocks in the range.
 *      results   - on successful return, set to the starting block number
 *            of the newly allocated contiguous range.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 */
int dbAlloc(struct inode *ip, s64 hint, s64 nblocks, s64 * results)
{
      int rc, agno;
      struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
      struct bmap *bmp;
      struct metapage *mp;
      s64 lblkno, blkno;
      struct dmap *dp;
      int l2nb;
      s64 mapSize;
      int writers;

      /* assert that nblocks is valid */
      assert(nblocks > 0);

#ifdef _STILL_TO_PORT
      /* DASD limit check                                     F226941 */
      if (OVER_LIMIT(ip, nblocks))
            return -ENOSPC;
#endif                        /* _STILL_TO_PORT */

      /* get the log2 number of blocks to be allocated.
       * if the number of blocks is not a log2 multiple, 
       * it will be rounded up to the next log2 multiple.
       */
      l2nb = BLKSTOL2(nblocks);

      bmp = JFS_SBI(ip->i_sb)->bmap;

//retry:        /* serialize w.r.t.extendfs() */
      mapSize = bmp->db_mapsize;

      /* the hint should be within the map */
      if (hint >= mapSize) {
            jfs_error(ip->i_sb, "dbAlloc: the hint is outside the map");
            return -EIO;
      }

      /* if the number of blocks to be allocated is greater than the
       * allocation group size, try to allocate anywhere.
       */
      if (l2nb > bmp->db_agl2size) {
            IWRITE_LOCK(ipbmap);

            rc = dbAllocAny(bmp, nblocks, l2nb, results);

            goto write_unlock;
      }

      /*
       * If no hint, let dbNextAG recommend an allocation group
       */
      if (hint == 0)
            goto pref_ag;

      /* we would like to allocate close to the hint.  adjust the
       * hint to the block following the hint since the allocators
       * will start looking for free space starting at this point.
       */
      blkno = hint + 1;

      if (blkno >= bmp->db_mapsize)
            goto pref_ag;

      agno = blkno >> bmp->db_agl2size;

      /* check if blkno crosses over into a new allocation group.
       * if so, check if we should allow allocations within this
       * allocation group.
       */
      if ((blkno & (bmp->db_agsize - 1)) == 0)
            /* check if the AG is currenly being written to.
             * if so, call dbNextAG() to find a non-busy
             * AG with sufficient free space.
             */
            if (atomic_read(&bmp->db_active[agno]))
                  goto pref_ag;

      /* check if the allocation request size can be satisfied from a
       * single dmap.  if so, try to allocate from the dmap containing
       * the hint using a tiered strategy.
       */
      if (nblocks <= BPERDMAP) {
            IREAD_LOCK(ipbmap);

            /* get the buffer for the dmap containing the hint.
             */
            rc = -EIO;
            lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
            mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
            if (mp == NULL)
                  goto read_unlock;

            dp = (struct dmap *) mp->data;

            /* first, try to satisfy the allocation request with the
             * blocks beginning at the hint.
             */
            if ((rc = dbAllocNext(bmp, dp, blkno, (int) nblocks))
                != -ENOSPC) {
                  if (rc == 0) {
                        *results = blkno;
                        mark_metapage_dirty(mp);
                  }

                  release_metapage(mp);
                  goto read_unlock;
            }

            writers = atomic_read(&bmp->db_active[agno]);
            if ((writers > 1) ||
                ((writers == 1) && (JFS_IP(ip)->active_ag != agno))) {
                  /*
                   * Someone else is writing in this allocation
                   * group.  To avoid fragmenting, try another ag
                   */
                  release_metapage(mp);
                  IREAD_UNLOCK(ipbmap);
                  goto pref_ag;
            }

            /* next, try to satisfy the allocation request with blocks
             * near the hint.
             */
            if ((rc =
                 dbAllocNear(bmp, dp, blkno, (int) nblocks, l2nb, results))
                != -ENOSPC) {
                  if (rc == 0)
                        mark_metapage_dirty(mp);

                  release_metapage(mp);
                  goto read_unlock;
            }

            /* try to satisfy the allocation request with blocks within
             * the same dmap as the hint.
             */
            if ((rc = dbAllocDmapLev(bmp, dp, (int) nblocks, l2nb, results))
                != -ENOSPC) {
                  if (rc == 0)
                        mark_metapage_dirty(mp);

                  release_metapage(mp);
                  goto read_unlock;
            }

            release_metapage(mp);
            IREAD_UNLOCK(ipbmap);
      }

      /* try to satisfy the allocation request with blocks within
       * the same allocation group as the hint.
       */
      IWRITE_LOCK(ipbmap);
      if ((rc = dbAllocAG(bmp, agno, nblocks, l2nb, results)) != -ENOSPC)
            goto write_unlock;

      IWRITE_UNLOCK(ipbmap);


      pref_ag:
      /*
       * Let dbNextAG recommend a preferred allocation group
       */
      agno = dbNextAG(ipbmap);
      IWRITE_LOCK(ipbmap);

      /* Try to allocate within this allocation group.  if that fails, try to
       * allocate anywhere in the map.
       */
      if ((rc = dbAllocAG(bmp, agno, nblocks, l2nb, results)) == -ENOSPC)
            rc = dbAllocAny(bmp, nblocks, l2nb, results);

      write_unlock:
      IWRITE_UNLOCK(ipbmap);

      return (rc);

      read_unlock:
      IREAD_UNLOCK(ipbmap);

      return (rc);
}

#ifdef _NOTYET
/*
 * NAME:    dbAllocExact()
 *
 * FUNCTION:    try to allocate the requested extent;
 *
 * PARAMETERS:
 *      ip  - pointer to in-core inode;
 *      blkno     - extent address;
 *      nblocks   - extent length;
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 */
int dbAllocExact(struct inode *ip, s64 blkno, int nblocks)
{
      int rc;
      struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
      struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;
      struct dmap *dp;
      s64 lblkno;
      struct metapage *mp;

      IREAD_LOCK(ipbmap);

      /*
       * validate extent request:
       *
       * note: defragfs policy:
       *  max 64 blocks will be moved.  
       *  allocation request size must be satisfied from a single dmap.
       */
      if (nblocks <= 0 || nblocks > BPERDMAP || blkno >= bmp->db_mapsize) {
            IREAD_UNLOCK(ipbmap);
            return -EINVAL;
      }

      if (nblocks > ((s64) 1 << bmp->db_maxfreebud)) {
            /* the free space is no longer available */
            IREAD_UNLOCK(ipbmap);
            return -ENOSPC;
      }

      /* read in the dmap covering the extent */
      lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
      mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
      if (mp == NULL) {
            IREAD_UNLOCK(ipbmap);
            return -EIO;
      }
      dp = (struct dmap *) mp->data;

      /* try to allocate the requested extent */
      rc = dbAllocNext(bmp, dp, blkno, nblocks);

      IREAD_UNLOCK(ipbmap);

      if (rc == 0)
            mark_metapage_dirty(mp);

      release_metapage(mp);

      return (rc);
}
#endif /* _NOTYET */

/*
 * NAME:    dbReAlloc()
 *
 * FUNCTION:    attempt to extend a current allocation by a specified
 *          number of blocks.
 *
 *          this routine attempts to satisfy the allocation request
 *          by first trying to extend the existing allocation in
 *          place by allocating the additional blocks as the blocks
 *          immediately following the current allocation.  if these
 *          blocks are not available, this routine will attempt to
 *          allocate a new set of contiguous blocks large enough
 *          to cover the existing allocation plus the additional
 *          number of blocks required.
 *
 * PARAMETERS:
 *      ip      -  pointer to in-core inode requiring allocation.
 *      blkno         -  starting block of the current allocation.
 *      nblocks       -  number of contiguous blocks within the current
 *                 allocation.
 *      addnblocks  -  number of blocks to add to the allocation.
 *      results   -      on successful return, set to the starting block number
 *                 of the existing allocation if the existing allocation
 *                 was extended in place or to a newly allocated contiguous
 *                 range if the existing allocation could not be extended
 *                 in place.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 */
int
dbReAlloc(struct inode *ip,
        s64 blkno, s64 nblocks, s64 addnblocks, s64 * results)
{
      int rc;

      /* try to extend the allocation in place.
       */
      if ((rc = dbExtend(ip, blkno, nblocks, addnblocks)) == 0) {
            *results = blkno;
            return (0);
      } else {
            if (rc != -ENOSPC)
                  return (rc);
      }

      /* could not extend the allocation in place, so allocate a
       * new set of blocks for the entire request (i.e. try to get
       * a range of contiguous blocks large enough to cover the
       * existing allocation plus the additional blocks.)
       */
      return (dbAlloc
            (ip, blkno + nblocks - 1, addnblocks + nblocks, results));
}


/*
 * NAME:    dbExtend()
 *
 * FUNCTION:    attempt to extend a current allocation by a specified
 *          number of blocks.
 *
 *          this routine attempts to satisfy the allocation request
 *          by first trying to extend the existing allocation in
 *          place by allocating the additional blocks as the blocks
 *          immediately following the current allocation.
 *
 * PARAMETERS:
 *      ip      -  pointer to in-core inode requiring allocation.
 *      blkno         -  starting block of the current allocation.
 *      nblocks       -  number of contiguous blocks within the current
 *                 allocation.
 *      addnblocks  -  number of blocks to add to the allocation.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 */
static int dbExtend(struct inode *ip, s64 blkno, s64 nblocks, s64 addnblocks)
{
      struct jfs_sb_info *sbi = JFS_SBI(ip->i_sb);
      s64 lblkno, lastblkno, extblkno;
      uint rel_block;
      struct metapage *mp;
      struct dmap *dp;
      int rc;
      struct inode *ipbmap = sbi->ipbmap;
      struct bmap *bmp;

      /*
       * We don't want a non-aligned extent to cross a page boundary
       */
      if (((rel_block = blkno & (sbi->nbperpage - 1))) &&
          (rel_block + nblocks + addnblocks > sbi->nbperpage))
            return -ENOSPC;

      /* get the last block of the current allocation */
      lastblkno = blkno + nblocks - 1;

      /* determine the block number of the block following
       * the existing allocation.
       */
      extblkno = lastblkno + 1;

      IREAD_LOCK(ipbmap);

      /* better be within the file system */
      bmp = sbi->bmap;
      if (lastblkno < 0 || lastblkno >= bmp->db_mapsize) {
            IREAD_UNLOCK(ipbmap);
            jfs_error(ip->i_sb,
                    "dbExtend: the block is outside the filesystem");
            return -EIO;
      }

      /* we'll attempt to extend the current allocation in place by
       * allocating the additional blocks as the blocks immediately
       * following the current allocation.  we only try to extend the
       * current allocation in place if the number of additional blocks
       * can fit into a dmap, the last block of the current allocation
       * is not the last block of the file system, and the start of the
       * inplace extension is not on an allocation group boundary.
       */
      if (addnblocks > BPERDMAP || extblkno >= bmp->db_mapsize ||
          (extblkno & (bmp->db_agsize - 1)) == 0) {
            IREAD_UNLOCK(ipbmap);
            return -ENOSPC;
      }

      /* get the buffer for the dmap containing the first block
       * of the extension.
       */
      lblkno = BLKTODMAP(extblkno, bmp->db_l2nbperpage);
      mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
      if (mp == NULL) {
            IREAD_UNLOCK(ipbmap);
            return -EIO;
      }

      dp = (struct dmap *) mp->data;

      /* try to allocate the blocks immediately following the
       * current allocation.
       */
      rc = dbAllocNext(bmp, dp, extblkno, (int) addnblocks);

      IREAD_UNLOCK(ipbmap);

      /* were we successful ? */
      if (rc == 0)
            write_metapage(mp);
      else
            /* we were not successful */
            release_metapage(mp);


      return (rc);
}


/*
 * NAME:    dbAllocNext()
 *
 * FUNCTION:    attempt to allocate the blocks of the specified block
 *          range within a dmap.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      dp  -  pointer to dmap.
 *      blkno     -  starting block number of the range.
 *      nblocks   -  number of contiguous free blocks of the range.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 *
 * serialization: IREAD_LOCK(ipbmap) held on entry/exit;
 */
static int dbAllocNext(struct bmap * bmp, struct dmap * dp, s64 blkno,
                   int nblocks)
{
      int dbitno, word, rembits, nb, nwords, wbitno, nw;
      int l2size;
      s8 *leaf;
      u32 mask;

      if (dp->tree.leafidx != cpu_to_le32(LEAFIND)) {
            jfs_error(bmp->db_ipbmap->i_sb,
                    "dbAllocNext: Corrupt dmap page");
            return -EIO;
      }

      /* pick up a pointer to the leaves of the dmap tree.
       */
      leaf = dp->tree.stree + le32_to_cpu(dp->tree.leafidx);

      /* determine the bit number and word within the dmap of the
       * starting block.
       */
      dbitno = blkno & (BPERDMAP - 1);
      word = dbitno >> L2DBWORD;

      /* check if the specified block range is contained within
       * this dmap.
       */
      if (dbitno + nblocks > BPERDMAP)
            return -ENOSPC;

      /* check if the starting leaf indicates that anything
       * is free.
       */
      if (leaf[word] == NOFREE)
            return -ENOSPC;

      /* check the dmaps words corresponding to block range to see
       * if the block range is free.  not all bits of the first and
       * last words may be contained within the block range.  if this
       * is the case, we'll work against those words (i.e. partial first
       * and/or last) on an individual basis (a single pass) and examine
       * the actual bits to determine if they are free.  a single pass
       * will be used for all dmap words fully contained within the
       * specified range.  within this pass, the leaves of the dmap
       * tree will be examined to determine if the blocks are free. a
       * single leaf may describe the free space of multiple dmap
       * words, so we may visit only a subset of the actual leaves
       * corresponding to the dmap words of the block range.
       */
      for (rembits = nblocks; rembits > 0; rembits -= nb, dbitno += nb) {
            /* determine the bit number within the word and
             * the number of bits within the word.
             */
            wbitno = dbitno & (DBWORD - 1);
            nb = min(rembits, DBWORD - wbitno);

            /* check if only part of the word is to be examined.
             */
            if (nb < DBWORD) {
                  /* check if the bits are free.
                   */
                  mask = (ONES << (DBWORD - nb) >> wbitno);
                  if ((mask & ~le32_to_cpu(dp->wmap[word])) != mask)
                        return -ENOSPC;

                  word += 1;
            } else {
                  /* one or more dmap words are fully contained
                   * within the block range.  determine how many
                   * words and how many bits.
                   */
                  nwords = rembits >> L2DBWORD;
                  nb = nwords << L2DBWORD;

                  /* now examine the appropriate leaves to determine
                   * if the blocks are free.
                   */
                  while (nwords > 0) {
                        /* does the leaf describe any free space ?
                         */
                        if (leaf[word] < BUDMIN)
                              return -ENOSPC;

                        /* determine the l2 number of bits provided
                         * by this leaf.
                         */
                        l2size =
                            min((int)leaf[word], NLSTOL2BSZ(nwords));

                        /* determine how many words were handled.
                         */
                        nw = BUDSIZE(l2size, BUDMIN);

                        nwords -= nw;
                        word += nw;
                  }
            }
      }

      /* allocate the blocks.
       */
      return (dbAllocDmap(bmp, dp, blkno, nblocks));
}


/*
 * NAME:    dbAllocNear()
 *
 * FUNCTION:    attempt to allocate a number of contiguous free blocks near
 *          a specified block (hint) within a dmap.
 *
 *          starting with the dmap leaf that covers the hint, we'll
 *          check the next four contiguous leaves for sufficient free
 *          space.  if sufficient free space is found, we'll allocate
 *          the desired free space.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      dp  -  pointer to dmap.
 *      blkno     -  block number to allocate near.
 *      nblocks   -  actual number of contiguous free blocks desired.
 *      l2nb      -  log2 number of contiguous free blocks desired.
 *      results   -  on successful return, set to the starting block number
 *             of the newly allocated range.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 *
 * serialization: IREAD_LOCK(ipbmap) held on entry/exit;
 */
static int
dbAllocNear(struct bmap * bmp,
          struct dmap * dp, s64 blkno, int nblocks, int l2nb, s64 * results)
{
      int word, lword, rc;
      s8 *leaf;

      if (dp->tree.leafidx != cpu_to_le32(LEAFIND)) {
            jfs_error(bmp->db_ipbmap->i_sb,
                    "dbAllocNear: Corrupt dmap page");
            return -EIO;
      }

      leaf = dp->tree.stree + le32_to_cpu(dp->tree.leafidx);

      /* determine the word within the dmap that holds the hint
       * (i.e. blkno).  also, determine the last word in the dmap
       * that we'll include in our examination.
       */
      word = (blkno & (BPERDMAP - 1)) >> L2DBWORD;
      lword = min(word + 4, LPERDMAP);

      /* examine the leaves for sufficient free space.
       */
      for (; word < lword; word++) {
            /* does the leaf describe sufficient free space ?
             */
            if (leaf[word] < l2nb)
                  continue;

            /* determine the block number within the file system
             * of the first block described by this dmap word.
             */
            blkno = le64_to_cpu(dp->start) + (word << L2DBWORD);

            /* if not all bits of the dmap word are free, get the
             * starting bit number within the dmap word of the required
             * string of free bits and adjust the block number with the
             * value.
             */
            if (leaf[word] < BUDMIN)
                  blkno +=
                      dbFindBits(le32_to_cpu(dp->wmap[word]), l2nb);

            /* allocate the blocks.
             */
            if ((rc = dbAllocDmap(bmp, dp, blkno, nblocks)) == 0)
                  *results = blkno;

            return (rc);
      }

      return -ENOSPC;
}


/*
 * NAME:    dbAllocAG()
 *
 * FUNCTION:    attempt to allocate the specified number of contiguous
 *          free blocks within the specified allocation group.
 *
 *          unless the allocation group size is equal to the number
 *          of blocks per dmap, the dmap control pages will be used to
 *          find the required free space, if available.  we start the
 *          search at the highest dmap control page level which
 *          distinctly describes the allocation group's free space
 *          (i.e. the highest level at which the allocation group's
 *          free space is not mixed in with that of any other group).
 *          in addition, we start the search within this level at a
 *          height of the dmapctl dmtree at which the nodes distinctly
 *          describe the allocation group's free space.  at this height,
 *          the allocation group's free space may be represented by 1
 *          or two sub-trees, depending on the allocation group size.
 *          we search the top nodes of these subtrees left to right for
 *          sufficient free space.  if sufficient free space is found,
 *          the subtree is searched to find the leftmost leaf that 
 *          has free space.  once we have made it to the leaf, we
 *          move the search to the next lower level dmap control page
 *          corresponding to this leaf.  we continue down the dmap control
 *          pages until we find the dmap that contains or starts the
 *          sufficient free space and we allocate at this dmap.
 *
 *          if the allocation group size is equal to the dmap size,
 *          we'll start at the dmap corresponding to the allocation
 *          group and attempt the allocation at this level.
 *
 *          the dmap control page search is also not performed if the
 *          allocation group is completely free and we go to the first
 *          dmap of the allocation group to do the allocation.  this is
 *          done because the allocation group may be part (not the first
 *          part) of a larger binary buddy system, causing the dmap
 *          control pages to indicate no free space (NOFREE) within
 *          the allocation group.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *    agno  - allocation group number.
 *      nblocks   -  actual number of contiguous free blocks desired.
 *      l2nb      -  log2 number of contiguous free blocks desired.
 *      results   -  on successful return, set to the starting block number
 *             of the newly allocated range.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 *
 * note: IWRITE_LOCK(ipmap) held on entry/exit;
 */
static int
dbAllocAG(struct bmap * bmp, int agno, s64 nblocks, int l2nb, s64 * results)
{
      struct metapage *mp;
      struct dmapctl *dcp;
      int rc, ti, i, k, m, n, agperlev;
      s64 blkno, lblkno;
      int budmin;

      /* allocation request should not be for more than the
       * allocation group size.
       */
      if (l2nb > bmp->db_agl2size) {
            jfs_error(bmp->db_ipbmap->i_sb,
                    "dbAllocAG: allocation request is larger than the "
                    "allocation group size");
            return -EIO;
      }

      /* determine the starting block number of the allocation
       * group.
       */
      blkno = (s64) agno << bmp->db_agl2size;

      /* check if the allocation group size is the minimum allocation
       * group size or if the allocation group is completely free. if
       * the allocation group size is the minimum size of BPERDMAP (i.e.
       * 1 dmap), there is no need to search the dmap control page (below)
       * that fully describes the allocation group since the allocation
       * group is already fully described by a dmap.  in this case, we
       * just call dbAllocCtl() to search the dmap tree and allocate the
       * required space if available.  
       *
       * if the allocation group is completely free, dbAllocCtl() is
       * also called to allocate the required space.  this is done for
       * two reasons.  first, it makes no sense searching the dmap control
       * pages for free space when we know that free space exists.  second,
       * the dmap control pages may indicate that the allocation group
       * has no free space if the allocation group is part (not the first
       * part) of a larger binary buddy system.
       */
      if (bmp->db_agsize == BPERDMAP
          || bmp->db_agfree[agno] == bmp->db_agsize) {
            rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
            if ((rc == -ENOSPC) &&
                (bmp->db_agfree[agno] == bmp->db_agsize)) {
                  printk(KERN_ERR "blkno = %Lx, blocks = %Lx\n",
                         (unsigned long long) blkno,
                         (unsigned long long) nblocks);
                  jfs_error(bmp->db_ipbmap->i_sb,
                          "dbAllocAG: dbAllocCtl failed in free AG");
            }
            return (rc);
      }

      /* the buffer for the dmap control page that fully describes the
       * allocation group.
       */
      lblkno = BLKTOCTL(blkno, bmp->db_l2nbperpage, bmp->db_aglevel);
      mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
      if (mp == NULL)
            return -EIO;
      dcp = (struct dmapctl *) mp->data;
      budmin = dcp->budmin;

      if (dcp->leafidx != cpu_to_le32(CTLLEAFIND)) {
            jfs_error(bmp->db_ipbmap->i_sb,
                    "dbAllocAG: Corrupt dmapctl page");
            release_metapage(mp);
            return -EIO;
      }

      /* search the subtree(s) of the dmap control page that describes
       * the allocation group, looking for sufficient free space.  to begin,
       * determine how many allocation groups are represented in a dmap
       * control page at the control page level (i.e. L0, L1, L2) that
       * fully describes an allocation group. next, determine the starting
       * tree index of this allocation group within the control page.
       */
      agperlev =
          (1 << (L2LPERCTL - (bmp->db_agheigth << 1))) / bmp->db_agwidth;
      ti = bmp->db_agstart + bmp->db_agwidth * (agno & (agperlev - 1));

      /* dmap control page trees fan-out by 4 and a single allocation 
       * group may be described by 1 or 2 subtrees within the ag level
       * dmap control page, depending upon the ag size. examine the ag's
       * subtrees for sufficient free space, starting with the leftmost
       * subtree.
       */
      for (i = 0; i < bmp->db_agwidth; i++, ti++) {
            /* is there sufficient free space ?
             */
            if (l2nb > dcp->stree[ti])
                  continue;

            /* sufficient free space found in a subtree. now search down
             * the subtree to find the leftmost leaf that describes this
             * free space.
             */
            for (k = bmp->db_agheigth; k > 0; k--) {
                  for (n = 0, m = (ti << 2) + 1; n < 4; n++) {
                        if (l2nb <= dcp->stree[m + n]) {
                              ti = m + n;
                              break;
                        }
                  }
                  if (n == 4) {
                        jfs_error(bmp->db_ipbmap->i_sb,
                                "dbAllocAG: failed descending stree");
                        release_metapage(mp);
                        return -EIO;
                  }
            }

            /* determine the block number within the file system
             * that corresponds to this leaf.
             */
            if (bmp->db_aglevel == 2)
                  blkno = 0;
            else if (bmp->db_aglevel == 1)
                  blkno &= ~(MAXL1SIZE - 1);
            else        /* bmp->db_aglevel == 0 */
                  blkno &= ~(MAXL0SIZE - 1);

            blkno +=
                ((s64) (ti - le32_to_cpu(dcp->leafidx))) << budmin;

            /* release the buffer in preparation for going down
             * the next level of dmap control pages.
             */
            release_metapage(mp);

            /* check if we need to continue to search down the lower
             * level dmap control pages.  we need to if the number of
             * blocks required is less than maximum number of blocks
             * described at the next lower level.
             */
            if (l2nb < budmin) {

                  /* search the lower level dmap control pages to get
                   * the starting block number of the the dmap that
                   * contains or starts off the free space.
                   */
                  if ((rc =
                       dbFindCtl(bmp, l2nb, bmp->db_aglevel - 1,
                               &blkno))) {
                        if (rc == -ENOSPC) {
                              jfs_error(bmp->db_ipbmap->i_sb,
                                      "dbAllocAG: control page "
                                      "inconsistent");
                              return -EIO;
                        }
                        return (rc);
                  }
            }

            /* allocate the blocks.
             */
            rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
            if (rc == -ENOSPC) {
                  jfs_error(bmp->db_ipbmap->i_sb,
                          "dbAllocAG: unable to allocate blocks");
                  rc = -EIO;
            }
            return (rc);
      }

      /* no space in the allocation group.  release the buffer and
       * return -ENOSPC.
       */
      release_metapage(mp);

      return -ENOSPC;
}


/*
 * NAME:    dbAllocAny()
 *
 * FUNCTION:    attempt to allocate the specified number of contiguous
 *          free blocks anywhere in the file system.
 *
 *          dbAllocAny() attempts to find the sufficient free space by
 *          searching down the dmap control pages, starting with the
 *          highest level (i.e. L0, L1, L2) control page.  if free space
 *          large enough to satisfy the desired free space is found, the
 *          desired free space is allocated.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      nblocks    -  actual number of contiguous free blocks desired.
 *      l2nb       -  log2 number of contiguous free blocks desired.
 *      results   -  on successful return, set to the starting block number
 *             of the newly allocated range.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 *
 * serialization: IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static int dbAllocAny(struct bmap * bmp, s64 nblocks, int l2nb, s64 * results)
{
      int rc;
      s64 blkno = 0;

      /* starting with the top level dmap control page, search
       * down the dmap control levels for sufficient free space.
       * if free space is found, dbFindCtl() returns the starting
       * block number of the dmap that contains or starts off the
       * range of free space.
       */
      if ((rc = dbFindCtl(bmp, l2nb, bmp->db_maxlevel, &blkno)))
            return (rc);

      /* allocate the blocks.
       */
      rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
      if (rc == -ENOSPC) {
            jfs_error(bmp->db_ipbmap->i_sb,
                    "dbAllocAny: unable to allocate blocks");
            return -EIO;
      }
      return (rc);
}


/*
 * NAME:    dbFindCtl()
 *
 * FUNCTION:    starting at a specified dmap control page level and block
 *          number, search down the dmap control levels for a range of
 *            contiguous free blocks large enough to satisfy an allocation
 *          request for the specified number of free blocks.
 *
 *          if sufficient contiguous free blocks are found, this routine
 *          returns the starting block number within a dmap page that
 *          contains or starts a range of contiqious free blocks that
 *          is sufficient in size.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      level     -  starting dmap control page level.
 *      l2nb      -  log2 number of contiguous free blocks desired.
 *      *blkno    -  on entry, starting block number for conducting the search.
 *             on successful return, the first block within a dmap page
 *             that contains or starts a range of contiguous free blocks.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 *
 * serialization: IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static int dbFindCtl(struct bmap * bmp, int l2nb, int level, s64 * blkno)
{
      int rc, leafidx, lev;
      s64 b, lblkno;
      struct dmapctl *dcp;
      int budmin;
      struct metapage *mp;

      /* starting at the specified dmap control page level and block
       * number, search down the dmap control levels for the starting
       * block number of a dmap page that contains or starts off 
       * sufficient free blocks.
       */
      for (lev = level, b = *blkno; lev >= 0; lev--) {
            /* get the buffer of the dmap control page for the block
             * number and level (i.e. L0, L1, L2).
             */
            lblkno = BLKTOCTL(b, bmp->db_l2nbperpage, lev);
            mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
            if (mp == NULL)
                  return -EIO;
            dcp = (struct dmapctl *) mp->data;
            budmin = dcp->budmin;

            if (dcp->leafidx != cpu_to_le32(CTLLEAFIND)) {
                  jfs_error(bmp->db_ipbmap->i_sb,
                          "dbFindCtl: Corrupt dmapctl page");
                  release_metapage(mp);
                  return -EIO;
            }

            /* search the tree within the dmap control page for
             * sufficent free space.  if sufficient free space is found,
             * dbFindLeaf() returns the index of the leaf at which
             * free space was found.
             */
            rc = dbFindLeaf((dmtree_t *) dcp, l2nb, &leafidx);

            /* release the buffer.
             */
            release_metapage(mp);

            /* space found ?
             */
            if (rc) {
                  if (lev != level) {
                        jfs_error(bmp->db_ipbmap->i_sb,
                                "dbFindCtl: dmap inconsistent");
                        return -EIO;
                  }
                  return -ENOSPC;
            }

            /* adjust the block number to reflect the location within
             * the dmap control page (i.e. the leaf) at which free 
             * space was found.
             */
            b += (((s64) leafidx) << budmin);

            /* we stop the search at this dmap control page level if
             * the number of blocks required is greater than or equal
             * to the maximum number of blocks described at the next
             * (lower) level.
             */
            if (l2nb >= budmin)
                  break;
      }

      *blkno = b;
      return (0);
}


/*
 * NAME:    dbAllocCtl()
 *
 * FUNCTION:    attempt to allocate a specified number of contiguous
 *          blocks starting within a specific dmap.  
 *          
 *          this routine is called by higher level routines that search
 *          the dmap control pages above the actual dmaps for contiguous
 *          free space.  the result of successful searches by these
 *          routines are the starting block numbers within dmaps, with
 *          the dmaps themselves containing the desired contiguous free
 *          space or starting a contiguous free space of desired size
 *          that is made up of the blocks of one or more dmaps. these
 *          calls should not fail due to insufficent resources.
 *
 *          this routine is called in some cases where it is not known
 *          whether it will fail due to insufficient resources.  more
 *          specifically, this occurs when allocating from an allocation
 *          group whose size is equal to the number of blocks per dmap.
 *          in this case, the dmap control pages are not examined prior
 *          to calling this routine (to save pathlength) and the call
 *          might fail.
 *
 *          for a request size that fits within a dmap, this routine relies
 *          upon the dmap's dmtree to find the requested contiguous free
 *          space.  for request sizes that are larger than a dmap, the
 *          requested free space will start at the first block of the
 *          first dmap (i.e. blkno).
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      nblocks    -  actual number of contiguous free blocks to allocate.
 *      l2nb       -  log2 number of contiguous free blocks to allocate.
 *      blkno      -  starting block number of the dmap to start the allocation
 *              from.
 *      results   -  on successful return, set to the starting block number
 *             of the newly allocated range.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 *
 * serialization: IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static int
dbAllocCtl(struct bmap * bmp, s64 nblocks, int l2nb, s64 blkno, s64 * results)
{
      int rc, nb;
      s64 b, lblkno, n;
      struct metapage *mp;
      struct dmap *dp;

      /* check if the allocation request is confined to a single dmap.
       */
      if (l2nb <= L2BPERDMAP) {
            /* get the buffer for the dmap.
             */
            lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
            mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
            if (mp == NULL)
                  return -EIO;
            dp = (struct dmap *) mp->data;

            /* try to allocate the blocks.
             */
            rc = dbAllocDmapLev(bmp, dp, (int) nblocks, l2nb, results);
            if (rc == 0)
                  mark_metapage_dirty(mp);

            release_metapage(mp);

            return (rc);
      }

      /* allocation request involving multiple dmaps. it must start on
       * a dmap boundary.
       */
      assert((blkno & (BPERDMAP - 1)) == 0);

      /* allocate the blocks dmap by dmap.
       */
      for (n = nblocks, b = blkno; n > 0; n -= nb, b += nb) {
            /* get the buffer for the dmap.
             */
            lblkno = BLKTODMAP(b, bmp->db_l2nbperpage);
            mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
            if (mp == NULL) {
                  rc = -EIO;
                  goto backout;
            }
            dp = (struct dmap *) mp->data;

            /* the dmap better be all free.
             */
            if (dp->tree.stree[ROOT] != L2BPERDMAP) {
                  release_metapage(mp);
                  jfs_error(bmp->db_ipbmap->i_sb,
                          "dbAllocCtl: the dmap is not all free");
                  rc = -EIO;
                  goto backout;
            }

            /* determine how many blocks to allocate from this dmap.
             */
            nb = min(n, (s64)BPERDMAP);

            /* allocate the blocks from the dmap.
             */
            if ((rc = dbAllocDmap(bmp, dp, b, nb))) {
                  release_metapage(mp);
                  goto backout;
            }

            /* write the buffer.
             */
            write_metapage(mp);
      }

      /* set the results (starting block number) and return.
       */
      *results = blkno;
      return (0);

      /* something failed in handling an allocation request involving
       * multiple dmaps.  we'll try to clean up by backing out any
       * allocation that has already happened for this request.  if
       * we fail in backing out the allocation, we'll mark the file
       * system to indicate that blocks have been leaked.
       */
      backout:

      /* try to backout the allocations dmap by dmap.
       */
      for (n = nblocks - n, b = blkno; n > 0;
           n -= BPERDMAP, b += BPERDMAP) {
            /* get the buffer for this dmap.
             */
            lblkno = BLKTODMAP(b, bmp->db_l2nbperpage);
            mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
            if (mp == NULL) {
                  /* could not back out.  mark the file system
                   * to indicate that we have leaked blocks.
                   */
                  jfs_error(bmp->db_ipbmap->i_sb,
                          "dbAllocCtl: I/O Error: Block Leakage.");
                  continue;
            }
            dp = (struct dmap *) mp->data;

            /* free the blocks is this dmap.
             */
            if (dbFreeDmap(bmp, dp, b, BPERDMAP)) {
                  /* could not back out.  mark the file system
                   * to indicate that we have leaked blocks.
                   */
                  release_metapage(mp);
                  jfs_error(bmp->db_ipbmap->i_sb,
                          "dbAllocCtl: Block Leakage.");
                  continue;
            }

            /* write the buffer.
             */
            write_metapage(mp);
      }

      return (rc);
}


/*
 * NAME:    dbAllocDmapLev()
 *
 * FUNCTION:    attempt to allocate a specified number of contiguous blocks
 *          from a specified dmap.
 *          
 *          this routine checks if the contiguous blocks are available.
 *          if so, nblocks of blocks are allocated; otherwise, ENOSPC is
 *          returned.
 *
 * PARAMETERS:
 *      mp  -  pointer to bmap descriptor
 *      dp  -  pointer to dmap to attempt to allocate blocks from. 
 *      l2nb      -  log2 number of contiguous block desired.
 *      nblocks   -  actual number of contiguous block desired.
 *      results   -  on successful return, set to the starting block number
 *             of the newly allocated range.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient disk resources
 *      -EIO      - i/o error
 *
 * serialization: IREAD_LOCK(ipbmap), e.g., from dbAlloc(), or 
 *    IWRITE_LOCK(ipbmap), e.g., dbAllocCtl(), held on entry/exit;
 */
static int
dbAllocDmapLev(struct bmap * bmp,
             struct dmap * dp, int nblocks, int l2nb, s64 * results)
{
      s64 blkno;
      int leafidx, rc;

      /* can't be more than a dmaps worth of blocks */
      assert(l2nb <= L2BPERDMAP);

      /* search the tree within the dmap page for sufficient
       * free space.  if sufficient free space is found, dbFindLeaf()
       * returns the index of the leaf at which free space was found.
       */
      if (dbFindLeaf((dmtree_t *) & dp->tree, l2nb, &leafidx))
            return -ENOSPC;

      /* determine the block number within the file system corresponding
       * to the leaf at which free space was found.
       */
      blkno = le64_to_cpu(dp->start) + (leafidx << L2DBWORD);

      /* if not all bits of the dmap word are free, get the starting
       * bit number within the dmap word of the required string of free
       * bits and adjust the block number with this value.
       */
      if (dp->tree.stree[leafidx + LEAFIND] < BUDMIN)
            blkno += dbFindBits(le32_to_cpu(dp->wmap[leafidx]), l2nb);

      /* allocate the blocks */
      if ((rc = dbAllocDmap(bmp, dp, blkno, nblocks)) == 0)
            *results = blkno;

      return (rc);
}


/*
 * NAME:    dbAllocDmap()
 *
 * FUNCTION:    adjust the disk allocation map to reflect the allocation
 *          of a specified block range within a dmap.
 *
 *          this routine allocates the specified blocks from the dmap
 *          through a call to dbAllocBits(). if the allocation of the
 *          block range causes the maximum string of free blocks within
 *          the dmap to change (i.e. the value of the root of the dmap's
 *          dmtree), this routine will cause this change to be reflected
 *          up through the appropriate levels of the dmap control pages
 *          by a call to dbAdjCtl() for the L0 dmap control page that
 *          covers this dmap.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      dp  -  pointer to dmap to allocate the block range from.
 *      blkno     -  starting block number of the block to be allocated.
 *      nblocks   -  number of blocks to be allocated.
 *
 * RETURN VALUES:
 *      0   - success
 *      -EIO      - i/o error
 *
 * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static int dbAllocDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
                   int nblocks)
{
      s8 oldroot;
      int rc;

      /* save the current value of the root (i.e. maximum free string)
       * of the dmap tree.
       */
      oldroot = dp->tree.stree[ROOT];

      /* allocate the specified (blocks) bits */
      dbAllocBits(bmp, dp, blkno, nblocks);

      /* if the root has not changed, done. */
      if (dp->tree.stree[ROOT] == oldroot)
            return (0);

      /* root changed. bubble the change up to the dmap control pages.
       * if the adjustment of the upper level control pages fails,
       * backout the bit allocation (thus making everything consistent).
       */
      if ((rc = dbAdjCtl(bmp, blkno, dp->tree.stree[ROOT], 1, 0)))
            dbFreeBits(bmp, dp, blkno, nblocks);

      return (rc);
}


/*
 * NAME:    dbFreeDmap()
 *
 * FUNCTION:    adjust the disk allocation map to reflect the allocation
 *          of a specified block range within a dmap.
 *
 *          this routine frees the specified blocks from the dmap through
 *          a call to dbFreeBits(). if the deallocation of the block range
 *          causes the maximum string of free blocks within the dmap to
 *          change (i.e. the value of the root of the dmap's dmtree), this
 *          routine will cause this change to be reflected up through the
 *            appropriate levels of the dmap control pages by a call to
 *          dbAdjCtl() for the L0 dmap control page that covers this dmap.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      dp  -  pointer to dmap to free the block range from.
 *      blkno     -  starting block number of the block to be freed.
 *      nblocks   -  number of blocks to be freed.
 *
 * RETURN VALUES:
 *      0   - success
 *      -EIO      - i/o error
 *
 * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static int dbFreeDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
                  int nblocks)
{
      s8 oldroot;
      int rc = 0, word;

      /* save the current value of the root (i.e. maximum free string)
       * of the dmap tree.
       */
      oldroot = dp->tree.stree[ROOT];

      /* free the specified (blocks) bits */
      rc = dbFreeBits(bmp, dp, blkno, nblocks);

      /* if error or the root has not changed, done. */
      if (rc || (dp->tree.stree[ROOT] == oldroot))
            return (rc);

      /* root changed. bubble the change up to the dmap control pages.
       * if the adjustment of the upper level control pages fails,
       * backout the deallocation. 
       */
      if ((rc = dbAdjCtl(bmp, blkno, dp->tree.stree[ROOT], 0, 0))) {
            word = (blkno & (BPERDMAP - 1)) >> L2DBWORD;

            /* as part of backing out the deallocation, we will have
             * to back split the dmap tree if the deallocation caused
             * the freed blocks to become part of a larger binary buddy
             * system.
             */
            if (dp->tree.stree[word] == NOFREE)
                  dbBackSplit((dmtree_t *) & dp->tree, word);

            dbAllocBits(bmp, dp, blkno, nblocks);
      }

      return (rc);
}


/*
 * NAME:    dbAllocBits()
 *
 * FUNCTION:    allocate a specified block range from a dmap.
 *
 *          this routine updates the dmap to reflect the working
 *          state allocation of the specified block range. it directly
 *          updates the bits of the working map and causes the adjustment
 *          of the binary buddy system described by the dmap's dmtree
 *          leaves to reflect the bits allocated.  it also causes the
 *          dmap's dmtree, as a whole, to reflect the allocated range.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      dp  -  pointer to dmap to allocate bits from.
 *      blkno     -  starting block number of the bits to be allocated.
 *      nblocks   -  number of bits to be allocated.
 *
 * RETURN VALUES: none
 *
 * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static void dbAllocBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
                  int nblocks)
{
      int dbitno, word, rembits, nb, nwords, wbitno, nw, agno;
      dmtree_t *tp = (dmtree_t *) & dp->tree;
      int size;
      s8 *leaf;

      /* pick up a pointer to the leaves of the dmap tree */
      leaf = dp->tree.stree + LEAFIND;

      /* determine the bit number and word within the dmap of the
       * starting block.
       */
      dbitno = blkno & (BPERDMAP - 1);
      word = dbitno >> L2DBWORD;

      /* block range better be within the dmap */
      assert(dbitno + nblocks <= BPERDMAP);

      /* allocate the bits of the dmap's words corresponding to the block
       * range. not all bits of the first and last words may be contained
       * within the block range.  if this is the case, we'll work against
       * those words (i.e. partial first and/or last) on an individual basis
       * (a single pass), allocating the bits of interest by hand and
       * updating the leaf corresponding to the dmap word. a single pass
       * will be used for all dmap words fully contained within the
       * specified range.  within this pass, the bits of all fully contained
       * dmap words will be marked as free in a single shot and the leaves
       * will be updated. a single leaf may describe the free space of
       * multiple dmap words, so we may update only a subset of the actual
       * leaves corresponding to the dmap words of the block range.
       */
      for (rembits = nblocks; rembits > 0; rembits -= nb, dbitno += nb) {
            /* determine the bit number within the word and
             * the number of bits within the word.
             */
            wbitno = dbitno & (DBWORD - 1);
            nb = min(rembits, DBWORD - wbitno);

            /* check if only part of a word is to be allocated.
             */
            if (nb < DBWORD) {
                  /* allocate (set to 1) the appropriate bits within
                   * this dmap word.
                   */
                  dp->wmap[word] |= cpu_to_le32(ONES << (DBWORD - nb)
                                          >> wbitno);

                  /* update the leaf for this dmap word. in addition
                   * to setting the leaf value to the binary buddy max
                   * of the updated dmap word, dbSplit() will split
                   * the binary system of the leaves if need be.
                   */
                  dbSplit(tp, word, BUDMIN,
                        dbMaxBud((u8 *) & dp->wmap[word]));

                  word += 1;
            } else {
                  /* one or more dmap words are fully contained
                   * within the block range.  determine how many
                   * words and allocate (set to 1) the bits of these
                   * words.
                   */
                  nwords = rembits >> L2DBWORD;
                  memset(&dp->wmap[word], (int) ONES, nwords * 4);

                  /* determine how many bits.
                   */
                  nb = nwords << L2DBWORD;

                  /* now update the appropriate leaves to reflect
                   * the allocated words.
                   */
                  for (; nwords > 0; nwords -= nw) {
                          if (leaf[word] < BUDMIN) {
                              jfs_error(bmp->db_ipbmap->i_sb,
                                      "dbAllocBits: leaf page "
                                      "corrupt");
                              break;
                        }

                        /* determine what the leaf value should be
                         * updated to as the minimum of the l2 number
                         * of bits being allocated and the l2 number
                         * of bits currently described by this leaf.
                         */
                        size = min((int)leaf[word], NLSTOL2BSZ(nwords));

                        /* update the leaf to reflect the allocation.
                         * in addition to setting the leaf value to
                         * NOFREE, dbSplit() will split the binary
                         * system of the leaves to reflect the current
                         * allocation (size).
                         */
                        dbSplit(tp, word, size, NOFREE);

                        /* get the number of dmap words handled */
                        nw = BUDSIZE(size, BUDMIN);
                        word += nw;
                  }
            }
      }

      /* update the free count for this dmap */
      dp->nfree = cpu_to_le32(le32_to_cpu(dp->nfree) - nblocks);

      BMAP_LOCK(bmp);

      /* if this allocation group is completely free,
       * update the maximum allocation group number if this allocation
       * group is the new max.
       */
      agno = blkno >> bmp->db_agl2size;
      if (agno > bmp->db_maxag)
            bmp->db_maxag = agno;

      /* update the free count for the allocation group and map */
      bmp->db_agfree[agno] -= nblocks;
      bmp->db_nfree -= nblocks;

      BMAP_UNLOCK(bmp);
}


/*
 * NAME:    dbFreeBits()
 *
 * FUNCTION:    free a specified block range from a dmap.
 *
 *          this routine updates the dmap to reflect the working
 *          state allocation of the specified block range. it directly
 *          updates the bits of the working map and causes the adjustment
 *          of the binary buddy system described by the dmap's dmtree
 *          leaves to reflect the bits freed.  it also causes the dmap's
 *          dmtree, as a whole, to reflect the deallocated range.
 *
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      dp  -  pointer to dmap to free bits from.
 *      blkno     -  starting block number of the bits to be freed.
 *      nblocks   -  number of bits to be freed.
 *
 * RETURN VALUES: 0 for success
 *
 * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static int dbFreeBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
                   int nblocks)
{
      int dbitno, word, rembits, nb, nwords, wbitno, nw, agno;
      dmtree_t *tp = (dmtree_t *) & dp->tree;
      int rc = 0;
      int size;

      /* determine the bit number and word within the dmap of the
       * starting block.
       */
      dbitno = blkno & (BPERDMAP - 1);
      word = dbitno >> L2DBWORD;

      /* block range better be within the dmap.
       */
      assert(dbitno + nblocks <= BPERDMAP);

      /* free the bits of the dmaps words corresponding to the block range.
       * not all bits of the first and last words may be contained within
       * the block range.  if this is the case, we'll work against those
       * words (i.e. partial first and/or last) on an individual basis
       * (a single pass), freeing the bits of interest by hand and updating
       * the leaf corresponding to the dmap word. a single pass will be used
       * for all dmap words fully contained within the specified range.  
       * within this pass, the bits of all fully contained dmap words will
       * be marked as free in a single shot and the leaves will be updated. a
       * single leaf may describe the free space of multiple dmap words,
       * so we may update only a subset of the actual leaves corresponding
       * to the dmap words of the block range.
       *
       * dbJoin() is used to update leaf values and will join the binary
       * buddy system of the leaves if the new leaf values indicate this
       * should be done.
       */
      for (rembits = nblocks; rembits > 0; rembits -= nb, dbitno += nb) {
            /* determine the bit number within the word and
             * the number of bits within the word.
             */
            wbitno = dbitno & (DBWORD - 1);
            nb = min(rembits, DBWORD - wbitno);

            /* check if only part of a word is to be freed.
             */
            if (nb < DBWORD) {
                  /* free (zero) the appropriate bits within this
                   * dmap word. 
                   */
                  dp->wmap[word] &=
                      cpu_to_le32(~(ONES << (DBWORD - nb)
                                >> wbitno));

                  /* update the leaf for this dmap word.
                   */
                  rc = dbJoin(tp, word,
                            dbMaxBud((u8 *) & dp->wmap[word]));
                  if (rc)
                        return rc;

                  word += 1;
            } else {
                  /* one or more dmap words are fully contained
                   * within the block range.  determine how many
                   * words and free (zero) the bits of these words.
                   */
                  nwords = rembits >> L2DBWORD;
                  memset(&dp->wmap[word], 0, nwords * 4);

                  /* determine how many bits.
                   */
                  nb = nwords << L2DBWORD;

                  /* now update the appropriate leaves to reflect
                   * the freed words.
                   */
                  for (; nwords > 0; nwords -= nw) {
                        /* determine what the leaf value should be
                         * updated to as the minimum of the l2 number
                         * of bits being freed and the l2 (max) number
                         * of bits that can be described by this leaf.
                         */
                        size =
                            min(LITOL2BSZ
                              (word, L2LPERDMAP, BUDMIN),
                              NLSTOL2BSZ(nwords));

                        /* update the leaf.
                         */
                        rc = dbJoin(tp, word, size);
                        if (rc)
                              return rc;

                        /* get the number of dmap words handled.
                         */
                        nw = BUDSIZE(size, BUDMIN);
                        word += nw;
                  }
            }
      }

      /* update the free count for this dmap.
       */
      dp->nfree = cpu_to_le32(le32_to_cpu(dp->nfree) + nblocks);

      BMAP_LOCK(bmp);

      /* update the free count for the allocation group and 
       * map.
       */
      agno = blkno >> bmp->db_agl2size;
      bmp->db_nfree += nblocks;
      bmp->db_agfree[agno] += nblocks;

      /* check if this allocation group is not completely free and
       * if it is currently the maximum (rightmost) allocation group.
       * if so, establish the new maximum allocation group number by
       * searching left for the first allocation group with allocation.
       */
      if ((bmp->db_agfree[agno] == bmp->db_agsize && agno == bmp->db_maxag) ||
          (agno == bmp->db_numag - 1 &&
           bmp->db_agfree[agno] == (bmp-> db_mapsize & (BPERDMAP - 1)))) {
            while (bmp->db_maxag > 0) {
                  bmp->db_maxag -= 1;
                  if (bmp->db_agfree[bmp->db_maxag] !=
                      bmp->db_agsize)
                        break;
            }

            /* re-establish the allocation group preference if the
             * current preference is right of the maximum allocation
             * group.
             */
            if (bmp->db_agpref > bmp->db_maxag)
                  bmp->db_agpref = bmp->db_maxag;
      }

      BMAP_UNLOCK(bmp);

      return 0;
}


/*
 * NAME:    dbAdjCtl()
 *
 * FUNCTION:      adjust a dmap control page at a specified level to reflect
 *          the change in a lower level dmap or dmap control page's
 *          maximum string of free blocks (i.e. a change in the root
 *          of the lower level object's dmtree) due to the allocation
 *          or deallocation of a range of blocks with a single dmap.
 *
 *          on entry, this routine is provided with the new value of
 *          the lower level dmap or dmap control page root and the
 *          starting block number of the block range whose allocation
 *          or deallocation resulted in the root change.  this range
 *          is respresented by a single leaf of the current dmapctl
 *          and the leaf will be updated with this value, possibly
 *          causing a binary buddy system within the leaves to be 
 *          split or joined.  the update may also cause the dmapctl's
 *          dmtree to be updated.
 *
 *          if the adjustment of the dmap control page, itself, causes its
 *          root to change, this change will be bubbled up to the next dmap
 *          control level by a recursive call to this routine, specifying
 *          the new root value and the next dmap control page level to
 *          be adjusted.
 * PARAMETERS:
 *      bmp -  pointer to bmap descriptor
 *      blkno     -  the first block of a block range within a dmap.  it is
 *             the allocation or deallocation of this block range that
 *             requires the dmap control page to be adjusted.
 *      newval    -  the new value of the lower level dmap or dmap control
 *             page root.
 *      alloc     -  TRUE if adjustment is due to an allocation.
 *      level     -  current level of dmap control page (i.e. L0, L1, L2) to
 *             be adjusted.
 *
 * RETURN VALUES:
 *      0   - success
 *      -EIO      - i/o error
 *
 * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static int
dbAdjCtl(struct bmap * bmp, s64 blkno, int newval, int alloc, int level)
{
      struct metapage *mp;
      s8 oldroot;
      int oldval;
      s64 lblkno;
      struct dmapctl *dcp;
      int rc, leafno, ti;

      /* get the buffer for the dmap control page for the specified
       * block number and control page level.
       */
      lblkno = BLKTOCTL(blkno, bmp->db_l2nbperpage, level);
      mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
      if (mp == NULL)
            return -EIO;
      dcp = (struct dmapctl *) mp->data;

      if (dcp->leafidx != cpu_to_le32(CTLLEAFIND)) {
            jfs_error(bmp->db_ipbmap->i_sb,
                    "dbAdjCtl: Corrupt dmapctl page");
            release_metapage(mp);
            return -EIO;
      }

      /* determine the leaf number corresponding to the block and
       * the index within the dmap control tree.
       */
      leafno = BLKTOCTLLEAF(blkno, dcp->budmin);
      ti = leafno + le32_to_cpu(dcp->leafidx);

      /* save the current leaf value and the current root level (i.e.
       * maximum l2 free string described by this dmapctl).
       */
      oldval = dcp->stree[ti];
      oldroot = dcp->stree[ROOT];

      /* check if this is a control page update for an allocation.
       * if so, update the leaf to reflect the new leaf value using
       * dbSplit(); otherwise (deallocation), use dbJoin() to udpate
       * the leaf with the new value.  in addition to updating the
       * leaf, dbSplit() will also split the binary buddy system of
       * the leaves, if required, and bubble new values within the
       * dmapctl tree, if required.  similarly, dbJoin() will join
       * the binary buddy system of leaves and bubble new values up
       * the dmapctl tree as required by the new leaf value.
       */
      if (alloc) {
            /* check if we are in the middle of a binary buddy
             * system.  this happens when we are performing the
             * first allocation out of an allocation group that
             * is part (not the first part) of a larger binary
             * buddy system.  if we are in the middle, back split
             * the system prior to calling dbSplit() which assumes
             * that it is at the front of a binary buddy system.
             */
            if (oldval == NOFREE) {
                  rc = dbBackSplit((dmtree_t *) dcp, leafno);
                  if (rc)
                        return rc;
                  oldval = dcp->stree[ti];
            }
            dbSplit((dmtree_t *) dcp, leafno, dcp->budmin, newval);
      } else {
            rc = dbJoin((dmtree_t *) dcp, leafno, newval);
            if (rc)
                  return rc;
      }

      /* check if the root of the current dmap control page changed due
       * to the update and if the current dmap control page is not at
       * the current top level (i.e. L0, L1, L2) of the map.  if so (i.e.
       * root changed and this is not the top level), call this routine
       * again (recursion) for the next higher level of the mapping to
       * reflect the change in root for the current dmap control page.
       */
      if (dcp->stree[ROOT] != oldroot) {
            /* are we below the top level of the map.  if so,
             * bubble the root up to the next higher level.
             */
            if (level < bmp->db_maxlevel) {
                  /* bubble up the new root of this dmap control page to
                   * the next level.
                   */
                  if ((rc =
                       dbAdjCtl(bmp, blkno, dcp->stree[ROOT], alloc,
                              level + 1))) {
                        /* something went wrong in bubbling up the new
                         * root value, so backout the changes to the
                         * current dmap control page.
                         */
                        if (alloc) {
                              dbJoin((dmtree_t *) dcp, leafno,
                                     oldval);
                        } else {
                              /* the dbJoin() above might have
                               * caused a larger binary buddy system
                               * to form and we may now be in the
                               * middle of it.  if this is the case,
                               * back split the buddies.
                               */
                              if (dcp->stree[ti] == NOFREE)
                                    dbBackSplit((dmtree_t *)
                                              dcp, leafno);
                              dbSplit((dmtree_t *) dcp, leafno,
                                    dcp->budmin, oldval);
                        }

                        /* release the buffer and return the error.
                         */
                        release_metapage(mp);
                        return (rc);
                  }
            } else {
                  /* we're at the top level of the map. update
                   * the bmap control page to reflect the size
                   * of the maximum free buddy system.
                   */
                  assert(level == bmp->db_maxlevel);
                  if (bmp->db_maxfreebud != oldroot) {
                        jfs_error(bmp->db_ipbmap->i_sb,
                                "dbAdjCtl: the maximum free buddy is "
                                "not the old root");
                  }
                  bmp->db_maxfreebud = dcp->stree[ROOT];
            }
      }

      /* write the buffer.
       */
      write_metapage(mp);

      return (0);
}


/*
 * NAME:    dbSplit()
 *
 * FUNCTION:    update the leaf of a dmtree with a new value, splitting
 *          the leaf from the binary buddy system of the dmtree's
 *          leaves, as required.
 *
 * PARAMETERS:
 *      tp  - pointer to the tree containing the leaf.
 *      leafno    - the number of the leaf to be updated.
 *      splitsz   - the size the binary buddy system starting at the leaf
 *            must be split to, specified as the log2 number of blocks.
 *      newval    - the new value for the leaf.
 *
 * RETURN VALUES: none
 *
 * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static void dbSplit(dmtree_t * tp, int leafno, int splitsz, int newval)
{
      int budsz;
      int cursz;
      s8 *leaf = tp->dmt_stree + le32_to_cpu(tp->dmt_leafidx);

      /* check if the leaf needs to be split.
       */
      if (leaf[leafno] > tp->dmt_budmin) {
            /* the split occurs by cutting the buddy system in half
             * at the specified leaf until we reach the specified
             * size.  pick up the starting split size (current size
             * - 1 in l2) and the corresponding buddy size.
             */
            cursz = leaf[leafno] - 1;
            budsz = BUDSIZE(cursz, tp->dmt_budmin);

            /* split until we reach the specified size.
             */
            while (cursz >= splitsz) {
                  /* update the buddy's leaf with its new value.
                   */
                  dbAdjTree(tp, leafno ^ budsz, cursz);

                  /* on to the next size and buddy.
                   */
                  cursz -= 1;
                  budsz >>= 1;
            }
      }

      /* adjust the dmap tree to reflect the specified leaf's new 
       * value.
       */
      dbAdjTree(tp, leafno, newval);
}


/*
 * NAME:    dbBackSplit()
 *
 * FUNCTION:    back split the binary buddy system of dmtree leaves
 *          that hold a specified leaf until the specified leaf
 *          starts its own binary buddy system.
 *
 *          the allocators typically perform allocations at the start
 *          of binary buddy systems and dbSplit() is used to accomplish
 *          any required splits.  in some cases, however, allocation
 *          may occur in the middle of a binary system and requires a
 *          back split, with the split proceeding out from the middle of
 *          the system (less efficient) rather than the start of the
 *          system (more efficient).  the cases in which a back split
 *          is required are rare and are limited to the first allocation
 *          within an allocation group which is a part (not first part)
 *          of a larger binary buddy system and a few exception cases
 *          in which a previous join operation must be backed out.
 *
 * PARAMETERS:
 *      tp  - pointer to the tree containing the leaf.
 *      leafno    - the number of the leaf to be updated.
 *
 * RETURN VALUES: none
 *
 * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
 */
static int dbBackSplit(dmtree_t * tp, int leafno)
{
      int budsz, bud, w, bsz, size;
      int cursz;
      s8 *leaf = tp->dmt_stree + le32_to_cpu(tp->dmt_leafidx);

      /* leaf should be part (not first part) of a binary
       * buddy system.
       */
      assert(leaf[leafno] == NOFREE);

      /* the back split is accomplished by iteratively finding the leaf
       * that starts the buddy system that contains the specified leaf and
       * splitting that system in two.  this iteration continues until
       * the specified leaf becomes the start of a buddy system. 
       *
       * determine maximum possible l2 size for the specified leaf.
       */
      size =
          LITOL2BSZ(leafno, le32_to_cpu(tp->dmt_l2nleafs),
                  tp->dmt_budmin);

      /* determine the number of leaves covered by this size.  this
       * is the buddy size that we will start with as we search for
       * the buddy system that contains the specified leaf.
       */
      budsz = BUDSIZE(size, tp->dmt_budmin);

      /* back split.
       */
      while (leaf[leafno] == NOFREE) {
            /* find the leftmost buddy leaf.
             */
            for (w = leafno, bsz = budsz;; bsz <<= 1,
                 w = (w < bud) ? w : bud) {
                  if (bsz >= le32_to_cpu(tp->dmt_nleafs)) {
                        jfs_err("JFS: block map error in dbBackSplit");
                        return -EIO;
                  }

                  /* determine the buddy.
                   */
                  bud = w ^ bsz;

                  /* check if this buddy is the start of the system.
                   */
                  if (leaf[bud] != NOFREE) {
                        /* split the leaf at the start of the
                         * system in two.
                         */
                        cursz = leaf[bud] - 1;
                        dbSplit(tp, bud, cursz, cursz);
                        break;
                  }
            }
      }

      if (leaf[leafno] != size) {
            jfs_err("JFS: wrong leaf value in dbBackSplit");
            return -EIO;
      }
      return 0;
}


/*
 * NAME:    dbJoin()
 *
 * FUNCTION:    update the leaf of a dmtree with a new value, joining
 *          the leaf with other leaves of the dmtree into a multi-leaf
 *          binary buddy system, as required.
 *
 * PARAMETERS:
 *      tp  - pointer to the tree containing the leaf.
 *      leafno    - the number of the leaf to be updated.
 *      newval    - the new value for the leaf.
 *
 * RETURN VALUES: none
 */
static int dbJoin(dmtree_t * tp, int leafno, int newval)
{
      int budsz, buddy;
      s8 *leaf;

      /* can the new leaf value require a join with other leaves ?
       */
      if (newval >= tp->dmt_budmin) {
            /* pickup a pointer to the leaves of the tree.
             */
            leaf = tp->dmt_stree + le32_to_cpu(tp->dmt_leafidx);

            /* try to join the specified leaf into a large binary
             * buddy system.  the join proceeds by attempting to join
             * the specified leafno with its buddy (leaf) at new value.
             * if the join occurs, we attempt to join the left leaf
             * of the joined buddies with its buddy at new value + 1.
             * we continue to join until we find a buddy that cannot be
             * joined (does not have a value equal to the size of the
             * last join) or until all leaves have been joined into a
             * single system.
             *
             * get the buddy size (number of words covered) of
             * the new value.
             */
            budsz = BUDSIZE(newval, tp->dmt_budmin);

            /* try to join.
             */
            while (budsz < le32_to_cpu(tp->dmt_nleafs)) {
                  /* get the buddy leaf.
                   */
                  buddy = leafno ^ budsz;

                  /* if the leaf's new value is greater than its
                   * buddy's value, we join no more.
                   */
                  if (newval > leaf[buddy])
                        break;

                  /* It shouldn't be less */
                  if (newval < leaf[buddy])
                        return -EIO;

                  /* check which (leafno or buddy) is the left buddy.
                   * the left buddy gets to claim the blocks resulting
                   * from the join while the right gets to claim none.
                   * the left buddy is also eligable to participate in
                   * a join at the next higher level while the right
                   * is not.
                   *
                   */
                  if (leafno < buddy) {
                        /* leafno is the left buddy.
                         */
                        dbAdjTree(tp, buddy, NOFREE);
                  } else {
                        /* buddy is the left buddy and becomes
                         * leafno.
                         */
                        dbAdjTree(tp, leafno, NOFREE);
                        leafno = buddy;
                  }

                  /* on to try the next join.
                   */
                  newval += 1;
                  budsz <<= 1;
            }
      }

      /* update the leaf value.
       */
      dbAdjTree(tp, leafno, newval);

      return 0;
}


/*
 * NAME:    dbAdjTree()
 *
 * FUNCTION:    update a leaf of a dmtree with a new value, adjusting
 *          the dmtree, as required, to reflect the new leaf value.
 *          the combination of any buddies must already be done before
 *          this is called.
 *
 * PARAMETERS:
 *      tp  - pointer to the tree to be adjusted.
 *      leafno    - the number of the leaf to be updated.
 *      newval    - the new value for the leaf.
 *
 * RETURN VALUES: none
 */
static void dbAdjTree(dmtree_t * tp, int leafno, int newval)
{
      int lp, pp, k;
      int max;

      /* pick up the index of the leaf for this leafno.
       */
      lp = leafno + le32_to_cpu(tp->dmt_leafidx);

      /* is the current value the same as the old value ?  if so,
       * there is nothing to do.
       */
      if (tp->dmt_stree[lp] == newval)
            return;

      /* set the new value.
       */
      tp->dmt_stree[lp] = newval;

      /* bubble the new value up the tree as required.
       */
      for (k = 0; k < le32_to_cpu(tp->dmt_height); k++) {
            /* get the index of the first leaf of the 4 leaf
             * group containing the specified leaf (leafno).
             */
            lp = ((lp - 1) & ~0x03) + 1;

            /* get the index of the parent of this 4 leaf group.
             */
            pp = (lp - 1) >> 2;

            /* determine the maximum of the 4 leaves.
             */
            max = TREEMAX(&tp->dmt_stree[lp]);

            /* if the maximum of the 4 is the same as the
             * parent's value, we're done.
             */
            if (tp->dmt_stree[pp] == max)
                  break;

            /* parent gets new value.
             */
            tp->dmt_stree[pp] = max;

            /* parent becomes leaf for next go-round.
             */
            lp = pp;
      }
}


/*
 * NAME:    dbFindLeaf()
 *
 * FUNCTION:    search a dmtree_t for sufficient free blocks, returning
 *          the index of a leaf describing the free blocks if 
 *          sufficient free blocks are found.
 *
 *          the search starts at the top of the dmtree_t tree and
 *          proceeds down the tree to the leftmost leaf with sufficient
 *          free space.
 *
 * PARAMETERS:
 *      tp  - pointer to the tree to be searched.
 *      l2nb      - log2 number of free blocks to search for.
 *    leafidx     - return pointer to be set to the index of the leaf
 *            describing at least l2nb free blocks if sufficient
 *            free blocks are found.
 *
 * RETURN VALUES:
 *      0   - success
 *      -ENOSPC   - insufficient free blocks. 
 */
static int dbFindLeaf(dmtree_t * tp, int l2nb, int *leafidx)
{
      int ti, n = 0, k, x = 0;

      /* first check the root of the tree to see if there is
       * sufficient free space.
       */
      if (l2nb > tp->dmt_stree[ROOT])
            return -ENOSPC;

      /* sufficient free space available. now search down the tree
       * starting at the next level for the leftmost leaf that
       * describes sufficient free space.
       */
      for (k = le32_to_cpu(tp->dmt_height), ti = 1;
           k > 0; k--, ti = ((ti + n) << 2) + 1) {
            /* search the four nodes at this level, starting from
             * the left.
             */
            for (x = ti, n = 0; n < 4; n++) {
                  /* sufficient free space found.  move to the next
                   * level (or quit if this is the last level).
                   */
                  if (l2nb <= tp->dmt_stree[x + n])
                        break;
            }

            /* better have found something since the higher
             * levels of the tree said it was here.
             */
            assert(n < 4);
      }

      /* set the return to the leftmost leaf describing sufficient
       * free space.
       */
      *leafidx = x + n - le32_to_cpu(tp->dmt_leafidx);

      return (0);
}


/*
 * NAME:    dbFindBits()
 *
 * FUNCTION:    find a specified number of binary buddy free bits within a
 *          dmap bitmap word value.
 *
 *          this routine searches the bitmap value for (1 << l2nb) free
 *          bits at (1 << l2nb) alignments within the value.
 *
 * PARAMETERS:
 *      word      -  dmap bitmap word value.
 *      l2nb      -  number of free bits specified as a log2 number.
 *
 * RETURN VALUES:
 *      starting bit number of free bits.
 */
static int dbFindBits(u32 word, int l2nb)
{
      int bitno, nb;
      u32 mask;

      /* get the number of bits.
       */
      nb = 1 << l2nb;
      assert(nb <= DBWORD);

      /* complement the word so we can use a mask (i.e. 0s represent
       * free bits) and compute the mask.
       */
      word = ~word;
      mask = ONES << (DBWORD - nb);

      /* scan the word for nb free bits at nb alignments.
       */
      for (bitno = 0; mask != 0; bitno += nb, mask >>= nb) {
            if ((mask & word) == mask)
                  break;
      }

      ASSERT(bitno < 32);

      /* return the bit number.
       */
      return (bitno);
}


/*
 * NAME:    dbMaxBud(u8 *cp)
 *
 * FUNCTION:    determine the largest binary buddy string of free
 *          bits within 32-bits of the map.
 *
 * PARAMETERS:
 *      cp  -  pointer to the 32-bit value.
 *
 * RETURN VALUES:
 *      largest binary buddy of free bits within a dmap word.
 */
static int dbMaxBud(u8 * cp)
{
      signed char tmp1, tmp2;

      /* check if the wmap word is all free. if so, the
       * free buddy size is BUDMIN.
       */
      if (*((uint *) cp) == 0)
            return (BUDMIN);

      /* check if the wmap word is half free. if so, the
       * free buddy size is BUDMIN-1.
       */
      if (*((u16 *) cp) == 0 || *((u16 *) cp + 1) == 0)
            return (BUDMIN - 1);

      /* not all free or half free. determine the free buddy
       * size thru table lookup using quarters of the wmap word.
       */
      tmp1 = max(budtab[cp[2]], budtab[cp[3]]);
      tmp2 = max(budtab[cp[0]], budtab[cp[1]]);
      return (max(tmp1, tmp2));
}


/*
 * NAME:    cnttz(uint word)
 *
 * FUNCTION:    determine the number of trailing zeros within a 32-bit
 *          value.
 *
 * PARAMETERS:
 *      value     -  32-bit value to be examined.
 *
 * RETURN VALUES:
 *      count of trailing zeros
 */
static int cnttz(u32 word)
{
      int n;

      for (n = 0; n < 32; n++, word >>= 1) {
            if (word & 0x01)
                  break;
      }

      return (n);
}


/*
 * NAME:    cntlz(u32 value)
 *
 * FUNCTION:    determine the number of leading zeros within a 32-bit
 *          value.
 *
 * PARAMETERS:
 *      value     -  32-bit value to be examined.
 *
 * RETURN VALUES:
 *      count of leading zeros
 */
static int cntlz(u32 value)
{
      int n;

      for (n = 0; n < 32; n++, value <<= 1) {
            if (value & HIGHORDER)
                  break;
      }
      return (n);
}


/*
 * NAME:    blkstol2(s64 nb)
 *
 * FUNCTION:      convert a block count to its log2 value. if the block
 *            count is not a l2 multiple, it is rounded up to the next
 *          larger l2 multiple.
 *
 * PARAMETERS:
 *      nb  -  number of blocks
 *
 * RETURN VALUES:
 *      log2 number of blocks
 */
static int blkstol2(s64 nb)
{
      int l2nb;
      s64 mask;         /* meant to be signed */

      mask = (s64) 1 << (64 - 1);

      /* count the leading bits.
       */
      for (l2nb = 0; l2nb < 64; l2nb++, mask >>= 1) {
            /* leading bit found.
             */
            if (nb & mask) {
                  /* determine the l2 value.
                   */
                  l2nb = (64 - 1) - l2nb;

                  /* check if we need to round up.
                   */
                  if (~mask & nb)
                        l2nb++;

                  return (l2nb);
            }
      }
      assert(0);
      return 0;         /* fix compiler warning */
}


/*
 * NAME:          dbAllocBottomUp()
 *
 * FUNCTION:      alloc the specified block range from the working block
 *          allocation map.
 *
 *          the blocks will be alloc from the working map one dmap
 *          at a time.
 *
 * PARAMETERS:
 *      ip  -  pointer to in-core inode;
 *      blkno     -  starting block number to be freed.
 *      nblocks   -  number of blocks to be freed.
 *
 * RETURN VALUES:
 *      0   - success
 *      -EIO      - i/o error
 */
int dbAllocBottomUp(struct inode *ip, s64 blkno, s64 nblocks)
{
      struct metapage *mp;
      struct dmap *dp;
      int nb, rc;
      s64 lblkno, rem;
      struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
      struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;

      IREAD_LOCK(ipbmap);

      /* block to be allocated better be within the mapsize. */
      ASSERT(nblocks <= bmp->db_mapsize - blkno);

      /*
       * allocate the blocks a dmap at a time.
       */
      mp = NULL;
      for (rem = nblocks; rem > 0; rem -= nb, blkno += nb) {
            /* release previous dmap if any */
            if (mp) {
                  write_metapage(mp);
            }

            /* get the buffer for the current dmap. */
            lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
            mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
            if (mp == NULL) {
                  IREAD_UNLOCK(ipbmap);
                  return -EIO;
            }
            dp = (struct dmap *) mp->data;

            /* determine the number of blocks to be allocated from
             * this dmap.
             */
            nb = min(rem, BPERDMAP - (blkno & (BPERDMAP - 1)));

            /* allocate the blocks. */
            if ((rc = dbAllocDmapBU(bmp, dp, blkno, nb))) {
                  release_metapage(mp);
                  IREAD_UNLOCK(ipbmap);
                  return (rc);
            }
      }

      /* write the last buffer. */
      write_metapage(mp);

      IREAD_UNLOCK(ipbmap);

      return (0);
}


static int dbAllocDmapBU(struct bmap * bmp, struct dmap * dp, s64 blkno,
                   int nblocks)
{
      int rc;
      int dbitno, word, rembits, nb, nwords, wbitno, agno;
      s8 oldroot, *leaf;
      struct dmaptree *tp = (struct dmaptree *) & dp->tree;

      /* save the current value of the root (i.e. maximum free string)
       * of the dmap tree.
       */
      oldroot = tp->stree[ROOT];

      /* pick up a pointer to the leaves of the dmap tree */
      leaf = tp->stree + LEAFIND;

      /* determine the bit number and word within the dmap of the
       * starting block.
       */
      dbitno = blkno & (BPERDMAP - 1);
      word = dbitno >> L2DBWORD;

      /* block range better be within the dmap */
      assert(dbitno + nblocks <= BPERDMAP);

      /* allocate the bits of the dmap's words corresponding to the block
       * range. not all bits of the first and last words may be contained
       * within the block range.  if this is the case, we'll work against
       * those words (i.e. partial first and/or last) on an individual basis
       * (a single pass), allocating the bits of interest by hand and
       * updating the leaf corresponding to the dmap word. a single pass
       * will be used for all dmap words fully contained within the
       * specified range.  within this pass, the bits of all fully contained
       * dmap words will be marked as free in a single shot and the leaves
       * will be updated. a single leaf may describe the free space of
       * multiple dmap words, so we may update only a subset of the actual
       * leaves corresponding to the dmap words of the block range.
       */
      for (rembits = nblocks; rembits > 0; rembits -= nb, dbitno += nb) {
            /* determine the bit number within the word and
             * the number of bits within the word.
             */
            wbitno = dbitno & (DBWORD - 1);
            nb = min(rembits, DBWORD - wbitno);

            /* check if only part of a word is to be allocated.
             */
            if (nb < DBWORD) {
                  /* allocate (set to 1) the appropriate bits within
                   * this dmap word.
                   */
                  dp->wmap[word] |= cpu_to_le32(ONES << (DBWORD - nb)
                                          >> wbitno);

                  word++;
            } else {
                  /* one or more dmap words are fully contained
                   * within the block range.  determine how many
                   * words and allocate (set to 1) the bits of these
                   * words.
                   */
                  nwords = rembits >> L2DBWORD;
                  memset(&dp->wmap[word], (int) ONES, nwords * 4);

                  /* determine how many bits */
                  nb = nwords << L2DBWORD;
                  word += nwords;
            }
      }

      /* update the free count for this dmap */
      dp->nfree = cpu_to_le32(le32_to_cpu(dp->nfree) - nblocks);

      /* reconstruct summary tree */
      dbInitDmapTree(dp);

      BMAP_LOCK(bmp);

      /* if this allocation group is completely free,
       * update the highest active allocation group number 
       * if this allocation group is the new max.
       */
      agno = blkno >> bmp->db_agl2size;
      if (agno > bmp->db_maxag)
            bmp->db_maxag = agno;

      /* update the free count for the allocation group and map */
      bmp->db_agfree[agno] -= nblocks;
      bmp->db_nfree -= nblocks;

      BMAP_UNLOCK(bmp);

      /* if the root has not changed, done. */
      if (tp->stree[ROOT] == oldroot)
            return (0);

      /* root changed. bubble the change up to the dmap control pages.
       * if the adjustment of the upper level control pages fails,
       * backout the bit allocation (thus making everything consistent).
       */
      if ((rc = dbAdjCtl(bmp, blkno, tp->stree[ROOT], 1, 0)))
            dbFreeBits(bmp, dp, blkno, nblocks);

      return (rc);
}


/*
 * NAME:    dbExtendFS()
 *
 * FUNCTION:      extend bmap from blkno for nblocks;
 *          dbExtendFS() updates bmap ready for dbAllocBottomUp();
 *
 * L2
 *  |
 *   L1---------------------------------L1
 *    |                                  |
 *     L0---------L0---------L0           L0---------L0---------L0
 *      |          |          |            |          |          |
 *       d0,...,dn  d0,...,dn  d0,...,dn    d0,...,dn  d0,...,dn  d0,.,dm;
 * L2L1L0d0,...,dnL0d0,...,dnL0d0,...,dnL1L0d0,...,dnL0d0,...,dnL0d0,..dm
 *
 * <---old---><----------------------------extend----------------------->   
 */
int dbExtendFS(struct inode *ipbmap, s64 blkno, s64 nblocks)
{
      struct jfs_sb_info *sbi = JFS_SBI(ipbmap->i_sb);
      int nbperpage = sbi->nbperpage;
      int i, i0 = TRUE, j, j0 = TRUE, k, n;
      s64 newsize;
      s64 p;
      struct metapage *mp, *l2mp, *l1mp = NULL, *l0mp = NULL;
      struct dmapctl *l2dcp, *l1dcp, *l0dcp;
      struct dmap *dp;
      s8 *l0leaf, *l1leaf, *l2leaf;
      struct bmap *bmp = sbi->bmap;
      int agno, l2agsize, oldl2agsize;
      s64 ag_rem;

      newsize = blkno + nblocks;

      jfs_info("dbExtendFS: blkno:%Ld nblocks:%Ld newsize:%Ld",
             (long long) blkno, (long long) nblocks, (long long) newsize);

      /*
       *      initialize bmap control page.
       *
       * all the data in bmap control page should exclude
       * the mkfs hidden dmap page.
       */

      /* update mapsize */
      bmp->db_mapsize = newsize;
      bmp->db_maxlevel = BMAPSZTOLEV(bmp->db_mapsize);

      /* compute new AG size */
      l2agsize = dbGetL2AGSize(newsize);
      oldl2agsize = bmp->db_agl2size;

      bmp->db_agl2size = l2agsize;
      bmp->db_agsize = 1 << l2agsize;

      /* compute new number of AG */
      agno = bmp->db_numag;
      bmp->db_numag = newsize >> l2agsize;
      bmp->db_numag += ((u32) newsize % (u32) bmp->db_agsize) ? 1 : 0;

      /*
       *      reconfigure db_agfree[] 
       * from old AG configuration to new AG configuration;
       *
       * coalesce contiguous k (newAGSize/oldAGSize) AGs;
       * i.e., (AGi, ..., AGj) where i = k*n and j = k*(n+1) - 1 to AGn;
       * note: new AG size = old AG size * (2**x).
       */
      if (l2agsize == oldl2agsize)
            goto extend;
      k = 1 << (l2agsize - oldl2agsize);
      ag_rem = bmp->db_agfree[0];   /* save agfree[0] */
      for (i = 0, n = 0; i < agno; n++) {
            bmp->db_agfree[n] = 0;  /* init collection point */

            /* coalesce cotiguous k AGs; */
            for (j = 0; j < k && i < agno; j++, i++) {
                  /* merge AGi to AGn */
                  bmp->db_agfree[n] += bmp->db_agfree[i];
            }
      }
      bmp->db_agfree[0] += ag_rem;  /* restore agfree[0] */

      for (; n < MAXAG; n++)
            bmp->db_agfree[n] = 0;

      /*
       * update highest active ag number
       */

      bmp->db_maxag = bmp->db_maxag / k;

      /*
       *      extend bmap
       *
       * update bit maps and corresponding level control pages;
       * global control page db_nfree, db_agfree[agno], db_maxfreebud;
       */
      extend:
      /* get L2 page */
      p = BMAPBLKNO + nbperpage;    /* L2 page */
      l2mp = read_metapage(ipbmap, p, PSIZE, 0);
      if (!l2mp) {
            jfs_error(ipbmap->i_sb, "dbExtendFS: L2 page could not be read");
            return -EIO;
      }
      l2dcp = (struct dmapctl *) l2mp->data;

      /* compute start L1 */
      k = blkno >> L2MAXL1SIZE;
      l2leaf = l2dcp->stree + CTLLEAFIND + k;
      p = BLKTOL1(blkno, sbi->l2nbperpage);     /* L1 page */

      /*
       * extend each L1 in L2
       */
      for (; k < LPERCTL; k++, p += nbperpage) {
            /* get L1 page */
            if (j0) {
                  /* read in L1 page: (blkno & (MAXL1SIZE - 1)) */
                  l1mp = read_metapage(ipbmap, p, PSIZE, 0);
                  if (l1mp == NULL)
                        goto errout;
                  l1dcp = (struct dmapctl *) l1mp->data;

                  /* compute start L0 */
                  j = (blkno & (MAXL1SIZE - 1)) >> L2MAXL0SIZE;
                  l1leaf = l1dcp->stree + CTLLEAFIND + j;
                  p = BLKTOL0(blkno, sbi->l2nbperpage);
                  j0 = FALSE;
            } else {
                  /* assign/init L1 page */
                  l1mp = get_metapage(ipbmap, p, PSIZE, 0);
                  if (l1mp == NULL)
                        goto errout;

                  l1dcp = (struct dmapctl *) l1mp->data;

                  /* compute start L0 */
                  j = 0;
                  l1leaf = l1dcp->stree + CTLLEAFIND;
                  p += nbperpage;   /* 1st L0 of L1.k  */
            }

            /*
             * extend each L0 in L1
             */
            for (; j < LPERCTL; j++) {
                  /* get L0 page */
                  if (i0) {
                        /* read in L0 page: (blkno & (MAXL0SIZE - 1)) */

                        l0mp = read_metapage(ipbmap, p, PSIZE, 0);
                        if (l0mp == NULL)
                              goto errout;
                        l0dcp = (struct dmapctl *) l0mp->data;

                        /* compute start dmap */
                        i = (blkno & (MAXL0SIZE - 1)) >>
                            L2BPERDMAP;
                        l0leaf = l0dcp->stree + CTLLEAFIND + i;
                        p = BLKTODMAP(blkno,
                                    sbi->l2nbperpage);
                        i0 = FALSE;
                  } else {
                        /* assign/init L0 page */
                        l0mp = get_metapage(ipbmap, p, PSIZE, 0);
                        if (l0mp == NULL)
                              goto errout;

                        l0dcp = (struct dmapctl *) l0mp->data;

                        /* compute start dmap */
                        i = 0;
                        l0leaf = l0dcp->stree + CTLLEAFIND;
                        p += nbperpage;   /* 1st dmap of L0.j */
                  }

                  /*
                   * extend each dmap in L0
                   */
                  for (; i < LPERCTL; i++) {
                        /*
                         * reconstruct the dmap page, and
                         * initialize corresponding parent L0 leaf
                         */
                        if ((n = blkno & (BPERDMAP - 1))) {
                              /* read in dmap page: */
                              mp = read_metapage(ipbmap, p,
                                             PSIZE, 0);
                              if (mp == NULL)
                                    goto errout;
                              n = min(nblocks, (s64)BPERDMAP - n);
                        } else {
                              /* assign/init dmap page */
                              mp = read_metapage(ipbmap, p,
                                             PSIZE, 0);
                              if (mp == NULL)
                                    goto errout;

                              n = min(nblocks, (s64)BPERDMAP);
                        }

                        dp = (struct dmap *) mp->data;
                        *l0leaf = dbInitDmap(dp, blkno, n);

                        bmp->db_nfree += n;
                        agno = le64_to_cpu(dp->start) >> l2agsize;
                        bmp->db_agfree[agno] += n;

                        write_metapage(mp);

                        l0leaf++;
                        p += nbperpage;

                        blkno += n;
                        nblocks -= n;
                        if (nblocks == 0)
                              break;
                  }     /* for each dmap in a L0 */

                  /*
                   * build current L0 page from its leaves, and 
                   * initialize corresponding parent L1 leaf
                   */
                  *l1leaf = dbInitDmapCtl(l0dcp, 0, ++i);
                  write_metapage(l0mp);
                  l0mp = NULL;

                  if (nblocks)
                        l1leaf++;   /* continue for next L0 */
                  else {
                        /* more than 1 L0 ? */
                        if (j > 0)
                              break;      /* build L1 page */
                        else {
                              /* summarize in global bmap page */
                              bmp->db_maxfreebud = *l1leaf;
                              release_metapage(l1mp);
                              release_metapage(l2mp);
                              goto finalize;
                        }
                  }
            }           /* for each L0 in a L1 */

            /*
             * build current L1 page from its leaves, and 
             * initialize corresponding parent L2 leaf
             */
            *l2leaf = dbInitDmapCtl(l1dcp, 1, ++j);
            write_metapage(l1mp);
            l1mp = NULL;

            if (nblocks)
                  l2leaf++;   /* continue for next L1 */
            else {
                  /* more than 1 L1 ? */
                  if (k > 0)
                        break;      /* build L2 page */
                  else {
                        /* summarize in global bmap page */
                        bmp->db_maxfreebud = *l2leaf;
                        release_metapage(l2mp);
                        goto finalize;
                  }
            }
      }                 /* for each L1 in a L2 */

      jfs_error(ipbmap->i_sb,
              "dbExtendFS: function has not returned as expected");
errout:
      if (l0mp)
            release_metapage(l0mp);
      if (l1mp)
            release_metapage(l1mp);
      release_metapage(l2mp);
      return -EIO;

      /*
       *      finalize bmap control page
       */
finalize:

      return 0;
}


/*
 *    dbFinalizeBmap()
 */
void dbFinalizeBmap(struct inode *ipbmap)
{
      struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;
      int actags, inactags, l2nl;
      s64 ag_rem, actfree, inactfree, avgfree;
      int i, n;

      /*
       *      finalize bmap control page
       */
//finalize:
      /* 
       * compute db_agpref: preferred ag to allocate from
       * (the leftmost ag with average free space in it);
       */
//agpref:
      /* get the number of active ags and inacitve ags */
      actags = bmp->db_maxag + 1;
      inactags = bmp->db_numag - actags;
      ag_rem = bmp->db_mapsize & (bmp->db_agsize - 1);      /* ??? */

      /* determine how many blocks are in the inactive allocation
       * groups. in doing this, we must account for the fact that
       * the rightmost group might be a partial group (i.e. file
       * system size is not a multiple of the group size).
       */
      inactfree = (inactags && ag_rem) ?
          ((inactags - 1) << bmp->db_agl2size) + ag_rem
          : inactags << bmp->db_agl2size;

      /* determine how many free blocks are in the active
       * allocation groups plus the average number of free blocks
       * within the active ags.
       */
      actfree = bmp->db_nfree - inactfree;
      avgfree = (u32) actfree / (u32) actags;

      /* if the preferred allocation group has not average free space.
       * re-establish the preferred group as the leftmost
       * group with average free space.
       */
      if (bmp->db_agfree[bmp->db_agpref] < avgfree) {
            for (bmp->db_agpref = 0; bmp->db_agpref < actags;
                 bmp->db_agpref++) {
                  if (bmp->db_agfree[bmp->db_agpref] >= avgfree)
                        break;
            }
            if (bmp->db_agpref >= bmp->db_numag) {
                  jfs_error(ipbmap->i_sb,
                          "cannot find ag with average freespace");
            }
      }

      /*
       * compute db_aglevel, db_agheigth, db_width, db_agstart:
       * an ag is covered in aglevel dmapctl summary tree, 
       * at agheight level height (from leaf) with agwidth number of nodes 
       * each, which starts at agstart index node of the smmary tree node 
       * array;
       */
      bmp->db_aglevel = BMAPSZTOLEV(bmp->db_agsize);
      l2nl =
          bmp->db_agl2size - (L2BPERDMAP + bmp->db_aglevel * L2LPERCTL);
      bmp->db_agheigth = l2nl >> 1;
      bmp->db_agwidth = 1 << (l2nl - (bmp->db_agheigth << 1));
      for (i = 5 - bmp->db_agheigth, bmp->db_agstart = 0, n = 1; i > 0;
           i--) {
            bmp->db_agstart += n;
            n <<= 2;
      }

}


/*
 * NAME:    dbInitDmap()/ujfs_idmap_page()
 *                                                                    
 * FUNCTION:      initialize working/persistent bitmap of the dmap page
 *          for the specified number of blocks:
 *                                                                    
 *          at entry, the bitmaps had been initialized as free (ZEROS);
 *          The number of blocks will only account for the actually 
 *          existing blocks. Blocks which don't actually exist in 
 *          the aggregate will be marked as allocated (ONES);
 *
 * PARAMETERS:
 *    dp    - pointer to page of map
 *    nblocks     - number of blocks this page
 *
 * RETURNS: NONE
 */
static int dbInitDmap(struct dmap * dp, s64 Blkno, int nblocks)
{
      int blkno, w, b, r, nw, nb, i;

      /* starting block number within the dmap */
      blkno = Blkno & (BPERDMAP - 1);

      if (blkno == 0) {
            dp->nblocks = dp->nfree = cpu_to_le32(nblocks);
            dp->start = cpu_to_le64(Blkno);

            if (nblocks == BPERDMAP) {
                  memset(&dp->wmap[0], 0, LPERDMAP * 4);
                  memset(&dp->pmap[0], 0, LPERDMAP * 4);
                  goto initTree;
            }
      } else {
            dp->nblocks =
                cpu_to_le32(le32_to_cpu(dp->nblocks) + nblocks);
            dp->nfree = cpu_to_le32(le32_to_cpu(dp->nfree) + nblocks);
      }

      /* word number containing start block number */
      w = blkno >> L2DBWORD;

      /*
       * free the bits corresponding to the block range (ZEROS):
       * note: not all bits of the first and last words may be contained 
       * within the block range.
       */
      for (r = nblocks; r > 0; r -= nb, blkno += nb) {
            /* number of bits preceding range to be freed in the word */
            b = blkno & (DBWORD - 1);
            /* number of bits to free in the word */
            nb = min(r, DBWORD - b);

            /* is partial word to be freed ? */
            if (nb < DBWORD) {
                  /* free (set to 0) from the bitmap word */
                  dp->wmap[w] &= cpu_to_le32(~(ONES << (DBWORD - nb)
                                         >> b));
                  dp->pmap[w] &= cpu_to_le32(~(ONES << (DBWORD - nb)
                                         >> b));

                  /* skip the word freed */
                  w++;
            } else {
                  /* free (set to 0) contiguous bitmap words */
                  nw = r >> L2DBWORD;
                  memset(&dp->wmap[w], 0, nw * 4);
                  memset(&dp->pmap[w], 0, nw * 4);

                  /* skip the words freed */
                  nb = nw << L2DBWORD;
                  w += nw;
            }
      }

      /*
       * mark bits following the range to be freed (non-existing 
       * blocks) as allocated (ONES)
       */

      if (blkno == BPERDMAP)
            goto initTree;

      /* the first word beyond the end of existing blocks */
      w = blkno >> L2DBWORD;

      /* does nblocks fall on a 32-bit boundary ? */
      b = blkno & (DBWORD - 1);
      if (b) {
            /* mark a partial word allocated */
            dp->wmap[w] = dp->pmap[w] = cpu_to_le32(ONES >> b);
            w++;
      }

      /* set the rest of the words in the page to allocated (ONES) */
      for (i = w; i < LPERDMAP; i++)
            dp->pmap[i] = dp->wmap[i] = cpu_to_le32(ONES);

      /*
       * init tree
       */
      initTree:
      return (dbInitDmapTree(dp));
}


/*
 * NAME:    dbInitDmapTree()/ujfs_complete_dmap()
 *                                                                    
 * FUNCTION:      initialize summary tree of the specified dmap:
 *
 *          at entry, bitmap of the dmap has been initialized;
 *                                                                    
 * PARAMETERS:
 *    dp    - dmap to complete
 *    blkno - starting block number for this dmap
 *    treemax     - will be filled in with max free for this dmap
 *
 * RETURNS: max free string at the root of the tree
 */
static int dbInitDmapTree(struct dmap * dp)
{
      struct dmaptree *tp;
      s8 *cp;
      int i;

      /* init fixed info of tree */
      tp = &dp->tree;
      tp->nleafs = cpu_to_le32(LPERDMAP);
      tp->l2nleafs = cpu_to_le32(L2LPERDMAP);
      tp->leafidx = cpu_to_le32(LEAFIND);
      tp->height = cpu_to_le32(4);
      tp->budmin = BUDMIN;

      /* init each leaf from corresponding wmap word:
       * note: leaf is set to NOFREE(-1) if all blocks of corresponding
       * bitmap word are allocated. 
       */
      cp = tp->stree + le32_to_cpu(tp->leafidx);
      for (i = 0; i < LPERDMAP; i++)
            *cp++ = dbMaxBud((u8 *) & dp->wmap[i]);

      /* build the dmap's binary buddy summary tree */
      return (dbInitTree(tp));
}


/*
 * NAME:    dbInitTree()/ujfs_adjtree()
 *                                                                    
 * FUNCTION:      initialize binary buddy summary tree of a dmap or dmapctl.
 *
 *          at entry, the leaves of the tree has been initialized 
 *          from corresponding bitmap word or root of summary tree
 *          of the child control page;
 *          configure binary buddy system at the leaf level, then
 *          bubble up the values of the leaf nodes up the tree.
 *
 * PARAMETERS:
 *    cp    - Pointer to the root of the tree
 *    l2leaves- Number of leaf nodes as a power of 2
 *    l2min - Number of blocks that can be covered by a leaf
 *            as a power of 2
 *
 * RETURNS: max free string at the root of the tree
 */
static int dbInitTree(struct dmaptree * dtp)
{
      int l2max, l2free, bsize, nextb, i;
      int child, parent, nparent;
      s8 *tp, *cp, *cp1;

      tp = dtp->stree;

      /* Determine the maximum free string possible for the leaves */
      l2max = le32_to_cpu(dtp->l2nleafs) + dtp->budmin;

      /*
       * configure the leaf levevl into binary buddy system
       *
       * Try to combine buddies starting with a buddy size of 1 
       * (i.e. two leaves). At a buddy size of 1 two buddy leaves 
       * can be combined if both buddies have a maximum free of l2min; 
       * the combination will result in the left-most buddy leaf having 
       * a maximum free of l2min+1.  
       * After processing all buddies for a given size, process buddies 
       * at the next higher buddy size (i.e. current size * 2) and 
       * the next maximum free (current free + 1).  
       * This continues until the maximum possible buddy combination 
       * yields maximum free.
       */
      for (l2free = dtp->budmin, bsize = 1; l2free < l2max;
           l2free++, bsize = nextb) {
            /* get next buddy size == current buddy pair size */
            nextb = bsize << 1;

            /* scan each adjacent buddy pair at current buddy size */
            for (i = 0, cp = tp + le32_to_cpu(dtp->leafidx);
                 i < le32_to_cpu(dtp->nleafs);
                 i += nextb, cp += nextb) {
                  /* coalesce if both adjacent buddies are max free */
                  if (*cp == l2free && *(cp + bsize) == l2free) {
                        *cp = l2free + 1; /* left take right */
                        *(cp + bsize) = -1;     /* right give left */
                  }
            }
      }

      /*
       * bubble summary information of leaves up the tree.
       *
       * Starting at the leaf node level, the four nodes described by
       * the higher level parent node are compared for a maximum free and 
       * this maximum becomes the value of the parent node.  
       * when all lower level nodes are processed in this fashion then 
       * move up to the next level (parent becomes a lower level node) and 
       * continue the process for that level.
       */
      for (child = le32_to_cpu(dtp->leafidx),
           nparent = le32_to_cpu(dtp->nleafs) >> 2;
           nparent > 0; nparent >>= 2, child = parent) {
            /* get index of 1st node of parent level */
            parent = (child - 1) >> 2;

            /* set the value of the parent node as the maximum 
             * of the four nodes of the current level.
             */
            for (i = 0, cp = tp + child, cp1 = tp + parent;
                 i < nparent; i++, cp += 4, cp1++)
                  *cp1 = TREEMAX(cp);
      }

      return (*tp);
}


/*
 *    dbInitDmapCtl()
 *
 * function: initialize dmapctl page
 */
static int dbInitDmapCtl(struct dmapctl * dcp, int level, int i)
{                       /* start leaf index not covered by range */
      s8 *cp;

      dcp->nleafs = cpu_to_le32(LPERCTL);
      dcp->l2nleafs = cpu_to_le32(L2LPERCTL);
      dcp->leafidx = cpu_to_le32(CTLLEAFIND);
      dcp->height = cpu_to_le32(5);
      dcp->budmin = L2BPERDMAP + L2LPERCTL * level;

      /*
       * initialize the leaves of current level that were not covered 
       * by the specified input block range (i.e. the leaves have no 
       * low level dmapctl or dmap).
       */
      cp = &dcp->stree[CTLLEAFIND + i];
      for (; i < LPERCTL; i++)
            *cp++ = NOFREE;

      /* build the dmap's binary buddy summary tree */
      return (dbInitTree((struct dmaptree *) dcp));
}


/*
 * NAME:    dbGetL2AGSize()/ujfs_getagl2size()
 *                                                                    
 * FUNCTION:      Determine log2(allocation group size) from aggregate size
 *                                                                    
 * PARAMETERS:
 *    nblocks     - Number of blocks in aggregate
 *
 * RETURNS: log2(allocation group size) in aggregate blocks
 */
static int dbGetL2AGSize(s64 nblocks)
{
      s64 sz;
      s64 m;
      int l2sz;

      if (nblocks < BPERDMAP * MAXAG)
            return (L2BPERDMAP);

      /* round up aggregate size to power of 2 */
      m = ((u64) 1 << (64 - 1));
      for (l2sz = 64; l2sz >= 0; l2sz--, m >>= 1) {
            if (m & nblocks)
                  break;
      }

      sz = (s64) 1 << l2sz;
      if (sz < nblocks)
            l2sz += 1;

      /* agsize = roundupSize/max_number_of_ag */
      return (l2sz - L2MAXAG);
}


/*
 * NAME:    dbMapFileSizeToMapSize()
 *                                                                    
 * FUNCTION:      compute number of blocks the block allocation map file 
 *          can cover from the map file size;
 *
 * RETURNS: Number of blocks which can be covered by this block map file;
 */

/*
 * maximum number of map pages at each level including control pages
 */
#define MAXL0PAGES      (1 + LPERCTL)
#define MAXL1PAGES      (1 + LPERCTL * MAXL0PAGES)
#define MAXL2PAGES      (1 + LPERCTL * MAXL1PAGES)

/*
 * convert number of map pages to the zero origin top dmapctl level
 */
#define BMAPPGTOLEV(npages)   \
      (((npages) <= 3 + MAXL0PAGES) ? 0 \
       : ((npages) <= 2 + MAXL1PAGES) ? 1 : 2)

s64 dbMapFileSizeToMapSize(struct inode * ipbmap)
{
      struct super_block *sb = ipbmap->i_sb;
      s64 nblocks;
      s64 npages, ndmaps;
      int level, i;
      int complete, factor;

      nblocks = ipbmap->i_size >> JFS_SBI(sb)->l2bsize;
      npages = nblocks >> JFS_SBI(sb)->l2nbperpage;
      level = BMAPPGTOLEV(npages);

      /* At each level, accumulate the number of dmap pages covered by 
       * the number of full child levels below it;
       * repeat for the last incomplete child level.
       */
      ndmaps = 0;
      npages--;         /* skip the first global control page */
      /* skip higher level control pages above top level covered by map */
      npages -= (2 - level);
      npages--;         /* skip top level's control page */
      for (i = level; i >= 0; i--) {
            factor =
                (i == 2) ? MAXL1PAGES : ((i == 1) ? MAXL0PAGES : 1);
            complete = (u32) npages / factor;
            ndmaps += complete * ((i == 2) ? LPERCTL * LPERCTL
                              : ((i == 1) ? LPERCTL : 1));

            /* pages in last/incomplete child */
            npages = (u32) npages % factor;
            /* skip incomplete child's level control page */
            npages--;
      }

      /* convert the number of dmaps into the number of blocks 
       * which can be covered by the dmaps;
       */
      nblocks = ndmaps << L2BPERDMAP;

      return (nblocks);
}

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