perf/ring_buffer: Prevent concurent ring buffer access

[linux/fpc-iii.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>

#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 "ocfs2_trace.h"

#include "buffer_head_io.h"

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

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,
                                             struct ocfs2_alloc_reservation *resv);

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);

/*
 * ocfs2_la_default_mb() - determine a default size, in megabytes of
 * the local alloc.
 *
 * Generally, we'd like to pick as large a local alloc as
 * possible. Performance on large workloads tends to scale
 * proportionally to la size. In addition to that, the reservations
 * code functions more efficiently as it can reserve more windows for
 * write.
 *
 * Some things work against us when trying to choose a large local alloc:
 *
 * - We need to ensure our sizing is picked to leave enough space in
 *   group descriptors for other allocations (such as block groups,
 *   etc). Picking default sizes which are a multiple of 4 could help
 *   - block groups are allocated in 2mb and 4mb chunks.
 *
 * - Likewise, we don't want to starve other nodes of bits on small
 *   file systems. This can easily be taken care of by limiting our
 *   default to a reasonable size (256M) on larger cluster sizes.
 *
 * - Some file systems can't support very large sizes - 4k and 8k in
 *   particular are limited to less than 128 and 256 megabytes respectively.
 *
 * The following reference table shows group descriptor and local
 * alloc maximums at various cluster sizes (4k blocksize)
 *
 * csize: 4K    group: 126M     la: 121M
 * csize: 8K    group: 252M     la: 243M
 * csize: 16K   group: 504M     la: 486M
 * csize: 32K   group: 1008M    la: 972M
 * csize: 64K   group: 2016M    la: 1944M
 * csize: 128K  group: 4032M    la: 3888M
 * csize: 256K  group: 8064M    la: 7776M
 * csize: 512K  group: 16128M   la: 15552M
 * csize: 1024K group: 32256M   la: 31104M
 */
#define OCFS2_LA_MAX_DEFAULT_MB 256
#define OCFS2_LA_OLD_DEFAULT    8
unsigned int ocfs2_la_default_mb(struct ocfs2_super *osb)
{
        unsigned int la_mb;
        unsigned int gd_mb;
        unsigned int la_max_mb;
        unsigned int megs_per_slot;
        struct super_block *sb = osb->sb;

        gd_mb = ocfs2_clusters_to_megabytes(osb->sb,
                8 * ocfs2_group_bitmap_size(sb, 0, osb->s_feature_incompat));

        /*
         * This takes care of files systems with very small group
         * descriptors - 512 byte blocksize at cluster sizes lower
         * than 16K and also 1k blocksize with 4k cluster size.
         */
        if ((sb->s_blocksize == 512 && osb->s_clustersize <= 8192)
            || (sb->s_blocksize == 1024 && osb->s_clustersize == 4096))
                return OCFS2_LA_OLD_DEFAULT;

        /*
         * Leave enough room for some block groups and make the final
         * value we work from a multiple of 4.
         */
        gd_mb -= 16;
        gd_mb &= 0xFFFFFFFB;

        la_mb = gd_mb;

        /*
         * Keep window sizes down to a reasonable default
         */
        if (la_mb > OCFS2_LA_MAX_DEFAULT_MB) {
                /*
                 * Some clustersize / blocksize combinations will have
                 * given us a larger than OCFS2_LA_MAX_DEFAULT_MB
                 * default size, but get poor distribution when
                 * limited to exactly 256 megabytes.
                 *
                 * As an example, 16K clustersize at 4K blocksize
                 * gives us a cluster group size of 504M. Paring the
                 * local alloc size down to 256 however, would give us
                 * only one window and around 200MB left in the
                 * cluster group. Instead, find the first size below
                 * 256 which would give us an even distribution.
                 *
                 * Larger cluster group sizes actually work out pretty
                 * well when pared to 256, so we don't have to do this
                 * for any group that fits more than two
                 * OCFS2_LA_MAX_DEFAULT_MB windows.
                 */
                if (gd_mb > (2 * OCFS2_LA_MAX_DEFAULT_MB))
                        la_mb = 256;
                else {
                        unsigned int gd_mult = gd_mb;

                        while (gd_mult > 256)
                                gd_mult = gd_mult >> 1;

                        la_mb = gd_mult;
                }
        }

        megs_per_slot = osb->osb_clusters_at_boot / osb->max_slots;
        megs_per_slot = ocfs2_clusters_to_megabytes(osb->sb, megs_per_slot);
        /* Too many nodes, too few disk clusters. */
        if (megs_per_slot < la_mb)
                la_mb = megs_per_slot;

        /* We can't store more bits than we can in a block. */
        la_max_mb = ocfs2_clusters_to_megabytes(osb->sb,
                                                ocfs2_local_alloc_size(sb) * 8);
        if (la_mb > la_max_mb)
                la_mb = la_max_mb;

        return la_mb;
}

void ocfs2_la_set_sizes(struct ocfs2_super *osb, int requested_mb)
{
        struct super_block *sb = osb->sb;
        unsigned int la_default_mb = ocfs2_la_default_mb(osb);
        unsigned int la_max_mb;

        la_max_mb = ocfs2_clusters_to_megabytes(sb,
                                                ocfs2_local_alloc_size(sb) * 8);

        trace_ocfs2_la_set_sizes(requested_mb, la_max_mb, la_default_mb);

        if (requested_mb == -1) {
                /* No user request - use defaults */
                osb->local_alloc_default_bits =
                        ocfs2_megabytes_to_clusters(sb, la_default_mb);
        } else if (requested_mb > la_max_mb) {
                /* Request is too big, we give the maximum available */
                osb->local_alloc_default_bits =
                        ocfs2_megabytes_to_clusters(sb, la_max_mb);
        } else {
                osb->local_alloc_default_bits =
                        ocfs2_megabytes_to_clusters(sb, requested_mb);
        }

        osb->local_alloc_bits = osb->local_alloc_default_bits;
}

static inline int ocfs2_la_state_enabled(struct ocfs2_super *osb)
{
        return (osb->local_alloc_state == OCFS2_LA_THROTTLED ||
                osb->local_alloc_state == OCFS2_LA_ENABLED);
}

void ocfs2_local_alloc_seen_free_bits(struct ocfs2_super *osb,
                                      unsigned int num_clusters)
{
        spin_lock(&osb->osb_lock);
        if (osb->local_alloc_state == OCFS2_LA_DISABLED ||
            osb->local_alloc_state == OCFS2_LA_THROTTLED)
                if (num_clusters >= osb->local_alloc_default_bits) {
                        cancel_delayed_work(&osb->la_enable_wq);
                        osb->local_alloc_state = OCFS2_LA_ENABLED;
                }
        spin_unlock(&osb->osb_lock);
}

void ocfs2_la_enable_worker(struct work_struct *work)
{
        struct ocfs2_super *osb =
                container_of(work, struct ocfs2_super,
                             la_enable_wq.work);
        spin_lock(&osb->osb_lock);
        osb->local_alloc_state = OCFS2_LA_ENABLED;
        spin_unlock(&osb->osb_lock);
}

/*
 * Tell us whether a given allocation should use the local alloc
 * file. Otherwise, it has to go to the main bitmap.
 *
 * This function does semi-dirty reads of local alloc size and state!
 * This is ok however, as the values are re-checked once under mutex.
 */
int ocfs2_alloc_should_use_local(struct ocfs2_super *osb, u64 bits)
{
        int ret = 0;
        int la_bits;

        spin_lock(&osb->osb_lock);
        la_bits = osb->local_alloc_bits;

        if (!ocfs2_la_state_enabled(osb))
                goto bail;

        /* 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))
                goto bail;

        ret = 1;
bail:
        trace_ocfs2_alloc_should_use_local(
             (unsigned long long)bits, osb->local_alloc_state, la_bits, ret);
        spin_unlock(&osb->osb_lock);
        return ret;
}

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;

        if (osb->local_alloc_bits == 0)
                goto bail;

        if (osb->local_alloc_bits >= osb->bitmap_cpg) {
                mlog(ML_NOTICE, "Requested local alloc window %d is larger "
                     "than max possible %u. Using defaults.\n",
                     osb->local_alloc_bits, (osb->bitmap_cpg - 1));
                osb->local_alloc_bits =
                        ocfs2_megabytes_to_clusters(osb->sb,
                                                    ocfs2_la_default_mb(osb));
        }

        /* 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_inode_block_full(inode, &alloc_bh,
                                             OCFS2_BH_IGNORE_CACHE);
        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)
                brelse(alloc_bh);
        iput(inode);

        trace_ocfs2_load_local_alloc(osb->local_alloc_bits);

        if (status)
                mlog_errno(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;

        cancel_delayed_work(&osb->la_enable_wq);
        flush_workqueue(osb->ocfs2_wq);

        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;

        ocfs2_resmap_uninit(&osb->osb_la_resmap);

        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;
        }

        inode_lock(main_bm_inode);

        status = ocfs2_inode_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_NOFS);
        if (!alloc_copy) {
                status = -ENOMEM;
                goto out_commit;
        }
        memcpy(alloc_copy, alloc, bh->b_size);

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

        ocfs2_clear_local_alloc(alloc);
        ocfs2_journal_dirty(handle, bh);

        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:
        brelse(main_bm_bh);

        ocfs2_inode_unlock(main_bm_inode, 1);

out_mutex:
        inode_unlock(main_bm_inode);
        iput(main_bm_inode);

out:
        iput(local_alloc_inode);

        kfree(alloc_copy);
}

/*
 * 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;

        trace_ocfs2_begin_local_alloc_recovery(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;
        }

        inode_lock(inode);

        status = ocfs2_read_inode_block_full(inode, &alloc_bh,
                                             OCFS2_BH_IGNORE_CACHE);
        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);

        ocfs2_compute_meta_ecc(osb->sb, alloc_bh->b_data, &alloc->i_check);
        status = ocfs2_write_block(osb, alloc_bh, INODE_CACHE(inode));
        if (status < 0)
                mlog_errno(status);

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

        brelse(alloc_bh);

        if (inode) {
                inode_unlock(inode);
                iput(inode);
        }

        if (status)
                mlog_errno(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;

        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;
        }

        inode_lock(main_bm_inode);

        status = ocfs2_inode_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_inode_unlock(main_bm_inode, 1);

out_mutex:
        inode_unlock(main_bm_inode);

        brelse(main_bm_bh);

        iput(main_bm_inode);

out:
        if (!status)
                ocfs2_init_steal_slots(osb);
        if (status)
                mlog_errno(status);
        return status;
}

/*
 * make sure we've got at least bits_wanted 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;

        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;
        }

        inode_lock(local_alloc_inode);

        /*
         * We must double check state and allocator bits because
         * another process may have changed them while holding i_mutex.
         */
        spin_lock(&osb->osb_lock);
        if (!ocfs2_la_state_enabled(osb) ||
            (bits_wanted > osb->local_alloc_bits)) {
                spin_unlock(&osb->osb_lock);
                status = -ENOSPC;
                goto bail;
        }
        spin_unlock(&osb->osb_lock);

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

#ifdef CONFIG_OCFS2_DEBUG_FS
        if (le32_to_cpu(alloc->id1.bitmap1.i_used) !=
            ocfs2_local_alloc_count_bits(alloc)) {
                status = ocfs2_error(osb->sb, "local alloc inode %llu says it has %u used bits, but a count shows %u\n",
                                (unsigned long long)le64_to_cpu(alloc->i_blkno),
                                le32_to_cpu(alloc->id1.bitmap1.i_used),
                                ocfs2_local_alloc_count_bits(alloc));
                goto bail;
        }
#endif

        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;
                }

                /*
                 * Under certain conditions, the window slide code
                 * might have reduced the number of bits available or
                 * disabled the the local alloc entirely. Re-check
                 * here and return -ENOSPC if necessary.
                 */
                status = -ENOSPC;
                if (!ocfs2_la_state_enabled(osb))
                        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)
                        goto bail;
        }

        ac->ac_inode = local_alloc_inode;
        /* We should never use localalloc from another slot */
        ac->ac_alloc_slot = osb->slot_num;
        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) {
                inode_unlock(local_alloc_inode);
                iput(local_alloc_inode);
        }

        trace_ocfs2_reserve_local_alloc_bits(
                (unsigned long long)ac->ac_max_block,
                bits_wanted, osb->slot_num, status);

        if (status)
                mlog_errno(status);
        return status;
}

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

        BUG_ON(ac->ac_which != OCFS2_AC_USE_LOCAL);

        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,
                                                  ac->ac_resv);
        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;
        *num_bits = bits_wanted;

        status = ocfs2_journal_access_di(handle,
                                         INODE_CACHE(local_alloc_inode),
                                         osb->local_alloc_bh,
                                         OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        ocfs2_resmap_claimed_bits(&osb->osb_la_resmap, ac->ac_resv, start,
                                  bits_wanted);

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

        le32_add_cpu(&alloc->id1.bitmap1.i_used, *num_bits);
        ocfs2_journal_dirty(handle, osb->local_alloc_bh);

bail:
        if (status)
                mlog_errno(status);
        return status;
}

int ocfs2_free_local_alloc_bits(struct ocfs2_super *osb,
                                handle_t *handle,
                                struct ocfs2_alloc_context *ac,
                                u32 bit_off,
                                u32 num_bits)
{
        int status, start;
        u32 clear_bits;
        struct inode *local_alloc_inode;
        void *bitmap;
        struct ocfs2_dinode *alloc;
        struct ocfs2_local_alloc *la;

        BUG_ON(ac->ac_which != OCFS2_AC_USE_LOCAL);

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

        bitmap = la->la_bitmap;
        start = bit_off - le32_to_cpu(la->la_bm_off);
        clear_bits = num_bits;

        status = ocfs2_journal_access_di(handle,
                        INODE_CACHE(local_alloc_inode),
                        osb->local_alloc_bh,
                        OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        while (clear_bits--)
                ocfs2_clear_bit(start++, bitmap);

        le32_add_cpu(&alloc->id1.bitmap1.i_used, -num_bits);
        ocfs2_journal_dirty(handle, osb->local_alloc_bh);

bail:
        return status;
}

static u32 ocfs2_local_alloc_count_bits(struct ocfs2_dinode *alloc)
{
        u32 count;
        struct ocfs2_local_alloc *la = OCFS2_LOCAL_ALLOC(alloc);

        count = memweight(la->la_bitmap, le16_to_cpu(la->la_size));

        trace_ocfs2_local_alloc_count_bits(count);
        return count;
}

static int ocfs2_local_alloc_find_clear_bits(struct ocfs2_super *osb,
                                     struct ocfs2_dinode *alloc,
                                     u32 *numbits,
                                     struct ocfs2_alloc_reservation *resv)
{
        int numfound = 0, bitoff, left, startoff, lastzero;
        int local_resv = 0;
        struct ocfs2_alloc_reservation r;
        void *bitmap = NULL;
        struct ocfs2_reservation_map *resmap = &osb->osb_la_resmap;

        if (!alloc->id1.bitmap1.i_total) {
                bitoff = -1;
                goto bail;
        }

        if (!resv) {
                local_resv = 1;
                ocfs2_resv_init_once(&r);
                ocfs2_resv_set_type(&r, OCFS2_RESV_FLAG_TMP);
                resv = &r;
        }

        numfound = *numbits;
        if (ocfs2_resmap_resv_bits(resmap, resv, &bitoff, &numfound) == 0) {
                if (numfound < *numbits)
                        *numbits = numfound;
                goto bail;
        }

        /*
         * Code error. While reservations are enabled, local
         * allocation should _always_ go through them.
         */
        BUG_ON(osb->osb_resv_level != 0);

        /*
         * Reservations are disabled. Handle this the old way.
         */

        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;
                }
        }

        trace_ocfs2_local_alloc_find_clear_bits_search_bitmap(bitoff, numfound);

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

bail:
        if (local_resv)
                ocfs2_resv_discard(resmap, resv);

        trace_ocfs2_local_alloc_find_clear_bits(*numbits,
                le32_to_cpu(alloc->id1.bitmap1.i_total),
                bitoff, numfound);

        return bitoff;
}

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

        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;
}

#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);

        trace_ocfs2_sync_local_to_main(
             le32_to_cpu(alloc->id1.bitmap1.i_total),
             le32_to_cpu(alloc->id1.bitmap1.i_used));

        if (!alloc->id1.bitmap1.i_total) {
                goto bail;
        }

        if (le32_to_cpu(alloc->id1.bitmap1.i_used) ==
            le32_to_cpu(alloc->id1.bitmap1.i_total)) {
                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);

                        trace_ocfs2_sync_local_to_main_free(
                             count, start - count,
                             (unsigned long long)la_start_blk,
                             (unsigned long long)blkno);

                        status = ocfs2_release_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:
        if (status)
                mlog_errno(status);
        return status;
}

enum ocfs2_la_event {
        OCFS2_LA_EVENT_SLIDE,           /* Normal window slide. */
        OCFS2_LA_EVENT_FRAGMENTED,      /* The global bitmap has
                                         * enough bits theoretically
                                         * free, but a contiguous
                                         * allocation could not be
                                         * found. */
        OCFS2_LA_EVENT_ENOSPC,          /* Global bitmap doesn't have
                                         * enough bits free to satisfy
                                         * our request. */
};
#define OCFS2_LA_ENABLE_INTERVAL (30 * HZ)
/*
 * Given an event, calculate the size of our next local alloc window.
 *
 * This should always be called under i_mutex of the local alloc inode
 * so that local alloc disabling doesn't race with processes trying to
 * use the allocator.
 *
 * Returns the state which the local alloc was left in. This value can
 * be ignored by some paths.
 */
static int ocfs2_recalc_la_window(struct ocfs2_super *osb,
                                  enum ocfs2_la_event event)
{
        unsigned int bits;
        int state;

        spin_lock(&osb->osb_lock);
        if (osb->local_alloc_state == OCFS2_LA_DISABLED) {
                WARN_ON_ONCE(osb->local_alloc_state == OCFS2_LA_DISABLED);
                goto out_unlock;
        }

        /*
         * ENOSPC and fragmentation are treated similarly for now.
         */
        if (event == OCFS2_LA_EVENT_ENOSPC ||
            event == OCFS2_LA_EVENT_FRAGMENTED) {
                /*
                 * We ran out of contiguous space in the primary
                 * bitmap. Drastically reduce the number of bits used
                 * by local alloc until we have to disable it.
                 */
                bits = osb->local_alloc_bits >> 1;
                if (bits > ocfs2_megabytes_to_clusters(osb->sb, 1)) {
                        /*
                         * By setting state to THROTTLED, we'll keep
                         * the number of local alloc bits used down
                         * until an event occurs which would give us
                         * reason to assume the bitmap situation might
                         * have changed.
                         */
                        osb->local_alloc_state = OCFS2_LA_THROTTLED;
                        osb->local_alloc_bits = bits;
                } else {
                        osb->local_alloc_state = OCFS2_LA_DISABLED;
                }
                queue_delayed_work(osb->ocfs2_wq, &osb->la_enable_wq,
                                   OCFS2_LA_ENABLE_INTERVAL);
                goto out_unlock;
        }

        /*
         * Don't increase the size of the local alloc window until we
         * know we might be able to fulfill the request. Otherwise, we
         * risk bouncing around the global bitmap during periods of
         * low space.
         */
        if (osb->local_alloc_state != OCFS2_LA_THROTTLED)
                osb->local_alloc_bits = osb->local_alloc_default_bits;

out_unlock:
        state = osb->local_alloc_state;
        spin_unlock(&osb->osb_lock);

        return state;
}

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;
        }

retry_enospc:
        (*ac)->ac_bits_wanted = osb->local_alloc_bits;
        status = ocfs2_reserve_cluster_bitmap_bits(osb, *ac);
        if (status == -ENOSPC) {
                if (ocfs2_recalc_la_window(osb, OCFS2_LA_EVENT_ENOSPC) ==
                    OCFS2_LA_DISABLED)
                        goto bail;

                ocfs2_free_ac_resource(*ac);
                memset(*ac, 0, sizeof(struct ocfs2_alloc_context));
                goto retry_enospc;
        }
        if (status < 0) {
                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;
        }

        if (status)
                mlog_errno(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;

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

        trace_ocfs2_local_alloc_new_window(
                le32_to_cpu(alloc->id1.bitmap1.i_total),
                osb->local_alloc_bits);

        /* 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(handle, ac, osb->local_alloc_bits,
                                      &cluster_off, &cluster_count);
        if (status == -ENOSPC) {
retry_enospc:
                /*
                 * Note: We could also try syncing the journal here to
                 * allow use of any free bits which the current
                 * transaction can't give us access to. --Mark
                 */
                if (ocfs2_recalc_la_window(osb, OCFS2_LA_EVENT_FRAGMENTED) ==
                    OCFS2_LA_DISABLED)
                        goto bail;

                ac->ac_bits_wanted = osb->local_alloc_bits;
                status = ocfs2_claim_clusters(handle, ac,
                                              osb->local_alloc_bits,
                                              &cluster_off,
                                              &cluster_count);
                if (status == -ENOSPC)
                        goto retry_enospc;
                /*
                 * We only shrunk the *minimum* number of in our
                 * request - it's entirely possible that the allocator
                 * might give us more than we asked for.
                 */
                if (status == 0) {
                        spin_lock(&osb->osb_lock);
                        osb->local_alloc_bits = cluster_count;
                        spin_unlock(&osb->osb_lock);
                }
        }
        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));

        ocfs2_resmap_restart(&osb->osb_la_resmap, cluster_count,
                             OCFS2_LOCAL_ALLOC(alloc)->la_bitmap);

        trace_ocfs2_local_alloc_new_window_result(
                OCFS2_LOCAL_ALLOC(alloc)->la_bm_off,
                le32_to_cpu(alloc->id1.bitmap1.i_total));

bail:
        if (status)
                mlog_errno(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;

        ocfs2_recalc_la_window(osb, OCFS2_LA_EVENT_SLIDE);

        /* 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_NOFS);
        if (!alloc_copy) {
                status = -ENOMEM;
                mlog_errno(status);
                goto bail;
        }
        memcpy(alloc_copy, alloc, osb->local_alloc_bh->b_size);

        status = ocfs2_journal_access_di(handle,
                                         INODE_CACHE(local_alloc_inode),
                                         osb->local_alloc_bh,
                                         OCFS2_JOURNAL_ACCESS_WRITE);
        if (status < 0) {
                mlog_errno(status);
                goto bail;
        }

        ocfs2_clear_local_alloc(alloc);
        ocfs2_journal_dirty(handle, osb->local_alloc_bh);

        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);

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

        brelse(main_bm_bh);

        iput(main_bm_inode);
        kfree(alloc_copy);

        if (ac)
                ocfs2_free_alloc_context(ac);

        if (status)
                mlog_errno(status);
        return status;
}