Merge branch 'agp-next' of git://git.kernel.org/pub/scm/linux/kernel/git/airlied...

[linux-2.6] / fs / jfs / jfs_dmap.c

/*
 *   Copyright (C) International Business Machines Corp., 2000-2004
 *
 *   This program is free software;  you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY;  without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
 *   the GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program;  if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

        return (0);
}


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

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

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

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

        return (0);
}

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

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

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

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

        diWriteSpecial(ipbmap, 0);

        return (0);
}


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

        IREAD_LOCK(ipbmap, 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,
                          "dbFree: block to be freed is outside the map");
                return -EIO;
        }

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

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

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

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

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

        IREAD_UNLOCK(ipbmap);

        return (0);
}


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

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

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

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

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

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

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

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

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

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

                                word += nwords;
                        }
                }

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

                lastlblkno = lblkno;

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

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

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

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

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

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

        return (0);
}


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

        BMAP_LOCK(bmp);

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

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

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

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

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

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

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

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

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

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

        mapSize = bmp->db_mapsize;

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

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

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

                goto write_unlock;
        }

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

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

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

        agno = blkno >> bmp->db_agl2size;

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

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

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

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

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

                        release_metapage(mp);
                        goto read_unlock;
                }

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

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

                        release_metapage(mp);
                        goto read_unlock;
                }

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

                        release_metapage(mp);
                        goto read_unlock;
                }

                release_metapage(mp);
                IREAD_UNLOCK(ipbmap);
        }

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

        IWRITE_UNLOCK(ipbmap);


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

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

      write_unlock:
        IWRITE_UNLOCK(ipbmap);

        return (rc);

      read_unlock:
        IREAD_UNLOCK(ipbmap);

        return (rc);
}

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

        IREAD_LOCK(ipbmap, RDWRLOCK_DMAP);

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

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

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

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

        IREAD_UNLOCK(ipbmap);

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

        release_metapage(mp);

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

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

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

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


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

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

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

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

        IREAD_LOCK(ipbmap, RDWRLOCK_DMAP);

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

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

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

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

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

        IREAD_UNLOCK(ipbmap);

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


        return (rc);
}


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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

                return (rc);
        }

        return -ENOSPC;
}


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        return -ENOSPC;
}


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

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

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


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

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

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

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

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

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

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

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

        *blkno = b;
        return (0);
}


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

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

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

                release_metapage(mp);

                return (rc);
        }

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

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

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

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

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

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

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

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

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

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

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

        return (rc);
}


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

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

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

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

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

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

        return (rc);
}


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

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

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

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

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

        return (rc);
}


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

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

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

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

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

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

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

        return (rc);
}


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

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

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

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

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

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

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

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

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

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

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

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

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

        /* update the free count for this dmap */
        le32_add_cpu(&dp->nfree, -nblocks);

        BMAP_LOCK(bmp);

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

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

        BMAP_UNLOCK(bmp);
}


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

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

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

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

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

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

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

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

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

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

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

        /* update the free count for this dmap.
         */
        le32_add_cpu(&dp->nfree, nblocks);

        BMAP_LOCK(bmp);

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

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

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

        BMAP_UNLOCK(bmp);

        return 0;
}


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

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

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

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

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

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

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

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

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

        return (0);
}


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

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

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

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

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


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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

        return 0;
}


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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

        return (0);
}


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

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

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

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

        ASSERT(bitno < 32);

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


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

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

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

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


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

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

        return (n);
}


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

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


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

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

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

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

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


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

        IREAD_LOCK(ipbmap, 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, *leaf;
        struct dmaptree *tp = (struct dmaptree *) & dp->tree;

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

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

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

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

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

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

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

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

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

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

        /*
         * update highest active ag number
         */

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

                                write_metapage(mp);

                                l0leaf++;
                                p += nbperpage;

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

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

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

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

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

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

        /*
         *      finalize bmap control page
         */
finalize:

        return 0;
}


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

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

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

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

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

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

}


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

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

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

                if (nblocks == BPERDMAP) {
                        memset(&dp->wmap[0], 0, LPERDMAP * 4);
                        memset(&dp->pmap[0], 0, LPERDMAP * 4);
                        goto initTree;
                }
        } else {
                le32_add_cpu(&dp->nblocks, nblocks);
                le32_add_cpu(&dp->nfree, nblocks);
        }

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

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

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

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

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

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

        if (blkno == BPERDMAP)
                goto initTree;

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

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

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

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


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

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

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

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


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

        tp = dtp->stree;

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

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

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

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

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

        return (*tp);
}


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

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

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

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


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

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

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

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

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


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

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

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

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

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

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

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

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

        return (nblocks);
}