/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * suballoc.c
 *
 * metadata alloc and free
 * Inspired by ext3 block groups.
 *
 * Copyright (C) 2002, 2004 Oracle.  All rights reserved.
 *
 * 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 021110-1307, USA.
 */

#include <linux/fs.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/highmem.h>

#define MLOG_MASK_PREFIX ML_DISK_ALLOC
#include <cluster/masklog.h>

#include "ocfs2.h"

#include "alloc.h"
#include "blockcheck.h"
#include "dlmglue.h"
#include "inode.h"
#include "journal.h"
#include "localalloc.h"
#include "suballoc.h"
#include "super.h"
#include "sysfile.h"
#include "uptodate.h"

#include "buffer_head_io.h"

#define NOT_ALLOC_NEW_GROUP             0
#define ALLOC_NEW_GROUP                 0x1
#define ALLOC_GROUPS_FROM_GLOBAL        0x2

#define OCFS2_MAX_INODES_TO_STEAL       1024

static inline void ocfs2_debug_bg(struct ocfs2_group_desc *bg);
static inline void ocfs2_debug_suballoc_inode(struct ocfs2_dinode *fe);
static inline u16 ocfs2_find_victim_chain(struct ocfs2_chain_list *cl);
static int ocfs2_block_group_fill(handle_t *handle,
                                  struct inode *alloc_inode,
                                  struct buffer_head *bg_bh,
                                  u64 group_blkno,
                                  u16 my_chain,
                                  struct ocfs2_chain_list *cl);
static int ocfs2_block_group_alloc(struct ocfs2_super *osb,
                                   struct inode *alloc_inode,
                                   struct buffer_head *bh,
                                   u64 max_block,
                                   u64 *last_alloc_group,
                                   int flags);

static int ocfs2_cluster_group_search(struct inode *inode,
                                      struct buffer_head *group_bh,
                                      u32 bits_wanted, u32 min_bits,
                                      u64 max_block,
                                      u16 *bit_off, u16 *bits_found);
static int ocfs2_block_group_search(struct inode *inode,
                                    struct buffer_head *group_bh,
                                    u32 bits_wanted, u32 min_bits,
                                    u64 max_block,
                                    u16 *bit_off, u16 *bits_found);
static int ocfs2_claim_suballoc_bits(struct ocfs2_super *osb,
                                     struct ocfs2_alloc_context *ac,
                                     handle_t *handle,
                                     u32 bits_wanted,
                                     u32 min_bits,
                                     u16 *bit_off,
                                     unsigned int *num_bits,
                                     u64 *bg_blkno);
static int ocfs2_test_bg_bit_allocatable(struct buffer_head *bg_bh,
                                         int nr);
static inline int ocfs2_block_group_set_bits(handle_t *handle,
                                             struct inode *alloc_inode,
                                             struct ocfs2_group_desc *bg,
                                             struct buffer_head *group_bh,
                                             unsigned int bit_off,
                                             unsigned int num_bits);
static inline int ocfs2_block_group_clear_bits(handle_t *handle,
                                               struct inode *alloc_inode,
                                               struct ocfs2_group_desc *bg,
                                               struct buffer_head *group_bh,
                                               unsigned int bit_off,
                                               unsigned int num_bits);

static int ocfs2_relink_block_group(handle_t *handle,
                                    struct inode *alloc_inode,
                                    struct buffer_head *fe_bh,
                                    struct buffer_head *bg_bh,
                                    struct buffer_head *prev_bg_bh,
                                    u16 chain);
static inline int ocfs2_block_group_reasonably_empty(struct ocfs2_group_desc *bg,
                                                     u32 wanted);
static inline u32 ocfs2_desc_bitmap_to_cluster_off(struct inode *inode,
                                                   u64 bg_blkno,
                                                   u16 bg_bit_off);
static inline void ocfs2_block_to_cluster_group(struct inode *inode,
                                                u64 data_blkno,
                                                u64 *bg_blkno,
                                                u16 *bg_bit_off);
static int ocfs2_reserve_clusters_with_limit(struct ocfs2_super *osb,
                                             u32 bits_wanted, u64 max_block,
                                             int flags,
                                             struct ocfs2_alloc_context **ac);

void ocfs2_free_ac_resource(struct ocfs2_alloc_context *ac)
{
        struct inode *inode = ac->ac_inode;

        if (inode) {
                if (ac->ac_which != OCFS2_AC_USE_LOCAL)
                        ocfs2_inode_unlock(inode, 1);

                mutex_unlock(&inode->i_mutex);

                iput(inode);
                ac->ac_inode = NULL;
        }
        brelse(ac->ac_bh);
        ac->ac_bh = NULL;
}

void ocfs2_free_alloc_context(struct ocfs2_alloc_context *ac)
{
        ocfs2_free_ac_resource(ac);
        kfree(ac);
}

static u32 ocfs2_bits_per_group(struct ocfs2_chain_list *cl)
{
        return (u32)le16_to_cpu(cl->cl_cpg) * (u32)le16_to_cpu(cl->cl_bpc);
}

#define do_error(fmt, ...)                                              \
        do{                                                             \
                if (clean_error)                                        \
                        mlog(ML_ERROR, fmt "\n", ##__VA_ARGS__);        \
                else                                                    \
                        ocfs2_error(sb, fmt, ##__VA_ARGS__);            \
        } while (0)

static int ocfs2_validate_gd_self(struct super_block *sb,
                                  struct buffer_head *bh,
                                  int clean_error)
{
        struct ocfs2_group_desc *gd = (struct ocfs2_group_desc *)bh->b_data;

        if (!OCFS2_IS_VALID_GROUP_DESC(gd)) {
                do_error("Group descriptor #%llu has bad signature %.*s",
                         (unsigned long long)bh->b_blocknr, 7,
                         gd->bg_signature);
                return -EINVAL;
        }

        if (le64_to_cpu(gd->bg_blkno) != bh->b_blocknr) {
                do_error("Group descriptor #%llu has an invalid bg_blkno "
                         "of %llu",
                         (unsigned long long)bh->b_blocknr,
                         (unsigned long long)le64_to_cpu(gd->bg_blkno));
                return -EINVAL;
        }

        if (le32_to_cpu(gd->bg_generation) != OCFS2_SB(sb)->fs_generation) {
                do_error("Group descriptor #%llu has an invalid "
                         "fs_generation of #%u",
                         (unsigned long long)bh->b_blocknr,
                         le32_to_cpu(gd->bg_generation));
                return -EINVAL;
        }

        if (le16_to_cpu(gd->bg_free_bits_count) > le16_to_cpu(gd->bg_bits)) {
                do_error("Group descriptor #%llu has bit count %u but "
                         "claims that %u are free",
                         (unsigned long long)bh->b_blocknr,
                         le16_to_cpu(gd->bg_bits),
                         le16_to_cpu(gd->bg_free_bits_count));
                return -EINVAL;
        }

        if (le16_to_cpu(gd->bg_bits) > (8 * le16_to_cpu(gd->bg_size))) {
                do_error("Group descriptor #%llu has bit count %u but "
                         "max bitmap bits of %u",
                         (unsigned long long)bh->b_blocknr,
                         le16_to_cpu(gd->bg_bits),
                         8 * le16_to_cpu(gd->bg_size));
                return -EINVAL;
        }

        return 0;
}

static int ocfs2_validate_gd_parent(struct super_block *sb,
                                    struct ocfs2_dinode *di,
                                    struct buffer_head *bh,
                                    int clean_error)
{
        unsigned int max_bits;
        struct ocfs2_group_desc *gd = (struct ocfs2_group_desc *)bh->b_data;

        if (di->i_blkno != gd->bg_parent_dinode) {
                do_error("Group descriptor #%llu has bad parent "
                         "pointer (%llu, expected %llu)",
                         (unsigned long long)bh->b_blocknr,
                         (unsigned long long)le64_to_cpu(gd->bg_parent_dinode),
                         (unsigned long long)le64_to_cpu(di->i_blkno));
                return -EINVAL;
        }

        max_bits = le16_to_cpu(di->id2.i_chain.cl_cpg) * le16_to_cpu(di->id2.i_chain.cl_bpc);
        if (le16_to_cpu(gd->bg_bits) > max_bits) {
                do_error("Group descriptor #%llu has bit count of %u",
                         (unsigned long long)bh->b_blocknr,
                         le16_to_cpu(gd->bg_bits));
                return -EINVAL;
        }

        if (le16_to_cpu(gd->bg_chain) >=
            le16_to_cpu(di->id2.i_chain.cl_next_free_rec)) {
                do_error("Group descriptor #%llu has bad chain %u",
                         (unsigned long long)bh->b_blocknr,
                         le16_to_cpu(gd->bg_chain));
                return -EINVAL;
        }

        return 0;
}

#undef do_error

/*
 * This version only prints errors.  It does not fail the filesystem, and
 * exists only for resize.
 */
int ocfs2_check_group_descriptor(struct super_block *sb,
                                 struct ocfs2_dinode *di,
                                 struct buffer_head *bh)
{
        int rc;
        struct ocfs2_group_desc *gd = (struct ocfs2_group_desc *)bh->b_data;

        BUG_ON(!buffer_uptodate(bh));

        /*
         * If the ecc fails, we return the error but otherwise
         * leave the filesystem running.  We know any error is
         * local to this block.
         */
        rc = ocfs2_validate_meta_ecc(sb, bh->b_data, &gd->bg_check);
        if (rc) {
                mlog(ML_ERROR,
                     "Checksum failed for group descriptor %llu\n",
                     (unsigned long long)bh->b_blocknr);
        } else
                rc = ocfs2_validate_gd_self(sb, bh, 1);
        if (!rc)
                rc = ocfs2_validate_gd_parent(sb, di, bh, 1);

        return rc;
}

static int ocfs2_validate_group_descriptor(struct super_block *sb,
                                           struct buffer_head *bh)
{
        int rc;
        struct ocfs2_group_desc *gd = (struct ocfs2_group_desc *)bh->b_data;

        mlog(0, "Validating group descriptor %llu\n",
             (unsigned long long)bh->b_blocknr);

        BUG_ON(!buffer_uptodate(bh));

        /*
         * If the ecc fails, we return the error but otherwise
         * leave the filesystem running.  We know any error is
         * local to this block.
         */
        rc = ocfs2_validate_meta_ecc(sb, bh->b_data, &gd->bg_check);
        if (rc)
                return rc;

        /*
         * Errors after here are fatal.
         */

        return ocfs2_validate_gd_self(sb, bh, 0);
}

int ocfs2_read_group_descriptor(struct inode *inode, struct ocfs2_dinode *di,
                                u64 gd_blkno, struct buffer_head **bh)
{
        int rc;
        struct buffer_head *tmp = *bh;

        rc = ocfs2_read_block(INODE_CACHE(inode), gd_blkno, &tmp,
                              ocfs2_validate_group_descriptor);
        if (rc)
                goto out;

        rc = ocfs2_validate_gd_parent(inode->i_sb, di, tmp, 0);
        if (rc) {
                brelse(tmp);
                goto out;
        }

        /* If ocfs2_read_block() got us a new bh, pass it up. */
        if (!*bh)
                *bh = tmp;

out:
        return rc;
}

static int ocfs2_block_group_fill(handle_t *handle,
                                  struct inode *alloc_inode,
                                  struct buffer_head *bg_bh,
                                  u64 group_blkno,
                                  u16 my_chain,
                                  struct ocfs2_chain_list *cl)
{
        int status = 0;
        struct ocfs2_group_desc *bg = (struct ocfs2_group_desc *) bg_bh->b_data;
        struct super_block * sb = alloc_inode->i_sb;

        mlog_entry_void();

        if (((unsigned long long) bg_bh->b_blocknr) != group_blkno) {
                ocfs2_error(alloc_inode->i_sb, "group block (%llu) != "
                            "b_blocknr (%llu)",
                            (unsigned long long)group_blkno,
                            (unsigned long long) bg_bh->b_blocknr);
                status = -EIO;
                goto bail;
        }

        status = ocfs2_journal_access_gd(handle,
                                         INODE_CACHE(alloc_inode),
                                         bg_bh,
                                         OCFS2_JOURNAL_ACCESS_CREATE);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        memset(bg, 0, sb->s_blocksize);
        strcpy(bg->bg_signature, OCFS2_GROUP_DESC_SIGNATURE);
        bg->bg_generation = cpu_to_le32(OCFS2_SB(sb)->fs_generation);
        bg->bg_size = cpu_to_le16(ocfs2_group_bitmap_size(sb));
        bg->bg_bits = cpu_to_le16(ocfs2_bits_per_group(cl));
        bg->bg_chain = cpu_to_le16(my_chain);
        bg->bg_next_group = cl->cl_recs[my_chain].c_blkno;
        bg->bg_parent_dinode = cpu_to_le64(OCFS2_I(alloc_inode)->ip_blkno);
        bg->bg_blkno = cpu_to_le64(group_blkno);
        /* set the 1st bit in the bitmap to account for the descriptor block */
        ocfs2_set_bit(0, (unsigned long *)bg->bg_bitmap);
        bg->bg_free_bits_count = cpu_to_le16(le16_to_cpu(bg->bg_bits) - 1);

        status = ocfs2_journal_dirty(handle, bg_bh);
        if (status < 0)
                mlog_errno(status);

        /* There is no need to zero out or otherwise initialize the
         * other blocks in a group - All valid FS metadata in a block
         * group stores the superblock fs_generation value at
         * allocation time. */

bail:
        mlog_exit(status);
        return status;
}

static inline u16 ocfs2_find_smallest_chain(struct ocfs2_chain_list *cl)
{
        u16 curr, best;

        best = curr = 0;
        while (curr < le16_to_cpu(cl->cl_count)) {
                if (le32_to_cpu(cl->cl_recs[best].c_total) >
                    le32_to_cpu(cl->cl_recs[curr].c_total))
                        best = curr;
                curr++;
        }
        return best;
}

/*
 * We expect the block group allocator to already be locked.
 */
static int ocfs2_block_group_alloc(struct ocfs2_super *osb,
                                   struct inode *alloc_inode,
                                   struct buffer_head *bh,
                                   u64 max_block,
                                   u64 *last_alloc_group,
                                   int flags)
{
        int status, credits;
        struct ocfs2_dinode *fe = (struct ocfs2_dinode *) bh->b_data;
        struct ocfs2_chain_list *cl;
        struct ocfs2_alloc_context *ac = NULL;
        handle_t *handle = NULL;
        u32 bit_off, num_bits;
        u16 alloc_rec;
        u64 bg_blkno;
        struct buffer_head *bg_bh = NULL;
        struct ocfs2_group_desc *bg;

        BUG_ON(ocfs2_is_cluster_bitmap(alloc_inode));

        mlog_entry_void();

        cl = &fe->id2.i_chain;
        status = ocfs2_reserve_clusters_with_limit(osb,
                                                   le16_to_cpu(cl->cl_cpg),
                                                   max_block, flags, &ac);
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        credits = ocfs2_calc_group_alloc_credits(osb->sb,
                                                 le16_to_cpu(cl->cl_cpg));
        handle = ocfs2_start_trans(osb, credits);
        if (IS_ERR(handle)) {
                status = PTR_ERR(handle);
                handle = NULL;
                mlog_errno(status);
                goto bail;
        }

        if (last_alloc_group && *last_alloc_group != 0) {
                mlog(0, "use old allocation group %llu for block group alloc\n",
                     (unsigned long long)*last_alloc_group);
                ac->ac_last_group = *last_alloc_group;
        }
        status = ocfs2_claim_clusters(osb,
                                      handle,
                                      ac,
                                      le16_to_cpu(cl->cl_cpg),
                                      &bit_off,
                                      &num_bits);
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        alloc_rec = ocfs2_find_smallest_chain(cl);

        /* setup the group */
        bg_blkno = ocfs2_clusters_to_blocks(osb->sb, bit_off);
        mlog(0, "new descriptor, record %u, at block %llu\n",
             alloc_rec, (unsigned long long)bg_blkno);

        bg_bh = sb_getblk(osb->sb, bg_blkno);
        if (!bg_bh) {
                status = -EIO;
                mlog_errno(status);
                goto bail;
        }
        ocfs2_set_new_buffer_uptodate(INODE_CACHE(alloc_inode), bg_bh);

        status = ocfs2_block_group_fill(handle,
                                        alloc_inode,
                                        bg_bh,
                                        bg_blkno,
                                        alloc_rec,
                                        cl);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        bg = (struct ocfs2_group_desc *) bg_bh->b_data;

        status = ocfs2_journal_access_di(handle, INODE_CACHE(alloc_inode),
                                         bh, OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        le32_add_cpu(&cl->cl_recs[alloc_rec].c_free,
                     le16_to_cpu(bg->bg_free_bits_count));
        le32_add_cpu(&cl->cl_recs[alloc_rec].c_total, le16_to_cpu(bg->bg_bits));
        cl->cl_recs[alloc_rec].c_blkno  = cpu_to_le64(bg_blkno);
        if (le16_to_cpu(cl->cl_next_free_rec) < le16_to_cpu(cl->cl_count))
                le16_add_cpu(&cl->cl_next_free_rec, 1);

        le32_add_cpu(&fe->id1.bitmap1.i_used, le16_to_cpu(bg->bg_bits) -
                                        le16_to_cpu(bg->bg_free_bits_count));
        le32_add_cpu(&fe->id1.bitmap1.i_total, le16_to_cpu(bg->bg_bits));
        le32_add_cpu(&fe->i_clusters, le16_to_cpu(cl->cl_cpg));

        status = ocfs2_journal_dirty(handle, bh);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        spin_lock(&OCFS2_I(alloc_inode)->ip_lock);
        OCFS2_I(alloc_inode)->ip_clusters = le32_to_cpu(fe->i_clusters);
        fe->i_size = cpu_to_le64(ocfs2_clusters_to_bytes(alloc_inode->i_sb,
                                             le32_to_cpu(fe->i_clusters)));
        spin_unlock(&OCFS2_I(alloc_inode)->ip_lock);
        i_size_write(alloc_inode, le64_to_cpu(fe->i_size));
        alloc_inode->i_blocks = ocfs2_inode_sector_count(alloc_inode);

        status = 0;

        /* save the new last alloc group so that the caller can cache it. */
        if (last_alloc_group)
                *last_alloc_group = ac->ac_last_group;

bail:
        if (handle)
                ocfs2_commit_trans(osb, handle);

        if (ac)
                ocfs2_free_alloc_context(ac);

        brelse(bg_bh);

        mlog_exit(status);
        return status;
}

static int ocfs2_reserve_suballoc_bits(struct ocfs2_super *osb,
                                       struct ocfs2_alloc_context *ac,
                                       int type,
                                       u32 slot,
                                       u64 *last_alloc_group,
                                       int flags)
{
        int status;
        u32 bits_wanted = ac->ac_bits_wanted;
        struct inode *alloc_inode;
        struct buffer_head *bh = NULL;
        struct ocfs2_dinode *fe;
        u32 free_bits;

        mlog_entry_void();

        alloc_inode = ocfs2_get_system_file_inode(osb, type, slot);
        if (!alloc_inode) {
                mlog_errno(-EINVAL);
                return -EINVAL;
        }

        mutex_lock(&alloc_inode->i_mutex);

        status = ocfs2_inode_lock(alloc_inode, &bh, 1);
        if (status < 0) {
                mutex_unlock(&alloc_inode->i_mutex);
                iput(alloc_inode);

                mlog_errno(status);
                return status;
        }

        ac->ac_inode = alloc_inode;
        ac->ac_alloc_slot = slot;

        fe = (struct ocfs2_dinode *) bh->b_data;

        /* The bh was validated by the inode read inside
         * ocfs2_inode_lock().  Any corruption is a code bug. */
        BUG_ON(!OCFS2_IS_VALID_DINODE(fe));

        if (!(fe->i_flags & cpu_to_le32(OCFS2_CHAIN_FL))) {
                ocfs2_error(alloc_inode->i_sb, "Invalid chain allocator %llu",
                            (unsigned long long)le64_to_cpu(fe->i_blkno));
                status = -EIO;
                goto bail;
        }

        free_bits = le32_to_cpu(fe->id1.bitmap1.i_total) -
                le32_to_cpu(fe->id1.bitmap1.i_used);

        if (bits_wanted > free_bits) {
                /* cluster bitmap never grows */
                if (ocfs2_is_cluster_bitmap(alloc_inode)) {
                        mlog(0, "Disk Full: wanted=%u, free_bits=%u\n",
                             bits_wanted, free_bits);
                        status = -ENOSPC;
                        goto bail;
                }

                if (!(flags & ALLOC_NEW_GROUP)) {
                        mlog(0, "Alloc File %u Full: wanted=%u, free_bits=%u, "
                             "and we don't alloc a new group for it.\n",
                             slot, bits_wanted, free_bits);
                        status = -ENOSPC;
                        goto bail;
                }

                status = ocfs2_block_group_alloc(osb, alloc_inode, bh,
                                                 ac->ac_max_block,
                                                 last_alloc_group, flags);
                if (status < 0) {
                        if (status != -ENOSPC)
                                mlog_errno(status);
                        goto bail;
                }
                atomic_inc(&osb->alloc_stats.bg_extends);

                /* You should never ask for this much metadata */
                BUG_ON(bits_wanted >
                       (le32_to_cpu(fe->id1.bitmap1.i_total)
                        - le32_to_cpu(fe->id1.bitmap1.i_used)));
        }

        get_bh(bh);
        ac->ac_bh = bh;
bail:
        brelse(bh);

        mlog_exit(status);
        return status;
}

int ocfs2_reserve_new_metadata_blocks(struct ocfs2_super *osb,
                                      int blocks,
                                      struct ocfs2_alloc_context **ac)
{
        int status;
        u32 slot;

        *ac = kzalloc(sizeof(struct ocfs2_alloc_context), GFP_KERNEL);
        if (!(*ac)) {
                status = -ENOMEM;
                mlog_errno(status);
                goto bail;
        }

        (*ac)->ac_bits_wanted = blocks;
        (*ac)->ac_which = OCFS2_AC_USE_META;
        slot = osb->slot_num;
        (*ac)->ac_group_search = ocfs2_block_group_search;

        status = ocfs2_reserve_suballoc_bits(osb, (*ac),
                                             EXTENT_ALLOC_SYSTEM_INODE,
                                             slot, NULL, ALLOC_NEW_GROUP);
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        status = 0;
bail:
        if ((status < 0) && *ac) {
                ocfs2_free_alloc_context(*ac);
                *ac = NULL;
        }

        mlog_exit(status);
        return status;
}

int ocfs2_reserve_new_metadata(struct ocfs2_super *osb,
                               struct ocfs2_extent_list *root_el,
                               struct ocfs2_alloc_context **ac)
{
        return ocfs2_reserve_new_metadata_blocks(osb,
                                        ocfs2_extend_meta_needed(root_el),
                                        ac);
}

static int ocfs2_steal_inode_from_other_nodes(struct ocfs2_super *osb,
                                              struct ocfs2_alloc_context *ac)
{
        int i, status = -ENOSPC;
        s16 slot = ocfs2_get_inode_steal_slot(osb);

        /* Start to steal inodes from the first slot after ours. */
        if (slot == OCFS2_INVALID_SLOT)
                slot = osb->slot_num + 1;

        for (i = 0; i < osb->max_slots; i++, slot++) {
                if (slot == osb->max_slots)
                        slot = 0;

                if (slot == osb->slot_num)
                        continue;

                status = ocfs2_reserve_suballoc_bits(osb, ac,
                                                     INODE_ALLOC_SYSTEM_INODE,
                                                     slot, NULL,
                                                     NOT_ALLOC_NEW_GROUP);
                if (status >= 0) {
                        ocfs2_set_inode_steal_slot(osb, slot);
                        break;
                }

                ocfs2_free_ac_resource(ac);
        }

        return status;
}

int ocfs2_reserve_new_inode(struct ocfs2_super *osb,
                            struct ocfs2_alloc_context **ac)
{
        int status;
        s16 slot = ocfs2_get_inode_steal_slot(osb);
        u64 alloc_group;

        *ac = kzalloc(sizeof(struct ocfs2_alloc_context), GFP_KERNEL);
        if (!(*ac)) {
                status = -ENOMEM;
                mlog_errno(status);
                goto bail;
        }

        (*ac)->ac_bits_wanted = 1;
        (*ac)->ac_which = OCFS2_AC_USE_INODE;

        (*ac)->ac_group_search = ocfs2_block_group_search;

        /*
         * stat(2) can't handle i_ino > 32bits, so we tell the
         * lower levels not to allocate us a block group past that
         * limit.  The 'inode64' mount option avoids this behavior.
         */
        if (!(osb->s_mount_opt & OCFS2_MOUNT_INODE64))
                (*ac)->ac_max_block = (u32)~0U;

        /*
         * slot is set when we successfully steal inode from other nodes.
         * It is reset in 3 places:
         * 1. when we flush the truncate log
         * 2. when we complete local alloc recovery.
         * 3. when we successfully allocate from our own slot.
         * After it is set, we will go on stealing inodes until we find the
         * need to check our slots to see whether there is some space for us.
         */
        if (slot != OCFS2_INVALID_SLOT &&
            atomic_read(&osb->s_num_inodes_stolen) < OCFS2_MAX_INODES_TO_STEAL)
                goto inode_steal;

        atomic_set(&osb->s_num_inodes_stolen, 0);
        alloc_group = osb->osb_inode_alloc_group;
        status = ocfs2_reserve_suballoc_bits(osb, *ac,
                                             INODE_ALLOC_SYSTEM_INODE,
                                             osb->slot_num,
                                             &alloc_group,
                                             ALLOC_NEW_GROUP |
                                             ALLOC_GROUPS_FROM_GLOBAL);
        if (status >= 0) {
                status = 0;

                spin_lock(&osb->osb_lock);
                osb->osb_inode_alloc_group = alloc_group;
                spin_unlock(&osb->osb_lock);
                mlog(0, "after reservation, new allocation group is "
                     "%llu\n", (unsigned long long)alloc_group);

                /*
                 * Some inodes must be freed by us, so try to allocate
                 * from our own next time.
                 */
                if (slot != OCFS2_INVALID_SLOT)
                        ocfs2_init_inode_steal_slot(osb);
                goto bail;
        } else if (status < 0 && status != -ENOSPC) {
                mlog_errno(status);
                goto bail;
        }

        ocfs2_free_ac_resource(*ac);

inode_steal:
        status = ocfs2_steal_inode_from_other_nodes(osb, *ac);
        atomic_inc(&osb->s_num_inodes_stolen);
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        status = 0;
bail:
        if ((status < 0) && *ac) {
                ocfs2_free_alloc_context(*ac);
                *ac = NULL;
        }

        mlog_exit(status);
        return status;
}

/* local alloc code has to do the same thing, so rather than do this
 * twice.. */
int ocfs2_reserve_cluster_bitmap_bits(struct ocfs2_super *osb,
                                      struct ocfs2_alloc_context *ac)
{
        int status;

        ac->ac_which = OCFS2_AC_USE_MAIN;
        ac->ac_group_search = ocfs2_cluster_group_search;

        status = ocfs2_reserve_suballoc_bits(osb, ac,
                                             GLOBAL_BITMAP_SYSTEM_INODE,
                                             OCFS2_INVALID_SLOT, NULL,
                                             ALLOC_NEW_GROUP);
        if (status < 0 && status != -ENOSPC) {
                mlog_errno(status);
                goto bail;
        }

bail:
        return status;
}

/* Callers don't need to care which bitmap (local alloc or main) to
 * use so we figure it out for them, but unfortunately this clutters
 * things a bit. */
static int ocfs2_reserve_clusters_with_limit(struct ocfs2_super *osb,
                                             u32 bits_wanted, u64 max_block,
                                             int flags,
                                             struct ocfs2_alloc_context **ac)
{
        int status;

        mlog_entry_void();

        *ac = kzalloc(sizeof(struct ocfs2_alloc_context), GFP_KERNEL);
        if (!(*ac)) {
                status = -ENOMEM;
                mlog_errno(status);
                goto bail;
        }

        (*ac)->ac_bits_wanted = bits_wanted;
        (*ac)->ac_max_block = max_block;

        status = -ENOSPC;
        if (!(flags & ALLOC_GROUPS_FROM_GLOBAL) &&
            ocfs2_alloc_should_use_local(osb, bits_wanted)) {
                status = ocfs2_reserve_local_alloc_bits(osb,
                                                        bits_wanted,
                                                        *ac);
                if (status == -EFBIG) {
                        /* The local alloc window is outside ac_max_block.
                         * use the main bitmap. */
                        status = -ENOSPC;
                } else if ((status < 0) && (status != -ENOSPC)) {
                        mlog_errno(status);
                        goto bail;
                }
        }

        if (status == -ENOSPC) {
                status = ocfs2_reserve_cluster_bitmap_bits(osb, *ac);
                if (status < 0) {
                        if (status != -ENOSPC)
                                mlog_errno(status);
                        goto bail;
                }
        }

        status = 0;
bail:
        if ((status < 0) && *ac) {
                ocfs2_free_alloc_context(*ac);
                *ac = NULL;
        }

        mlog_exit(status);
        return status;
}

int ocfs2_reserve_clusters(struct ocfs2_super *osb,
                           u32 bits_wanted,
                           struct ocfs2_alloc_context **ac)
{
        return ocfs2_reserve_clusters_with_limit(osb, bits_wanted, 0,
                                                 ALLOC_NEW_GROUP, ac);
}

/*
 * More or less lifted from ext3. I'll leave their description below:
 *
 * "For ext3 allocations, we must not reuse any blocks which are
 * allocated in the bitmap buffer's "last committed data" copy.  This
 * prevents deletes from freeing up the page for reuse until we have
 * committed the delete transaction.
 *
 * If we didn't do this, then deleting something and reallocating it as
 * data would allow the old block to be overwritten before the
 * transaction committed (because we force data to disk before commit).
 * This would lead to corruption if we crashed between overwriting the
 * data and committing the delete.
 *
 * @@@ We may want to make this allocation behaviour conditional on
 * data-writes at some point, and disable it for metadata allocations or
 * sync-data inodes."
 *
 * Note: OCFS2 already does this differently for metadata vs data
 * allocations, as those bitmaps are separate and undo access is never
 * called on a metadata group descriptor.
 */
static int ocfs2_test_bg_bit_allocatable(struct buffer_head *bg_bh,
                                         int nr)
{
        struct ocfs2_group_desc *bg = (struct ocfs2_group_desc *) bg_bh->b_data;
        int ret;

        if (ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap))
                return 0;

        if (!buffer_jbd(bg_bh))
                return 1;

        jbd_lock_bh_state(bg_bh);
        bg = (struct ocfs2_group_desc *) bh2jh(bg_bh)->b_committed_data;
        if (bg)
                ret = !ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap);
        else
                ret = 1;
        jbd_unlock_bh_state(bg_bh);

        return ret;
}

static int ocfs2_block_group_find_clear_bits(struct ocfs2_super *osb,
                                             struct buffer_head *bg_bh,
                                             unsigned int bits_wanted,
                                             unsigned int total_bits,
                                             u16 *bit_off,
                                             u16 *bits_found)
{
        void *bitmap;
        u16 best_offset, best_size;
        int offset, start, found, status = 0;
        struct ocfs2_group_desc *bg = (struct ocfs2_group_desc *) bg_bh->b_data;

        /* Callers got this descriptor from
         * ocfs2_read_group_descriptor().  Any corruption is a code bug. */
        BUG_ON(!OCFS2_IS_VALID_GROUP_DESC(bg));

        found = start = best_offset = best_size = 0;
        bitmap = bg->bg_bitmap;

        while((offset = ocfs2_find_next_zero_bit(bitmap, total_bits, start)) != -1) {
                if (offset == total_bits)
                        break;

                if (!ocfs2_test_bg_bit_allocatable(bg_bh, offset)) {
                        /* We found a zero, but we can't use it as it
                         * hasn't been put to disk yet! */
                        found = 0;
                        start = offset + 1;
                } else if (offset == start) {
                        /* we found a zero */
                        found++;
                        /* move start to the next bit to test */
                        start++;
                } else {
                        /* got a zero after some ones */
                        found = 1;
                        start = offset + 1;
                }
                if (found > best_size) {
                        best_size = found;
                        best_offset = start - found;
                }
                /* we got everything we needed */
                if (found == bits_wanted) {
                        /* mlog(0, "Found it all!\n"); */
                        break;
                }
        }

        /* XXX: I think the first clause is equivalent to the second
         *      - jlbec */
        if (found == bits_wanted) {
                *bit_off = start - found;
                *bits_found = found;
        } else if (best_size) {
                *bit_off = best_offset;

                *bits_found = best_size;
        } else {
                status = -ENOSPC;
                /* No error log here -- see the comment above
                 * ocfs2_test_bg_bit_allocatable */
        }

        return status;
}

static inline int ocfs2_block_group_set_bits(handle_t *handle,
                                             struct inode *alloc_inode,
                                             struct ocfs2_group_desc *bg,
                                             struct buffer_head *group_bh,
                                             unsigned int bit_off,
                                             unsigned int num_bits)
{
        int status;
        void *bitmap = bg->bg_bitmap;
        int journal_type = OCFS2_JOURNAL_ACCESS_WRITE;

        mlog_entry_void();

        /* All callers get the descriptor via
         * ocfs2_read_group_descriptor().  Any corruption is a code bug. */
        BUG_ON(!OCFS2_IS_VALID_GROUP_DESC(bg));
        BUG_ON(le16_to_cpu(bg->bg_free_bits_count) < num_bits);

        mlog(0, "block_group_set_bits: off = %u, num = %u\n", bit_off,
             num_bits);

        if (ocfs2_is_cluster_bitmap(alloc_inode))
                journal_type = OCFS2_JOURNAL_ACCESS_UNDO;

        status = ocfs2_journal_access_gd(handle,
                                         INODE_CACHE(alloc_inode),
                                         group_bh,
                                         journal_type);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        le16_add_cpu(&bg->bg_free_bits_count, -num_bits);

        while(num_bits--)
                ocfs2_set_bit(bit_off++, bitmap);

        status = ocfs2_journal_dirty(handle,
                                     group_bh);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

bail:
        mlog_exit(status);
        return status;
}

/* find the one with the most empty bits */
static inline u16 ocfs2_find_victim_chain(struct ocfs2_chain_list *cl)
{
        u16 curr, best;

        BUG_ON(!cl->cl_next_free_rec);

        best = curr = 0;
        while (curr < le16_to_cpu(cl->cl_next_free_rec)) {
                if (le32_to_cpu(cl->cl_recs[curr].c_free) >
                    le32_to_cpu(cl->cl_recs[best].c_free))
                        best = curr;
                curr++;
        }

        BUG_ON(best >= le16_to_cpu(cl->cl_next_free_rec));
        return best;
}

static int ocfs2_relink_block_group(handle_t *handle,
                                    struct inode *alloc_inode,
                                    struct buffer_head *fe_bh,
                                    struct buffer_head *bg_bh,
                                    struct buffer_head *prev_bg_bh,
                                    u16 chain)
{
        int status;
        /* there is a really tiny chance the journal calls could fail,
         * but we wouldn't want inconsistent blocks in *any* case. */
        u64 fe_ptr, bg_ptr, prev_bg_ptr;
        struct ocfs2_dinode *fe = (struct ocfs2_dinode *) fe_bh->b_data;
        struct ocfs2_group_desc *bg = (struct ocfs2_group_desc *) bg_bh->b_data;
        struct ocfs2_group_desc *prev_bg = (struct ocfs2_group_desc *) prev_bg_bh->b_data;

        /* The caller got these descriptors from
         * ocfs2_read_group_descriptor().  Any corruption is a code bug. */
        BUG_ON(!OCFS2_IS_VALID_GROUP_DESC(bg));
        BUG_ON(!OCFS2_IS_VALID_GROUP_DESC(prev_bg));

        mlog(0, "Suballoc %llu, chain %u, move group %llu to top, prev = %llu\n",
             (unsigned long long)le64_to_cpu(fe->i_blkno), chain,
             (unsigned long long)le64_to_cpu(bg->bg_blkno),
             (unsigned long long)le64_to_cpu(prev_bg->bg_blkno));

        fe_ptr = le64_to_cpu(fe->id2.i_chain.cl_recs[chain].c_blkno);
        bg_ptr = le64_to_cpu(bg->bg_next_group);
        prev_bg_ptr = le64_to_cpu(prev_bg->bg_next_group);

        status = ocfs2_journal_access_gd(handle, INODE_CACHE(alloc_inode),
                                         prev_bg_bh,
                                         OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto out_rollback;
        }

        prev_bg->bg_next_group = bg->bg_next_group;

        status = ocfs2_journal_dirty(handle, prev_bg_bh);
        if (status < 0) {
                mlog_errno(status);
                goto out_rollback;
        }

        status = ocfs2_journal_access_gd(handle, INODE_CACHE(alloc_inode),
                                         bg_bh, OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto out_rollback;
        }

        bg->bg_next_group = fe->id2.i_chain.cl_recs[chain].c_blkno;

        status = ocfs2_journal_dirty(handle, bg_bh);
        if (status < 0) {
                mlog_errno(status);
                goto out_rollback;
        }

        status = ocfs2_journal_access_di(handle, INODE_CACHE(alloc_inode),
                                         fe_bh, OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto out_rollback;
        }

        fe->id2.i_chain.cl_recs[chain].c_blkno = bg->bg_blkno;

        status = ocfs2_journal_dirty(handle, fe_bh);
        if (status < 0) {
                mlog_errno(status);
                goto out_rollback;
        }

        status = 0;
out_rollback:
        if (status < 0) {
                fe->id2.i_chain.cl_recs[chain].c_blkno = cpu_to_le64(fe_ptr);
                bg->bg_next_group = cpu_to_le64(bg_ptr);
                prev_bg->bg_next_group = cpu_to_le64(prev_bg_ptr);
        }

        mlog_exit(status);
        return status;
}

static inline int ocfs2_block_group_reasonably_empty(struct ocfs2_group_desc *bg,
                                                     u32 wanted)
{
        return le16_to_cpu(bg->bg_free_bits_count) > wanted;
}

/* return 0 on success, -ENOSPC to keep searching and any other < 0
 * value on error. */
static int ocfs2_cluster_group_search(struct inode *inode,
                                      struct buffer_head *group_bh,
                                      u32 bits_wanted, u32 min_bits,
                                      u64 max_block,
                                      u16 *bit_off, u16 *bits_found)
{
        int search = -ENOSPC;
        int ret;
        u64 blkoff;
        struct ocfs2_group_desc *gd = (struct ocfs2_group_desc *) group_bh->b_data;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        u16 tmp_off, tmp_found;
        unsigned int max_bits, gd_cluster_off;

        BUG_ON(!ocfs2_is_cluster_bitmap(inode));

        if (gd->bg_free_bits_count) {
                max_bits = le16_to_cpu(gd->bg_bits);

                /* Tail groups in cluster bitmaps which aren't cpg
                 * aligned are prone to partial extention by a failed
                 * fs resize. If the file system resize never got to
                 * update the dinode cluster count, then we don't want
                 * to trust any clusters past it, regardless of what
                 * the group descriptor says. */
                gd_cluster_off = ocfs2_blocks_to_clusters(inode->i_sb,
                                                          le64_to_cpu(gd->bg_blkno));
                if ((gd_cluster_off + max_bits) >
                    OCFS2_I(inode)->ip_clusters) {
                        max_bits = OCFS2_I(inode)->ip_clusters - gd_cluster_off;
                        mlog(0, "Desc %llu, bg_bits %u, clusters %u, use %u\n",
                             (unsigned long long)le64_to_cpu(gd->bg_blkno),
                             le16_to_cpu(gd->bg_bits),
                             OCFS2_I(inode)->ip_clusters, max_bits);
                }

                ret = ocfs2_block_group_find_clear_bits(OCFS2_SB(inode->i_sb),
                                                        group_bh, bits_wanted,
                                                        max_bits,
                                                        &tmp_off, &tmp_found);
                if (ret)
                        return ret;

                if (max_block) {
                        blkoff = ocfs2_clusters_to_blocks(inode->i_sb,
                                                          gd_cluster_off +
                                                          tmp_off + tmp_found);
                        mlog(0, "Checking %llu against %llu\n",
                             (unsigned long long)blkoff,
                             (unsigned long long)max_block);
                        if (blkoff > max_block)
                                return -ENOSPC;
                }

                /* ocfs2_block_group_find_clear_bits() might
                 * return success, but we still want to return
                 * -ENOSPC unless it found the minimum number
                 * of bits. */
                if (min_bits <= tmp_found) {
                        *bit_off = tmp_off;
                        *bits_found = tmp_found;
                        search = 0; /* success */
                } else if (tmp_found) {
                        /*
                         * Don't show bits which we'll be returning
                         * for allocation to the local alloc bitmap.
                         */
                        ocfs2_local_alloc_seen_free_bits(osb, tmp_found);
                }
        }

        return search;
}

static int ocfs2_block_group_search(struct inode *inode,
                                    struct buffer_head *group_bh,
                                    u32 bits_wanted, u32 min_bits,
                                    u64 max_block,
                                    u16 *bit_off, u16 *bits_found)
{
        int ret = -ENOSPC;
        u64 blkoff;
        struct ocfs2_group_desc *bg = (struct ocfs2_group_desc *) group_bh->b_data;

        BUG_ON(min_bits != 1);
        BUG_ON(ocfs2_is_cluster_bitmap(inode));

        if (bg->bg_free_bits_count) {
                ret = ocfs2_block_group_find_clear_bits(OCFS2_SB(inode->i_sb),
                                                        group_bh, bits_wanted,
                                                        le16_to_cpu(bg->bg_bits),
                                                        bit_off, bits_found);
                if (!ret && max_block) {
                        blkoff = le64_to_cpu(bg->bg_blkno) + *bit_off +
                                *bits_found;
                        mlog(0, "Checking %llu against %llu\n",
                             (unsigned long long)blkoff,
                             (unsigned long long)max_block);
                        if (blkoff > max_block)
                                ret = -ENOSPC;
                }
        }

        return ret;
}

static int ocfs2_alloc_dinode_update_counts(struct inode *inode,
                                       handle_t *handle,
                                       struct buffer_head *di_bh,
                                       u32 num_bits,
                                       u16 chain)
{
        int ret;
        u32 tmp_used;
        struct ocfs2_dinode *di = (struct ocfs2_dinode *) di_bh->b_data;
        struct ocfs2_chain_list *cl = (struct ocfs2_chain_list *) &di->id2.i_chain;

        ret = ocfs2_journal_access_di(handle, INODE_CACHE(inode), di_bh,
                                      OCFS2_JOURNAL_ACCESS_WRITE);
        if (ret < 0) {
                mlog_errno(ret);
                goto out;
        }

        tmp_used = le32_to_cpu(di->id1.bitmap1.i_used);
        di->id1.bitmap1.i_used = cpu_to_le32(num_bits + tmp_used);
        le32_add_cpu(&cl->cl_recs[chain].c_free, -num_bits);

        ret = ocfs2_journal_dirty(handle, di_bh);
        if (ret < 0)
                mlog_errno(ret);

out:
        return ret;
}

static int ocfs2_search_one_group(struct ocfs2_alloc_context *ac,
                                  handle_t *handle,
                                  u32 bits_wanted,
                                  u32 min_bits,
                                  u16 *bit_off,
                                  unsigned int *num_bits,
                                  u64 gd_blkno,
                                  u16 *bits_left)
{
        int ret;
        u16 found;
        struct buffer_head *group_bh = NULL;
        struct ocfs2_group_desc *gd;
        struct ocfs2_dinode *di = (struct ocfs2_dinode *)ac->ac_bh->b_data;
        struct inode *alloc_inode = ac->ac_inode;

        ret = ocfs2_read_group_descriptor(alloc_inode, di, gd_blkno,
                                          &group_bh);
        if (ret < 0) {
                mlog_errno(ret);
                return ret;
        }

        gd = (struct ocfs2_group_desc *) group_bh->b_data;
        ret = ac->ac_group_search(alloc_inode, group_bh, bits_wanted, min_bits,
                                  ac->ac_max_block, bit_off, &found);
        if (ret < 0) {
                if (ret != -ENOSPC)
                        mlog_errno(ret);
                goto out;
        }

        *num_bits = found;

        ret = ocfs2_alloc_dinode_update_counts(alloc_inode, handle, ac->ac_bh,
                                               *num_bits,
                                               le16_to_cpu(gd->bg_chain));
        if (ret < 0) {
                mlog_errno(ret);
                goto out;
        }

        ret = ocfs2_block_group_set_bits(handle, alloc_inode, gd, group_bh,
                                         *bit_off, *num_bits);
        if (ret < 0)
                mlog_errno(ret);

        *bits_left = le16_to_cpu(gd->bg_free_bits_count);

out:
        brelse(group_bh);

        return ret;
}

static int ocfs2_search_chain(struct ocfs2_alloc_context *ac,
                              handle_t *handle,
                              u32 bits_wanted,
                              u32 min_bits,
                              u16 *bit_off,
                              unsigned int *num_bits,
                              u64 *bg_blkno,
                              u16 *bits_left)
{
        int status;
        u16 chain, tmp_bits;
        u32 tmp_used;
        u64 next_group;
        struct inode *alloc_inode = ac->ac_inode;
        struct buffer_head *group_bh = NULL;
        struct buffer_head *prev_group_bh = NULL;
        struct ocfs2_dinode *fe = (struct ocfs2_dinode *) ac->ac_bh->b_data;
        struct ocfs2_chain_list *cl = (struct ocfs2_chain_list *) &fe->id2.i_chain;
        struct ocfs2_group_desc *bg;

        chain = ac->ac_chain;
        mlog(0, "trying to alloc %u bits from chain %u, inode %llu\n",
             bits_wanted, chain,
             (unsigned long long)OCFS2_I(alloc_inode)->ip_blkno);

        status = ocfs2_read_group_descriptor(alloc_inode, fe,
                                             le64_to_cpu(cl->cl_recs[chain].c_blkno),
                                             &group_bh);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }
        bg = (struct ocfs2_group_desc *) group_bh->b_data;

        status = -ENOSPC;
        /* for now, the chain search is a bit simplistic. We just use
         * the 1st group with any empty bits. */
        while ((status = ac->ac_group_search(alloc_inode, group_bh,
                                             bits_wanted, min_bits,
                                             ac->ac_max_block, bit_off,
                                             &tmp_bits)) == -ENOSPC) {
                if (!bg->bg_next_group)
                        break;

                brelse(prev_group_bh);
                prev_group_bh = NULL;

                next_group = le64_to_cpu(bg->bg_next_group);
                prev_group_bh = group_bh;
                group_bh = NULL;
                status = ocfs2_read_group_descriptor(alloc_inode, fe,
                                                     next_group, &group_bh);
                if (status < 0) {
                        mlog_errno(status);
                        goto bail;
                }
                bg = (struct ocfs2_group_desc *) group_bh->b_data;
        }
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        mlog(0, "alloc succeeds: we give %u bits from block group %llu\n",
             tmp_bits, (unsigned long long)le64_to_cpu(bg->bg_blkno));

        *num_bits = tmp_bits;

        BUG_ON(*num_bits == 0);

        /*
         * Keep track of previous block descriptor read. When
         * we find a target, if we have read more than X
         * number of descriptors, and the target is reasonably
         * empty, relink him to top of his chain.
         *
         * We've read 0 extra blocks and only send one more to
         * the transaction, yet the next guy to search has a
         * much easier time.
         *
         * Do this *after* figuring out how many bits we're taking out
         * of our target group.
         */
        if (ac->ac_allow_chain_relink &&
            (prev_group_bh) &&
            (ocfs2_block_group_reasonably_empty(bg, *num_bits))) {
                status = ocfs2_relink_block_group(handle, alloc_inode,
                                                  ac->ac_bh, group_bh,
                                                  prev_group_bh, chain);
                if (status < 0) {
                        mlog_errno(status);
                        goto bail;
                }
        }

        /* Ok, claim our bits now: set the info on dinode, chainlist
         * and then the group */
        status = ocfs2_journal_access_di(handle,
                                         INODE_CACHE(alloc_inode),
                                         ac->ac_bh,
                                         OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
        fe->id1.bitmap1.i_used = cpu_to_le32(*num_bits + tmp_used);
        le32_add_cpu(&cl->cl_recs[chain].c_free, -(*num_bits));

        status = ocfs2_journal_dirty(handle,
                                     ac->ac_bh);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        status = ocfs2_block_group_set_bits(handle,
                                            alloc_inode,
                                            bg,
                                            group_bh,
                                            *bit_off,
                                            *num_bits);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        mlog(0, "Allocated %u bits from suballocator %llu\n", *num_bits,
             (unsigned long long)le64_to_cpu(fe->i_blkno));

        *bg_blkno = le64_to_cpu(bg->bg_blkno);
        *bits_left = le16_to_cpu(bg->bg_free_bits_count);
bail:
        brelse(group_bh);
        brelse(prev_group_bh);

        mlog_exit(status);
        return status;
}

/* will give out up to bits_wanted contiguous bits. */
static int ocfs2_claim_suballoc_bits(struct ocfs2_super *osb,
                                     struct ocfs2_alloc_context *ac,
                                     handle_t *handle,
                                     u32 bits_wanted,
                                     u32 min_bits,
                                     u16 *bit_off,
                                     unsigned int *num_bits,
                                     u64 *bg_blkno)
{
        int status;
        u16 victim, i;
        u16 bits_left = 0;
        u64 hint_blkno = ac->ac_last_group;
        struct ocfs2_chain_list *cl;
        struct ocfs2_dinode *fe;

        mlog_entry_void();

        BUG_ON(ac->ac_bits_given >= ac->ac_bits_wanted);
        BUG_ON(bits_wanted > (ac->ac_bits_wanted - ac->ac_bits_given));
        BUG_ON(!ac->ac_bh);

        fe = (struct ocfs2_dinode *) ac->ac_bh->b_data;

        /* The bh was validated by the inode read during
         * ocfs2_reserve_suballoc_bits().  Any corruption is a code bug. */
        BUG_ON(!OCFS2_IS_VALID_DINODE(fe));

        if (le32_to_cpu(fe->id1.bitmap1.i_used) >=
            le32_to_cpu(fe->id1.bitmap1.i_total)) {
                ocfs2_error(osb->sb, "Chain allocator dinode %llu has %u used "
                            "bits but only %u total.",
                            (unsigned long long)le64_to_cpu(fe->i_blkno),
                            le32_to_cpu(fe->id1.bitmap1.i_used),
                            le32_to_cpu(fe->id1.bitmap1.i_total));
                status = -EIO;
                goto bail;
        }

        if (hint_blkno) {
                /* Attempt to short-circuit the usual search mechanism
                 * by jumping straight to the most recently used
                 * allocation group. This helps us mantain some
                 * contiguousness across allocations. */
                status = ocfs2_search_one_group(ac, handle, bits_wanted,
                                                min_bits, bit_off, num_bits,
                                                hint_blkno, &bits_left);
                if (!status) {
                        /* Be careful to update *bg_blkno here as the
                         * caller is expecting it to be filled in, and
                         * ocfs2_search_one_group() won't do that for
                         * us. */
                        *bg_blkno = hint_blkno;
                        goto set_hint;
                }
                if (status < 0 && status != -ENOSPC) {
                        mlog_errno(status);
                        goto bail;
                }
        }

        cl = (struct ocfs2_chain_list *) &fe->id2.i_chain;

        victim = ocfs2_find_victim_chain(cl);
        ac->ac_chain = victim;
        ac->ac_allow_chain_relink = 1;

        status = ocfs2_search_chain(ac, handle, bits_wanted, min_bits, bit_off,
                                    num_bits, bg_blkno, &bits_left);
        if (!status)
                goto set_hint;
        if (status < 0 && status != -ENOSPC) {
                mlog_errno(status);
                goto bail;
        }

        mlog(0, "Search of victim chain %u came up with nothing, "
             "trying all chains now.\n", victim);

        /* If we didn't pick a good victim, then just default to
         * searching each chain in order. Don't allow chain relinking
         * because we only calculate enough journal credits for one
         * relink per alloc. */
        ac->ac_allow_chain_relink = 0;
        for (i = 0; i < le16_to_cpu(cl->cl_next_free_rec); i ++) {
                if (i == victim)
                        continue;
                if (!cl->cl_recs[i].c_free)
                        continue;

                ac->ac_chain = i;
                status = ocfs2_search_chain(ac, handle, bits_wanted, min_bits,
                                            bit_off, num_bits, bg_blkno,
                                            &bits_left);
                if (!status)
                        break;
                if (status < 0 && status != -ENOSPC) {
                        mlog_errno(status);
                        goto bail;
                }
        }

set_hint:
        if (status != -ENOSPC) {
                /* If the next search of this group is not likely to
                 * yield a suitable extent, then we reset the last
                 * group hint so as to not waste a disk read */
                if (bits_left < min_bits)
                        ac->ac_last_group = 0;
                else
                        ac->ac_last_group = *bg_blkno;
        }

bail:
        mlog_exit(status);
        return status;
}

int ocfs2_claim_metadata(struct ocfs2_super *osb,
                         handle_t *handle,
                         struct ocfs2_alloc_context *ac,
                         u32 bits_wanted,
                         u16 *suballoc_bit_start,
                         unsigned int *num_bits,
                         u64 *blkno_start)
{
        int status;
        u64 bg_blkno;

        BUG_ON(!ac);
        BUG_ON(ac->ac_bits_wanted < (ac->ac_bits_given + bits_wanted));
        BUG_ON(ac->ac_which != OCFS2_AC_USE_META);

        status = ocfs2_claim_suballoc_bits(osb,
                                           ac,
                                           handle,
                                           bits_wanted,
                                           1,
                                           suballoc_bit_start,
                                           num_bits,
                                           &bg_blkno);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }
        atomic_inc(&osb->alloc_stats.bg_allocs);

        *blkno_start = bg_blkno + (u64) *suballoc_bit_start;
        ac->ac_bits_given += (*num_bits);
        status = 0;
bail:
        mlog_exit(status);
        return status;
}

static void ocfs2_init_inode_ac_group(struct inode *dir,
                                      struct buffer_head *parent_fe_bh,
                                      struct ocfs2_alloc_context *ac)
{
        struct ocfs2_dinode *fe = (struct ocfs2_dinode *)parent_fe_bh->b_data;
        /*
         * Try to allocate inodes from some specific group.
         *
         * If the parent dir has recorded the last group used in allocation,
         * cool, use it. Otherwise if we try to allocate new inode from the
         * same slot the parent dir belongs to, use the same chunk.
         *
         * We are very careful here to avoid the mistake of setting
         * ac_last_group to a group descriptor from a different (unlocked) slot.
         */
        if (OCFS2_I(dir)->ip_last_used_group &&
            OCFS2_I(dir)->ip_last_used_slot == ac->ac_alloc_slot)
                ac->ac_last_group = OCFS2_I(dir)->ip_last_used_group;
        else if (le16_to_cpu(fe->i_suballoc_slot) == ac->ac_alloc_slot)
                ac->ac_last_group = ocfs2_which_suballoc_group(
                                        le64_to_cpu(fe->i_blkno),
                                        le16_to_cpu(fe->i_suballoc_bit));
}

static inline void ocfs2_save_inode_ac_group(struct inode *dir,
                                             struct ocfs2_alloc_context *ac)
{
        OCFS2_I(dir)->ip_last_used_group = ac->ac_last_group;
        OCFS2_I(dir)->ip_last_used_slot = ac->ac_alloc_slot;
}

int ocfs2_claim_new_inode(struct ocfs2_super *osb,
                          handle_t *handle,
                          struct inode *dir,
                          struct buffer_head *parent_fe_bh,
                          struct ocfs2_alloc_context *ac,
                          u16 *suballoc_bit,
                          u64 *fe_blkno)
{
        int status;
        unsigned int num_bits;
        u64 bg_blkno;

        mlog_entry_void();

        BUG_ON(!ac);
        BUG_ON(ac->ac_bits_given != 0);
        BUG_ON(ac->ac_bits_wanted != 1);
        BUG_ON(ac->ac_which != OCFS2_AC_USE_INODE);

        ocfs2_init_inode_ac_group(dir, parent_fe_bh, ac);

        status = ocfs2_claim_suballoc_bits(osb,
                                           ac,
                                           handle,
                                           1,
                                           1,
                                           suballoc_bit,
                                           &num_bits,
                                           &bg_blkno);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }
        atomic_inc(&osb->alloc_stats.bg_allocs);

        BUG_ON(num_bits != 1);

        *fe_blkno = bg_blkno + (u64) (*suballoc_bit);
        ac->ac_bits_given++;
        ocfs2_save_inode_ac_group(dir, ac);
        status = 0;
bail:
        mlog_exit(status);
        return status;
}

/* translate a group desc. blkno and it's bitmap offset into
 * disk cluster offset. */
static inline u32 ocfs2_desc_bitmap_to_cluster_off(struct inode *inode,
                                                   u64 bg_blkno,
                                                   u16 bg_bit_off)
{
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        u32 cluster = 0;

        BUG_ON(!ocfs2_is_cluster_bitmap(inode));

        if (bg_blkno != osb->first_cluster_group_blkno)
                cluster = ocfs2_blocks_to_clusters(inode->i_sb, bg_blkno);
        cluster += (u32) bg_bit_off;
        return cluster;
}

/* given a cluster offset, calculate which block group it belongs to
 * and return that block offset. */
u64 ocfs2_which_cluster_group(struct inode *inode, u32 cluster)
{
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        u32 group_no;

        BUG_ON(!ocfs2_is_cluster_bitmap(inode));

        group_no = cluster / osb->bitmap_cpg;
        if (!group_no)
                return osb->first_cluster_group_blkno;
        return ocfs2_clusters_to_blocks(inode->i_sb,
                                        group_no * osb->bitmap_cpg);
}

/* given the block number of a cluster start, calculate which cluster
 * group and descriptor bitmap offset that corresponds to. */
static inline void ocfs2_block_to_cluster_group(struct inode *inode,
                                                u64 data_blkno,
                                                u64 *bg_blkno,
                                                u16 *bg_bit_off)
{
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
        u32 data_cluster = ocfs2_blocks_to_clusters(osb->sb, data_blkno);

        BUG_ON(!ocfs2_is_cluster_bitmap(inode));

        *bg_blkno = ocfs2_which_cluster_group(inode,
                                              data_cluster);

        if (*bg_blkno == osb->first_cluster_group_blkno)
                *bg_bit_off = (u16) data_cluster;
        else
                *bg_bit_off = (u16) ocfs2_blocks_to_clusters(osb->sb,
                                                             data_blkno - *bg_blkno);
}

/*
 * min_bits - minimum contiguous chunk from this total allocation we
 * can handle. set to what we asked for originally for a full
 * contig. allocation, set to '1' to indicate we can deal with extents
 * of any size.
 */
int __ocfs2_claim_clusters(struct ocfs2_super *osb,
                           handle_t *handle,
                           struct ocfs2_alloc_context *ac,
                           u32 min_clusters,
                           u32 max_clusters,
                           u32 *cluster_start,
                           u32 *num_clusters)
{
        int status;
        unsigned int bits_wanted = max_clusters;
        u64 bg_blkno = 0;
        u16 bg_bit_off;

        mlog_entry_void();

        BUG_ON(ac->ac_bits_given >= ac->ac_bits_wanted);

        BUG_ON(ac->ac_which != OCFS2_AC_USE_LOCAL
               && ac->ac_which != OCFS2_AC_USE_MAIN);

        if (ac->ac_which == OCFS2_AC_USE_LOCAL) {
                status = ocfs2_claim_local_alloc_bits(osb,
                                                      handle,
                                                      ac,
                                                      bits_wanted,
                                                      cluster_start,
                                                      num_clusters);
                if (!status)
                        atomic_inc(&osb->alloc_stats.local_data);
        } else {
                if (min_clusters > (osb->bitmap_cpg - 1)) {
                        /* The only paths asking for contiguousness
                         * should know about this already. */
                        mlog(ML_ERROR, "minimum allocation requested %u exceeds "
                             "group bitmap size %u!\n", min_clusters,
                             osb->bitmap_cpg);
                        status = -ENOSPC;
                        goto bail;
                }
                /* clamp the current request down to a realistic size. */
                if (bits_wanted > (osb->bitmap_cpg - 1))
                        bits_wanted = osb->bitmap_cpg - 1;

                status = ocfs2_claim_suballoc_bits(osb,
                                                   ac,
                                                   handle,
                                                   bits_wanted,
                                                   min_clusters,
                                                   &bg_bit_off,
                                                   num_clusters,
                                                   &bg_blkno);
                if (!status) {
                        *cluster_start =
                                ocfs2_desc_bitmap_to_cluster_off(ac->ac_inode,
                                                                 bg_blkno,
                                                                 bg_bit_off);
                        atomic_inc(&osb->alloc_stats.bitmap_data);
                }
        }
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        ac->ac_bits_given += *num_clusters;

bail:
        mlog_exit(status);
        return status;
}

int ocfs2_claim_clusters(struct ocfs2_super *osb,
                         handle_t *handle,
                         struct ocfs2_alloc_context *ac,
                         u32 min_clusters,
                         u32 *cluster_start,
                         u32 *num_clusters)
{
        unsigned int bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;

        return __ocfs2_claim_clusters(osb, handle, ac, min_clusters,
                                      bits_wanted, cluster_start, num_clusters);
}

static inline int ocfs2_block_group_clear_bits(handle_t *handle,
                                               struct inode *alloc_inode,
                                               struct ocfs2_group_desc *bg,
                                               struct buffer_head *group_bh,
                                               unsigned int bit_off,
                                               unsigned int num_bits)
{
        int status;
        unsigned int tmp;
        int journal_type = OCFS2_JOURNAL_ACCESS_WRITE;
        struct ocfs2_group_desc *undo_bg = NULL;
        int cluster_bitmap = 0;

        mlog_entry_void();

        /* The caller got this descriptor from
         * ocfs2_read_group_descriptor().  Any corruption is a code bug. */
        BUG_ON(!OCFS2_IS_VALID_GROUP_DESC(bg));

        mlog(0, "off = %u, num = %u\n", bit_off, num_bits);

        if (ocfs2_is_cluster_bitmap(alloc_inode))
                journal_type = OCFS2_JOURNAL_ACCESS_UNDO;

        status = ocfs2_journal_access_gd(handle, INODE_CACHE(alloc_inode),
                                         group_bh, journal_type);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        if (ocfs2_is_cluster_bitmap(alloc_inode))
                cluster_bitmap = 1;

        if (cluster_bitmap) {
                jbd_lock_bh_state(group_bh);
                undo_bg = (struct ocfs2_group_desc *)
                                        bh2jh(group_bh)->b_committed_data;
                BUG_ON(!undo_bg);
        }

        tmp = num_bits;
        while(tmp--) {
                ocfs2_clear_bit((bit_off + tmp),
                                (unsigned long *) bg->bg_bitmap);
                if (cluster_bitmap)
                        ocfs2_set_bit(bit_off + tmp,
                                      (unsigned long *) undo_bg->bg_bitmap);
        }
        le16_add_cpu(&bg->bg_free_bits_count, num_bits);

        if (cluster_bitmap)
                jbd_unlock_bh_state(group_bh);

        status = ocfs2_journal_dirty(handle, group_bh);
        if (status < 0)
                mlog_errno(status);
bail:
        return status;
}

/*
 * expects the suballoc inode to already be locked.
 */
int ocfs2_free_suballoc_bits(handle_t *handle,
                             struct inode *alloc_inode,
                             struct buffer_head *alloc_bh,
                             unsigned int start_bit,
                             u64 bg_blkno,
                             unsigned int count)
{
        int status = 0;
        u32 tmp_used;
        struct ocfs2_dinode *fe = (struct ocfs2_dinode *) alloc_bh->b_data;
        struct ocfs2_chain_list *cl = &fe->id2.i_chain;
        struct buffer_head *group_bh = NULL;
        struct ocfs2_group_desc *group;

        mlog_entry_void();

        /* The alloc_bh comes from ocfs2_free_dinode() or
         * ocfs2_free_clusters().  The callers have all locked the
         * allocator and gotten alloc_bh from the lock call.  This
         * validates the dinode buffer.  Any corruption that has happended
         * is a code bug. */
        BUG_ON(!OCFS2_IS_VALID_DINODE(fe));
        BUG_ON((count + start_bit) > ocfs2_bits_per_group(cl));

        mlog(0, "%llu: freeing %u bits from group %llu, starting at %u\n",
             (unsigned long long)OCFS2_I(alloc_inode)->ip_blkno, count,
             (unsigned long long)bg_blkno, start_bit);

        status = ocfs2_read_group_descriptor(alloc_inode, fe, bg_blkno,
                                             &group_bh);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }
        group = (struct ocfs2_group_desc *) group_bh->b_data;

        BUG_ON((count + start_bit) > le16_to_cpu(group->bg_bits));

        status = ocfs2_block_group_clear_bits(handle, alloc_inode,
                                              group, group_bh,
                                              start_bit, count);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        status = ocfs2_journal_access_di(handle, INODE_CACHE(alloc_inode),
                                         alloc_bh, OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);

                goto bail;
        }

        le32_add_cpu(&cl->cl_recs[le16_to_cpu(group->bg_chain)].c_free,
                     count);
        tmp_used = le32_to_cpu(fe->id1.bitmap1.i_used);
        fe->id1.bitmap1.i_used = cpu_to_le32(tmp_used - count);

        status = ocfs2_journal_dirty(handle, alloc_bh);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

bail:
        brelse(group_bh);

        mlog_exit(status);
        return status;
}

int ocfs2_free_dinode(handle_t *handle,
                      struct inode *inode_alloc_inode,
                      struct buffer_head *inode_alloc_bh,
                      struct ocfs2_dinode *di)
{
        u64 blk = le64_to_cpu(di->i_blkno);
        u16 bit = le16_to_cpu(di->i_suballoc_bit);
        u64 bg_blkno = ocfs2_which_suballoc_group(blk, bit);

        return ocfs2_free_suballoc_bits(handle, inode_alloc_inode,
                                        inode_alloc_bh, bit, bg_blkno, 1);
}

int ocfs2_free_clusters(handle_t *handle,
                       struct inode *bitmap_inode,
                       struct buffer_head *bitmap_bh,
                       u64 start_blk,
                       unsigned int num_clusters)
{
        int status;
        u16 bg_start_bit;
        u64 bg_blkno;
        struct ocfs2_dinode *fe;

        /* You can't ever have a contiguous set of clusters
         * bigger than a block group bitmap so we never have to worry
         * about looping on them. */

        mlog_entry_void();

        /* This is expensive. We can safely remove once this stuff has
         * gotten tested really well. */
        BUG_ON(start_blk != ocfs2_clusters_to_blocks(bitmap_inode->i_sb, ocfs2_blocks_to_clusters(bitmap_inode->i_sb, start_blk)));

        fe = (struct ocfs2_dinode *) bitmap_bh->b_data;

        ocfs2_block_to_cluster_group(bitmap_inode, start_blk, &bg_blkno,
                                     &bg_start_bit);

        mlog(0, "want to free %u clusters starting at block %llu\n",
             num_clusters, (unsigned long long)start_blk);
        mlog(0, "bg_blkno = %llu, bg_start_bit = %u\n",
             (unsigned long long)bg_blkno, bg_start_bit);

        status = ocfs2_free_suballoc_bits(handle, bitmap_inode, bitmap_bh,
                                          bg_start_bit, bg_blkno,
                                          num_clusters);
        if (status < 0) {
                mlog_errno(status);
                goto out;
        }

        ocfs2_local_alloc_seen_free_bits(OCFS2_SB(bitmap_inode->i_sb),
                                         num_clusters);

out:
        mlog_exit(status);
        return status;
}

static inline void ocfs2_debug_bg(struct ocfs2_group_desc *bg)
{
        printk("Block Group:\n");
        printk("bg_signature:       %s\n", bg->bg_signature);
        printk("bg_size:            %u\n", bg->bg_size);
        printk("bg_bits:            %u\n", bg->bg_bits);
        printk("bg_free_bits_count: %u\n", bg->bg_free_bits_count);
        printk("bg_chain:           %u\n", bg->bg_chain);
        printk("bg_generation:      %u\n", le32_to_cpu(bg->bg_generation));
        printk("bg_next_group:      %llu\n",
               (unsigned long long)bg->bg_next_group);
        printk("bg_parent_dinode:   %llu\n",
               (unsigned long long)bg->bg_parent_dinode);
        printk("bg_blkno:           %llu\n",
               (unsigned long long)bg->bg_blkno);
}

static inline void ocfs2_debug_suballoc_inode(struct ocfs2_dinode *fe)
{
        int i;

        printk("Suballoc Inode %llu:\n", (unsigned long long)fe->i_blkno);
        printk("i_signature:                  %s\n", fe->i_signature);
        printk("i_size:                       %llu\n",
               (unsigned long long)fe->i_size);
        printk("i_clusters:                   %u\n", fe->i_clusters);
        printk("i_generation:                 %u\n",
               le32_to_cpu(fe->i_generation));
        printk("id1.bitmap1.i_used:           %u\n",
               le32_to_cpu(fe->id1.bitmap1.i_used));
        printk("id1.bitmap1.i_total:          %u\n",
               le32_to_cpu(fe->id1.bitmap1.i_total));
        printk("id2.i_chain.cl_cpg:           %u\n", fe->id2.i_chain.cl_cpg);
        printk("id2.i_chain.cl_bpc:           %u\n", fe->id2.i_chain.cl_bpc);
        printk("id2.i_chain.cl_count:         %u\n", fe->id2.i_chain.cl_count);
        printk("id2.i_chain.cl_next_free_rec: %u\n",
               fe->id2.i_chain.cl_next_free_rec);
        for(i = 0; i < fe->id2.i_chain.cl_next_free_rec; i++) {
                printk("fe->id2.i_chain.cl_recs[%d].c_free:  %u\n", i,
                       fe->id2.i_chain.cl_recs[i].c_free);
                printk("fe->id2.i_chain.cl_recs[%d].c_total: %u\n", i,
                       fe->id2.i_chain.cl_recs[i].c_total);
                printk("fe->id2.i_chain.cl_recs[%d].c_blkno: %llu\n", i,
                       (unsigned long long)fe->id2.i_chain.cl_recs[i].c_blkno);
        }
}

/*
 * For a given allocation, determine which allocators will need to be
 * accessed, and lock them, reserving the appropriate number of bits.
 *
 * Sparse file systems call this from ocfs2_write_begin_nolock()
 * and ocfs2_allocate_unwritten_extents().
 *
 * File systems which don't support holes call this from
 * ocfs2_extend_allocation().
 */
int ocfs2_lock_allocators(struct inode *inode,
                          struct ocfs2_extent_tree *et,
                          u32 clusters_to_add, u32 extents_to_split,
                          struct ocfs2_alloc_context **data_ac,
                          struct ocfs2_alloc_context **meta_ac)
{
        int ret = 0, num_free_extents;
        unsigned int max_recs_needed = clusters_to_add + 2 * extents_to_split;
        struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);

        *meta_ac = NULL;
        if (data_ac)
                *data_ac = NULL;

        BUG_ON(clusters_to_add != 0 && data_ac == NULL);

        num_free_extents = ocfs2_num_free_extents(osb, et);
        if (num_free_extents < 0) {
                ret = num_free_extents;
                mlog_errno(ret);
                goto out;
        }

        /*
         * Sparse allocation file systems need to be more conservative
         * with reserving room for expansion - the actual allocation
         * happens while we've got a journal handle open so re-taking
         * a cluster lock (because we ran out of room for another
         * extent) will violate ordering rules.
         *
         * Most of the time we'll only be seeing this 1 cluster at a time
         * anyway.
         *
         * Always lock for any unwritten extents - we might want to
         * add blocks during a split.
         */
        if (!num_free_extents ||
            (ocfs2_sparse_alloc(osb) && num_free_extents < max_recs_needed)) {
                ret = ocfs2_reserve_new_metadata(osb, et->et_root_el, meta_ac);
                if (ret < 0) {
                        if (ret != -ENOSPC)
                                mlog_errno(ret);
                        goto out;
                }
        }

        if (clusters_to_add == 0)
                goto out;

        ret = ocfs2_reserve_clusters(osb, clusters_to_add, data_ac);
        if (ret < 0) {
                if (ret != -ENOSPC)
                        mlog_errno(ret);
                goto out;
        }

out:
        if (ret) {
                if (*meta_ac) {
                        ocfs2_free_alloc_context(*meta_ac);
                        *meta_ac = NULL;
                }

                /*
                 * We cannot have an error and a non null *data_ac.
                 */
        }

        return ret;
}

/*
 * Read the inode specified by blkno to get suballoc_slot and
 * suballoc_bit.
 */
static int ocfs2_get_suballoc_slot_bit(struct ocfs2_super *osb, u64 blkno,
                                       u16 *suballoc_slot, u16 *suballoc_bit)
{
        int status;
        struct buffer_head *inode_bh = NULL;
        struct ocfs2_dinode *inode_fe;

        mlog_entry("blkno: %llu\n", (unsigned long long)blkno);

        /* dirty read disk */
        status = ocfs2_read_blocks_sync(osb, blkno, 1, &inode_bh);
        if (status < 0) {
                mlog(ML_ERROR, "read block %llu failed %d\n",
                     (unsigned long long)blkno, status);
                goto bail;
        }

        inode_fe = (struct ocfs2_dinode *) inode_bh->b_data;
        if (!OCFS2_IS_VALID_DINODE(inode_fe)) {
                mlog(ML_ERROR, "invalid inode %llu requested\n",
                     (unsigned long long)blkno);
                status = -EINVAL;
                goto bail;
        }

        if (le16_to_cpu(inode_fe->i_suballoc_slot) != (u16)OCFS2_INVALID_SLOT &&
            (u32)le16_to_cpu(inode_fe->i_suballoc_slot) > osb->max_slots - 1) {
                mlog(ML_ERROR, "inode %llu has invalid suballoc slot %u\n",
                     (unsigned long long)blkno,
                     (u32)le16_to_cpu(inode_fe->i_suballoc_slot));
                status = -EINVAL;
                goto bail;
        }

        if (suballoc_slot)
                *suballoc_slot = le16_to_cpu(inode_fe->i_suballoc_slot);
        if (suballoc_bit)
                *suballoc_bit = le16_to_cpu(inode_fe->i_suballoc_bit);

bail:
        brelse(inode_bh);

        mlog_exit(status);
        return status;
}

/*
 * test whether bit is SET in allocator bitmap or not.  on success, 0
 * is returned and *res is 1 for SET; 0 otherwise.  when fails, errno
 * is returned and *res is meaningless.  Call this after you have
 * cluster locked against suballoc, or you may get a result based on
 * non-up2date contents
 */
static int ocfs2_test_suballoc_bit(struct ocfs2_super *osb,
                                   struct inode *suballoc,
                                   struct buffer_head *alloc_bh, u64 blkno,
                                   u16 bit, int *res)
{
        struct ocfs2_dinode *alloc_fe;
        struct ocfs2_group_desc *group;
        struct buffer_head *group_bh = NULL;
        u64 bg_blkno;
        int status;

        mlog_entry("blkno: %llu bit: %u\n", (unsigned long long)blkno,
                   (unsigned int)bit);

        alloc_fe = (struct ocfs2_dinode *)alloc_bh->b_data;
        if ((bit + 1) > ocfs2_bits_per_group(&alloc_fe->id2.i_chain)) {
                mlog(ML_ERROR, "suballoc bit %u out of range of %u\n",
                     (unsigned int)bit,
                     ocfs2_bits_per_group(&alloc_fe->id2.i_chain));
                status = -EINVAL;
                goto bail;
        }

        bg_blkno = ocfs2_which_suballoc_group(blkno, bit);
        status = ocfs2_read_group_descriptor(suballoc, alloc_fe, bg_blkno,
                                             &group_bh);
        if (status < 0) {
                mlog(ML_ERROR, "read group %llu failed %d\n",
                     (unsigned long long)bg_blkno, status);
                goto bail;
        }

        group = (struct ocfs2_group_desc *) group_bh->b_data;
        *res = ocfs2_test_bit(bit, (unsigned long *)group->bg_bitmap);

bail:
        brelse(group_bh);

        mlog_exit(status);
        return status;
}

/*
 * Test if the bit representing this inode (blkno) is set in the
 * suballocator.
 *
 * On success, 0 is returned and *res is 1 for SET; 0 otherwise.
 *
 * In the event of failure, a negative value is returned and *res is
 * meaningless.
 *
 * Callers must make sure to hold nfs_sync_lock to prevent
 * ocfs2_delete_inode() on another node from accessing the same
 * suballocator concurrently.
 */
int ocfs2_test_inode_bit(struct ocfs2_super *osb, u64 blkno, int *res)
{
        int status;
        u16 suballoc_bit = 0, suballoc_slot = 0;
        struct inode *inode_alloc_inode;
        struct buffer_head *alloc_bh = NULL;

        mlog_entry("blkno: %llu", (unsigned long long)blkno);

        status = ocfs2_get_suballoc_slot_bit(osb, blkno, &suballoc_slot,
                                             &suballoc_bit);
        if (status < 0) {
                mlog(ML_ERROR, "get alloc slot and bit failed %d\n", status);
                goto bail;
        }

        inode_alloc_inode =
                ocfs2_get_system_file_inode(osb, INODE_ALLOC_SYSTEM_INODE,
                                            suballoc_slot);
        if (!inode_alloc_inode) {
                /* the error code could be inaccurate, but we are not able to
                 * get the correct one. */
                status = -EINVAL;
                mlog(ML_ERROR, "unable to get alloc inode in slot %u\n",
                     (u32)suballoc_slot);
                goto bail;
        }

        mutex_lock(&inode_alloc_inode->i_mutex);
        status = ocfs2_inode_lock(inode_alloc_inode, &alloc_bh, 0);
        if (status < 0) {
                mutex_unlock(&inode_alloc_inode->i_mutex);
                mlog(ML_ERROR, "lock on alloc inode on slot %u failed %d\n",
                     (u32)suballoc_slot, status);
                goto bail;
        }

        status = ocfs2_test_suballoc_bit(osb, inode_alloc_inode, alloc_bh,
                                         blkno, suballoc_bit, res);
        if (status < 0)
                mlog(ML_ERROR, "test suballoc bit failed %d\n", status);

        ocfs2_inode_unlock(inode_alloc_inode, 0);
        mutex_unlock(&inode_alloc_inode->i_mutex);

        iput(inode_alloc_inode);
        brelse(alloc_bh);
bail:
        mlog_exit(status);
        return status;
}