inotify: fix race

[linux-2.6.22.y-op.git] / fs / ocfs2 / localalloc.c

/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * localalloc.c
 *
 * Node local data allocation
 *
 * 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>
#include <linux/bitops.h>

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

#include "ocfs2.h"

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

#include "buffer_head_io.h"

#define OCFS2_LOCAL_ALLOC(dinode)       (&((dinode)->id2.i_lab))

static inline int ocfs2_local_alloc_window_bits(struct ocfs2_super *osb);

static u32 ocfs2_local_alloc_count_bits(struct ocfs2_dinode *alloc);

static int ocfs2_local_alloc_find_clear_bits(struct ocfs2_super *osb,
                                             struct ocfs2_dinode *alloc,
                                             u32 numbits);

static void ocfs2_clear_local_alloc(struct ocfs2_dinode *alloc);

static int ocfs2_sync_local_to_main(struct ocfs2_super *osb,
                                    handle_t *handle,
                                    struct ocfs2_dinode *alloc,
                                    struct inode *main_bm_inode,
                                    struct buffer_head *main_bm_bh);

static int ocfs2_local_alloc_reserve_for_window(struct ocfs2_super *osb,
                                                struct ocfs2_alloc_context **ac,
                                                struct inode **bitmap_inode,
                                                struct buffer_head **bitmap_bh);

static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
                                        handle_t *handle,
                                        struct ocfs2_alloc_context *ac);

static int ocfs2_local_alloc_slide_window(struct ocfs2_super *osb,
                                          struct inode *local_alloc_inode);

/*
 * Determine how large our local alloc window should be, in bits.
 *
 * These values (and the behavior in ocfs2_alloc_should_use_local) have
 * been chosen so that most allocations, including new block groups go
 * through local alloc.
 */
static inline int ocfs2_local_alloc_window_bits(struct ocfs2_super *osb)
{
        BUG_ON(osb->s_clustersize_bits < 12);

        return 2048 >> (osb->s_clustersize_bits - 12);
}

/*
 * Tell us whether a given allocation should use the local alloc
 * file. Otherwise, it has to go to the main bitmap.
 */
int ocfs2_alloc_should_use_local(struct ocfs2_super *osb, u64 bits)
{
        int la_bits = ocfs2_local_alloc_window_bits(osb);

        if (osb->local_alloc_state != OCFS2_LA_ENABLED)
                return 0;

        /* la_bits should be at least twice the size (in clusters) of
         * a new block group. We want to be sure block group
         * allocations go through the local alloc, so allow an
         * allocation to take up to half the bitmap. */
        if (bits > (la_bits / 2))
                return 0;

        return 1;
}

int ocfs2_load_local_alloc(struct ocfs2_super *osb)
{
        int status = 0;
        struct ocfs2_dinode *alloc = NULL;
        struct buffer_head *alloc_bh = NULL;
        u32 num_used;
        struct inode *inode = NULL;
        struct ocfs2_local_alloc *la;

        mlog_entry_void();

        /* read the alloc off disk */
        inode = ocfs2_get_system_file_inode(osb, LOCAL_ALLOC_SYSTEM_INODE,
                                            osb->slot_num);
        if (!inode) {
                status = -EINVAL;
                mlog_errno(status);
                goto bail;
        }

        status = ocfs2_read_block(osb, OCFS2_I(inode)->ip_blkno,
                                  &alloc_bh, 0, inode);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        alloc = (struct ocfs2_dinode *) alloc_bh->b_data;
        la = OCFS2_LOCAL_ALLOC(alloc);

        if (!(le32_to_cpu(alloc->i_flags) &
            (OCFS2_LOCAL_ALLOC_FL|OCFS2_BITMAP_FL))) {
                mlog(ML_ERROR, "Invalid local alloc inode, %llu\n",
                     (unsigned long long)OCFS2_I(inode)->ip_blkno);
                status = -EINVAL;
                goto bail;
        }

        if ((la->la_size == 0) ||
            (le16_to_cpu(la->la_size) > ocfs2_local_alloc_size(inode->i_sb))) {
                mlog(ML_ERROR, "Local alloc size is invalid (la_size = %u)\n",
                     le16_to_cpu(la->la_size));
                status = -EINVAL;
                goto bail;
        }

        /* do a little verification. */
        num_used = ocfs2_local_alloc_count_bits(alloc);

        /* hopefully the local alloc has always been recovered before
         * we load it. */
        if (num_used
            || alloc->id1.bitmap1.i_used
            || alloc->id1.bitmap1.i_total
            || la->la_bm_off)
                mlog(ML_ERROR, "Local alloc hasn't been recovered!\n"
                     "found = %u, set = %u, taken = %u, off = %u\n",
                     num_used, le32_to_cpu(alloc->id1.bitmap1.i_used),
                     le32_to_cpu(alloc->id1.bitmap1.i_total),
                     OCFS2_LOCAL_ALLOC(alloc)->la_bm_off);

        osb->local_alloc_bh = alloc_bh;
        osb->local_alloc_state = OCFS2_LA_ENABLED;

bail:
        if (status < 0)
                if (alloc_bh)
                        brelse(alloc_bh);
        if (inode)
                iput(inode);

        mlog_exit(status);
        return status;
}

/*
 * return any unused bits to the bitmap and write out a clean
 * local_alloc.
 *
 * local_alloc_bh is optional. If not passed, we will simply use the
 * one off osb. If you do pass it however, be warned that it *will* be
 * returned brelse'd and NULL'd out.*/
void ocfs2_shutdown_local_alloc(struct ocfs2_super *osb)
{
        int status;
        handle_t *handle;
        struct inode *local_alloc_inode = NULL;
        struct buffer_head *bh = NULL;
        struct buffer_head *main_bm_bh = NULL;
        struct inode *main_bm_inode = NULL;
        struct ocfs2_dinode *alloc_copy = NULL;
        struct ocfs2_dinode *alloc = NULL;

        mlog_entry_void();

        if (osb->local_alloc_state == OCFS2_LA_UNUSED)
                goto out;

        local_alloc_inode =
                ocfs2_get_system_file_inode(osb,
                                            LOCAL_ALLOC_SYSTEM_INODE,
                                            osb->slot_num);
        if (!local_alloc_inode) {
                status = -ENOENT;
                mlog_errno(status);
                goto out;
        }

        osb->local_alloc_state = OCFS2_LA_DISABLED;

        main_bm_inode = ocfs2_get_system_file_inode(osb,
                                                    GLOBAL_BITMAP_SYSTEM_INODE,
                                                    OCFS2_INVALID_SLOT);
        if (!main_bm_inode) {
                status = -EINVAL;
                mlog_errno(status);
                goto out;
        }

        mutex_lock(&main_bm_inode->i_mutex);

        status = ocfs2_meta_lock(main_bm_inode, &main_bm_bh, 1);
        if (status < 0) {
                mlog_errno(status);
                goto out_mutex;
        }

        /* WINDOW_MOVE_CREDITS is a bit heavy... */
        handle = ocfs2_start_trans(osb, OCFS2_WINDOW_MOVE_CREDITS);
        if (IS_ERR(handle)) {
                mlog_errno(PTR_ERR(handle));
                handle = NULL;
                goto out_unlock;
        }

        bh = osb->local_alloc_bh;
        alloc = (struct ocfs2_dinode *) bh->b_data;

        alloc_copy = kmalloc(bh->b_size, GFP_KERNEL);
        if (!alloc_copy) {
                status = -ENOMEM;
                goto out_commit;
        }
        memcpy(alloc_copy, alloc, bh->b_size);

        status = ocfs2_journal_access(handle, local_alloc_inode, bh,
                                      OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto out_commit;
        }

        ocfs2_clear_local_alloc(alloc);

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

        brelse(bh);
        osb->local_alloc_bh = NULL;
        osb->local_alloc_state = OCFS2_LA_UNUSED;

        status = ocfs2_sync_local_to_main(osb, handle, alloc_copy,
                                          main_bm_inode, main_bm_bh);
        if (status < 0)
                mlog_errno(status);

out_commit:
        ocfs2_commit_trans(osb, handle);

out_unlock:
        if (main_bm_bh)
                brelse(main_bm_bh);

        ocfs2_meta_unlock(main_bm_inode, 1);

out_mutex:
        mutex_unlock(&main_bm_inode->i_mutex);
        iput(main_bm_inode);

out:
        if (local_alloc_inode)
                iput(local_alloc_inode);

        if (alloc_copy)
                kfree(alloc_copy);

        mlog_exit_void();
}

/*
 * We want to free the bitmap bits outside of any recovery context as
 * we'll need a cluster lock to do so, but we must clear the local
 * alloc before giving up the recovered nodes journal. To solve this,
 * we kmalloc a copy of the local alloc before it's change for the
 * caller to process with ocfs2_complete_local_alloc_recovery
 */
int ocfs2_begin_local_alloc_recovery(struct ocfs2_super *osb,
                                     int slot_num,
                                     struct ocfs2_dinode **alloc_copy)
{
        int status = 0;
        struct buffer_head *alloc_bh = NULL;
        struct inode *inode = NULL;
        struct ocfs2_dinode *alloc;

        mlog_entry("(slot_num = %d)\n", slot_num);

        *alloc_copy = NULL;

        inode = ocfs2_get_system_file_inode(osb,
                                            LOCAL_ALLOC_SYSTEM_INODE,
                                            slot_num);
        if (!inode) {
                status = -EINVAL;
                mlog_errno(status);
                goto bail;
        }

        mutex_lock(&inode->i_mutex);

        status = ocfs2_read_block(osb, OCFS2_I(inode)->ip_blkno,
                                  &alloc_bh, 0, inode);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        *alloc_copy = kmalloc(alloc_bh->b_size, GFP_KERNEL);
        if (!(*alloc_copy)) {
                status = -ENOMEM;
                goto bail;
        }
        memcpy((*alloc_copy), alloc_bh->b_data, alloc_bh->b_size);

        alloc = (struct ocfs2_dinode *) alloc_bh->b_data;
        ocfs2_clear_local_alloc(alloc);

        status = ocfs2_write_block(osb, alloc_bh, inode);
        if (status < 0)
                mlog_errno(status);

bail:
        if ((status < 0) && (*alloc_copy)) {
                kfree(*alloc_copy);
                *alloc_copy = NULL;
        }

        if (alloc_bh)
                brelse(alloc_bh);

        if (inode) {
                mutex_unlock(&inode->i_mutex);
                iput(inode);
        }

        mlog_exit(status);
        return status;
}

/*
 * Step 2: By now, we've completed the journal recovery, we've stamped
 * a clean local alloc on disk and dropped the node out of the
 * recovery map. Dlm locks will no longer stall, so lets clear out the
 * main bitmap.
 */
int ocfs2_complete_local_alloc_recovery(struct ocfs2_super *osb,
                                        struct ocfs2_dinode *alloc)
{
        int status;
        handle_t *handle;
        struct buffer_head *main_bm_bh = NULL;
        struct inode *main_bm_inode;

        mlog_entry_void();

        main_bm_inode = ocfs2_get_system_file_inode(osb,
                                                    GLOBAL_BITMAP_SYSTEM_INODE,
                                                    OCFS2_INVALID_SLOT);
        if (!main_bm_inode) {
                status = -EINVAL;
                mlog_errno(status);
                goto out;
        }

        mutex_lock(&main_bm_inode->i_mutex);

        status = ocfs2_meta_lock(main_bm_inode, &main_bm_bh, 1);
        if (status < 0) {
                mlog_errno(status);
                goto out_mutex;
        }

        handle = ocfs2_start_trans(osb, OCFS2_WINDOW_MOVE_CREDITS);
        if (IS_ERR(handle)) {
                status = PTR_ERR(handle);
                handle = NULL;
                mlog_errno(status);
                goto out_unlock;
        }

        /* we want the bitmap change to be recorded on disk asap */
        handle->h_sync = 1;

        status = ocfs2_sync_local_to_main(osb, handle, alloc,
                                          main_bm_inode, main_bm_bh);
        if (status < 0)
                mlog_errno(status);

        ocfs2_commit_trans(osb, handle);

out_unlock:
        ocfs2_meta_unlock(main_bm_inode, 1);

out_mutex:
        mutex_unlock(&main_bm_inode->i_mutex);

        if (main_bm_bh)
                brelse(main_bm_bh);

        iput(main_bm_inode);

out:
        mlog_exit(status);
        return status;
}

/*
 * make sure we've got at least bitswanted contiguous bits in the
 * local alloc. You lose them when you drop i_mutex.
 *
 * We will add ourselves to the transaction passed in, but may start
 * our own in order to shift windows.
 */
int ocfs2_reserve_local_alloc_bits(struct ocfs2_super *osb,
                                   u32 bits_wanted,
                                   struct ocfs2_alloc_context *ac)
{
        int status;
        struct ocfs2_dinode *alloc;
        struct inode *local_alloc_inode;
        unsigned int free_bits;

        mlog_entry_void();

        BUG_ON(!ac);

        local_alloc_inode =
                ocfs2_get_system_file_inode(osb,
                                            LOCAL_ALLOC_SYSTEM_INODE,
                                            osb->slot_num);
        if (!local_alloc_inode) {
                status = -ENOENT;
                mlog_errno(status);
                goto bail;
        }

        mutex_lock(&local_alloc_inode->i_mutex);

        if (osb->local_alloc_state != OCFS2_LA_ENABLED) {
                status = -ENOSPC;
                goto bail;
        }

        if (bits_wanted > ocfs2_local_alloc_window_bits(osb)) {
                mlog(0, "Asking for more than my max window size!\n");
                status = -ENOSPC;
                goto bail;
        }

        alloc = (struct ocfs2_dinode *) osb->local_alloc_bh->b_data;

        if (le32_to_cpu(alloc->id1.bitmap1.i_used) !=
            ocfs2_local_alloc_count_bits(alloc)) {
                ocfs2_error(osb->sb, "local alloc inode %llu says it has "
                            "%u free bits, but a count shows %u",
                            (unsigned long long)le64_to_cpu(alloc->i_blkno),
                            le32_to_cpu(alloc->id1.bitmap1.i_used),
                            ocfs2_local_alloc_count_bits(alloc));
                status = -EIO;
                goto bail;
        }

        free_bits = le32_to_cpu(alloc->id1.bitmap1.i_total) -
                le32_to_cpu(alloc->id1.bitmap1.i_used);
        if (bits_wanted > free_bits) {
                /* uhoh, window change time. */
                status =
                        ocfs2_local_alloc_slide_window(osb, local_alloc_inode);
                if (status < 0) {
                        if (status != -ENOSPC)
                                mlog_errno(status);
                        goto bail;
                }
        }

        ac->ac_inode = local_alloc_inode;
        ac->ac_which = OCFS2_AC_USE_LOCAL;
        get_bh(osb->local_alloc_bh);
        ac->ac_bh = osb->local_alloc_bh;
        status = 0;
bail:
        if (status < 0 && local_alloc_inode)
                iput(local_alloc_inode);

        mlog_exit(status);
        return status;
}

int ocfs2_claim_local_alloc_bits(struct ocfs2_super *osb,
                                 handle_t *handle,
                                 struct ocfs2_alloc_context *ac,
                                 u32 min_bits,
                                 u32 *bit_off,
                                 u32 *num_bits)
{
        int status, start;
        struct inode *local_alloc_inode;
        u32 bits_wanted;
        void *bitmap;
        struct ocfs2_dinode *alloc;
        struct ocfs2_local_alloc *la;

        mlog_entry_void();
        BUG_ON(ac->ac_which != OCFS2_AC_USE_LOCAL);

        bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;
        local_alloc_inode = ac->ac_inode;
        alloc = (struct ocfs2_dinode *) osb->local_alloc_bh->b_data;
        la = OCFS2_LOCAL_ALLOC(alloc);

        start = ocfs2_local_alloc_find_clear_bits(osb, alloc, bits_wanted);
        if (start == -1) {
                /* TODO: Shouldn't we just BUG here? */
                status = -ENOSPC;
                mlog_errno(status);
                goto bail;
        }

        bitmap = la->la_bitmap;
        *bit_off = le32_to_cpu(la->la_bm_off) + start;
        /* local alloc is always contiguous by nature -- we never
         * delete bits from it! */
        *num_bits = bits_wanted;

        status = ocfs2_journal_access(handle, local_alloc_inode,
                                      osb->local_alloc_bh,
                                      OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        while(bits_wanted--)
                ocfs2_set_bit(start++, bitmap);

        alloc->id1.bitmap1.i_used = cpu_to_le32(*num_bits +
                                le32_to_cpu(alloc->id1.bitmap1.i_used));

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

        status = 0;
bail:
        mlog_exit(status);
        return status;
}

static u32 ocfs2_local_alloc_count_bits(struct ocfs2_dinode *alloc)
{
        int i;
        u8 *buffer;
        u32 count = 0;
        struct ocfs2_local_alloc *la = OCFS2_LOCAL_ALLOC(alloc);

        mlog_entry_void();

        buffer = la->la_bitmap;
        for (i = 0; i < le16_to_cpu(la->la_size); i++)
                count += hweight8(buffer[i]);

        mlog_exit(count);
        return count;
}

static int ocfs2_local_alloc_find_clear_bits(struct ocfs2_super *osb,
                                             struct ocfs2_dinode *alloc,
                                             u32 numbits)
{
        int numfound, bitoff, left, startoff, lastzero;
        void *bitmap = NULL;

        mlog_entry("(numbits wanted = %u)\n", numbits);

        if (!alloc->id1.bitmap1.i_total) {
                mlog(0, "No bits in my window!\n");
                bitoff = -1;
                goto bail;
        }

        bitmap = OCFS2_LOCAL_ALLOC(alloc)->la_bitmap;

        numfound = bitoff = startoff = 0;
        lastzero = -1;
        left = le32_to_cpu(alloc->id1.bitmap1.i_total);
        while ((bitoff = ocfs2_find_next_zero_bit(bitmap, left, startoff)) != -1) {
                if (bitoff == left) {
                        /* mlog(0, "bitoff (%d) == left", bitoff); */
                        break;
                }
                /* mlog(0, "Found a zero: bitoff = %d, startoff = %d, "
                   "numfound = %d\n", bitoff, startoff, numfound);*/

                /* Ok, we found a zero bit... is it contig. or do we
                 * start over?*/
                if (bitoff == startoff) {
                        /* we found a zero */
                        numfound++;
                        startoff++;
                } else {
                        /* got a zero after some ones */
                        numfound = 1;
                        startoff = bitoff+1;
                }
                /* we got everything we needed */
                if (numfound == numbits) {
                        /* mlog(0, "Found it all!\n"); */
                        break;
                }
        }

        mlog(0, "Exiting loop, bitoff = %d, numfound = %d\n", bitoff,
             numfound);

        if (numfound == numbits)
                bitoff = startoff - numfound;
        else
                bitoff = -1;

bail:
        mlog_exit(bitoff);
        return bitoff;
}

static void ocfs2_clear_local_alloc(struct ocfs2_dinode *alloc)
{
        struct ocfs2_local_alloc *la = OCFS2_LOCAL_ALLOC(alloc);
        int i;
        mlog_entry_void();

        alloc->id1.bitmap1.i_total = 0;
        alloc->id1.bitmap1.i_used = 0;
        la->la_bm_off = 0;
        for(i = 0; i < le16_to_cpu(la->la_size); i++)
                la->la_bitmap[i] = 0;

        mlog_exit_void();
}

#if 0
/* turn this on and uncomment below to aid debugging window shifts. */
static void ocfs2_verify_zero_bits(unsigned long *bitmap,
                                   unsigned int start,
                                   unsigned int count)
{
        unsigned int tmp = count;
        while(tmp--) {
                if (ocfs2_test_bit(start + tmp, bitmap)) {
                        printk("ocfs2_verify_zero_bits: start = %u, count = "
                               "%u\n", start, count);
                        printk("ocfs2_verify_zero_bits: bit %u is set!",
                               start + tmp);
                        BUG();
                }
        }
}
#endif

/*
 * sync the local alloc to main bitmap.
 *
 * assumes you've already locked the main bitmap -- the bitmap inode
 * passed is used for caching.
 */
static int ocfs2_sync_local_to_main(struct ocfs2_super *osb,
                                    handle_t *handle,
                                    struct ocfs2_dinode *alloc,
                                    struct inode *main_bm_inode,
                                    struct buffer_head *main_bm_bh)
{
        int status = 0;
        int bit_off, left, count, start;
        u64 la_start_blk;
        u64 blkno;
        void *bitmap;
        struct ocfs2_local_alloc *la = OCFS2_LOCAL_ALLOC(alloc);

        mlog_entry("total = %u, COUNT = %u, used = %u\n",
                   le32_to_cpu(alloc->id1.bitmap1.i_total),
                   ocfs2_local_alloc_count_bits(alloc),
                   le32_to_cpu(alloc->id1.bitmap1.i_used));

        if (!alloc->id1.bitmap1.i_total) {
                mlog(0, "nothing to sync!\n");
                goto bail;
        }

        if (le32_to_cpu(alloc->id1.bitmap1.i_used) ==
            le32_to_cpu(alloc->id1.bitmap1.i_total)) {
                mlog(0, "all bits were taken!\n");
                goto bail;
        }

        la_start_blk = ocfs2_clusters_to_blocks(osb->sb,
                                                le32_to_cpu(la->la_bm_off));
        bitmap = la->la_bitmap;
        start = count = bit_off = 0;
        left = le32_to_cpu(alloc->id1.bitmap1.i_total);

        while ((bit_off = ocfs2_find_next_zero_bit(bitmap, left, start))
               != -1) {
                if ((bit_off < left) && (bit_off == start)) {
                        count++;
                        start++;
                        continue;
                }
                if (count) {
                        blkno = la_start_blk +
                                ocfs2_clusters_to_blocks(osb->sb,
                                                         start - count);

                        mlog(0, "freeing %u bits starting at local alloc bit "
                             "%u (la_start_blk = %llu, blkno = %llu)\n",
                             count, start - count,
                             (unsigned long long)la_start_blk,
                             (unsigned long long)blkno);

                        status = ocfs2_free_clusters(handle, main_bm_inode,
                                                     main_bm_bh, blkno, count);
                        if (status < 0) {
                                mlog_errno(status);
                                goto bail;
                        }
                }
                if (bit_off >= left)
                        break;
                count = 1;
                start = bit_off + 1;
        }

bail:
        mlog_exit(status);
        return status;
}

static int ocfs2_local_alloc_reserve_for_window(struct ocfs2_super *osb,
                                                struct ocfs2_alloc_context **ac,
                                                struct inode **bitmap_inode,
                                                struct buffer_head **bitmap_bh)
{
        int status;

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

        (*ac)->ac_bits_wanted = ocfs2_local_alloc_window_bits(osb);

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

        *bitmap_inode = (*ac)->ac_inode;
        igrab(*bitmap_inode);
        *bitmap_bh = (*ac)->ac_bh;
        get_bh(*bitmap_bh);
        status = 0;
bail:
        if ((status < 0) && *ac) {
                ocfs2_free_alloc_context(*ac);
                *ac = NULL;
        }

        mlog_exit(status);
        return status;
}

/*
 * pass it the bitmap lock in lock_bh if you have it.
 */
static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
                                        handle_t *handle,
                                        struct ocfs2_alloc_context *ac)
{
        int status = 0;
        u32 cluster_off, cluster_count;
        struct ocfs2_dinode *alloc = NULL;
        struct ocfs2_local_alloc *la;

        mlog_entry_void();

        alloc = (struct ocfs2_dinode *) osb->local_alloc_bh->b_data;
        la = OCFS2_LOCAL_ALLOC(alloc);

        if (alloc->id1.bitmap1.i_total)
                mlog(0, "asking me to alloc a new window over a non-empty "
                     "one\n");

        mlog(0, "Allocating %u clusters for a new window.\n",
             ocfs2_local_alloc_window_bits(osb));

        /* Instruct the allocation code to try the most recently used
         * cluster group. We'll re-record the group used this pass
         * below. */
        ac->ac_last_group = osb->la_last_gd;

        /* we used the generic suballoc reserve function, but we set
         * everything up nicely, so there's no reason why we can't use
         * the more specific cluster api to claim bits. */
        status = ocfs2_claim_clusters(osb, handle, ac,
                                      ocfs2_local_alloc_window_bits(osb),
                                      &cluster_off, &cluster_count);
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        osb->la_last_gd = ac->ac_last_group;

        la->la_bm_off = cpu_to_le32(cluster_off);
        alloc->id1.bitmap1.i_total = cpu_to_le32(cluster_count);
        /* just in case... In the future when we find space ourselves,
         * we don't have to get all contiguous -- but we'll have to
         * set all previously used bits in bitmap and update
         * la_bits_set before setting the bits in the main bitmap. */
        alloc->id1.bitmap1.i_used = 0;
        memset(OCFS2_LOCAL_ALLOC(alloc)->la_bitmap, 0,
               le16_to_cpu(la->la_size));

        mlog(0, "New window allocated:\n");
        mlog(0, "window la_bm_off = %u\n",
             OCFS2_LOCAL_ALLOC(alloc)->la_bm_off);
        mlog(0, "window bits = %u\n", le32_to_cpu(alloc->id1.bitmap1.i_total));

bail:
        mlog_exit(status);
        return status;
}

/* Note that we do *NOT* lock the local alloc inode here as
 * it's been locked already for us. */
static int ocfs2_local_alloc_slide_window(struct ocfs2_super *osb,
                                          struct inode *local_alloc_inode)
{
        int status = 0;
        struct buffer_head *main_bm_bh = NULL;
        struct inode *main_bm_inode = NULL;
        handle_t *handle = NULL;
        struct ocfs2_dinode *alloc;
        struct ocfs2_dinode *alloc_copy = NULL;
        struct ocfs2_alloc_context *ac = NULL;

        mlog_entry_void();

        /* This will lock the main bitmap for us. */
        status = ocfs2_local_alloc_reserve_for_window(osb,
                                                      &ac,
                                                      &main_bm_inode,
                                                      &main_bm_bh);
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        handle = ocfs2_start_trans(osb, OCFS2_WINDOW_MOVE_CREDITS);
        if (IS_ERR(handle)) {
                status = PTR_ERR(handle);
                handle = NULL;
                mlog_errno(status);
                goto bail;
        }

        alloc = (struct ocfs2_dinode *) osb->local_alloc_bh->b_data;

        /* We want to clear the local alloc before doing anything
         * else, so that if we error later during this operation,
         * local alloc shutdown won't try to double free main bitmap
         * bits. Make a copy so the sync function knows which bits to
         * free. */
        alloc_copy = kmalloc(osb->local_alloc_bh->b_size, GFP_KERNEL);
        if (!alloc_copy) {
                status = -ENOMEM;
                mlog_errno(status);
                goto bail;
        }
        memcpy(alloc_copy, alloc, osb->local_alloc_bh->b_size);

        status = ocfs2_journal_access(handle, local_alloc_inode,
                                      osb->local_alloc_bh,
                                      OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        ocfs2_clear_local_alloc(alloc);

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

        status = ocfs2_sync_local_to_main(osb, handle, alloc_copy,
                                          main_bm_inode, main_bm_bh);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        status = ocfs2_local_alloc_new_window(osb, handle, ac);
        if (status < 0) {
                if (status != -ENOSPC)
                        mlog_errno(status);
                goto bail;
        }

        atomic_inc(&osb->alloc_stats.moves);

        status = 0;
bail:
        if (handle)
                ocfs2_commit_trans(osb, handle);

        if (main_bm_bh)
                brelse(main_bm_bh);

        if (main_bm_inode)
                iput(main_bm_inode);

        if (alloc_copy)
                kfree(alloc_copy);

        if (ac)
                ocfs2_free_alloc_context(ac);

        mlog_exit(status);
        return status;
}