/*
   *   Copyright (C) International Business Machines Corp., 2000-2004
   *
   *   This program is free software;  you can redistribute it and/or modify
   *   it under the terms of the GNU General Public License as published by

   *   the Free Software Foundation; either version 2 of the License, or

   *   (at your option) any later version.

   *

   *   This program is distributed in the hope that it will be useful,
   *   but WITHOUT ANY WARRANTY;  without even the implied warranty of
   *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
   *   the GNU General Public License for more details.
   *
   *   You should have received a copy of the GNU General Public License

   *   along with this program;  if not, write to the Free Software

   *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
   */
  
  #include <linux/fs.h>

  #include <linux/slab.h>

  #include "jfs_incore.h"
  #include "jfs_superblock.h"
  #include "jfs_dmap.h"
  #include "jfs_imap.h"
  #include "jfs_lock.h"
  #include "jfs_metapage.h"
  #include "jfs_debug.h"
  
  /*

   *	SERIALIZATION of the Block Allocation Map.
   *
   *	the working state of the block allocation map is accessed in
   *	two directions:

   *

   *	1) allocation and free requests that start at the dmap
   *	   level and move up through the dmap control pages (i.e.
   *	   the vast majority of requests).

   *
   *	2) allocation requests that start at dmap control page

   *	   level and work down towards the dmaps.

   *

   *	the serialization scheme used here is as follows.
   *
   *	requests which start at the bottom are serialized against each
   *	other through buffers and each requests holds onto its buffers
   *	as it works it way up from a single dmap to the required level

   *	of dmap control page.
   *	requests that start at the top are serialized against each other
   *	and request that start from the bottom by the multiple read/single
   *	write inode lock of the bmap inode. requests starting at the top
   *	take this lock in write mode while request starting at the bottom
   *	take the lock in read mode.  a single top-down request may proceed

   *	exclusively while multiple bottoms-up requests may proceed
   *	simultaneously (under the protection of busy buffers).
   *

   *	in addition to information found in dmaps and dmap control pages,
   *	the working state of the block allocation map also includes read/
   *	write information maintained in the bmap descriptor (i.e. total
   *	free block count, allocation group level free block counts).
   *	a single exclusive lock (BMAP_LOCK) is used to guard this information
   *	in the face of multiple-bottoms up requests.
   *	(lock ordering: IREAD_LOCK, BMAP_LOCK);

   *

   *	accesses to the persistent state of the block allocation map (limited
   *	to the persistent bitmaps in dmaps) is guarded by (busy) buffers.
   */

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

  
  /*
   * forward references
   */
  static void dbAllocBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
  			int nblocks);
  static void dbSplit(dmtree_t * tp, int leafno, int splitsz, int newval);

  static int dbBackSplit(dmtree_t * tp, int leafno);

  static int dbJoin(dmtree_t * tp, int leafno, int newval);

  static void dbAdjTree(dmtree_t * tp, int leafno, int newval);
  static int dbAdjCtl(struct bmap * bmp, s64 blkno, int newval, int alloc,
  		    int level);
  static int dbAllocAny(struct bmap * bmp, s64 nblocks, int l2nb, s64 * results);
  static int dbAllocNext(struct bmap * bmp, struct dmap * dp, s64 blkno,
  		       int nblocks);
  static int dbAllocNear(struct bmap * bmp, struct dmap * dp, s64 blkno,
  		       int nblocks,
  		       int l2nb, s64 * results);
  static int dbAllocDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
  		       int nblocks);
  static int dbAllocDmapLev(struct bmap * bmp, struct dmap * dp, int nblocks,
  			  int l2nb,
  			  s64 * results);
  static int dbAllocAG(struct bmap * bmp, int agno, s64 nblocks, int l2nb,
  		     s64 * results);
  static int dbAllocCtl(struct bmap * bmp, s64 nblocks, int l2nb, s64 blkno,
  		      s64 * results);
  static int dbExtend(struct inode *ip, s64 blkno, s64 nblocks, s64 addnblocks);
  static int dbFindBits(u32 word, int l2nb);
  static int dbFindCtl(struct bmap * bmp, int l2nb, int level, s64 * blkno);
  static int dbFindLeaf(dmtree_t * tp, int l2nb, int *leafidx);

  static int dbFreeBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
  		      int nblocks);

  static int dbFreeDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
  		      int nblocks);
  static int dbMaxBud(u8 * cp);
  s64 dbMapFileSizeToMapSize(struct inode *ipbmap);
  static int blkstol2(s64 nb);
  
  static int cntlz(u32 value);
  static int cnttz(u32 word);
  
  static int dbAllocDmapBU(struct bmap * bmp, struct dmap * dp, s64 blkno,
  			 int nblocks);
  static int dbInitDmap(struct dmap * dp, s64 blkno, int nblocks);
  static int dbInitDmapTree(struct dmap * dp);
  static int dbInitTree(struct dmaptree * dtp);
  static int dbInitDmapCtl(struct dmapctl * dcp, int level, int i);
  static int dbGetL2AGSize(s64 nblocks);
  
  /*
   *	buddy table
   *

   * table used for determining buddy sizes within characters of

   * dmap bitmap words.  the characters themselves serve as indexes
   * into the table, with the table elements yielding the maximum
   * binary buddy of free bits within the character.
   */

  static const s8 budtab[256] = {

  	3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
  	2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  	2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  	2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  	2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
  	2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
  	2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0,
  	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, -1
  };
  
  
  /*

   * NAME:	dbMount()

   *
   * FUNCTION:	initializate the block allocation map.
   *
   *		memory is allocated for the in-core bmap descriptor and
   *		the in-core descriptor is initialized from disk.
   *
   * PARAMETERS:

   *	ipbmap	- pointer to in-core inode for the block map.

   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOMEM	- insufficient memory
   *	-EIO	- i/o error

   */
  int dbMount(struct inode *ipbmap)
  {
  	struct bmap *bmp;
  	struct dbmap_disk *dbmp_le;
  	struct metapage *mp;
  	int i;
  
  	/*
  	 * allocate/initialize the in-memory bmap descriptor
  	 */
  	/* allocate memory for the in-memory bmap descriptor */
  	bmp = kmalloc(sizeof(struct bmap), GFP_KERNEL);
  	if (bmp == NULL)
  		return -ENOMEM;
  
  	/* read the on-disk bmap descriptor. */
  	mp = read_metapage(ipbmap,
  			   BMAPBLKNO << JFS_SBI(ipbmap->i_sb)->l2nbperpage,
  			   PSIZE, 0);
  	if (mp == NULL) {
  		kfree(bmp);
  		return -EIO;
  	}
  
  	/* copy the on-disk bmap descriptor to its in-memory version. */
  	dbmp_le = (struct dbmap_disk *) mp->data;
  	bmp->db_mapsize = le64_to_cpu(dbmp_le->dn_mapsize);
  	bmp->db_nfree = le64_to_cpu(dbmp_le->dn_nfree);
  	bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
  	bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
  	bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
  	bmp->db_maxag = le32_to_cpu(dbmp_le->dn_maxag);
  	bmp->db_agpref = le32_to_cpu(dbmp_le->dn_agpref);
  	bmp->db_aglevel = le32_to_cpu(dbmp_le->dn_aglevel);

  	bmp->db_agheight = le32_to_cpu(dbmp_le->dn_agheight);

  	bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);
  	bmp->db_agstart = le32_to_cpu(dbmp_le->dn_agstart);
  	bmp->db_agl2size = le32_to_cpu(dbmp_le->dn_agl2size);
  	for (i = 0; i < MAXAG; i++)
  		bmp->db_agfree[i] = le64_to_cpu(dbmp_le->dn_agfree[i]);
  	bmp->db_agsize = le64_to_cpu(dbmp_le->dn_agsize);
  	bmp->db_maxfreebud = dbmp_le->dn_maxfreebud;
  
  	/* release the buffer. */
  	release_metapage(mp);
  
  	/* bind the bmap inode and the bmap descriptor to each other. */
  	bmp->db_ipbmap = ipbmap;
  	JFS_SBI(ipbmap->i_sb)->bmap = bmp;
  
  	memset(bmp->db_active, 0, sizeof(bmp->db_active));

  
  	/*
  	 * allocate/initialize the bmap lock
  	 */
  	BMAP_LOCK_INIT(bmp);
  
  	return (0);
  }
  
  
  /*

   * NAME:	dbUnmount()

   *
   * FUNCTION:	terminate the block allocation map in preparation for
   *		file system unmount.
   *

   *		the in-core bmap descriptor is written to disk and

   *		the memory for this descriptor is freed.
   *
   * PARAMETERS:

   *	ipbmap	- pointer to in-core inode for the block map.

   *
   * RETURN VALUES:

   *	0	- success
   *	-EIO	- i/o error

   */
  int dbUnmount(struct inode *ipbmap, int mounterror)
  {
  	struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;

  
  	if (!(mounterror || isReadOnly(ipbmap)))
  		dbSync(ipbmap);
  
  	/*
  	 * Invalidate the page cache buffers
  	 */
  	truncate_inode_pages(ipbmap->i_mapping, 0);

  	/* free the memory for the in-memory bmap. */
  	kfree(bmp);
  
  	return (0);
  }
  
  /*
   *	dbSync()
   */
  int dbSync(struct inode *ipbmap)
  {
  	struct dbmap_disk *dbmp_le;
  	struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;
  	struct metapage *mp;
  	int i;
  
  	/*
  	 * write bmap global control page
  	 */
  	/* get the buffer for the on-disk bmap descriptor. */
  	mp = read_metapage(ipbmap,
  			   BMAPBLKNO << JFS_SBI(ipbmap->i_sb)->l2nbperpage,
  			   PSIZE, 0);
  	if (mp == NULL) {
  		jfs_err("dbSync: read_metapage failed!");
  		return -EIO;
  	}
  	/* copy the in-memory version of the bmap to the on-disk version */
  	dbmp_le = (struct dbmap_disk *) mp->data;
  	dbmp_le->dn_mapsize = cpu_to_le64(bmp->db_mapsize);
  	dbmp_le->dn_nfree = cpu_to_le64(bmp->db_nfree);
  	dbmp_le->dn_l2nbperpage = cpu_to_le32(bmp->db_l2nbperpage);
  	dbmp_le->dn_numag = cpu_to_le32(bmp->db_numag);
  	dbmp_le->dn_maxlevel = cpu_to_le32(bmp->db_maxlevel);
  	dbmp_le->dn_maxag = cpu_to_le32(bmp->db_maxag);
  	dbmp_le->dn_agpref = cpu_to_le32(bmp->db_agpref);
  	dbmp_le->dn_aglevel = cpu_to_le32(bmp->db_aglevel);

  	dbmp_le->dn_agheight = cpu_to_le32(bmp->db_agheight);

  	dbmp_le->dn_agwidth = cpu_to_le32(bmp->db_agwidth);
  	dbmp_le->dn_agstart = cpu_to_le32(bmp->db_agstart);
  	dbmp_le->dn_agl2size = cpu_to_le32(bmp->db_agl2size);
  	for (i = 0; i < MAXAG; i++)
  		dbmp_le->dn_agfree[i] = cpu_to_le64(bmp->db_agfree[i]);
  	dbmp_le->dn_agsize = cpu_to_le64(bmp->db_agsize);
  	dbmp_le->dn_maxfreebud = bmp->db_maxfreebud;
  
  	/* write the buffer */
  	write_metapage(mp);
  
  	/*
  	 * write out dirty pages of bmap
  	 */

  	filemap_write_and_wait(ipbmap->i_mapping);

  	diWriteSpecial(ipbmap, 0);
  
  	return (0);
  }
  
  
  /*

   * NAME:	dbFree()

   *
   * FUNCTION:	free the specified block range from the working block
   *		allocation map.
   *
   *		the blocks will be free from the working map one dmap
   *		at a time.
   *
   * PARAMETERS:

   *	ip	- pointer to in-core inode;
   *	blkno	- starting block number to be freed.
   *	nblocks	- number of blocks to be freed.

   *
   * RETURN VALUES:

   *	0	- success
   *	-EIO	- i/o error

   */
  int dbFree(struct inode *ip, s64 blkno, s64 nblocks)
  {
  	struct metapage *mp;
  	struct dmap *dp;
  	int nb, rc;
  	s64 lblkno, rem;
  	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
  	struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;

  	IREAD_LOCK(ipbmap, RDWRLOCK_DMAP);

  
  	/* block to be freed better be within the mapsize. */
  	if (unlikely((blkno == 0) || (blkno + nblocks > bmp->db_mapsize))) {
  		IREAD_UNLOCK(ipbmap);
  		printk(KERN_ERR "blkno = %Lx, nblocks = %Lx
  ",
  		       (unsigned long long) blkno,
  		       (unsigned long long) nblocks);
  		jfs_error(ip->i_sb,
  			  "dbFree: block to be freed is outside the map");
  		return -EIO;
  	}
  
  	/*
  	 * free the blocks a dmap at a time.
  	 */
  	mp = NULL;
  	for (rem = nblocks; rem > 0; rem -= nb, blkno += nb) {
  		/* release previous dmap if any */
  		if (mp) {
  			write_metapage(mp);
  		}
  
  		/* get the buffer for the current dmap. */
  		lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
  		mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
  		if (mp == NULL) {
  			IREAD_UNLOCK(ipbmap);
  			return -EIO;
  		}
  		dp = (struct dmap *) mp->data;
  
  		/* determine the number of blocks to be freed from
  		 * this dmap.
  		 */
  		nb = min(rem, BPERDMAP - (blkno & (BPERDMAP - 1)));

  		/* free the blocks. */
  		if ((rc = dbFreeDmap(bmp, dp, blkno, nb))) {

  			jfs_error(ip->i_sb, "dbFree: error in block map
  ");

  			release_metapage(mp);
  			IREAD_UNLOCK(ipbmap);
  			return (rc);
  		}

  	}
  
  	/* write the last buffer. */
  	write_metapage(mp);
  
  	IREAD_UNLOCK(ipbmap);
  
  	return (0);
  }
  
  
  /*
   * NAME:	dbUpdatePMap()
   *

   * FUNCTION:	update the allocation state (free or allocate) of the

   *		specified block range in the persistent block allocation map.

   *

   *		the blocks will be updated in the persistent map one
   *		dmap at a time.
   *
   * PARAMETERS:

   *	ipbmap	- pointer to in-core inode for the block map.
   *	free	- 'true' if block range is to be freed from the persistent
   *		  map; 'false' if it is to be allocated.
   *	blkno	- starting block number of the range.
   *	nblocks	- number of contiguous blocks in the range.
   *	tblk	- transaction block;

   *
   * RETURN VALUES:

   *	0	- success
   *	-EIO	- i/o error

   */
  int
  dbUpdatePMap(struct inode *ipbmap,
  	     int free, s64 blkno, s64 nblocks, struct tblock * tblk)
  {
  	int nblks, dbitno, wbitno, rbits;
  	int word, nbits, nwords;
  	struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;
  	s64 lblkno, rem, lastlblkno;
  	u32 mask;
  	struct dmap *dp;
  	struct metapage *mp;
  	struct jfs_log *log;
  	int lsn, difft, diffp;

  	unsigned long flags;

  
  	/* the blocks better be within the mapsize. */
  	if (blkno + nblocks > bmp->db_mapsize) {
  		printk(KERN_ERR "blkno = %Lx, nblocks = %Lx
  ",
  		       (unsigned long long) blkno,
  		       (unsigned long long) nblocks);
  		jfs_error(ipbmap->i_sb,
  			  "dbUpdatePMap: blocks are outside the map");
  		return -EIO;
  	}
  
  	/* compute delta of transaction lsn from log syncpt */
  	lsn = tblk->lsn;
  	log = (struct jfs_log *) JFS_SBI(tblk->sb)->log;
  	logdiff(difft, lsn, log);
  
  	/*
  	 * update the block state a dmap at a time.
  	 */
  	mp = NULL;
  	lastlblkno = 0;
  	for (rem = nblocks; rem > 0; rem -= nblks, blkno += nblks) {
  		/* get the buffer for the current dmap. */
  		lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
  		if (lblkno != lastlblkno) {
  			if (mp) {
  				write_metapage(mp);
  			}
  
  			mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE,
  					   0);
  			if (mp == NULL)
  				return -EIO;

  			metapage_wait_for_io(mp);

  		}
  		dp = (struct dmap *) mp->data;
  
  		/* determine the bit number and word within the dmap of
  		 * the starting block.  also determine how many blocks
  		 * are to be updated within this dmap.
  		 */
  		dbitno = blkno & (BPERDMAP - 1);
  		word = dbitno >> L2DBWORD;
  		nblks = min(rem, (s64)BPERDMAP - dbitno);
  
  		/* update the bits of the dmap words. the first and last
  		 * words may only have a subset of their bits updated. if
  		 * this is the case, we'll work against that word (i.e.

  		 * partial first and/or last) only in a single pass.  a

  		 * single pass will also be used to update all words that
  		 * are to have all their bits updated.
  		 */
  		for (rbits = nblks; rbits > 0;
  		     rbits -= nbits, dbitno += nbits) {
  			/* determine the bit number within the word and
  			 * the number of bits within the word.
  			 */
  			wbitno = dbitno & (DBWORD - 1);
  			nbits = min(rbits, DBWORD - wbitno);
  
  			/* check if only part of the word is to be updated. */
  			if (nbits < DBWORD) {
  				/* update (free or allocate) the bits
  				 * in this word.
  				 */
  				mask =
  				    (ONES << (DBWORD - nbits) >> wbitno);
  				if (free)
  					dp->pmap[word] &=
  					    cpu_to_le32(~mask);
  				else
  					dp->pmap[word] |=
  					    cpu_to_le32(mask);
  
  				word += 1;
  			} else {
  				/* one or more words are to have all
  				 * their bits updated.  determine how
  				 * many words and how many bits.
  				 */
  				nwords = rbits >> L2DBWORD;
  				nbits = nwords << L2DBWORD;
  
  				/* update (free or allocate) the bits
  				 * in these words.
  				 */
  				if (free)
  					memset(&dp->pmap[word], 0,
  					       nwords * 4);
  				else
  					memset(&dp->pmap[word], (int) ONES,
  					       nwords * 4);
  
  				word += nwords;
  			}
  		}
  
  		/*
  		 * update dmap lsn
  		 */
  		if (lblkno == lastlblkno)
  			continue;
  
  		lastlblkno = lblkno;

  		LOGSYNC_LOCK(log, flags);

  		if (mp->lsn != 0) {
  			/* inherit older/smaller lsn */
  			logdiff(diffp, mp->lsn, log);
  			if (difft < diffp) {
  				mp->lsn = lsn;
  
  				/* move bp after tblock in logsync list */

  				list_move(&mp->synclist, &tblk->synclist);

  			}
  
  			/* inherit younger/larger clsn */

  			logdiff(difft, tblk->clsn, log);
  			logdiff(diffp, mp->clsn, log);
  			if (difft > diffp)
  				mp->clsn = tblk->clsn;

  		} else {
  			mp->log = log;
  			mp->lsn = lsn;
  
  			/* insert bp after tblock in logsync list */

  			log->count++;
  			list_add(&mp->synclist, &tblk->synclist);
  
  			mp->clsn = tblk->clsn;

  		}

  		LOGSYNC_UNLOCK(log, flags);

  	}
  
  	/* write the last buffer. */
  	if (mp) {
  		write_metapage(mp);
  	}
  
  	return (0);
  }
  
  
  /*
   * NAME:	dbNextAG()
   *

   * FUNCTION:	find the preferred allocation group for new allocations.

   *
   *		Within the allocation groups, we maintain a preferred
   *		allocation group which consists of a group with at least
   *		average free space.  It is the preferred group that we target
   *		new inode allocation towards.  The tie-in between inode
   *		allocation and block allocation occurs as we allocate the
   *		first (data) block of an inode and specify the inode (block)
   *		as the allocation hint for this block.
   *
   *		We try to avoid having more than one open file growing in
   *		an allocation group, as this will lead to fragmentation.
   *		This differs from the old OS/2 method of trying to keep
   *		empty ags around for large allocations.
   *
   * PARAMETERS:

   *	ipbmap	- pointer to in-core inode for the block map.

   *
   * RETURN VALUES:

   *	the preferred allocation group number.

   */
  int dbNextAG(struct inode *ipbmap)
  {
  	s64 avgfree;
  	int agpref;
  	s64 hwm = 0;
  	int i;
  	int next_best = -1;
  	struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;
  
  	BMAP_LOCK(bmp);
  
  	/* determine the average number of free blocks within the ags. */
  	avgfree = (u32)bmp->db_nfree / bmp->db_numag;
  
  	/*
  	 * if the current preferred ag does not have an active allocator
  	 * and has at least average freespace, return it
  	 */
  	agpref = bmp->db_agpref;
  	if ((atomic_read(&bmp->db_active[agpref]) == 0) &&
  	    (bmp->db_agfree[agpref] >= avgfree))
  		goto unlock;
  
  	/* From the last preferred ag, find the next one with at least
  	 * average free space.
  	 */
  	for (i = 0 ; i < bmp->db_numag; i++, agpref++) {
  		if (agpref == bmp->db_numag)
  			agpref = 0;
  
  		if (atomic_read(&bmp->db_active[agpref]))
  			/* open file is currently growing in this ag */
  			continue;
  		if (bmp->db_agfree[agpref] >= avgfree) {
  			/* Return this one */
  			bmp->db_agpref = agpref;
  			goto unlock;
  		} else if (bmp->db_agfree[agpref] > hwm) {
  			/* Less than avg. freespace, but best so far */
  			hwm = bmp->db_agfree[agpref];
  			next_best = agpref;
  		}
  	}
  
  	/*
  	 * If no inactive ag was found with average freespace, use the
  	 * next best
  	 */
  	if (next_best != -1)
  		bmp->db_agpref = next_best;
  	/* else leave db_agpref unchanged */
  unlock:
  	BMAP_UNLOCK(bmp);
  
  	/* return the preferred group.
  	 */
  	return (bmp->db_agpref);
  }
  
  /*
   * NAME:	dbAlloc()
   *

   * FUNCTION:	attempt to allocate a specified number of contiguous free

   *		blocks from the working allocation block map.
   *
   *		the block allocation policy uses hints and a multi-step
   *		approach.
   *

   *		for allocation requests smaller than the number of blocks

   *		per dmap, we first try to allocate the new blocks
   *		immediately following the hint.  if these blocks are not
   *		available, we try to allocate blocks near the hint.  if

   *		no blocks near the hint are available, we next try to

   *		allocate within the same dmap as contains the hint.
   *
   *		if no blocks are available in the dmap or the allocation
   *		request is larger than the dmap size, we try to allocate
   *		within the same allocation group as contains the hint. if
   *		this does not succeed, we finally try to allocate anywhere
   *		within the aggregate.
   *
   *		we also try to allocate anywhere within the aggregate for
   *		for allocation requests larger than the allocation group
   *		size or requests that specify no hint value.
   *
   * PARAMETERS:

   *	ip	- pointer to in-core inode;
   *	hint	- allocation hint.
   *	nblocks	- number of contiguous blocks in the range.
   *	results	- on successful return, set to the starting block number

   *		  of the newly allocated contiguous range.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   */
  int dbAlloc(struct inode *ip, s64 hint, s64 nblocks, s64 * results)
  {
  	int rc, agno;
  	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
  	struct bmap *bmp;
  	struct metapage *mp;
  	s64 lblkno, blkno;
  	struct dmap *dp;
  	int l2nb;
  	s64 mapSize;
  	int writers;
  
  	/* assert that nblocks is valid */
  	assert(nblocks > 0);

  	/* 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;

  	mapSize = bmp->db_mapsize;
  
  	/* the hint should be within the map */
  	if (hint >= mapSize) {
  		jfs_error(ip->i_sb, "dbAlloc: the hint is outside the map");
  		return -EIO;
  	}
  
  	/* if the number of blocks to be allocated is greater than the
  	 * allocation group size, try to allocate anywhere.
  	 */
  	if (l2nb > bmp->db_agl2size) {

  		IWRITE_LOCK(ipbmap, RDWRLOCK_DMAP);

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

  
  		goto write_unlock;
  	}
  
  	/*
  	 * If no hint, let dbNextAG recommend an allocation group
  	 */
  	if (hint == 0)
  		goto pref_ag;
  
  	/* we would like to allocate close to the hint.  adjust the
  	 * hint to the block following the hint since the allocators
  	 * will start looking for free space starting at this point.
  	 */
  	blkno = hint + 1;
  
  	if (blkno >= bmp->db_mapsize)
  		goto pref_ag;
  
  	agno = blkno >> bmp->db_agl2size;
  
  	/* check if blkno crosses over into a new allocation group.
  	 * if so, check if we should allow allocations within this
  	 * allocation group.
  	 */
  	if ((blkno & (bmp->db_agsize - 1)) == 0)

  		/* check if the AG is currently 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, RDWRLOCK_DMAP);

  
  		/* get the buffer for the dmap containing the hint.
  		 */
  		rc = -EIO;
  		lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
  		mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
  		if (mp == NULL)
  			goto read_unlock;
  
  		dp = (struct dmap *) mp->data;
  
  		/* first, try to satisfy the allocation request with the
  		 * blocks beginning at the hint.
  		 */
  		if ((rc = dbAllocNext(bmp, dp, blkno, (int) nblocks))
  		    != -ENOSPC) {
  			if (rc == 0) {
  				*results = blkno;

  				mark_metapage_dirty(mp);
  			}
  
  			release_metapage(mp);
  			goto read_unlock;
  		}
  
  		writers = atomic_read(&bmp->db_active[agno]);
  		if ((writers > 1) ||
  		    ((writers == 1) && (JFS_IP(ip)->active_ag != agno))) {
  			/*
  			 * Someone else is writing in this allocation
  			 * group.  To avoid fragmenting, try another ag
  			 */
  			release_metapage(mp);
  			IREAD_UNLOCK(ipbmap);
  			goto pref_ag;
  		}
  
  		/* next, try to satisfy the allocation request with blocks
  		 * near the hint.
  		 */
  		if ((rc =
  		     dbAllocNear(bmp, dp, blkno, (int) nblocks, l2nb, results))
  		    != -ENOSPC) {

  			if (rc == 0)

  				mark_metapage_dirty(mp);

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

  			if (rc == 0)

  				mark_metapage_dirty(mp);

  
  			release_metapage(mp);
  			goto read_unlock;
  		}
  
  		release_metapage(mp);
  		IREAD_UNLOCK(ipbmap);
  	}
  
  	/* try to satisfy the allocation request with blocks within
  	 * the same allocation group as the hint.
  	 */

  	IWRITE_LOCK(ipbmap, RDWRLOCK_DMAP);

  	if ((rc = dbAllocAG(bmp, agno, nblocks, l2nb, results)) != -ENOSPC)

  		goto write_unlock;

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

  	IWRITE_LOCK(ipbmap, RDWRLOCK_DMAP);

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

  
        write_unlock:
  	IWRITE_UNLOCK(ipbmap);
  
  	return (rc);
  
        read_unlock:
  	IREAD_UNLOCK(ipbmap);
  
  	return (rc);
  }
  
  #ifdef _NOTYET
  /*
   * NAME:	dbAllocExact()
   *

   * FUNCTION:	try to allocate the requested extent;

   *
   * PARAMETERS:

   *	ip	- pointer to in-core inode;
   *	blkno	- extent address;
   *	nblocks	- extent length;

   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   */
  int dbAllocExact(struct inode *ip, s64 blkno, int nblocks)
  {
  	int rc;
  	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
  	struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;
  	struct dmap *dp;
  	s64 lblkno;
  	struct metapage *mp;

  	IREAD_LOCK(ipbmap, RDWRLOCK_DMAP);

  
  	/*
  	 * validate extent request:
  	 *
  	 * note: defragfs policy:

  	 *  max 64 blocks will be moved.

  	 *  allocation request size must be satisfied from a single dmap.
  	 */
  	if (nblocks <= 0 || nblocks > BPERDMAP || blkno >= bmp->db_mapsize) {
  		IREAD_UNLOCK(ipbmap);
  		return -EINVAL;
  	}
  
  	if (nblocks > ((s64) 1 << bmp->db_maxfreebud)) {
  		/* the free space is no longer available */
  		IREAD_UNLOCK(ipbmap);
  		return -ENOSPC;
  	}
  
  	/* read in the dmap covering the extent */
  	lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
  	mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
  	if (mp == NULL) {
  		IREAD_UNLOCK(ipbmap);
  		return -EIO;
  	}
  	dp = (struct dmap *) mp->data;
  
  	/* try to allocate the requested extent */
  	rc = dbAllocNext(bmp, dp, blkno, nblocks);
  
  	IREAD_UNLOCK(ipbmap);

  	if (rc == 0)

  		mark_metapage_dirty(mp);

  	release_metapage(mp);
  
  	return (rc);
  }
  #endif /* _NOTYET */
  
  /*
   * NAME:	dbReAlloc()
   *

   * FUNCTION:	attempt to extend a current allocation by a specified

   *		number of blocks.
   *
   *		this routine attempts to satisfy the allocation request
   *		by first trying to extend the existing allocation in
   *		place by allocating the additional blocks as the blocks
   *		immediately following the current allocation.  if these
   *		blocks are not available, this routine will attempt to
   *		allocate a new set of contiguous blocks large enough
   *		to cover the existing allocation plus the additional
   *		number of blocks required.
   *
   * PARAMETERS:

   *	ip	    -  pointer to in-core inode requiring allocation.
   *	blkno	    -  starting block of the current allocation.
   *	nblocks	    -  number of contiguous blocks within the current

   *		       allocation.

   *	addnblocks  -  number of blocks to add to the allocation.
   *	results	-      on successful return, set to the starting block number

   *		       of the existing allocation if the existing allocation
   *		       was extended in place or to a newly allocated contiguous
   *		       range if the existing allocation could not be extended
   *		       in place.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   */
  int
  dbReAlloc(struct inode *ip,
  	  s64 blkno, s64 nblocks, s64 addnblocks, s64 * results)
  {
  	int rc;
  
  	/* try to extend the allocation in place.
  	 */
  	if ((rc = dbExtend(ip, blkno, nblocks, addnblocks)) == 0) {
  		*results = blkno;
  		return (0);
  	} else {
  		if (rc != -ENOSPC)
  			return (rc);
  	}
  
  	/* could not extend the allocation in place, so allocate a
  	 * new set of blocks for the entire request (i.e. try to get
  	 * a range of contiguous blocks large enough to cover the
  	 * existing allocation plus the additional blocks.)
  	 */
  	return (dbAlloc
  		(ip, blkno + nblocks - 1, addnblocks + nblocks, results));
  }
  
  
  /*
   * NAME:	dbExtend()
   *

   * FUNCTION:	attempt to extend a current allocation by a specified

   *		number of blocks.
   *
   *		this routine attempts to satisfy the allocation request
   *		by first trying to extend the existing allocation in
   *		place by allocating the additional blocks as the blocks
   *		immediately following the current allocation.
   *
   * PARAMETERS:

   *	ip	    -  pointer to in-core inode requiring allocation.
   *	blkno	    -  starting block of the current allocation.
   *	nblocks	    -  number of contiguous blocks within the current

   *		       allocation.

   *	addnblocks  -  number of blocks to add to the allocation.

   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   */
  static int dbExtend(struct inode *ip, s64 blkno, s64 nblocks, s64 addnblocks)
  {
  	struct jfs_sb_info *sbi = JFS_SBI(ip->i_sb);
  	s64 lblkno, lastblkno, extblkno;
  	uint rel_block;
  	struct metapage *mp;
  	struct dmap *dp;
  	int rc;
  	struct inode *ipbmap = sbi->ipbmap;
  	struct bmap *bmp;
  
  	/*
  	 * We don't want a non-aligned extent to cross a page boundary
  	 */
  	if (((rel_block = blkno & (sbi->nbperpage - 1))) &&
  	    (rel_block + nblocks + addnblocks > sbi->nbperpage))
  		return -ENOSPC;
  
  	/* get the last block of the current allocation */
  	lastblkno = blkno + nblocks - 1;
  
  	/* determine the block number of the block following
  	 * the existing allocation.
  	 */
  	extblkno = lastblkno + 1;

  	IREAD_LOCK(ipbmap, RDWRLOCK_DMAP);

  
  	/* better be within the file system */
  	bmp = sbi->bmap;
  	if (lastblkno < 0 || lastblkno >= bmp->db_mapsize) {
  		IREAD_UNLOCK(ipbmap);
  		jfs_error(ip->i_sb,
  			  "dbExtend: the block is outside the filesystem");
  		return -EIO;
  	}
  
  	/* we'll attempt to extend the current allocation in place by
  	 * allocating the additional blocks as the blocks immediately
  	 * following the current allocation.  we only try to extend the
  	 * current allocation in place if the number of additional blocks
  	 * can fit into a dmap, the last block of the current allocation
  	 * is not the last block of the file system, and the start of the
  	 * inplace extension is not on an allocation group boundary.
  	 */
  	if (addnblocks > BPERDMAP || extblkno >= bmp->db_mapsize ||
  	    (extblkno & (bmp->db_agsize - 1)) == 0) {
  		IREAD_UNLOCK(ipbmap);
  		return -ENOSPC;
  	}
  
  	/* get the buffer for the dmap containing the first block
  	 * of the extension.
  	 */
  	lblkno = BLKTODMAP(extblkno, bmp->db_l2nbperpage);
  	mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
  	if (mp == NULL) {
  		IREAD_UNLOCK(ipbmap);
  		return -EIO;
  	}

  	dp = (struct dmap *) mp->data;
  
  	/* try to allocate the blocks immediately following the
  	 * current allocation.
  	 */
  	rc = dbAllocNext(bmp, dp, extblkno, (int) addnblocks);
  
  	IREAD_UNLOCK(ipbmap);
  
  	/* were we successful ? */

  	if (rc == 0)

  		write_metapage(mp);

  	else

  		/* we were not successful */
  		release_metapage(mp);
  
  
  	return (rc);
  }
  
  
  /*
   * NAME:	dbAllocNext()
   *

   * FUNCTION:	attempt to allocate the blocks of the specified block

   *		range within a dmap.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	dp	-  pointer to dmap.
   *	blkno	-  starting block number of the range.
   *	nblocks	-  number of contiguous free blocks of the range.

   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   *
   * serialization: IREAD_LOCK(ipbmap) held on entry/exit;
   */
  static int dbAllocNext(struct bmap * bmp, struct dmap * dp, s64 blkno,
  		       int nblocks)
  {
  	int dbitno, word, rembits, nb, nwords, wbitno, nw;
  	int l2size;
  	s8 *leaf;
  	u32 mask;
  
  	if (dp->tree.leafidx != cpu_to_le32(LEAFIND)) {
  		jfs_error(bmp->db_ipbmap->i_sb,
  			  "dbAllocNext: Corrupt dmap page");
  		return -EIO;
  	}
  
  	/* pick up a pointer to the leaves of the dmap tree.
  	 */
  	leaf = dp->tree.stree + le32_to_cpu(dp->tree.leafidx);
  
  	/* determine the bit number and word within the dmap of the
  	 * starting block.
  	 */
  	dbitno = blkno & (BPERDMAP - 1);
  	word = dbitno >> L2DBWORD;
  
  	/* check if the specified block range is contained within
  	 * this dmap.
  	 */
  	if (dbitno + nblocks > BPERDMAP)
  		return -ENOSPC;
  
  	/* check if the starting leaf indicates that anything
  	 * is free.
  	 */
  	if (leaf[word] == NOFREE)
  		return -ENOSPC;
  
  	/* check the dmaps words corresponding to block range to see
  	 * if the block range is free.  not all bits of the first and
  	 * last words may be contained within the block range.  if this
  	 * is the case, we'll work against those words (i.e. partial first
  	 * and/or last) on an individual basis (a single pass) and examine
  	 * the actual bits to determine if they are free.  a single pass
  	 * will be used for all dmap words fully contained within the
  	 * specified range.  within this pass, the leaves of the dmap
  	 * tree will be examined to determine if the blocks are free. a
  	 * single leaf may describe the free space of multiple dmap
  	 * words, so we may visit only a subset of the actual leaves
  	 * corresponding to the dmap words of the block range.
  	 */
  	for (rembits = nblocks; rembits > 0; rembits -= nb, dbitno += nb) {
  		/* determine the bit number within the word and
  		 * the number of bits within the word.
  		 */
  		wbitno = dbitno & (DBWORD - 1);
  		nb = min(rembits, DBWORD - wbitno);
  
  		/* check if only part of the word is to be examined.
  		 */
  		if (nb < DBWORD) {
  			/* check if the bits are free.
  			 */
  			mask = (ONES << (DBWORD - nb) >> wbitno);
  			if ((mask & ~le32_to_cpu(dp->wmap[word])) != mask)
  				return -ENOSPC;
  
  			word += 1;
  		} else {
  			/* one or more dmap words are fully contained
  			 * within the block range.  determine how many
  			 * words and how many bits.
  			 */
  			nwords = rembits >> L2DBWORD;
  			nb = nwords << L2DBWORD;
  
  			/* now examine the appropriate leaves to determine
  			 * if the blocks are free.
  			 */
  			while (nwords > 0) {
  				/* does the leaf describe any free space ?
  				 */
  				if (leaf[word] < BUDMIN)
  					return -ENOSPC;
  
  				/* determine the l2 number of bits provided
  				 * by this leaf.
  				 */
  				l2size =
  				    min((int)leaf[word], NLSTOL2BSZ(nwords));
  
  				/* determine how many words were handled.
  				 */
  				nw = BUDSIZE(l2size, BUDMIN);
  
  				nwords -= nw;
  				word += nw;
  			}
  		}
  	}
  
  	/* allocate the blocks.
  	 */
  	return (dbAllocDmap(bmp, dp, blkno, nblocks));
  }
  
  
  /*
   * NAME:	dbAllocNear()
   *

   * FUNCTION:	attempt to allocate a number of contiguous free blocks near

   *		a specified block (hint) within a dmap.
   *
   *		starting with the dmap leaf that covers the hint, we'll
   *		check the next four contiguous leaves for sufficient free
   *		space.  if sufficient free space is found, we'll allocate
   *		the desired free space.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	dp	-  pointer to dmap.
   *	blkno	-  block number to allocate near.
   *	nblocks	-  actual number of contiguous free blocks desired.
   *	l2nb	-  log2 number of contiguous free blocks desired.
   *	results	-  on successful return, set to the starting block number

   *		   of the newly allocated range.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   *
   * serialization: IREAD_LOCK(ipbmap) held on entry/exit;
   */
  static int
  dbAllocNear(struct bmap * bmp,
  	    struct dmap * dp, s64 blkno, int nblocks, int l2nb, s64 * results)
  {
  	int word, lword, rc;
  	s8 *leaf;
  
  	if (dp->tree.leafidx != cpu_to_le32(LEAFIND)) {
  		jfs_error(bmp->db_ipbmap->i_sb,
  			  "dbAllocNear: Corrupt dmap page");
  		return -EIO;
  	}
  
  	leaf = dp->tree.stree + le32_to_cpu(dp->tree.leafidx);
  
  	/* determine the word within the dmap that holds the hint
  	 * (i.e. blkno).  also, determine the last word in the dmap
  	 * that we'll include in our examination.
  	 */
  	word = (blkno & (BPERDMAP - 1)) >> L2DBWORD;
  	lword = min(word + 4, LPERDMAP);
  
  	/* examine the leaves for sufficient free space.
  	 */
  	for (; word < lword; word++) {
  		/* does the leaf describe sufficient free space ?
  		 */
  		if (leaf[word] < l2nb)
  			continue;
  
  		/* determine the block number within the file system
  		 * of the first block described by this dmap word.
  		 */
  		blkno = le64_to_cpu(dp->start) + (word << L2DBWORD);
  
  		/* if not all bits of the dmap word are free, get the
  		 * starting bit number within the dmap word of the required
  		 * string of free bits and adjust the block number with the
  		 * value.
  		 */
  		if (leaf[word] < BUDMIN)
  			blkno +=
  			    dbFindBits(le32_to_cpu(dp->wmap[word]), l2nb);
  
  		/* allocate the blocks.
  		 */
  		if ((rc = dbAllocDmap(bmp, dp, blkno, nblocks)) == 0)
  			*results = blkno;
  
  		return (rc);
  	}
  
  	return -ENOSPC;
  }
  
  
  /*
   * NAME:	dbAllocAG()
   *

   * FUNCTION:	attempt to allocate the specified number of contiguous

   *		free blocks within the specified allocation group.
   *
   *		unless the allocation group size is equal to the number
   *		of blocks per dmap, the dmap control pages will be used to
   *		find the required free space, if available.  we start the
   *		search at the highest dmap control page level which
   *		distinctly describes the allocation group's free space
   *		(i.e. the highest level at which the allocation group's
   *		free space is not mixed in with that of any other group).
   *		in addition, we start the search within this level at a
   *		height of the dmapctl dmtree at which the nodes distinctly
   *		describe the allocation group's free space.  at this height,
   *		the allocation group's free space may be represented by 1
   *		or two sub-trees, depending on the allocation group size.
   *		we search the top nodes of these subtrees left to right for
   *		sufficient free space.  if sufficient free space is found,

   *		the subtree is searched to find the leftmost leaf that

   *		has free space.  once we have made it to the leaf, we
   *		move the search to the next lower level dmap control page
   *		corresponding to this leaf.  we continue down the dmap control
   *		pages until we find the dmap that contains or starts the
   *		sufficient free space and we allocate at this dmap.
   *
   *		if the allocation group size is equal to the dmap size,
   *		we'll start at the dmap corresponding to the allocation
   *		group and attempt the allocation at this level.
   *
   *		the dmap control page search is also not performed if the
   *		allocation group is completely free and we go to the first
   *		dmap of the allocation group to do the allocation.  this is
   *		done because the allocation group may be part (not the first
   *		part) of a larger binary buddy system, causing the dmap
   *		control pages to indicate no free space (NOFREE) within
   *		the allocation group.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor

   *	agno	- allocation group number.

   *	nblocks	-  actual number of contiguous free blocks desired.
   *	l2nb	-  log2 number of contiguous free blocks desired.
   *	results	-  on successful return, set to the starting block number

   *		   of the newly allocated range.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   *
   * note: IWRITE_LOCK(ipmap) held on entry/exit;
   */
  static int
  dbAllocAG(struct bmap * bmp, int agno, s64 nblocks, int l2nb, s64 * results)
  {
  	struct metapage *mp;
  	struct dmapctl *dcp;
  	int rc, ti, i, k, m, n, agperlev;
  	s64 blkno, lblkno;
  	int budmin;
  
  	/* allocation request should not be for more than the
  	 * allocation group size.
  	 */
  	if (l2nb > bmp->db_agl2size) {
  		jfs_error(bmp->db_ipbmap->i_sb,
  			  "dbAllocAG: allocation request is larger than the "
  			  "allocation group size");
  		return -EIO;
  	}
  
  	/* determine the starting block number of the allocation
  	 * group.
  	 */
  	blkno = (s64) agno << bmp->db_agl2size;
  
  	/* check if the allocation group size is the minimum allocation
  	 * group size or if the allocation group is completely free. if
  	 * the allocation group size is the minimum size of BPERDMAP (i.e.
  	 * 1 dmap), there is no need to search the dmap control page (below)
  	 * that fully describes the allocation group since the allocation
  	 * group is already fully described by a dmap.  in this case, we
  	 * just call dbAllocCtl() to search the dmap tree and allocate the

  	 * required space if available.

  	 *
  	 * if the allocation group is completely free, dbAllocCtl() is
  	 * also called to allocate the required space.  this is done for
  	 * two reasons.  first, it makes no sense searching the dmap control
  	 * pages for free space when we know that free space exists.  second,
  	 * the dmap control pages may indicate that the allocation group
  	 * has no free space if the allocation group is part (not the first
  	 * part) of a larger binary buddy system.
  	 */
  	if (bmp->db_agsize == BPERDMAP
  	    || bmp->db_agfree[agno] == bmp->db_agsize) {
  		rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
  		if ((rc == -ENOSPC) &&
  		    (bmp->db_agfree[agno] == bmp->db_agsize)) {
  			printk(KERN_ERR "blkno = %Lx, blocks = %Lx
  ",
  			       (unsigned long long) blkno,
  			       (unsigned long long) nblocks);
  			jfs_error(bmp->db_ipbmap->i_sb,
  				  "dbAllocAG: dbAllocCtl failed in free AG");
  		}
  		return (rc);
  	}
  
  	/* the buffer for the dmap control page that fully describes the
  	 * allocation group.
  	 */
  	lblkno = BLKTOCTL(blkno, bmp->db_l2nbperpage, bmp->db_aglevel);
  	mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
  	if (mp == NULL)
  		return -EIO;
  	dcp = (struct dmapctl *) mp->data;
  	budmin = dcp->budmin;
  
  	if (dcp->leafidx != cpu_to_le32(CTLLEAFIND)) {
  		jfs_error(bmp->db_ipbmap->i_sb,
  			  "dbAllocAG: Corrupt dmapctl page");
  		release_metapage(mp);
  		return -EIO;
  	}
  
  	/* search the subtree(s) of the dmap control page that describes
  	 * the allocation group, looking for sufficient free space.  to begin,
  	 * determine how many allocation groups are represented in a dmap
  	 * control page at the control page level (i.e. L0, L1, L2) that
  	 * fully describes an allocation group. next, determine the starting
  	 * tree index of this allocation group within the control page.
  	 */
  	agperlev =

  	    (1 << (L2LPERCTL - (bmp->db_agheight << 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_agheight; k > 0; k--) {

  			for (n = 0, m = (ti << 2) + 1; n < 4; n++) {
  				if (l2nb <= dcp->stree[m + n]) {
  					ti = m + n;
  					break;
  				}
  			}
  			if (n == 4) {
  				jfs_error(bmp->db_ipbmap->i_sb,
  					  "dbAllocAG: failed descending stree");
  				release_metapage(mp);
  				return -EIO;
  			}
  		}
  
  		/* determine the block number within the file system
  		 * that corresponds to this leaf.
  		 */
  		if (bmp->db_aglevel == 2)
  			blkno = 0;
  		else if (bmp->db_aglevel == 1)
  			blkno &= ~(MAXL1SIZE - 1);
  		else		/* bmp->db_aglevel == 0 */
  			blkno &= ~(MAXL0SIZE - 1);
  
  		blkno +=
  		    ((s64) (ti - le32_to_cpu(dcp->leafidx))) << budmin;
  
  		/* release the buffer in preparation for going down
  		 * the next level of dmap control pages.
  		 */
  		release_metapage(mp);
  
  		/* check if we need to continue to search down the lower
  		 * level dmap control pages.  we need to if the number of
  		 * blocks required is less than maximum number of blocks
  		 * described at the next lower level.
  		 */
  		if (l2nb < budmin) {
  
  			/* search the lower level dmap control pages to get

  			 * the starting block number of the dmap that

  			 * contains or starts off the free space.
  			 */
  			if ((rc =
  			     dbFindCtl(bmp, l2nb, bmp->db_aglevel - 1,
  				       &blkno))) {
  				if (rc == -ENOSPC) {
  					jfs_error(bmp->db_ipbmap->i_sb,
  						  "dbAllocAG: control page "
  						  "inconsistent");
  					return -EIO;
  				}
  				return (rc);
  			}
  		}
  
  		/* allocate the blocks.
  		 */
  		rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
  		if (rc == -ENOSPC) {
  			jfs_error(bmp->db_ipbmap->i_sb,
  				  "dbAllocAG: unable to allocate blocks");
  			rc = -EIO;
  		}
  		return (rc);
  	}
  
  	/* no space in the allocation group.  release the buffer and
  	 * return -ENOSPC.
  	 */
  	release_metapage(mp);
  
  	return -ENOSPC;
  }
  
  
  /*
   * NAME:	dbAllocAny()
   *

   * FUNCTION:	attempt to allocate the specified number of contiguous

   *		free blocks anywhere in the file system.
   *
   *		dbAllocAny() attempts to find the sufficient free space by
   *		searching down the dmap control pages, starting with the
   *		highest level (i.e. L0, L1, L2) control page.  if free space
   *		large enough to satisfy the desired free space is found, the
   *		desired free space is allocated.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	nblocks	 -  actual number of contiguous free blocks desired.
   *	l2nb	 -  log2 number of contiguous free blocks desired.
   *	results	-  on successful return, set to the starting block number

   *		   of the newly allocated range.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   *
   * serialization: IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static int dbAllocAny(struct bmap * bmp, s64 nblocks, int l2nb, s64 * results)
  {
  	int rc;
  	s64 blkno = 0;
  
  	/* starting with the top level dmap control page, search
  	 * down the dmap control levels for sufficient free space.
  	 * if free space is found, dbFindCtl() returns the starting
  	 * block number of the dmap that contains or starts off the
  	 * range of free space.
  	 */
  	if ((rc = dbFindCtl(bmp, l2nb, bmp->db_maxlevel, &blkno)))
  		return (rc);
  
  	/* allocate the blocks.
  	 */
  	rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
  	if (rc == -ENOSPC) {
  		jfs_error(bmp->db_ipbmap->i_sb,
  			  "dbAllocAny: unable to allocate blocks");
  		return -EIO;
  	}
  	return (rc);
  }
  
  
  /*
   * NAME:	dbFindCtl()
   *

   * FUNCTION:	starting at a specified dmap control page level and block

   *		number, search down the dmap control levels for a range of

   *		contiguous free blocks large enough to satisfy an allocation

   *		request for the specified number of free blocks.
   *
   *		if sufficient contiguous free blocks are found, this routine
   *		returns the starting block number within a dmap page that
   *		contains or starts a range of contiqious free blocks that
   *		is sufficient in size.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	level	-  starting dmap control page level.
   *	l2nb	-  log2 number of contiguous free blocks desired.
   *	*blkno	-  on entry, starting block number for conducting the search.

   *		   on successful return, the first block within a dmap page
   *		   that contains or starts a range of contiguous free blocks.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   *
   * serialization: IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static int dbFindCtl(struct bmap * bmp, int l2nb, int level, s64 * blkno)
  {
  	int rc, leafidx, lev;
  	s64 b, lblkno;
  	struct dmapctl *dcp;
  	int budmin;
  	struct metapage *mp;
  
  	/* starting at the specified dmap control page level and block
  	 * number, search down the dmap control levels for the starting

  	 * block number of a dmap page that contains or starts off

  	 * sufficient free blocks.
  	 */
  	for (lev = level, b = *blkno; lev >= 0; lev--) {
  		/* get the buffer of the dmap control page for the block
  		 * number and level (i.e. L0, L1, L2).
  		 */
  		lblkno = BLKTOCTL(b, bmp->db_l2nbperpage, lev);
  		mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
  		if (mp == NULL)
  			return -EIO;
  		dcp = (struct dmapctl *) mp->data;
  		budmin = dcp->budmin;
  
  		if (dcp->leafidx != cpu_to_le32(CTLLEAFIND)) {
  			jfs_error(bmp->db_ipbmap->i_sb,
  				  "dbFindCtl: Corrupt dmapctl page");
  			release_metapage(mp);
  			return -EIO;
  		}
  
  		/* search the tree within the dmap control page for

  		 * sufficient free space.  if sufficient free space is found,

  		 * dbFindLeaf() returns the index of the leaf at which
  		 * free space was found.
  		 */
  		rc = dbFindLeaf((dmtree_t *) dcp, l2nb, &leafidx);
  
  		/* release the buffer.
  		 */
  		release_metapage(mp);
  
  		/* space found ?
  		 */
  		if (rc) {
  			if (lev != level) {
  				jfs_error(bmp->db_ipbmap->i_sb,
  					  "dbFindCtl: dmap inconsistent");
  				return -EIO;
  			}
  			return -ENOSPC;
  		}
  
  		/* adjust the block number to reflect the location within

  		 * the dmap control page (i.e. the leaf) at which free

  		 * space was found.
  		 */
  		b += (((s64) leafidx) << budmin);
  
  		/* we stop the search at this dmap control page level if
  		 * the number of blocks required is greater than or equal
  		 * to the maximum number of blocks described at the next
  		 * (lower) level.
  		 */
  		if (l2nb >= budmin)
  			break;
  	}
  
  	*blkno = b;
  	return (0);
  }
  
  
  /*
   * NAME:	dbAllocCtl()
   *

   * FUNCTION:	attempt to allocate a specified number of contiguous

   *		blocks starting within a specific dmap.
   *

   *		this routine is called by higher level routines that search
   *		the dmap control pages above the actual dmaps for contiguous
   *		free space.  the result of successful searches by these

   *		routines are the starting block numbers within dmaps, with

   *		the dmaps themselves containing the desired contiguous free
   *		space or starting a contiguous free space of desired size
   *		that is made up of the blocks of one or more dmaps. these
   *		calls should not fail due to insufficent resources.
   *
   *		this routine is called in some cases where it is not known
   *		whether it will fail due to insufficient resources.  more
   *		specifically, this occurs when allocating from an allocation
   *		group whose size is equal to the number of blocks per dmap.
   *		in this case, the dmap control pages are not examined prior
   *		to calling this routine (to save pathlength) and the call
   *		might fail.
   *
   *		for a request size that fits within a dmap, this routine relies
   *		upon the dmap's dmtree to find the requested contiguous free
   *		space.  for request sizes that are larger than a dmap, the
   *		requested free space will start at the first block of the
   *		first dmap (i.e. blkno).
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	nblocks	 -  actual number of contiguous free blocks to allocate.
   *	l2nb	 -  log2 number of contiguous free blocks to allocate.
   *	blkno	 -  starting block number of the dmap to start the allocation

   *		    from.

   *	results	-  on successful return, set to the starting block number

   *		   of the newly allocated range.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   *
   * serialization: IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static int
  dbAllocCtl(struct bmap * bmp, s64 nblocks, int l2nb, s64 blkno, s64 * results)
  {
  	int rc, nb;
  	s64 b, lblkno, n;
  	struct metapage *mp;
  	struct dmap *dp;
  
  	/* check if the allocation request is confined to a single dmap.
  	 */
  	if (l2nb <= L2BPERDMAP) {
  		/* get the buffer for the dmap.
  		 */
  		lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
  		mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
  		if (mp == NULL)
  			return -EIO;
  		dp = (struct dmap *) mp->data;
  
  		/* try to allocate the blocks.
  		 */
  		rc = dbAllocDmapLev(bmp, dp, (int) nblocks, l2nb, results);
  		if (rc == 0)
  			mark_metapage_dirty(mp);
  
  		release_metapage(mp);
  
  		return (rc);
  	}
  
  	/* allocation request involving multiple dmaps. it must start on
  	 * a dmap boundary.
  	 */
  	assert((blkno & (BPERDMAP - 1)) == 0);
  
  	/* allocate the blocks dmap by dmap.
  	 */
  	for (n = nblocks, b = blkno; n > 0; n -= nb, b += nb) {
  		/* get the buffer for the dmap.
  		 */
  		lblkno = BLKTODMAP(b, bmp->db_l2nbperpage);
  		mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
  		if (mp == NULL) {
  			rc = -EIO;
  			goto backout;
  		}
  		dp = (struct dmap *) mp->data;
  
  		/* the dmap better be all free.
  		 */
  		if (dp->tree.stree[ROOT] != L2BPERDMAP) {
  			release_metapage(mp);
  			jfs_error(bmp->db_ipbmap->i_sb,
  				  "dbAllocCtl: the dmap is not all free");
  			rc = -EIO;
  			goto backout;
  		}
  
  		/* determine how many blocks to allocate from this dmap.
  		 */
  		nb = min(n, (s64)BPERDMAP);
  
  		/* allocate the blocks from the dmap.
  		 */
  		if ((rc = dbAllocDmap(bmp, dp, b, nb))) {
  			release_metapage(mp);
  			goto backout;
  		}
  
  		/* write the buffer.
  		 */
  		write_metapage(mp);
  	}
  
  	/* set the results (starting block number) and return.
  	 */
  	*results = blkno;
  	return (0);
  
  	/* something failed in handling an allocation request involving
  	 * multiple dmaps.  we'll try to clean up by backing out any
  	 * allocation that has already happened for this request.  if
  	 * we fail in backing out the allocation, we'll mark the file
  	 * system to indicate that blocks have been leaked.
  	 */
        backout:
  
  	/* try to backout the allocations dmap by dmap.
  	 */
  	for (n = nblocks - n, b = blkno; n > 0;
  	     n -= BPERDMAP, b += BPERDMAP) {
  		/* get the buffer for this dmap.
  		 */
  		lblkno = BLKTODMAP(b, bmp->db_l2nbperpage);
  		mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
  		if (mp == NULL) {
  			/* could not back out.  mark the file system
  			 * to indicate that we have leaked blocks.
  			 */
  			jfs_error(bmp->db_ipbmap->i_sb,
  				  "dbAllocCtl: I/O Error: Block Leakage.");
  			continue;
  		}
  		dp = (struct dmap *) mp->data;
  
  		/* free the blocks is this dmap.
  		 */
  		if (dbFreeDmap(bmp, dp, b, BPERDMAP)) {
  			/* could not back out.  mark the file system
  			 * to indicate that we have leaked blocks.
  			 */
  			release_metapage(mp);
  			jfs_error(bmp->db_ipbmap->i_sb,
  				  "dbAllocCtl: Block Leakage.");
  			continue;
  		}
  
  		/* write the buffer.
  		 */
  		write_metapage(mp);
  	}
  
  	return (rc);
  }
  
  
  /*
   * NAME:	dbAllocDmapLev()
   *

   * FUNCTION:	attempt to allocate a specified number of contiguous blocks

   *		from a specified dmap.

   *

   *		this routine checks if the contiguous blocks are available.
   *		if so, nblocks of blocks are allocated; otherwise, ENOSPC is
   *		returned.
   *
   * PARAMETERS:

   *	mp	-  pointer to bmap descriptor
   *	dp	-  pointer to dmap to attempt to allocate blocks from.
   *	l2nb	-  log2 number of contiguous block desired.
   *	nblocks	-  actual number of contiguous block desired.
   *	results	-  on successful return, set to the starting block number

   *		   of the newly allocated range.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient disk resources
   *	-EIO	- i/o error

   *

   * serialization: IREAD_LOCK(ipbmap), e.g., from dbAlloc(), or

   *	IWRITE_LOCK(ipbmap), e.g., dbAllocCtl(), held on entry/exit;
   */
  static int
  dbAllocDmapLev(struct bmap * bmp,
  	       struct dmap * dp, int nblocks, int l2nb, s64 * results)
  {
  	s64 blkno;
  	int leafidx, rc;
  
  	/* can't be more than a dmaps worth of blocks */
  	assert(l2nb <= L2BPERDMAP);
  
  	/* search the tree within the dmap page for sufficient
  	 * free space.  if sufficient free space is found, dbFindLeaf()
  	 * returns the index of the leaf at which free space was found.
  	 */
  	if (dbFindLeaf((dmtree_t *) & dp->tree, l2nb, &leafidx))
  		return -ENOSPC;
  
  	/* determine the block number within the file system corresponding
  	 * to the leaf at which free space was found.
  	 */
  	blkno = le64_to_cpu(dp->start) + (leafidx << L2DBWORD);
  
  	/* if not all bits of the dmap word are free, get the starting
  	 * bit number within the dmap word of the required string of free
  	 * bits and adjust the block number with this value.
  	 */
  	if (dp->tree.stree[leafidx + LEAFIND] < BUDMIN)
  		blkno += dbFindBits(le32_to_cpu(dp->wmap[leafidx]), l2nb);
  
  	/* allocate the blocks */
  	if ((rc = dbAllocDmap(bmp, dp, blkno, nblocks)) == 0)
  		*results = blkno;
  
  	return (rc);
  }
  
  
  /*
   * NAME:	dbAllocDmap()
   *

   * FUNCTION:	adjust the disk allocation map to reflect the allocation

   *		of a specified block range within a dmap.
   *
   *		this routine allocates the specified blocks from the dmap
   *		through a call to dbAllocBits(). if the allocation of the
   *		block range causes the maximum string of free blocks within
   *		the dmap to change (i.e. the value of the root of the dmap's
   *		dmtree), this routine will cause this change to be reflected
   *		up through the appropriate levels of the dmap control pages
   *		by a call to dbAdjCtl() for the L0 dmap control page that
   *		covers this dmap.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	dp	-  pointer to dmap to allocate the block range from.
   *	blkno	-  starting block number of the block to be allocated.
   *	nblocks	-  number of blocks to be allocated.

   *
   * RETURN VALUES:

   *	0	- success
   *	-EIO	- i/o error

   *
   * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static int dbAllocDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
  		       int nblocks)
  {
  	s8 oldroot;
  	int rc;
  
  	/* save the current value of the root (i.e. maximum free string)
  	 * of the dmap tree.
  	 */
  	oldroot = dp->tree.stree[ROOT];
  
  	/* allocate the specified (blocks) bits */
  	dbAllocBits(bmp, dp, blkno, nblocks);
  
  	/* if the root has not changed, done. */
  	if (dp->tree.stree[ROOT] == oldroot)
  		return (0);
  
  	/* root changed. bubble the change up to the dmap control pages.
  	 * if the adjustment of the upper level control pages fails,
  	 * backout the bit allocation (thus making everything consistent).
  	 */
  	if ((rc = dbAdjCtl(bmp, blkno, dp->tree.stree[ROOT], 1, 0)))
  		dbFreeBits(bmp, dp, blkno, nblocks);
  
  	return (rc);
  }
  
  
  /*
   * NAME:	dbFreeDmap()
   *

   * FUNCTION:	adjust the disk allocation map to reflect the allocation

   *		of a specified block range within a dmap.
   *
   *		this routine frees the specified blocks from the dmap through
   *		a call to dbFreeBits(). if the deallocation of the block range
   *		causes the maximum string of free blocks within the dmap to
   *		change (i.e. the value of the root of the dmap's dmtree), this
   *		routine will cause this change to be reflected up through the

   *		appropriate levels of the dmap control pages by a call to

   *		dbAdjCtl() for the L0 dmap control page that covers this dmap.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	dp	-  pointer to dmap to free the block range from.
   *	blkno	-  starting block number of the block to be freed.
   *	nblocks	-  number of blocks to be freed.

   *
   * RETURN VALUES:

   *	0	- success
   *	-EIO	- i/o error

   *
   * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static int dbFreeDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
  		      int nblocks)
  {
  	s8 oldroot;

  	int rc = 0, word;

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

  	rc = dbFreeBits(bmp, dp, blkno, nblocks);

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

  
  	/* root changed. bubble the change up to the dmap control pages.
  	 * if the adjustment of the upper level control pages fails,

  	 * backout the deallocation.

  	 */
  	if ((rc = dbAdjCtl(bmp, blkno, dp->tree.stree[ROOT], 0, 0))) {
  		word = (blkno & (BPERDMAP - 1)) >> L2DBWORD;
  
  		/* as part of backing out the deallocation, we will have
  		 * to back split the dmap tree if the deallocation caused
  		 * the freed blocks to become part of a larger binary buddy
  		 * system.
  		 */
  		if (dp->tree.stree[word] == NOFREE)
  			dbBackSplit((dmtree_t *) & dp->tree, word);
  
  		dbAllocBits(bmp, dp, blkno, nblocks);
  	}
  
  	return (rc);
  }
  
  
  /*
   * NAME:	dbAllocBits()
   *

   * FUNCTION:	allocate a specified block range from a dmap.

   *
   *		this routine updates the dmap to reflect the working
   *		state allocation of the specified block range. it directly
   *		updates the bits of the working map and causes the adjustment
   *		of the binary buddy system described by the dmap's dmtree
   *		leaves to reflect the bits allocated.  it also causes the
   *		dmap's dmtree, as a whole, to reflect the allocated range.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	dp	-  pointer to dmap to allocate bits from.
   *	blkno	-  starting block number of the bits to be allocated.
   *	nblocks	-  number of bits to be allocated.

   *
   * RETURN VALUES: none
   *
   * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static void dbAllocBits(struct bmap * bmp, struct dmap * dp, s64 blkno,
  			int nblocks)
  {
  	int dbitno, word, rembits, nb, nwords, wbitno, nw, agno;
  	dmtree_t *tp = (dmtree_t *) & dp->tree;
  	int size;
  	s8 *leaf;
  
  	/* pick up a pointer to the leaves of the dmap tree */
  	leaf = dp->tree.stree + LEAFIND;
  
  	/* determine the bit number and word within the dmap of the
  	 * starting block.
  	 */
  	dbitno = blkno & (BPERDMAP - 1);
  	word = dbitno >> L2DBWORD;
  
  	/* block range better be within the dmap */
  	assert(dbitno + nblocks <= BPERDMAP);
  
  	/* allocate the bits of the dmap's words corresponding to the block
  	 * range. not all bits of the first and last words may be contained
  	 * within the block range.  if this is the case, we'll work against
  	 * those words (i.e. partial first and/or last) on an individual basis
  	 * (a single pass), allocating the bits of interest by hand and
  	 * updating the leaf corresponding to the dmap word. a single pass
  	 * will be used for all dmap words fully contained within the
  	 * specified range.  within this pass, the bits of all fully contained
  	 * dmap words will be marked as free in a single shot and the leaves
  	 * will be updated. a single leaf may describe the free space of
  	 * multiple dmap words, so we may update only a subset of the actual
  	 * leaves corresponding to the dmap words of the block range.
  	 */
  	for (rembits = nblocks; rembits > 0; rembits -= nb, dbitno += nb) {
  		/* determine the bit number within the word and
  		 * the number of bits within the word.
  		 */
  		wbitno = dbitno & (DBWORD - 1);
  		nb = min(rembits, DBWORD - wbitno);
  
  		/* check if only part of a word is to be allocated.
  		 */
  		if (nb < DBWORD) {
  			/* allocate (set to 1) the appropriate bits within
  			 * this dmap word.
  			 */
  			dp->wmap[word] |= cpu_to_le32(ONES << (DBWORD - nb)
  						      >> wbitno);
  
  			/* update the leaf for this dmap word. in addition
  			 * to setting the leaf value to the binary buddy max
  			 * of the updated dmap word, dbSplit() will split
  			 * the binary system of the leaves if need be.
  			 */
  			dbSplit(tp, word, BUDMIN,
  				dbMaxBud((u8 *) & dp->wmap[word]));
  
  			word += 1;
  		} else {
  			/* one or more dmap words are fully contained
  			 * within the block range.  determine how many
  			 * words and allocate (set to 1) the bits of these
  			 * words.
  			 */
  			nwords = rembits >> L2DBWORD;
  			memset(&dp->wmap[word], (int) ONES, nwords * 4);
  
  			/* determine how many bits.
  			 */
  			nb = nwords << L2DBWORD;
  
  			/* now update the appropriate leaves to reflect
  			 * the allocated words.
  			 */
  			for (; nwords > 0; nwords -= nw) {

  				if (leaf[word] < BUDMIN) {

  					jfs_error(bmp->db_ipbmap->i_sb,
  						  "dbAllocBits: leaf page "
  						  "corrupt");
  					break;
  				}
  
  				/* determine what the leaf value should be
  				 * updated to as the minimum of the l2 number
  				 * of bits being allocated and the l2 number
  				 * of bits currently described by this leaf.
  				 */
  				size = min((int)leaf[word], NLSTOL2BSZ(nwords));
  
  				/* update the leaf to reflect the allocation.
  				 * in addition to setting the leaf value to
  				 * NOFREE, dbSplit() will split the binary
  				 * system of the leaves to reflect the current
  				 * allocation (size).
  				 */
  				dbSplit(tp, word, size, NOFREE);
  
  				/* get the number of dmap words handled */
  				nw = BUDSIZE(size, BUDMIN);
  				word += nw;
  			}
  		}
  	}
  
  	/* update the free count for this dmap */

  	le32_add_cpu(&dp->nfree, -nblocks);

  
  	BMAP_LOCK(bmp);
  
  	/* if this allocation group is completely free,
  	 * update the maximum allocation group number if this allocation
  	 * group is the new max.
  	 */
  	agno = blkno >> bmp->db_agl2size;
  	if (agno > bmp->db_maxag)
  		bmp->db_maxag = agno;
  
  	/* update the free count for the allocation group and map */
  	bmp->db_agfree[agno] -= nblocks;
  	bmp->db_nfree -= nblocks;
  
  	BMAP_UNLOCK(bmp);
  }
  
  
  /*
   * NAME:	dbFreeBits()
   *

   * FUNCTION:	free a specified block range from a dmap.

   *
   *		this routine updates the dmap to reflect the working
   *		state allocation of the specified block range. it directly
   *		updates the bits of the working map and causes the adjustment
   *		of the binary buddy system described by the dmap's dmtree
   *		leaves to reflect the bits freed.  it also causes the dmap's
   *		dmtree, as a whole, to reflect the deallocated range.
   *
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	dp	-  pointer to dmap to free bits from.
   *	blkno	-  starting block number of the bits to be freed.
   *	nblocks	-  number of bits to be freed.

   *

   * RETURN VALUES: 0 for success

   *
   * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
   */

  static int dbFreeBits(struct bmap * bmp, struct dmap * dp, s64 blkno,

  		       int nblocks)
  {
  	int dbitno, word, rembits, nb, nwords, wbitno, nw, agno;
  	dmtree_t *tp = (dmtree_t *) & dp->tree;

  	int rc = 0;

  	int size;
  
  	/* determine the bit number and word within the dmap of the
  	 * starting block.
  	 */
  	dbitno = blkno & (BPERDMAP - 1);
  	word = dbitno >> L2DBWORD;
  
  	/* block range better be within the dmap.
  	 */
  	assert(dbitno + nblocks <= BPERDMAP);
  
  	/* free the bits of the dmaps words corresponding to the block range.
  	 * not all bits of the first and last words may be contained within
  	 * the block range.  if this is the case, we'll work against those
  	 * words (i.e. partial first and/or last) on an individual basis
  	 * (a single pass), freeing the bits of interest by hand and updating
  	 * the leaf corresponding to the dmap word. a single pass will be used

  	 * for all dmap words fully contained within the specified range.

  	 * within this pass, the bits of all fully contained dmap words will
  	 * be marked as free in a single shot and the leaves will be updated. a
  	 * single leaf may describe the free space of multiple dmap words,
  	 * so we may update only a subset of the actual leaves corresponding
  	 * to the dmap words of the block range.
  	 *
  	 * dbJoin() is used to update leaf values and will join the binary
  	 * buddy system of the leaves if the new leaf values indicate this
  	 * should be done.
  	 */
  	for (rembits = nblocks; rembits > 0; rembits -= nb, dbitno += nb) {
  		/* determine the bit number within the word and
  		 * the number of bits within the word.
  		 */
  		wbitno = dbitno & (DBWORD - 1);
  		nb = min(rembits, DBWORD - wbitno);
  
  		/* check if only part of a word is to be freed.
  		 */
  		if (nb < DBWORD) {
  			/* free (zero) the appropriate bits within this

  			 * dmap word.

  			 */
  			dp->wmap[word] &=
  			    cpu_to_le32(~(ONES << (DBWORD - nb)
  					  >> wbitno));
  
  			/* update the leaf for this dmap word.
  			 */

  			rc = dbJoin(tp, word,
  				    dbMaxBud((u8 *) & dp->wmap[word]));
  			if (rc)
  				return rc;

  
  			word += 1;
  		} else {
  			/* one or more dmap words are fully contained
  			 * within the block range.  determine how many
  			 * words and free (zero) the bits of these words.
  			 */
  			nwords = rembits >> L2DBWORD;
  			memset(&dp->wmap[word], 0, nwords * 4);
  
  			/* determine how many bits.
  			 */
  			nb = nwords << L2DBWORD;
  
  			/* now update the appropriate leaves to reflect
  			 * the freed words.
  			 */
  			for (; nwords > 0; nwords -= nw) {
  				/* determine what the leaf value should be
  				 * updated to as the minimum of the l2 number
  				 * of bits being freed and the l2 (max) number
  				 * of bits that can be described by this leaf.
  				 */
  				size =
  				    min(LITOL2BSZ
  					(word, L2LPERDMAP, BUDMIN),
  					NLSTOL2BSZ(nwords));
  
  				/* update the leaf.
  				 */

  				rc = dbJoin(tp, word, size);
  				if (rc)
  					return rc;

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

  	le32_add_cpu(&dp->nfree, nblocks);

  
  	BMAP_LOCK(bmp);

  	/* update the free count for the allocation group and

  	 * map.
  	 */
  	agno = blkno >> bmp->db_agl2size;
  	bmp->db_nfree += nblocks;
  	bmp->db_agfree[agno] += nblocks;
  
  	/* check if this allocation group is not completely free and
  	 * if it is currently the maximum (rightmost) allocation group.
  	 * if so, establish the new maximum allocation group number by
  	 * searching left for the first allocation group with allocation.
  	 */
  	if ((bmp->db_agfree[agno] == bmp->db_agsize && agno == bmp->db_maxag) ||
  	    (agno == bmp->db_numag - 1 &&
  	     bmp->db_agfree[agno] == (bmp-> db_mapsize & (BPERDMAP - 1)))) {
  		while (bmp->db_maxag > 0) {
  			bmp->db_maxag -= 1;
  			if (bmp->db_agfree[bmp->db_maxag] !=
  			    bmp->db_agsize)
  				break;
  		}
  
  		/* re-establish the allocation group preference if the
  		 * current preference is right of the maximum allocation
  		 * group.
  		 */
  		if (bmp->db_agpref > bmp->db_maxag)
  			bmp->db_agpref = bmp->db_maxag;
  	}
  
  	BMAP_UNLOCK(bmp);

  
  	return 0;

  }
  
  
  /*
   * NAME:	dbAdjCtl()
   *
   * FUNCTION:	adjust a dmap control page at a specified level to reflect
   *		the change in a lower level dmap or dmap control page's
   *		maximum string of free blocks (i.e. a change in the root
   *		of the lower level object's dmtree) due to the allocation
   *		or deallocation of a range of blocks with a single dmap.
   *
   *		on entry, this routine is provided with the new value of
   *		the lower level dmap or dmap control page root and the
   *		starting block number of the block range whose allocation
   *		or deallocation resulted in the root change.  this range
   *		is respresented by a single leaf of the current dmapctl
   *		and the leaf will be updated with this value, possibly

   *		causing a binary buddy system within the leaves to be

   *		split or joined.  the update may also cause the dmapctl's
   *		dmtree to be updated.
   *
   *		if the adjustment of the dmap control page, itself, causes its
   *		root to change, this change will be bubbled up to the next dmap
   *		control level by a recursive call to this routine, specifying
   *		the new root value and the next dmap control page level to
   *		be adjusted.
   * PARAMETERS:

   *	bmp	-  pointer to bmap descriptor
   *	blkno	-  the first block of a block range within a dmap.  it is

   *		   the allocation or deallocation of this block range that
   *		   requires the dmap control page to be adjusted.

   *	newval	-  the new value of the lower level dmap or dmap control

   *		   page root.

   *	alloc	-  'true' if adjustment is due to an allocation.
   *	level	-  current level of dmap control page (i.e. L0, L1, L2) to

   *		   be adjusted.
   *
   * RETURN VALUES:

   *	0	- success
   *	-EIO	- i/o error

   *
   * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static int
  dbAdjCtl(struct bmap * bmp, s64 blkno, int newval, int alloc, int level)
  {
  	struct metapage *mp;
  	s8 oldroot;
  	int oldval;
  	s64 lblkno;
  	struct dmapctl *dcp;
  	int rc, leafno, ti;
  
  	/* get the buffer for the dmap control page for the specified
  	 * block number and control page level.
  	 */
  	lblkno = BLKTOCTL(blkno, bmp->db_l2nbperpage, level);
  	mp = read_metapage(bmp->db_ipbmap, lblkno, PSIZE, 0);
  	if (mp == NULL)
  		return -EIO;
  	dcp = (struct dmapctl *) mp->data;
  
  	if (dcp->leafidx != cpu_to_le32(CTLLEAFIND)) {
  		jfs_error(bmp->db_ipbmap->i_sb,
  			  "dbAdjCtl: Corrupt dmapctl page");
  		release_metapage(mp);
  		return -EIO;
  	}
  
  	/* determine the leaf number corresponding to the block and
  	 * the index within the dmap control tree.
  	 */
  	leafno = BLKTOCTLLEAF(blkno, dcp->budmin);
  	ti = leafno + le32_to_cpu(dcp->leafidx);
  
  	/* save the current leaf value and the current root level (i.e.
  	 * maximum l2 free string described by this dmapctl).
  	 */
  	oldval = dcp->stree[ti];
  	oldroot = dcp->stree[ROOT];
  
  	/* check if this is a control page update for an allocation.
  	 * if so, update the leaf to reflect the new leaf value using

  	 * dbSplit(); otherwise (deallocation), use dbJoin() to update

  	 * the leaf with the new value.  in addition to updating the
  	 * leaf, dbSplit() will also split the binary buddy system of
  	 * the leaves, if required, and bubble new values within the
  	 * dmapctl tree, if required.  similarly, dbJoin() will join
  	 * the binary buddy system of leaves and bubble new values up
  	 * the dmapctl tree as required by the new leaf value.
  	 */
  	if (alloc) {
  		/* check if we are in the middle of a binary buddy
  		 * system.  this happens when we are performing the
  		 * first allocation out of an allocation group that
  		 * is part (not the first part) of a larger binary
  		 * buddy system.  if we are in the middle, back split
  		 * the system prior to calling dbSplit() which assumes
  		 * that it is at the front of a binary buddy system.
  		 */
  		if (oldval == NOFREE) {

  			rc = dbBackSplit((dmtree_t *) dcp, leafno);
  			if (rc)
  				return rc;

  			oldval = dcp->stree[ti];
  		}
  		dbSplit((dmtree_t *) dcp, leafno, dcp->budmin, newval);
  	} else {

  		rc = dbJoin((dmtree_t *) dcp, leafno, newval);
  		if (rc)
  			return rc;

  	}
  
  	/* check if the root of the current dmap control page changed due
  	 * to the update and if the current dmap control page is not at
  	 * the current top level (i.e. L0, L1, L2) of the map.  if so (i.e.
  	 * root changed and this is not the top level), call this routine
  	 * again (recursion) for the next higher level of the mapping to
  	 * reflect the change in root for the current dmap control page.
  	 */
  	if (dcp->stree[ROOT] != oldroot) {
  		/* are we below the top level of the map.  if so,
  		 * bubble the root up to the next higher level.
  		 */
  		if (level < bmp->db_maxlevel) {
  			/* bubble up the new root of this dmap control page to
  			 * the next level.
  			 */
  			if ((rc =
  			     dbAdjCtl(bmp, blkno, dcp->stree[ROOT], alloc,
  				      level + 1))) {
  				/* something went wrong in bubbling up the new
  				 * root value, so backout the changes to the
  				 * current dmap control page.
  				 */
  				if (alloc) {
  					dbJoin((dmtree_t *) dcp, leafno,
  					       oldval);
  				} else {
  					/* the dbJoin() above might have
  					 * caused a larger binary buddy system
  					 * to form and we may now be in the
  					 * middle of it.  if this is the case,
  					 * back split the buddies.
  					 */
  					if (dcp->stree[ti] == NOFREE)
  						dbBackSplit((dmtree_t *)
  							    dcp, leafno);
  					dbSplit((dmtree_t *) dcp, leafno,
  						dcp->budmin, oldval);
  				}
  
  				/* release the buffer and return the error.
  				 */
  				release_metapage(mp);
  				return (rc);
  			}
  		} else {
  			/* we're at the top level of the map. update
  			 * the bmap control page to reflect the size
  			 * of the maximum free buddy system.
  			 */
  			assert(level == bmp->db_maxlevel);
  			if (bmp->db_maxfreebud != oldroot) {
  				jfs_error(bmp->db_ipbmap->i_sb,
  					  "dbAdjCtl: the maximum free buddy is "
  					  "not the old root");
  			}
  			bmp->db_maxfreebud = dcp->stree[ROOT];
  		}
  	}
  
  	/* write the buffer.
  	 */
  	write_metapage(mp);
  
  	return (0);
  }
  
  
  /*
   * NAME:	dbSplit()
   *

   * FUNCTION:	update the leaf of a dmtree with a new value, splitting

   *		the leaf from the binary buddy system of the dmtree's
   *		leaves, as required.
   *
   * PARAMETERS:

   *	tp	- pointer to the tree containing the leaf.
   *	leafno	- the number of the leaf to be updated.
   *	splitsz	- the size the binary buddy system starting at the leaf

   *		  must be split to, specified as the log2 number of blocks.

   *	newval	- the new value for the leaf.

   *
   * RETURN VALUES: none
   *
   * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
   */
  static void dbSplit(dmtree_t * tp, int leafno, int splitsz, int newval)
  {
  	int budsz;
  	int cursz;
  	s8 *leaf = tp->dmt_stree + le32_to_cpu(tp->dmt_leafidx);
  
  	/* check if the leaf needs to be split.
  	 */
  	if (leaf[leafno] > tp->dmt_budmin) {
  		/* the split occurs by cutting the buddy system in half
  		 * at the specified leaf until we reach the specified
  		 * size.  pick up the starting split size (current size
  		 * - 1 in l2) and the corresponding buddy size.
  		 */
  		cursz = leaf[leafno] - 1;
  		budsz = BUDSIZE(cursz, tp->dmt_budmin);
  
  		/* split until we reach the specified size.
  		 */
  		while (cursz >= splitsz) {
  			/* update the buddy's leaf with its new value.
  			 */
  			dbAdjTree(tp, leafno ^ budsz, cursz);
  
  			/* on to the next size and buddy.
  			 */
  			cursz -= 1;
  			budsz >>= 1;
  		}
  	}

  	/* adjust the dmap tree to reflect the specified leaf's new

  	 * value.
  	 */
  	dbAdjTree(tp, leafno, newval);
  }
  
  
  /*
   * NAME:	dbBackSplit()
   *

   * FUNCTION:	back split the binary buddy system of dmtree leaves

   *		that hold a specified leaf until the specified leaf
   *		starts its own binary buddy system.
   *
   *		the allocators typically perform allocations at the start
   *		of binary buddy systems and dbSplit() is used to accomplish
   *		any required splits.  in some cases, however, allocation
   *		may occur in the middle of a binary system and requires a
   *		back split, with the split proceeding out from the middle of
   *		the system (less efficient) rather than the start of the
   *		system (more efficient).  the cases in which a back split
   *		is required are rare and are limited to the first allocation
   *		within an allocation group which is a part (not first part)
   *		of a larger binary buddy system and a few exception cases
   *		in which a previous join operation must be backed out.
   *
   * PARAMETERS:

   *	tp	- pointer to the tree containing the leaf.
   *	leafno	- the number of the leaf to be updated.

   *
   * RETURN VALUES: none
   *
   * serialization: IREAD_LOCK(ipbmap) or IWRITE_LOCK(ipbmap) held on entry/exit;
   */

  static int dbBackSplit(dmtree_t * tp, int leafno)

  {
  	int budsz, bud, w, bsz, size;
  	int cursz;
  	s8 *leaf = tp->dmt_stree + le32_to_cpu(tp->dmt_leafidx);
  
  	/* leaf should be part (not first part) of a binary
  	 * buddy system.
  	 */
  	assert(leaf[leafno] == NOFREE);
  
  	/* the back split is accomplished by iteratively finding the leaf
  	 * that starts the buddy system that contains the specified leaf and
  	 * splitting that system in two.  this iteration continues until

  	 * the specified leaf becomes the start of a buddy system.

  	 *
  	 * determine maximum possible l2 size for the specified leaf.
  	 */
  	size =
  	    LITOL2BSZ(leafno, le32_to_cpu(tp->dmt_l2nleafs),
  		      tp->dmt_budmin);
  
  	/* determine the number of leaves covered by this size.  this
  	 * is the buddy size that we will start with as we search for
  	 * the buddy system that contains the specified leaf.
  	 */
  	budsz = BUDSIZE(size, tp->dmt_budmin);
  
  	/* back split.
  	 */
  	while (leaf[leafno] == NOFREE) {
  		/* find the leftmost buddy leaf.
  		 */
  		for (w = leafno, bsz = budsz;; bsz <<= 1,
  		     w = (w < bud) ? w : bud) {

  			if (bsz >= le32_to_cpu(tp->dmt_nleafs)) {
  				jfs_err("JFS: block map error in dbBackSplit");
  				return -EIO;
  			}

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

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

  }
  
  
  /*
   * NAME:	dbJoin()
   *

   * FUNCTION:	update the leaf of a dmtree with a new value, joining

   *		the leaf with other leaves of the dmtree into a multi-leaf
   *		binary buddy system, as required.
   *
   * PARAMETERS:

   *	tp	- pointer to the tree containing the leaf.
   *	leafno	- the number of the leaf to be updated.
   *	newval	- the new value for the leaf.

   *
   * RETURN VALUES: none
   */

  static int dbJoin(dmtree_t * tp, int leafno, int newval)

  {
  	int budsz, buddy;
  	s8 *leaf;
  
  	/* can the new leaf value require a join with other leaves ?
  	 */
  	if (newval >= tp->dmt_budmin) {
  		/* pickup a pointer to the leaves of the tree.
  		 */
  		leaf = tp->dmt_stree + le32_to_cpu(tp->dmt_leafidx);
  
  		/* try to join the specified leaf into a large binary
  		 * buddy system.  the join proceeds by attempting to join
  		 * the specified leafno with its buddy (leaf) at new value.
  		 * if the join occurs, we attempt to join the left leaf
  		 * of the joined buddies with its buddy at new value + 1.
  		 * we continue to join until we find a buddy that cannot be
  		 * joined (does not have a value equal to the size of the
  		 * last join) or until all leaves have been joined into a
  		 * single system.
  		 *
  		 * get the buddy size (number of words covered) of
  		 * the new value.
  		 */
  		budsz = BUDSIZE(newval, tp->dmt_budmin);
  
  		/* try to join.
  		 */
  		while (budsz < le32_to_cpu(tp->dmt_nleafs)) {
  			/* get the buddy leaf.
  			 */
  			buddy = leafno ^ budsz;
  
  			/* if the leaf's new value is greater than its
  			 * buddy's value, we join no more.
  			 */
  			if (newval > leaf[buddy])
  				break;

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

  
  			/* check which (leafno or buddy) is the left buddy.
  			 * the left buddy gets to claim the blocks resulting
  			 * from the join while the right gets to claim none.

  			 * the left buddy is also eligible to participate in

  			 * a join at the next higher level while the right
  			 * is not.
  			 *
  			 */
  			if (leafno < buddy) {
  				/* leafno is the left buddy.
  				 */
  				dbAdjTree(tp, buddy, NOFREE);
  			} else {
  				/* buddy is the left buddy and becomes
  				 * leafno.
  				 */
  				dbAdjTree(tp, leafno, NOFREE);
  				leafno = buddy;
  			}
  
  			/* on to try the next join.
  			 */
  			newval += 1;
  			budsz <<= 1;
  		}
  	}
  
  	/* update the leaf value.
  	 */
  	dbAdjTree(tp, leafno, newval);

  
  	return 0;

  }
  
  
  /*
   * NAME:	dbAdjTree()
   *

   * FUNCTION:	update a leaf of a dmtree with a new value, adjusting

   *		the dmtree, as required, to reflect the new leaf value.
   *		the combination of any buddies must already be done before
   *		this is called.
   *
   * PARAMETERS:

   *	tp	- pointer to the tree to be adjusted.
   *	leafno	- the number of the leaf to be updated.
   *	newval	- the new value for the leaf.

   *
   * RETURN VALUES: none
   */
  static void dbAdjTree(dmtree_t * tp, int leafno, int newval)
  {
  	int lp, pp, k;
  	int max;
  
  	/* pick up the index of the leaf for this leafno.
  	 */
  	lp = leafno + le32_to_cpu(tp->dmt_leafidx);
  
  	/* is the current value the same as the old value ?  if so,
  	 * there is nothing to do.
  	 */
  	if (tp->dmt_stree[lp] == newval)
  		return;
  
  	/* set the new value.
  	 */
  	tp->dmt_stree[lp] = newval;
  
  	/* bubble the new value up the tree as required.
  	 */
  	for (k = 0; k < le32_to_cpu(tp->dmt_height); k++) {
  		/* get the index of the first leaf of the 4 leaf
  		 * group containing the specified leaf (leafno).
  		 */
  		lp = ((lp - 1) & ~0x03) + 1;
  
  		/* get the index of the parent of this 4 leaf group.
  		 */
  		pp = (lp - 1) >> 2;
  
  		/* determine the maximum of the 4 leaves.
  		 */
  		max = TREEMAX(&tp->dmt_stree[lp]);
  
  		/* if the maximum of the 4 is the same as the
  		 * parent's value, we're done.
  		 */
  		if (tp->dmt_stree[pp] == max)
  			break;
  
  		/* parent gets new value.
  		 */
  		tp->dmt_stree[pp] = max;
  
  		/* parent becomes leaf for next go-round.
  		 */
  		lp = pp;
  	}
  }
  
  
  /*
   * NAME:	dbFindLeaf()
   *

   * FUNCTION:	search a dmtree_t for sufficient free blocks, returning

   *		the index of a leaf describing the free blocks if

   *		sufficient free blocks are found.
   *
   *		the search starts at the top of the dmtree_t tree and
   *		proceeds down the tree to the leftmost leaf with sufficient
   *		free space.
   *
   * PARAMETERS:

   *	tp	- pointer to the tree to be searched.
   *	l2nb	- log2 number of free blocks to search for.

   *	leafidx	- return pointer to be set to the index of the leaf
   *		  describing at least l2nb free blocks if sufficient
   *		  free blocks are found.
   *
   * RETURN VALUES:

   *	0	- success
   *	-ENOSPC	- insufficient free blocks.

   */
  static int dbFindLeaf(dmtree_t * tp, int l2nb, int *leafidx)
  {
  	int ti, n = 0, k, x = 0;
  
  	/* first check the root of the tree to see if there is
  	 * sufficient free space.
  	 */
  	if (l2nb > tp->dmt_stree[ROOT])
  		return -ENOSPC;
  
  	/* sufficient free space available. now search down the tree
  	 * starting at the next level for the leftmost leaf that
  	 * describes sufficient free space.
  	 */
  	for (k = le32_to_cpu(tp->dmt_height), ti = 1;
  	     k > 0; k--, ti = ((ti + n) << 2) + 1) {
  		/* search the four nodes at this level, starting from
  		 * the left.
  		 */
  		for (x = ti, n = 0; n < 4; n++) {
  			/* sufficient free space found.  move to the next
  			 * level (or quit if this is the last level).
  			 */
  			if (l2nb <= tp->dmt_stree[x + n])
  				break;
  		}
  
  		/* better have found something since the higher
  		 * levels of the tree said it was here.
  		 */
  		assert(n < 4);
  	}
  
  	/* set the return to the leftmost leaf describing sufficient
  	 * free space.
  	 */
  	*leafidx = x + n - le32_to_cpu(tp->dmt_leafidx);
  
  	return (0);
  }
  
  
  /*
   * NAME:	dbFindBits()
   *

   * FUNCTION:	find a specified number of binary buddy free bits within a

   *		dmap bitmap word value.
   *
   *		this routine searches the bitmap value for (1 << l2nb) free
   *		bits at (1 << l2nb) alignments within the value.
   *
   * PARAMETERS:

   *	word	-  dmap bitmap word value.
   *	l2nb	-  number of free bits specified as a log2 number.

   *
   * RETURN VALUES:

   *	starting bit number of free bits.

   */
  static int dbFindBits(u32 word, int l2nb)
  {
  	int bitno, nb;
  	u32 mask;
  
  	/* get the number of bits.
  	 */
  	nb = 1 << l2nb;
  	assert(nb <= DBWORD);
  
  	/* complement the word so we can use a mask (i.e. 0s represent
  	 * free bits) and compute the mask.
  	 */
  	word = ~word;
  	mask = ONES << (DBWORD - nb);
  
  	/* scan the word for nb free bits at nb alignments.
  	 */
  	for (bitno = 0; mask != 0; bitno += nb, mask >>= nb) {
  		if ((mask & word) == mask)
  			break;
  	}
  
  	ASSERT(bitno < 32);
  
  	/* return the bit number.
  	 */
  	return (bitno);
  }
  
  
  /*
   * NAME:	dbMaxBud(u8 *cp)
   *

   * FUNCTION:	determine the largest binary buddy string of free

   *		bits within 32-bits of the map.
   *
   * PARAMETERS:

   *	cp	-  pointer to the 32-bit value.

   *
   * RETURN VALUES:

   *	largest binary buddy of free bits within a dmap word.

   */
  static int dbMaxBud(u8 * cp)
  {
  	signed char tmp1, tmp2;
  
  	/* check if the wmap word is all free. if so, the
  	 * free buddy size is BUDMIN.
  	 */
  	if (*((uint *) cp) == 0)
  		return (BUDMIN);
  
  	/* check if the wmap word is half free. if so, the
  	 * free buddy size is BUDMIN-1.
  	 */
  	if (*((u16 *) cp) == 0 || *((u16 *) cp + 1) == 0)
  		return (BUDMIN - 1);
  
  	/* not all free or half free. determine the free buddy
  	 * size thru table lookup using quarters of the wmap word.
  	 */
  	tmp1 = max(budtab[cp[2]], budtab[cp[3]]);
  	tmp2 = max(budtab[cp[0]], budtab[cp[1]]);
  	return (max(tmp1, tmp2));
  }
  
  
  /*
   * NAME:	cnttz(uint word)
   *

   * FUNCTION:	determine the number of trailing zeros within a 32-bit

   *		value.
   *
   * PARAMETERS:

   *	value	-  32-bit value to be examined.

   *
   * RETURN VALUES:

   *	count of trailing zeros

   */
  static int cnttz(u32 word)
  {
  	int n;
  
  	for (n = 0; n < 32; n++, word >>= 1) {
  		if (word & 0x01)
  			break;
  	}
  
  	return (n);
  }
  
  
  /*
   * NAME:	cntlz(u32 value)
   *

   * FUNCTION:	determine the number of leading zeros within a 32-bit

   *		value.
   *
   * PARAMETERS:

   *	value	-  32-bit value to be examined.

   *
   * RETURN VALUES:

   *	count of leading zeros

   */
  static int cntlz(u32 value)
  {
  	int n;
  
  	for (n = 0; n < 32; n++, value <<= 1) {
  		if (value & HIGHORDER)
  			break;
  	}
  	return (n);
  }
  
  
  /*
   * NAME:	blkstol2(s64 nb)
   *
   * FUNCTION:	convert a block count to its log2 value. if the block

   *		count is not a l2 multiple, it is rounded up to the next

   *		larger l2 multiple.
   *
   * PARAMETERS:

   *	nb	-  number of blocks

   *
   * RETURN VALUES:

   *	log2 number of blocks

   */

  static int blkstol2(s64 nb)

  {
  	int l2nb;
  	s64 mask;		/* meant to be signed */
  
  	mask = (s64) 1 << (64 - 1);
  
  	/* count the leading bits.
  	 */
  	for (l2nb = 0; l2nb < 64; l2nb++, mask >>= 1) {
  		/* leading bit found.
  		 */
  		if (nb & mask) {
  			/* determine the l2 value.
  			 */
  			l2nb = (64 - 1) - l2nb;
  
  			/* check if we need to round up.
  			 */
  			if (~mask & nb)
  				l2nb++;
  
  			return (l2nb);
  		}
  	}
  	assert(0);
  	return 0;		/* fix compiler warning */
  }
  
  
  /*

   * NAME:	dbAllocBottomUp()

   *
   * FUNCTION:	alloc the specified block range from the working block
   *		allocation map.
   *
   *		the blocks will be alloc from the working map one dmap
   *		at a time.
   *
   * PARAMETERS:

   *	ip	-  pointer to in-core inode;
   *	blkno	-  starting block number to be freed.
   *	nblocks	-  number of blocks to be freed.

   *
   * RETURN VALUES:

   *	0	- success
   *	-EIO	- i/o error

   */
  int dbAllocBottomUp(struct inode *ip, s64 blkno, s64 nblocks)
  {
  	struct metapage *mp;
  	struct dmap *dp;
  	int nb, rc;
  	s64 lblkno, rem;
  	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
  	struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;

  	IREAD_LOCK(ipbmap, RDWRLOCK_DMAP);

  
  	/* block to be allocated better be within the mapsize. */
  	ASSERT(nblocks <= bmp->db_mapsize - blkno);
  
  	/*
  	 * allocate the blocks a dmap at a time.
  	 */
  	mp = NULL;
  	for (rem = nblocks; rem > 0; rem -= nb, blkno += nb) {
  		/* release previous dmap if any */
  		if (mp) {
  			write_metapage(mp);
  		}
  
  		/* get the buffer for the current dmap. */
  		lblkno = BLKTODMAP(blkno, bmp->db_l2nbperpage);
  		mp = read_metapage(ipbmap, lblkno, PSIZE, 0);
  		if (mp == NULL) {
  			IREAD_UNLOCK(ipbmap);
  			return -EIO;
  		}
  		dp = (struct dmap *) mp->data;
  
  		/* determine the number of blocks to be allocated from
  		 * this dmap.
  		 */
  		nb = min(rem, BPERDMAP - (blkno & (BPERDMAP - 1)));

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

  	}
  
  	/* write the last buffer. */
  	write_metapage(mp);
  
  	IREAD_UNLOCK(ipbmap);
  
  	return (0);
  }
  
  
  static int dbAllocDmapBU(struct bmap * bmp, struct dmap * dp, s64 blkno,
  			 int nblocks)
  {
  	int rc;
  	int dbitno, word, rembits, nb, nwords, wbitno, agno;

  	s8 oldroot;

  	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];

  	/* 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 */

  	le32_add_cpu(&dp->nfree, -nblocks);

  
  	/* reconstruct summary tree */
  	dbInitDmapTree(dp);
  
  	BMAP_LOCK(bmp);
  
  	/* if this allocation group is completely free,

  	 * update the highest active allocation group number

  	 * if this allocation group is the new max.
  	 */
  	agno = blkno >> bmp->db_agl2size;
  	if (agno > bmp->db_maxag)
  		bmp->db_maxag = agno;
  
  	/* update the free count for the allocation group and map */
  	bmp->db_agfree[agno] -= nblocks;
  	bmp->db_nfree -= nblocks;
  
  	BMAP_UNLOCK(bmp);
  
  	/* if the root has not changed, done. */
  	if (tp->stree[ROOT] == oldroot)
  		return (0);
  
  	/* root changed. bubble the change up to the dmap control pages.
  	 * if the adjustment of the upper level control pages fails,
  	 * backout the bit allocation (thus making everything consistent).
  	 */
  	if ((rc = dbAdjCtl(bmp, blkno, tp->stree[ROOT], 1, 0)))
  		dbFreeBits(bmp, dp, blkno, nblocks);
  
  	return (rc);
  }
  
  
  /*
   * NAME:	dbExtendFS()
   *
   * FUNCTION:	extend bmap from blkno for nblocks;

   *		dbExtendFS() updates bmap ready for dbAllocBottomUp();

   *
   * L2
   *  |
   *   L1---------------------------------L1

   *    |					 |
   *     L0---------L0---------L0		  L0---------L0---------L0
   *      |	   |	      |		   |	      |		 |
   *	 d0,...,dn  d0,...,dn  d0,...,dn    d0,...,dn  d0,...,dn  d0,.,dm;

   * L2L1L0d0,...,dnL0d0,...,dnL0d0,...,dnL1L0d0,...,dnL0d0,...,dnL0d0,..dm
   *

   * <---old---><----------------------------extend----------------------->

   */
  int dbExtendFS(struct inode *ipbmap, s64 blkno,	s64 nblocks)
  {
  	struct jfs_sb_info *sbi = JFS_SBI(ipbmap->i_sb);
  	int nbperpage = sbi->nbperpage;

  	int i, i0 = true, j, j0 = true, k, n;

  	s64 newsize;
  	s64 p;
  	struct metapage *mp, *l2mp, *l1mp = NULL, *l0mp = NULL;
  	struct dmapctl *l2dcp, *l1dcp, *l0dcp;
  	struct dmap *dp;
  	s8 *l0leaf, *l1leaf, *l2leaf;
  	struct bmap *bmp = sbi->bmap;
  	int agno, l2agsize, oldl2agsize;
  	s64 ag_rem;
  
  	newsize = blkno + nblocks;
  
  	jfs_info("dbExtendFS: blkno:%Ld nblocks:%Ld newsize:%Ld",
  		 (long long) blkno, (long long) nblocks, (long long) newsize);
  
  	/*

  	 *	initialize bmap control page.

  	 *
  	 * all the data in bmap control page should exclude
  	 * the mkfs hidden dmap page.
  	 */
  
  	/* update mapsize */
  	bmp->db_mapsize = newsize;
  	bmp->db_maxlevel = BMAPSZTOLEV(bmp->db_mapsize);
  
  	/* compute new AG size */
  	l2agsize = dbGetL2AGSize(newsize);
  	oldl2agsize = bmp->db_agl2size;
  
  	bmp->db_agl2size = l2agsize;
  	bmp->db_agsize = 1 << l2agsize;
  
  	/* compute new number of AG */
  	agno = bmp->db_numag;
  	bmp->db_numag = newsize >> l2agsize;
  	bmp->db_numag += ((u32) newsize % (u32) bmp->db_agsize) ? 1 : 0;
  
  	/*

  	 *	reconfigure db_agfree[]

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

  		/* coalesce contiguous k AGs; */

  		for (j = 0; j < k && i < agno; j++, i++) {
  			/* merge AGi to AGn */
  			bmp->db_agfree[n] += bmp->db_agfree[i];
  		}
  	}
  	bmp->db_agfree[0] += ag_rem;	/* restore agfree[0] */
  
  	for (; n < MAXAG; n++)
  		bmp->db_agfree[n] = 0;
  
  	/*
  	 * update highest active ag number
  	 */
  
  	bmp->db_maxag = bmp->db_maxag / k;
  
  	/*

  	 *	extend bmap

  	 *
  	 * update bit maps and corresponding level control pages;
  	 * global control page db_nfree, db_agfree[agno], db_maxfreebud;
  	 */
        extend:
  	/* get L2 page */
  	p = BMAPBLKNO + nbperpage;	/* L2 page */
  	l2mp = read_metapage(ipbmap, p, PSIZE, 0);
  	if (!l2mp) {
  		jfs_error(ipbmap->i_sb, "dbExtendFS: L2 page could not be read");
  		return -EIO;
  	}
  	l2dcp = (struct dmapctl *) l2mp->data;
  
  	/* compute start L1 */
  	k = blkno >> L2MAXL1SIZE;
  	l2leaf = l2dcp->stree + CTLLEAFIND + k;
  	p = BLKTOL1(blkno, sbi->l2nbperpage);	/* L1 page */
  
  	/*
  	 * extend each L1 in L2
  	 */
  	for (; k < LPERCTL; k++, p += nbperpage) {
  		/* get L1 page */
  		if (j0) {
  			/* read in L1 page: (blkno & (MAXL1SIZE - 1)) */
  			l1mp = read_metapage(ipbmap, p, PSIZE, 0);
  			if (l1mp == NULL)
  				goto errout;
  			l1dcp = (struct dmapctl *) l1mp->data;
  
  			/* compute start L0 */
  			j = (blkno & (MAXL1SIZE - 1)) >> L2MAXL0SIZE;
  			l1leaf = l1dcp->stree + CTLLEAFIND + j;
  			p = BLKTOL0(blkno, sbi->l2nbperpage);

  			j0 = false;

  		} else {
  			/* assign/init L1 page */
  			l1mp = get_metapage(ipbmap, p, PSIZE, 0);
  			if (l1mp == NULL)
  				goto errout;
  
  			l1dcp = (struct dmapctl *) l1mp->data;
  
  			/* compute start L0 */
  			j = 0;
  			l1leaf = l1dcp->stree + CTLLEAFIND;

  			p += nbperpage;	/* 1st L0 of L1.k */

  		}
  
  		/*
  		 * extend each L0 in L1
  		 */
  		for (; j < LPERCTL; j++) {
  			/* get L0 page */
  			if (i0) {
  				/* read in L0 page: (blkno & (MAXL0SIZE - 1)) */
  
  				l0mp = read_metapage(ipbmap, p, PSIZE, 0);
  				if (l0mp == NULL)
  					goto errout;
  				l0dcp = (struct dmapctl *) l0mp->data;
  
  				/* compute start dmap */
  				i = (blkno & (MAXL0SIZE - 1)) >>
  				    L2BPERDMAP;
  				l0leaf = l0dcp->stree + CTLLEAFIND + i;
  				p = BLKTODMAP(blkno,
  					      sbi->l2nbperpage);

  				i0 = false;

  			} else {
  				/* assign/init L0 page */
  				l0mp = get_metapage(ipbmap, p, PSIZE, 0);
  				if (l0mp == NULL)
  					goto errout;
  
  				l0dcp = (struct dmapctl *) l0mp->data;
  
  				/* compute start dmap */
  				i = 0;
  				l0leaf = l0dcp->stree + CTLLEAFIND;
  				p += nbperpage;	/* 1st dmap of L0.j */
  			}
  
  			/*
  			 * extend each dmap in L0
  			 */
  			for (; i < LPERCTL; i++) {
  				/*
  				 * reconstruct the dmap page, and
  				 * initialize corresponding parent L0 leaf
  				 */
  				if ((n = blkno & (BPERDMAP - 1))) {
  					/* read in dmap page: */
  					mp = read_metapage(ipbmap, p,
  							   PSIZE, 0);
  					if (mp == NULL)
  						goto errout;
  					n = min(nblocks, (s64)BPERDMAP - n);
  				} else {
  					/* assign/init dmap page */
  					mp = read_metapage(ipbmap, p,
  							   PSIZE, 0);
  					if (mp == NULL)
  						goto errout;
  
  					n = min(nblocks, (s64)BPERDMAP);
  				}
  
  				dp = (struct dmap *) mp->data;
  				*l0leaf = dbInitDmap(dp, blkno, n);
  
  				bmp->db_nfree += n;
  				agno = le64_to_cpu(dp->start) >> l2agsize;
  				bmp->db_agfree[agno] += n;
  
  				write_metapage(mp);
  
  				l0leaf++;
  				p += nbperpage;
  
  				blkno += n;
  				nblocks -= n;
  				if (nblocks == 0)
  					break;
  			}	/* for each dmap in a L0 */
  
  			/*

  			 * build current L0 page from its leaves, and

  			 * initialize corresponding parent L1 leaf
  			 */
  			*l1leaf = dbInitDmapCtl(l0dcp, 0, ++i);
  			write_metapage(l0mp);
  			l0mp = NULL;
  
  			if (nblocks)
  				l1leaf++;	/* continue for next L0 */
  			else {
  				/* more than 1 L0 ? */
  				if (j > 0)
  					break;	/* build L1 page */
  				else {
  					/* summarize in global bmap page */
  					bmp->db_maxfreebud = *l1leaf;
  					release_metapage(l1mp);
  					release_metapage(l2mp);
  					goto finalize;
  				}
  			}
  		}		/* for each L0 in a L1 */
  
  		/*

  		 * build current L1 page from its leaves, and

  		 * initialize corresponding parent L2 leaf
  		 */
  		*l2leaf = dbInitDmapCtl(l1dcp, 1, ++j);
  		write_metapage(l1mp);
  		l1mp = NULL;
  
  		if (nblocks)
  			l2leaf++;	/* continue for next L1 */
  		else {
  			/* more than 1 L1 ? */
  			if (k > 0)
  				break;	/* build L2 page */
  			else {
  				/* summarize in global bmap page */
  				bmp->db_maxfreebud = *l2leaf;
  				release_metapage(l2mp);
  				goto finalize;
  			}
  		}
  	}			/* for each L1 in a L2 */
  
  	jfs_error(ipbmap->i_sb,
  		  "dbExtendFS: function has not returned as expected");
  errout:
  	if (l0mp)
  		release_metapage(l0mp);
  	if (l1mp)
  		release_metapage(l1mp);
  	release_metapage(l2mp);
  	return -EIO;
  
  	/*

  	 *	finalize bmap control page

  	 */
  finalize:
  
  	return 0;
  }
  
  
  /*
   *	dbFinalizeBmap()
   */
  void dbFinalizeBmap(struct inode *ipbmap)
  {
  	struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;
  	int actags, inactags, l2nl;
  	s64 ag_rem, actfree, inactfree, avgfree;
  	int i, n;
  
  	/*

  	 *	finalize bmap control page

  	 */
  //finalize:

  	/*

  	 * compute db_agpref: preferred ag to allocate from
  	 * (the leftmost ag with average free space in it);
  	 */
  //agpref:
  	/* get the number of active ags and inacitve ags */
  	actags = bmp->db_maxag + 1;
  	inactags = bmp->db_numag - actags;
  	ag_rem = bmp->db_mapsize & (bmp->db_agsize - 1);	/* ??? */
  
  	/* determine how many blocks are in the inactive allocation
  	 * groups. in doing this, we must account for the fact that
  	 * the rightmost group might be a partial group (i.e. file
  	 * system size is not a multiple of the group size).
  	 */
  	inactfree = (inactags && ag_rem) ?
  	    ((inactags - 1) << bmp->db_agl2size) + ag_rem
  	    : inactags << bmp->db_agl2size;
  
  	/* determine how many free blocks are in the active
  	 * allocation groups plus the average number of free blocks
  	 * within the active ags.
  	 */
  	actfree = bmp->db_nfree - inactfree;
  	avgfree = (u32) actfree / (u32) actags;
  
  	/* if the preferred allocation group has not average free space.
  	 * re-establish the preferred group as the leftmost
  	 * group with average free space.
  	 */
  	if (bmp->db_agfree[bmp->db_agpref] < avgfree) {
  		for (bmp->db_agpref = 0; bmp->db_agpref < actags;
  		     bmp->db_agpref++) {
  			if (bmp->db_agfree[bmp->db_agpref] >= avgfree)
  				break;
  		}
  		if (bmp->db_agpref >= bmp->db_numag) {
  			jfs_error(ipbmap->i_sb,
  				  "cannot find ag with average freespace");
  		}
  	}
  
  	/*

  	 * compute db_aglevel, db_agheight, 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_agheight = l2nl >> 1;
  	bmp->db_agwidth = 1 << (l2nl - (bmp->db_agheight << 1));
  	for (i = 5 - bmp->db_agheight, bmp->db_agstart = 0, n = 1; i > 0;

  	     i--) {
  		bmp->db_agstart += n;
  		n <<= 2;
  	}
  
  }
  
  
  /*
   * NAME:	dbInitDmap()/ujfs_idmap_page()

   *

   * FUNCTION:	initialize working/persistent bitmap of the dmap page
   *		for the specified number of blocks:

   *

   *		at entry, the bitmaps had been initialized as free (ZEROS);

   *		The number of blocks will only account for the actually
   *		existing blocks. Blocks which don't actually exist in

   *		the aggregate will be marked as allocated (ONES);
   *
   * PARAMETERS:
   *	dp	- pointer to page of map
   *	nblocks	- number of blocks this page
   *
   * RETURNS: NONE
   */
  static int dbInitDmap(struct dmap * dp, s64 Blkno, int nblocks)
  {
  	int blkno, w, b, r, nw, nb, i;
  
  	/* starting block number within the dmap */
  	blkno = Blkno & (BPERDMAP - 1);
  
  	if (blkno == 0) {
  		dp->nblocks = dp->nfree = cpu_to_le32(nblocks);
  		dp->start = cpu_to_le64(Blkno);
  
  		if (nblocks == BPERDMAP) {
  			memset(&dp->wmap[0], 0, LPERDMAP * 4);
  			memset(&dp->pmap[0], 0, LPERDMAP * 4);
  			goto initTree;
  		}
  	} else {

  		le32_add_cpu(&dp->nblocks, nblocks);
  		le32_add_cpu(&dp->nfree, nblocks);

  	}
  
  	/* word number containing start block number */
  	w = blkno >> L2DBWORD;
  
  	/*
  	 * free the bits corresponding to the block range (ZEROS):

  	 * note: not all bits of the first and last words may be contained

  	 * within the block range.
  	 */
  	for (r = nblocks; r > 0; r -= nb, blkno += nb) {
  		/* number of bits preceding range to be freed in the word */
  		b = blkno & (DBWORD - 1);
  		/* number of bits to free in the word */
  		nb = min(r, DBWORD - b);
  
  		/* is partial word to be freed ? */
  		if (nb < DBWORD) {
  			/* free (set to 0) from the bitmap word */
  			dp->wmap[w] &= cpu_to_le32(~(ONES << (DBWORD - nb)
  						     >> b));
  			dp->pmap[w] &= cpu_to_le32(~(ONES << (DBWORD - nb)
  						     >> b));
  
  			/* skip the word freed */
  			w++;
  		} else {
  			/* free (set to 0) contiguous bitmap words */
  			nw = r >> L2DBWORD;
  			memset(&dp->wmap[w], 0, nw * 4);
  			memset(&dp->pmap[w], 0, nw * 4);
  
  			/* skip the words freed */
  			nb = nw << L2DBWORD;
  			w += nw;
  		}
  	}
  
  	/*

  	 * mark bits following the range to be freed (non-existing

  	 * blocks) as allocated (ONES)
  	 */
  
  	if (blkno == BPERDMAP)
  		goto initTree;
  
  	/* the first word beyond the end of existing blocks */
  	w = blkno >> L2DBWORD;
  
  	/* does nblocks fall on a 32-bit boundary ? */
  	b = blkno & (DBWORD - 1);
  	if (b) {
  		/* mark a partial word allocated */
  		dp->wmap[w] = dp->pmap[w] = cpu_to_le32(ONES >> b);
  		w++;
  	}
  
  	/* set the rest of the words in the page to allocated (ONES) */
  	for (i = w; i < LPERDMAP; i++)
  		dp->pmap[i] = dp->wmap[i] = cpu_to_le32(ONES);
  
  	/*
  	 * init tree
  	 */
        initTree:
  	return (dbInitDmapTree(dp));
  }
  
  
  /*
   * NAME:	dbInitDmapTree()/ujfs_complete_dmap()

   *

   * FUNCTION:	initialize summary tree of the specified dmap:
   *
   *		at entry, bitmap of the dmap has been initialized;

   *

   * PARAMETERS:
   *	dp	- dmap to complete
   *	blkno	- starting block number for this dmap
   *	treemax	- will be filled in with max free for this dmap
   *
   * RETURNS:	max free string at the root of the tree
   */
  static int dbInitDmapTree(struct dmap * dp)
  {
  	struct dmaptree *tp;
  	s8 *cp;
  	int i;
  
  	/* init fixed info of tree */
  	tp = &dp->tree;
  	tp->nleafs = cpu_to_le32(LPERDMAP);
  	tp->l2nleafs = cpu_to_le32(L2LPERDMAP);
  	tp->leafidx = cpu_to_le32(LEAFIND);
  	tp->height = cpu_to_le32(4);
  	tp->budmin = BUDMIN;
  
  	/* init each leaf from corresponding wmap word:
  	 * note: leaf is set to NOFREE(-1) if all blocks of corresponding

  	 * bitmap word are allocated.

  	 */
  	cp = tp->stree + le32_to_cpu(tp->leafidx);
  	for (i = 0; i < LPERDMAP; i++)
  		*cp++ = dbMaxBud((u8 *) & dp->wmap[i]);
  
  	/* build the dmap's binary buddy summary tree */
  	return (dbInitTree(tp));
  }
  
  
  /*
   * NAME:	dbInitTree()/ujfs_adjtree()

   *

   * FUNCTION:	initialize binary buddy summary tree of a dmap or dmapctl.
   *

   *		at entry, the leaves of the tree has been initialized

   *		from corresponding bitmap word or root of summary tree
   *		of the child control page;
   *		configure binary buddy system at the leaf level, then
   *		bubble up the values of the leaf nodes up the tree.
   *
   * PARAMETERS:
   *	cp	- Pointer to the root of the tree
   *	l2leaves- Number of leaf nodes as a power of 2
   *	l2min	- Number of blocks that can be covered by a leaf
   *		  as a power of 2
   *
   * RETURNS: max free string at the root of the tree
   */
  static int dbInitTree(struct dmaptree * dtp)
  {
  	int l2max, l2free, bsize, nextb, i;
  	int child, parent, nparent;
  	s8 *tp, *cp, *cp1;
  
  	tp = dtp->stree;
  
  	/* Determine the maximum free string possible for the leaves */
  	l2max = le32_to_cpu(dtp->l2nleafs) + dtp->budmin;
  
  	/*
  	 * configure the leaf levevl into binary buddy system
  	 *

  	 * Try to combine buddies starting with a buddy size of 1
  	 * (i.e. two leaves). At a buddy size of 1 two buddy leaves
  	 * can be combined if both buddies have a maximum free of l2min;
  	 * the combination will result in the left-most buddy leaf having
  	 * a maximum free of l2min+1.
  	 * After processing all buddies for a given size, process buddies
  	 * at the next higher buddy size (i.e. current size * 2) and
  	 * the next maximum free (current free + 1).
  	 * This continues until the maximum possible buddy combination

  	 * yields maximum free.
  	 */
  	for (l2free = dtp->budmin, bsize = 1; l2free < l2max;
  	     l2free++, bsize = nextb) {
  		/* get next buddy size == current buddy pair size */
  		nextb = bsize << 1;
  
  		/* scan each adjacent buddy pair at current buddy size */
  		for (i = 0, cp = tp + le32_to_cpu(dtp->leafidx);
  		     i < le32_to_cpu(dtp->nleafs);
  		     i += nextb, cp += nextb) {
  			/* coalesce if both adjacent buddies are max free */
  			if (*cp == l2free && *(cp + bsize) == l2free) {
  				*cp = l2free + 1;	/* left take right */
  				*(cp + bsize) = -1;	/* right give left */
  			}
  		}
  	}
  
  	/*
  	 * bubble summary information of leaves up the tree.
  	 *
  	 * Starting at the leaf node level, the four nodes described by

  	 * the higher level parent node are compared for a maximum free and
  	 * this maximum becomes the value of the parent node.
  	 * when all lower level nodes are processed in this fashion then
  	 * move up to the next level (parent becomes a lower level node) and

  	 * continue the process for that level.
  	 */
  	for (child = le32_to_cpu(dtp->leafidx),
  	     nparent = le32_to_cpu(dtp->nleafs) >> 2;
  	     nparent > 0; nparent >>= 2, child = parent) {
  		/* get index of 1st node of parent level */
  		parent = (child - 1) >> 2;

  		/* set the value of the parent node as the maximum

  		 * of the four nodes of the current level.
  		 */
  		for (i = 0, cp = tp + child, cp1 = tp + parent;
  		     i < nparent; i++, cp += 4, cp1++)
  			*cp1 = TREEMAX(cp);
  	}
  
  	return (*tp);
  }
  
  
  /*
   *	dbInitDmapCtl()
   *
   * function: initialize dmapctl page
   */
  static int dbInitDmapCtl(struct dmapctl * dcp, int level, int i)
  {				/* start leaf index not covered by range */
  	s8 *cp;
  
  	dcp->nleafs = cpu_to_le32(LPERCTL);
  	dcp->l2nleafs = cpu_to_le32(L2LPERCTL);
  	dcp->leafidx = cpu_to_le32(CTLLEAFIND);
  	dcp->height = cpu_to_le32(5);
  	dcp->budmin = L2BPERDMAP + L2LPERCTL * level;
  
  	/*

  	 * initialize the leaves of current level that were not covered
  	 * by the specified input block range (i.e. the leaves have no

  	 * low level dmapctl or dmap).
  	 */
  	cp = &dcp->stree[CTLLEAFIND + i];
  	for (; i < LPERCTL; i++)
  		*cp++ = NOFREE;
  
  	/* build the dmap's binary buddy summary tree */
  	return (dbInitTree((struct dmaptree *) dcp));
  }
  
  
  /*
   * NAME:	dbGetL2AGSize()/ujfs_getagl2size()

   *

   * FUNCTION:	Determine log2(allocation group size) from aggregate size

   *

   * PARAMETERS:
   *	nblocks	- Number of blocks in aggregate
   *
   * RETURNS: log2(allocation group size) in aggregate blocks
   */
  static int dbGetL2AGSize(s64 nblocks)
  {
  	s64 sz;
  	s64 m;
  	int l2sz;
  
  	if (nblocks < BPERDMAP * MAXAG)
  		return (L2BPERDMAP);
  
  	/* round up aggregate size to power of 2 */
  	m = ((u64) 1 << (64 - 1));
  	for (l2sz = 64; l2sz >= 0; l2sz--, m >>= 1) {
  		if (m & nblocks)
  			break;
  	}
  
  	sz = (s64) 1 << l2sz;
  	if (sz < nblocks)
  		l2sz += 1;
  
  	/* agsize = roundupSize/max_number_of_ag */
  	return (l2sz - L2MAXAG);
  }
  
  
  /*
   * NAME:	dbMapFileSizeToMapSize()

   *
   * FUNCTION:	compute number of blocks the block allocation map file

   *		can cover from the map file size;
   *
   * RETURNS:	Number of blocks which can be covered by this block map file;
   */
  
  /*
   * maximum number of map pages at each level including control pages
   */
  #define MAXL0PAGES	(1 + LPERCTL)
  #define MAXL1PAGES	(1 + LPERCTL * MAXL0PAGES)
  #define MAXL2PAGES	(1 + LPERCTL * MAXL1PAGES)
  
  /*
   * convert number of map pages to the zero origin top dmapctl level
   */
  #define BMAPPGTOLEV(npages)	\

  	(((npages) <= 3 + MAXL0PAGES) ? 0 : \
  	 ((npages) <= 2 + MAXL1PAGES) ? 1 : 2)

  
  s64 dbMapFileSizeToMapSize(struct inode * ipbmap)
  {
  	struct super_block *sb = ipbmap->i_sb;
  	s64 nblocks;
  	s64 npages, ndmaps;
  	int level, i;
  	int complete, factor;
  
  	nblocks = ipbmap->i_size >> JFS_SBI(sb)->l2bsize;
  	npages = nblocks >> JFS_SBI(sb)->l2nbperpage;
  	level = BMAPPGTOLEV(npages);

  	/* At each level, accumulate the number of dmap pages covered by

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

  		ndmaps += complete * ((i == 2) ? LPERCTL * LPERCTL :
  				      ((i == 1) ? LPERCTL : 1));

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

  	/* convert the number of dmaps into the number of blocks

  	 * which can be covered by the dmaps;
  	 */
  	nblocks = ndmaps << L2BPERDMAP;
  
  	return (nblocks);
  }