free-space-cache.c

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/*
 * Copyright (C) 2008 Red Hat.  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 v2 as published by the Free Software Foundation.
 *
 * 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/pagemap.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/math64.h>
#include <linux/ratelimit.h>
#include "ctree.h"
#include "free-space-cache.h"
#include "transaction.h"
#include "disk-io.h"
#include "extent_io.h"
#include "inode-map.h"

#define BITS_PER_BITMAP     (PAGE_CACHE_SIZE * 8)
#define MAX_CACHE_BYTES_PER_GIG (32 * 1024)

static int link_free_space(struct btrfs_free_space_ctl *ctl,
               struct btrfs_free_space *info);
static void unlink_free_space(struct btrfs_free_space_ctl *ctl,
                  struct btrfs_free_space *info);

static struct inode *__lookup_free_space_inode(struct btrfs_root *root,
                           struct btrfs_path *path,
                           u64 offset)
{
    struct btrfs_key key;
    struct btrfs_key location;
    struct btrfs_disk_key disk_key;
    struct btrfs_free_space_header *header;
    struct extent_buffer *leaf;
    struct inode *inode = NULL;
    int ret;

    key.objectid = BTRFS_FREE_SPACE_OBJECTID;
    key.offset = offset;
    key.type = 0;

    ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
    if (ret < 0)
        return ERR_PTR(ret);
    if (ret > 0) {
        btrfs_release_path(path);
        return ERR_PTR(-ENOENT);
    }

    leaf = path->nodes[0];
    header = btrfs_item_ptr(leaf, path->slots[0],
                struct btrfs_free_space_header);
    btrfs_free_space_key(leaf, header, &disk_key);
    btrfs_disk_key_to_cpu(&location, &disk_key);
    btrfs_release_path(path);

    inode = btrfs_iget(root->fs_info->sb, &location, root, NULL);
    if (!inode)
        return ERR_PTR(-ENOENT);
    if (IS_ERR(inode))
        return inode;
    if (is_bad_inode(inode)) {
        iput(inode);
        return ERR_PTR(-ENOENT);
    }

    mapping_set_gfp_mask(inode->i_mapping,
            mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS);

    return inode;
}

struct inode *lookup_free_space_inode(struct btrfs_root *root,
                      struct btrfs_block_group_cache
                      *block_group, struct btrfs_path *path)
{
    struct inode *inode = NULL;
    u32 flags = BTRFS_INODE_NODATASUM | BTRFS_INODE_NODATACOW;

    spin_lock(&block_group->lock);
    if (block_group->inode)
        inode = igrab(block_group->inode);
    spin_unlock(&block_group->lock);
    if (inode)
        return inode;

    inode = __lookup_free_space_inode(root, path,
                      block_group->key.objectid);
    if (IS_ERR(inode))
        return inode;

    spin_lock(&block_group->lock);
    if (!((BTRFS_I(inode)->flags & flags) == flags)) {
        printk(KERN_INFO "Old style space inode found, converting.\n");
        BTRFS_I(inode)->flags |= BTRFS_INODE_NODATASUM |
            BTRFS_INODE_NODATACOW;
        block_group->disk_cache_state = BTRFS_DC_CLEAR;
    }

    if (!block_group->iref) {
        block_group->inode = igrab(inode);
        block_group->iref = 1;
    }
    spin_unlock(&block_group->lock);

    return inode;
}

int __create_free_space_inode(struct btrfs_root *root,
                  struct btrfs_trans_handle *trans,
                  struct btrfs_path *path, u64 ino, u64 offset)
{
    struct btrfs_key key;
    struct btrfs_disk_key disk_key;
    struct btrfs_free_space_header *header;
    struct btrfs_inode_item *inode_item;
    struct extent_buffer *leaf;
    u64 flags = BTRFS_INODE_NOCOMPRESS | BTRFS_INODE_PREALLOC;
    int ret;

    ret = btrfs_insert_empty_inode(trans, root, path, ino);
    if (ret)
        return ret;

    /* We inline crc's for the free disk space cache */
    if (ino != BTRFS_FREE_INO_OBJECTID)
        flags |= BTRFS_INODE_NODATASUM | BTRFS_INODE_NODATACOW;

    leaf = path->nodes[0];
    inode_item = btrfs_item_ptr(leaf, path->slots[0],
                    struct btrfs_inode_item);
    btrfs_item_key(leaf, &disk_key, path->slots[0]);
    memset_extent_buffer(leaf, 0, (unsigned long)inode_item,
                 sizeof(*inode_item));
    btrfs_set_inode_generation(leaf, inode_item, trans->transid);
    btrfs_set_inode_size(leaf, inode_item, 0);
    btrfs_set_inode_nbytes(leaf, inode_item, 0);
    btrfs_set_inode_uid(leaf, inode_item, 0);
    btrfs_set_inode_gid(leaf, inode_item, 0);
    btrfs_set_inode_mode(leaf, inode_item, S_IFREG | 0600);
    btrfs_set_inode_flags(leaf, inode_item, flags);
    btrfs_set_inode_nlink(leaf, inode_item, 1);
    btrfs_set_inode_transid(leaf, inode_item, trans->transid);
    btrfs_set_inode_block_group(leaf, inode_item, offset);
    btrfs_mark_buffer_dirty(leaf);
    btrfs_release_path(path);

    key.objectid = BTRFS_FREE_SPACE_OBJECTID;
    key.offset = offset;
    key.type = 0;

    ret = btrfs_insert_empty_item(trans, root, path, &key,
                      sizeof(struct btrfs_free_space_header));
    if (ret < 0) {
        btrfs_release_path(path);
        return ret;
    }
    leaf = path->nodes[0];
    header = btrfs_item_ptr(leaf, path->slots[0],
                struct btrfs_free_space_header);
    memset_extent_buffer(leaf, 0, (unsigned long)header, sizeof(*header));
    btrfs_set_free_space_key(leaf, header, &disk_key);
    btrfs_mark_buffer_dirty(leaf);
    btrfs_release_path(path);

    return 0;
}

int create_free_space_inode(struct btrfs_root *root,
                struct btrfs_trans_handle *trans,
                struct btrfs_block_group_cache *block_group,
                struct btrfs_path *path)
{
    int ret;
    u64 ino;

    ret = btrfs_find_free_objectid(root, &ino);
    if (ret < 0)
        return ret;

    return __create_free_space_inode(root, trans, path, ino,
                     block_group->key.objectid);
}

int btrfs_truncate_free_space_cache(struct btrfs_root *root,
                    struct btrfs_trans_handle *trans,
                    struct btrfs_path *path,
                    struct inode *inode)
{
    struct btrfs_block_rsv *rsv;
    u64 needed_bytes;
    loff_t oldsize;
    int ret = 0;

    rsv = trans->block_rsv;
    trans->block_rsv = &root->fs_info->global_block_rsv;

    /* 1 for slack space, 1 for updating the inode */
    needed_bytes = btrfs_calc_trunc_metadata_size(root, 1) +
        btrfs_calc_trans_metadata_size(root, 1);

    spin_lock(&trans->block_rsv->lock);
    if (trans->block_rsv->reserved < needed_bytes) {
        spin_unlock(&trans->block_rsv->lock);
        trans->block_rsv = rsv;
        return -ENOSPC;
    }
    spin_unlock(&trans->block_rsv->lock);

    oldsize = i_size_read(inode);
    btrfs_i_size_write(inode, 0);
    truncate_pagecache(inode, oldsize, 0);

    /*
     * We don't need an orphan item because truncating the free space cache
     * will never be split across transactions.
     */
    ret = btrfs_truncate_inode_items(trans, root, inode,
                     0, BTRFS_EXTENT_DATA_KEY);

    if (ret) {
        trans->block_rsv = rsv;
        btrfs_abort_transaction(trans, root, ret);
        return ret;
    }

    ret = btrfs_update_inode(trans, root, inode);
    if (ret)
        btrfs_abort_transaction(trans, root, ret);
    trans->block_rsv = rsv;

    return ret;
}

static int readahead_cache(struct inode *inode)
{
    struct file_ra_state *ra;
    unsigned long last_index;

    ra = kzalloc(sizeof(*ra), GFP_NOFS);
    if (!ra)
        return -ENOMEM;

    file_ra_state_init(ra, inode->i_mapping);
    last_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;

    page_cache_sync_readahead(inode->i_mapping, ra, NULL, 0, last_index);

    kfree(ra);

    return 0;
}

struct io_ctl {
    void *cur, *orig;
    struct page *page;
    struct page **pages;
    struct btrfs_root *root;
    unsigned long size;
    int index;
    int num_pages;
    unsigned check_crcs:1;
};

static int io_ctl_init(struct io_ctl *io_ctl, struct inode *inode,
               struct btrfs_root *root)
{
    memset(io_ctl, 0, sizeof(struct io_ctl));
    io_ctl->num_pages = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >>
        PAGE_CACHE_SHIFT;
    io_ctl->pages = kzalloc(sizeof(struct page *) * io_ctl->num_pages,
                GFP_NOFS);
    if (!io_ctl->pages)
        return -ENOMEM;
    io_ctl->root = root;
    if (btrfs_ino(inode) != BTRFS_FREE_INO_OBJECTID)
        io_ctl->check_crcs = 1;
    return 0;
}

static void io_ctl_free(struct io_ctl *io_ctl)
{
    kfree(io_ctl->pages);
}

static void io_ctl_unmap_page(struct io_ctl *io_ctl)
{
    if (io_ctl->cur) {
        kunmap(io_ctl->page);
        io_ctl->cur = NULL;
        io_ctl->orig = NULL;
    }
}

static void io_ctl_map_page(struct io_ctl *io_ctl, int clear)
{
    WARN_ON(io_ctl->cur);
    BUG_ON(io_ctl->index >= io_ctl->num_pages);
    io_ctl->page = io_ctl->pages[io_ctl->index++];
    io_ctl->cur = kmap(io_ctl->page);
    io_ctl->orig = io_ctl->cur;
    io_ctl->size = PAGE_CACHE_SIZE;
    if (clear)
        memset(io_ctl->cur, 0, PAGE_CACHE_SIZE);
}

static void io_ctl_drop_pages(struct io_ctl *io_ctl)
{
    int i;

    io_ctl_unmap_page(io_ctl);

    for (i = 0; i < io_ctl->num_pages; i++) {
        if (io_ctl->pages[i]) {
            ClearPageChecked(io_ctl->pages[i]);
            unlock_page(io_ctl->pages[i]);
            page_cache_release(io_ctl->pages[i]);
        }
    }
}

static int io_ctl_prepare_pages(struct io_ctl *io_ctl, struct inode *inode,
                int uptodate)
{
    struct page *page;
    gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
    int i;

    for (i = 0; i < io_ctl->num_pages; i++) {
        page = find_or_create_page(inode->i_mapping, i, mask);
        if (!page) {
            io_ctl_drop_pages(io_ctl);
            return -ENOMEM;
        }
        io_ctl->pages[i] = page;
        if (uptodate && !PageUptodate(page)) {
            btrfs_readpage(NULL, page);
            lock_page(page);
            if (!PageUptodate(page)) {
                printk(KERN_ERR "btrfs: error reading free "
                       "space cache\n");
                io_ctl_drop_pages(io_ctl);
                return -EIO;
            }
        }
    }

    for (i = 0; i < io_ctl->num_pages; i++) {
        clear_page_dirty_for_io(io_ctl->pages[i]);
        set_page_extent_mapped(io_ctl->pages[i]);
    }

    return 0;
}

static void io_ctl_set_generation(struct io_ctl *io_ctl, u64 generation)
{
    __le64 *val;

    io_ctl_map_page(io_ctl, 1);

    /*
     * Skip the csum areas.  If we don't check crcs then we just have a
     * 64bit chunk at the front of the first page.
     */
    if (io_ctl->check_crcs) {
        io_ctl->cur += (sizeof(u32) * io_ctl->num_pages);
        io_ctl->size -= sizeof(u64) + (sizeof(u32) * io_ctl->num_pages);
    } else {
        io_ctl->cur += sizeof(u64);
        io_ctl->size -= sizeof(u64) * 2;
    }

    val = io_ctl->cur;
    *val = cpu_to_le64(generation);
    io_ctl->cur += sizeof(u64);
}

static int io_ctl_check_generation(struct io_ctl *io_ctl, u64 generation)
{
    __le64 *gen;

    /*
     * Skip the crc area.  If we don't check crcs then we just have a 64bit
     * chunk at the front of the first page.
     */
    if (io_ctl->check_crcs) {
        io_ctl->cur += sizeof(u32) * io_ctl->num_pages;
        io_ctl->size -= sizeof(u64) +
            (sizeof(u32) * io_ctl->num_pages);
    } else {
        io_ctl->cur += sizeof(u64);
        io_ctl->size -= sizeof(u64) * 2;
    }

    gen = io_ctl->cur;
    if (le64_to_cpu(*gen) != generation) {
        printk_ratelimited(KERN_ERR "btrfs: space cache generation "
                   "(%Lu) does not match inode (%Lu)\n", *gen,
                   generation);
        io_ctl_unmap_page(io_ctl);
        return -EIO;
    }
    io_ctl->cur += sizeof(u64);
    return 0;
}

static void io_ctl_set_crc(struct io_ctl *io_ctl, int index)
{
    u32 *tmp;
    u32 crc = ~(u32)0;
    unsigned offset = 0;

    if (!io_ctl->check_crcs) {
        io_ctl_unmap_page(io_ctl);
        return;
    }

    if (index == 0)
        offset = sizeof(u32) * io_ctl->num_pages;

    crc = btrfs_csum_data(io_ctl->root, io_ctl->orig + offset, crc,
                  PAGE_CACHE_SIZE - offset);
    btrfs_csum_final(crc, (char *)&crc);
    io_ctl_unmap_page(io_ctl);
    tmp = kmap(io_ctl->pages[0]);
    tmp += index;
    *tmp = crc;
    kunmap(io_ctl->pages[0]);
}

static int io_ctl_check_crc(struct io_ctl *io_ctl, int index)
{
    u32 *tmp, val;
    u32 crc = ~(u32)0;
    unsigned offset = 0;

    if (!io_ctl->check_crcs) {
        io_ctl_map_page(io_ctl, 0);
        return 0;
    }

    if (index == 0)
        offset = sizeof(u32) * io_ctl->num_pages;

    tmp = kmap(io_ctl->pages[0]);
    tmp += index;
    val = *tmp;
    kunmap(io_ctl->pages[0]);

    io_ctl_map_page(io_ctl, 0);
    crc = btrfs_csum_data(io_ctl->root, io_ctl->orig + offset, crc,
                  PAGE_CACHE_SIZE - offset);
    btrfs_csum_final(crc, (char *)&crc);
    if (val != crc) {
        printk_ratelimited(KERN_ERR "btrfs: csum mismatch on free "
                   "space cache\n");
        io_ctl_unmap_page(io_ctl);
        return -EIO;
    }

    return 0;
}

static int io_ctl_add_entry(struct io_ctl *io_ctl, u64 offset, u64 bytes,
                void *bitmap)
{
    struct btrfs_free_space_entry *entry;

    if (!io_ctl->cur)
        return -ENOSPC;

    entry = io_ctl->cur;
    entry->offset = cpu_to_le64(offset);
    entry->bytes = cpu_to_le64(bytes);
    entry->type = (bitmap) ? BTRFS_FREE_SPACE_BITMAP :
        BTRFS_FREE_SPACE_EXTENT;
    io_ctl->cur += sizeof(struct btrfs_free_space_entry);
    io_ctl->size -= sizeof(struct btrfs_free_space_entry);

    if (io_ctl->size >= sizeof(struct btrfs_free_space_entry))
        return 0;

    io_ctl_set_crc(io_ctl, io_ctl->index - 1);

    /* No more pages to map */
    if (io_ctl->index >= io_ctl->num_pages)
        return 0;

    /* map the next page */
    io_ctl_map_page(io_ctl, 1);
    return 0;
}

static int io_ctl_add_bitmap(struct io_ctl *io_ctl, void *bitmap)
{
    if (!io_ctl->cur)
        return -ENOSPC;

    /*
     * If we aren't at the start of the current page, unmap this one and
     * map the next one if there is any left.
     */
    if (io_ctl->cur != io_ctl->orig) {
        io_ctl_set_crc(io_ctl, io_ctl->index - 1);
        if (io_ctl->index >= io_ctl->num_pages)
            return -ENOSPC;
        io_ctl_map_page(io_ctl, 0);
    }

    memcpy(io_ctl->cur, bitmap, PAGE_CACHE_SIZE);
    io_ctl_set_crc(io_ctl, io_ctl->index - 1);
    if (io_ctl->index < io_ctl->num_pages)
        io_ctl_map_page(io_ctl, 0);
    return 0;
}

static void io_ctl_zero_remaining_pages(struct io_ctl *io_ctl)
{
    /*
     * If we're not on the boundary we know we've modified the page and we
     * need to crc the page.
     */
    if (io_ctl->cur != io_ctl->orig)
        io_ctl_set_crc(io_ctl, io_ctl->index - 1);
    else
        io_ctl_unmap_page(io_ctl);

    while (io_ctl->index < io_ctl->num_pages) {
        io_ctl_map_page(io_ctl, 1);
        io_ctl_set_crc(io_ctl, io_ctl->index - 1);
    }
}

static int io_ctl_read_entry(struct io_ctl *io_ctl,
                struct btrfs_free_space *entry, u8 *type)
{
    struct btrfs_free_space_entry *e;
    int ret;

    if (!io_ctl->cur) {
        ret = io_ctl_check_crc(io_ctl, io_ctl->index);
        if (ret)
            return ret;
    }

    e = io_ctl->cur;
    entry->offset = le64_to_cpu(e->offset);
    entry->bytes = le64_to_cpu(e->bytes);
    *type = e->type;
    io_ctl->cur += sizeof(struct btrfs_free_space_entry);
    io_ctl->size -= sizeof(struct btrfs_free_space_entry);

    if (io_ctl->size >= sizeof(struct btrfs_free_space_entry))
        return 0;

    io_ctl_unmap_page(io_ctl);

    return 0;
}

static int io_ctl_read_bitmap(struct io_ctl *io_ctl,
                  struct btrfs_free_space *entry)
{
    int ret;

    ret = io_ctl_check_crc(io_ctl, io_ctl->index);
    if (ret)
        return ret;

    memcpy(entry->bitmap, io_ctl->cur, PAGE_CACHE_SIZE);
    io_ctl_unmap_page(io_ctl);

    return 0;
}

/*
 * Since we attach pinned extents after the fact we can have contiguous sections
 * of free space that are split up in entries.  This poses a problem with the
 * tree logging stuff since it could have allocated across what appears to be 2
 * entries since we would have merged the entries when adding the pinned extents
 * back to the free space cache.  So run through the space cache that we just
 * loaded and merge contiguous entries.  This will make the log replay stuff not
 * blow up and it will make for nicer allocator behavior.
 */
static void merge_space_tree(struct btrfs_free_space_ctl *ctl)
{
    struct btrfs_free_space *e, *prev = NULL;
    struct rb_node *n;

again:
    spin_lock(&ctl->tree_lock);
    for (n = rb_first(&ctl->free_space_offset); n; n = rb_next(n)) {
        e = rb_entry(n, struct btrfs_free_space, offset_index);
        if (!prev)
            goto next;
        if (e->bitmap || prev->bitmap)
            goto next;
        if (prev->offset + prev->bytes == e->offset) {
            unlink_free_space(ctl, prev);
            unlink_free_space(ctl, e);
            prev->bytes += e->bytes;
            kmem_cache_free(btrfs_free_space_cachep, e);
            link_free_space(ctl, prev);
            prev = NULL;
            spin_unlock(&ctl->tree_lock);
            goto again;
        }
next:
        prev = e;
    }
    spin_unlock(&ctl->tree_lock);
}

int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
                struct btrfs_free_space_ctl *ctl,
                struct btrfs_path *path, u64 offset)
{
    struct btrfs_free_space_header *header;
    struct extent_buffer *leaf;
    struct io_ctl io_ctl;
    struct btrfs_key key;
    struct btrfs_free_space *e, *n;
    struct list_head bitmaps;
    u64 num_entries;
    u64 num_bitmaps;
    u64 generation;
    u8 type;
    int ret = 0;

    INIT_LIST_HEAD(&bitmaps);

    /* Nothing in the space cache, goodbye */
    if (!i_size_read(inode))
        return 0;

    key.objectid = BTRFS_FREE_SPACE_OBJECTID;
    key.offset = offset;
    key.type = 0;

    ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
    if (ret < 0)
        return 0;
    else if (ret > 0) {
        btrfs_release_path(path);
        return 0;
    }

    ret = -1;

    leaf = path->nodes[0];
    header = btrfs_item_ptr(leaf, path->slots[0],
                struct btrfs_free_space_header);
    num_entries = btrfs_free_space_entries(leaf, header);
    num_bitmaps = btrfs_free_space_bitmaps(leaf, header);
    generation = btrfs_free_space_generation(leaf, header);
    btrfs_release_path(path);

    if (BTRFS_I(inode)->generation != generation) {
        printk(KERN_ERR "btrfs: free space inode generation (%llu) did"
               " not match free space cache generation (%llu)\n",
               (unsigned long long)BTRFS_I(inode)->generation,
               (unsigned long long)generation);
        return 0;
    }

    if (!num_entries)
        return 0;

    ret = io_ctl_init(&io_ctl, inode, root);
    if (ret)
        return ret;

    ret = readahead_cache(inode);
    if (ret)
        goto out;

    ret = io_ctl_prepare_pages(&io_ctl, inode, 1);
    if (ret)
        goto out;

    ret = io_ctl_check_crc(&io_ctl, 0);
    if (ret)
        goto free_cache;

    ret = io_ctl_check_generation(&io_ctl, generation);
    if (ret)
        goto free_cache;

    while (num_entries) {
        e = kmem_cache_zalloc(btrfs_free_space_cachep,
                      GFP_NOFS);
        if (!e)
            goto free_cache;

        ret = io_ctl_read_entry(&io_ctl, e, &type);
        if (ret) {
            kmem_cache_free(btrfs_free_space_cachep, e);
            goto free_cache;
        }

        if (!e->bytes) {
            kmem_cache_free(btrfs_free_space_cachep, e);
            goto free_cache;
        }

        if (type == BTRFS_FREE_SPACE_EXTENT) {
            spin_lock(&ctl->tree_lock);
            ret = link_free_space(ctl, e);
            spin_unlock(&ctl->tree_lock);
            if (ret) {
                printk(KERN_ERR "Duplicate entries in "
                       "free space cache, dumping\n");
                kmem_cache_free(btrfs_free_space_cachep, e);
                goto free_cache;
            }
        } else {
            BUG_ON(!num_bitmaps);
            num_bitmaps--;
            e->bitmap = kzalloc(PAGE_CACHE_SIZE, GFP_NOFS);
            if (!e->bitmap) {
                kmem_cache_free(
                    btrfs_free_space_cachep, e);
                goto free_cache;
            }
            spin_lock(&ctl->tree_lock);
            ret = link_free_space(ctl, e);
            ctl->total_bitmaps++;
            ctl->op->recalc_thresholds(ctl);
            spin_unlock(&ctl->tree_lock);
            if (ret) {
                printk(KERN_ERR "Duplicate entries in "
                       "free space cache, dumping\n");
                kmem_cache_free(btrfs_free_space_cachep, e);
                goto free_cache;
            }
            list_add_tail(&e->list, &bitmaps);
        }

        num_entries--;
    }

    io_ctl_unmap_page(&io_ctl);

    /*
     * We add the bitmaps at the end of the entries in order that
     * the bitmap entries are added to the cache.
     */
    list_for_each_entry_safe(e, n, &bitmaps, list) {
        list_del_init(&e->list);
        ret = io_ctl_read_bitmap(&io_ctl, e);
        if (ret)
            goto free_cache;
    }

    io_ctl_drop_pages(&io_ctl);
    merge_space_tree(ctl);
    ret = 1;
out:
    io_ctl_free(&io_ctl);
    return ret;
free_cache:
    io_ctl_drop_pages(&io_ctl);
    __btrfs_remove_free_space_cache(ctl);
    goto out;
}

int load_free_space_cache(struct btrfs_fs_info *fs_info,
              struct btrfs_block_group_cache *block_group)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_root *root = fs_info->tree_root;
    struct inode *inode;
    struct btrfs_path *path;
    int ret = 0;
    bool matched;
    u64 used = btrfs_block_group_used(&block_group->item);

    /*
     * If this block group has been marked to be cleared for one reason or
     * another then we can't trust the on disk cache, so just return.
     */
    spin_lock(&block_group->lock);
    if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
        spin_unlock(&block_group->lock);
        return 0;
    }
    spin_unlock(&block_group->lock);

    path = btrfs_alloc_path();
    if (!path)
        return 0;
    path->search_commit_root = 1;
    path->skip_locking = 1;

    inode = lookup_free_space_inode(root, block_group, path);
    if (IS_ERR(inode)) {
        btrfs_free_path(path);
        return 0;
    }

    /* We may have converted the inode and made the cache invalid. */
    spin_lock(&block_group->lock);
    if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
        spin_unlock(&block_group->lock);
        btrfs_free_path(path);
        goto out;
    }
    spin_unlock(&block_group->lock);

    ret = __load_free_space_cache(fs_info->tree_root, inode, ctl,
                      path, block_group->key.objectid);
    btrfs_free_path(path);
    if (ret <= 0)
        goto out;

    spin_lock(&ctl->tree_lock);
    matched = (ctl->free_space == (block_group->key.offset - used -
                       block_group->bytes_super));
    spin_unlock(&ctl->tree_lock);

    if (!matched) {
        __btrfs_remove_free_space_cache(ctl);
        printk(KERN_ERR "block group %llu has an wrong amount of free "
               "space\n", block_group->key.objectid);
        ret = -1;
    }
out:
    if (ret < 0) {
        /* This cache is bogus, make sure it gets cleared */
        spin_lock(&block_group->lock);
        block_group->disk_cache_state = BTRFS_DC_CLEAR;
        spin_unlock(&block_group->lock);
        ret = 0;

        printk(KERN_ERR "btrfs: failed to load free space cache "
               "for block group %llu\n", block_group->key.objectid);
    }

    iput(inode);
    return ret;
}

int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
                struct btrfs_free_space_ctl *ctl,
                struct btrfs_block_group_cache *block_group,
                struct btrfs_trans_handle *trans,
                struct btrfs_path *path, u64 offset)
{
    struct btrfs_free_space_header *header;
    struct extent_buffer *leaf;
    struct rb_node *node;
    struct list_head *pos, *n;
    struct extent_state *cached_state = NULL;
    struct btrfs_free_cluster *cluster = NULL;
    struct extent_io_tree *unpin = NULL;
    struct io_ctl io_ctl;
    struct list_head bitmap_list;
    struct btrfs_key key;
    u64 start, extent_start, extent_end, len;
    int entries = 0;
    int bitmaps = 0;
    int ret;
    int err = -1;

    INIT_LIST_HEAD(&bitmap_list);

    if (!i_size_read(inode))
        return -1;

    ret = io_ctl_init(&io_ctl, inode, root);
    if (ret)
        return -1;

    /* Get the cluster for this block_group if it exists */
    if (block_group && !list_empty(&block_group->cluster_list))
        cluster = list_entry(block_group->cluster_list.next,
                     struct btrfs_free_cluster,
                     block_group_list);

    /* Lock all pages first so we can lock the extent safely. */
    io_ctl_prepare_pages(&io_ctl, inode, 0);

    lock_extent_bits(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1,
             0, &cached_state);

    node = rb_first(&ctl->free_space_offset);
    if (!node && cluster) {
        node = rb_first(&cluster->root);
        cluster = NULL;
    }

    /* Make sure we can fit our crcs into the first page */
    if (io_ctl.check_crcs &&
        (io_ctl.num_pages * sizeof(u32)) >= PAGE_CACHE_SIZE) {
        WARN_ON(1);
        goto out_nospc;
    }

    io_ctl_set_generation(&io_ctl, trans->transid);

    /* Write out the extent entries */
    while (node) {
        struct btrfs_free_space *e;

        e = rb_entry(node, struct btrfs_free_space, offset_index);
        entries++;

        ret = io_ctl_add_entry(&io_ctl, e->offset, e->bytes,
                       e->bitmap);
        if (ret)
            goto out_nospc;

        if (e->bitmap) {
            list_add_tail(&e->list, &bitmap_list);
            bitmaps++;
        }
        node = rb_next(node);
        if (!node && cluster) {
            node = rb_first(&cluster->root);
            cluster = NULL;
        }
    }

    /*
     * We want to add any pinned extents to our free space cache
     * so we don't leak the space
     */

    /*
     * We shouldn't have switched the pinned extents yet so this is the
     * right one
     */
    unpin = root->fs_info->pinned_extents;

    if (block_group)
        start = block_group->key.objectid;

    while (block_group && (start < block_group->key.objectid +
                   block_group->key.offset)) {
        ret = find_first_extent_bit(unpin, start,
                        &extent_start, &extent_end,
                        EXTENT_DIRTY, NULL);
        if (ret) {
            ret = 0;
            break;
        }

        /* This pinned extent is out of our range */
        if (extent_start >= block_group->key.objectid +
            block_group->key.offset)
            break;

        extent_start = max(extent_start, start);
        extent_end = min(block_group->key.objectid +
                 block_group->key.offset, extent_end + 1);
        len = extent_end - extent_start;

        entries++;
        ret = io_ctl_add_entry(&io_ctl, extent_start, len, NULL);
        if (ret)
            goto out_nospc;

        start = extent_end;
    }

    /* Write out the bitmaps */
    list_for_each_safe(pos, n, &bitmap_list) {
        struct btrfs_free_space *entry =
            list_entry(pos, struct btrfs_free_space, list);

        ret = io_ctl_add_bitmap(&io_ctl, entry->bitmap);
        if (ret)
            goto out_nospc;
        list_del_init(&entry->list);
    }

    /* Zero out the rest of the pages just to make sure */
    io_ctl_zero_remaining_pages(&io_ctl);

    ret = btrfs_dirty_pages(root, inode, io_ctl.pages, io_ctl.num_pages,
                0, i_size_read(inode), &cached_state);
    io_ctl_drop_pages(&io_ctl);
    unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
                 i_size_read(inode) - 1, &cached_state, GFP_NOFS);

    if (ret)
        goto out;


    btrfs_wait_ordered_range(inode, 0, (u64)-1);

    key.objectid = BTRFS_FREE_SPACE_OBJECTID;
    key.offset = offset;
    key.type = 0;

    ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
    if (ret < 0) {
        clear_extent_bit(&BTRFS_I(inode)->io_tree, 0, inode->i_size - 1,
                 EXTENT_DIRTY | EXTENT_DELALLOC, 0, 0, NULL,
                 GFP_NOFS);
        goto out;
    }
    leaf = path->nodes[0];
    if (ret > 0) {
        struct btrfs_key found_key;
        BUG_ON(!path->slots[0]);
        path->slots[0]--;
        btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
        if (found_key.objectid != BTRFS_FREE_SPACE_OBJECTID ||
            found_key.offset != offset) {
            clear_extent_bit(&BTRFS_I(inode)->io_tree, 0,
                     inode->i_size - 1,
                     EXTENT_DIRTY | EXTENT_DELALLOC, 0, 0,
                     NULL, GFP_NOFS);
            btrfs_release_path(path);
            goto out;
        }
    }

    BTRFS_I(inode)->generation = trans->transid;
    header = btrfs_item_ptr(leaf, path->slots[0],
                struct btrfs_free_space_header);
    btrfs_set_free_space_entries(leaf, header, entries);
    btrfs_set_free_space_bitmaps(leaf, header, bitmaps);
    btrfs_set_free_space_generation(leaf, header, trans->transid);
    btrfs_mark_buffer_dirty(leaf);
    btrfs_release_path(path);

    err = 0;
out:
    io_ctl_free(&io_ctl);
    if (err) {
        invalidate_inode_pages2(inode->i_mapping);
        BTRFS_I(inode)->generation = 0;
    }
    btrfs_update_inode(trans, root, inode);
    return err;

out_nospc:
    list_for_each_safe(pos, n, &bitmap_list) {
        struct btrfs_free_space *entry =
            list_entry(pos, struct btrfs_free_space, list);
        list_del_init(&entry->list);
    }
    io_ctl_drop_pages(&io_ctl);
    unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
                 i_size_read(inode) - 1, &cached_state, GFP_NOFS);
    goto out;
}

int btrfs_write_out_cache(struct btrfs_root *root,
              struct btrfs_trans_handle *trans,
              struct btrfs_block_group_cache *block_group,
              struct btrfs_path *path)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct inode *inode;
    int ret = 0;

    root = root->fs_info->tree_root;

    spin_lock(&block_group->lock);
    if (block_group->disk_cache_state < BTRFS_DC_SETUP) {
        spin_unlock(&block_group->lock);
        return 0;
    }
    spin_unlock(&block_group->lock);

    inode = lookup_free_space_inode(root, block_group, path);
    if (IS_ERR(inode))
        return 0;

    ret = __btrfs_write_out_cache(root, inode, ctl, block_group, trans,
                      path, block_group->key.objectid);
    if (ret) {
        spin_lock(&block_group->lock);
        block_group->disk_cache_state = BTRFS_DC_ERROR;
        spin_unlock(&block_group->lock);
        ret = 0;
#ifdef DEBUG
        printk(KERN_ERR "btrfs: failed to write free space cache "
               "for block group %llu\n", block_group->key.objectid);
#endif
    }

    iput(inode);
    return ret;
}

static inline unsigned long offset_to_bit(u64 bitmap_start, u32 unit,
                      u64 offset)
{
    BUG_ON(offset < bitmap_start);
    offset -= bitmap_start;
    return (unsigned long)(div_u64(offset, unit));
}

static inline unsigned long bytes_to_bits(u64 bytes, u32 unit)
{
    return (unsigned long)(div_u64(bytes, unit));
}

static inline u64 offset_to_bitmap(struct btrfs_free_space_ctl *ctl,
                   u64 offset)
{
    u64 bitmap_start;
    u64 bytes_per_bitmap;

    bytes_per_bitmap = BITS_PER_BITMAP * ctl->unit;
    bitmap_start = offset - ctl->start;
    bitmap_start = div64_u64(bitmap_start, bytes_per_bitmap);
    bitmap_start *= bytes_per_bitmap;
    bitmap_start += ctl->start;

    return bitmap_start;
}

static int tree_insert_offset(struct rb_root *root, u64 offset,
                  struct rb_node *node, int bitmap)
{
    struct rb_node **p = &root->rb_node;
    struct rb_node *parent = NULL;
    struct btrfs_free_space *info;

    while (*p) {
        parent = *p;
        info = rb_entry(parent, struct btrfs_free_space, offset_index);

        if (offset < info->offset) {
            p = &(*p)->rb_left;
        } else if (offset > info->offset) {
            p = &(*p)->rb_right;
        } else {
            /*
             * we could have a bitmap entry and an extent entry
             * share the same offset.  If this is the case, we want
             * the extent entry to always be found first if we do a
             * linear search through the tree, since we want to have
             * the quickest allocation time, and allocating from an
             * extent is faster than allocating from a bitmap.  So
             * if we're inserting a bitmap and we find an entry at
             * this offset, we want to go right, or after this entry
             * logically.  If we are inserting an extent and we've
             * found a bitmap, we want to go left, or before
             * logically.
             */
            if (bitmap) {
                if (info->bitmap) {
                    WARN_ON_ONCE(1);
                    return -EEXIST;
                }
                p = &(*p)->rb_right;
            } else {
                if (!info->bitmap) {
                    WARN_ON_ONCE(1);
                    return -EEXIST;
                }
                p = &(*p)->rb_left;
            }
        }
    }

    rb_link_node(node, parent, p);
    rb_insert_color(node, root);

    return 0;
}

/*
 * searches the tree for the given offset.
 *
 * fuzzy - If this is set, then we are trying to make an allocation, and we just
 * want a section that has at least bytes size and comes at or after the given
 * offset.
 */
static struct btrfs_free_space *
tree_search_offset(struct btrfs_free_space_ctl *ctl,
           u64 offset, int bitmap_only, int fuzzy)
{
    struct rb_node *n = ctl->free_space_offset.rb_node;
    struct btrfs_free_space *entry, *prev = NULL;

    /* find entry that is closest to the 'offset' */
    while (1) {
        if (!n) {
            entry = NULL;
            break;
        }

        entry = rb_entry(n, struct btrfs_free_space, offset_index);
        prev = entry;

        if (offset < entry->offset)
            n = n->rb_left;
        else if (offset > entry->offset)
            n = n->rb_right;
        else
            break;
    }

    if (bitmap_only) {
        if (!entry)
            return NULL;
        if (entry->bitmap)
            return entry;

        /*
         * bitmap entry and extent entry may share same offset,
         * in that case, bitmap entry comes after extent entry.
         */
        n = rb_next(n);
        if (!n)
            return NULL;
        entry = rb_entry(n, struct btrfs_free_space, offset_index);
        if (entry->offset != offset)
            return NULL;

        WARN_ON(!entry->bitmap);
        return entry;
    } else if (entry) {
        if (entry->bitmap) {
            /*
             * if previous extent entry covers the offset,
             * we should return it instead of the bitmap entry
             */
            n = &entry->offset_index;
            while (1) {
                n = rb_prev(n);
                if (!n)
                    break;
                prev = rb_entry(n, struct btrfs_free_space,
                        offset_index);
                if (!prev->bitmap) {
                    if (prev->offset + prev->bytes > offset)
                        entry = prev;
                    break;
                }
            }
        }
        return entry;
    }

    if (!prev)
        return NULL;

    /* find last entry before the 'offset' */
    entry = prev;
    if (entry->offset > offset) {
        n = rb_prev(&entry->offset_index);
        if (n) {
            entry = rb_entry(n, struct btrfs_free_space,
                    offset_index);
            BUG_ON(entry->offset > offset);
        } else {
            if (fuzzy)
                return entry;
            else
                return NULL;
        }
    }

    if (entry->bitmap) {
        n = &entry->offset_index;
        while (1) {
            n = rb_prev(n);
            if (!n)
                break;
            prev = rb_entry(n, struct btrfs_free_space,
                    offset_index);
            if (!prev->bitmap) {
                if (prev->offset + prev->bytes > offset)
                    return prev;
                break;
            }
        }
        if (entry->offset + BITS_PER_BITMAP * ctl->unit > offset)
            return entry;
    } else if (entry->offset + entry->bytes > offset)
        return entry;

    if (!fuzzy)
        return NULL;

    while (1) {
        if (entry->bitmap) {
            if (entry->offset + BITS_PER_BITMAP *
                ctl->unit > offset)
                break;
        } else {
            if (entry->offset + entry->bytes > offset)
                break;
        }

        n = rb_next(&entry->offset_index);
        if (!n)
            return NULL;
        entry = rb_entry(n, struct btrfs_free_space, offset_index);
    }
    return entry;
}

static inline void
__unlink_free_space(struct btrfs_free_space_ctl *ctl,
            struct btrfs_free_space *info)
{
    rb_erase(&info->offset_index, &ctl->free_space_offset);
    ctl->free_extents--;
}

static void unlink_free_space(struct btrfs_free_space_ctl *ctl,
                  struct btrfs_free_space *info)
{
    __unlink_free_space(ctl, info);
    ctl->free_space -= info->bytes;
}

static int link_free_space(struct btrfs_free_space_ctl *ctl,
               struct btrfs_free_space *info)
{
    int ret = 0;

    BUG_ON(!info->bitmap && !info->bytes);
    ret = tree_insert_offset(&ctl->free_space_offset, info->offset,
                 &info->offset_index, (info->bitmap != NULL));
    if (ret)
        return ret;

    ctl->free_space += info->bytes;
    ctl->free_extents++;
    return ret;
}

static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
{
    struct btrfs_block_group_cache *block_group = ctl->private;
    u64 max_bytes;
    u64 bitmap_bytes;
    u64 extent_bytes;
    u64 size = block_group->key.offset;
    u64 bytes_per_bg = BITS_PER_BITMAP * block_group->sectorsize;
    int max_bitmaps = div64_u64(size + bytes_per_bg - 1, bytes_per_bg);

    BUG_ON(ctl->total_bitmaps > max_bitmaps);

    /*
     * The goal is to keep the total amount of memory used per 1gb of space
     * at or below 32k, so we need to adjust how much memory we allow to be
     * used by extent based free space tracking
     */
    if (size < 1024 * 1024 * 1024)
        max_bytes = MAX_CACHE_BYTES_PER_GIG;
    else
        max_bytes = MAX_CACHE_BYTES_PER_GIG *
            div64_u64(size, 1024 * 1024 * 1024);

    /*
     * we want to account for 1 more bitmap than what we have so we can make
     * sure we don't go over our overall goal of MAX_CACHE_BYTES_PER_GIG as
     * we add more bitmaps.
     */
    bitmap_bytes = (ctl->total_bitmaps + 1) * PAGE_CACHE_SIZE;

    if (bitmap_bytes >= max_bytes) {
        ctl->extents_thresh = 0;
        return;
    }

    /*
     * we want the extent entry threshold to always be at most 1/2 the maxw
     * bytes we can have, or whatever is less than that.
     */
    extent_bytes = max_bytes - bitmap_bytes;
    extent_bytes = min_t(u64, extent_bytes, div64_u64(max_bytes, 2));

    ctl->extents_thresh =
        div64_u64(extent_bytes, (sizeof(struct btrfs_free_space)));
}

static inline void __bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
                       struct btrfs_free_space *info,
                       u64 offset, u64 bytes)
{
    unsigned long start, count;

    start = offset_to_bit(info->offset, ctl->unit, offset);
    count = bytes_to_bits(bytes, ctl->unit);
    BUG_ON(start + count > BITS_PER_BITMAP);

    bitmap_clear(info->bitmap, start, count);

    info->bytes -= bytes;
}

static void bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
                  struct btrfs_free_space *info, u64 offset,
                  u64 bytes)
{
    __bitmap_clear_bits(ctl, info, offset, bytes);
    ctl->free_space -= bytes;
}

static void bitmap_set_bits(struct btrfs_free_space_ctl *ctl,
                struct btrfs_free_space *info, u64 offset,
                u64 bytes)
{
    unsigned long start, count;

    start = offset_to_bit(info->offset, ctl->unit, offset);
    count = bytes_to_bits(bytes, ctl->unit);
    BUG_ON(start + count > BITS_PER_BITMAP);

    bitmap_set(info->bitmap, start, count);

    info->bytes += bytes;
    ctl->free_space += bytes;
}

static int search_bitmap(struct btrfs_free_space_ctl *ctl,
             struct btrfs_free_space *bitmap_info, u64 *offset,
             u64 *bytes)
{
    unsigned long found_bits = 0;
    unsigned long bits, i;
    unsigned long next_zero;

    i = offset_to_bit(bitmap_info->offset, ctl->unit,
              max_t(u64, *offset, bitmap_info->offset));
    bits = bytes_to_bits(*bytes, ctl->unit);

    for_each_set_bit_from(i, bitmap_info->bitmap, BITS_PER_BITMAP) {
        next_zero = find_next_zero_bit(bitmap_info->bitmap,
                           BITS_PER_BITMAP, i);
        if ((next_zero - i) >= bits) {
            found_bits = next_zero - i;
            break;
        }
        i = next_zero;
    }

    if (found_bits) {
        *offset = (u64)(i * ctl->unit) + bitmap_info->offset;
        *bytes = (u64)(found_bits) * ctl->unit;
        return 0;
    }

    return -1;
}

static struct btrfs_free_space *
find_free_space(struct btrfs_free_space_ctl *ctl, u64 *offset, u64 *bytes)
{
    struct btrfs_free_space *entry;
    struct rb_node *node;
    int ret;

    if (!ctl->free_space_offset.rb_node)
        return NULL;

    entry = tree_search_offset(ctl, offset_to_bitmap(ctl, *offset), 0, 1);
    if (!entry)
        return NULL;

    for (node = &entry->offset_index; node; node = rb_next(node)) {
        entry = rb_entry(node, struct btrfs_free_space, offset_index);
        if (entry->bytes < *bytes)
            continue;

        if (entry->bitmap) {
            ret = search_bitmap(ctl, entry, offset, bytes);
            if (!ret)
                return entry;
            continue;
        }

        *offset = entry->offset;
        *bytes = entry->bytes;
        return entry;
    }

    return NULL;
}

static void add_new_bitmap(struct btrfs_free_space_ctl *ctl,
               struct btrfs_free_space *info, u64 offset)
{
    info->offset = offset_to_bitmap(ctl, offset);
    info->bytes = 0;
    INIT_LIST_HEAD(&info->list);
    link_free_space(ctl, info);
    ctl->total_bitmaps++;

    ctl->op->recalc_thresholds(ctl);
}

static void free_bitmap(struct btrfs_free_space_ctl *ctl,
            struct btrfs_free_space *bitmap_info)
{
    unlink_free_space(ctl, bitmap_info);
    kfree(bitmap_info->bitmap);
    kmem_cache_free(btrfs_free_space_cachep, bitmap_info);
    ctl->total_bitmaps--;
    ctl->op->recalc_thresholds(ctl);
}

static noinline int remove_from_bitmap(struct btrfs_free_space_ctl *ctl,
                  struct btrfs_free_space *bitmap_info,
                  u64 *offset, u64 *bytes)
{
    u64 end;
    u64 search_start, search_bytes;
    int ret;

again:
    end = bitmap_info->offset + (u64)(BITS_PER_BITMAP * ctl->unit) - 1;

    /*
     * We need to search for bits in this bitmap.  We could only cover some
     * of the extent in this bitmap thanks to how we add space, so we need
     * to search for as much as it as we can and clear that amount, and then
     * go searching for the next bit.
     */
    search_start = *offset;
    search_bytes = ctl->unit;
    search_bytes = min(search_bytes, end - search_start + 1);
    ret = search_bitmap(ctl, bitmap_info, &search_start, &search_bytes);
    BUG_ON(ret < 0 || search_start != *offset);

    /* We may have found more bits than what we need */
    search_bytes = min(search_bytes, *bytes);

    /* Cannot clear past the end of the bitmap */
    search_bytes = min(search_bytes, end - search_start + 1);

    bitmap_clear_bits(ctl, bitmap_info, search_start, search_bytes);
    *offset += search_bytes;
    *bytes -= search_bytes;

    if (*bytes) {
        struct rb_node *next = rb_next(&bitmap_info->offset_index);
        if (!bitmap_info->bytes)
            free_bitmap(ctl, bitmap_info);

        /*
         * no entry after this bitmap, but we still have bytes to
         * remove, so something has gone wrong.
         */
        if (!next)
            return -EINVAL;

        bitmap_info = rb_entry(next, struct btrfs_free_space,
                       offset_index);

        /*
         * if the next entry isn't a bitmap we need to return to let the
         * extent stuff do its work.
         */
        if (!bitmap_info->bitmap)
            return -EAGAIN;

        /*
         * Ok the next item is a bitmap, but it may not actually hold
         * the information for the rest of this free space stuff, so
         * look for it, and if we don't find it return so we can try
         * everything over again.
         */
        search_start = *offset;
        search_bytes = ctl->unit;
        ret = search_bitmap(ctl, bitmap_info, &search_start,
                    &search_bytes);
        if (ret < 0 || search_start != *offset)
            return -EAGAIN;

        goto again;
    } else if (!bitmap_info->bytes)
        free_bitmap(ctl, bitmap_info);

    return 0;
}

static u64 add_bytes_to_bitmap(struct btrfs_free_space_ctl *ctl,
                   struct btrfs_free_space *info, u64 offset,
                   u64 bytes)
{
    u64 bytes_to_set = 0;
    u64 end;

    end = info->offset + (u64)(BITS_PER_BITMAP * ctl->unit);

    bytes_to_set = min(end - offset, bytes);

    bitmap_set_bits(ctl, info, offset, bytes_to_set);

    return bytes_to_set;

}

static bool use_bitmap(struct btrfs_free_space_ctl *ctl,
              struct btrfs_free_space *info)
{
    struct btrfs_block_group_cache *block_group = ctl->private;

    /*
     * If we are below the extents threshold then we can add this as an
     * extent, and don't have to deal with the bitmap
     */
    if (ctl->free_extents < ctl->extents_thresh) {
        /*
         * If this block group has some small extents we don't want to
         * use up all of our free slots in the cache with them, we want
         * to reserve them to larger extents, however if we have plent
         * of cache left then go ahead an dadd them, no sense in adding
         * the overhead of a bitmap if we don't have to.
         */
        if (info->bytes <= block_group->sectorsize * 4) {
            if (ctl->free_extents * 2 <= ctl->extents_thresh)
                return false;
        } else {
            return false;
        }
    }

    /*
     * some block groups are so tiny they can't be enveloped by a bitmap, so
     * don't even bother to create a bitmap for this
     */
    if (BITS_PER_BITMAP * block_group->sectorsize >
        block_group->key.offset)
        return false;

    return true;
}

static struct btrfs_free_space_op free_space_op = {
    .recalc_thresholds  = recalculate_thresholds,
    .use_bitmap     = use_bitmap,
};

static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl,
                  struct btrfs_free_space *info)
{
    struct btrfs_free_space *bitmap_info;
    struct btrfs_block_group_cache *block_group = NULL;
    int added = 0;
    u64 bytes, offset, bytes_added;
    int ret;

    bytes = info->bytes;
    offset = info->offset;

    if (!ctl->op->use_bitmap(ctl, info))
        return 0;

    if (ctl->op == &free_space_op)
        block_group = ctl->private;
again:
    /*
     * Since we link bitmaps right into the cluster we need to see if we
     * have a cluster here, and if so and it has our bitmap we need to add
     * the free space to that bitmap.
     */
    if (block_group && !list_empty(&block_group->cluster_list)) {
        struct btrfs_free_cluster *cluster;
        struct rb_node *node;
        struct btrfs_free_space *entry;

        cluster = list_entry(block_group->cluster_list.next,
                     struct btrfs_free_cluster,
                     block_group_list);
        spin_lock(&cluster->lock);
        node = rb_first(&cluster->root);
        if (!node) {
            spin_unlock(&cluster->lock);
            goto no_cluster_bitmap;
        }

        entry = rb_entry(node, struct btrfs_free_space, offset_index);
        if (!entry->bitmap) {
            spin_unlock(&cluster->lock);
            goto no_cluster_bitmap;
        }

        if (entry->offset == offset_to_bitmap(ctl, offset)) {
            bytes_added = add_bytes_to_bitmap(ctl, entry,
                              offset, bytes);
            bytes -= bytes_added;
            offset += bytes_added;
        }
        spin_unlock(&cluster->lock);
        if (!bytes) {
            ret = 1;
            goto out;
        }
    }

no_cluster_bitmap:
    bitmap_info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                     1, 0);
    if (!bitmap_info) {
        BUG_ON(added);
        goto new_bitmap;
    }

    bytes_added = add_bytes_to_bitmap(ctl, bitmap_info, offset, bytes);
    bytes -= bytes_added;
    offset += bytes_added;
    added = 0;

    if (!bytes) {
        ret = 1;
        goto out;
    } else
        goto again;

new_bitmap:
    if (info && info->bitmap) {
        add_new_bitmap(ctl, info, offset);
        added = 1;
        info = NULL;
        goto again;
    } else {
        spin_unlock(&ctl->tree_lock);

        /* no pre-allocated info, allocate a new one */
        if (!info) {
            info = kmem_cache_zalloc(btrfs_free_space_cachep,
                         GFP_NOFS);
            if (!info) {
                spin_lock(&ctl->tree_lock);
                ret = -ENOMEM;
                goto out;
            }
        }

        /* allocate the bitmap */
        info->bitmap = kzalloc(PAGE_CACHE_SIZE, GFP_NOFS);
        spin_lock(&ctl->tree_lock);
        if (!info->bitmap) {
            ret = -ENOMEM;
            goto out;
        }
        goto again;
    }

out:
    if (info) {
        if (info->bitmap)
            kfree(info->bitmap);
        kmem_cache_free(btrfs_free_space_cachep, info);
    }

    return ret;
}

static bool try_merge_free_space(struct btrfs_free_space_ctl *ctl,
              struct btrfs_free_space *info, bool update_stat)
{
    struct btrfs_free_space *left_info;
    struct btrfs_free_space *right_info;
    bool merged = false;
    u64 offset = info->offset;
    u64 bytes = info->bytes;

    /*
     * first we want to see if there is free space adjacent to the range we
     * are adding, if there is remove that struct and add a new one to
     * cover the entire range
     */
    right_info = tree_search_offset(ctl, offset + bytes, 0, 0);
    if (right_info && rb_prev(&right_info->offset_index))
        left_info = rb_entry(rb_prev(&right_info->offset_index),
                     struct btrfs_free_space, offset_index);
    else
        left_info = tree_search_offset(ctl, offset - 1, 0, 0);

    if (right_info && !right_info->bitmap) {
        if (update_stat)
            unlink_free_space(ctl, right_info);
        else
            __unlink_free_space(ctl, right_info);
        info->bytes += right_info->bytes;
        kmem_cache_free(btrfs_free_space_cachep, right_info);
        merged = true;
    }

    if (left_info && !left_info->bitmap &&
        left_info->offset + left_info->bytes == offset) {
        if (update_stat)
            unlink_free_space(ctl, left_info);
        else
            __unlink_free_space(ctl, left_info);
        info->offset = left_info->offset;
        info->bytes += left_info->bytes;
        kmem_cache_free(btrfs_free_space_cachep, left_info);
        merged = true;
    }

    return merged;
}

int __btrfs_add_free_space(struct btrfs_free_space_ctl *ctl,
               u64 offset, u64 bytes)
{
    struct btrfs_free_space *info;
    int ret = 0;

    info = kmem_cache_zalloc(btrfs_free_space_cachep, GFP_NOFS);
    if (!info)
        return -ENOMEM;

    info->offset = offset;
    info->bytes = bytes;

    spin_lock(&ctl->tree_lock);

    if (try_merge_free_space(ctl, info, true))
        goto link;

    /*
     * There was no extent directly to the left or right of this new
     * extent then we know we're going to have to allocate a new extent, so
     * before we do that see if we need to drop this into a bitmap
     */
    ret = insert_into_bitmap(ctl, info);
    if (ret < 0) {
        goto out;
    } else if (ret) {
        ret = 0;
        goto out;
    }
link:
    ret = link_free_space(ctl, info);
    if (ret)
        kmem_cache_free(btrfs_free_space_cachep, info);
out:
    spin_unlock(&ctl->tree_lock);

    if (ret) {
        printk(KERN_CRIT "btrfs: unable to add free space :%d\n", ret);
        BUG_ON(ret == -EEXIST);
    }

    return ret;
}

int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
                u64 offset, u64 bytes)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *info;
    int ret = 0;

    spin_lock(&ctl->tree_lock);

again:
    if (!bytes)
        goto out_lock;

    info = tree_search_offset(ctl, offset, 0, 0);
    if (!info) {
        /*
         * oops didn't find an extent that matched the space we wanted
         * to remove, look for a bitmap instead
         */
        info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                      1, 0);
        if (!info) {
            /* the tree logging code might be calling us before we
             * have fully loaded the free space rbtree for this
             * block group.  So it is possible the entry won't
             * be in the rbtree yet at all.  The caching code
             * will make sure not to put it in the rbtree if
             * the logging code has pinned it.
             */
            goto out_lock;
        }
    }

    if (!info->bitmap) {
        unlink_free_space(ctl, info);
        if (offset == info->offset) {
            u64 to_free = min(bytes, info->bytes);

            info->bytes -= to_free;
            info->offset += to_free;
            if (info->bytes) {
                ret = link_free_space(ctl, info);
                WARN_ON(ret);
            } else {
                kmem_cache_free(btrfs_free_space_cachep, info);
            }

            offset += to_free;
            bytes -= to_free;
            goto again;
        } else {
            u64 old_end = info->bytes + info->offset;

            info->bytes = offset - info->offset;
            ret = link_free_space(ctl, info);
            WARN_ON(ret);
            if (ret)
                goto out_lock;

            /* Not enough bytes in this entry to satisfy us */
            if (old_end < offset + bytes) {
                bytes -= old_end - offset;
                offset = old_end;
                goto again;
            } else if (old_end == offset + bytes) {
                /* all done */
                goto out_lock;
            }
            spin_unlock(&ctl->tree_lock);

            ret = btrfs_add_free_space(block_group, offset + bytes,
                           old_end - (offset + bytes));
            WARN_ON(ret);
            goto out;
        }
    }

    ret = remove_from_bitmap(ctl, info, &offset, &bytes);
    if (ret == -EAGAIN)
        goto again;
    BUG_ON(ret); /* logic error */
out_lock:
    spin_unlock(&ctl->tree_lock);
out:
    return ret;
}

void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
               u64 bytes)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *info;
    struct rb_node *n;
    int count = 0;

    for (n = rb_first(&ctl->free_space_offset); n; n = rb_next(n)) {
        info = rb_entry(n, struct btrfs_free_space, offset_index);
        if (info->bytes >= bytes && !block_group->ro)
            count++;
        printk(KERN_CRIT "entry offset %llu, bytes %llu, bitmap %s\n",
               (unsigned long long)info->offset,
               (unsigned long long)info->bytes,
               (info->bitmap) ? "yes" : "no");
    }
    printk(KERN_INFO "block group has cluster?: %s\n",
           list_empty(&block_group->cluster_list) ? "no" : "yes");
    printk(KERN_INFO "%d blocks of free space at or bigger than bytes is"
           "\n", count);
}

void btrfs_init_free_space_ctl(struct btrfs_block_group_cache *block_group)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;

    spin_lock_init(&ctl->tree_lock);
    ctl->unit = block_group->sectorsize;
    ctl->start = block_group->key.objectid;
    ctl->private = block_group;
    ctl->op = &free_space_op;

    /*
     * we only want to have 32k of ram per block group for keeping
     * track of free space, and if we pass 1/2 of that we want to
     * start converting things over to using bitmaps
     */
    ctl->extents_thresh = ((1024 * 32) / 2) /
                sizeof(struct btrfs_free_space);
}

/*
 * for a given cluster, put all of its extents back into the free
 * space cache.  If the block group passed doesn't match the block group
 * pointed to by the cluster, someone else raced in and freed the
 * cluster already.  In that case, we just return without changing anything
 */
static int
__btrfs_return_cluster_to_free_space(
                 struct btrfs_block_group_cache *block_group,
                 struct btrfs_free_cluster *cluster)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *entry;
    struct rb_node *node;

    spin_lock(&cluster->lock);
    if (cluster->block_group != block_group)
        goto out;

    cluster->block_group = NULL;
    cluster->window_start = 0;
    list_del_init(&cluster->block_group_list);

    node = rb_first(&cluster->root);
    while (node) {
        bool bitmap;

        entry = rb_entry(node, struct btrfs_free_space, offset_index);
        node = rb_next(&entry->offset_index);
        rb_erase(&entry->offset_index, &cluster->root);

        bitmap = (entry->bitmap != NULL);
        if (!bitmap)
            try_merge_free_space(ctl, entry, false);
        tree_insert_offset(&ctl->free_space_offset,
                   entry->offset, &entry->offset_index, bitmap);
    }
    cluster->root = RB_ROOT;

out:
    spin_unlock(&cluster->lock);
    btrfs_put_block_group(block_group);
    return 0;
}

void __btrfs_remove_free_space_cache_locked(struct btrfs_free_space_ctl *ctl)
{
    struct btrfs_free_space *info;
    struct rb_node *node;

    while ((node = rb_last(&ctl->free_space_offset)) != NULL) {
        info = rb_entry(node, struct btrfs_free_space, offset_index);
        if (!info->bitmap) {
            unlink_free_space(ctl, info);
            kmem_cache_free(btrfs_free_space_cachep, info);
        } else {
            free_bitmap(ctl, info);
        }
        if (need_resched()) {
            spin_unlock(&ctl->tree_lock);
            cond_resched();
            spin_lock(&ctl->tree_lock);
        }
    }
}

void __btrfs_remove_free_space_cache(struct btrfs_free_space_ctl *ctl)
{
    spin_lock(&ctl->tree_lock);
    __btrfs_remove_free_space_cache_locked(ctl);
    spin_unlock(&ctl->tree_lock);
}

void btrfs_remove_free_space_cache(struct btrfs_block_group_cache *block_group)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_cluster *cluster;
    struct list_head *head;

    spin_lock(&ctl->tree_lock);
    while ((head = block_group->cluster_list.next) !=
           &block_group->cluster_list) {
        cluster = list_entry(head, struct btrfs_free_cluster,
                     block_group_list);

        WARN_ON(cluster->block_group != block_group);
        __btrfs_return_cluster_to_free_space(block_group, cluster);
        if (need_resched()) {
            spin_unlock(&ctl->tree_lock);
            cond_resched();
            spin_lock(&ctl->tree_lock);
        }
    }
    __btrfs_remove_free_space_cache_locked(ctl);
    spin_unlock(&ctl->tree_lock);

}

u64 btrfs_find_space_for_alloc(struct btrfs_block_group_cache *block_group,
                   u64 offset, u64 bytes, u64 empty_size)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *entry = NULL;
    u64 bytes_search = bytes + empty_size;
    u64 ret = 0;

    spin_lock(&ctl->tree_lock);
    entry = find_free_space(ctl, &offset, &bytes_search);
    if (!entry)
        goto out;

    ret = offset;
    if (entry->bitmap) {
        bitmap_clear_bits(ctl, entry, offset, bytes);
        if (!entry->bytes)
            free_bitmap(ctl, entry);
    } else {
        unlink_free_space(ctl, entry);
        entry->offset += bytes;
        entry->bytes -= bytes;
        if (!entry->bytes)
            kmem_cache_free(btrfs_free_space_cachep, entry);
        else
            link_free_space(ctl, entry);
    }

out:
    spin_unlock(&ctl->tree_lock);

    return ret;
}

/*
 * given a cluster, put all of its extents back into the free space
 * cache.  If a block group is passed, this function will only free
 * a cluster that belongs to the passed block group.
 *
 * Otherwise, it'll get a reference on the block group pointed to by the
 * cluster and remove the cluster from it.
 */
int btrfs_return_cluster_to_free_space(
                   struct btrfs_block_group_cache *block_group,
                   struct btrfs_free_cluster *cluster)
{
    struct btrfs_free_space_ctl *ctl;
    int ret;

    /* first, get a safe pointer to the block group */
    spin_lock(&cluster->lock);
    if (!block_group) {
        block_group = cluster->block_group;
        if (!block_group) {
            spin_unlock(&cluster->lock);
            return 0;
        }
    } else if (cluster->block_group != block_group) {
        /* someone else has already freed it don't redo their work */
        spin_unlock(&cluster->lock);
        return 0;
    }
    atomic_inc(&block_group->count);
    spin_unlock(&cluster->lock);

    ctl = block_group->free_space_ctl;

    /* now return any extents the cluster had on it */
    spin_lock(&ctl->tree_lock);
    ret = __btrfs_return_cluster_to_free_space(block_group, cluster);
    spin_unlock(&ctl->tree_lock);

    /* finally drop our ref */
    btrfs_put_block_group(block_group);
    return ret;
}

static u64 btrfs_alloc_from_bitmap(struct btrfs_block_group_cache *block_group,
                   struct btrfs_free_cluster *cluster,
                   struct btrfs_free_space *entry,
                   u64 bytes, u64 min_start)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    int err;
    u64 search_start = cluster->window_start;
    u64 search_bytes = bytes;
    u64 ret = 0;

    search_start = min_start;
    search_bytes = bytes;

    err = search_bitmap(ctl, entry, &search_start, &search_bytes);
    if (err)
        return 0;

    ret = search_start;
    __bitmap_clear_bits(ctl, entry, ret, bytes);

    return ret;
}

/*
 * given a cluster, try to allocate 'bytes' from it, returns 0
 * if it couldn't find anything suitably large, or a logical disk offset
 * if things worked out
 */
u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group,
                 struct btrfs_free_cluster *cluster, u64 bytes,
                 u64 min_start)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *entry = NULL;
    struct rb_node *node;
    u64 ret = 0;

    spin_lock(&cluster->lock);
    if (bytes > cluster->max_size)
        goto out;

    if (cluster->block_group != block_group)
        goto out;

    node = rb_first(&cluster->root);
    if (!node)
        goto out;

    entry = rb_entry(node, struct btrfs_free_space, offset_index);
    while(1) {
        if (entry->bytes < bytes ||
            (!entry->bitmap && entry->offset < min_start)) {
            node = rb_next(&entry->offset_index);
            if (!node)
                break;
            entry = rb_entry(node, struct btrfs_free_space,
                     offset_index);
            continue;
        }

        if (entry->bitmap) {
            ret = btrfs_alloc_from_bitmap(block_group,
                              cluster, entry, bytes,
                              cluster->window_start);
            if (ret == 0) {
                node = rb_next(&entry->offset_index);
                if (!node)
                    break;
                entry = rb_entry(node, struct btrfs_free_space,
                         offset_index);
                continue;
            }
            cluster->window_start += bytes;
        } else {
            ret = entry->offset;

            entry->offset += bytes;
            entry->bytes -= bytes;
        }

        if (entry->bytes == 0)
            rb_erase(&entry->offset_index, &cluster->root);
        break;
    }
out:
    spin_unlock(&cluster->lock);

    if (!ret)
        return 0;

    spin_lock(&ctl->tree_lock);

    ctl->free_space -= bytes;
    if (entry->bytes == 0) {
        ctl->free_extents--;
        if (entry->bitmap) {
            kfree(entry->bitmap);
            ctl->total_bitmaps--;
            ctl->op->recalc_thresholds(ctl);
        }
        kmem_cache_free(btrfs_free_space_cachep, entry);
    }

    spin_unlock(&ctl->tree_lock);

    return ret;
}

static int btrfs_bitmap_cluster(struct btrfs_block_group_cache *block_group,
                struct btrfs_free_space *entry,
                struct btrfs_free_cluster *cluster,
                u64 offset, u64 bytes,
                u64 cont1_bytes, u64 min_bytes)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    unsigned long next_zero;
    unsigned long i;
    unsigned long want_bits;
    unsigned long min_bits;
    unsigned long found_bits;
    unsigned long start = 0;
    unsigned long total_found = 0;
    int ret;

    i = offset_to_bit(entry->offset, block_group->sectorsize,
              max_t(u64, offset, entry->offset));
    want_bits = bytes_to_bits(bytes, block_group->sectorsize);
    min_bits = bytes_to_bits(min_bytes, block_group->sectorsize);

again:
    found_bits = 0;
    for_each_set_bit_from(i, entry->bitmap, BITS_PER_BITMAP) {
        next_zero = find_next_zero_bit(entry->bitmap,
                           BITS_PER_BITMAP, i);
        if (next_zero - i >= min_bits) {
            found_bits = next_zero - i;
            break;
        }
        i = next_zero;
    }

    if (!found_bits)
        return -ENOSPC;

    if (!total_found) {
        start = i;
        cluster->max_size = 0;
    }

    total_found += found_bits;

    if (cluster->max_size < found_bits * block_group->sectorsize)
        cluster->max_size = found_bits * block_group->sectorsize;

    if (total_found < want_bits || cluster->max_size < cont1_bytes) {
        i = next_zero + 1;
        goto again;
    }

    cluster->window_start = start * block_group->sectorsize +
        entry->offset;
    rb_erase(&entry->offset_index, &ctl->free_space_offset);
    ret = tree_insert_offset(&cluster->root, entry->offset,
                 &entry->offset_index, 1);
    BUG_ON(ret); /* -EEXIST; Logic error */

    trace_btrfs_setup_cluster(block_group, cluster,
                  total_found * block_group->sectorsize, 1);
    return 0;
}

/*
 * This searches the block group for just extents to fill the cluster with.
 * Try to find a cluster with at least bytes total bytes, at least one
 * extent of cont1_bytes, and other clusters of at least min_bytes.
 */
static noinline int
setup_cluster_no_bitmap(struct btrfs_block_group_cache *block_group,
            struct btrfs_free_cluster *cluster,
            struct list_head *bitmaps, u64 offset, u64 bytes,
            u64 cont1_bytes, u64 min_bytes)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *first = NULL;
    struct btrfs_free_space *entry = NULL;
    struct btrfs_free_space *last;
    struct rb_node *node;
    u64 window_start;
    u64 window_free;
    u64 max_extent;
    u64 total_size = 0;

    entry = tree_search_offset(ctl, offset, 0, 1);
    if (!entry)
        return -ENOSPC;

    /*
     * We don't want bitmaps, so just move along until we find a normal
     * extent entry.
     */
    while (entry->bitmap || entry->bytes < min_bytes) {
        if (entry->bitmap && list_empty(&entry->list))
            list_add_tail(&entry->list, bitmaps);
        node = rb_next(&entry->offset_index);
        if (!node)
            return -ENOSPC;
        entry = rb_entry(node, struct btrfs_free_space, offset_index);
    }

    window_start = entry->offset;
    window_free = entry->bytes;
    max_extent = entry->bytes;
    first = entry;
    last = entry;

    for (node = rb_next(&entry->offset_index); node;
         node = rb_next(&entry->offset_index)) {
        entry = rb_entry(node, struct btrfs_free_space, offset_index);

        if (entry->bitmap) {
            if (list_empty(&entry->list))
                list_add_tail(&entry->list, bitmaps);
            continue;
        }

        if (entry->bytes < min_bytes)
            continue;

        last = entry;
        window_free += entry->bytes;
        if (entry->bytes > max_extent)
            max_extent = entry->bytes;
    }

    if (window_free < bytes || max_extent < cont1_bytes)
        return -ENOSPC;

    cluster->window_start = first->offset;

    node = &first->offset_index;

    /*
     * now we've found our entries, pull them out of the free space
     * cache and put them into the cluster rbtree
     */
    do {
        int ret;

        entry = rb_entry(node, struct btrfs_free_space, offset_index);
        node = rb_next(&entry->offset_index);
        if (entry->bitmap || entry->bytes < min_bytes)
            continue;

        rb_erase(&entry->offset_index, &ctl->free_space_offset);
        ret = tree_insert_offset(&cluster->root, entry->offset,
                     &entry->offset_index, 0);
        total_size += entry->bytes;
        BUG_ON(ret); /* -EEXIST; Logic error */
    } while (node && entry != last);

    cluster->max_size = max_extent;
    trace_btrfs_setup_cluster(block_group, cluster, total_size, 0);
    return 0;
}

/*
 * This specifically looks for bitmaps that may work in the cluster, we assume
 * that we have already failed to find extents that will work.
 */
static noinline int
setup_cluster_bitmap(struct btrfs_block_group_cache *block_group,
             struct btrfs_free_cluster *cluster,
             struct list_head *bitmaps, u64 offset, u64 bytes,
             u64 cont1_bytes, u64 min_bytes)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *entry;
    int ret = -ENOSPC;
    u64 bitmap_offset = offset_to_bitmap(ctl, offset);

    if (ctl->total_bitmaps == 0)
        return -ENOSPC;

    /*
     * The bitmap that covers offset won't be in the list unless offset
     * is just its start offset.
     */
    entry = list_first_entry(bitmaps, struct btrfs_free_space, list);
    if (entry->offset != bitmap_offset) {
        entry = tree_search_offset(ctl, bitmap_offset, 1, 0);
        if (entry && list_empty(&entry->list))
            list_add(&entry->list, bitmaps);
    }

    list_for_each_entry(entry, bitmaps, list) {
        if (entry->bytes < bytes)
            continue;
        ret = btrfs_bitmap_cluster(block_group, entry, cluster, offset,
                       bytes, cont1_bytes, min_bytes);
        if (!ret)
            return 0;
    }

    /*
     * The bitmaps list has all the bitmaps that record free space
     * starting after offset, so no more search is required.
     */
    return -ENOSPC;
}

/*
 * here we try to find a cluster of blocks in a block group.  The goal
 * is to find at least bytes+empty_size.
 * We might not find them all in one contiguous area.
 *
 * returns zero and sets up cluster if things worked out, otherwise
 * it returns -enospc
 */
int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_block_group_cache *block_group,
                 struct btrfs_free_cluster *cluster,
                 u64 offset, u64 bytes, u64 empty_size)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *entry, *tmp;
    LIST_HEAD(bitmaps);
    u64 min_bytes;
    u64 cont1_bytes;
    int ret;

    /*
     * Choose the minimum extent size we'll require for this
     * cluster.  For SSD_SPREAD, don't allow any fragmentation.
     * For metadata, allow allocates with smaller extents.  For
     * data, keep it dense.
     */
    if (btrfs_test_opt(root, SSD_SPREAD)) {
        cont1_bytes = min_bytes = bytes + empty_size;
    } else if (block_group->flags & BTRFS_BLOCK_GROUP_METADATA) {
        cont1_bytes = bytes;
        min_bytes = block_group->sectorsize;
    } else {
        cont1_bytes = max(bytes, (bytes + empty_size) >> 2);
        min_bytes = block_group->sectorsize;
    }

    spin_lock(&ctl->tree_lock);

    /*
     * If we know we don't have enough space to make a cluster don't even
     * bother doing all the work to try and find one.
     */
    if (ctl->free_space < bytes) {
        spin_unlock(&ctl->tree_lock);
        return -ENOSPC;
    }

    spin_lock(&cluster->lock);

    /* someone already found a cluster, hooray */
    if (cluster->block_group) {
        ret = 0;
        goto out;
    }

    trace_btrfs_find_cluster(block_group, offset, bytes, empty_size,
                 min_bytes);

    INIT_LIST_HEAD(&bitmaps);
    ret = setup_cluster_no_bitmap(block_group, cluster, &bitmaps, offset,
                      bytes + empty_size,
                      cont1_bytes, min_bytes);
    if (ret)
        ret = setup_cluster_bitmap(block_group, cluster, &bitmaps,
                       offset, bytes + empty_size,
                       cont1_bytes, min_bytes);

    /* Clear our temporary list */
    list_for_each_entry_safe(entry, tmp, &bitmaps, list)
        list_del_init(&entry->list);

    if (!ret) {
        atomic_inc(&block_group->count);
        list_add_tail(&cluster->block_group_list,
                  &block_group->cluster_list);
        cluster->block_group = block_group;
    } else {
        trace_btrfs_failed_cluster_setup(block_group);
    }
out:
    spin_unlock(&cluster->lock);
    spin_unlock(&ctl->tree_lock);

    return ret;
}

/*
 * simple code to zero out a cluster
 */
void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
{
    spin_lock_init(&cluster->lock);
    spin_lock_init(&cluster->refill_lock);
    cluster->root = RB_ROOT;
    cluster->max_size = 0;
    INIT_LIST_HEAD(&cluster->block_group_list);
    cluster->block_group = NULL;
}

static int do_trimming(struct btrfs_block_group_cache *block_group,
               u64 *total_trimmed, u64 start, u64 bytes,
               u64 reserved_start, u64 reserved_bytes)
{
    struct btrfs_space_info *space_info = block_group->space_info;
    struct btrfs_fs_info *fs_info = block_group->fs_info;
    int ret;
    int update = 0;
    u64 trimmed = 0;

    spin_lock(&space_info->lock);
    spin_lock(&block_group->lock);
    if (!block_group->ro) {
        block_group->reserved += reserved_bytes;
        space_info->bytes_reserved += reserved_bytes;
        update = 1;
    }
    spin_unlock(&block_group->lock);
    spin_unlock(&space_info->lock);

    ret = btrfs_error_discard_extent(fs_info->extent_root,
                     start, bytes, &trimmed);
    if (!ret)
        *total_trimmed += trimmed;

    btrfs_add_free_space(block_group, reserved_start, reserved_bytes);

    if (update) {
        spin_lock(&space_info->lock);
        spin_lock(&block_group->lock);
        if (block_group->ro)
            space_info->bytes_readonly += reserved_bytes;
        block_group->reserved -= reserved_bytes;
        space_info->bytes_reserved -= reserved_bytes;
        spin_unlock(&space_info->lock);
        spin_unlock(&block_group->lock);
    }

    return ret;
}

static int trim_no_bitmap(struct btrfs_block_group_cache *block_group,
              u64 *total_trimmed, u64 start, u64 end, u64 minlen)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *entry;
    struct rb_node *node;
    int ret = 0;
    u64 extent_start;
    u64 extent_bytes;
    u64 bytes;

    while (start < end) {
        spin_lock(&ctl->tree_lock);

        if (ctl->free_space < minlen) {
            spin_unlock(&ctl->tree_lock);
            break;
        }

        entry = tree_search_offset(ctl, start, 0, 1);
        if (!entry) {
            spin_unlock(&ctl->tree_lock);
            break;
        }

        /* skip bitmaps */
        while (entry->bitmap) {
            node = rb_next(&entry->offset_index);
            if (!node) {
                spin_unlock(&ctl->tree_lock);
                goto out;
            }
            entry = rb_entry(node, struct btrfs_free_space,
                     offset_index);
        }

        if (entry->offset >= end) {
            spin_unlock(&ctl->tree_lock);
            break;
        }

        extent_start = entry->offset;
        extent_bytes = entry->bytes;
        start = max(start, extent_start);
        bytes = min(extent_start + extent_bytes, end) - start;
        if (bytes < minlen) {
            spin_unlock(&ctl->tree_lock);
            goto next;
        }

        unlink_free_space(ctl, entry);
        kmem_cache_free(btrfs_free_space_cachep, entry);

        spin_unlock(&ctl->tree_lock);

        ret = do_trimming(block_group, total_trimmed, start, bytes,
                  extent_start, extent_bytes);
        if (ret)
            break;
next:
        start += bytes;

        if (fatal_signal_pending(current)) {
            ret = -ERESTARTSYS;
            break;
        }

        cond_resched();
    }
out:
    return ret;
}

static int trim_bitmaps(struct btrfs_block_group_cache *block_group,
            u64 *total_trimmed, u64 start, u64 end, u64 minlen)
{
    struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
    struct btrfs_free_space *entry;
    int ret = 0;
    int ret2;
    u64 bytes;
    u64 offset = offset_to_bitmap(ctl, start);

    while (offset < end) {
        bool next_bitmap = false;

        spin_lock(&ctl->tree_lock);

        if (ctl->free_space < minlen) {
            spin_unlock(&ctl->tree_lock);
            break;
        }

        entry = tree_search_offset(ctl, offset, 1, 0);
        if (!entry) {
            spin_unlock(&ctl->tree_lock);
            next_bitmap = true;
            goto next;
        }

        bytes = minlen;
        ret2 = search_bitmap(ctl, entry, &start, &bytes);
        if (ret2 || start >= end) {
            spin_unlock(&ctl->tree_lock);
            next_bitmap = true;
            goto next;
        }

        bytes = min(bytes, end - start);
        if (bytes < minlen) {
            spin_unlock(&ctl->tree_lock);
            goto next;
        }

        bitmap_clear_bits(ctl, entry, start, bytes);
        if (entry->bytes == 0)
            free_bitmap(ctl, entry);

        spin_unlock(&ctl->tree_lock);

        ret = do_trimming(block_group, total_trimmed, start, bytes,
                  start, bytes);
        if (ret)
            break;
next:
        if (next_bitmap) {
            offset += BITS_PER_BITMAP * ctl->unit;
        } else {
            start += bytes;
            if (start >= offset + BITS_PER_BITMAP * ctl->unit)
                offset += BITS_PER_BITMAP * ctl->unit;
        }

        if (fatal_signal_pending(current)) {
            ret = -ERESTARTSYS;
            break;
        }

        cond_resched();
    }

    return ret;
}

int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
               u64 *trimmed, u64 start, u64 end, u64 minlen)
{
    int ret;

    *trimmed = 0;

    ret = trim_no_bitmap(block_group, trimmed, start, end, minlen);
    if (ret)
        return ret;

    ret = trim_bitmaps(block_group, trimmed, start, end, minlen);

    return ret;
}

/*
 * Find the left-most item in the cache tree, and then return the
 * smallest inode number in the item.
 *
 * Note: the returned inode number may not be the smallest one in
 * the tree, if the left-most item is a bitmap.
 */
u64 btrfs_find_ino_for_alloc(struct btrfs_root *fs_root)
{
    struct btrfs_free_space_ctl *ctl = fs_root->free_ino_ctl;
    struct btrfs_free_space *entry = NULL;
    u64 ino = 0;

    spin_lock(&ctl->tree_lock);

    if (RB_EMPTY_ROOT(&ctl->free_space_offset))
        goto out;

    entry = rb_entry(rb_first(&ctl->free_space_offset),
             struct btrfs_free_space, offset_index);

    if (!entry->bitmap) {
        ino = entry->offset;

        unlink_free_space(ctl, entry);
        entry->offset++;
        entry->bytes--;
        if (!entry->bytes)
            kmem_cache_free(btrfs_free_space_cachep, entry);
        else
            link_free_space(ctl, entry);
    } else {
        u64 offset = 0;
        u64 count = 1;
        int ret;

        ret = search_bitmap(ctl, entry, &offset, &count);
        /* Logic error; Should be empty if it can't find anything */
        BUG_ON(ret);

        ino = offset;
        bitmap_clear_bits(ctl, entry, offset, 1);
        if (entry->bytes == 0)
            free_bitmap(ctl, entry);
    }
out:
    spin_unlock(&ctl->tree_lock);

    return ino;
}

struct inode *lookup_free_ino_inode(struct btrfs_root *root,
                    struct btrfs_path *path)
{
    struct inode *inode = NULL;

    spin_lock(&root->cache_lock);
    if (root->cache_inode)
        inode = igrab(root->cache_inode);
    spin_unlock(&root->cache_lock);
    if (inode)
        return inode;

    inode = __lookup_free_space_inode(root, path, 0);
    if (IS_ERR(inode))
        return inode;

    spin_lock(&root->cache_lock);
    if (!btrfs_fs_closing(root->fs_info))
        root->cache_inode = igrab(inode);
    spin_unlock(&root->cache_lock);

    return inode;
}

int create_free_ino_inode(struct btrfs_root *root,
              struct btrfs_trans_handle *trans,
              struct btrfs_path *path)
{
    return __create_free_space_inode(root, trans, path,
                     BTRFS_FREE_INO_OBJECTID, 0);
}

int load_free_ino_cache(struct btrfs_fs_info *fs_info, struct btrfs_root *root)
{
    struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
    struct btrfs_path *path;
    struct inode *inode;
    int ret = 0;
    u64 root_gen = btrfs_root_generation(&root->root_item);

    if (!btrfs_test_opt(root, INODE_MAP_CACHE))
        return 0;

    /*
     * If we're unmounting then just return, since this does a search on the
     * normal root and not the commit root and we could deadlock.
     */
    if (btrfs_fs_closing(fs_info))
        return 0;

    path = btrfs_alloc_path();
    if (!path)
        return 0;

    inode = lookup_free_ino_inode(root, path);
    if (IS_ERR(inode))
        goto out;

    if (root_gen != BTRFS_I(inode)->generation)
        goto out_put;

    ret = __load_free_space_cache(root, inode, ctl, path, 0);

    if (ret < 0)
        printk(KERN_ERR "btrfs: failed to load free ino cache for "
               "root %llu\n", root->root_key.objectid);
out_put:
    iput(inode);
out:
    btrfs_free_path(path);
    return ret;
}

int btrfs_write_out_ino_cache(struct btrfs_root *root,
                  struct btrfs_trans_handle *trans,
                  struct btrfs_path *path)
{
    struct btrfs_free_space_ctl *ctl = root->free_ino_ctl;
    struct inode *inode;
    int ret;

    if (!btrfs_test_opt(root, INODE_MAP_CACHE))
        return 0;

    inode = lookup_free_ino_inode(root, path);
    if (IS_ERR(inode))
        return 0;

    ret = __btrfs_write_out_cache(root, inode, ctl, NULL, trans, path, 0);
    if (ret) {
        btrfs_delalloc_release_metadata(inode, inode->i_size);
#ifdef DEBUG
        printk(KERN_ERR "btrfs: failed to write free ino cache "
               "for root %llu\n", root->root_key.objectid);
#endif
    }

    iput(inode);
    return ret;
}