FreeBSD/Linux Kernel Cross Reference
sys/fs/jfs/jfs_dmap.c

     /*
      *   Copyright (c) International Business Machines Corp., 2000-2002
      *
      *   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_dmap.h"
    #include "jfs_imap.h"
    #include "jfs_lock.h"
    #include "jfs_metapage.h"
    #include "jfs_superblock.h"
    #include "jfs_debug.h"
    
    /*
     *      Debug code for double-checking block map
     */
    /* #define      _JFS_DEBUG_DMAP 1 */
    
    #ifdef  _JFS_DEBUG_DMAP
    #define DBINITMAP(size,ipbmap,results) \
            DBinitmap(size,ipbmap,results)
    #define DBALLOC(dbmap,mapsize,blkno,nblocks) \
            DBAlloc(dbmap,mapsize,blkno,nblocks)
    #define DBFREE(dbmap,mapsize,blkno,nblocks) \
            DBFree(dbmap,mapsize,blkno,nblocks)
    #define DBALLOCCK(dbmap,mapsize,blkno,nblocks) \
            DBAllocCK(dbmap,mapsize,blkno,nblocks)
    #define DBFREECK(dbmap,mapsize,blkno,nblocks) \
            DBFreeCK(dbmap,mapsize,blkno,nblocks)
    
    static void DBinitmap(s64, struct inode *, u32 **);
    static void DBAlloc(uint *, s64, s64, s64);
    static void DBFree(uint *, s64, s64, s64);
    static void DBAllocCK(uint *, s64, s64, s64);
    static void DBFreeCK(uint *, s64, s64, s64);
    #else
    #define DBINITMAP(size,ipbmap,results)
    #define DBALLOC(dbmap, mapsize, blkno, nblocks)
    #define DBFREE(dbmap, mapsize, blkno, nblocks)
    #define DBALLOCCK(dbmap, mapsize, blkno, nblocks)
    #define DBFREECK(dbmap, mapsize, blkno, nblocks)
    #endif                          /* _JFS_DEBUG_DMAP */
    
    /*
     *      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)     init_MUTEX(&bmp->db_bmaplock)
    #define BMAP_LOCK(bmp)          down(&bmp->db_bmaplock)
    #define BMAP_UNLOCK(bmp)        up(&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 void dbBackSplit(dmtree_t * tp, int leafno);
   static void 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);
   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 void 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);
   int blkstol2(s64 nb);
   void fsDirty(void);
   
   int cntlz(u32 value);
   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.
    */
   signed char 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 *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 *) 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));
           DBINITMAP(bmp->db_mapsize, ipbmap, &bmp->db_DBmap);
   
           /*
            * 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;
           int i;
   
           if (!(mounterror || isReadOnly(ipbmap)))
                   dbSync(ipbmap);
   
           /*
            * Invalidate the page cache buffers
            */
           truncate_inode_pages(ipbmap->i_mapping, 0);
   
           /*
            * Sanity Check
            */
           for (i = 0; i < bmp->db_numag; i++)
                   if (atomic_read(&bmp->db_active[i]))
                           printk(KERN_ERR "dbUnmount: db_active[%d] = %d\n",
                                  i, atomic_read(&bmp->db_active[i]));
   
           /* free the memory for the in-memory bmap. */
           kfree(bmp);
   
           return (0);
   }
   
   /*
    *      dbSync()
    */
   int dbSync(struct inode *ipbmap)
   {
           struct dbmap *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 *) 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
            */
           fsync_inode_data_buffers(ipbmap);
   
           ipbmap->i_state |= I_DIRTY;
           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 + nblocks > bmp->db_mapsize)) {
                   /*
                    * Trying to catch a bug here
                    */
                   printk(KERN_ERR
                          "JFS: dbFree asked to free block larger than mapsize\n");
                   printk(KERN_ERR
                          "blkno = 0x%Lx, nblocks = 0x%Lx, mapsize = 0x%Lx\n",
                          blkno, nblocks, bmp->db_mapsize);
                   printk(KERN_ERR "ino = %ld, cflag = %lx\n", ip->i_ino,
                          JFS_IP(ip)->cflag);
                   dump_stack();
                   /* Make sure fsck fixes things back up */
                   updateSuper(ip->i_sb, FM_DIRTY);
                   return -EIO;    /* Nobody checks the return code */
           }
   
           /*
            * 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)));
   
                   DBALLOCCK(bmp->db_DBmap, bmp->db_mapsize, blkno, nb);
   
                   /* free the blocks. */
                   if ((rc = dbFreeDmap(bmp, dp, blkno, nb))) {
                           release_metapage(mp);
                           IREAD_UNLOCK(ipbmap);
                           return (rc);
                   }
   
                   DBFREE(bmp->db_DBmap, bmp->db_mapsize, blkno, nb);
           }
   
           /* 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;
   
           /* the blocks better be within the mapsize. */
           assert(blkno + nblocks <= bmp->db_mapsize);
   
           /* 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);
                   }
                   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;
   
                   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 */
                                   LOGSYNC_LOCK(log);
                                   list_del(&mp->synclist);
                                   list_add(&mp->synclist, &tblk->synclist);
                                   LOGSYNC_UNLOCK(log);
                           }
   
                           /* inherit younger/larger clsn */
                           LOGSYNC_LOCK(log);
                           logdiff(difft, tblk->clsn, log);
                           logdiff(diffp, mp->clsn, log);
                           if (difft > diffp)
                                   mp->clsn = tblk->clsn;
                           LOGSYNC_UNLOCK(log);
                   } else {
                           mp->log = log;
                           mp->lsn = lsn;
   
                           /* insert bp after tblock in logsync list */
                           LOGSYNC_LOCK(log);
   
                           log->count++;
                           list_add(&mp->synclist, &tblk->synclist);
   
                           mp->clsn = tblk->clsn;
                           LOGSYNC_UNLOCK(log);
                   }
           }
   
           /* 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 */
           assert(hint < mapSize);
   
           /* 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);
                   if (rc == 0) {
                           DBALLOC(bmp->db_DBmap, bmp->db_mapsize, *results,
                                   nblocks);
                   }
   
                   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;
                                   DBALLOC(bmp->db_DBmap, bmp->db_mapsize,
                                           *results, nblocks);
                                   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) {
                                   DBALLOC(bmp->db_DBmap, bmp->db_mapsize,
                                           *results, nblocks);
                                   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) {
                                   DBALLOC(bmp->db_DBmap, bmp->db_mapsize,
                                           *results, nblocks);
                                   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) {
                   if (rc == 0)
                           DBALLOC(bmp->db_DBmap, bmp->db_mapsize,
                                   *results, nblocks);
                   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);
           if (rc == 0) {
                   DBALLOC(bmp->db_DBmap, bmp->db_mapsize, *results, nblocks);
           }
   
         write_unlock:
           IWRITE_UNLOCK(ipbmap);
   
           return (rc);
   
         read_unlock:
           IREAD_UNLOCK(ipbmap);
   
           return (rc);
   }
   
   
   /*
    * 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) {
                  DBALLOC(bmp->db_DBmap, bmp->db_mapsize, blkno, nblocks);
                  mark_metapage_dirty(mp);
          }
          release_metapage(mp);
  
          return (rc);
  }
  
  
  /*
   * 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
   */
  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;
          assert(lastblkno >= 0 && lastblkno < bmp->db_mapsize);
  
          /* 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 boundry.
           */
          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);
          }
  
          DBALLOCCK(bmp->db_DBmap, bmp->db_mapsize, blkno, nblocks);
          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) {
                  DBALLOC(bmp->db_DBmap, bmp->db_mapsize, extblkno,
                          addnblocks);
                  write_metapage(mp);
          } else {
                  /* we were not successful */
                  release_metapage(mp);
                  assert(rc == ENOSPC || rc == EIO);
          }
  
          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;
  
          /* 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 = 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.
           */
          assert(l2nb <= bmp->db_agl2size);
  
          /* 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);
                  /* assert(!(rc == ENOSPC && bmp->db_agfree[agno] == bmp->db_agsize)); */
                  if ((rc == ENOSPC) &&
                      (bmp->db_agfree[agno] == bmp->db_agsize)) {
                          jfs_err("dbAllocAG: removed assert, but still need to "
                                  "debug here\nblkno = 0x%Lx, nblocks = 0x%Lx",
                                  (unsigned long long) blkno,
                                  (unsigned long long) nblocks);
                  }
                  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;
  
          /* 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;
                                  }
                          }
                          assert(n < 4);
                  }
  
                  /* 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))) {
                                  assert(rc != ENOSPC);
                                  return (rc);
                          }
                  }
  
                  /* allocate the blocks.
                   */
                  rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
                  assert(rc != ENOSPC);
                  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);
          assert(rc != ENOSPC);
          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;
  
                  /* 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) {
                          assert(lev == level);
                          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.
                   */
                  assert(dp->tree.stree[ROOT] == L2BPERDMAP);
  
                  /* 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.
                           */
                          fsDirty();      /* !!! */
                          jfs_err("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);
                          fsDirty();      /* !!! */
                          jfs_err("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, 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 */
          dbFreeBits(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 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) {
                                  assert(leaf[word] >= BUDMIN);
  
                                  /* 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: none
   *
   * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static void 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 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.
                           */
                          dbJoin(tp, word,
                                 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 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.
                                   */
                                  dbJoin(tp, word, size);
  
                                  /* 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);
  }
  
  
  /*
   * 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;
  
          /* 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) {
                          dbBackSplit((dmtree_t *) dcp, leafno);
                          oldval = dcp->stree[ti];
                  }
                  dbSplit((dmtree_t *) dcp, leafno, dcp->budmin, newval);
          } else {
                  dbJoin((dmtree_t *) dcp, leafno, newval);
          }
  
          /* 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);
                          assert(bmp->db_maxfreebud == oldroot);
                          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 void 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) {
                          assert(bsz < le32_to_cpu(tp->dmt_nleafs));
  
                          /* 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;
                          }
                  }
          }
  
          assert(leaf[leafno] == size);
  }
  
  
  /*
   * 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 void 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;
  
                          assert(newval == leaf[buddy]);
  
                          /* 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);
  }
  
  
  /*
   * 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
   */
  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
   */
  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
   */
  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:        fsDirty()
   *
   * FUNCTION:    xxx
   *
   * PARAMETERS:
   *      ipmnt   - mount inode
   *
   * RETURN VALUES:
   *      none
   */
  void fsDirty()
  {
          printk("fsDirty(): bye-bye\n");
          assert(0);
  }
  
  
  /*
   * 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)));
  
                  DBFREECK(bmp->db_DBmap, bmp->db_mapsize, blkno, nb);
  
                  /* allocate the blocks. */
                  if ((rc = dbAllocDmapBU(bmp, dp, blkno, nb))) {
                          release_metapage(mp);
                          IREAD_UNLOCK(ipbmap);
                          return (rc);
                  }
  
                  DBALLOC(bmp->db_DBmap, bmp->db_mapsize, blkno, nb);
          }
  
          /* 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, *l0mp;
          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);
          assert(l2mp);
          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);
  
                          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);
  
                  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 */
  
          assert(0);
  
          /*
           *      finalize bmap control page
           */
        finalize:
  
          return 0;
  
        errout:
          return EIO;
  }
  
  
  /*
   *      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;
                  }
                  assert(bmp->db_agpref < bmp->db_numag);
          }
  
          /*
           * 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;
          }
  
  /*
  printk("bmap: agpref:%d aglevel:%d agheigth:%d agwidth:%d\n",
          bmp->db_agpref, bmp->db_aglevel, bmp->db_agheigth, bmp->db_agwidth);
  */
  }
  
  
  /*
   * 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;
  /*
  printk("sbh_dmap:  in dbInitDmap blkno:%Ld nblocks:%ld\n", Blkno, nblocks); 
  */
  
          /* 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)
           */
  /*
  printk("sbh_dmap:  in dbInitDmap, preparing to mark unbacked, blkno:%ld nblocks:%ld\n",
                  blkno, nblocks); 
  */
  
          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);
  /*
  printk("sbh_dmap:  in dbInitDmap, b:%ld w:%ld mask: %lx\n", b, w, (ONES>>b)); 
  */
          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] = 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);
  }
  
  
  #ifdef  _JFS_DEBUG_DMAP
  /*
   *      DBinitmap()
   */
  static void DBinitmap(s64 size, struct inode *ipbmap, u32 ** results)
  {
          int npages;
          u32 *dbmap, *d;
          int n;
          s64 lblkno, cur_block;
          struct dmap *dp;
          struct metapage *mp;
  
          npages = size / 32768;
          npages += (size % 32768) ? 1 : 0;
  
          dbmap = (u32 *) xmalloc(npages * 4096, L2PSIZE, kernel_heap);
          if (dbmap == NULL)
                  assert(0);
  
          for (n = 0, d = dbmap; n < npages; n++, d += 1024)
                  bzero(d, 4096);
  
          /* Need to initialize from disk map pages
           */
          for (d = dbmap, cur_block = 0; cur_block < size;
               cur_block += BPERDMAP, d += LPERDMAP) {
                  lblkno = BLKTODMAP(cur_block,
                                     JFS_SBI(ipbmap->i_sb)->bmap->
                                     db_l2nbperpage);
                  mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
                  if (mp == NULL) {
                          assert(0);
                  }
                  dp = (struct dmap *) mp->data;
  
                  for (n = 0; n < LPERDMAP; n++)
                          d[n] = le32_to_cpu(dp->wmap[n]);
  
                  release_metapage(mp);
          }
  
          *results = dbmap;
  }
  
  
  /*
   *      DBAlloc()
   */
  void DBAlloc(uint * dbmap, s64 mapsize, s64 blkno, s64 nblocks)
  {
          int word, nb, bitno;
          u32 mask;
  
          assert(blkno > 0 && blkno < mapsize);
          assert(nblocks > 0 && nblocks <= mapsize);
  
          assert(blkno + nblocks <= mapsize);
  
          dbmap += (blkno / 32);
          while (nblocks > 0) {
                  bitno = blkno & (32 - 1);
                  nb = min(nblocks, 32 - bitno);
  
                  mask = (0xffffffff << (32 - nb) >> bitno);
                  assert((mask & *dbmap) == 0);
                  *dbmap |= mask;
  
                  dbmap++;
                  blkno += nb;
                  nblocks -= nb;
          }
  }
  
  
  /*
   *      DBFree()
   */
  static void DBFree(uint * dbmap, s64 mapsize, s64 blkno, s64 nblocks)
  {
          int word, nb, bitno;
          u32 mask;
  
          assert(blkno > 0 && blkno < mapsize);
          assert(nblocks > 0 && nblocks <= mapsize);
  
          assert(blkno + nblocks <= mapsize);
  
          dbmap += (blkno / 32);
          while (nblocks > 0) {
                  bitno = blkno & (32 - 1);
                  nb = min(nblocks, 32 - bitno);
  
                  mask = (0xffffffff << (32 - nb) >> bitno);
                  assert((mask & *dbmap) == mask);
                  *dbmap &= ~mask;
  
                  dbmap++;
                  blkno += nb;
                  nblocks -= nb;
          }
  }
  
  
  /*
   *      DBAllocCK()
   */
  static void DBAllocCK(uint * dbmap, s64 mapsize, s64 blkno, s64 nblocks)
  {
          int word, nb, bitno;
          u32 mask;
  
          assert(blkno > 0 && blkno < mapsize);
          assert(nblocks > 0 && nblocks <= mapsize);
  
          assert(blkno + nblocks <= mapsize);
  
          dbmap += (blkno / 32);
          while (nblocks > 0) {
                  bitno = blkno & (32 - 1);
                  nb = min(nblocks, 32 - bitno);
  
                  mask = (0xffffffff << (32 - nb) >> bitno);
                  assert((mask & *dbmap) == mask);
  
                  dbmap++;
                  blkno += nb;
                  nblocks -= nb;
          }
  }
  
  
  /*
   *      DBFreeCK()
   */
  static void DBFreeCK(uint * dbmap, s64 mapsize, s64 blkno, s64 nblocks)
  {
          int word, nb, bitno;
          u32 mask;
  
          assert(blkno > 0 && blkno < mapsize);
          assert(nblocks > 0 && nblocks <= mapsize);
  
          assert(blkno + nblocks <= mapsize);
  
          dbmap += (blkno / 32);
          while (nblocks > 0) {
                  bitno = blkno & (32 - 1);
                  nb = min(nblocks, 32 - bitno);
  
                  mask = (0xffffffff << (32 - nb) >> bitno);
                  assert((mask & *dbmap) == 0);
  
                  dbmap++;
                  blkno += nb;
                  nblocks -= nb;
          }
  }
  
  
  /*
   *      dbPrtMap()
   */
  static void dbPrtMap(struct bmap * bmp)
  {
          printk("   mapsize:   %d%d\n", bmp->db_mapsize);
          printk("   nfree:     %d%d\n", bmp->db_nfree);
          printk("   numag:     %d\n", bmp->db_numag);
          printk("   agsize:    %d%d\n", bmp->db_agsize);
          printk("   agl2size:  %d\n", bmp->db_agl2size);
          printk("   agwidth:   %d\n", bmp->db_agwidth);
          printk("   agstart:   %d\n", bmp->db_agstart);
          printk("   agheigth:  %d\n", bmp->db_agheigth);
          printk("   aglevel:   %d\n", bmp->db_aglevel);
          printk("   maxlevel:  %d\n", bmp->db_maxlevel);
          printk("   maxag:     %d\n", bmp->db_maxag);
          printk("   agpref:    %d\n", bmp->db_agpref);
          printk("   l2nbppg:   %d\n", bmp->db_l2nbperpage);
  }
  
  
  /*
   *      dbPrtCtl()
   */
  static void dbPrtCtl(struct dmapctl * dcp)
  {
          int i, j, n;
  
          printk("   height:    %08x\n", le32_to_cpu(dcp->height));
          printk("   leafidx:   %08x\n", le32_to_cpu(dcp->leafidx));
          printk("   budmin:    %08x\n", dcp->budmin);
          printk("   nleafs:    %08x\n", le32_to_cpu(dcp->nleafs));
          printk("   l2nleafs:  %08x\n", le32_to_cpu(dcp->l2nleafs));
  
          printk("\n Tree:\n");
          for (i = 0; i < CTLLEAFIND; i += 8) {
                  n = min(8, CTLLEAFIND - i);
  
                  for (j = 0; j < n; j++)
                          printf("  [%03x]: %02x", i + j,
                                 (char) dcp->stree[i + j]);
                  printf("\n");
          }
  
          printk("\n Tree Leaves:\n");
          for (i = 0; i < LPERCTL; i += 8) {
                  n = min(8, LPERCTL - i);
  
                  for (j = 0; j < n; j++)
                          printf("  [%03x]: %02x",
                                 i + j,
                                 (char) dcp->stree[i + j + CTLLEAFIND]);
                  printf("\n");
          }
  }
  #endif                          /* _JFS_DEBUG_DMAP */