Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4061 insertions, 0 deletions

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
new file mode 100644
index 0000000000..11c77757ea
--- /dev/null
+++ b/fs/jfs/jfs_dmap.c
@@ -0,0 +1,4061 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *   Copyright (C) International Business Machines Corp., 2000-2004
+ *   Portions Copyright (C) Tino Reichardt, 2012
+ */
+
+#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"
+#include "jfs_discard.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, bool is_ctl);
+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);
+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
+ *	-EINVAL - wrong bmap data
+ */
+int dbMount(struct inode *ipbmap)
+{
+	struct bmap *bmp;
+	struct dbmap_disk *dbmp_le;
+	struct metapage *mp;
+	int i, err;
+
+	/*
+	 * 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) {
+		err = -EIO;
+		goto err_kfree_bmp;
+	}
+
+	/* 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);
+	if (bmp->db_l2nbperpage > L2PSIZE - L2MINBLOCKSIZE ||
+		bmp->db_l2nbperpage < 0) {
+		err = -EINVAL;
+		goto err_release_metapage;
+	}
+
+	bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
+	if (!bmp->db_numag) {
+		err = -EINVAL;
+		goto err_release_metapage;
+	}
+
+	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);
+	if (bmp->db_maxag >= MAXAG || bmp->db_maxag < 0 ||
+		bmp->db_agpref >= MAXAG || bmp->db_agpref < 0) {
+		err = -EINVAL;
+		goto err_release_metapage;
+	}
+
+	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);
+	if (bmp->db_agl2size > L2MAXL2SIZE - L2MAXAG ||
+	    bmp->db_agl2size < 0) {
+		err = -EINVAL;
+		goto err_release_metapage;
+	}
+
+	if (((bmp->db_mapsize - 1) >> bmp->db_agl2size) > MAXAG) {
+		err = -EINVAL;
+		goto err_release_metapage;
+	}
+
+	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);
+
+err_release_metapage:
+	release_metapage(mp);
+err_kfree_bmp:
+	kfree(bmp);
+	return err;
+}
+
+
+/*
+ * 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);
+	JFS_SBI(ipbmap->i_sb)->bmap = NULL;
+
+	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;
+	struct super_block *sb = ipbmap->i_sb;
+
+	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\n",
+		       (unsigned long long) blkno,
+		       (unsigned long long) nblocks);
+		jfs_error(ip->i_sb, "block to be freed is outside the map\n");
+		return -EIO;
+	}
+
+	/**
+	 * TRIM the blocks, when mounted with discard option
+	 */
+	if (JFS_SBI(sb)->flag & JFS_DISCARD)
+		if (JFS_SBI(sb)->minblks_trim <= nblocks)
+			jfs_issue_discard(ipbmap, blkno, nblocks);
+
+	/*
+	 * 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, "error in block map\n");
+			release_metapage(mp);
+			IREAD_UNLOCK(ipbmap);
+			return (rc);
+		}
+	}
+
+	/* write the last buffer. */
+	if (mp)
+		write_metapage(mp);
+
+	IREAD_UNLOCK(ipbmap);
+
+	return (0);
+}
+
+
+/*
+ * NAME:	dbUpdatePMap()
+ *
+ * FUNCTION:	update the allocation state (free or allocate) of the
+ *		specified block range in the persistent block allocation map.
+ *
+ *		the blocks will be updated in the persistent map one
+ *		dmap at a time.
+ *
+ * PARAMETERS:
+ *	ipbmap	- pointer to in-core inode for the block map.
+ *	free	- 'true' if block range is to be freed from the persistent
+ *		  map; 'false' if it is to be allocated.
+ *	blkno	- starting block number of the range.
+ *	nblocks	- number of contiguous blocks in the range.
+ *	tblk	- transaction block;
+ *
+ * RETURN VALUES:
+ *	0	- success
+ *	-EIO	- i/o error
+ */
+int
+dbUpdatePMap(struct inode *ipbmap,
+	     int free, s64 blkno, s64 nblocks, struct tblock * tblk)
+{
+	int nblks, dbitno, wbitno, rbits;
+	int word, nbits, nwords;
+	struct bmap *bmp = JFS_SBI(ipbmap->i_sb)->bmap;
+	s64 lblkno, rem, lastlblkno;
+	u32 mask;
+	struct dmap *dp;
+	struct metapage *mp;
+	struct jfs_log *log;
+	int lsn, difft, diffp;
+	unsigned long flags;
+
+	/* the blocks better be within the mapsize. */
+	if (blkno + nblocks > bmp->db_mapsize) {
+		printk(KERN_ERR "blkno = %Lx, nblocks = %Lx\n",
+		       (unsigned long long) blkno,
+		       (unsigned long long) nblocks);
+		jfs_error(ipbmap->i_sb, "blocks are outside the map\n");
+		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 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, "the hint is outside the map\n");
+		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);
+}
+
+/*
+ * 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, "the block is outside the filesystem\n");
+		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, "Corrupt dmap page\n");
+		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_t(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, "Corrupt dmap page\n");
+		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,
+			  "allocation request is larger than the allocation group size\n");
+		return -EIO;
+	}
+
+	/* determine the starting block number of the allocation
+	 * group.
+	 */
+	blkno = (s64) agno << bmp->db_agl2size;
+
+	/* check if the allocation group size is the minimum allocation
+	 * group size or if the allocation group is completely free. if
+	 * the allocation group size is the minimum size of BPERDMAP (i.e.
+	 * 1 dmap), there is no need to search the dmap control page (below)
+	 * that fully describes the allocation group since the allocation
+	 * group is already fully described by a dmap.  in this case, we
+	 * just call dbAllocCtl() to search the dmap tree and allocate the
+	 * required space if available.
+	 *
+	 * if the allocation group is completely free, dbAllocCtl() is
+	 * also called to allocate the required space.  this is done for
+	 * two reasons.  first, it makes no sense searching the dmap control
+	 * pages for free space when we know that free space exists.  second,
+	 * the dmap control pages may indicate that the allocation group
+	 * has no free space if the allocation group is part (not the first
+	 * part) of a larger binary buddy system.
+	 */
+	if (bmp->db_agsize == BPERDMAP
+	    || bmp->db_agfree[agno] == bmp->db_agsize) {
+		rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
+		if ((rc == -ENOSPC) &&
+		    (bmp->db_agfree[agno] == bmp->db_agsize)) {
+			printk(KERN_ERR "blkno = %Lx, blocks = %Lx\n",
+			       (unsigned long long) blkno,
+			       (unsigned long long) nblocks);
+			jfs_error(bmp->db_ipbmap->i_sb,
+				  "dbAllocCtl failed in free AG\n");
+		}
+		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, "Corrupt dmapctl page\n");
+		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,
+					  "failed descending stree\n");
+				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,
+						  "control page inconsistent\n");
+					return -EIO;
+				}
+				return (rc);
+			}
+		}
+
+		/* allocate the blocks.
+		 */
+		rc = dbAllocCtl(bmp, nblocks, l2nb, blkno, results);
+		if (rc == -ENOSPC) {
+			jfs_error(bmp->db_ipbmap->i_sb,
+				  "unable to allocate blocks\n");
+			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, "unable to allocate blocks\n");
+		return -EIO;
+	}
+	return (rc);
+}
+
+
+/*
+ * NAME:	dbDiscardAG()
+ *
+ * FUNCTION:	attempt to discard (TRIM) all free blocks of specific AG
+ *
+ *		algorithm:
+ *		1) allocate blocks, as large as possible and save them
+ *		   while holding IWRITE_LOCK on ipbmap
+ *		2) trim all these saved block/length values
+ *		3) mark the blocks free again
+ *
+ *		benefit:
+ *		- we work only on one ag at some time, minimizing how long we
+ *		  need to lock ipbmap
+ *		- reading / writing the fs is possible most time, even on
+ *		  trimming
+ *
+ *		downside:
+ *		- we write two times to the dmapctl and dmap pages
+ *		- but for me, this seems the best way, better ideas?
+ *		/TR 2012
+ *
+ * PARAMETERS:
+ *	ip	- pointer to in-core inode
+ *	agno	- ag to trim
+ *	minlen	- minimum value of contiguous blocks
+ *
+ * RETURN VALUES:
+ *	s64	- actual number of blocks trimmed
+ */
+s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen)
+{
+	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
+	struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;
+	s64 nblocks, blkno;
+	u64 trimmed = 0;
+	int rc, l2nb;
+	struct super_block *sb = ipbmap->i_sb;
+
+	struct range2trim {
+		u64 blkno;
+		u64 nblocks;
+	} *totrim, *tt;
+
+	/* max blkno / nblocks pairs to trim */
+	int count = 0, range_cnt;
+	u64 max_ranges;
+
+	/* prevent others from writing new stuff here, while trimming */
+	IWRITE_LOCK(ipbmap, RDWRLOCK_DMAP);
+
+	nblocks = bmp->db_agfree[agno];
+	max_ranges = nblocks;
+	do_div(max_ranges, minlen);
+	range_cnt = min_t(u64, max_ranges + 1, 32 * 1024);
+	totrim = kmalloc_array(range_cnt, sizeof(struct range2trim), GFP_NOFS);
+	if (totrim == NULL) {
+		jfs_error(bmp->db_ipbmap->i_sb, "no memory for trim array\n");
+		IWRITE_UNLOCK(ipbmap);
+		return 0;
+	}
+
+	tt = totrim;
+	while (nblocks >= minlen) {
+		l2nb = BLKSTOL2(nblocks);
+
+		/* 0 = okay, -EIO = fatal, -ENOSPC -> try smaller block */
+		rc = dbAllocAG(bmp, agno, nblocks, l2nb, &blkno);
+		if (rc == 0) {
+			tt->blkno = blkno;
+			tt->nblocks = nblocks;
+			tt++; count++;
+
+			/* the whole ag is free, trim now */
+			if (bmp->db_agfree[agno] == 0)
+				break;
+
+			/* give a hint for the next while */
+			nblocks = bmp->db_agfree[agno];
+			continue;
+		} else if (rc == -ENOSPC) {
+			/* search for next smaller log2 block */
+			l2nb = BLKSTOL2(nblocks) - 1;
+			nblocks = 1LL << l2nb;
+		} else {
+			/* Trim any already allocated blocks */
+			jfs_error(bmp->db_ipbmap->i_sb, "-EIO\n");
+			break;
+		}
+
+		/* check, if our trim array is full */
+		if (unlikely(count >= range_cnt - 1))
+			break;
+	}
+	IWRITE_UNLOCK(ipbmap);
+
+	tt->nblocks = 0; /* mark the current end */
+	for (tt = totrim; tt->nblocks != 0; tt++) {
+		/* when mounted with online discard, dbFree() will
+		 * call jfs_issue_discard() itself */
+		if (!(JFS_SBI(sb)->flag & JFS_DISCARD))
+			jfs_issue_discard(ip, tt->blkno, tt->nblocks);
+		dbFree(ip, tt->blkno, tt->nblocks);
+		trimmed += tt->nblocks;
+	}
+	kfree(totrim);
+
+	return trimmed;
+}
+
+/*
+ * 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,
+				  "Corrupt dmapctl page\n");
+			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, true);
+
+		/* release the buffer.
+		 */
+		release_metapage(mp);
+
+		/* space found ?
+		 */
+		if (rc) {
+			if (lev != level) {
+				jfs_error(bmp->db_ipbmap->i_sb,
+					  "dmap inconsistent\n");
+				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,
+				  "the dmap is not all free\n");
+			rc = -EIO;
+			goto backout;
+		}
+
+		/* determine how many blocks to allocate from this dmap.
+		 */
+		nb = min_t(s64, n, 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,
+				  "I/O Error: Block Leakage\n");
+			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, "Block Leakage\n");
+			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, false))
+		return -ENOSPC;
+
+	if (leafidx < 0)
+		return -EIO;
+
+	/* 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,
+						  "leaf page corrupt\n");
+					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_t(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, "Corrupt dmapctl page\n");
+		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) {
+				release_metapage(mp);
+				return rc;
+			}
+			oldval = dcp->stree[ti];
+		}
+		dbSplit((dmtree_t *) dcp, leafno, dcp->budmin, newval);
+	} else {
+		rc = dbJoin((dmtree_t *) dcp, leafno, newval);
+		if (rc) {
+			release_metapage(mp);
+			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,
+					  "the maximum free buddy is not the old root\n");
+			}
+			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.
+ *	is_ctl	- determines if the tree is of type ctl
+ *
+ * RETURN VALUES:
+ *	0	- success
+ *	-ENOSPC	- insufficient free blocks.
+ */
+static int dbFindLeaf(dmtree_t *tp, int l2nb, int *leafidx, bool is_ctl)
+{
+	int ti, n = 0, k, x = 0;
+	int max_size;
+
+	max_size = is_ctl ? CTLTREESIZE : TREESIZE;
+
+	/* 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 (x + n > max_size)
+				return -ENOSPC;
+			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, "L2 page could not be read\n");
+		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_t(s64, nblocks, 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, "function has not returned as expected\n");
+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 inactive 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\n");
+		}
+	}
+
+	/*
+	 * 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 level 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)
+
+/*
+ * 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);
+}