extent-tree.c

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/*
 * Copyright (C) 2007 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 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/sched.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/sort.h>
#include <linux/rcupdate.h>
#include <linux/kthread.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include "compat.h"
#include "hash.h"
#include "ctree.h"
#include "disk-io.h"
#include "print-tree.h"
#include "transaction.h"
#include "volumes.h"
#include "locking.h"
#include "free-space-cache.h"

#undef SCRAMBLE_DELAYED_REFS

/*
 * control flags for do_chunk_alloc's force field
 * CHUNK_ALLOC_NO_FORCE means to only allocate a chunk
 * if we really need one.
 *
 * CHUNK_ALLOC_LIMITED means to only try and allocate one
 * if we have very few chunks already allocated.  This is
 * used as part of the clustering code to help make sure
 * we have a good pool of storage to cluster in, without
 * filling the FS with empty chunks
 *
 * CHUNK_ALLOC_FORCE means it must try to allocate one
 *
 */
enum {
    CHUNK_ALLOC_NO_FORCE = 0,
    CHUNK_ALLOC_LIMITED = 1,
    CHUNK_ALLOC_FORCE = 2,
};

/*
 * Control how reservations are dealt with.
 *
 * RESERVE_FREE - freeing a reservation.
 * RESERVE_ALLOC - allocating space and we need to update bytes_may_use for
 *   ENOSPC accounting
 * RESERVE_ALLOC_NO_ACCOUNT - allocating space and we should not update
 *   bytes_may_use as the ENOSPC accounting is done elsewhere
 */
enum {
    RESERVE_FREE = 0,
    RESERVE_ALLOC = 1,
    RESERVE_ALLOC_NO_ACCOUNT = 2,
};

static int update_block_group(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root,
                  u64 bytenr, u64 num_bytes, int alloc);
static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
                struct btrfs_root *root,
                u64 bytenr, u64 num_bytes, u64 parent,
                u64 root_objectid, u64 owner_objectid,
                u64 owner_offset, int refs_to_drop,
                struct btrfs_delayed_extent_op *extra_op);
static void __run_delayed_extent_op(struct btrfs_delayed_extent_op *extent_op,
                    struct extent_buffer *leaf,
                    struct btrfs_extent_item *ei);
static int alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      u64 parent, u64 root_objectid,
                      u64 flags, u64 owner, u64 offset,
                      struct btrfs_key *ins, int ref_mod);
static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     u64 parent, u64 root_objectid,
                     u64 flags, struct btrfs_disk_key *key,
                     int level, struct btrfs_key *ins);
static int do_chunk_alloc(struct btrfs_trans_handle *trans,
              struct btrfs_root *extent_root, u64 flags,
              int force);
static int find_next_key(struct btrfs_path *path, int level,
             struct btrfs_key *key);
static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
                int dump_block_groups);
static int btrfs_update_reserved_bytes(struct btrfs_block_group_cache *cache,
                       u64 num_bytes, int reserve);

static noinline int
block_group_cache_done(struct btrfs_block_group_cache *cache)
{
    smp_mb();
    return cache->cached == BTRFS_CACHE_FINISHED;
}

static int block_group_bits(struct btrfs_block_group_cache *cache, u64 bits)
{
    return (cache->flags & bits) == bits;
}

static void btrfs_get_block_group(struct btrfs_block_group_cache *cache)
{
    atomic_inc(&cache->count);
}

void btrfs_put_block_group(struct btrfs_block_group_cache *cache)
{
    if (atomic_dec_and_test(&cache->count)) {
        WARN_ON(cache->pinned > 0);
        WARN_ON(cache->reserved > 0);
        kfree(cache->free_space_ctl);
        kfree(cache);
    }
}

/*
 * this adds the block group to the fs_info rb tree for the block group
 * cache
 */
static int btrfs_add_block_group_cache(struct btrfs_fs_info *info,
                struct btrfs_block_group_cache *block_group)
{
    struct rb_node **p;
    struct rb_node *parent = NULL;
    struct btrfs_block_group_cache *cache;

    spin_lock(&info->block_group_cache_lock);
    p = &info->block_group_cache_tree.rb_node;

    while (*p) {
        parent = *p;
        cache = rb_entry(parent, struct btrfs_block_group_cache,
                 cache_node);
        if (block_group->key.objectid < cache->key.objectid) {
            p = &(*p)->rb_left;
        } else if (block_group->key.objectid > cache->key.objectid) {
            p = &(*p)->rb_right;
        } else {
            spin_unlock(&info->block_group_cache_lock);
            return -EEXIST;
        }
    }

    rb_link_node(&block_group->cache_node, parent, p);
    rb_insert_color(&block_group->cache_node,
            &info->block_group_cache_tree);
    spin_unlock(&info->block_group_cache_lock);

    return 0;
}

/*
 * This will return the block group at or after bytenr if contains is 0, else
 * it will return the block group that contains the bytenr
 */
static struct btrfs_block_group_cache *
block_group_cache_tree_search(struct btrfs_fs_info *info, u64 bytenr,
                  int contains)
{
    struct btrfs_block_group_cache *cache, *ret = NULL;
    struct rb_node *n;
    u64 end, start;

    spin_lock(&info->block_group_cache_lock);
    n = info->block_group_cache_tree.rb_node;

    while (n) {
        cache = rb_entry(n, struct btrfs_block_group_cache,
                 cache_node);
        end = cache->key.objectid + cache->key.offset - 1;
        start = cache->key.objectid;

        if (bytenr < start) {
            if (!contains && (!ret || start < ret->key.objectid))
                ret = cache;
            n = n->rb_left;
        } else if (bytenr > start) {
            if (contains && bytenr <= end) {
                ret = cache;
                break;
            }
            n = n->rb_right;
        } else {
            ret = cache;
            break;
        }
    }
    if (ret)
        btrfs_get_block_group(ret);
    spin_unlock(&info->block_group_cache_lock);

    return ret;
}

static int add_excluded_extent(struct btrfs_root *root,
                   u64 start, u64 num_bytes)
{
    u64 end = start + num_bytes - 1;
    set_extent_bits(&root->fs_info->freed_extents[0],
            start, end, EXTENT_UPTODATE, GFP_NOFS);
    set_extent_bits(&root->fs_info->freed_extents[1],
            start, end, EXTENT_UPTODATE, GFP_NOFS);
    return 0;
}

static void free_excluded_extents(struct btrfs_root *root,
                  struct btrfs_block_group_cache *cache)
{
    u64 start, end;

    start = cache->key.objectid;
    end = start + cache->key.offset - 1;

    clear_extent_bits(&root->fs_info->freed_extents[0],
              start, end, EXTENT_UPTODATE, GFP_NOFS);
    clear_extent_bits(&root->fs_info->freed_extents[1],
              start, end, EXTENT_UPTODATE, GFP_NOFS);
}

static int exclude_super_stripes(struct btrfs_root *root,
                 struct btrfs_block_group_cache *cache)
{
    u64 bytenr;
    u64 *logical;
    int stripe_len;
    int i, nr, ret;

    if (cache->key.objectid < BTRFS_SUPER_INFO_OFFSET) {
        stripe_len = BTRFS_SUPER_INFO_OFFSET - cache->key.objectid;
        cache->bytes_super += stripe_len;
        ret = add_excluded_extent(root, cache->key.objectid,
                      stripe_len);
        BUG_ON(ret); /* -ENOMEM */
    }

    for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
        bytenr = btrfs_sb_offset(i);
        ret = btrfs_rmap_block(&root->fs_info->mapping_tree,
                       cache->key.objectid, bytenr,
                       0, &logical, &nr, &stripe_len);
        BUG_ON(ret); /* -ENOMEM */

        while (nr--) {
            cache->bytes_super += stripe_len;
            ret = add_excluded_extent(root, logical[nr],
                          stripe_len);
            BUG_ON(ret); /* -ENOMEM */
        }

        kfree(logical);
    }
    return 0;
}

static struct btrfs_caching_control *
get_caching_control(struct btrfs_block_group_cache *cache)
{
    struct btrfs_caching_control *ctl;

    spin_lock(&cache->lock);
    if (cache->cached != BTRFS_CACHE_STARTED) {
        spin_unlock(&cache->lock);
        return NULL;
    }

    /* We're loading it the fast way, so we don't have a caching_ctl. */
    if (!cache->caching_ctl) {
        spin_unlock(&cache->lock);
        return NULL;
    }

    ctl = cache->caching_ctl;
    atomic_inc(&ctl->count);
    spin_unlock(&cache->lock);
    return ctl;
}

static void put_caching_control(struct btrfs_caching_control *ctl)
{
    if (atomic_dec_and_test(&ctl->count))
        kfree(ctl);
}

/*
 * this is only called by cache_block_group, since we could have freed extents
 * we need to check the pinned_extents for any extents that can't be used yet
 * since their free space will be released as soon as the transaction commits.
 */
static u64 add_new_free_space(struct btrfs_block_group_cache *block_group,
                  struct btrfs_fs_info *info, u64 start, u64 end)
{
    u64 extent_start, extent_end, size, total_added = 0;
    int ret;

    while (start < end) {
        ret = find_first_extent_bit(info->pinned_extents, start,
                        &extent_start, &extent_end,
                        EXTENT_DIRTY | EXTENT_UPTODATE,
                        NULL);
        if (ret)
            break;

        if (extent_start <= start) {
            start = extent_end + 1;
        } else if (extent_start > start && extent_start < end) {
            size = extent_start - start;
            total_added += size;
            ret = btrfs_add_free_space(block_group, start,
                           size);
            BUG_ON(ret); /* -ENOMEM or logic error */
            start = extent_end + 1;
        } else {
            break;
        }
    }

    if (start < end) {
        size = end - start;
        total_added += size;
        ret = btrfs_add_free_space(block_group, start, size);
        BUG_ON(ret); /* -ENOMEM or logic error */
    }

    return total_added;
}

static noinline void caching_thread(struct btrfs_work *work)
{
    struct btrfs_block_group_cache *block_group;
    struct btrfs_fs_info *fs_info;
    struct btrfs_caching_control *caching_ctl;
    struct btrfs_root *extent_root;
    struct btrfs_path *path;
    struct extent_buffer *leaf;
    struct btrfs_key key;
    u64 total_found = 0;
    u64 last = 0;
    u32 nritems;
    int ret = 0;

    caching_ctl = container_of(work, struct btrfs_caching_control, work);
    block_group = caching_ctl->block_group;
    fs_info = block_group->fs_info;
    extent_root = fs_info->extent_root;

    path = btrfs_alloc_path();
    if (!path)
        goto out;

    last = max_t(u64, block_group->key.objectid, BTRFS_SUPER_INFO_OFFSET);

    /*
     * We don't want to deadlock with somebody trying to allocate a new
     * extent for the extent root while also trying to search the extent
     * root to add free space.  So we skip locking and search the commit
     * root, since its read-only
     */
    path->skip_locking = 1;
    path->search_commit_root = 1;
    path->reada = 1;

    key.objectid = last;
    key.offset = 0;
    key.type = BTRFS_EXTENT_ITEM_KEY;
again:
    mutex_lock(&caching_ctl->mutex);
    /* need to make sure the commit_root doesn't disappear */
    down_read(&fs_info->extent_commit_sem);

    ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
    if (ret < 0)
        goto err;

    leaf = path->nodes[0];
    nritems = btrfs_header_nritems(leaf);

    while (1) {
        if (btrfs_fs_closing(fs_info) > 1) {
            last = (u64)-1;
            break;
        }

        if (path->slots[0] < nritems) {
            btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        } else {
            ret = find_next_key(path, 0, &key);
            if (ret)
                break;

            if (need_resched() ||
                btrfs_next_leaf(extent_root, path)) {
                caching_ctl->progress = last;
                btrfs_release_path(path);
                up_read(&fs_info->extent_commit_sem);
                mutex_unlock(&caching_ctl->mutex);
                cond_resched();
                goto again;
            }
            leaf = path->nodes[0];
            nritems = btrfs_header_nritems(leaf);
            continue;
        }

        if (key.objectid < block_group->key.objectid) {
            path->slots[0]++;
            continue;
        }

        if (key.objectid >= block_group->key.objectid +
            block_group->key.offset)
            break;

        if (key.type == BTRFS_EXTENT_ITEM_KEY) {
            total_found += add_new_free_space(block_group,
                              fs_info, last,
                              key.objectid);
            last = key.objectid + key.offset;

            if (total_found > (1024 * 1024 * 2)) {
                total_found = 0;
                wake_up(&caching_ctl->wait);
            }
        }
        path->slots[0]++;
    }
    ret = 0;

    total_found += add_new_free_space(block_group, fs_info, last,
                      block_group->key.objectid +
                      block_group->key.offset);
    caching_ctl->progress = (u64)-1;

    spin_lock(&block_group->lock);
    block_group->caching_ctl = NULL;
    block_group->cached = BTRFS_CACHE_FINISHED;
    spin_unlock(&block_group->lock);

err:
    btrfs_free_path(path);
    up_read(&fs_info->extent_commit_sem);

    free_excluded_extents(extent_root, block_group);

    mutex_unlock(&caching_ctl->mutex);
out:
    wake_up(&caching_ctl->wait);

    put_caching_control(caching_ctl);
    btrfs_put_block_group(block_group);
}

static int cache_block_group(struct btrfs_block_group_cache *cache,
                 struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 int load_cache_only)
{
    DEFINE_WAIT(wait);
    struct btrfs_fs_info *fs_info = cache->fs_info;
    struct btrfs_caching_control *caching_ctl;
    int ret = 0;

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

    INIT_LIST_HEAD(&caching_ctl->list);
    mutex_init(&caching_ctl->mutex);
    init_waitqueue_head(&caching_ctl->wait);
    caching_ctl->block_group = cache;
    caching_ctl->progress = cache->key.objectid;
    atomic_set(&caching_ctl->count, 1);
    caching_ctl->work.func = caching_thread;

    spin_lock(&cache->lock);
    /*
     * This should be a rare occasion, but this could happen I think in the
     * case where one thread starts to load the space cache info, and then
     * some other thread starts a transaction commit which tries to do an
     * allocation while the other thread is still loading the space cache
     * info.  The previous loop should have kept us from choosing this block
     * group, but if we've moved to the state where we will wait on caching
     * block groups we need to first check if we're doing a fast load here,
     * so we can wait for it to finish, otherwise we could end up allocating
     * from a block group who's cache gets evicted for one reason or
     * another.
     */
    while (cache->cached == BTRFS_CACHE_FAST) {
        struct btrfs_caching_control *ctl;

        ctl = cache->caching_ctl;
        atomic_inc(&ctl->count);
        prepare_to_wait(&ctl->wait, &wait, TASK_UNINTERRUPTIBLE);
        spin_unlock(&cache->lock);

        schedule();

        finish_wait(&ctl->wait, &wait);
        put_caching_control(ctl);
        spin_lock(&cache->lock);
    }

    if (cache->cached != BTRFS_CACHE_NO) {
        spin_unlock(&cache->lock);
        kfree(caching_ctl);
        return 0;
    }
    WARN_ON(cache->caching_ctl);
    cache->caching_ctl = caching_ctl;
    cache->cached = BTRFS_CACHE_FAST;
    spin_unlock(&cache->lock);

    /*
     * We can't do the read from on-disk cache during a commit since we need
     * to have the normal tree locking.  Also if we are currently trying to
     * allocate blocks for the tree root we can't do the fast caching since
     * we likely hold important locks.
     */
    if (fs_info->mount_opt & BTRFS_MOUNT_SPACE_CACHE) {
        ret = load_free_space_cache(fs_info, cache);

        spin_lock(&cache->lock);
        if (ret == 1) {
            cache->caching_ctl = NULL;
            cache->cached = BTRFS_CACHE_FINISHED;
            cache->last_byte_to_unpin = (u64)-1;
        } else {
            if (load_cache_only) {
                cache->caching_ctl = NULL;
                cache->cached = BTRFS_CACHE_NO;
            } else {
                cache->cached = BTRFS_CACHE_STARTED;
            }
        }
        spin_unlock(&cache->lock);
        wake_up(&caching_ctl->wait);
        if (ret == 1) {
            put_caching_control(caching_ctl);
            free_excluded_extents(fs_info->extent_root, cache);
            return 0;
        }
    } else {
        /*
         * We are not going to do the fast caching, set cached to the
         * appropriate value and wakeup any waiters.
         */
        spin_lock(&cache->lock);
        if (load_cache_only) {
            cache->caching_ctl = NULL;
            cache->cached = BTRFS_CACHE_NO;
        } else {
            cache->cached = BTRFS_CACHE_STARTED;
        }
        spin_unlock(&cache->lock);
        wake_up(&caching_ctl->wait);
    }

    if (load_cache_only) {
        put_caching_control(caching_ctl);
        return 0;
    }

    down_write(&fs_info->extent_commit_sem);
    atomic_inc(&caching_ctl->count);
    list_add_tail(&caching_ctl->list, &fs_info->caching_block_groups);
    up_write(&fs_info->extent_commit_sem);

    btrfs_get_block_group(cache);

    btrfs_queue_worker(&fs_info->caching_workers, &caching_ctl->work);

    return ret;
}

/*
 * return the block group that starts at or after bytenr
 */
static struct btrfs_block_group_cache *
btrfs_lookup_first_block_group(struct btrfs_fs_info *info, u64 bytenr)
{
    struct btrfs_block_group_cache *cache;

    cache = block_group_cache_tree_search(info, bytenr, 0);

    return cache;
}

/*
 * return the block group that contains the given bytenr
 */
struct btrfs_block_group_cache *btrfs_lookup_block_group(
                         struct btrfs_fs_info *info,
                         u64 bytenr)
{
    struct btrfs_block_group_cache *cache;

    cache = block_group_cache_tree_search(info, bytenr, 1);

    return cache;
}

static struct btrfs_space_info *__find_space_info(struct btrfs_fs_info *info,
                          u64 flags)
{
    struct list_head *head = &info->space_info;
    struct btrfs_space_info *found;

    flags &= BTRFS_BLOCK_GROUP_TYPE_MASK;

    rcu_read_lock();
    list_for_each_entry_rcu(found, head, list) {
        if (found->flags & flags) {
            rcu_read_unlock();
            return found;
        }
    }
    rcu_read_unlock();
    return NULL;
}

/*
 * after adding space to the filesystem, we need to clear the full flags
 * on all the space infos.
 */
void btrfs_clear_space_info_full(struct btrfs_fs_info *info)
{
    struct list_head *head = &info->space_info;
    struct btrfs_space_info *found;

    rcu_read_lock();
    list_for_each_entry_rcu(found, head, list)
        found->full = 0;
    rcu_read_unlock();
}

static u64 div_factor(u64 num, int factor)
{
    if (factor == 10)
        return num;
    num *= factor;
    do_div(num, 10);
    return num;
}

static u64 div_factor_fine(u64 num, int factor)
{
    if (factor == 100)
        return num;
    num *= factor;
    do_div(num, 100);
    return num;
}

u64 btrfs_find_block_group(struct btrfs_root *root,
               u64 search_start, u64 search_hint, int owner)
{
    struct btrfs_block_group_cache *cache;
    u64 used;
    u64 last = max(search_hint, search_start);
    u64 group_start = 0;
    int full_search = 0;
    int factor = 9;
    int wrapped = 0;
again:
    while (1) {
        cache = btrfs_lookup_first_block_group(root->fs_info, last);
        if (!cache)
            break;

        spin_lock(&cache->lock);
        last = cache->key.objectid + cache->key.offset;
        used = btrfs_block_group_used(&cache->item);

        if ((full_search || !cache->ro) &&
            block_group_bits(cache, BTRFS_BLOCK_GROUP_METADATA)) {
            if (used + cache->pinned + cache->reserved <
                div_factor(cache->key.offset, factor)) {
                group_start = cache->key.objectid;
                spin_unlock(&cache->lock);
                btrfs_put_block_group(cache);
                goto found;
            }
        }
        spin_unlock(&cache->lock);
        btrfs_put_block_group(cache);
        cond_resched();
    }
    if (!wrapped) {
        last = search_start;
        wrapped = 1;
        goto again;
    }
    if (!full_search && factor < 10) {
        last = search_start;
        full_search = 1;
        factor = 10;
        goto again;
    }
found:
    return group_start;
}

/* simple helper to search for an existing extent at a given offset */
int btrfs_lookup_extent(struct btrfs_root *root, u64 start, u64 len)
{
    int ret;
    struct btrfs_key key;
    struct btrfs_path *path;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    key.objectid = start;
    key.offset = len;
    btrfs_set_key_type(&key, BTRFS_EXTENT_ITEM_KEY);
    ret = btrfs_search_slot(NULL, root->fs_info->extent_root, &key, path,
                0, 0);
    btrfs_free_path(path);
    return ret;
}

/*
 * helper function to lookup reference count and flags of extent.
 *
 * the head node for delayed ref is used to store the sum of all the
 * reference count modifications queued up in the rbtree. the head
 * node may also store the extent flags to set. This way you can check
 * to see what the reference count and extent flags would be if all of
 * the delayed refs are not processed.
 */
int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root, u64 bytenr,
                 u64 num_bytes, u64 *refs, u64 *flags)
{
    struct btrfs_delayed_ref_head *head;
    struct btrfs_delayed_ref_root *delayed_refs;
    struct btrfs_path *path;
    struct btrfs_extent_item *ei;
    struct extent_buffer *leaf;
    struct btrfs_key key;
    u32 item_size;
    u64 num_refs;
    u64 extent_flags;
    int ret;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    key.objectid = bytenr;
    key.type = BTRFS_EXTENT_ITEM_KEY;
    key.offset = num_bytes;
    if (!trans) {
        path->skip_locking = 1;
        path->search_commit_root = 1;
    }
again:
    ret = btrfs_search_slot(trans, root->fs_info->extent_root,
                &key, path, 0, 0);
    if (ret < 0)
        goto out_free;

    if (ret == 0) {
        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        if (item_size >= sizeof(*ei)) {
            ei = btrfs_item_ptr(leaf, path->slots[0],
                        struct btrfs_extent_item);
            num_refs = btrfs_extent_refs(leaf, ei);
            extent_flags = btrfs_extent_flags(leaf, ei);
        } else {
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
            struct btrfs_extent_item_v0 *ei0;
            BUG_ON(item_size != sizeof(*ei0));
            ei0 = btrfs_item_ptr(leaf, path->slots[0],
                         struct btrfs_extent_item_v0);
            num_refs = btrfs_extent_refs_v0(leaf, ei0);
            /* FIXME: this isn't correct for data */
            extent_flags = BTRFS_BLOCK_FLAG_FULL_BACKREF;
#else
            BUG();
#endif
        }
        BUG_ON(num_refs == 0);
    } else {
        num_refs = 0;
        extent_flags = 0;
        ret = 0;
    }

    if (!trans)
        goto out;

    delayed_refs = &trans->transaction->delayed_refs;
    spin_lock(&delayed_refs->lock);
    head = btrfs_find_delayed_ref_head(trans, bytenr);
    if (head) {
        if (!mutex_trylock(&head->mutex)) {
            atomic_inc(&head->node.refs);
            spin_unlock(&delayed_refs->lock);

            btrfs_release_path(path);

            /*
             * Mutex was contended, block until it's released and try
             * again
             */
            mutex_lock(&head->mutex);
            mutex_unlock(&head->mutex);
            btrfs_put_delayed_ref(&head->node);
            goto again;
        }
        if (head->extent_op && head->extent_op->update_flags)
            extent_flags |= head->extent_op->flags_to_set;
        else
            BUG_ON(num_refs == 0);

        num_refs += head->node.ref_mod;
        mutex_unlock(&head->mutex);
    }
    spin_unlock(&delayed_refs->lock);
out:
    WARN_ON(num_refs == 0);
    if (refs)
        *refs = num_refs;
    if (flags)
        *flags = extent_flags;
out_free:
    btrfs_free_path(path);
    return ret;
}

/*
 * Back reference rules.  Back refs have three main goals:
 *
 * 1) differentiate between all holders of references to an extent so that
 *    when a reference is dropped we can make sure it was a valid reference
 *    before freeing the extent.
 *
 * 2) Provide enough information to quickly find the holders of an extent
 *    if we notice a given block is corrupted or bad.
 *
 * 3) Make it easy to migrate blocks for FS shrinking or storage pool
 *    maintenance.  This is actually the same as #2, but with a slightly
 *    different use case.
 *
 * There are two kinds of back refs. The implicit back refs is optimized
 * for pointers in non-shared tree blocks. For a given pointer in a block,
 * back refs of this kind provide information about the block's owner tree
 * and the pointer's key. These information allow us to find the block by
 * b-tree searching. The full back refs is for pointers in tree blocks not
 * referenced by their owner trees. The location of tree block is recorded
 * in the back refs. Actually the full back refs is generic, and can be
 * used in all cases the implicit back refs is used. The major shortcoming
 * of the full back refs is its overhead. Every time a tree block gets
 * COWed, we have to update back refs entry for all pointers in it.
 *
 * For a newly allocated tree block, we use implicit back refs for
 * pointers in it. This means most tree related operations only involve
 * implicit back refs. For a tree block created in old transaction, the
 * only way to drop a reference to it is COW it. So we can detect the
 * event that tree block loses its owner tree's reference and do the
 * back refs conversion.
 *
 * When a tree block is COW'd through a tree, there are four cases:
 *
 * The reference count of the block is one and the tree is the block's
 * owner tree. Nothing to do in this case.
 *
 * The reference count of the block is one and the tree is not the
 * block's owner tree. In this case, full back refs is used for pointers
 * in the block. Remove these full back refs, add implicit back refs for
 * every pointers in the new block.
 *
 * The reference count of the block is greater than one and the tree is
 * the block's owner tree. In this case, implicit back refs is used for
 * pointers in the block. Add full back refs for every pointers in the
 * block, increase lower level extents' reference counts. The original
 * implicit back refs are entailed to the new block.
 *
 * The reference count of the block is greater than one and the tree is
 * not the block's owner tree. Add implicit back refs for every pointer in
 * the new block, increase lower level extents' reference count.
 *
 * Back Reference Key composing:
 *
 * The key objectid corresponds to the first byte in the extent,
 * The key type is used to differentiate between types of back refs.
 * There are different meanings of the key offset for different types
 * of back refs.
 *
 * File extents can be referenced by:
 *
 * - multiple snapshots, subvolumes, or different generations in one subvol
 * - different files inside a single subvolume
 * - different offsets inside a file (bookend extents in file.c)
 *
 * The extent ref structure for the implicit back refs has fields for:
 *
 * - Objectid of the subvolume root
 * - objectid of the file holding the reference
 * - original offset in the file
 * - how many bookend extents
 *
 * The key offset for the implicit back refs is hash of the first
 * three fields.
 *
 * The extent ref structure for the full back refs has field for:
 *
 * - number of pointers in the tree leaf
 *
 * The key offset for the implicit back refs is the first byte of
 * the tree leaf
 *
 * When a file extent is allocated, The implicit back refs is used.
 * the fields are filled in:
 *
 *     (root_key.objectid, inode objectid, offset in file, 1)
 *
 * When a file extent is removed file truncation, we find the
 * corresponding implicit back refs and check the following fields:
 *
 *     (btrfs_header_owner(leaf), inode objectid, offset in file)
 *
 * Btree extents can be referenced by:
 *
 * - Different subvolumes
 *
 * Both the implicit back refs and the full back refs for tree blocks
 * only consist of key. The key offset for the implicit back refs is
 * objectid of block's owner tree. The key offset for the full back refs
 * is the first byte of parent block.
 *
 * When implicit back refs is used, information about the lowest key and
 * level of the tree block are required. These information are stored in
 * tree block info structure.
 */

#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
static int convert_extent_item_v0(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root,
                  struct btrfs_path *path,
                  u64 owner, u32 extra_size)
{
    struct btrfs_extent_item *item;
    struct btrfs_extent_item_v0 *ei0;
    struct btrfs_extent_ref_v0 *ref0;
    struct btrfs_tree_block_info *bi;
    struct extent_buffer *leaf;
    struct btrfs_key key;
    struct btrfs_key found_key;
    u32 new_size = sizeof(*item);
    u64 refs;
    int ret;

    leaf = path->nodes[0];
    BUG_ON(btrfs_item_size_nr(leaf, path->slots[0]) != sizeof(*ei0));

    btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
    ei0 = btrfs_item_ptr(leaf, path->slots[0],
                 struct btrfs_extent_item_v0);
    refs = btrfs_extent_refs_v0(leaf, ei0);

    if (owner == (u64)-1) {
        while (1) {
            if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                ret = btrfs_next_leaf(root, path);
                if (ret < 0)
                    return ret;
                BUG_ON(ret > 0); /* Corruption */
                leaf = path->nodes[0];
            }
            btrfs_item_key_to_cpu(leaf, &found_key,
                          path->slots[0]);
            BUG_ON(key.objectid != found_key.objectid);
            if (found_key.type != BTRFS_EXTENT_REF_V0_KEY) {
                path->slots[0]++;
                continue;
            }
            ref0 = btrfs_item_ptr(leaf, path->slots[0],
                          struct btrfs_extent_ref_v0);
            owner = btrfs_ref_objectid_v0(leaf, ref0);
            break;
        }
    }
    btrfs_release_path(path);

    if (owner < BTRFS_FIRST_FREE_OBJECTID)
        new_size += sizeof(*bi);

    new_size -= sizeof(*ei0);
    ret = btrfs_search_slot(trans, root, &key, path,
                new_size + extra_size, 1);
    if (ret < 0)
        return ret;
    BUG_ON(ret); /* Corruption */

    btrfs_extend_item(trans, root, path, new_size);

    leaf = path->nodes[0];
    item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
    btrfs_set_extent_refs(leaf, item, refs);
    /* FIXME: get real generation */
    btrfs_set_extent_generation(leaf, item, 0);
    if (owner < BTRFS_FIRST_FREE_OBJECTID) {
        btrfs_set_extent_flags(leaf, item,
                       BTRFS_EXTENT_FLAG_TREE_BLOCK |
                       BTRFS_BLOCK_FLAG_FULL_BACKREF);
        bi = (struct btrfs_tree_block_info *)(item + 1);
        /* FIXME: get first key of the block */
        memset_extent_buffer(leaf, 0, (unsigned long)bi, sizeof(*bi));
        btrfs_set_tree_block_level(leaf, bi, (int)owner);
    } else {
        btrfs_set_extent_flags(leaf, item, BTRFS_EXTENT_FLAG_DATA);
    }
    btrfs_mark_buffer_dirty(leaf);
    return 0;
}
#endif

static u64 hash_extent_data_ref(u64 root_objectid, u64 owner, u64 offset)
{
    u32 high_crc = ~(u32)0;
    u32 low_crc = ~(u32)0;
    __le64 lenum;

    lenum = cpu_to_le64(root_objectid);
    high_crc = crc32c(high_crc, &lenum, sizeof(lenum));
    lenum = cpu_to_le64(owner);
    low_crc = crc32c(low_crc, &lenum, sizeof(lenum));
    lenum = cpu_to_le64(offset);
    low_crc = crc32c(low_crc, &lenum, sizeof(lenum));

    return ((u64)high_crc << 31) ^ (u64)low_crc;
}

static u64 hash_extent_data_ref_item(struct extent_buffer *leaf,
                     struct btrfs_extent_data_ref *ref)
{
    return hash_extent_data_ref(btrfs_extent_data_ref_root(leaf, ref),
                    btrfs_extent_data_ref_objectid(leaf, ref),
                    btrfs_extent_data_ref_offset(leaf, ref));
}

static int match_extent_data_ref(struct extent_buffer *leaf,
                 struct btrfs_extent_data_ref *ref,
                 u64 root_objectid, u64 owner, u64 offset)
{
    if (btrfs_extent_data_ref_root(leaf, ref) != root_objectid ||
        btrfs_extent_data_ref_objectid(leaf, ref) != owner ||
        btrfs_extent_data_ref_offset(leaf, ref) != offset)
        return 0;
    return 1;
}

static noinline int lookup_extent_data_ref(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root,
                       struct btrfs_path *path,
                       u64 bytenr, u64 parent,
                       u64 root_objectid,
                       u64 owner, u64 offset)
{
    struct btrfs_key key;
    struct btrfs_extent_data_ref *ref;
    struct extent_buffer *leaf;
    u32 nritems;
    int ret;
    int recow;
    int err = -ENOENT;

    key.objectid = bytenr;
    if (parent) {
        key.type = BTRFS_SHARED_DATA_REF_KEY;
        key.offset = parent;
    } else {
        key.type = BTRFS_EXTENT_DATA_REF_KEY;
        key.offset = hash_extent_data_ref(root_objectid,
                          owner, offset);
    }
again:
    recow = 0;
    ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
    if (ret < 0) {
        err = ret;
        goto fail;
    }

    if (parent) {
        if (!ret)
            return 0;
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        key.type = BTRFS_EXTENT_REF_V0_KEY;
        btrfs_release_path(path);
        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret < 0) {
            err = ret;
            goto fail;
        }
        if (!ret)
            return 0;
#endif
        goto fail;
    }

    leaf = path->nodes[0];
    nritems = btrfs_header_nritems(leaf);
    while (1) {
        if (path->slots[0] >= nritems) {
            ret = btrfs_next_leaf(root, path);
            if (ret < 0)
                err = ret;
            if (ret)
                goto fail;

            leaf = path->nodes[0];
            nritems = btrfs_header_nritems(leaf);
            recow = 1;
        }

        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
        if (key.objectid != bytenr ||
            key.type != BTRFS_EXTENT_DATA_REF_KEY)
            goto fail;

        ref = btrfs_item_ptr(leaf, path->slots[0],
                     struct btrfs_extent_data_ref);

        if (match_extent_data_ref(leaf, ref, root_objectid,
                      owner, offset)) {
            if (recow) {
                btrfs_release_path(path);
                goto again;
            }
            err = 0;
            break;
        }
        path->slots[0]++;
    }
fail:
    return err;
}

static noinline int insert_extent_data_ref(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root,
                       struct btrfs_path *path,
                       u64 bytenr, u64 parent,
                       u64 root_objectid, u64 owner,
                       u64 offset, int refs_to_add)
{
    struct btrfs_key key;
    struct extent_buffer *leaf;
    u32 size;
    u32 num_refs;
    int ret;

    key.objectid = bytenr;
    if (parent) {
        key.type = BTRFS_SHARED_DATA_REF_KEY;
        key.offset = parent;
        size = sizeof(struct btrfs_shared_data_ref);
    } else {
        key.type = BTRFS_EXTENT_DATA_REF_KEY;
        key.offset = hash_extent_data_ref(root_objectid,
                          owner, offset);
        size = sizeof(struct btrfs_extent_data_ref);
    }

    ret = btrfs_insert_empty_item(trans, root, path, &key, size);
    if (ret && ret != -EEXIST)
        goto fail;

    leaf = path->nodes[0];
    if (parent) {
        struct btrfs_shared_data_ref *ref;
        ref = btrfs_item_ptr(leaf, path->slots[0],
                     struct btrfs_shared_data_ref);
        if (ret == 0) {
            btrfs_set_shared_data_ref_count(leaf, ref, refs_to_add);
        } else {
            num_refs = btrfs_shared_data_ref_count(leaf, ref);
            num_refs += refs_to_add;
            btrfs_set_shared_data_ref_count(leaf, ref, num_refs);
        }
    } else {
        struct btrfs_extent_data_ref *ref;
        while (ret == -EEXIST) {
            ref = btrfs_item_ptr(leaf, path->slots[0],
                         struct btrfs_extent_data_ref);
            if (match_extent_data_ref(leaf, ref, root_objectid,
                          owner, offset))
                break;
            btrfs_release_path(path);
            key.offset++;
            ret = btrfs_insert_empty_item(trans, root, path, &key,
                              size);
            if (ret && ret != -EEXIST)
                goto fail;

            leaf = path->nodes[0];
        }
        ref = btrfs_item_ptr(leaf, path->slots[0],
                     struct btrfs_extent_data_ref);
        if (ret == 0) {
            btrfs_set_extent_data_ref_root(leaf, ref,
                               root_objectid);
            btrfs_set_extent_data_ref_objectid(leaf, ref, owner);
            btrfs_set_extent_data_ref_offset(leaf, ref, offset);
            btrfs_set_extent_data_ref_count(leaf, ref, refs_to_add);
        } else {
            num_refs = btrfs_extent_data_ref_count(leaf, ref);
            num_refs += refs_to_add;
            btrfs_set_extent_data_ref_count(leaf, ref, num_refs);
        }
    }
    btrfs_mark_buffer_dirty(leaf);
    ret = 0;
fail:
    btrfs_release_path(path);
    return ret;
}

static noinline int remove_extent_data_ref(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root,
                       struct btrfs_path *path,
                       int refs_to_drop)
{
    struct btrfs_key key;
    struct btrfs_extent_data_ref *ref1 = NULL;
    struct btrfs_shared_data_ref *ref2 = NULL;
    struct extent_buffer *leaf;
    u32 num_refs = 0;
    int ret = 0;

    leaf = path->nodes[0];
    btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

    if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
        ref1 = btrfs_item_ptr(leaf, path->slots[0],
                      struct btrfs_extent_data_ref);
        num_refs = btrfs_extent_data_ref_count(leaf, ref1);
    } else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
        ref2 = btrfs_item_ptr(leaf, path->slots[0],
                      struct btrfs_shared_data_ref);
        num_refs = btrfs_shared_data_ref_count(leaf, ref2);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
    } else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
        struct btrfs_extent_ref_v0 *ref0;
        ref0 = btrfs_item_ptr(leaf, path->slots[0],
                      struct btrfs_extent_ref_v0);
        num_refs = btrfs_ref_count_v0(leaf, ref0);
#endif
    } else {
        BUG();
    }

    BUG_ON(num_refs < refs_to_drop);
    num_refs -= refs_to_drop;

    if (num_refs == 0) {
        ret = btrfs_del_item(trans, root, path);
    } else {
        if (key.type == BTRFS_EXTENT_DATA_REF_KEY)
            btrfs_set_extent_data_ref_count(leaf, ref1, num_refs);
        else if (key.type == BTRFS_SHARED_DATA_REF_KEY)
            btrfs_set_shared_data_ref_count(leaf, ref2, num_refs);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        else {
            struct btrfs_extent_ref_v0 *ref0;
            ref0 = btrfs_item_ptr(leaf, path->slots[0],
                    struct btrfs_extent_ref_v0);
            btrfs_set_ref_count_v0(leaf, ref0, num_refs);
        }
#endif
        btrfs_mark_buffer_dirty(leaf);
    }
    return ret;
}

static noinline u32 extent_data_ref_count(struct btrfs_root *root,
                      struct btrfs_path *path,
                      struct btrfs_extent_inline_ref *iref)
{
    struct btrfs_key key;
    struct extent_buffer *leaf;
    struct btrfs_extent_data_ref *ref1;
    struct btrfs_shared_data_ref *ref2;
    u32 num_refs = 0;

    leaf = path->nodes[0];
    btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
    if (iref) {
        if (btrfs_extent_inline_ref_type(leaf, iref) ==
            BTRFS_EXTENT_DATA_REF_KEY) {
            ref1 = (struct btrfs_extent_data_ref *)(&iref->offset);
            num_refs = btrfs_extent_data_ref_count(leaf, ref1);
        } else {
            ref2 = (struct btrfs_shared_data_ref *)(iref + 1);
            num_refs = btrfs_shared_data_ref_count(leaf, ref2);
        }
    } else if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
        ref1 = btrfs_item_ptr(leaf, path->slots[0],
                      struct btrfs_extent_data_ref);
        num_refs = btrfs_extent_data_ref_count(leaf, ref1);
    } else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
        ref2 = btrfs_item_ptr(leaf, path->slots[0],
                      struct btrfs_shared_data_ref);
        num_refs = btrfs_shared_data_ref_count(leaf, ref2);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
    } else if (key.type == BTRFS_EXTENT_REF_V0_KEY) {
        struct btrfs_extent_ref_v0 *ref0;
        ref0 = btrfs_item_ptr(leaf, path->slots[0],
                      struct btrfs_extent_ref_v0);
        num_refs = btrfs_ref_count_v0(leaf, ref0);
#endif
    } else {
        WARN_ON(1);
    }
    return num_refs;
}

static noinline int lookup_tree_block_ref(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      struct btrfs_path *path,
                      u64 bytenr, u64 parent,
                      u64 root_objectid)
{
    struct btrfs_key key;
    int ret;

    key.objectid = bytenr;
    if (parent) {
        key.type = BTRFS_SHARED_BLOCK_REF_KEY;
        key.offset = parent;
    } else {
        key.type = BTRFS_TREE_BLOCK_REF_KEY;
        key.offset = root_objectid;
    }

    ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
    if (ret > 0)
        ret = -ENOENT;
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
    if (ret == -ENOENT && parent) {
        btrfs_release_path(path);
        key.type = BTRFS_EXTENT_REF_V0_KEY;
        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret > 0)
            ret = -ENOENT;
    }
#endif
    return ret;
}

static noinline int insert_tree_block_ref(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      struct btrfs_path *path,
                      u64 bytenr, u64 parent,
                      u64 root_objectid)
{
    struct btrfs_key key;
    int ret;

    key.objectid = bytenr;
    if (parent) {
        key.type = BTRFS_SHARED_BLOCK_REF_KEY;
        key.offset = parent;
    } else {
        key.type = BTRFS_TREE_BLOCK_REF_KEY;
        key.offset = root_objectid;
    }

    ret = btrfs_insert_empty_item(trans, root, path, &key, 0);
    btrfs_release_path(path);
    return ret;
}

static inline int extent_ref_type(u64 parent, u64 owner)
{
    int type;
    if (owner < BTRFS_FIRST_FREE_OBJECTID) {
        if (parent > 0)
            type = BTRFS_SHARED_BLOCK_REF_KEY;
        else
            type = BTRFS_TREE_BLOCK_REF_KEY;
    } else {
        if (parent > 0)
            type = BTRFS_SHARED_DATA_REF_KEY;
        else
            type = BTRFS_EXTENT_DATA_REF_KEY;
    }
    return type;
}

static int find_next_key(struct btrfs_path *path, int level,
             struct btrfs_key *key)

{
    for (; level < BTRFS_MAX_LEVEL; level++) {
        if (!path->nodes[level])
            break;
        if (path->slots[level] + 1 >=
            btrfs_header_nritems(path->nodes[level]))
            continue;
        if (level == 0)
            btrfs_item_key_to_cpu(path->nodes[level], key,
                          path->slots[level] + 1);
        else
            btrfs_node_key_to_cpu(path->nodes[level], key,
                          path->slots[level] + 1);
        return 0;
    }
    return 1;
}

/*
 * look for inline back ref. if back ref is found, *ref_ret is set
 * to the address of inline back ref, and 0 is returned.
 *
 * if back ref isn't found, *ref_ret is set to the address where it
 * should be inserted, and -ENOENT is returned.
 *
 * if insert is true and there are too many inline back refs, the path
 * points to the extent item, and -EAGAIN is returned.
 *
 * NOTE: inline back refs are ordered in the same way that back ref
 *   items in the tree are ordered.
 */
static noinline_for_stack
int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 struct btrfs_extent_inline_ref **ref_ret,
                 u64 bytenr, u64 num_bytes,
                 u64 parent, u64 root_objectid,
                 u64 owner, u64 offset, int insert)
{
    struct btrfs_key key;
    struct extent_buffer *leaf;
    struct btrfs_extent_item *ei;
    struct btrfs_extent_inline_ref *iref;
    u64 flags;
    u64 item_size;
    unsigned long ptr;
    unsigned long end;
    int extra_size;
    int type;
    int want;
    int ret;
    int err = 0;

    key.objectid = bytenr;
    key.type = BTRFS_EXTENT_ITEM_KEY;
    key.offset = num_bytes;

    want = extent_ref_type(parent, owner);
    if (insert) {
        extra_size = btrfs_extent_inline_ref_size(want);
        path->keep_locks = 1;
    } else
        extra_size = -1;
    ret = btrfs_search_slot(trans, root, &key, path, extra_size, 1);
    if (ret < 0) {
        err = ret;
        goto out;
    }
    if (ret && !insert) {
        err = -ENOENT;
        goto out;
    }
    BUG_ON(ret); /* Corruption */

    leaf = path->nodes[0];
    item_size = btrfs_item_size_nr(leaf, path->slots[0]);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
    if (item_size < sizeof(*ei)) {
        if (!insert) {
            err = -ENOENT;
            goto out;
        }
        ret = convert_extent_item_v0(trans, root, path, owner,
                         extra_size);
        if (ret < 0) {
            err = ret;
            goto out;
        }
        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
    }
#endif
    BUG_ON(item_size < sizeof(*ei));

    ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
    flags = btrfs_extent_flags(leaf, ei);

    ptr = (unsigned long)(ei + 1);
    end = (unsigned long)ei + item_size;

    if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
        ptr += sizeof(struct btrfs_tree_block_info);
        BUG_ON(ptr > end);
    } else {
        BUG_ON(!(flags & BTRFS_EXTENT_FLAG_DATA));
    }

    err = -ENOENT;
    while (1) {
        if (ptr >= end) {
            WARN_ON(ptr > end);
            break;
        }
        iref = (struct btrfs_extent_inline_ref *)ptr;
        type = btrfs_extent_inline_ref_type(leaf, iref);
        if (want < type)
            break;
        if (want > type) {
            ptr += btrfs_extent_inline_ref_size(type);
            continue;
        }

        if (type == BTRFS_EXTENT_DATA_REF_KEY) {
            struct btrfs_extent_data_ref *dref;
            dref = (struct btrfs_extent_data_ref *)(&iref->offset);
            if (match_extent_data_ref(leaf, dref, root_objectid,
                          owner, offset)) {
                err = 0;
                break;
            }
            if (hash_extent_data_ref_item(leaf, dref) <
                hash_extent_data_ref(root_objectid, owner, offset))
                break;
        } else {
            u64 ref_offset;
            ref_offset = btrfs_extent_inline_ref_offset(leaf, iref);
            if (parent > 0) {
                if (parent == ref_offset) {
                    err = 0;
                    break;
                }
                if (ref_offset < parent)
                    break;
            } else {
                if (root_objectid == ref_offset) {
                    err = 0;
                    break;
                }
                if (ref_offset < root_objectid)
                    break;
            }
        }
        ptr += btrfs_extent_inline_ref_size(type);
    }
    if (err == -ENOENT && insert) {
        if (item_size + extra_size >=
            BTRFS_MAX_EXTENT_ITEM_SIZE(root)) {
            err = -EAGAIN;
            goto out;
        }
        /*
         * To add new inline back ref, we have to make sure
         * there is no corresponding back ref item.
         * For simplicity, we just do not add new inline back
         * ref if there is any kind of item for this block
         */
        if (find_next_key(path, 0, &key) == 0 &&
            key.objectid == bytenr &&
            key.type < BTRFS_BLOCK_GROUP_ITEM_KEY) {
            err = -EAGAIN;
            goto out;
        }
    }
    *ref_ret = (struct btrfs_extent_inline_ref *)ptr;
out:
    if (insert) {
        path->keep_locks = 0;
        btrfs_unlock_up_safe(path, 1);
    }
    return err;
}

/*
 * helper to add new inline back ref
 */
static noinline_for_stack
void setup_inline_extent_backref(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 struct btrfs_extent_inline_ref *iref,
                 u64 parent, u64 root_objectid,
                 u64 owner, u64 offset, int refs_to_add,
                 struct btrfs_delayed_extent_op *extent_op)
{
    struct extent_buffer *leaf;
    struct btrfs_extent_item *ei;
    unsigned long ptr;
    unsigned long end;
    unsigned long item_offset;
    u64 refs;
    int size;
    int type;

    leaf = path->nodes[0];
    ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
    item_offset = (unsigned long)iref - (unsigned long)ei;

    type = extent_ref_type(parent, owner);
    size = btrfs_extent_inline_ref_size(type);

    btrfs_extend_item(trans, root, path, size);

    ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
    refs = btrfs_extent_refs(leaf, ei);
    refs += refs_to_add;
    btrfs_set_extent_refs(leaf, ei, refs);
    if (extent_op)
        __run_delayed_extent_op(extent_op, leaf, ei);

    ptr = (unsigned long)ei + item_offset;
    end = (unsigned long)ei + btrfs_item_size_nr(leaf, path->slots[0]);
    if (ptr < end - size)
        memmove_extent_buffer(leaf, ptr + size, ptr,
                      end - size - ptr);

    iref = (struct btrfs_extent_inline_ref *)ptr;
    btrfs_set_extent_inline_ref_type(leaf, iref, type);
    if (type == BTRFS_EXTENT_DATA_REF_KEY) {
        struct btrfs_extent_data_ref *dref;
        dref = (struct btrfs_extent_data_ref *)(&iref->offset);
        btrfs_set_extent_data_ref_root(leaf, dref, root_objectid);
        btrfs_set_extent_data_ref_objectid(leaf, dref, owner);
        btrfs_set_extent_data_ref_offset(leaf, dref, offset);
        btrfs_set_extent_data_ref_count(leaf, dref, refs_to_add);
    } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
        struct btrfs_shared_data_ref *sref;
        sref = (struct btrfs_shared_data_ref *)(iref + 1);
        btrfs_set_shared_data_ref_count(leaf, sref, refs_to_add);
        btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
    } else if (type == BTRFS_SHARED_BLOCK_REF_KEY) {
        btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
    } else {
        btrfs_set_extent_inline_ref_offset(leaf, iref, root_objectid);
    }
    btrfs_mark_buffer_dirty(leaf);
}

static int lookup_extent_backref(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 struct btrfs_extent_inline_ref **ref_ret,
                 u64 bytenr, u64 num_bytes, u64 parent,
                 u64 root_objectid, u64 owner, u64 offset)
{
    int ret;

    ret = lookup_inline_extent_backref(trans, root, path, ref_ret,
                       bytenr, num_bytes, parent,
                       root_objectid, owner, offset, 0);
    if (ret != -ENOENT)
        return ret;

    btrfs_release_path(path);
    *ref_ret = NULL;

    if (owner < BTRFS_FIRST_FREE_OBJECTID) {
        ret = lookup_tree_block_ref(trans, root, path, bytenr, parent,
                        root_objectid);
    } else {
        ret = lookup_extent_data_ref(trans, root, path, bytenr, parent,
                         root_objectid, owner, offset);
    }
    return ret;
}

/*
 * helper to update/remove inline back ref
 */
static noinline_for_stack
void update_inline_extent_backref(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root,
                  struct btrfs_path *path,
                  struct btrfs_extent_inline_ref *iref,
                  int refs_to_mod,
                  struct btrfs_delayed_extent_op *extent_op)
{
    struct extent_buffer *leaf;
    struct btrfs_extent_item *ei;
    struct btrfs_extent_data_ref *dref = NULL;
    struct btrfs_shared_data_ref *sref = NULL;
    unsigned long ptr;
    unsigned long end;
    u32 item_size;
    int size;
    int type;
    u64 refs;

    leaf = path->nodes[0];
    ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
    refs = btrfs_extent_refs(leaf, ei);
    WARN_ON(refs_to_mod < 0 && refs + refs_to_mod <= 0);
    refs += refs_to_mod;
    btrfs_set_extent_refs(leaf, ei, refs);
    if (extent_op)
        __run_delayed_extent_op(extent_op, leaf, ei);

    type = btrfs_extent_inline_ref_type(leaf, iref);

    if (type == BTRFS_EXTENT_DATA_REF_KEY) {
        dref = (struct btrfs_extent_data_ref *)(&iref->offset);
        refs = btrfs_extent_data_ref_count(leaf, dref);
    } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
        sref = (struct btrfs_shared_data_ref *)(iref + 1);
        refs = btrfs_shared_data_ref_count(leaf, sref);
    } else {
        refs = 1;
        BUG_ON(refs_to_mod != -1);
    }

    BUG_ON(refs_to_mod < 0 && refs < -refs_to_mod);
    refs += refs_to_mod;

    if (refs > 0) {
        if (type == BTRFS_EXTENT_DATA_REF_KEY)
            btrfs_set_extent_data_ref_count(leaf, dref, refs);
        else
            btrfs_set_shared_data_ref_count(leaf, sref, refs);
    } else {
        size =  btrfs_extent_inline_ref_size(type);
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        ptr = (unsigned long)iref;
        end = (unsigned long)ei + item_size;
        if (ptr + size < end)
            memmove_extent_buffer(leaf, ptr, ptr + size,
                          end - ptr - size);
        item_size -= size;
        btrfs_truncate_item(trans, root, path, item_size, 1);
    }
    btrfs_mark_buffer_dirty(leaf);
}

static noinline_for_stack
int insert_inline_extent_backref(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 u64 bytenr, u64 num_bytes, u64 parent,
                 u64 root_objectid, u64 owner,
                 u64 offset, int refs_to_add,
                 struct btrfs_delayed_extent_op *extent_op)
{
    struct btrfs_extent_inline_ref *iref;
    int ret;

    ret = lookup_inline_extent_backref(trans, root, path, &iref,
                       bytenr, num_bytes, parent,
                       root_objectid, owner, offset, 1);
    if (ret == 0) {
        BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID);
        update_inline_extent_backref(trans, root, path, iref,
                         refs_to_add, extent_op);
    } else if (ret == -ENOENT) {
        setup_inline_extent_backref(trans, root, path, iref, parent,
                        root_objectid, owner, offset,
                        refs_to_add, extent_op);
        ret = 0;
    }
    return ret;
}

static int insert_extent_backref(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 u64 bytenr, u64 parent, u64 root_objectid,
                 u64 owner, u64 offset, int refs_to_add)
{
    int ret;
    if (owner < BTRFS_FIRST_FREE_OBJECTID) {
        BUG_ON(refs_to_add != 1);
        ret = insert_tree_block_ref(trans, root, path, bytenr,
                        parent, root_objectid);
    } else {
        ret = insert_extent_data_ref(trans, root, path, bytenr,
                         parent, root_objectid,
                         owner, offset, refs_to_add);
    }
    return ret;
}

static int remove_extent_backref(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 struct btrfs_extent_inline_ref *iref,
                 int refs_to_drop, int is_data)
{
    int ret = 0;

    BUG_ON(!is_data && refs_to_drop != 1);
    if (iref) {
        update_inline_extent_backref(trans, root, path, iref,
                         -refs_to_drop, NULL);
    } else if (is_data) {
        ret = remove_extent_data_ref(trans, root, path, refs_to_drop);
    } else {
        ret = btrfs_del_item(trans, root, path);
    }
    return ret;
}

static int btrfs_issue_discard(struct block_device *bdev,
                u64 start, u64 len)
{
    return blkdev_issue_discard(bdev, start >> 9, len >> 9, GFP_NOFS, 0);
}

static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
                u64 num_bytes, u64 *actual_bytes)
{
    int ret;
    u64 discarded_bytes = 0;
    struct btrfs_bio *bbio = NULL;


    /* Tell the block device(s) that the sectors can be discarded */
    ret = btrfs_map_block(&root->fs_info->mapping_tree, REQ_DISCARD,
                  bytenr, &num_bytes, &bbio, 0);
    /* Error condition is -ENOMEM */
    if (!ret) {
        struct btrfs_bio_stripe *stripe = bbio->stripes;
        int i;


        for (i = 0; i < bbio->num_stripes; i++, stripe++) {
            if (!stripe->dev->can_discard)
                continue;

            ret = btrfs_issue_discard(stripe->dev->bdev,
                          stripe->physical,
                          stripe->length);
            if (!ret)
                discarded_bytes += stripe->length;
            else if (ret != -EOPNOTSUPP)
                break; /* Logic errors or -ENOMEM, or -EIO but I don't know how that could happen JDM */

            /*
             * Just in case we get back EOPNOTSUPP for some reason,
             * just ignore the return value so we don't screw up
             * people calling discard_extent.
             */
            ret = 0;
        }
        kfree(bbio);
    }

    if (actual_bytes)
        *actual_bytes = discarded_bytes;


    return ret;
}

/* Can return -ENOMEM */
int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
             struct btrfs_root *root,
             u64 bytenr, u64 num_bytes, u64 parent,
             u64 root_objectid, u64 owner, u64 offset, int for_cow)
{
    int ret;
    struct btrfs_fs_info *fs_info = root->fs_info;

    BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID &&
           root_objectid == BTRFS_TREE_LOG_OBJECTID);

    if (owner < BTRFS_FIRST_FREE_OBJECTID) {
        ret = btrfs_add_delayed_tree_ref(fs_info, trans, bytenr,
                    num_bytes,
                    parent, root_objectid, (int)owner,
                    BTRFS_ADD_DELAYED_REF, NULL, for_cow);
    } else {
        ret = btrfs_add_delayed_data_ref(fs_info, trans, bytenr,
                    num_bytes,
                    parent, root_objectid, owner, offset,
                    BTRFS_ADD_DELAYED_REF, NULL, for_cow);
    }
    return ret;
}

static int __btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root,
                  u64 bytenr, u64 num_bytes,
                  u64 parent, u64 root_objectid,
                  u64 owner, u64 offset, int refs_to_add,
                  struct btrfs_delayed_extent_op *extent_op)
{
    struct btrfs_path *path;
    struct extent_buffer *leaf;
    struct btrfs_extent_item *item;
    u64 refs;
    int ret;
    int err = 0;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    path->reada = 1;
    path->leave_spinning = 1;
    /* this will setup the path even if it fails to insert the back ref */
    ret = insert_inline_extent_backref(trans, root->fs_info->extent_root,
                       path, bytenr, num_bytes, parent,
                       root_objectid, owner, offset,
                       refs_to_add, extent_op);
    if (ret == 0)
        goto out;

    if (ret != -EAGAIN) {
        err = ret;
        goto out;
    }

    leaf = path->nodes[0];
    item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
    refs = btrfs_extent_refs(leaf, item);
    btrfs_set_extent_refs(leaf, item, refs + refs_to_add);
    if (extent_op)
        __run_delayed_extent_op(extent_op, leaf, item);

    btrfs_mark_buffer_dirty(leaf);
    btrfs_release_path(path);

    path->reada = 1;
    path->leave_spinning = 1;

    /* now insert the actual backref */
    ret = insert_extent_backref(trans, root->fs_info->extent_root,
                    path, bytenr, parent, root_objectid,
                    owner, offset, refs_to_add);
    if (ret)
        btrfs_abort_transaction(trans, root, ret);
out:
    btrfs_free_path(path);
    return err;
}

static int run_delayed_data_ref(struct btrfs_trans_handle *trans,
                struct btrfs_root *root,
                struct btrfs_delayed_ref_node *node,
                struct btrfs_delayed_extent_op *extent_op,
                int insert_reserved)
{
    int ret = 0;
    struct btrfs_delayed_data_ref *ref;
    struct btrfs_key ins;
    u64 parent = 0;
    u64 ref_root = 0;
    u64 flags = 0;

    ins.objectid = node->bytenr;
    ins.offset = node->num_bytes;
    ins.type = BTRFS_EXTENT_ITEM_KEY;

    ref = btrfs_delayed_node_to_data_ref(node);
    if (node->type == BTRFS_SHARED_DATA_REF_KEY)
        parent = ref->parent;
    else
        ref_root = ref->root;

    if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
        if (extent_op) {
            BUG_ON(extent_op->update_key);
            flags |= extent_op->flags_to_set;
        }
        ret = alloc_reserved_file_extent(trans, root,
                         parent, ref_root, flags,
                         ref->objectid, ref->offset,
                         &ins, node->ref_mod);
    } else if (node->action == BTRFS_ADD_DELAYED_REF) {
        ret = __btrfs_inc_extent_ref(trans, root, node->bytenr,
                         node->num_bytes, parent,
                         ref_root, ref->objectid,
                         ref->offset, node->ref_mod,
                         extent_op);
    } else if (node->action == BTRFS_DROP_DELAYED_REF) {
        ret = __btrfs_free_extent(trans, root, node->bytenr,
                      node->num_bytes, parent,
                      ref_root, ref->objectid,
                      ref->offset, node->ref_mod,
                      extent_op);
    } else {
        BUG();
    }
    return ret;
}

static void __run_delayed_extent_op(struct btrfs_delayed_extent_op *extent_op,
                    struct extent_buffer *leaf,
                    struct btrfs_extent_item *ei)
{
    u64 flags = btrfs_extent_flags(leaf, ei);
    if (extent_op->update_flags) {
        flags |= extent_op->flags_to_set;
        btrfs_set_extent_flags(leaf, ei, flags);
    }

    if (extent_op->update_key) {
        struct btrfs_tree_block_info *bi;
        BUG_ON(!(flags & BTRFS_EXTENT_FLAG_TREE_BLOCK));
        bi = (struct btrfs_tree_block_info *)(ei + 1);
        btrfs_set_tree_block_key(leaf, bi, &extent_op->key);
    }
}

static int run_delayed_extent_op(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_delayed_ref_node *node,
                 struct btrfs_delayed_extent_op *extent_op)
{
    struct btrfs_key key;
    struct btrfs_path *path;
    struct btrfs_extent_item *ei;
    struct extent_buffer *leaf;
    u32 item_size;
    int ret;
    int err = 0;

    if (trans->aborted)
        return 0;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    key.objectid = node->bytenr;
    key.type = BTRFS_EXTENT_ITEM_KEY;
    key.offset = node->num_bytes;

    path->reada = 1;
    path->leave_spinning = 1;
    ret = btrfs_search_slot(trans, root->fs_info->extent_root, &key,
                path, 0, 1);
    if (ret < 0) {
        err = ret;
        goto out;
    }
    if (ret > 0) {
        err = -EIO;
        goto out;
    }

    leaf = path->nodes[0];
    item_size = btrfs_item_size_nr(leaf, path->slots[0]);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
    if (item_size < sizeof(*ei)) {
        ret = convert_extent_item_v0(trans, root->fs_info->extent_root,
                         path, (u64)-1, 0);
        if (ret < 0) {
            err = ret;
            goto out;
        }
        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
    }
#endif
    BUG_ON(item_size < sizeof(*ei));
    ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
    __run_delayed_extent_op(extent_op, leaf, ei);

    btrfs_mark_buffer_dirty(leaf);
out:
    btrfs_free_path(path);
    return err;
}

static int run_delayed_tree_ref(struct btrfs_trans_handle *trans,
                struct btrfs_root *root,
                struct btrfs_delayed_ref_node *node,
                struct btrfs_delayed_extent_op *extent_op,
                int insert_reserved)
{
    int ret = 0;
    struct btrfs_delayed_tree_ref *ref;
    struct btrfs_key ins;
    u64 parent = 0;
    u64 ref_root = 0;

    ins.objectid = node->bytenr;
    ins.offset = node->num_bytes;
    ins.type = BTRFS_EXTENT_ITEM_KEY;

    ref = btrfs_delayed_node_to_tree_ref(node);
    if (node->type == BTRFS_SHARED_BLOCK_REF_KEY)
        parent = ref->parent;
    else
        ref_root = ref->root;

    BUG_ON(node->ref_mod != 1);
    if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
        BUG_ON(!extent_op || !extent_op->update_flags ||
               !extent_op->update_key);
        ret = alloc_reserved_tree_block(trans, root,
                        parent, ref_root,
                        extent_op->flags_to_set,
                        &extent_op->key,
                        ref->level, &ins);
    } else if (node->action == BTRFS_ADD_DELAYED_REF) {
        ret = __btrfs_inc_extent_ref(trans, root, node->bytenr,
                         node->num_bytes, parent, ref_root,
                         ref->level, 0, 1, extent_op);
    } else if (node->action == BTRFS_DROP_DELAYED_REF) {
        ret = __btrfs_free_extent(trans, root, node->bytenr,
                      node->num_bytes, parent, ref_root,
                      ref->level, 0, 1, extent_op);
    } else {
        BUG();
    }
    return ret;
}

/* helper function to actually process a single delayed ref entry */
static int run_one_delayed_ref(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root,
                   struct btrfs_delayed_ref_node *node,
                   struct btrfs_delayed_extent_op *extent_op,
                   int insert_reserved)
{
    int ret = 0;

    if (trans->aborted)
        return 0;

    if (btrfs_delayed_ref_is_head(node)) {
        struct btrfs_delayed_ref_head *head;
        /*
         * we've hit the end of the chain and we were supposed
         * to insert this extent into the tree.  But, it got
         * deleted before we ever needed to insert it, so all
         * we have to do is clean up the accounting
         */
        BUG_ON(extent_op);
        head = btrfs_delayed_node_to_head(node);
        if (insert_reserved) {
            btrfs_pin_extent(root, node->bytenr,
                     node->num_bytes, 1);
            if (head->is_data) {
                ret = btrfs_del_csums(trans, root,
                              node->bytenr,
                              node->num_bytes);
            }
        }
        mutex_unlock(&head->mutex);
        return ret;
    }

    if (node->type == BTRFS_TREE_BLOCK_REF_KEY ||
        node->type == BTRFS_SHARED_BLOCK_REF_KEY)
        ret = run_delayed_tree_ref(trans, root, node, extent_op,
                       insert_reserved);
    else if (node->type == BTRFS_EXTENT_DATA_REF_KEY ||
         node->type == BTRFS_SHARED_DATA_REF_KEY)
        ret = run_delayed_data_ref(trans, root, node, extent_op,
                       insert_reserved);
    else
        BUG();
    return ret;
}

static noinline struct btrfs_delayed_ref_node *
select_delayed_ref(struct btrfs_delayed_ref_head *head)
{
    struct rb_node *node;
    struct btrfs_delayed_ref_node *ref;
    int action = BTRFS_ADD_DELAYED_REF;
again:
    /*
     * select delayed ref of type BTRFS_ADD_DELAYED_REF first.
     * this prevents ref count from going down to zero when
     * there still are pending delayed ref.
     */
    node = rb_prev(&head->node.rb_node);
    while (1) {
        if (!node)
            break;
        ref = rb_entry(node, struct btrfs_delayed_ref_node,
                rb_node);
        if (ref->bytenr != head->node.bytenr)
            break;
        if (ref->action == action)
            return ref;
        node = rb_prev(node);
    }
    if (action == BTRFS_ADD_DELAYED_REF) {
        action = BTRFS_DROP_DELAYED_REF;
        goto again;
    }
    return NULL;
}

/*
 * Returns 0 on success or if called with an already aborted transaction.
 * Returns -ENOMEM or -EIO on failure and will abort the transaction.
 */
static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root,
                       struct list_head *cluster)
{
    struct btrfs_delayed_ref_root *delayed_refs;
    struct btrfs_delayed_ref_node *ref;
    struct btrfs_delayed_ref_head *locked_ref = NULL;
    struct btrfs_delayed_extent_op *extent_op;
    struct btrfs_fs_info *fs_info = root->fs_info;
    int ret;
    int count = 0;
    int must_insert_reserved = 0;

    delayed_refs = &trans->transaction->delayed_refs;
    while (1) {
        if (!locked_ref) {
            /* pick a new head ref from the cluster list */
            if (list_empty(cluster))
                break;

            locked_ref = list_entry(cluster->next,
                     struct btrfs_delayed_ref_head, cluster);

            /* grab the lock that says we are going to process
             * all the refs for this head */
            ret = btrfs_delayed_ref_lock(trans, locked_ref);

            /*
             * we may have dropped the spin lock to get the head
             * mutex lock, and that might have given someone else
             * time to free the head.  If that's true, it has been
             * removed from our list and we can move on.
             */
            if (ret == -EAGAIN) {
                locked_ref = NULL;
                count++;
                continue;
            }
        }

        /*
         * We need to try and merge add/drops of the same ref since we
         * can run into issues with relocate dropping the implicit ref
         * and then it being added back again before the drop can
         * finish.  If we merged anything we need to re-loop so we can
         * get a good ref.
         */
        btrfs_merge_delayed_refs(trans, fs_info, delayed_refs,
                     locked_ref);

        /*
         * locked_ref is the head node, so we have to go one
         * node back for any delayed ref updates
         */
        ref = select_delayed_ref(locked_ref);

        if (ref && ref->seq &&
            btrfs_check_delayed_seq(fs_info, delayed_refs, ref->seq)) {
            /*
             * there are still refs with lower seq numbers in the
             * process of being added. Don't run this ref yet.
             */
            list_del_init(&locked_ref->cluster);
            mutex_unlock(&locked_ref->mutex);
            locked_ref = NULL;
            delayed_refs->num_heads_ready++;
            spin_unlock(&delayed_refs->lock);
            cond_resched();
            spin_lock(&delayed_refs->lock);
            continue;
        }

        /*
         * record the must insert reserved flag before we
         * drop the spin lock.
         */
        must_insert_reserved = locked_ref->must_insert_reserved;
        locked_ref->must_insert_reserved = 0;

        extent_op = locked_ref->extent_op;
        locked_ref->extent_op = NULL;

        if (!ref) {
            /* All delayed refs have been processed, Go ahead
             * and send the head node to run_one_delayed_ref,
             * so that any accounting fixes can happen
             */
            ref = &locked_ref->node;

            if (extent_op && must_insert_reserved) {
                kfree(extent_op);
                extent_op = NULL;
            }

            if (extent_op) {
                spin_unlock(&delayed_refs->lock);

                ret = run_delayed_extent_op(trans, root,
                                ref, extent_op);
                kfree(extent_op);

                if (ret) {
                    printk(KERN_DEBUG "btrfs: run_delayed_extent_op returned %d\n", ret);
                    spin_lock(&delayed_refs->lock);
                    return ret;
                }

                goto next;
            }

            list_del_init(&locked_ref->cluster);
            locked_ref = NULL;
        }

        ref->in_tree = 0;
        rb_erase(&ref->rb_node, &delayed_refs->root);
        delayed_refs->num_entries--;
        if (locked_ref) {
            /*
             * when we play the delayed ref, also correct the
             * ref_mod on head
             */
            switch (ref->action) {
            case BTRFS_ADD_DELAYED_REF:
            case BTRFS_ADD_DELAYED_EXTENT:
                locked_ref->node.ref_mod -= ref->ref_mod;
                break;
            case BTRFS_DROP_DELAYED_REF:
                locked_ref->node.ref_mod += ref->ref_mod;
                break;
            default:
                WARN_ON(1);
            }
        }
        spin_unlock(&delayed_refs->lock);

        ret = run_one_delayed_ref(trans, root, ref, extent_op,
                      must_insert_reserved);

        btrfs_put_delayed_ref(ref);
        kfree(extent_op);
        count++;

        if (ret) {
            printk(KERN_DEBUG "btrfs: run_one_delayed_ref returned %d\n", ret);
            spin_lock(&delayed_refs->lock);
            return ret;
        }

next:
        cond_resched();
        spin_lock(&delayed_refs->lock);
    }
    return count;
}

#ifdef SCRAMBLE_DELAYED_REFS
/*
 * Normally delayed refs get processed in ascending bytenr order. This
 * correlates in most cases to the order added. To expose dependencies on this
 * order, we start to process the tree in the middle instead of the beginning
 */
static u64 find_middle(struct rb_root *root)
{
    struct rb_node *n = root->rb_node;
    struct btrfs_delayed_ref_node *entry;
    int alt = 1;
    u64 middle;
    u64 first = 0, last = 0;

    n = rb_first(root);
    if (n) {
        entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
        first = entry->bytenr;
    }
    n = rb_last(root);
    if (n) {
        entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
        last = entry->bytenr;
    }
    n = root->rb_node;

    while (n) {
        entry = rb_entry(n, struct btrfs_delayed_ref_node, rb_node);
        WARN_ON(!entry->in_tree);

        middle = entry->bytenr;

        if (alt)
            n = n->rb_left;
        else
            n = n->rb_right;

        alt = 1 - alt;
    }
    return middle;
}
#endif

int btrfs_delayed_refs_qgroup_accounting(struct btrfs_trans_handle *trans,
                     struct btrfs_fs_info *fs_info)
{
    struct qgroup_update *qgroup_update;
    int ret = 0;

    if (list_empty(&trans->qgroup_ref_list) !=
        !trans->delayed_ref_elem.seq) {
        /* list without seq or seq without list */
        printk(KERN_ERR "btrfs: qgroup accounting update error, list is%s empty, seq is %llu\n",
            list_empty(&trans->qgroup_ref_list) ? "" : " not",
            trans->delayed_ref_elem.seq);
        BUG();
    }

    if (!trans->delayed_ref_elem.seq)
        return 0;

    while (!list_empty(&trans->qgroup_ref_list)) {
        qgroup_update = list_first_entry(&trans->qgroup_ref_list,
                         struct qgroup_update, list);
        list_del(&qgroup_update->list);
        if (!ret)
            ret = btrfs_qgroup_account_ref(
                    trans, fs_info, qgroup_update->node,
                    qgroup_update->extent_op);
        kfree(qgroup_update);
    }

    btrfs_put_tree_mod_seq(fs_info, &trans->delayed_ref_elem);

    return ret;
}

/*
 * this starts processing the delayed reference count updates and
 * extent insertions we have queued up so far.  count can be
 * 0, which means to process everything in the tree at the start
 * of the run (but not newly added entries), or it can be some target
 * number you'd like to process.
 *
 * Returns 0 on success or if called with an aborted transaction
 * Returns <0 on error and aborts the transaction
 */
int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
               struct btrfs_root *root, unsigned long count)
{
    struct rb_node *node;
    struct btrfs_delayed_ref_root *delayed_refs;
    struct btrfs_delayed_ref_node *ref;
    struct list_head cluster;
    int ret;
    u64 delayed_start;
    int run_all = count == (unsigned long)-1;
    int run_most = 0;
    int loops;

    /* We'll clean this up in btrfs_cleanup_transaction */
    if (trans->aborted)
        return 0;

    if (root == root->fs_info->extent_root)
        root = root->fs_info->tree_root;

    btrfs_delayed_refs_qgroup_accounting(trans, root->fs_info);

    delayed_refs = &trans->transaction->delayed_refs;
    INIT_LIST_HEAD(&cluster);
again:
    loops = 0;
    spin_lock(&delayed_refs->lock);

#ifdef SCRAMBLE_DELAYED_REFS
    delayed_refs->run_delayed_start = find_middle(&delayed_refs->root);
#endif

    if (count == 0) {
        count = delayed_refs->num_entries * 2;
        run_most = 1;
    }
    while (1) {
        if (!(run_all || run_most) &&
            delayed_refs->num_heads_ready < 64)
            break;

        /*
         * go find something we can process in the rbtree.  We start at
         * the beginning of the tree, and then build a cluster
         * of refs to process starting at the first one we are able to
         * lock
         */
        delayed_start = delayed_refs->run_delayed_start;
        ret = btrfs_find_ref_cluster(trans, &cluster,
                         delayed_refs->run_delayed_start);
        if (ret)
            break;

        ret = run_clustered_refs(trans, root, &cluster);
        if (ret < 0) {
            spin_unlock(&delayed_refs->lock);
            btrfs_abort_transaction(trans, root, ret);
            return ret;
        }

        count -= min_t(unsigned long, ret, count);

        if (count == 0)
            break;

        if (delayed_start >= delayed_refs->run_delayed_start) {
            if (loops == 0) {
                /*
                 * btrfs_find_ref_cluster looped. let's do one
                 * more cycle. if we don't run any delayed ref
                 * during that cycle (because we can't because
                 * all of them are blocked), bail out.
                 */
                loops = 1;
            } else {
                /*
                 * no runnable refs left, stop trying
                 */
                BUG_ON(run_all);
                break;
            }
        }
        if (ret) {
            /* refs were run, let's reset staleness detection */
            loops = 0;
        }
    }

    if (run_all) {
        if (!list_empty(&trans->new_bgs)) {
            spin_unlock(&delayed_refs->lock);
            btrfs_create_pending_block_groups(trans, root);
            spin_lock(&delayed_refs->lock);
        }

        node = rb_first(&delayed_refs->root);
        if (!node)
            goto out;
        count = (unsigned long)-1;

        while (node) {
            ref = rb_entry(node, struct btrfs_delayed_ref_node,
                       rb_node);
            if (btrfs_delayed_ref_is_head(ref)) {
                struct btrfs_delayed_ref_head *head;

                head = btrfs_delayed_node_to_head(ref);
                atomic_inc(&ref->refs);

                spin_unlock(&delayed_refs->lock);
                /*
                 * Mutex was contended, block until it's
                 * released and try again
                 */
                mutex_lock(&head->mutex);
                mutex_unlock(&head->mutex);

                btrfs_put_delayed_ref(ref);
                cond_resched();
                goto again;
            }
            node = rb_next(node);
        }
        spin_unlock(&delayed_refs->lock);
        schedule_timeout(1);
        goto again;
    }
out:
    spin_unlock(&delayed_refs->lock);
    assert_qgroups_uptodate(trans);
    return 0;
}

int btrfs_set_disk_extent_flags(struct btrfs_trans_handle *trans,
                struct btrfs_root *root,
                u64 bytenr, u64 num_bytes, u64 flags,
                int is_data)
{
    struct btrfs_delayed_extent_op *extent_op;
    int ret;

    extent_op = kmalloc(sizeof(*extent_op), GFP_NOFS);
    if (!extent_op)
        return -ENOMEM;

    extent_op->flags_to_set = flags;
    extent_op->update_flags = 1;
    extent_op->update_key = 0;
    extent_op->is_data = is_data ? 1 : 0;

    ret = btrfs_add_delayed_extent_op(root->fs_info, trans, bytenr,
                      num_bytes, extent_op);
    if (ret)
        kfree(extent_op);
    return ret;
}

static noinline int check_delayed_ref(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      struct btrfs_path *path,
                      u64 objectid, u64 offset, u64 bytenr)
{
    struct btrfs_delayed_ref_head *head;
    struct btrfs_delayed_ref_node *ref;
    struct btrfs_delayed_data_ref *data_ref;
    struct btrfs_delayed_ref_root *delayed_refs;
    struct rb_node *node;
    int ret = 0;

    ret = -ENOENT;
    delayed_refs = &trans->transaction->delayed_refs;
    spin_lock(&delayed_refs->lock);
    head = btrfs_find_delayed_ref_head(trans, bytenr);
    if (!head)
        goto out;

    if (!mutex_trylock(&head->mutex)) {
        atomic_inc(&head->node.refs);
        spin_unlock(&delayed_refs->lock);

        btrfs_release_path(path);

        /*
         * Mutex was contended, block until it's released and let
         * caller try again
         */
        mutex_lock(&head->mutex);
        mutex_unlock(&head->mutex);
        btrfs_put_delayed_ref(&head->node);
        return -EAGAIN;
    }

    node = rb_prev(&head->node.rb_node);
    if (!node)
        goto out_unlock;

    ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);

    if (ref->bytenr != bytenr)
        goto out_unlock;

    ret = 1;
    if (ref->type != BTRFS_EXTENT_DATA_REF_KEY)
        goto out_unlock;

    data_ref = btrfs_delayed_node_to_data_ref(ref);

    node = rb_prev(node);
    if (node) {
        int seq = ref->seq;

        ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);
        if (ref->bytenr == bytenr && ref->seq == seq)
            goto out_unlock;
    }

    if (data_ref->root != root->root_key.objectid ||
        data_ref->objectid != objectid || data_ref->offset != offset)
        goto out_unlock;

    ret = 0;
out_unlock:
    mutex_unlock(&head->mutex);
out:
    spin_unlock(&delayed_refs->lock);
    return ret;
}

static noinline int check_committed_ref(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root,
                    struct btrfs_path *path,
                    u64 objectid, u64 offset, u64 bytenr)
{
    struct btrfs_root *extent_root = root->fs_info->extent_root;
    struct extent_buffer *leaf;
    struct btrfs_extent_data_ref *ref;
    struct btrfs_extent_inline_ref *iref;
    struct btrfs_extent_item *ei;
    struct btrfs_key key;
    u32 item_size;
    int ret;

    key.objectid = bytenr;
    key.offset = (u64)-1;
    key.type = BTRFS_EXTENT_ITEM_KEY;

    ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
    if (ret < 0)
        goto out;
    BUG_ON(ret == 0); /* Corruption */

    ret = -ENOENT;
    if (path->slots[0] == 0)
        goto out;

    path->slots[0]--;
    leaf = path->nodes[0];
    btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

    if (key.objectid != bytenr || key.type != BTRFS_EXTENT_ITEM_KEY)
        goto out;

    ret = 1;
    item_size = btrfs_item_size_nr(leaf, path->slots[0]);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
    if (item_size < sizeof(*ei)) {
        WARN_ON(item_size != sizeof(struct btrfs_extent_item_v0));
        goto out;
    }
#endif
    ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);

    if (item_size != sizeof(*ei) +
        btrfs_extent_inline_ref_size(BTRFS_EXTENT_DATA_REF_KEY))
        goto out;

    if (btrfs_extent_generation(leaf, ei) <=
        btrfs_root_last_snapshot(&root->root_item))
        goto out;

    iref = (struct btrfs_extent_inline_ref *)(ei + 1);
    if (btrfs_extent_inline_ref_type(leaf, iref) !=
        BTRFS_EXTENT_DATA_REF_KEY)
        goto out;

    ref = (struct btrfs_extent_data_ref *)(&iref->offset);
    if (btrfs_extent_refs(leaf, ei) !=
        btrfs_extent_data_ref_count(leaf, ref) ||
        btrfs_extent_data_ref_root(leaf, ref) !=
        root->root_key.objectid ||
        btrfs_extent_data_ref_objectid(leaf, ref) != objectid ||
        btrfs_extent_data_ref_offset(leaf, ref) != offset)
        goto out;

    ret = 0;
out:
    return ret;
}

int btrfs_cross_ref_exist(struct btrfs_trans_handle *trans,
              struct btrfs_root *root,
              u64 objectid, u64 offset, u64 bytenr)
{
    struct btrfs_path *path;
    int ret;
    int ret2;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOENT;

    do {
        ret = check_committed_ref(trans, root, path, objectid,
                      offset, bytenr);
        if (ret && ret != -ENOENT)
            goto out;

        ret2 = check_delayed_ref(trans, root, path, objectid,
                     offset, bytenr);
    } while (ret2 == -EAGAIN);

    if (ret2 && ret2 != -ENOENT) {
        ret = ret2;
        goto out;
    }

    if (ret != -ENOENT || ret2 != -ENOENT)
        ret = 0;
out:
    btrfs_free_path(path);
    if (root->root_key.objectid == BTRFS_DATA_RELOC_TREE_OBJECTID)
        WARN_ON(ret > 0);
    return ret;
}

static int __btrfs_mod_ref(struct btrfs_trans_handle *trans,
               struct btrfs_root *root,
               struct extent_buffer *buf,
               int full_backref, int inc, int for_cow)
{
    u64 bytenr;
    u64 num_bytes;
    u64 parent;
    u64 ref_root;
    u32 nritems;
    struct btrfs_key key;
    struct btrfs_file_extent_item *fi;
    int i;
    int level;
    int ret = 0;
    int (*process_func)(struct btrfs_trans_handle *, struct btrfs_root *,
                u64, u64, u64, u64, u64, u64, int);

    ref_root = btrfs_header_owner(buf);
    nritems = btrfs_header_nritems(buf);
    level = btrfs_header_level(buf);

    if (!root->ref_cows && level == 0)
        return 0;

    if (inc)
        process_func = btrfs_inc_extent_ref;
    else
        process_func = btrfs_free_extent;

    if (full_backref)
        parent = buf->start;
    else
        parent = 0;

    for (i = 0; i < nritems; i++) {
        if (level == 0) {
            btrfs_item_key_to_cpu(buf, &key, i);
            if (btrfs_key_type(&key) != BTRFS_EXTENT_DATA_KEY)
                continue;
            fi = btrfs_item_ptr(buf, i,
                        struct btrfs_file_extent_item);
            if (btrfs_file_extent_type(buf, fi) ==
                BTRFS_FILE_EXTENT_INLINE)
                continue;
            bytenr = btrfs_file_extent_disk_bytenr(buf, fi);
            if (bytenr == 0)
                continue;

            num_bytes = btrfs_file_extent_disk_num_bytes(buf, fi);
            key.offset -= btrfs_file_extent_offset(buf, fi);
            ret = process_func(trans, root, bytenr, num_bytes,
                       parent, ref_root, key.objectid,
                       key.offset, for_cow);
            if (ret)
                goto fail;
        } else {
            bytenr = btrfs_node_blockptr(buf, i);
            num_bytes = btrfs_level_size(root, level - 1);
            ret = process_func(trans, root, bytenr, num_bytes,
                       parent, ref_root, level - 1, 0,
                       for_cow);
            if (ret)
                goto fail;
        }
    }
    return 0;
fail:
    return ret;
}

int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
          struct extent_buffer *buf, int full_backref, int for_cow)
{
    return __btrfs_mod_ref(trans, root, buf, full_backref, 1, for_cow);
}

int btrfs_dec_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
          struct extent_buffer *buf, int full_backref, int for_cow)
{
    return __btrfs_mod_ref(trans, root, buf, full_backref, 0, for_cow);
}

static int write_one_cache_group(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 struct btrfs_block_group_cache *cache)
{
    int ret;
    struct btrfs_root *extent_root = root->fs_info->extent_root;
    unsigned long bi;
    struct extent_buffer *leaf;

    ret = btrfs_search_slot(trans, extent_root, &cache->key, path, 0, 1);
    if (ret < 0)
        goto fail;
    BUG_ON(ret); /* Corruption */

    leaf = path->nodes[0];
    bi = btrfs_item_ptr_offset(leaf, path->slots[0]);
    write_extent_buffer(leaf, &cache->item, bi, sizeof(cache->item));
    btrfs_mark_buffer_dirty(leaf);
    btrfs_release_path(path);
fail:
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        return ret;
    }
    return 0;

}

static struct btrfs_block_group_cache *
next_block_group(struct btrfs_root *root,
         struct btrfs_block_group_cache *cache)
{
    struct rb_node *node;
    spin_lock(&root->fs_info->block_group_cache_lock);
    node = rb_next(&cache->cache_node);
    btrfs_put_block_group(cache);
    if (node) {
        cache = rb_entry(node, struct btrfs_block_group_cache,
                 cache_node);
        btrfs_get_block_group(cache);
    } else
        cache = NULL;
    spin_unlock(&root->fs_info->block_group_cache_lock);
    return cache;
}

static int cache_save_setup(struct btrfs_block_group_cache *block_group,
                struct btrfs_trans_handle *trans,
                struct btrfs_path *path)
{
    struct btrfs_root *root = block_group->fs_info->tree_root;
    struct inode *inode = NULL;
    u64 alloc_hint = 0;
    int dcs = BTRFS_DC_ERROR;
    int num_pages = 0;
    int retries = 0;
    int ret = 0;

    /*
     * If this block group is smaller than 100 megs don't bother caching the
     * block group.
     */
    if (block_group->key.offset < (100 * 1024 * 1024)) {
        spin_lock(&block_group->lock);
        block_group->disk_cache_state = BTRFS_DC_WRITTEN;
        spin_unlock(&block_group->lock);
        return 0;
    }

again:
    inode = lookup_free_space_inode(root, block_group, path);
    if (IS_ERR(inode) && PTR_ERR(inode) != -ENOENT) {
        ret = PTR_ERR(inode);
        btrfs_release_path(path);
        goto out;
    }

    if (IS_ERR(inode)) {
        BUG_ON(retries);
        retries++;

        if (block_group->ro)
            goto out_free;

        ret = create_free_space_inode(root, trans, block_group, path);
        if (ret)
            goto out_free;
        goto again;
    }

    /* We've already setup this transaction, go ahead and exit */
    if (block_group->cache_generation == trans->transid &&
        i_size_read(inode)) {
        dcs = BTRFS_DC_SETUP;
        goto out_put;
    }

    /*
     * We want to set the generation to 0, that way if anything goes wrong
     * from here on out we know not to trust this cache when we load up next
     * time.
     */
    BTRFS_I(inode)->generation = 0;
    ret = btrfs_update_inode(trans, root, inode);
    WARN_ON(ret);

    if (i_size_read(inode) > 0) {
        ret = btrfs_truncate_free_space_cache(root, trans, path,
                              inode);
        if (ret)
            goto out_put;
    }

    spin_lock(&block_group->lock);
    if (block_group->cached != BTRFS_CACHE_FINISHED ||
        !btrfs_test_opt(root, SPACE_CACHE)) {
        /*
         * don't bother trying to write stuff out _if_
         * a) we're not cached,
         * b) we're with nospace_cache mount option.
         */
        dcs = BTRFS_DC_WRITTEN;
        spin_unlock(&block_group->lock);
        goto out_put;
    }
    spin_unlock(&block_group->lock);

    /*
     * Try to preallocate enough space based on how big the block group is.
     * Keep in mind this has to include any pinned space which could end up
     * taking up quite a bit since it's not folded into the other space
     * cache.
     */
    num_pages = (int)div64_u64(block_group->key.offset, 256 * 1024 * 1024);
    if (!num_pages)
        num_pages = 1;

    num_pages *= 16;
    num_pages *= PAGE_CACHE_SIZE;

    ret = btrfs_check_data_free_space(inode, num_pages);
    if (ret)
        goto out_put;

    ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, num_pages,
                          num_pages, num_pages,
                          &alloc_hint);
    if (!ret)
        dcs = BTRFS_DC_SETUP;
    btrfs_free_reserved_data_space(inode, num_pages);

out_put:
    iput(inode);
out_free:
    btrfs_release_path(path);
out:
    spin_lock(&block_group->lock);
    if (!ret && dcs == BTRFS_DC_SETUP)
        block_group->cache_generation = trans->transid;
    block_group->disk_cache_state = dcs;
    spin_unlock(&block_group->lock);

    return ret;
}

int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root)
{
    struct btrfs_block_group_cache *cache;
    int err = 0;
    struct btrfs_path *path;
    u64 last = 0;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

again:
    while (1) {
        cache = btrfs_lookup_first_block_group(root->fs_info, last);
        while (cache) {
            if (cache->disk_cache_state == BTRFS_DC_CLEAR)
                break;
            cache = next_block_group(root, cache);
        }
        if (!cache) {
            if (last == 0)
                break;
            last = 0;
            continue;
        }
        err = cache_save_setup(cache, trans, path);
        last = cache->key.objectid + cache->key.offset;
        btrfs_put_block_group(cache);
    }

    while (1) {
        if (last == 0) {
            err = btrfs_run_delayed_refs(trans, root,
                             (unsigned long)-1);
            if (err) /* File system offline */
                goto out;
        }

        cache = btrfs_lookup_first_block_group(root->fs_info, last);
        while (cache) {
            if (cache->disk_cache_state == BTRFS_DC_CLEAR) {
                btrfs_put_block_group(cache);
                goto again;
            }

            if (cache->dirty)
                break;
            cache = next_block_group(root, cache);
        }
        if (!cache) {
            if (last == 0)
                break;
            last = 0;
            continue;
        }

        if (cache->disk_cache_state == BTRFS_DC_SETUP)
            cache->disk_cache_state = BTRFS_DC_NEED_WRITE;
        cache->dirty = 0;
        last = cache->key.objectid + cache->key.offset;

        err = write_one_cache_group(trans, root, path, cache);
        if (err) /* File system offline */
            goto out;

        btrfs_put_block_group(cache);
    }

    while (1) {
        /*
         * I don't think this is needed since we're just marking our
         * preallocated extent as written, but just in case it can't
         * hurt.
         */
        if (last == 0) {
            err = btrfs_run_delayed_refs(trans, root,
                             (unsigned long)-1);
            if (err) /* File system offline */
                goto out;
        }

        cache = btrfs_lookup_first_block_group(root->fs_info, last);
        while (cache) {
            /*
             * Really this shouldn't happen, but it could if we
             * couldn't write the entire preallocated extent and
             * splitting the extent resulted in a new block.
             */
            if (cache->dirty) {
                btrfs_put_block_group(cache);
                goto again;
            }
            if (cache->disk_cache_state == BTRFS_DC_NEED_WRITE)
                break;
            cache = next_block_group(root, cache);
        }
        if (!cache) {
            if (last == 0)
                break;
            last = 0;
            continue;
        }

        err = btrfs_write_out_cache(root, trans, cache, path);

        /*
         * If we didn't have an error then the cache state is still
         * NEED_WRITE, so we can set it to WRITTEN.
         */
        if (!err && cache->disk_cache_state == BTRFS_DC_NEED_WRITE)
            cache->disk_cache_state = BTRFS_DC_WRITTEN;
        last = cache->key.objectid + cache->key.offset;
        btrfs_put_block_group(cache);
    }
out:

    btrfs_free_path(path);
    return err;
}

int btrfs_extent_readonly(struct btrfs_root *root, u64 bytenr)
{
    struct btrfs_block_group_cache *block_group;
    int readonly = 0;

    block_group = btrfs_lookup_block_group(root->fs_info, bytenr);
    if (!block_group || block_group->ro)
        readonly = 1;
    if (block_group)
        btrfs_put_block_group(block_group);
    return readonly;
}

static int update_space_info(struct btrfs_fs_info *info, u64 flags,
                 u64 total_bytes, u64 bytes_used,
                 struct btrfs_space_info **space_info)
{
    struct btrfs_space_info *found;
    int i;
    int factor;

    if (flags & (BTRFS_BLOCK_GROUP_DUP | BTRFS_BLOCK_GROUP_RAID1 |
             BTRFS_BLOCK_GROUP_RAID10))
        factor = 2;
    else
        factor = 1;

    found = __find_space_info(info, flags);
    if (found) {
        spin_lock(&found->lock);
        found->total_bytes += total_bytes;
        found->disk_total += total_bytes * factor;
        found->bytes_used += bytes_used;
        found->disk_used += bytes_used * factor;
        found->full = 0;
        spin_unlock(&found->lock);
        *space_info = found;
        return 0;
    }
    found = kzalloc(sizeof(*found), GFP_NOFS);
    if (!found)
        return -ENOMEM;

    for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
        INIT_LIST_HEAD(&found->block_groups[i]);
    init_rwsem(&found->groups_sem);
    spin_lock_init(&found->lock);
    found->flags = flags & BTRFS_BLOCK_GROUP_TYPE_MASK;
    found->total_bytes = total_bytes;
    found->disk_total = total_bytes * factor;
    found->bytes_used = bytes_used;
    found->disk_used = bytes_used * factor;
    found->bytes_pinned = 0;
    found->bytes_reserved = 0;
    found->bytes_readonly = 0;
    found->bytes_may_use = 0;
    found->full = 0;
    found->force_alloc = CHUNK_ALLOC_NO_FORCE;
    found->chunk_alloc = 0;
    found->flush = 0;
    init_waitqueue_head(&found->wait);
    *space_info = found;
    list_add_rcu(&found->list, &info->space_info);
    if (flags & BTRFS_BLOCK_GROUP_DATA)
        info->data_sinfo = found;
    return 0;
}

static void set_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
{
    u64 extra_flags = chunk_to_extended(flags) &
                BTRFS_EXTENDED_PROFILE_MASK;

    if (flags & BTRFS_BLOCK_GROUP_DATA)
        fs_info->avail_data_alloc_bits |= extra_flags;
    if (flags & BTRFS_BLOCK_GROUP_METADATA)
        fs_info->avail_metadata_alloc_bits |= extra_flags;
    if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
        fs_info->avail_system_alloc_bits |= extra_flags;
}

/*
 * returns target flags in extended format or 0 if restripe for this
 * chunk_type is not in progress
 *
 * should be called with either volume_mutex or balance_lock held
 */
static u64 get_restripe_target(struct btrfs_fs_info *fs_info, u64 flags)
{
    struct btrfs_balance_control *bctl = fs_info->balance_ctl;
    u64 target = 0;

    if (!bctl)
        return 0;

    if (flags & BTRFS_BLOCK_GROUP_DATA &&
        bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) {
        target = BTRFS_BLOCK_GROUP_DATA | bctl->data.target;
    } else if (flags & BTRFS_BLOCK_GROUP_SYSTEM &&
           bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) {
        target = BTRFS_BLOCK_GROUP_SYSTEM | bctl->sys.target;
    } else if (flags & BTRFS_BLOCK_GROUP_METADATA &&
           bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) {
        target = BTRFS_BLOCK_GROUP_METADATA | bctl->meta.target;
    }

    return target;
}

/*
 * @flags: available profiles in extended format (see ctree.h)
 *
 * Returns reduced profile in chunk format.  If profile changing is in
 * progress (either running or paused) picks the target profile (if it's
 * already available), otherwise falls back to plain reducing.
 */
u64 btrfs_reduce_alloc_profile(struct btrfs_root *root, u64 flags)
{
    /*
     * we add in the count of missing devices because we want
     * to make sure that any RAID levels on a degraded FS
     * continue to be honored.
     */
    u64 num_devices = root->fs_info->fs_devices->rw_devices +
        root->fs_info->fs_devices->missing_devices;
    u64 target;

    /*
     * see if restripe for this chunk_type is in progress, if so
     * try to reduce to the target profile
     */
    spin_lock(&root->fs_info->balance_lock);
    target = get_restripe_target(root->fs_info, flags);
    if (target) {
        /* pick target profile only if it's already available */
        if ((flags & target) & BTRFS_EXTENDED_PROFILE_MASK) {
            spin_unlock(&root->fs_info->balance_lock);
            return extended_to_chunk(target);
        }
    }
    spin_unlock(&root->fs_info->balance_lock);

    if (num_devices == 1)
        flags &= ~(BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_RAID0);
    if (num_devices < 4)
        flags &= ~BTRFS_BLOCK_GROUP_RAID10;

    if ((flags & BTRFS_BLOCK_GROUP_DUP) &&
        (flags & (BTRFS_BLOCK_GROUP_RAID1 |
              BTRFS_BLOCK_GROUP_RAID10))) {
        flags &= ~BTRFS_BLOCK_GROUP_DUP;
    }

    if ((flags & BTRFS_BLOCK_GROUP_RAID1) &&
        (flags & BTRFS_BLOCK_GROUP_RAID10)) {
        flags &= ~BTRFS_BLOCK_GROUP_RAID1;
    }

    if ((flags & BTRFS_BLOCK_GROUP_RAID0) &&
        ((flags & BTRFS_BLOCK_GROUP_RAID1) |
         (flags & BTRFS_BLOCK_GROUP_RAID10) |
         (flags & BTRFS_BLOCK_GROUP_DUP))) {
        flags &= ~BTRFS_BLOCK_GROUP_RAID0;
    }

    return extended_to_chunk(flags);
}

static u64 get_alloc_profile(struct btrfs_root *root, u64 flags)
{
    if (flags & BTRFS_BLOCK_GROUP_DATA)
        flags |= root->fs_info->avail_data_alloc_bits;
    else if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
        flags |= root->fs_info->avail_system_alloc_bits;
    else if (flags & BTRFS_BLOCK_GROUP_METADATA)
        flags |= root->fs_info->avail_metadata_alloc_bits;

    return btrfs_reduce_alloc_profile(root, flags);
}

u64 btrfs_get_alloc_profile(struct btrfs_root *root, int data)
{
    u64 flags;

    if (data)
        flags = BTRFS_BLOCK_GROUP_DATA;
    else if (root == root->fs_info->chunk_root)
        flags = BTRFS_BLOCK_GROUP_SYSTEM;
    else
        flags = BTRFS_BLOCK_GROUP_METADATA;

    return get_alloc_profile(root, flags);
}

/*
 * This will check the space that the inode allocates from to make sure we have
 * enough space for bytes.
 */
int btrfs_check_data_free_space(struct inode *inode, u64 bytes)
{
    struct btrfs_space_info *data_sinfo;
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct btrfs_fs_info *fs_info = root->fs_info;
    u64 used;
    int ret = 0, committed = 0, alloc_chunk = 1;

    /* make sure bytes are sectorsize aligned */
    bytes = (bytes + root->sectorsize - 1) & ~((u64)root->sectorsize - 1);

    if (root == root->fs_info->tree_root ||
        BTRFS_I(inode)->location.objectid == BTRFS_FREE_INO_OBJECTID) {
        alloc_chunk = 0;
        committed = 1;
    }

    data_sinfo = fs_info->data_sinfo;
    if (!data_sinfo)
        goto alloc;

again:
    /* make sure we have enough space to handle the data first */
    spin_lock(&data_sinfo->lock);
    used = data_sinfo->bytes_used + data_sinfo->bytes_reserved +
        data_sinfo->bytes_pinned + data_sinfo->bytes_readonly +
        data_sinfo->bytes_may_use;

    if (used + bytes > data_sinfo->total_bytes) {
        struct btrfs_trans_handle *trans;

        /*
         * if we don't have enough free bytes in this space then we need
         * to alloc a new chunk.
         */
        if (!data_sinfo->full && alloc_chunk) {
            u64 alloc_target;

            data_sinfo->force_alloc = CHUNK_ALLOC_FORCE;
            spin_unlock(&data_sinfo->lock);
alloc:
            alloc_target = btrfs_get_alloc_profile(root, 1);
            trans = btrfs_join_transaction(root);
            if (IS_ERR(trans))
                return PTR_ERR(trans);

            ret = do_chunk_alloc(trans, root->fs_info->extent_root,
                         alloc_target,
                         CHUNK_ALLOC_NO_FORCE);
            btrfs_end_transaction(trans, root);
            if (ret < 0) {
                if (ret != -ENOSPC)
                    return ret;
                else
                    goto commit_trans;
            }

            if (!data_sinfo)
                data_sinfo = fs_info->data_sinfo;

            goto again;
        }

        /*
         * If we have less pinned bytes than we want to allocate then
         * don't bother committing the transaction, it won't help us.
         */
        if (data_sinfo->bytes_pinned < bytes)
            committed = 1;
        spin_unlock(&data_sinfo->lock);

        /* commit the current transaction and try again */
commit_trans:
        if (!committed &&
            !atomic_read(&root->fs_info->open_ioctl_trans)) {
            committed = 1;
            trans = btrfs_join_transaction(root);
            if (IS_ERR(trans))
                return PTR_ERR(trans);
            ret = btrfs_commit_transaction(trans, root);
            if (ret)
                return ret;
            goto again;
        }

        return -ENOSPC;
    }
    data_sinfo->bytes_may_use += bytes;
    trace_btrfs_space_reservation(root->fs_info, "space_info",
                      data_sinfo->flags, bytes, 1);
    spin_unlock(&data_sinfo->lock);

    return 0;
}

/*
 * Called if we need to clear a data reservation for this inode.
 */
void btrfs_free_reserved_data_space(struct inode *inode, u64 bytes)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct btrfs_space_info *data_sinfo;

    /* make sure bytes are sectorsize aligned */
    bytes = (bytes + root->sectorsize - 1) & ~((u64)root->sectorsize - 1);

    data_sinfo = root->fs_info->data_sinfo;
    spin_lock(&data_sinfo->lock);
    data_sinfo->bytes_may_use -= bytes;
    trace_btrfs_space_reservation(root->fs_info, "space_info",
                      data_sinfo->flags, bytes, 0);
    spin_unlock(&data_sinfo->lock);
}

static void force_metadata_allocation(struct btrfs_fs_info *info)
{
    struct list_head *head = &info->space_info;
    struct btrfs_space_info *found;

    rcu_read_lock();
    list_for_each_entry_rcu(found, head, list) {
        if (found->flags & BTRFS_BLOCK_GROUP_METADATA)
            found->force_alloc = CHUNK_ALLOC_FORCE;
    }
    rcu_read_unlock();
}

static int should_alloc_chunk(struct btrfs_root *root,
                  struct btrfs_space_info *sinfo, int force)
{
    struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
    u64 num_bytes = sinfo->total_bytes - sinfo->bytes_readonly;
    u64 num_allocated = sinfo->bytes_used + sinfo->bytes_reserved;
    u64 thresh;

    if (force == CHUNK_ALLOC_FORCE)
        return 1;

    /*
     * We need to take into account the global rsv because for all intents
     * and purposes it's used space.  Don't worry about locking the
     * global_rsv, it doesn't change except when the transaction commits.
     */
    if (sinfo->flags & BTRFS_BLOCK_GROUP_METADATA)
        num_allocated += global_rsv->size;

    /*
     * in limited mode, we want to have some free space up to
     * about 1% of the FS size.
     */
    if (force == CHUNK_ALLOC_LIMITED) {
        thresh = btrfs_super_total_bytes(root->fs_info->super_copy);
        thresh = max_t(u64, 64 * 1024 * 1024,
                   div_factor_fine(thresh, 1));

        if (num_bytes - num_allocated < thresh)
            return 1;
    }

    if (num_allocated + 2 * 1024 * 1024 < div_factor(num_bytes, 8))
        return 0;
    return 1;
}

static u64 get_system_chunk_thresh(struct btrfs_root *root, u64 type)
{
    u64 num_dev;

    if (type & BTRFS_BLOCK_GROUP_RAID10 ||
        type & BTRFS_BLOCK_GROUP_RAID0)
        num_dev = root->fs_info->fs_devices->rw_devices;
    else if (type & BTRFS_BLOCK_GROUP_RAID1)
        num_dev = 2;
    else
        num_dev = 1;    /* DUP or single */

    /* metadata for updaing devices and chunk tree */
    return btrfs_calc_trans_metadata_size(root, num_dev + 1);
}

static void check_system_chunk(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root, u64 type)
{
    struct btrfs_space_info *info;
    u64 left;
    u64 thresh;

    info = __find_space_info(root->fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
    spin_lock(&info->lock);
    left = info->total_bytes - info->bytes_used - info->bytes_pinned -
        info->bytes_reserved - info->bytes_readonly;
    spin_unlock(&info->lock);

    thresh = get_system_chunk_thresh(root, type);
    if (left < thresh && btrfs_test_opt(root, ENOSPC_DEBUG)) {
        printk(KERN_INFO "left=%llu, need=%llu, flags=%llu\n",
               left, thresh, type);
        dump_space_info(info, 0, 0);
    }

    if (left < thresh) {
        u64 flags;

        flags = btrfs_get_alloc_profile(root->fs_info->chunk_root, 0);
        btrfs_alloc_chunk(trans, root, flags);
    }
}

static int do_chunk_alloc(struct btrfs_trans_handle *trans,
              struct btrfs_root *extent_root, u64 flags, int force)
{
    struct btrfs_space_info *space_info;
    struct btrfs_fs_info *fs_info = extent_root->fs_info;
    int wait_for_alloc = 0;
    int ret = 0;

    space_info = __find_space_info(extent_root->fs_info, flags);
    if (!space_info) {
        ret = update_space_info(extent_root->fs_info, flags,
                    0, 0, &space_info);
        BUG_ON(ret); /* -ENOMEM */
    }
    BUG_ON(!space_info); /* Logic error */

again:
    spin_lock(&space_info->lock);
    if (force < space_info->force_alloc)
        force = space_info->force_alloc;
    if (space_info->full) {
        spin_unlock(&space_info->lock);
        return 0;
    }

    if (!should_alloc_chunk(extent_root, space_info, force)) {
        spin_unlock(&space_info->lock);
        return 0;
    } else if (space_info->chunk_alloc) {
        wait_for_alloc = 1;
    } else {
        space_info->chunk_alloc = 1;
    }

    spin_unlock(&space_info->lock);

    mutex_lock(&fs_info->chunk_mutex);

    /*
     * The chunk_mutex is held throughout the entirety of a chunk
     * allocation, so once we've acquired the chunk_mutex we know that the
     * other guy is done and we need to recheck and see if we should
     * allocate.
     */
    if (wait_for_alloc) {
        mutex_unlock(&fs_info->chunk_mutex);
        wait_for_alloc = 0;
        goto again;
    }

    /*
     * If we have mixed data/metadata chunks we want to make sure we keep
     * allocating mixed chunks instead of individual chunks.
     */
    if (btrfs_mixed_space_info(space_info))
        flags |= (BTRFS_BLOCK_GROUP_DATA | BTRFS_BLOCK_GROUP_METADATA);

    /*
     * if we're doing a data chunk, go ahead and make sure that
     * we keep a reasonable number of metadata chunks allocated in the
     * FS as well.
     */
    if (flags & BTRFS_BLOCK_GROUP_DATA && fs_info->metadata_ratio) {
        fs_info->data_chunk_allocations++;
        if (!(fs_info->data_chunk_allocations %
              fs_info->metadata_ratio))
            force_metadata_allocation(fs_info);
    }

    /*
     * Check if we have enough space in SYSTEM chunk because we may need
     * to update devices.
     */
    check_system_chunk(trans, extent_root, flags);

    ret = btrfs_alloc_chunk(trans, extent_root, flags);
    if (ret < 0 && ret != -ENOSPC)
        goto out;

    spin_lock(&space_info->lock);
    if (ret)
        space_info->full = 1;
    else
        ret = 1;

    space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
    space_info->chunk_alloc = 0;
    spin_unlock(&space_info->lock);
out:
    mutex_unlock(&fs_info->chunk_mutex);
    return ret;
}

static int can_overcommit(struct btrfs_root *root,
              struct btrfs_space_info *space_info, u64 bytes,
              int flush)
{
    u64 profile = btrfs_get_alloc_profile(root, 0);
    u64 avail;
    u64 used;

    used = space_info->bytes_used + space_info->bytes_reserved +
        space_info->bytes_pinned + space_info->bytes_readonly +
        space_info->bytes_may_use;

    spin_lock(&root->fs_info->free_chunk_lock);
    avail = root->fs_info->free_chunk_space;
    spin_unlock(&root->fs_info->free_chunk_lock);

    /*
     * If we have dup, raid1 or raid10 then only half of the free
     * space is actually useable.
     */
    if (profile & (BTRFS_BLOCK_GROUP_DUP |
               BTRFS_BLOCK_GROUP_RAID1 |
               BTRFS_BLOCK_GROUP_RAID10))
        avail >>= 1;

    /*
     * If we aren't flushing don't let us overcommit too much, say
     * 1/8th of the space.  If we can flush, let it overcommit up to
     * 1/2 of the space.
     */
    if (flush)
        avail >>= 3;
    else
        avail >>= 1;

    if (used + bytes < space_info->total_bytes + avail)
        return 1;
    return 0;
}

/*
 * shrink metadata reservation for delalloc
 */
static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
                bool wait_ordered)
{
    struct btrfs_block_rsv *block_rsv;
    struct btrfs_space_info *space_info;
    struct btrfs_trans_handle *trans;
    u64 delalloc_bytes;
    u64 max_reclaim;
    long time_left;
    unsigned long nr_pages = (2 * 1024 * 1024) >> PAGE_CACHE_SHIFT;
    int loops = 0;

    trans = (struct btrfs_trans_handle *)current->journal_info;
    block_rsv = &root->fs_info->delalloc_block_rsv;
    space_info = block_rsv->space_info;

    smp_mb();
    delalloc_bytes = root->fs_info->delalloc_bytes;
    if (delalloc_bytes == 0) {
        if (trans)
            return;
        btrfs_wait_ordered_extents(root, 0);
        return;
    }

    while (delalloc_bytes && loops < 3) {
        max_reclaim = min(delalloc_bytes, to_reclaim);
        nr_pages = max_reclaim >> PAGE_CACHE_SHIFT;
        writeback_inodes_sb_nr_if_idle(root->fs_info->sb, nr_pages,
                           WB_REASON_FS_FREE_SPACE);

        /*
         * We need to wait for the async pages to actually start before
         * we do anything.
         */
        wait_event(root->fs_info->async_submit_wait,
               !atomic_read(&root->fs_info->async_delalloc_pages));

        spin_lock(&space_info->lock);
        if (can_overcommit(root, space_info, orig, !trans)) {
            spin_unlock(&space_info->lock);
            break;
        }
        spin_unlock(&space_info->lock);

        loops++;
        if (wait_ordered && !trans) {
            btrfs_wait_ordered_extents(root, 0);
        } else {
            time_left = schedule_timeout_killable(1);
            if (time_left)
                break;
        }
        smp_mb();
        delalloc_bytes = root->fs_info->delalloc_bytes;
    }
}

static int may_commit_transaction(struct btrfs_root *root,
                  struct btrfs_space_info *space_info,
                  u64 bytes, int force)
{
    struct btrfs_block_rsv *delayed_rsv = &root->fs_info->delayed_block_rsv;
    struct btrfs_trans_handle *trans;

    trans = (struct btrfs_trans_handle *)current->journal_info;
    if (trans)
        return -EAGAIN;

    if (force)
        goto commit;

    /* See if there is enough pinned space to make this reservation */
    spin_lock(&space_info->lock);
    if (space_info->bytes_pinned >= bytes) {
        spin_unlock(&space_info->lock);
        goto commit;
    }
    spin_unlock(&space_info->lock);

    /*
     * See if there is some space in the delayed insertion reservation for
     * this reservation.
     */
    if (space_info != delayed_rsv->space_info)
        return -ENOSPC;

    spin_lock(&space_info->lock);
    spin_lock(&delayed_rsv->lock);
    if (space_info->bytes_pinned + delayed_rsv->size < bytes) {
        spin_unlock(&delayed_rsv->lock);
        spin_unlock(&space_info->lock);
        return -ENOSPC;
    }
    spin_unlock(&delayed_rsv->lock);
    spin_unlock(&space_info->lock);

commit:
    trans = btrfs_join_transaction(root);
    if (IS_ERR(trans))
        return -ENOSPC;

    return btrfs_commit_transaction(trans, root);
}

enum flush_state {
    FLUSH_DELAYED_ITEMS_NR  =   1,
    FLUSH_DELAYED_ITEMS =   2,
    FLUSH_DELALLOC      =   3,
    FLUSH_DELALLOC_WAIT =   4,
    ALLOC_CHUNK     =   5,
    COMMIT_TRANS        =   6,
};

static int flush_space(struct btrfs_root *root,
               struct btrfs_space_info *space_info, u64 num_bytes,
               u64 orig_bytes, int state)
{
    struct btrfs_trans_handle *trans;
    int nr;
    int ret = 0;

    switch (state) {
    case FLUSH_DELAYED_ITEMS_NR:
    case FLUSH_DELAYED_ITEMS:
        if (state == FLUSH_DELAYED_ITEMS_NR) {
            u64 bytes = btrfs_calc_trans_metadata_size(root, 1);

            nr = (int)div64_u64(num_bytes, bytes);
            if (!nr)
                nr = 1;
            nr *= 2;
        } else {
            nr = -1;
        }
        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans)) {
            ret = PTR_ERR(trans);
            break;
        }
        ret = btrfs_run_delayed_items_nr(trans, root, nr);
        btrfs_end_transaction(trans, root);
        break;
    case FLUSH_DELALLOC:
    case FLUSH_DELALLOC_WAIT:
        shrink_delalloc(root, num_bytes, orig_bytes,
                state == FLUSH_DELALLOC_WAIT);
        break;
    case ALLOC_CHUNK:
        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans)) {
            ret = PTR_ERR(trans);
            break;
        }
        ret = do_chunk_alloc(trans, root->fs_info->extent_root,
                     btrfs_get_alloc_profile(root, 0),
                     CHUNK_ALLOC_NO_FORCE);
        btrfs_end_transaction(trans, root);
        if (ret == -ENOSPC)
            ret = 0;
        break;
    case COMMIT_TRANS:
        ret = may_commit_transaction(root, space_info, orig_bytes, 0);
        break;
    default:
        ret = -ENOSPC;
        break;
    }

    return ret;
}
static int reserve_metadata_bytes(struct btrfs_root *root,
                  struct btrfs_block_rsv *block_rsv,
                  u64 orig_bytes, int flush)
{
    struct btrfs_space_info *space_info = block_rsv->space_info;
    u64 used;
    u64 num_bytes = orig_bytes;
    int flush_state = FLUSH_DELAYED_ITEMS_NR;
    int ret = 0;
    bool flushing = false;

again:
    ret = 0;
    spin_lock(&space_info->lock);
    /*
     * We only want to wait if somebody other than us is flushing and we are
     * actually alloed to flush.
     */
    while (flush && !flushing && space_info->flush) {
        spin_unlock(&space_info->lock);
        /*
         * If we have a trans handle we can't wait because the flusher
         * may have to commit the transaction, which would mean we would
         * deadlock since we are waiting for the flusher to finish, but
         * hold the current transaction open.
         */
        if (current->journal_info)
            return -EAGAIN;
        ret = wait_event_killable(space_info->wait, !space_info->flush);
        /* Must have been killed, return */
        if (ret)
            return -EINTR;

        spin_lock(&space_info->lock);
    }

    ret = -ENOSPC;
    used = space_info->bytes_used + space_info->bytes_reserved +
        space_info->bytes_pinned + space_info->bytes_readonly +
        space_info->bytes_may_use;

    /*
     * The idea here is that we've not already over-reserved the block group
     * then we can go ahead and save our reservation first and then start
     * flushing if we need to.  Otherwise if we've already overcommitted
     * lets start flushing stuff first and then come back and try to make
     * our reservation.
     */
    if (used <= space_info->total_bytes) {
        if (used + orig_bytes <= space_info->total_bytes) {
            space_info->bytes_may_use += orig_bytes;
            trace_btrfs_space_reservation(root->fs_info,
                "space_info", space_info->flags, orig_bytes, 1);
            ret = 0;
        } else {
            /*
             * Ok set num_bytes to orig_bytes since we aren't
             * overocmmitted, this way we only try and reclaim what
             * we need.
             */
            num_bytes = orig_bytes;
        }
    } else {
        /*
         * Ok we're over committed, set num_bytes to the overcommitted
         * amount plus the amount of bytes that we need for this
         * reservation.
         */
        num_bytes = used - space_info->total_bytes +
            (orig_bytes * 2);
    }

    if (ret && can_overcommit(root, space_info, orig_bytes, flush)) {
        space_info->bytes_may_use += orig_bytes;
        trace_btrfs_space_reservation(root->fs_info, "space_info",
                          space_info->flags, orig_bytes,
                          1);
        ret = 0;
    }

    /*
     * Couldn't make our reservation, save our place so while we're trying
     * to reclaim space we can actually use it instead of somebody else
     * stealing it from us.
     */
    if (ret && flush) {
        flushing = true;
        space_info->flush = 1;
    }

    spin_unlock(&space_info->lock);

    if (!ret || !flush)
        goto out;

    ret = flush_space(root, space_info, num_bytes, orig_bytes,
              flush_state);
    flush_state++;
    if (!ret)
        goto again;
    else if (flush_state <= COMMIT_TRANS)
        goto again;

out:
    if (flushing) {
        spin_lock(&space_info->lock);
        space_info->flush = 0;
        wake_up_all(&space_info->wait);
        spin_unlock(&space_info->lock);
    }
    return ret;
}

static struct btrfs_block_rsv *get_block_rsv(
                    const struct btrfs_trans_handle *trans,
                    const struct btrfs_root *root)
{
    struct btrfs_block_rsv *block_rsv = NULL;

    if (root->ref_cows)
        block_rsv = trans->block_rsv;

    if (root == root->fs_info->csum_root && trans->adding_csums)
        block_rsv = trans->block_rsv;

    if (!block_rsv)
        block_rsv = root->block_rsv;

    if (!block_rsv)
        block_rsv = &root->fs_info->empty_block_rsv;

    return block_rsv;
}

static int block_rsv_use_bytes(struct btrfs_block_rsv *block_rsv,
                   u64 num_bytes)
{
    int ret = -ENOSPC;
    spin_lock(&block_rsv->lock);
    if (block_rsv->reserved >= num_bytes) {
        block_rsv->reserved -= num_bytes;
        if (block_rsv->reserved < block_rsv->size)
            block_rsv->full = 0;
        ret = 0;
    }
    spin_unlock(&block_rsv->lock);
    return ret;
}

static void block_rsv_add_bytes(struct btrfs_block_rsv *block_rsv,
                u64 num_bytes, int update_size)
{
    spin_lock(&block_rsv->lock);
    block_rsv->reserved += num_bytes;
    if (update_size)
        block_rsv->size += num_bytes;
    else if (block_rsv->reserved >= block_rsv->size)
        block_rsv->full = 1;
    spin_unlock(&block_rsv->lock);
}

static void block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
                    struct btrfs_block_rsv *block_rsv,
                    struct btrfs_block_rsv *dest, u64 num_bytes)
{
    struct btrfs_space_info *space_info = block_rsv->space_info;

    spin_lock(&block_rsv->lock);
    if (num_bytes == (u64)-1)
        num_bytes = block_rsv->size;
    block_rsv->size -= num_bytes;
    if (block_rsv->reserved >= block_rsv->size) {
        num_bytes = block_rsv->reserved - block_rsv->size;
        block_rsv->reserved = block_rsv->size;
        block_rsv->full = 1;
    } else {
        num_bytes = 0;
    }
    spin_unlock(&block_rsv->lock);

    if (num_bytes > 0) {
        if (dest) {
            spin_lock(&dest->lock);
            if (!dest->full) {
                u64 bytes_to_add;

                bytes_to_add = dest->size - dest->reserved;
                bytes_to_add = min(num_bytes, bytes_to_add);
                dest->reserved += bytes_to_add;
                if (dest->reserved >= dest->size)
                    dest->full = 1;
                num_bytes -= bytes_to_add;
            }
            spin_unlock(&dest->lock);
        }
        if (num_bytes) {
            spin_lock(&space_info->lock);
            space_info->bytes_may_use -= num_bytes;
            trace_btrfs_space_reservation(fs_info, "space_info",
                    space_info->flags, num_bytes, 0);
            space_info->reservation_progress++;
            spin_unlock(&space_info->lock);
        }
    }
}

static int block_rsv_migrate_bytes(struct btrfs_block_rsv *src,
                   struct btrfs_block_rsv *dst, u64 num_bytes)
{
    int ret;

    ret = block_rsv_use_bytes(src, num_bytes);
    if (ret)
        return ret;

    block_rsv_add_bytes(dst, num_bytes, 1);
    return 0;
}

void btrfs_init_block_rsv(struct btrfs_block_rsv *rsv, unsigned short type)
{
    memset(rsv, 0, sizeof(*rsv));
    spin_lock_init(&rsv->lock);
    rsv->type = type;
}

struct btrfs_block_rsv *btrfs_alloc_block_rsv(struct btrfs_root *root,
                          unsigned short type)
{
    struct btrfs_block_rsv *block_rsv;
    struct btrfs_fs_info *fs_info = root->fs_info;

    block_rsv = kmalloc(sizeof(*block_rsv), GFP_NOFS);
    if (!block_rsv)
        return NULL;

    btrfs_init_block_rsv(block_rsv, type);
    block_rsv->space_info = __find_space_info(fs_info,
                          BTRFS_BLOCK_GROUP_METADATA);
    return block_rsv;
}

void btrfs_free_block_rsv(struct btrfs_root *root,
              struct btrfs_block_rsv *rsv)
{
    if (!rsv)
        return;
    btrfs_block_rsv_release(root, rsv, (u64)-1);
    kfree(rsv);
}

static inline int __block_rsv_add(struct btrfs_root *root,
                  struct btrfs_block_rsv *block_rsv,
                  u64 num_bytes, int flush)
{
    int ret;

    if (num_bytes == 0)
        return 0;

    ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
    if (!ret) {
        block_rsv_add_bytes(block_rsv, num_bytes, 1);
        return 0;
    }

    return ret;
}

int btrfs_block_rsv_add(struct btrfs_root *root,
            struct btrfs_block_rsv *block_rsv,
            u64 num_bytes)
{
    return __block_rsv_add(root, block_rsv, num_bytes, 1);
}

int btrfs_block_rsv_add_noflush(struct btrfs_root *root,
                struct btrfs_block_rsv *block_rsv,
                u64 num_bytes)
{
    return __block_rsv_add(root, block_rsv, num_bytes, 0);
}

int btrfs_block_rsv_check(struct btrfs_root *root,
              struct btrfs_block_rsv *block_rsv, int min_factor)
{
    u64 num_bytes = 0;
    int ret = -ENOSPC;

    if (!block_rsv)
        return 0;

    spin_lock(&block_rsv->lock);
    num_bytes = div_factor(block_rsv->size, min_factor);
    if (block_rsv->reserved >= num_bytes)
        ret = 0;
    spin_unlock(&block_rsv->lock);

    return ret;
}

static inline int __btrfs_block_rsv_refill(struct btrfs_root *root,
                       struct btrfs_block_rsv *block_rsv,
                       u64 min_reserved, int flush)
{
    u64 num_bytes = 0;
    int ret = -ENOSPC;

    if (!block_rsv)
        return 0;

    spin_lock(&block_rsv->lock);
    num_bytes = min_reserved;
    if (block_rsv->reserved >= num_bytes)
        ret = 0;
    else
        num_bytes -= block_rsv->reserved;
    spin_unlock(&block_rsv->lock);

    if (!ret)
        return 0;

    ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
    if (!ret) {
        block_rsv_add_bytes(block_rsv, num_bytes, 0);
        return 0;
    }

    return ret;
}

int btrfs_block_rsv_refill(struct btrfs_root *root,
               struct btrfs_block_rsv *block_rsv,
               u64 min_reserved)
{
    return __btrfs_block_rsv_refill(root, block_rsv, min_reserved, 1);
}

int btrfs_block_rsv_refill_noflush(struct btrfs_root *root,
                   struct btrfs_block_rsv *block_rsv,
                   u64 min_reserved)
{
    return __btrfs_block_rsv_refill(root, block_rsv, min_reserved, 0);
}

int btrfs_block_rsv_migrate(struct btrfs_block_rsv *src_rsv,
                struct btrfs_block_rsv *dst_rsv,
                u64 num_bytes)
{
    return block_rsv_migrate_bytes(src_rsv, dst_rsv, num_bytes);
}

void btrfs_block_rsv_release(struct btrfs_root *root,
                 struct btrfs_block_rsv *block_rsv,
                 u64 num_bytes)
{
    struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
    if (global_rsv->full || global_rsv == block_rsv ||
        block_rsv->space_info != global_rsv->space_info)
        global_rsv = NULL;
    block_rsv_release_bytes(root->fs_info, block_rsv, global_rsv,
                num_bytes);
}

/*
 * helper to calculate size of global block reservation.
 * the desired value is sum of space used by extent tree,
 * checksum tree and root tree
 */
static u64 calc_global_metadata_size(struct btrfs_fs_info *fs_info)
{
    struct btrfs_space_info *sinfo;
    u64 num_bytes;
    u64 meta_used;
    u64 data_used;
    int csum_size = btrfs_super_csum_size(fs_info->super_copy);

    sinfo = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_DATA);
    spin_lock(&sinfo->lock);
    data_used = sinfo->bytes_used;
    spin_unlock(&sinfo->lock);

    sinfo = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
    spin_lock(&sinfo->lock);
    if (sinfo->flags & BTRFS_BLOCK_GROUP_DATA)
        data_used = 0;
    meta_used = sinfo->bytes_used;
    spin_unlock(&sinfo->lock);

    num_bytes = (data_used >> fs_info->sb->s_blocksize_bits) *
            csum_size * 2;
    num_bytes += div64_u64(data_used + meta_used, 50);

    if (num_bytes * 3 > meta_used)
        num_bytes = div64_u64(meta_used, 3);

    return ALIGN(num_bytes, fs_info->extent_root->leafsize << 10);
}

static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
{
    struct btrfs_block_rsv *block_rsv = &fs_info->global_block_rsv;
    struct btrfs_space_info *sinfo = block_rsv->space_info;
    u64 num_bytes;

    num_bytes = calc_global_metadata_size(fs_info);

    spin_lock(&sinfo->lock);
    spin_lock(&block_rsv->lock);

    block_rsv->size = num_bytes;

    num_bytes = sinfo->bytes_used + sinfo->bytes_pinned +
            sinfo->bytes_reserved + sinfo->bytes_readonly +
            sinfo->bytes_may_use;

    if (sinfo->total_bytes > num_bytes) {
        num_bytes = sinfo->total_bytes - num_bytes;
        block_rsv->reserved += num_bytes;
        sinfo->bytes_may_use += num_bytes;
        trace_btrfs_space_reservation(fs_info, "space_info",
                      sinfo->flags, num_bytes, 1);
    }

    if (block_rsv->reserved >= block_rsv->size) {
        num_bytes = block_rsv->reserved - block_rsv->size;
        sinfo->bytes_may_use -= num_bytes;
        trace_btrfs_space_reservation(fs_info, "space_info",
                      sinfo->flags, num_bytes, 0);
        sinfo->reservation_progress++;
        block_rsv->reserved = block_rsv->size;
        block_rsv->full = 1;
    }

    spin_unlock(&block_rsv->lock);
    spin_unlock(&sinfo->lock);
}

static void init_global_block_rsv(struct btrfs_fs_info *fs_info)
{
    struct btrfs_space_info *space_info;

    space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
    fs_info->chunk_block_rsv.space_info = space_info;

    space_info = __find_space_info(fs_info, BTRFS_BLOCK_GROUP_METADATA);
    fs_info->global_block_rsv.space_info = space_info;
    fs_info->delalloc_block_rsv.space_info = space_info;
    fs_info->trans_block_rsv.space_info = space_info;
    fs_info->empty_block_rsv.space_info = space_info;
    fs_info->delayed_block_rsv.space_info = space_info;

    fs_info->extent_root->block_rsv = &fs_info->global_block_rsv;
    fs_info->csum_root->block_rsv = &fs_info->global_block_rsv;
    fs_info->dev_root->block_rsv = &fs_info->global_block_rsv;
    fs_info->tree_root->block_rsv = &fs_info->global_block_rsv;
    fs_info->chunk_root->block_rsv = &fs_info->chunk_block_rsv;

    update_global_block_rsv(fs_info);
}

static void release_global_block_rsv(struct btrfs_fs_info *fs_info)
{
    block_rsv_release_bytes(fs_info, &fs_info->global_block_rsv, NULL,
                (u64)-1);
    WARN_ON(fs_info->delalloc_block_rsv.size > 0);
    WARN_ON(fs_info->delalloc_block_rsv.reserved > 0);
    WARN_ON(fs_info->trans_block_rsv.size > 0);
    WARN_ON(fs_info->trans_block_rsv.reserved > 0);
    WARN_ON(fs_info->chunk_block_rsv.size > 0);
    WARN_ON(fs_info->chunk_block_rsv.reserved > 0);
    WARN_ON(fs_info->delayed_block_rsv.size > 0);
    WARN_ON(fs_info->delayed_block_rsv.reserved > 0);
}

void btrfs_trans_release_metadata(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root)
{
    if (!trans->block_rsv)
        return;

    if (!trans->bytes_reserved)
        return;

    trace_btrfs_space_reservation(root->fs_info, "transaction",
                      trans->transid, trans->bytes_reserved, 0);
    btrfs_block_rsv_release(root, trans->block_rsv, trans->bytes_reserved);
    trans->bytes_reserved = 0;
}

/* Can only return 0 or -ENOSPC */
int btrfs_orphan_reserve_metadata(struct btrfs_trans_handle *trans,
                  struct inode *inode)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct btrfs_block_rsv *src_rsv = get_block_rsv(trans, root);
    struct btrfs_block_rsv *dst_rsv = root->orphan_block_rsv;

    /*
     * We need to hold space in order to delete our orphan item once we've
     * added it, so this takes the reservation so we can release it later
     * when we are truly done with the orphan item.
     */
    u64 num_bytes = btrfs_calc_trans_metadata_size(root, 1);
    trace_btrfs_space_reservation(root->fs_info, "orphan",
                      btrfs_ino(inode), num_bytes, 1);
    return block_rsv_migrate_bytes(src_rsv, dst_rsv, num_bytes);
}

void btrfs_orphan_release_metadata(struct inode *inode)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    u64 num_bytes = btrfs_calc_trans_metadata_size(root, 1);
    trace_btrfs_space_reservation(root->fs_info, "orphan",
                      btrfs_ino(inode), num_bytes, 0);
    btrfs_block_rsv_release(root, root->orphan_block_rsv, num_bytes);
}

int btrfs_snap_reserve_metadata(struct btrfs_trans_handle *trans,
                struct btrfs_pending_snapshot *pending)
{
    struct btrfs_root *root = pending->root;
    struct btrfs_block_rsv *src_rsv = get_block_rsv(trans, root);
    struct btrfs_block_rsv *dst_rsv = &pending->block_rsv;
    /*
     * two for root back/forward refs, two for directory entries,
     * one for root of the snapshot and one for parent inode.
     */
    u64 num_bytes = btrfs_calc_trans_metadata_size(root, 6);
    dst_rsv->space_info = src_rsv->space_info;
    return block_rsv_migrate_bytes(src_rsv, dst_rsv, num_bytes);
}

static unsigned drop_outstanding_extent(struct inode *inode)
{
    unsigned drop_inode_space = 0;
    unsigned dropped_extents = 0;

    BUG_ON(!BTRFS_I(inode)->outstanding_extents);
    BTRFS_I(inode)->outstanding_extents--;

    if (BTRFS_I(inode)->outstanding_extents == 0 &&
        test_and_clear_bit(BTRFS_INODE_DELALLOC_META_RESERVED,
                   &BTRFS_I(inode)->runtime_flags))
        drop_inode_space = 1;

    /*
     * If we have more or the same amount of outsanding extents than we have
     * reserved then we need to leave the reserved extents count alone.
     */
    if (BTRFS_I(inode)->outstanding_extents >=
        BTRFS_I(inode)->reserved_extents)
        return drop_inode_space;

    dropped_extents = BTRFS_I(inode)->reserved_extents -
        BTRFS_I(inode)->outstanding_extents;
    BTRFS_I(inode)->reserved_extents -= dropped_extents;
    return dropped_extents + drop_inode_space;
}

static u64 calc_csum_metadata_size(struct inode *inode, u64 num_bytes,
                   int reserve)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    u64 csum_size;
    int num_csums_per_leaf;
    int num_csums;
    int old_csums;

    if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM &&
        BTRFS_I(inode)->csum_bytes == 0)
        return 0;

    old_csums = (int)div64_u64(BTRFS_I(inode)->csum_bytes, root->sectorsize);
    if (reserve)
        BTRFS_I(inode)->csum_bytes += num_bytes;
    else
        BTRFS_I(inode)->csum_bytes -= num_bytes;
    csum_size = BTRFS_LEAF_DATA_SIZE(root) - sizeof(struct btrfs_item);
    num_csums_per_leaf = (int)div64_u64(csum_size,
                        sizeof(struct btrfs_csum_item) +
                        sizeof(struct btrfs_disk_key));
    num_csums = (int)div64_u64(BTRFS_I(inode)->csum_bytes, root->sectorsize);
    num_csums = num_csums + num_csums_per_leaf - 1;
    num_csums = num_csums / num_csums_per_leaf;

    old_csums = old_csums + num_csums_per_leaf - 1;
    old_csums = old_csums / num_csums_per_leaf;

    /* No change, no need to reserve more */
    if (old_csums == num_csums)
        return 0;

    if (reserve)
        return btrfs_calc_trans_metadata_size(root,
                              num_csums - old_csums);

    return btrfs_calc_trans_metadata_size(root, old_csums - num_csums);
}

int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct btrfs_block_rsv *block_rsv = &root->fs_info->delalloc_block_rsv;
    u64 to_reserve = 0;
    u64 csum_bytes;
    unsigned nr_extents = 0;
    int extra_reserve = 0;
    int flush = 1;
    int ret;

    /* Need to be holding the i_mutex here if we aren't free space cache */
    if (btrfs_is_free_space_inode(inode))
        flush = 0;

    if (flush && btrfs_transaction_in_commit(root->fs_info))
        schedule_timeout(1);

    mutex_lock(&BTRFS_I(inode)->delalloc_mutex);
    num_bytes = ALIGN(num_bytes, root->sectorsize);

    spin_lock(&BTRFS_I(inode)->lock);
    BTRFS_I(inode)->outstanding_extents++;

    if (BTRFS_I(inode)->outstanding_extents >
        BTRFS_I(inode)->reserved_extents)
        nr_extents = BTRFS_I(inode)->outstanding_extents -
            BTRFS_I(inode)->reserved_extents;

    /*
     * Add an item to reserve for updating the inode when we complete the
     * delalloc io.
     */
    if (!test_bit(BTRFS_INODE_DELALLOC_META_RESERVED,
              &BTRFS_I(inode)->runtime_flags)) {
        nr_extents++;
        extra_reserve = 1;
    }

    to_reserve = btrfs_calc_trans_metadata_size(root, nr_extents);
    to_reserve += calc_csum_metadata_size(inode, num_bytes, 1);
    csum_bytes = BTRFS_I(inode)->csum_bytes;
    spin_unlock(&BTRFS_I(inode)->lock);

    if (root->fs_info->quota_enabled) {
        ret = btrfs_qgroup_reserve(root, num_bytes +
                       nr_extents * root->leafsize);
        if (ret) {
            mutex_unlock(&BTRFS_I(inode)->delalloc_mutex);
            return ret;
        }
    }

    ret = reserve_metadata_bytes(root, block_rsv, to_reserve, flush);
    if (ret) {
        u64 to_free = 0;
        unsigned dropped;

        spin_lock(&BTRFS_I(inode)->lock);
        dropped = drop_outstanding_extent(inode);
        /*
         * If the inodes csum_bytes is the same as the original
         * csum_bytes then we know we haven't raced with any free()ers
         * so we can just reduce our inodes csum bytes and carry on.
         * Otherwise we have to do the normal free thing to account for
         * the case that the free side didn't free up its reserve
         * because of this outstanding reservation.
         */
        if (BTRFS_I(inode)->csum_bytes == csum_bytes)
            calc_csum_metadata_size(inode, num_bytes, 0);
        else
            to_free = calc_csum_metadata_size(inode, num_bytes, 0);
        spin_unlock(&BTRFS_I(inode)->lock);
        if (dropped)
            to_free += btrfs_calc_trans_metadata_size(root, dropped);

        if (to_free) {
            btrfs_block_rsv_release(root, block_rsv, to_free);
            trace_btrfs_space_reservation(root->fs_info,
                              "delalloc",
                              btrfs_ino(inode),
                              to_free, 0);
        }
        mutex_unlock(&BTRFS_I(inode)->delalloc_mutex);
        return ret;
    }

    spin_lock(&BTRFS_I(inode)->lock);
    if (extra_reserve) {
        set_bit(BTRFS_INODE_DELALLOC_META_RESERVED,
            &BTRFS_I(inode)->runtime_flags);
        nr_extents--;
    }
    BTRFS_I(inode)->reserved_extents += nr_extents;
    spin_unlock(&BTRFS_I(inode)->lock);
    mutex_unlock(&BTRFS_I(inode)->delalloc_mutex);

    if (to_reserve)
        trace_btrfs_space_reservation(root->fs_info,"delalloc",
                          btrfs_ino(inode), to_reserve, 1);
    block_rsv_add_bytes(block_rsv, to_reserve, 1);

    return 0;
}

void btrfs_delalloc_release_metadata(struct inode *inode, u64 num_bytes)
{
    struct btrfs_root *root = BTRFS_I(inode)->root;
    u64 to_free = 0;
    unsigned dropped;

    num_bytes = ALIGN(num_bytes, root->sectorsize);
    spin_lock(&BTRFS_I(inode)->lock);
    dropped = drop_outstanding_extent(inode);

    to_free = calc_csum_metadata_size(inode, num_bytes, 0);
    spin_unlock(&BTRFS_I(inode)->lock);
    if (dropped > 0)
        to_free += btrfs_calc_trans_metadata_size(root, dropped);

    trace_btrfs_space_reservation(root->fs_info, "delalloc",
                      btrfs_ino(inode), to_free, 0);
    if (root->fs_info->quota_enabled) {
        btrfs_qgroup_free(root, num_bytes +
                    dropped * root->leafsize);
    }

    btrfs_block_rsv_release(root, &root->fs_info->delalloc_block_rsv,
                to_free);
}

int btrfs_delalloc_reserve_space(struct inode *inode, u64 num_bytes)
{
    int ret;

    ret = btrfs_check_data_free_space(inode, num_bytes);
    if (ret)
        return ret;

    ret = btrfs_delalloc_reserve_metadata(inode, num_bytes);
    if (ret) {
        btrfs_free_reserved_data_space(inode, num_bytes);
        return ret;
    }

    return 0;
}

void btrfs_delalloc_release_space(struct inode *inode, u64 num_bytes)
{
    btrfs_delalloc_release_metadata(inode, num_bytes);
    btrfs_free_reserved_data_space(inode, num_bytes);
}

static int update_block_group(struct btrfs_trans_handle *trans,
                  struct btrfs_root *root,
                  u64 bytenr, u64 num_bytes, int alloc)
{
    struct btrfs_block_group_cache *cache = NULL;
    struct btrfs_fs_info *info = root->fs_info;
    u64 total = num_bytes;
    u64 old_val;
    u64 byte_in_group;
    int factor;

    /* block accounting for super block */
    spin_lock(&info->delalloc_lock);
    old_val = btrfs_super_bytes_used(info->super_copy);
    if (alloc)
        old_val += num_bytes;
    else
        old_val -= num_bytes;
    btrfs_set_super_bytes_used(info->super_copy, old_val);
    spin_unlock(&info->delalloc_lock);

    while (total) {
        cache = btrfs_lookup_block_group(info, bytenr);
        if (!cache)
            return -ENOENT;
        if (cache->flags & (BTRFS_BLOCK_GROUP_DUP |
                    BTRFS_BLOCK_GROUP_RAID1 |
                    BTRFS_BLOCK_GROUP_RAID10))
            factor = 2;
        else
            factor = 1;
        /*
         * If this block group has free space cache written out, we
         * need to make sure to load it if we are removing space.  This
         * is because we need the unpinning stage to actually add the
         * space back to the block group, otherwise we will leak space.
         */
        if (!alloc && cache->cached == BTRFS_CACHE_NO)
            cache_block_group(cache, trans, NULL, 1);

        byte_in_group = bytenr - cache->key.objectid;
        WARN_ON(byte_in_group > cache->key.offset);

        spin_lock(&cache->space_info->lock);
        spin_lock(&cache->lock);

        if (btrfs_test_opt(root, SPACE_CACHE) &&
            cache->disk_cache_state < BTRFS_DC_CLEAR)
            cache->disk_cache_state = BTRFS_DC_CLEAR;

        cache->dirty = 1;
        old_val = btrfs_block_group_used(&cache->item);
        num_bytes = min(total, cache->key.offset - byte_in_group);
        if (alloc) {
            old_val += num_bytes;
            btrfs_set_block_group_used(&cache->item, old_val);
            cache->reserved -= num_bytes;
            cache->space_info->bytes_reserved -= num_bytes;
            cache->space_info->bytes_used += num_bytes;
            cache->space_info->disk_used += num_bytes * factor;
            spin_unlock(&cache->lock);
            spin_unlock(&cache->space_info->lock);
        } else {
            old_val -= num_bytes;
            btrfs_set_block_group_used(&cache->item, old_val);
            cache->pinned += num_bytes;
            cache->space_info->bytes_pinned += num_bytes;
            cache->space_info->bytes_used -= num_bytes;
            cache->space_info->disk_used -= num_bytes * factor;
            spin_unlock(&cache->lock);
            spin_unlock(&cache->space_info->lock);

            set_extent_dirty(info->pinned_extents,
                     bytenr, bytenr + num_bytes - 1,
                     GFP_NOFS | __GFP_NOFAIL);
        }
        btrfs_put_block_group(cache);
        total -= num_bytes;
        bytenr += num_bytes;
    }
    return 0;
}

static u64 first_logical_byte(struct btrfs_root *root, u64 search_start)
{
    struct btrfs_block_group_cache *cache;
    u64 bytenr;

    cache = btrfs_lookup_first_block_group(root->fs_info, search_start);
    if (!cache)
        return 0;

    bytenr = cache->key.objectid;
    btrfs_put_block_group(cache);

    return bytenr;
}

static int pin_down_extent(struct btrfs_root *root,
               struct btrfs_block_group_cache *cache,
               u64 bytenr, u64 num_bytes, int reserved)
{
    spin_lock(&cache->space_info->lock);
    spin_lock(&cache->lock);
    cache->pinned += num_bytes;
    cache->space_info->bytes_pinned += num_bytes;
    if (reserved) {
        cache->reserved -= num_bytes;
        cache->space_info->bytes_reserved -= num_bytes;
    }
    spin_unlock(&cache->lock);
    spin_unlock(&cache->space_info->lock);

    set_extent_dirty(root->fs_info->pinned_extents, bytenr,
             bytenr + num_bytes - 1, GFP_NOFS | __GFP_NOFAIL);
    return 0;
}

/*
 * this function must be called within transaction
 */
int btrfs_pin_extent(struct btrfs_root *root,
             u64 bytenr, u64 num_bytes, int reserved)
{
    struct btrfs_block_group_cache *cache;

    cache = btrfs_lookup_block_group(root->fs_info, bytenr);
    BUG_ON(!cache); /* Logic error */

    pin_down_extent(root, cache, bytenr, num_bytes, reserved);

    btrfs_put_block_group(cache);
    return 0;
}

/*
 * this function must be called within transaction
 */
int btrfs_pin_extent_for_log_replay(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root,
                    u64 bytenr, u64 num_bytes)
{
    struct btrfs_block_group_cache *cache;

    cache = btrfs_lookup_block_group(root->fs_info, bytenr);
    BUG_ON(!cache); /* Logic error */

    /*
     * pull in the free space cache (if any) so that our pin
     * removes the free space from the cache.  We have load_only set
     * to one because the slow code to read in the free extents does check
     * the pinned extents.
     */
    cache_block_group(cache, trans, root, 1);

    pin_down_extent(root, cache, bytenr, num_bytes, 0);

    /* remove us from the free space cache (if we're there at all) */
    btrfs_remove_free_space(cache, bytenr, num_bytes);
    btrfs_put_block_group(cache);
    return 0;
}

static int btrfs_update_reserved_bytes(struct btrfs_block_group_cache *cache,
                       u64 num_bytes, int reserve)
{
    struct btrfs_space_info *space_info = cache->space_info;
    int ret = 0;

    spin_lock(&space_info->lock);
    spin_lock(&cache->lock);
    if (reserve != RESERVE_FREE) {
        if (cache->ro) {
            ret = -EAGAIN;
        } else {
            cache->reserved += num_bytes;
            space_info->bytes_reserved += num_bytes;
            if (reserve == RESERVE_ALLOC) {
                trace_btrfs_space_reservation(cache->fs_info,
                        "space_info", space_info->flags,
                        num_bytes, 0);
                space_info->bytes_may_use -= num_bytes;
            }
        }
    } else {
        if (cache->ro)
            space_info->bytes_readonly += num_bytes;
        cache->reserved -= num_bytes;
        space_info->bytes_reserved -= num_bytes;
        space_info->reservation_progress++;
    }
    spin_unlock(&cache->lock);
    spin_unlock(&space_info->lock);
    return ret;
}

void btrfs_prepare_extent_commit(struct btrfs_trans_handle *trans,
                struct btrfs_root *root)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct btrfs_caching_control *next;
    struct btrfs_caching_control *caching_ctl;
    struct btrfs_block_group_cache *cache;

    down_write(&fs_info->extent_commit_sem);

    list_for_each_entry_safe(caching_ctl, next,
                 &fs_info->caching_block_groups, list) {
        cache = caching_ctl->block_group;
        if (block_group_cache_done(cache)) {
            cache->last_byte_to_unpin = (u64)-1;
            list_del_init(&caching_ctl->list);
            put_caching_control(caching_ctl);
        } else {
            cache->last_byte_to_unpin = caching_ctl->progress;
        }
    }

    if (fs_info->pinned_extents == &fs_info->freed_extents[0])
        fs_info->pinned_extents = &fs_info->freed_extents[1];
    else
        fs_info->pinned_extents = &fs_info->freed_extents[0];

    up_write(&fs_info->extent_commit_sem);

    update_global_block_rsv(fs_info);
}

static int unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct btrfs_block_group_cache *cache = NULL;
    u64 len;

    while (start <= end) {
        if (!cache ||
            start >= cache->key.objectid + cache->key.offset) {
            if (cache)
                btrfs_put_block_group(cache);
            cache = btrfs_lookup_block_group(fs_info, start);
            BUG_ON(!cache); /* Logic error */
        }

        len = cache->key.objectid + cache->key.offset - start;
        len = min(len, end + 1 - start);

        if (start < cache->last_byte_to_unpin) {
            len = min(len, cache->last_byte_to_unpin - start);
            btrfs_add_free_space(cache, start, len);
        }

        start += len;

        spin_lock(&cache->space_info->lock);
        spin_lock(&cache->lock);
        cache->pinned -= len;
        cache->space_info->bytes_pinned -= len;
        if (cache->ro)
            cache->space_info->bytes_readonly += len;
        spin_unlock(&cache->lock);
        spin_unlock(&cache->space_info->lock);
    }

    if (cache)
        btrfs_put_block_group(cache);
    return 0;
}

int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct extent_io_tree *unpin;
    u64 start;
    u64 end;
    int ret;

    if (trans->aborted)
        return 0;

    if (fs_info->pinned_extents == &fs_info->freed_extents[0])
        unpin = &fs_info->freed_extents[1];
    else
        unpin = &fs_info->freed_extents[0];

    while (1) {
        ret = find_first_extent_bit(unpin, 0, &start, &end,
                        EXTENT_DIRTY, NULL);
        if (ret)
            break;

        if (btrfs_test_opt(root, DISCARD))
            ret = btrfs_discard_extent(root, start,
                           end + 1 - start, NULL);

        clear_extent_dirty(unpin, start, end, GFP_NOFS);
        unpin_extent_range(root, start, end);
        cond_resched();
    }

    return 0;
}

static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
                struct btrfs_root *root,
                u64 bytenr, u64 num_bytes, u64 parent,
                u64 root_objectid, u64 owner_objectid,
                u64 owner_offset, int refs_to_drop,
                struct btrfs_delayed_extent_op *extent_op)
{
    struct btrfs_key key;
    struct btrfs_path *path;
    struct btrfs_fs_info *info = root->fs_info;
    struct btrfs_root *extent_root = info->extent_root;
    struct extent_buffer *leaf;
    struct btrfs_extent_item *ei;
    struct btrfs_extent_inline_ref *iref;
    int ret;
    int is_data;
    int extent_slot = 0;
    int found_extent = 0;
    int num_to_del = 1;
    u32 item_size;
    u64 refs;

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    path->reada = 1;
    path->leave_spinning = 1;

    is_data = owner_objectid >= BTRFS_FIRST_FREE_OBJECTID;
    BUG_ON(!is_data && refs_to_drop != 1);

    ret = lookup_extent_backref(trans, extent_root, path, &iref,
                    bytenr, num_bytes, parent,
                    root_objectid, owner_objectid,
                    owner_offset);
    if (ret == 0) {
        extent_slot = path->slots[0];
        while (extent_slot >= 0) {
            btrfs_item_key_to_cpu(path->nodes[0], &key,
                          extent_slot);
            if (key.objectid != bytenr)
                break;
            if (key.type == BTRFS_EXTENT_ITEM_KEY &&
                key.offset == num_bytes) {
                found_extent = 1;
                break;
            }
            if (path->slots[0] - extent_slot > 5)
                break;
            extent_slot--;
        }
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
        item_size = btrfs_item_size_nr(path->nodes[0], extent_slot);
        if (found_extent && item_size < sizeof(*ei))
            found_extent = 0;
#endif
        if (!found_extent) {
            BUG_ON(iref);
            ret = remove_extent_backref(trans, extent_root, path,
                            NULL, refs_to_drop,
                            is_data);
            if (ret) {
                btrfs_abort_transaction(trans, extent_root, ret);
                goto out;
            }
            btrfs_release_path(path);
            path->leave_spinning = 1;

            key.objectid = bytenr;
            key.type = BTRFS_EXTENT_ITEM_KEY;
            key.offset = num_bytes;

            ret = btrfs_search_slot(trans, extent_root,
                        &key, path, -1, 1);
            if (ret) {
                printk(KERN_ERR "umm, got %d back from search"
                       ", was looking for %llu\n", ret,
                       (unsigned long long)bytenr);
                if (ret > 0)
                    btrfs_print_leaf(extent_root,
                             path->nodes[0]);
            }
            if (ret < 0) {
                btrfs_abort_transaction(trans, extent_root, ret);
                goto out;
            }
            extent_slot = path->slots[0];
        }
    } else if (ret == -ENOENT) {
        btrfs_print_leaf(extent_root, path->nodes[0]);
        WARN_ON(1);
        printk(KERN_ERR "btrfs unable to find ref byte nr %llu "
               "parent %llu root %llu  owner %llu offset %llu\n",
               (unsigned long long)bytenr,
               (unsigned long long)parent,
               (unsigned long long)root_objectid,
               (unsigned long long)owner_objectid,
               (unsigned long long)owner_offset);
    } else {
        btrfs_abort_transaction(trans, extent_root, ret);
        goto out;
    }

    leaf = path->nodes[0];
    item_size = btrfs_item_size_nr(leaf, extent_slot);
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
    if (item_size < sizeof(*ei)) {
        BUG_ON(found_extent || extent_slot != path->slots[0]);
        ret = convert_extent_item_v0(trans, extent_root, path,
                         owner_objectid, 0);
        if (ret < 0) {
            btrfs_abort_transaction(trans, extent_root, ret);
            goto out;
        }

        btrfs_release_path(path);
        path->leave_spinning = 1;

        key.objectid = bytenr;
        key.type = BTRFS_EXTENT_ITEM_KEY;
        key.offset = num_bytes;

        ret = btrfs_search_slot(trans, extent_root, &key, path,
                    -1, 1);
        if (ret) {
            printk(KERN_ERR "umm, got %d back from search"
                   ", was looking for %llu\n", ret,
                   (unsigned long long)bytenr);
            btrfs_print_leaf(extent_root, path->nodes[0]);
        }
        if (ret < 0) {
            btrfs_abort_transaction(trans, extent_root, ret);
            goto out;
        }

        extent_slot = path->slots[0];
        leaf = path->nodes[0];
        item_size = btrfs_item_size_nr(leaf, extent_slot);
    }
#endif
    BUG_ON(item_size < sizeof(*ei));
    ei = btrfs_item_ptr(leaf, extent_slot,
                struct btrfs_extent_item);
    if (owner_objectid < BTRFS_FIRST_FREE_OBJECTID) {
        struct btrfs_tree_block_info *bi;
        BUG_ON(item_size < sizeof(*ei) + sizeof(*bi));
        bi = (struct btrfs_tree_block_info *)(ei + 1);
        WARN_ON(owner_objectid != btrfs_tree_block_level(leaf, bi));
    }

    refs = btrfs_extent_refs(leaf, ei);
    BUG_ON(refs < refs_to_drop);
    refs -= refs_to_drop;

    if (refs > 0) {
        if (extent_op)
            __run_delayed_extent_op(extent_op, leaf, ei);
        /*
         * In the case of inline back ref, reference count will
         * be updated by remove_extent_backref
         */
        if (iref) {
            BUG_ON(!found_extent);
        } else {
            btrfs_set_extent_refs(leaf, ei, refs);
            btrfs_mark_buffer_dirty(leaf);
        }
        if (found_extent) {
            ret = remove_extent_backref(trans, extent_root, path,
                            iref, refs_to_drop,
                            is_data);
            if (ret) {
                btrfs_abort_transaction(trans, extent_root, ret);
                goto out;
            }
        }
    } else {
        if (found_extent) {
            BUG_ON(is_data && refs_to_drop !=
                   extent_data_ref_count(root, path, iref));
            if (iref) {
                BUG_ON(path->slots[0] != extent_slot);
            } else {
                BUG_ON(path->slots[0] != extent_slot + 1);
                path->slots[0] = extent_slot;
                num_to_del = 2;
            }
        }

        ret = btrfs_del_items(trans, extent_root, path, path->slots[0],
                      num_to_del);
        if (ret) {
            btrfs_abort_transaction(trans, extent_root, ret);
            goto out;
        }
        btrfs_release_path(path);

        if (is_data) {
            ret = btrfs_del_csums(trans, root, bytenr, num_bytes);
            if (ret) {
                btrfs_abort_transaction(trans, extent_root, ret);
                goto out;
            }
        }

        ret = update_block_group(trans, root, bytenr, num_bytes, 0);
        if (ret) {
            btrfs_abort_transaction(trans, extent_root, ret);
            goto out;
        }
    }
out:
    btrfs_free_path(path);
    return ret;
}

/*
 * when we free an block, it is possible (and likely) that we free the last
 * delayed ref for that extent as well.  This searches the delayed ref tree for
 * a given extent, and if there are no other delayed refs to be processed, it
 * removes it from the tree.
 */
static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root, u64 bytenr)
{
    struct btrfs_delayed_ref_head *head;
    struct btrfs_delayed_ref_root *delayed_refs;
    struct btrfs_delayed_ref_node *ref;
    struct rb_node *node;
    int ret = 0;

    delayed_refs = &trans->transaction->delayed_refs;
    spin_lock(&delayed_refs->lock);
    head = btrfs_find_delayed_ref_head(trans, bytenr);
    if (!head)
        goto out;

    node = rb_prev(&head->node.rb_node);
    if (!node)
        goto out;

    ref = rb_entry(node, struct btrfs_delayed_ref_node, rb_node);

    /* there are still entries for this ref, we can't drop it */
    if (ref->bytenr == bytenr)
        goto out;

    if (head->extent_op) {
        if (!head->must_insert_reserved)
            goto out;
        kfree(head->extent_op);
        head->extent_op = NULL;
    }

    /*
     * waiting for the lock here would deadlock.  If someone else has it
     * locked they are already in the process of dropping it anyway
     */
    if (!mutex_trylock(&head->mutex))
        goto out;

    /*
     * at this point we have a head with no other entries.  Go
     * ahead and process it.
     */
    head->node.in_tree = 0;
    rb_erase(&head->node.rb_node, &delayed_refs->root);

    delayed_refs->num_entries--;

    /*
     * we don't take a ref on the node because we're removing it from the
     * tree, so we just steal the ref the tree was holding.
     */
    delayed_refs->num_heads--;
    if (list_empty(&head->cluster))
        delayed_refs->num_heads_ready--;

    list_del_init(&head->cluster);
    spin_unlock(&delayed_refs->lock);

    BUG_ON(head->extent_op);
    if (head->must_insert_reserved)
        ret = 1;

    mutex_unlock(&head->mutex);
    btrfs_put_delayed_ref(&head->node);
    return ret;
out:
    spin_unlock(&delayed_refs->lock);
    return 0;
}

void btrfs_free_tree_block(struct btrfs_trans_handle *trans,
               struct btrfs_root *root,
               struct extent_buffer *buf,
               u64 parent, int last_ref)
{
    struct btrfs_block_group_cache *cache = NULL;
    int ret;

    if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) {
        ret = btrfs_add_delayed_tree_ref(root->fs_info, trans,
                    buf->start, buf->len,
                    parent, root->root_key.objectid,
                    btrfs_header_level(buf),
                    BTRFS_DROP_DELAYED_REF, NULL, 0);
        BUG_ON(ret); /* -ENOMEM */
    }

    if (!last_ref)
        return;

    cache = btrfs_lookup_block_group(root->fs_info, buf->start);

    if (btrfs_header_generation(buf) == trans->transid) {
        if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) {
            ret = check_ref_cleanup(trans, root, buf->start);
            if (!ret)
                goto out;
        }

        if (btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
            pin_down_extent(root, cache, buf->start, buf->len, 1);
            goto out;
        }

        WARN_ON(test_bit(EXTENT_BUFFER_DIRTY, &buf->bflags));

        btrfs_add_free_space(cache, buf->start, buf->len);
        btrfs_update_reserved_bytes(cache, buf->len, RESERVE_FREE);
    }
out:
    /*
     * Deleting the buffer, clear the corrupt flag since it doesn't matter
     * anymore.
     */
    clear_bit(EXTENT_BUFFER_CORRUPT, &buf->bflags);
    btrfs_put_block_group(cache);
}

/* Can return -ENOMEM */
int btrfs_free_extent(struct btrfs_trans_handle *trans, struct btrfs_root *root,
              u64 bytenr, u64 num_bytes, u64 parent, u64 root_objectid,
              u64 owner, u64 offset, int for_cow)
{
    int ret;
    struct btrfs_fs_info *fs_info = root->fs_info;

    /*
     * tree log blocks never actually go into the extent allocation
     * tree, just update pinning info and exit early.
     */
    if (root_objectid == BTRFS_TREE_LOG_OBJECTID) {
        WARN_ON(owner >= BTRFS_FIRST_FREE_OBJECTID);
        /* unlocks the pinned mutex */
        btrfs_pin_extent(root, bytenr, num_bytes, 1);
        ret = 0;
    } else if (owner < BTRFS_FIRST_FREE_OBJECTID) {
        ret = btrfs_add_delayed_tree_ref(fs_info, trans, bytenr,
                    num_bytes,
                    parent, root_objectid, (int)owner,
                    BTRFS_DROP_DELAYED_REF, NULL, for_cow);
    } else {
        ret = btrfs_add_delayed_data_ref(fs_info, trans, bytenr,
                        num_bytes,
                        parent, root_objectid, owner,
                        offset, BTRFS_DROP_DELAYED_REF,
                        NULL, for_cow);
    }
    return ret;
}

static u64 stripe_align(struct btrfs_root *root, u64 val)
{
    u64 mask = ((u64)root->stripesize - 1);
    u64 ret = (val + mask) & ~mask;
    return ret;
}

/*
 * when we wait for progress in the block group caching, its because
 * our allocation attempt failed at least once.  So, we must sleep
 * and let some progress happen before we try again.
 *
 * This function will sleep at least once waiting for new free space to
 * show up, and then it will check the block group free space numbers
 * for our min num_bytes.  Another option is to have it go ahead
 * and look in the rbtree for a free extent of a given size, but this
 * is a good start.
 */
static noinline int
wait_block_group_cache_progress(struct btrfs_block_group_cache *cache,
                u64 num_bytes)
{
    struct btrfs_caching_control *caching_ctl;
    DEFINE_WAIT(wait);

    caching_ctl = get_caching_control(cache);
    if (!caching_ctl)
        return 0;

    wait_event(caching_ctl->wait, block_group_cache_done(cache) ||
           (cache->free_space_ctl->free_space >= num_bytes));

    put_caching_control(caching_ctl);
    return 0;
}

static noinline int
wait_block_group_cache_done(struct btrfs_block_group_cache *cache)
{
    struct btrfs_caching_control *caching_ctl;
    DEFINE_WAIT(wait);

    caching_ctl = get_caching_control(cache);
    if (!caching_ctl)
        return 0;

    wait_event(caching_ctl->wait, block_group_cache_done(cache));

    put_caching_control(caching_ctl);
    return 0;
}

static int __get_block_group_index(u64 flags)
{
    int index;

    if (flags & BTRFS_BLOCK_GROUP_RAID10)
        index = 0;
    else if (flags & BTRFS_BLOCK_GROUP_RAID1)
        index = 1;
    else if (flags & BTRFS_BLOCK_GROUP_DUP)
        index = 2;
    else if (flags & BTRFS_BLOCK_GROUP_RAID0)
        index = 3;
    else
        index = 4;

    return index;
}

static int get_block_group_index(struct btrfs_block_group_cache *cache)
{
    return __get_block_group_index(cache->flags);
}

enum btrfs_loop_type {
    LOOP_CACHING_NOWAIT = 0,
    LOOP_CACHING_WAIT = 1,
    LOOP_ALLOC_CHUNK = 2,
    LOOP_NO_EMPTY_SIZE = 3,
};

/*
 * walks the btree of allocated extents and find a hole of a given size.
 * The key ins is changed to record the hole:
 * ins->objectid == block start
 * ins->flags = BTRFS_EXTENT_ITEM_KEY
 * ins->offset == number of blocks
 * Any available blocks before search_start are skipped.
 */
static noinline int find_free_extent(struct btrfs_trans_handle *trans,
                     struct btrfs_root *orig_root,
                     u64 num_bytes, u64 empty_size,
                     u64 hint_byte, struct btrfs_key *ins,
                     u64 data)
{
    int ret = 0;
    struct btrfs_root *root = orig_root->fs_info->extent_root;
    struct btrfs_free_cluster *last_ptr = NULL;
    struct btrfs_block_group_cache *block_group = NULL;
    struct btrfs_block_group_cache *used_block_group;
    u64 search_start = 0;
    int empty_cluster = 2 * 1024 * 1024;
    struct btrfs_space_info *space_info;
    int loop = 0;
    int index = 0;
    int alloc_type = (data & BTRFS_BLOCK_GROUP_DATA) ?
        RESERVE_ALLOC_NO_ACCOUNT : RESERVE_ALLOC;
    bool found_uncached_bg = false;
    bool failed_cluster_refill = false;
    bool failed_alloc = false;
    bool use_cluster = true;
    bool have_caching_bg = false;

    WARN_ON(num_bytes < root->sectorsize);
    btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
    ins->objectid = 0;
    ins->offset = 0;

    trace_find_free_extent(orig_root, num_bytes, empty_size, data);

    space_info = __find_space_info(root->fs_info, data);
    if (!space_info) {
        printk(KERN_ERR "No space info for %llu\n", data);
        return -ENOSPC;
    }

    /*
     * If the space info is for both data and metadata it means we have a
     * small filesystem and we can't use the clustering stuff.
     */
    if (btrfs_mixed_space_info(space_info))
        use_cluster = false;

    if (data & BTRFS_BLOCK_GROUP_METADATA && use_cluster) {
        last_ptr = &root->fs_info->meta_alloc_cluster;
        if (!btrfs_test_opt(root, SSD))
            empty_cluster = 64 * 1024;
    }

    if ((data & BTRFS_BLOCK_GROUP_DATA) && use_cluster &&
        btrfs_test_opt(root, SSD)) {
        last_ptr = &root->fs_info->data_alloc_cluster;
    }

    if (last_ptr) {
        spin_lock(&last_ptr->lock);
        if (last_ptr->block_group)
            hint_byte = last_ptr->window_start;
        spin_unlock(&last_ptr->lock);
    }

    search_start = max(search_start, first_logical_byte(root, 0));
    search_start = max(search_start, hint_byte);

    if (!last_ptr)
        empty_cluster = 0;

    if (search_start == hint_byte) {
        block_group = btrfs_lookup_block_group(root->fs_info,
                               search_start);
        used_block_group = block_group;
        /*
         * we don't want to use the block group if it doesn't match our
         * allocation bits, or if its not cached.
         *
         * However if we are re-searching with an ideal block group
         * picked out then we don't care that the block group is cached.
         */
        if (block_group && block_group_bits(block_group, data) &&
            block_group->cached != BTRFS_CACHE_NO) {
            down_read(&space_info->groups_sem);
            if (list_empty(&block_group->list) ||
                block_group->ro) {
                /*
                 * someone is removing this block group,
                 * we can't jump into the have_block_group
                 * target because our list pointers are not
                 * valid
                 */
                btrfs_put_block_group(block_group);
                up_read(&space_info->groups_sem);
            } else {
                index = get_block_group_index(block_group);
                goto have_block_group;
            }
        } else if (block_group) {
            btrfs_put_block_group(block_group);
        }
    }
search:
    have_caching_bg = false;
    down_read(&space_info->groups_sem);
    list_for_each_entry(block_group, &space_info->block_groups[index],
                list) {
        u64 offset;
        int cached;

        used_block_group = block_group;
        btrfs_get_block_group(block_group);
        search_start = block_group->key.objectid;

        /*
         * this can happen if we end up cycling through all the
         * raid types, but we want to make sure we only allocate
         * for the proper type.
         */
        if (!block_group_bits(block_group, data)) {
            u64 extra = BTRFS_BLOCK_GROUP_DUP |
                BTRFS_BLOCK_GROUP_RAID1 |
                BTRFS_BLOCK_GROUP_RAID10;

            /*
             * if they asked for extra copies and this block group
             * doesn't provide them, bail.  This does allow us to
             * fill raid0 from raid1.
             */
            if ((data & extra) && !(block_group->flags & extra))
                goto loop;
        }

have_block_group:
        cached = block_group_cache_done(block_group);
        if (unlikely(!cached)) {
            found_uncached_bg = true;
            ret = cache_block_group(block_group, trans,
                        orig_root, 0);
            BUG_ON(ret < 0);
            ret = 0;
        }

        if (unlikely(block_group->ro))
            goto loop;

        /*
         * Ok we want to try and use the cluster allocator, so
         * lets look there
         */
        if (last_ptr) {
            /*
             * the refill lock keeps out other
             * people trying to start a new cluster
             */
            spin_lock(&last_ptr->refill_lock);
            used_block_group = last_ptr->block_group;
            if (used_block_group != block_group &&
                (!used_block_group ||
                 used_block_group->ro ||
                 !block_group_bits(used_block_group, data))) {
                used_block_group = block_group;
                goto refill_cluster;
            }

            if (used_block_group != block_group)
                btrfs_get_block_group(used_block_group);

            offset = btrfs_alloc_from_cluster(used_block_group,
              last_ptr, num_bytes, used_block_group->key.objectid);
            if (offset) {
                /* we have a block, we're done */
                spin_unlock(&last_ptr->refill_lock);
                trace_btrfs_reserve_extent_cluster(root,
                    block_group, search_start, num_bytes);
                goto checks;
            }

            WARN_ON(last_ptr->block_group != used_block_group);
            if (used_block_group != block_group) {
                btrfs_put_block_group(used_block_group);
                used_block_group = block_group;
            }
refill_cluster:
            BUG_ON(used_block_group != block_group);
            /* If we are on LOOP_NO_EMPTY_SIZE, we can't
             * set up a new clusters, so lets just skip it
             * and let the allocator find whatever block
             * it can find.  If we reach this point, we
             * will have tried the cluster allocator
             * plenty of times and not have found
             * anything, so we are likely way too
             * fragmented for the clustering stuff to find
             * anything.
             *
             * However, if the cluster is taken from the
             * current block group, release the cluster
             * first, so that we stand a better chance of
             * succeeding in the unclustered
             * allocation.  */
            if (loop >= LOOP_NO_EMPTY_SIZE &&
                last_ptr->block_group != block_group) {
                spin_unlock(&last_ptr->refill_lock);
                goto unclustered_alloc;
            }

            /*
             * this cluster didn't work out, free it and
             * start over
             */
            btrfs_return_cluster_to_free_space(NULL, last_ptr);

            if (loop >= LOOP_NO_EMPTY_SIZE) {
                spin_unlock(&last_ptr->refill_lock);
                goto unclustered_alloc;
            }

            /* allocate a cluster in this block group */
            ret = btrfs_find_space_cluster(trans, root,
                           block_group, last_ptr,
                           search_start, num_bytes,
                           empty_cluster + empty_size);
            if (ret == 0) {
                /*
                 * now pull our allocation out of this
                 * cluster
                 */
                offset = btrfs_alloc_from_cluster(block_group,
                          last_ptr, num_bytes,
                          search_start);
                if (offset) {
                    /* we found one, proceed */
                    spin_unlock(&last_ptr->refill_lock);
                    trace_btrfs_reserve_extent_cluster(root,
                        block_group, search_start,
                        num_bytes);
                    goto checks;
                }
            } else if (!cached && loop > LOOP_CACHING_NOWAIT
                   && !failed_cluster_refill) {
                spin_unlock(&last_ptr->refill_lock);

                failed_cluster_refill = true;
                wait_block_group_cache_progress(block_group,
                       num_bytes + empty_cluster + empty_size);
                goto have_block_group;
            }

            /*
             * at this point we either didn't find a cluster
             * or we weren't able to allocate a block from our
             * cluster.  Free the cluster we've been trying
             * to use, and go to the next block group
             */
            btrfs_return_cluster_to_free_space(NULL, last_ptr);
            spin_unlock(&last_ptr->refill_lock);
            goto loop;
        }

unclustered_alloc:
        spin_lock(&block_group->free_space_ctl->tree_lock);
        if (cached &&
            block_group->free_space_ctl->free_space <
            num_bytes + empty_cluster + empty_size) {
            spin_unlock(&block_group->free_space_ctl->tree_lock);
            goto loop;
        }
        spin_unlock(&block_group->free_space_ctl->tree_lock);

        offset = btrfs_find_space_for_alloc(block_group, search_start,
                            num_bytes, empty_size);
        /*
         * If we didn't find a chunk, and we haven't failed on this
         * block group before, and this block group is in the middle of
         * caching and we are ok with waiting, then go ahead and wait
         * for progress to be made, and set failed_alloc to true.
         *
         * If failed_alloc is true then we've already waited on this
         * block group once and should move on to the next block group.
         */
        if (!offset && !failed_alloc && !cached &&
            loop > LOOP_CACHING_NOWAIT) {
            wait_block_group_cache_progress(block_group,
                        num_bytes + empty_size);
            failed_alloc = true;
            goto have_block_group;
        } else if (!offset) {
            if (!cached)
                have_caching_bg = true;
            goto loop;
        }
checks:
        search_start = stripe_align(root, offset);

        /* move on to the next group */
        if (search_start + num_bytes >
            used_block_group->key.objectid + used_block_group->key.offset) {
            btrfs_add_free_space(used_block_group, offset, num_bytes);
            goto loop;
        }

        if (offset < search_start)
            btrfs_add_free_space(used_block_group, offset,
                         search_start - offset);
        BUG_ON(offset > search_start);

        ret = btrfs_update_reserved_bytes(used_block_group, num_bytes,
                          alloc_type);
        if (ret == -EAGAIN) {
            btrfs_add_free_space(used_block_group, offset, num_bytes);
            goto loop;
        }

        /* we are all good, lets return */
        ins->objectid = search_start;
        ins->offset = num_bytes;

        trace_btrfs_reserve_extent(orig_root, block_group,
                       search_start, num_bytes);
        if (used_block_group != block_group)
            btrfs_put_block_group(used_block_group);
        btrfs_put_block_group(block_group);
        break;
loop:
        failed_cluster_refill = false;
        failed_alloc = false;
        BUG_ON(index != get_block_group_index(block_group));
        if (used_block_group != block_group)
            btrfs_put_block_group(used_block_group);
        btrfs_put_block_group(block_group);
    }
    up_read(&space_info->groups_sem);

    if (!ins->objectid && loop >= LOOP_CACHING_WAIT && have_caching_bg)
        goto search;

    if (!ins->objectid && ++index < BTRFS_NR_RAID_TYPES)
        goto search;

    /*
     * LOOP_CACHING_NOWAIT, search partially cached block groups, kicking
     *          caching kthreads as we move along
     * LOOP_CACHING_WAIT, search everything, and wait if our bg is caching
     * LOOP_ALLOC_CHUNK, force a chunk allocation and try again
     * LOOP_NO_EMPTY_SIZE, set empty_size and empty_cluster to 0 and try
     *          again
     */
    if (!ins->objectid && loop < LOOP_NO_EMPTY_SIZE) {
        index = 0;
        loop++;
        if (loop == LOOP_ALLOC_CHUNK) {
            ret = do_chunk_alloc(trans, root, data,
                         CHUNK_ALLOC_FORCE);
            /*
             * Do not bail out on ENOSPC since we
             * can do more things.
             */
            if (ret < 0 && ret != -ENOSPC) {
                btrfs_abort_transaction(trans,
                            root, ret);
                goto out;
            }
        }

        if (loop == LOOP_NO_EMPTY_SIZE) {
            empty_size = 0;
            empty_cluster = 0;
        }

        goto search;
    } else if (!ins->objectid) {
        ret = -ENOSPC;
    } else if (ins->objectid) {
        ret = 0;
    }
out:

    return ret;
}

static void dump_space_info(struct btrfs_space_info *info, u64 bytes,
                int dump_block_groups)
{
    struct btrfs_block_group_cache *cache;
    int index = 0;

    spin_lock(&info->lock);
    printk(KERN_INFO "space_info %llu has %llu free, is %sfull\n",
           (unsigned long long)info->flags,
           (unsigned long long)(info->total_bytes - info->bytes_used -
                    info->bytes_pinned - info->bytes_reserved -
                    info->bytes_readonly),
           (info->full) ? "" : "not ");
    printk(KERN_INFO "space_info total=%llu, used=%llu, pinned=%llu, "
           "reserved=%llu, may_use=%llu, readonly=%llu\n",
           (unsigned long long)info->total_bytes,
           (unsigned long long)info->bytes_used,
           (unsigned long long)info->bytes_pinned,
           (unsigned long long)info->bytes_reserved,
           (unsigned long long)info->bytes_may_use,
           (unsigned long long)info->bytes_readonly);
    spin_unlock(&info->lock);

    if (!dump_block_groups)
        return;

    down_read(&info->groups_sem);
again:
    list_for_each_entry(cache, &info->block_groups[index], list) {
        spin_lock(&cache->lock);
        printk(KERN_INFO "block group %llu has %llu bytes, %llu used %llu pinned %llu reserved %s\n",
               (unsigned long long)cache->key.objectid,
               (unsigned long long)cache->key.offset,
               (unsigned long long)btrfs_block_group_used(&cache->item),
               (unsigned long long)cache->pinned,
               (unsigned long long)cache->reserved,
               cache->ro ? "[readonly]" : "");
        btrfs_dump_free_space(cache, bytes);
        spin_unlock(&cache->lock);
    }
    if (++index < BTRFS_NR_RAID_TYPES)
        goto again;
    up_read(&info->groups_sem);
}

int btrfs_reserve_extent(struct btrfs_trans_handle *trans,
             struct btrfs_root *root,
             u64 num_bytes, u64 min_alloc_size,
             u64 empty_size, u64 hint_byte,
             struct btrfs_key *ins, u64 data)
{
    bool final_tried = false;
    int ret;

    data = btrfs_get_alloc_profile(root, data);
again:
    WARN_ON(num_bytes < root->sectorsize);
    ret = find_free_extent(trans, root, num_bytes, empty_size,
                   hint_byte, ins, data);

    if (ret == -ENOSPC) {
        if (!final_tried) {
            num_bytes = num_bytes >> 1;
            num_bytes = num_bytes & ~(root->sectorsize - 1);
            num_bytes = max(num_bytes, min_alloc_size);
            if (num_bytes == min_alloc_size)
                final_tried = true;
            goto again;
        } else if (btrfs_test_opt(root, ENOSPC_DEBUG)) {
            struct btrfs_space_info *sinfo;

            sinfo = __find_space_info(root->fs_info, data);
            printk(KERN_ERR "btrfs allocation failed flags %llu, "
                   "wanted %llu\n", (unsigned long long)data,
                   (unsigned long long)num_bytes);
            if (sinfo)
                dump_space_info(sinfo, num_bytes, 1);
        }
    }

    trace_btrfs_reserved_extent_alloc(root, ins->objectid, ins->offset);

    return ret;
}

static int __btrfs_free_reserved_extent(struct btrfs_root *root,
                    u64 start, u64 len, int pin)
{
    struct btrfs_block_group_cache *cache;
    int ret = 0;

    cache = btrfs_lookup_block_group(root->fs_info, start);
    if (!cache) {
        printk(KERN_ERR "Unable to find block group for %llu\n",
               (unsigned long long)start);
        return -ENOSPC;
    }

    if (btrfs_test_opt(root, DISCARD))
        ret = btrfs_discard_extent(root, start, len, NULL);

    if (pin)
        pin_down_extent(root, cache, start, len, 1);
    else {
        btrfs_add_free_space(cache, start, len);
        btrfs_update_reserved_bytes(cache, len, RESERVE_FREE);
    }
    btrfs_put_block_group(cache);

    trace_btrfs_reserved_extent_free(root, start, len);

    return ret;
}

int btrfs_free_reserved_extent(struct btrfs_root *root,
                    u64 start, u64 len)
{
    return __btrfs_free_reserved_extent(root, start, len, 0);
}

int btrfs_free_and_pin_reserved_extent(struct btrfs_root *root,
                       u64 start, u64 len)
{
    return __btrfs_free_reserved_extent(root, start, len, 1);
}

static int alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      u64 parent, u64 root_objectid,
                      u64 flags, u64 owner, u64 offset,
                      struct btrfs_key *ins, int ref_mod)
{
    int ret;
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct btrfs_extent_item *extent_item;
    struct btrfs_extent_inline_ref *iref;
    struct btrfs_path *path;
    struct extent_buffer *leaf;
    int type;
    u32 size;

    if (parent > 0)
        type = BTRFS_SHARED_DATA_REF_KEY;
    else
        type = BTRFS_EXTENT_DATA_REF_KEY;

    size = sizeof(*extent_item) + btrfs_extent_inline_ref_size(type);

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    path->leave_spinning = 1;
    ret = btrfs_insert_empty_item(trans, fs_info->extent_root, path,
                      ins, size);
    if (ret) {
        btrfs_free_path(path);
        return ret;
    }

    leaf = path->nodes[0];
    extent_item = btrfs_item_ptr(leaf, path->slots[0],
                     struct btrfs_extent_item);
    btrfs_set_extent_refs(leaf, extent_item, ref_mod);
    btrfs_set_extent_generation(leaf, extent_item, trans->transid);
    btrfs_set_extent_flags(leaf, extent_item,
                   flags | BTRFS_EXTENT_FLAG_DATA);

    iref = (struct btrfs_extent_inline_ref *)(extent_item + 1);
    btrfs_set_extent_inline_ref_type(leaf, iref, type);
    if (parent > 0) {
        struct btrfs_shared_data_ref *ref;
        ref = (struct btrfs_shared_data_ref *)(iref + 1);
        btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
        btrfs_set_shared_data_ref_count(leaf, ref, ref_mod);
    } else {
        struct btrfs_extent_data_ref *ref;
        ref = (struct btrfs_extent_data_ref *)(&iref->offset);
        btrfs_set_extent_data_ref_root(leaf, ref, root_objectid);
        btrfs_set_extent_data_ref_objectid(leaf, ref, owner);
        btrfs_set_extent_data_ref_offset(leaf, ref, offset);
        btrfs_set_extent_data_ref_count(leaf, ref, ref_mod);
    }

    btrfs_mark_buffer_dirty(path->nodes[0]);
    btrfs_free_path(path);

    ret = update_block_group(trans, root, ins->objectid, ins->offset, 1);
    if (ret) { /* -ENOENT, logic error */
        printk(KERN_ERR "btrfs update block group failed for %llu "
               "%llu\n", (unsigned long long)ins->objectid,
               (unsigned long long)ins->offset);
        BUG();
    }
    return ret;
}

static int alloc_reserved_tree_block(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     u64 parent, u64 root_objectid,
                     u64 flags, struct btrfs_disk_key *key,
                     int level, struct btrfs_key *ins)
{
    int ret;
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct btrfs_extent_item *extent_item;
    struct btrfs_tree_block_info *block_info;
    struct btrfs_extent_inline_ref *iref;
    struct btrfs_path *path;
    struct extent_buffer *leaf;
    u32 size = sizeof(*extent_item) + sizeof(*block_info) + sizeof(*iref);

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    path->leave_spinning = 1;
    ret = btrfs_insert_empty_item(trans, fs_info->extent_root, path,
                      ins, size);
    if (ret) {
        btrfs_free_path(path);
        return ret;
    }

    leaf = path->nodes[0];
    extent_item = btrfs_item_ptr(leaf, path->slots[0],
                     struct btrfs_extent_item);
    btrfs_set_extent_refs(leaf, extent_item, 1);
    btrfs_set_extent_generation(leaf, extent_item, trans->transid);
    btrfs_set_extent_flags(leaf, extent_item,
                   flags | BTRFS_EXTENT_FLAG_TREE_BLOCK);
    block_info = (struct btrfs_tree_block_info *)(extent_item + 1);

    btrfs_set_tree_block_key(leaf, block_info, key);
    btrfs_set_tree_block_level(leaf, block_info, level);

    iref = (struct btrfs_extent_inline_ref *)(block_info + 1);
    if (parent > 0) {
        BUG_ON(!(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF));
        btrfs_set_extent_inline_ref_type(leaf, iref,
                         BTRFS_SHARED_BLOCK_REF_KEY);
        btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
    } else {
        btrfs_set_extent_inline_ref_type(leaf, iref,
                         BTRFS_TREE_BLOCK_REF_KEY);
        btrfs_set_extent_inline_ref_offset(leaf, iref, root_objectid);
    }

    btrfs_mark_buffer_dirty(leaf);
    btrfs_free_path(path);

    ret = update_block_group(trans, root, ins->objectid, ins->offset, 1);
    if (ret) { /* -ENOENT, logic error */
        printk(KERN_ERR "btrfs update block group failed for %llu "
               "%llu\n", (unsigned long long)ins->objectid,
               (unsigned long long)ins->offset);
        BUG();
    }
    return ret;
}

int btrfs_alloc_reserved_file_extent(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     u64 root_objectid, u64 owner,
                     u64 offset, struct btrfs_key *ins)
{
    int ret;

    BUG_ON(root_objectid == BTRFS_TREE_LOG_OBJECTID);

    ret = btrfs_add_delayed_data_ref(root->fs_info, trans, ins->objectid,
                     ins->offset, 0,
                     root_objectid, owner, offset,
                     BTRFS_ADD_DELAYED_EXTENT, NULL, 0);
    return ret;
}

/*
 * this is used by the tree logging recovery code.  It records that
 * an extent has been allocated and makes sure to clear the free
 * space cache bits as well
 */
int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root,
                   u64 root_objectid, u64 owner, u64 offset,
                   struct btrfs_key *ins)
{
    int ret;
    struct btrfs_block_group_cache *block_group;
    struct btrfs_caching_control *caching_ctl;
    u64 start = ins->objectid;
    u64 num_bytes = ins->offset;

    block_group = btrfs_lookup_block_group(root->fs_info, ins->objectid);
    cache_block_group(block_group, trans, NULL, 0);
    caching_ctl = get_caching_control(block_group);

    if (!caching_ctl) {
        BUG_ON(!block_group_cache_done(block_group));
        ret = btrfs_remove_free_space(block_group, start, num_bytes);
        BUG_ON(ret); /* -ENOMEM */
    } else {
        mutex_lock(&caching_ctl->mutex);

        if (start >= caching_ctl->progress) {
            ret = add_excluded_extent(root, start, num_bytes);
            BUG_ON(ret); /* -ENOMEM */
        } else if (start + num_bytes <= caching_ctl->progress) {
            ret = btrfs_remove_free_space(block_group,
                              start, num_bytes);
            BUG_ON(ret); /* -ENOMEM */
        } else {
            num_bytes = caching_ctl->progress - start;
            ret = btrfs_remove_free_space(block_group,
                              start, num_bytes);
            BUG_ON(ret); /* -ENOMEM */

            start = caching_ctl->progress;
            num_bytes = ins->objectid + ins->offset -
                    caching_ctl->progress;
            ret = add_excluded_extent(root, start, num_bytes);
            BUG_ON(ret); /* -ENOMEM */
        }

        mutex_unlock(&caching_ctl->mutex);
        put_caching_control(caching_ctl);
    }

    ret = btrfs_update_reserved_bytes(block_group, ins->offset,
                      RESERVE_ALLOC_NO_ACCOUNT);
    BUG_ON(ret); /* logic error */
    btrfs_put_block_group(block_group);
    ret = alloc_reserved_file_extent(trans, root, 0, root_objectid,
                     0, owner, offset, ins, 1);
    return ret;
}

struct extent_buffer *btrfs_init_new_buffer(struct btrfs_trans_handle *trans,
                        struct btrfs_root *root,
                        u64 bytenr, u32 blocksize,
                        int level)
{
    struct extent_buffer *buf;

    buf = btrfs_find_create_tree_block(root, bytenr, blocksize);
    if (!buf)
        return ERR_PTR(-ENOMEM);
    btrfs_set_header_generation(buf, trans->transid);
    btrfs_set_buffer_lockdep_class(root->root_key.objectid, buf, level);
    btrfs_tree_lock(buf);
    clean_tree_block(trans, root, buf);
    clear_bit(EXTENT_BUFFER_STALE, &buf->bflags);

    btrfs_set_lock_blocking(buf);
    btrfs_set_buffer_uptodate(buf);

    if (root->root_key.objectid == BTRFS_TREE_LOG_OBJECTID) {
        /*
         * we allow two log transactions at a time, use different
         * EXENT bit to differentiate dirty pages.
         */
        if (root->log_transid % 2 == 0)
            set_extent_dirty(&root->dirty_log_pages, buf->start,
                    buf->start + buf->len - 1, GFP_NOFS);
        else
            set_extent_new(&root->dirty_log_pages, buf->start,
                    buf->start + buf->len - 1, GFP_NOFS);
    } else {
        set_extent_dirty(&trans->transaction->dirty_pages, buf->start,
             buf->start + buf->len - 1, GFP_NOFS);
    }
    trans->blocks_used++;
    /* this returns a buffer locked for blocking */
    return buf;
}

static struct btrfs_block_rsv *
use_block_rsv(struct btrfs_trans_handle *trans,
          struct btrfs_root *root, u32 blocksize)
{
    struct btrfs_block_rsv *block_rsv;
    struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
    int ret;

    block_rsv = get_block_rsv(trans, root);

    if (block_rsv->size == 0) {
        ret = reserve_metadata_bytes(root, block_rsv, blocksize, 0);
        /*
         * If we couldn't reserve metadata bytes try and use some from
         * the global reserve.
         */
        if (ret && block_rsv != global_rsv) {
            ret = block_rsv_use_bytes(global_rsv, blocksize);
            if (!ret)
                return global_rsv;
            return ERR_PTR(ret);
        } else if (ret) {
            return ERR_PTR(ret);
        }
        return block_rsv;
    }

    ret = block_rsv_use_bytes(block_rsv, blocksize);
    if (!ret)
        return block_rsv;
    if (ret && !block_rsv->failfast) {
        static DEFINE_RATELIMIT_STATE(_rs,
                DEFAULT_RATELIMIT_INTERVAL,
                /*DEFAULT_RATELIMIT_BURST*/ 2);
        if (__ratelimit(&_rs)) {
            printk(KERN_DEBUG "btrfs: block rsv returned %d\n", ret);
            WARN_ON(1);
        }
        ret = reserve_metadata_bytes(root, block_rsv, blocksize, 0);
        if (!ret) {
            return block_rsv;
        } else if (ret && block_rsv != global_rsv) {
            ret = block_rsv_use_bytes(global_rsv, blocksize);
            if (!ret)
                return global_rsv;
        }
    }

    return ERR_PTR(-ENOSPC);
}

static void unuse_block_rsv(struct btrfs_fs_info *fs_info,
                struct btrfs_block_rsv *block_rsv, u32 blocksize)
{
    block_rsv_add_bytes(block_rsv, blocksize, 0);
    block_rsv_release_bytes(fs_info, block_rsv, NULL, 0);
}

/*
 * finds a free extent and does all the dirty work required for allocation
 * returns the key for the extent through ins, and a tree buffer for
 * the first block of the extent through buf.
 *
 * returns the tree buffer or NULL.
 */
struct extent_buffer *btrfs_alloc_free_block(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root, u32 blocksize,
                    u64 parent, u64 root_objectid,
                    struct btrfs_disk_key *key, int level,
                    u64 hint, u64 empty_size)
{
    struct btrfs_key ins;
    struct btrfs_block_rsv *block_rsv;
    struct extent_buffer *buf;
    u64 flags = 0;
    int ret;


    block_rsv = use_block_rsv(trans, root, blocksize);
    if (IS_ERR(block_rsv))
        return ERR_CAST(block_rsv);

    ret = btrfs_reserve_extent(trans, root, blocksize, blocksize,
                   empty_size, hint, &ins, 0);
    if (ret) {
        unuse_block_rsv(root->fs_info, block_rsv, blocksize);
        return ERR_PTR(ret);
    }

    buf = btrfs_init_new_buffer(trans, root, ins.objectid,
                    blocksize, level);
    BUG_ON(IS_ERR(buf)); /* -ENOMEM */

    if (root_objectid == BTRFS_TREE_RELOC_OBJECTID) {
        if (parent == 0)
            parent = ins.objectid;
        flags |= BTRFS_BLOCK_FLAG_FULL_BACKREF;
    } else
        BUG_ON(parent > 0);

    if (root_objectid != BTRFS_TREE_LOG_OBJECTID) {
        struct btrfs_delayed_extent_op *extent_op;
        extent_op = kmalloc(sizeof(*extent_op), GFP_NOFS);
        BUG_ON(!extent_op); /* -ENOMEM */
        if (key)
            memcpy(&extent_op->key, key, sizeof(extent_op->key));
        else
            memset(&extent_op->key, 0, sizeof(extent_op->key));
        extent_op->flags_to_set = flags;
        extent_op->update_key = 1;
        extent_op->update_flags = 1;
        extent_op->is_data = 0;

        ret = btrfs_add_delayed_tree_ref(root->fs_info, trans,
                    ins.objectid,
                    ins.offset, parent, root_objectid,
                    level, BTRFS_ADD_DELAYED_EXTENT,
                    extent_op, 0);
        BUG_ON(ret); /* -ENOMEM */
    }
    return buf;
}

struct walk_control {
    u64 refs[BTRFS_MAX_LEVEL];
    u64 flags[BTRFS_MAX_LEVEL];
    struct btrfs_key update_progress;
    int stage;
    int level;
    int shared_level;
    int update_ref;
    int keep_locks;
    int reada_slot;
    int reada_count;
    int for_reloc;
};

#define DROP_REFERENCE  1
#define UPDATE_BACKREF  2

static noinline void reada_walk_down(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     struct walk_control *wc,
                     struct btrfs_path *path)
{
    u64 bytenr;
    u64 generation;
    u64 refs;
    u64 flags;
    u32 nritems;
    u32 blocksize;
    struct btrfs_key key;
    struct extent_buffer *eb;
    int ret;
    int slot;
    int nread = 0;

    if (path->slots[wc->level] < wc->reada_slot) {
        wc->reada_count = wc->reada_count * 2 / 3;
        wc->reada_count = max(wc->reada_count, 2);
    } else {
        wc->reada_count = wc->reada_count * 3 / 2;
        wc->reada_count = min_t(int, wc->reada_count,
                    BTRFS_NODEPTRS_PER_BLOCK(root));
    }

    eb = path->nodes[wc->level];
    nritems = btrfs_header_nritems(eb);
    blocksize = btrfs_level_size(root, wc->level - 1);

    for (slot = path->slots[wc->level]; slot < nritems; slot++) {
        if (nread >= wc->reada_count)
            break;

        cond_resched();
        bytenr = btrfs_node_blockptr(eb, slot);
        generation = btrfs_node_ptr_generation(eb, slot);

        if (slot == path->slots[wc->level])
            goto reada;

        if (wc->stage == UPDATE_BACKREF &&
            generation <= root->root_key.offset)
            continue;

        /* We don't lock the tree block, it's OK to be racy here */
        ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize,
                           &refs, &flags);
        /* We don't care about errors in readahead. */
        if (ret < 0)
            continue;
        BUG_ON(refs == 0);

        if (wc->stage == DROP_REFERENCE) {
            if (refs == 1)
                goto reada;

            if (wc->level == 1 &&
                (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                continue;
            if (!wc->update_ref ||
                generation <= root->root_key.offset)
                continue;
            btrfs_node_key_to_cpu(eb, &key, slot);
            ret = btrfs_comp_cpu_keys(&key,
                          &wc->update_progress);
            if (ret < 0)
                continue;
        } else {
            if (wc->level == 1 &&
                (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                continue;
        }
reada:
        ret = readahead_tree_block(root, bytenr, blocksize,
                       generation);
        if (ret)
            break;
        nread++;
    }
    wc->reada_slot = slot;
}

/*
 * hepler to process tree block while walking down the tree.
 *
 * when wc->stage == UPDATE_BACKREF, this function updates
 * back refs for pointers in the block.
 *
 * NOTE: return value 1 means we should stop walking down.
 */
static noinline int walk_down_proc(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root,
                   struct btrfs_path *path,
                   struct walk_control *wc, int lookup_info)
{
    int level = wc->level;
    struct extent_buffer *eb = path->nodes[level];
    u64 flag = BTRFS_BLOCK_FLAG_FULL_BACKREF;
    int ret;

    if (wc->stage == UPDATE_BACKREF &&
        btrfs_header_owner(eb) != root->root_key.objectid)
        return 1;

    /*
     * when reference count of tree block is 1, it won't increase
     * again. once full backref flag is set, we never clear it.
     */
    if (lookup_info &&
        ((wc->stage == DROP_REFERENCE && wc->refs[level] != 1) ||
         (wc->stage == UPDATE_BACKREF && !(wc->flags[level] & flag)))) {
        BUG_ON(!path->locks[level]);
        ret = btrfs_lookup_extent_info(trans, root,
                           eb->start, eb->len,
                           &wc->refs[level],
                           &wc->flags[level]);
        BUG_ON(ret == -ENOMEM);
        if (ret)
            return ret;
        BUG_ON(wc->refs[level] == 0);
    }

    if (wc->stage == DROP_REFERENCE) {
        if (wc->refs[level] > 1)
            return 1;

        if (path->locks[level] && !wc->keep_locks) {
            btrfs_tree_unlock_rw(eb, path->locks[level]);
            path->locks[level] = 0;
        }
        return 0;
    }

    /* wc->stage == UPDATE_BACKREF */
    if (!(wc->flags[level] & flag)) {
        BUG_ON(!path->locks[level]);
        ret = btrfs_inc_ref(trans, root, eb, 1, wc->for_reloc);
        BUG_ON(ret); /* -ENOMEM */
        ret = btrfs_dec_ref(trans, root, eb, 0, wc->for_reloc);
        BUG_ON(ret); /* -ENOMEM */
        ret = btrfs_set_disk_extent_flags(trans, root, eb->start,
                          eb->len, flag, 0);
        BUG_ON(ret); /* -ENOMEM */
        wc->flags[level] |= flag;
    }

    /*
     * the block is shared by multiple trees, so it's not good to
     * keep the tree lock
     */
    if (path->locks[level] && level > 0) {
        btrfs_tree_unlock_rw(eb, path->locks[level]);
        path->locks[level] = 0;
    }
    return 0;
}

/*
 * hepler to process tree block pointer.
 *
 * when wc->stage == DROP_REFERENCE, this function checks
 * reference count of the block pointed to. if the block
 * is shared and we need update back refs for the subtree
 * rooted at the block, this function changes wc->stage to
 * UPDATE_BACKREF. if the block is shared and there is no
 * need to update back, this function drops the reference
 * to the block.
 *
 * NOTE: return value 1 means we should stop walking down.
 */
static noinline int do_walk_down(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 struct walk_control *wc, int *lookup_info)
{
    u64 bytenr;
    u64 generation;
    u64 parent;
    u32 blocksize;
    struct btrfs_key key;
    struct extent_buffer *next;
    int level = wc->level;
    int reada = 0;
    int ret = 0;

    generation = btrfs_node_ptr_generation(path->nodes[level],
                           path->slots[level]);
    /*
     * if the lower level block was created before the snapshot
     * was created, we know there is no need to update back refs
     * for the subtree
     */
    if (wc->stage == UPDATE_BACKREF &&
        generation <= root->root_key.offset) {
        *lookup_info = 1;
        return 1;
    }

    bytenr = btrfs_node_blockptr(path->nodes[level], path->slots[level]);
    blocksize = btrfs_level_size(root, level - 1);

    next = btrfs_find_tree_block(root, bytenr, blocksize);
    if (!next) {
        next = btrfs_find_create_tree_block(root, bytenr, blocksize);
        if (!next)
            return -ENOMEM;
        reada = 1;
    }
    btrfs_tree_lock(next);
    btrfs_set_lock_blocking(next);

    ret = btrfs_lookup_extent_info(trans, root, bytenr, blocksize,
                       &wc->refs[level - 1],
                       &wc->flags[level - 1]);
    if (ret < 0) {
        btrfs_tree_unlock(next);
        return ret;
    }

    BUG_ON(wc->refs[level - 1] == 0);
    *lookup_info = 0;

    if (wc->stage == DROP_REFERENCE) {
        if (wc->refs[level - 1] > 1) {
            if (level == 1 &&
                (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF))
                goto skip;

            if (!wc->update_ref ||
                generation <= root->root_key.offset)
                goto skip;

            btrfs_node_key_to_cpu(path->nodes[level], &key,
                          path->slots[level]);
            ret = btrfs_comp_cpu_keys(&key, &wc->update_progress);
            if (ret < 0)
                goto skip;

            wc->stage = UPDATE_BACKREF;
            wc->shared_level = level - 1;
        }
    } else {
        if (level == 1 &&
            (wc->flags[0] & BTRFS_BLOCK_FLAG_FULL_BACKREF))
            goto skip;
    }

    if (!btrfs_buffer_uptodate(next, generation, 0)) {
        btrfs_tree_unlock(next);
        free_extent_buffer(next);
        next = NULL;
        *lookup_info = 1;
    }

    if (!next) {
        if (reada && level == 1)
            reada_walk_down(trans, root, wc, path);
        next = read_tree_block(root, bytenr, blocksize, generation);
        if (!next)
            return -EIO;
        btrfs_tree_lock(next);
        btrfs_set_lock_blocking(next);
    }

    level--;
    BUG_ON(level != btrfs_header_level(next));
    path->nodes[level] = next;
    path->slots[level] = 0;
    path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
    wc->level = level;
    if (wc->level == 1)
        wc->reada_slot = 0;
    return 0;
skip:
    wc->refs[level - 1] = 0;
    wc->flags[level - 1] = 0;
    if (wc->stage == DROP_REFERENCE) {
        if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF) {
            parent = path->nodes[level]->start;
        } else {
            BUG_ON(root->root_key.objectid !=
                   btrfs_header_owner(path->nodes[level]));
            parent = 0;
        }

        ret = btrfs_free_extent(trans, root, bytenr, blocksize, parent,
                root->root_key.objectid, level - 1, 0, 0);
        BUG_ON(ret); /* -ENOMEM */
    }
    btrfs_tree_unlock(next);
    free_extent_buffer(next);
    *lookup_info = 1;
    return 1;
}

/*
 * hepler to process tree block while walking up the tree.
 *
 * when wc->stage == DROP_REFERENCE, this function drops
 * reference count on the block.
 *
 * when wc->stage == UPDATE_BACKREF, this function changes
 * wc->stage back to DROP_REFERENCE if we changed wc->stage
 * to UPDATE_BACKREF previously while processing the block.
 *
 * NOTE: return value 1 means we should stop walking up.
 */
static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 struct walk_control *wc)
{
    int ret;
    int level = wc->level;
    struct extent_buffer *eb = path->nodes[level];
    u64 parent = 0;

    if (wc->stage == UPDATE_BACKREF) {
        BUG_ON(wc->shared_level < level);
        if (level < wc->shared_level)
            goto out;

        ret = find_next_key(path, level + 1, &wc->update_progress);
        if (ret > 0)
            wc->update_ref = 0;

        wc->stage = DROP_REFERENCE;
        wc->shared_level = -1;
        path->slots[level] = 0;

        /*
         * check reference count again if the block isn't locked.
         * we should start walking down the tree again if reference
         * count is one.
         */
        if (!path->locks[level]) {
            BUG_ON(level == 0);
            btrfs_tree_lock(eb);
            btrfs_set_lock_blocking(eb);
            path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;

            ret = btrfs_lookup_extent_info(trans, root,
                               eb->start, eb->len,
                               &wc->refs[level],
                               &wc->flags[level]);
            if (ret < 0) {
                btrfs_tree_unlock_rw(eb, path->locks[level]);
                return ret;
            }
            BUG_ON(wc->refs[level] == 0);
            if (wc->refs[level] == 1) {
                btrfs_tree_unlock_rw(eb, path->locks[level]);
                return 1;
            }
        }
    }

    /* wc->stage == DROP_REFERENCE */
    BUG_ON(wc->refs[level] > 1 && !path->locks[level]);

    if (wc->refs[level] == 1) {
        if (level == 0) {
            if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
                ret = btrfs_dec_ref(trans, root, eb, 1,
                            wc->for_reloc);
            else
                ret = btrfs_dec_ref(trans, root, eb, 0,
                            wc->for_reloc);
            BUG_ON(ret); /* -ENOMEM */
        }
        /* make block locked assertion in clean_tree_block happy */
        if (!path->locks[level] &&
            btrfs_header_generation(eb) == trans->transid) {
            btrfs_tree_lock(eb);
            btrfs_set_lock_blocking(eb);
            path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
        }
        clean_tree_block(trans, root, eb);
    }

    if (eb == root->node) {
        if (wc->flags[level] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
            parent = eb->start;
        else
            BUG_ON(root->root_key.objectid !=
                   btrfs_header_owner(eb));
    } else {
        if (wc->flags[level + 1] & BTRFS_BLOCK_FLAG_FULL_BACKREF)
            parent = path->nodes[level + 1]->start;
        else
            BUG_ON(root->root_key.objectid !=
                   btrfs_header_owner(path->nodes[level + 1]));
    }

    btrfs_free_tree_block(trans, root, eb, parent, wc->refs[level] == 1);
out:
    wc->refs[level] = 0;
    wc->flags[level] = 0;
    return 0;
}

static noinline int walk_down_tree(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root,
                   struct btrfs_path *path,
                   struct walk_control *wc)
{
    int level = wc->level;
    int lookup_info = 1;
    int ret;

    while (level >= 0) {
        ret = walk_down_proc(trans, root, path, wc, lookup_info);
        if (ret > 0)
            break;

        if (level == 0)
            break;

        if (path->slots[level] >=
            btrfs_header_nritems(path->nodes[level]))
            break;

        ret = do_walk_down(trans, root, path, wc, &lookup_info);
        if (ret > 0) {
            path->slots[level]++;
            continue;
        } else if (ret < 0)
            return ret;
        level = wc->level;
    }
    return 0;
}

static noinline int walk_up_tree(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root,
                 struct btrfs_path *path,
                 struct walk_control *wc, int max_level)
{
    int level = wc->level;
    int ret;

    path->slots[level] = btrfs_header_nritems(path->nodes[level]);
    while (level < max_level && path->nodes[level]) {
        wc->level = level;
        if (path->slots[level] + 1 <
            btrfs_header_nritems(path->nodes[level])) {
            path->slots[level]++;
            return 0;
        } else {
            ret = walk_up_proc(trans, root, path, wc);
            if (ret > 0)
                return 0;

            if (path->locks[level]) {
                btrfs_tree_unlock_rw(path->nodes[level],
                             path->locks[level]);
                path->locks[level] = 0;
            }
            free_extent_buffer(path->nodes[level]);
            path->nodes[level] = NULL;
            level++;
        }
    }
    return 1;
}

/*
 * drop a subvolume tree.
 *
 * this function traverses the tree freeing any blocks that only
 * referenced by the tree.
 *
 * when a shared tree block is found. this function decreases its
 * reference count by one. if update_ref is true, this function
 * also make sure backrefs for the shared block and all lower level
 * blocks are properly updated.
 */
int btrfs_drop_snapshot(struct btrfs_root *root,
             struct btrfs_block_rsv *block_rsv, int update_ref,
             int for_reloc)
{
    struct btrfs_path *path;
    struct btrfs_trans_handle *trans;
    struct btrfs_root *tree_root = root->fs_info->tree_root;
    struct btrfs_root_item *root_item = &root->root_item;
    struct walk_control *wc;
    struct btrfs_key key;
    int err = 0;
    int ret;
    int level;

    path = btrfs_alloc_path();
    if (!path) {
        err = -ENOMEM;
        goto out;
    }

    wc = kzalloc(sizeof(*wc), GFP_NOFS);
    if (!wc) {
        btrfs_free_path(path);
        err = -ENOMEM;
        goto out;
    }

    trans = btrfs_start_transaction(tree_root, 0);
    if (IS_ERR(trans)) {
        err = PTR_ERR(trans);
        goto out_free;
    }

    if (block_rsv)
        trans->block_rsv = block_rsv;

    if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
        level = btrfs_header_level(root->node);
        path->nodes[level] = btrfs_lock_root_node(root);
        btrfs_set_lock_blocking(path->nodes[level]);
        path->slots[level] = 0;
        path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;
        memset(&wc->update_progress, 0,
               sizeof(wc->update_progress));
    } else {
        btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);
        memcpy(&wc->update_progress, &key,
               sizeof(wc->update_progress));

        level = root_item->drop_level;
        BUG_ON(level == 0);
        path->lowest_level = level;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        path->lowest_level = 0;
        if (ret < 0) {
            err = ret;
            goto out_end_trans;
        }
        WARN_ON(ret > 0);

        /*
         * unlock our path, this is safe because only this
         * function is allowed to delete this snapshot
         */
        btrfs_unlock_up_safe(path, 0);

        level = btrfs_header_level(root->node);
        while (1) {
            btrfs_tree_lock(path->nodes[level]);
            btrfs_set_lock_blocking(path->nodes[level]);

            ret = btrfs_lookup_extent_info(trans, root,
                        path->nodes[level]->start,
                        path->nodes[level]->len,
                        &wc->refs[level],
                        &wc->flags[level]);
            if (ret < 0) {
                err = ret;
                goto out_end_trans;
            }
            BUG_ON(wc->refs[level] == 0);

            if (level == root_item->drop_level)
                break;

            btrfs_tree_unlock(path->nodes[level]);
            WARN_ON(wc->refs[level] != 1);
            level--;
        }
    }

    wc->level = level;
    wc->shared_level = -1;
    wc->stage = DROP_REFERENCE;
    wc->update_ref = update_ref;
    wc->keep_locks = 0;
    wc->for_reloc = for_reloc;
    wc->reada_count = BTRFS_NODEPTRS_PER_BLOCK(root);

    while (1) {
        ret = walk_down_tree(trans, root, path, wc);
        if (ret < 0) {
            err = ret;
            break;
        }

        ret = walk_up_tree(trans, root, path, wc, BTRFS_MAX_LEVEL);
        if (ret < 0) {
            err = ret;
            break;
        }

        if (ret > 0) {
            BUG_ON(wc->stage != DROP_REFERENCE);
            break;
        }

        if (wc->stage == DROP_REFERENCE) {
            level = wc->level;
            btrfs_node_key(path->nodes[level],
                       &root_item->drop_progress,
                       path->slots[level]);
            root_item->drop_level = level;
        }

        BUG_ON(wc->level == 0);
        if (btrfs_should_end_transaction(trans, tree_root)) {
            ret = btrfs_update_root(trans, tree_root,
                        &root->root_key,
                        root_item);
            if (ret) {
                btrfs_abort_transaction(trans, tree_root, ret);
                err = ret;
                goto out_end_trans;
            }

            btrfs_end_transaction_throttle(trans, tree_root);
            trans = btrfs_start_transaction(tree_root, 0);
            if (IS_ERR(trans)) {
                err = PTR_ERR(trans);
                goto out_free;
            }
            if (block_rsv)
                trans->block_rsv = block_rsv;
        }
    }
    btrfs_release_path(path);
    if (err)
        goto out_end_trans;

    ret = btrfs_del_root(trans, tree_root, &root->root_key);
    if (ret) {
        btrfs_abort_transaction(trans, tree_root, ret);
        goto out_end_trans;
    }

    if (root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID) {
        ret = btrfs_find_last_root(tree_root, root->root_key.objectid,
                       NULL, NULL);
        if (ret < 0) {
            btrfs_abort_transaction(trans, tree_root, ret);
            err = ret;
            goto out_end_trans;
        } else if (ret > 0) {
            /* if we fail to delete the orphan item this time
             * around, it'll get picked up the next time.
             *
             * The most common failure here is just -ENOENT.
             */
            btrfs_del_orphan_item(trans, tree_root,
                          root->root_key.objectid);
        }
    }

    if (root->in_radix) {
        btrfs_free_fs_root(tree_root->fs_info, root);
    } else {
        free_extent_buffer(root->node);
        free_extent_buffer(root->commit_root);
        kfree(root);
    }
out_end_trans:
    btrfs_end_transaction_throttle(trans, tree_root);
out_free:
    kfree(wc);
    btrfs_free_path(path);
out:
    if (err)
        btrfs_std_error(root->fs_info, err);
    return err;
}

/*
 * drop subtree rooted at tree block 'node'.
 *
 * NOTE: this function will unlock and release tree block 'node'
 * only used by relocation code
 */
int btrfs_drop_subtree(struct btrfs_trans_handle *trans,
            struct btrfs_root *root,
            struct extent_buffer *node,
            struct extent_buffer *parent)
{
    struct btrfs_path *path;
    struct walk_control *wc;
    int level;
    int parent_level;
    int ret = 0;
    int wret;

    BUG_ON(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID);

    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;

    wc = kzalloc(sizeof(*wc), GFP_NOFS);
    if (!wc) {
        btrfs_free_path(path);
        return -ENOMEM;
    }

    btrfs_assert_tree_locked(parent);
    parent_level = btrfs_header_level(parent);
    extent_buffer_get(parent);
    path->nodes[parent_level] = parent;
    path->slots[parent_level] = btrfs_header_nritems(parent);

    btrfs_assert_tree_locked(node);
    level = btrfs_header_level(node);
    path->nodes[level] = node;
    path->slots[level] = 0;
    path->locks[level] = BTRFS_WRITE_LOCK_BLOCKING;

    wc->refs[parent_level] = 1;
    wc->flags[parent_level] = BTRFS_BLOCK_FLAG_FULL_BACKREF;
    wc->level = level;
    wc->shared_level = -1;
    wc->stage = DROP_REFERENCE;
    wc->update_ref = 0;
    wc->keep_locks = 1;
    wc->for_reloc = 1;
    wc->reada_count = BTRFS_NODEPTRS_PER_BLOCK(root);

    while (1) {
        wret = walk_down_tree(trans, root, path, wc);
        if (wret < 0) {
            ret = wret;
            break;
        }

        wret = walk_up_tree(trans, root, path, wc, parent_level);
        if (wret < 0)
            ret = wret;
        if (wret != 0)
            break;
    }

    kfree(wc);
    btrfs_free_path(path);
    return ret;
}

static u64 update_block_group_flags(struct btrfs_root *root, u64 flags)
{
    u64 num_devices;
    u64 stripped;

    /*
     * if restripe for this chunk_type is on pick target profile and
     * return, otherwise do the usual balance
     */
    stripped = get_restripe_target(root->fs_info, flags);
    if (stripped)
        return extended_to_chunk(stripped);

    /*
     * we add in the count of missing devices because we want
     * to make sure that any RAID levels on a degraded FS
     * continue to be honored.
     */
    num_devices = root->fs_info->fs_devices->rw_devices +
        root->fs_info->fs_devices->missing_devices;

    stripped = BTRFS_BLOCK_GROUP_RAID0 |
        BTRFS_BLOCK_GROUP_RAID1 | BTRFS_BLOCK_GROUP_RAID10;

    if (num_devices == 1) {
        stripped |= BTRFS_BLOCK_GROUP_DUP;
        stripped = flags & ~stripped;

        /* turn raid0 into single device chunks */
        if (flags & BTRFS_BLOCK_GROUP_RAID0)
            return stripped;

        /* turn mirroring into duplication */
        if (flags & (BTRFS_BLOCK_GROUP_RAID1 |
                 BTRFS_BLOCK_GROUP_RAID10))
            return stripped | BTRFS_BLOCK_GROUP_DUP;
    } else {
        /* they already had raid on here, just return */
        if (flags & stripped)
            return flags;

        stripped |= BTRFS_BLOCK_GROUP_DUP;
        stripped = flags & ~stripped;

        /* switch duplicated blocks with raid1 */
        if (flags & BTRFS_BLOCK_GROUP_DUP)
            return stripped | BTRFS_BLOCK_GROUP_RAID1;

        /* this is drive concat, leave it alone */
    }

    return flags;
}

static int set_block_group_ro(struct btrfs_block_group_cache *cache, int force)
{
    struct btrfs_space_info *sinfo = cache->space_info;
    u64 num_bytes;
    u64 min_allocable_bytes;
    int ret = -ENOSPC;


    /*
     * We need some metadata space and system metadata space for
     * allocating chunks in some corner cases until we force to set
     * it to be readonly.
     */
    if ((sinfo->flags &
         (BTRFS_BLOCK_GROUP_SYSTEM | BTRFS_BLOCK_GROUP_METADATA)) &&
        !force)
        min_allocable_bytes = 1 * 1024 * 1024;
    else
        min_allocable_bytes = 0;

    spin_lock(&sinfo->lock);
    spin_lock(&cache->lock);

    if (cache->ro) {
        ret = 0;
        goto out;
    }

    num_bytes = cache->key.offset - cache->reserved - cache->pinned -
            cache->bytes_super - btrfs_block_group_used(&cache->item);

    if (sinfo->bytes_used + sinfo->bytes_reserved + sinfo->bytes_pinned +
        sinfo->bytes_may_use + sinfo->bytes_readonly + num_bytes +
        min_allocable_bytes <= sinfo->total_bytes) {
        sinfo->bytes_readonly += num_bytes;
        cache->ro = 1;
        ret = 0;
    }
out:
    spin_unlock(&cache->lock);
    spin_unlock(&sinfo->lock);
    return ret;
}

int btrfs_set_block_group_ro(struct btrfs_root *root,
                 struct btrfs_block_group_cache *cache)

{
    struct btrfs_trans_handle *trans;
    u64 alloc_flags;
    int ret;

    BUG_ON(cache->ro);

    trans = btrfs_join_transaction(root);
    if (IS_ERR(trans))
        return PTR_ERR(trans);

    alloc_flags = update_block_group_flags(root, cache->flags);
    if (alloc_flags != cache->flags) {
        ret = do_chunk_alloc(trans, root, alloc_flags,
                     CHUNK_ALLOC_FORCE);
        if (ret < 0)
            goto out;
    }

    ret = set_block_group_ro(cache, 0);
    if (!ret)
        goto out;
    alloc_flags = get_alloc_profile(root, cache->space_info->flags);
    ret = do_chunk_alloc(trans, root, alloc_flags,
                 CHUNK_ALLOC_FORCE);
    if (ret < 0)
        goto out;
    ret = set_block_group_ro(cache, 0);
out:
    btrfs_end_transaction(trans, root);
    return ret;
}

int btrfs_force_chunk_alloc(struct btrfs_trans_handle *trans,
                struct btrfs_root *root, u64 type)
{
    u64 alloc_flags = get_alloc_profile(root, type);
    return do_chunk_alloc(trans, root, alloc_flags,
                  CHUNK_ALLOC_FORCE);
}

/*
 * helper to account the unused space of all the readonly block group in the
 * list. takes mirrors into account.
 */
static u64 __btrfs_get_ro_block_group_free_space(struct list_head *groups_list)
{
    struct btrfs_block_group_cache *block_group;
    u64 free_bytes = 0;
    int factor;

    list_for_each_entry(block_group, groups_list, list) {
        spin_lock(&block_group->lock);

        if (!block_group->ro) {
            spin_unlock(&block_group->lock);
            continue;
        }

        if (block_group->flags & (BTRFS_BLOCK_GROUP_RAID1 |
                      BTRFS_BLOCK_GROUP_RAID10 |
                      BTRFS_BLOCK_GROUP_DUP))
            factor = 2;
        else
            factor = 1;

        free_bytes += (block_group->key.offset -
                   btrfs_block_group_used(&block_group->item)) *
                   factor;

        spin_unlock(&block_group->lock);
    }

    return free_bytes;
}

/*
 * helper to account the unused space of all the readonly block group in the
 * space_info. takes mirrors into account.
 */
u64 btrfs_account_ro_block_groups_free_space(struct btrfs_space_info *sinfo)
{
    int i;
    u64 free_bytes = 0;

    spin_lock(&sinfo->lock);

    for(i = 0; i < BTRFS_NR_RAID_TYPES; i++)
        if (!list_empty(&sinfo->block_groups[i]))
            free_bytes += __btrfs_get_ro_block_group_free_space(
                        &sinfo->block_groups[i]);

    spin_unlock(&sinfo->lock);

    return free_bytes;
}

void btrfs_set_block_group_rw(struct btrfs_root *root,
                  struct btrfs_block_group_cache *cache)
{
    struct btrfs_space_info *sinfo = cache->space_info;
    u64 num_bytes;

    BUG_ON(!cache->ro);

    spin_lock(&sinfo->lock);
    spin_lock(&cache->lock);
    num_bytes = cache->key.offset - cache->reserved - cache->pinned -
            cache->bytes_super - btrfs_block_group_used(&cache->item);
    sinfo->bytes_readonly -= num_bytes;
    cache->ro = 0;
    spin_unlock(&cache->lock);
    spin_unlock(&sinfo->lock);
}

/*
 * checks to see if its even possible to relocate this block group.
 *
 * @return - -1 if it's not a good idea to relocate this block group, 0 if its
 * ok to go ahead and try.
 */
int btrfs_can_relocate(struct btrfs_root *root, u64 bytenr)
{
    struct btrfs_block_group_cache *block_group;
    struct btrfs_space_info *space_info;
    struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
    struct btrfs_device *device;
    u64 min_free;
    u64 dev_min = 1;
    u64 dev_nr = 0;
    u64 target;
    int index;
    int full = 0;
    int ret = 0;

    block_group = btrfs_lookup_block_group(root->fs_info, bytenr);

    /* odd, couldn't find the block group, leave it alone */
    if (!block_group)
        return -1;

    min_free = btrfs_block_group_used(&block_group->item);

    /* no bytes used, we're good */
    if (!min_free)
        goto out;

    space_info = block_group->space_info;
    spin_lock(&space_info->lock);

    full = space_info->full;

    /*
     * if this is the last block group we have in this space, we can't
     * relocate it unless we're able to allocate a new chunk below.
     *
     * Otherwise, we need to make sure we have room in the space to handle
     * all of the extents from this block group.  If we can, we're good
     */
    if ((space_info->total_bytes != block_group->key.offset) &&
        (space_info->bytes_used + space_info->bytes_reserved +
         space_info->bytes_pinned + space_info->bytes_readonly +
         min_free < space_info->total_bytes)) {
        spin_unlock(&space_info->lock);
        goto out;
    }
    spin_unlock(&space_info->lock);

    /*
     * ok we don't have enough space, but maybe we have free space on our
     * devices to allocate new chunks for relocation, so loop through our
     * alloc devices and guess if we have enough space.  if this block
     * group is going to be restriped, run checks against the target
     * profile instead of the current one.
     */
    ret = -1;

    /*
     * index:
     *      0: raid10
     *      1: raid1
     *      2: dup
     *      3: raid0
     *      4: single
     */
    target = get_restripe_target(root->fs_info, block_group->flags);
    if (target) {
        index = __get_block_group_index(extended_to_chunk(target));
    } else {
        /*
         * this is just a balance, so if we were marked as full
         * we know there is no space for a new chunk
         */
        if (full)
            goto out;

        index = get_block_group_index(block_group);
    }

    if (index == 0) {
        dev_min = 4;
        /* Divide by 2 */
        min_free >>= 1;
    } else if (index == 1) {
        dev_min = 2;
    } else if (index == 2) {
        /* Multiply by 2 */
        min_free <<= 1;
    } else if (index == 3) {
        dev_min = fs_devices->rw_devices;
        do_div(min_free, dev_min);
    }

    mutex_lock(&root->fs_info->chunk_mutex);
    list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
        u64 dev_offset;

        /*
         * check to make sure we can actually find a chunk with enough
         * space to fit our block group in.
         */
        if (device->total_bytes > device->bytes_used + min_free) {
            ret = find_free_dev_extent(device, min_free,
                           &dev_offset, NULL);
            if (!ret)
                dev_nr++;

            if (dev_nr >= dev_min)
                break;

            ret = -1;
        }
    }
    mutex_unlock(&root->fs_info->chunk_mutex);
out:
    btrfs_put_block_group(block_group);
    return ret;
}

static int find_first_block_group(struct btrfs_root *root,
        struct btrfs_path *path, struct btrfs_key *key)
{
    int ret = 0;
    struct btrfs_key found_key;
    struct extent_buffer *leaf;
    int slot;

    ret = btrfs_search_slot(NULL, root, key, path, 0, 0);
    if (ret < 0)
        goto out;

    while (1) {
        slot = path->slots[0];
        leaf = path->nodes[0];
        if (slot >= btrfs_header_nritems(leaf)) {
            ret = btrfs_next_leaf(root, path);
            if (ret == 0)
                continue;
            if (ret < 0)
                goto out;
            break;
        }
        btrfs_item_key_to_cpu(leaf, &found_key, slot);

        if (found_key.objectid >= key->objectid &&
            found_key.type == BTRFS_BLOCK_GROUP_ITEM_KEY) {
            ret = 0;
            goto out;
        }
        path->slots[0]++;
    }
out:
    return ret;
}

void btrfs_put_block_group_cache(struct btrfs_fs_info *info)
{
    struct btrfs_block_group_cache *block_group;
    u64 last = 0;

    while (1) {
        struct inode *inode;

        block_group = btrfs_lookup_first_block_group(info, last);
        while (block_group) {
            spin_lock(&block_group->lock);
            if (block_group->iref)
                break;
            spin_unlock(&block_group->lock);
            block_group = next_block_group(info->tree_root,
                               block_group);
        }
        if (!block_group) {
            if (last == 0)
                break;
            last = 0;
            continue;
        }

        inode = block_group->inode;
        block_group->iref = 0;
        block_group->inode = NULL;
        spin_unlock(&block_group->lock);
        iput(inode);
        last = block_group->key.objectid + block_group->key.offset;
        btrfs_put_block_group(block_group);
    }
}

int btrfs_free_block_groups(struct btrfs_fs_info *info)
{
    struct btrfs_block_group_cache *block_group;
    struct btrfs_space_info *space_info;
    struct btrfs_caching_control *caching_ctl;
    struct rb_node *n;

    down_write(&info->extent_commit_sem);
    while (!list_empty(&info->caching_block_groups)) {
        caching_ctl = list_entry(info->caching_block_groups.next,
                     struct btrfs_caching_control, list);
        list_del(&caching_ctl->list);
        put_caching_control(caching_ctl);
    }
    up_write(&info->extent_commit_sem);

    spin_lock(&info->block_group_cache_lock);
    while ((n = rb_last(&info->block_group_cache_tree)) != NULL) {
        block_group = rb_entry(n, struct btrfs_block_group_cache,
                       cache_node);
        rb_erase(&block_group->cache_node,
             &info->block_group_cache_tree);
        spin_unlock(&info->block_group_cache_lock);

        down_write(&block_group->space_info->groups_sem);
        list_del(&block_group->list);
        up_write(&block_group->space_info->groups_sem);

        if (block_group->cached == BTRFS_CACHE_STARTED)
            wait_block_group_cache_done(block_group);

        /*
         * We haven't cached this block group, which means we could
         * possibly have excluded extents on this block group.
         */
        if (block_group->cached == BTRFS_CACHE_NO)
            free_excluded_extents(info->extent_root, block_group);

        btrfs_remove_free_space_cache(block_group);
        btrfs_put_block_group(block_group);

        spin_lock(&info->block_group_cache_lock);
    }
    spin_unlock(&info->block_group_cache_lock);

    /* now that all the block groups are freed, go through and
     * free all the space_info structs.  This is only called during
     * the final stages of unmount, and so we know nobody is
     * using them.  We call synchronize_rcu() once before we start,
     * just to be on the safe side.
     */
    synchronize_rcu();

    release_global_block_rsv(info);

    while(!list_empty(&info->space_info)) {
        space_info = list_entry(info->space_info.next,
                    struct btrfs_space_info,
                    list);
        if (space_info->bytes_pinned > 0 ||
            space_info->bytes_reserved > 0 ||
            space_info->bytes_may_use > 0) {
            WARN_ON(1);
            dump_space_info(space_info, 0, 0);
        }
        list_del(&space_info->list);
        kfree(space_info);
    }
    return 0;
}

static void __link_block_group(struct btrfs_space_info *space_info,
                   struct btrfs_block_group_cache *cache)
{
    int index = get_block_group_index(cache);

    down_write(&space_info->groups_sem);
    list_add_tail(&cache->list, &space_info->block_groups[index]);
    up_write(&space_info->groups_sem);
}

int btrfs_read_block_groups(struct btrfs_root *root)
{
    struct btrfs_path *path;
    int ret;
    struct btrfs_block_group_cache *cache;
    struct btrfs_fs_info *info = root->fs_info;
    struct btrfs_space_info *space_info;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct extent_buffer *leaf;
    int need_clear = 0;
    u64 cache_gen;

    root = info->extent_root;
    key.objectid = 0;
    key.offset = 0;
    btrfs_set_key_type(&key, BTRFS_BLOCK_GROUP_ITEM_KEY);
    path = btrfs_alloc_path();
    if (!path)
        return -ENOMEM;
    path->reada = 1;

    cache_gen = btrfs_super_cache_generation(root->fs_info->super_copy);
    if (btrfs_test_opt(root, SPACE_CACHE) &&
        btrfs_super_generation(root->fs_info->super_copy) != cache_gen)
        need_clear = 1;
    if (btrfs_test_opt(root, CLEAR_CACHE))
        need_clear = 1;

    while (1) {
        ret = find_first_block_group(root, path, &key);
        if (ret > 0)
            break;
        if (ret != 0)
            goto error;
        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
        cache = kzalloc(sizeof(*cache), GFP_NOFS);
        if (!cache) {
            ret = -ENOMEM;
            goto error;
        }
        cache->free_space_ctl = kzalloc(sizeof(*cache->free_space_ctl),
                        GFP_NOFS);
        if (!cache->free_space_ctl) {
            kfree(cache);
            ret = -ENOMEM;
            goto error;
        }

        atomic_set(&cache->count, 1);
        spin_lock_init(&cache->lock);
        cache->fs_info = info;
        INIT_LIST_HEAD(&cache->list);
        INIT_LIST_HEAD(&cache->cluster_list);

        if (need_clear) {
            /*
             * When we mount with old space cache, we need to
             * set BTRFS_DC_CLEAR and set dirty flag.
             *
             * a) Setting 'BTRFS_DC_CLEAR' makes sure that we
             *    truncate the old free space cache inode and
             *    setup a new one.
             * b) Setting 'dirty flag' makes sure that we flush
             *    the new space cache info onto disk.
             */
            cache->disk_cache_state = BTRFS_DC_CLEAR;
            if (btrfs_test_opt(root, SPACE_CACHE))
                cache->dirty = 1;
        }

        read_extent_buffer(leaf, &cache->item,
                   btrfs_item_ptr_offset(leaf, path->slots[0]),
                   sizeof(cache->item));
        memcpy(&cache->key, &found_key, sizeof(found_key));

        key.objectid = found_key.objectid + found_key.offset;
        btrfs_release_path(path);
        cache->flags = btrfs_block_group_flags(&cache->item);
        cache->sectorsize = root->sectorsize;

        btrfs_init_free_space_ctl(cache);

        /*
         * We need to exclude the super stripes now so that the space
         * info has super bytes accounted for, otherwise we'll think
         * we have more space than we actually do.
         */
        exclude_super_stripes(root, cache);

        /*
         * check for two cases, either we are full, and therefore
         * don't need to bother with the caching work since we won't
         * find any space, or we are empty, and we can just add all
         * the space in and be done with it.  This saves us _alot_ of
         * time, particularly in the full case.
         */
        if (found_key.offset == btrfs_block_group_used(&cache->item)) {
            cache->last_byte_to_unpin = (u64)-1;
            cache->cached = BTRFS_CACHE_FINISHED;
            free_excluded_extents(root, cache);
        } else if (btrfs_block_group_used(&cache->item) == 0) {
            cache->last_byte_to_unpin = (u64)-1;
            cache->cached = BTRFS_CACHE_FINISHED;
            add_new_free_space(cache, root->fs_info,
                       found_key.objectid,
                       found_key.objectid +
                       found_key.offset);
            free_excluded_extents(root, cache);
        }

        ret = update_space_info(info, cache->flags, found_key.offset,
                    btrfs_block_group_used(&cache->item),
                    &space_info);
        BUG_ON(ret); /* -ENOMEM */
        cache->space_info = space_info;
        spin_lock(&cache->space_info->lock);
        cache->space_info->bytes_readonly += cache->bytes_super;
        spin_unlock(&cache->space_info->lock);

        __link_block_group(space_info, cache);

        ret = btrfs_add_block_group_cache(root->fs_info, cache);
        BUG_ON(ret); /* Logic error */

        set_avail_alloc_bits(root->fs_info, cache->flags);
        if (btrfs_chunk_readonly(root, cache->key.objectid))
            set_block_group_ro(cache, 1);
    }

    list_for_each_entry_rcu(space_info, &root->fs_info->space_info, list) {
        if (!(get_alloc_profile(root, space_info->flags) &
              (BTRFS_BLOCK_GROUP_RAID10 |
               BTRFS_BLOCK_GROUP_RAID1 |
               BTRFS_BLOCK_GROUP_DUP)))
            continue;
        /*
         * avoid allocating from un-mirrored block group if there are
         * mirrored block groups.
         */
        list_for_each_entry(cache, &space_info->block_groups[3], list)
            set_block_group_ro(cache, 1);
        list_for_each_entry(cache, &space_info->block_groups[4], list)
            set_block_group_ro(cache, 1);
    }

    init_global_block_rsv(info);
    ret = 0;
error:
    btrfs_free_path(path);
    return ret;
}

void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root)
{
    struct btrfs_block_group_cache *block_group, *tmp;
    struct btrfs_root *extent_root = root->fs_info->extent_root;
    struct btrfs_block_group_item item;
    struct btrfs_key key;
    int ret = 0;

    list_for_each_entry_safe(block_group, tmp, &trans->new_bgs,
                 new_bg_list) {
        list_del_init(&block_group->new_bg_list);

        if (ret)
            continue;

        spin_lock(&block_group->lock);
        memcpy(&item, &block_group->item, sizeof(item));
        memcpy(&key, &block_group->key, sizeof(key));
        spin_unlock(&block_group->lock);

        ret = btrfs_insert_item(trans, extent_root, &key, &item,
                    sizeof(item));
        if (ret)
            btrfs_abort_transaction(trans, extent_root, ret);
    }
}

int btrfs_make_block_group(struct btrfs_trans_handle *trans,
               struct btrfs_root *root, u64 bytes_used,
               u64 type, u64 chunk_objectid, u64 chunk_offset,
               u64 size)
{
    int ret;
    struct btrfs_root *extent_root;
    struct btrfs_block_group_cache *cache;

    extent_root = root->fs_info->extent_root;

    root->fs_info->last_trans_log_full_commit = trans->transid;

    cache = kzalloc(sizeof(*cache), GFP_NOFS);
    if (!cache)
        return -ENOMEM;
    cache->free_space_ctl = kzalloc(sizeof(*cache->free_space_ctl),
                    GFP_NOFS);
    if (!cache->free_space_ctl) {
        kfree(cache);
        return -ENOMEM;
    }

    cache->key.objectid = chunk_offset;
    cache->key.offset = size;
    cache->key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
    cache->sectorsize = root->sectorsize;
    cache->fs_info = root->fs_info;

    atomic_set(&cache->count, 1);
    spin_lock_init(&cache->lock);
    INIT_LIST_HEAD(&cache->list);
    INIT_LIST_HEAD(&cache->cluster_list);
    INIT_LIST_HEAD(&cache->new_bg_list);

    btrfs_init_free_space_ctl(cache);

    btrfs_set_block_group_used(&cache->item, bytes_used);
    btrfs_set_block_group_chunk_objectid(&cache->item, chunk_objectid);
    cache->flags = type;
    btrfs_set_block_group_flags(&cache->item, type);

    cache->last_byte_to_unpin = (u64)-1;
    cache->cached = BTRFS_CACHE_FINISHED;
    exclude_super_stripes(root, cache);

    add_new_free_space(cache, root->fs_info, chunk_offset,
               chunk_offset + size);

    free_excluded_extents(root, cache);

    ret = update_space_info(root->fs_info, cache->flags, size, bytes_used,
                &cache->space_info);
    BUG_ON(ret); /* -ENOMEM */
    update_global_block_rsv(root->fs_info);

    spin_lock(&cache->space_info->lock);
    cache->space_info->bytes_readonly += cache->bytes_super;
    spin_unlock(&cache->space_info->lock);

    __link_block_group(cache->space_info, cache);

    ret = btrfs_add_block_group_cache(root->fs_info, cache);
    BUG_ON(ret); /* Logic error */

    list_add_tail(&cache->new_bg_list, &trans->new_bgs);

    set_avail_alloc_bits(extent_root->fs_info, type);

    return 0;
}

static void clear_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
{
    u64 extra_flags = chunk_to_extended(flags) &
                BTRFS_EXTENDED_PROFILE_MASK;

    if (flags & BTRFS_BLOCK_GROUP_DATA)
        fs_info->avail_data_alloc_bits &= ~extra_flags;
    if (flags & BTRFS_BLOCK_GROUP_METADATA)
        fs_info->avail_metadata_alloc_bits &= ~extra_flags;
    if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
        fs_info->avail_system_alloc_bits &= ~extra_flags;
}

int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
                 struct btrfs_root *root, u64 group_start)
{
    struct btrfs_path *path;
    struct btrfs_block_group_cache *block_group;
    struct btrfs_free_cluster *cluster;
    struct btrfs_root *tree_root = root->fs_info->tree_root;
    struct btrfs_key key;
    struct inode *inode;
    int ret;
    int index;
    int factor;

    root = root->fs_info->extent_root;

    block_group = btrfs_lookup_block_group(root->fs_info, group_start);
    BUG_ON(!block_group);
    BUG_ON(!block_group->ro);

    /*
     * Free the reserved super bytes from this block group before
     * remove it.
     */
    free_excluded_extents(root, block_group);

    memcpy(&key, &block_group->key, sizeof(key));
    index = get_block_group_index(block_group);
    if (block_group->flags & (BTRFS_BLOCK_GROUP_DUP |
                  BTRFS_BLOCK_GROUP_RAID1 |
                  BTRFS_BLOCK_GROUP_RAID10))
        factor = 2;
    else
        factor = 1;

    /* make sure this block group isn't part of an allocation cluster */
    cluster = &root->fs_info->data_alloc_cluster;
    spin_lock(&cluster->refill_lock);
    btrfs_return_cluster_to_free_space(block_group, cluster);
    spin_unlock(&cluster->refill_lock);

    /*
     * make sure this block group isn't part of a metadata
     * allocation cluster
     */
    cluster = &root->fs_info->meta_alloc_cluster;
    spin_lock(&cluster->refill_lock);
    btrfs_return_cluster_to_free_space(block_group, cluster);
    spin_unlock(&cluster->refill_lock);

    path = btrfs_alloc_path();
    if (!path) {
        ret = -ENOMEM;
        goto out;
    }

    inode = lookup_free_space_inode(tree_root, block_group, path);
    if (!IS_ERR(inode)) {
        ret = btrfs_orphan_add(trans, inode);
        if (ret) {
            btrfs_add_delayed_iput(inode);
            goto out;
        }
        clear_nlink(inode);
        /* One for the block groups ref */
        spin_lock(&block_group->lock);
        if (block_group->iref) {
            block_group->iref = 0;
            block_group->inode = NULL;
            spin_unlock(&block_group->lock);
            iput(inode);
        } else {
            spin_unlock(&block_group->lock);
        }
        /* One for our lookup ref */
        btrfs_add_delayed_iput(inode);
    }

    key.objectid = BTRFS_FREE_SPACE_OBJECTID;
    key.offset = block_group->key.objectid;
    key.type = 0;

    ret = btrfs_search_slot(trans, tree_root, &key, path, -1, 1);
    if (ret < 0)
        goto out;
    if (ret > 0)
        btrfs_release_path(path);
    if (ret == 0) {
        ret = btrfs_del_item(trans, tree_root, path);
        if (ret)
            goto out;
        btrfs_release_path(path);
    }

    spin_lock(&root->fs_info->block_group_cache_lock);
    rb_erase(&block_group->cache_node,
         &root->fs_info->block_group_cache_tree);
    spin_unlock(&root->fs_info->block_group_cache_lock);

    down_write(&block_group->space_info->groups_sem);
    /*
     * we must use list_del_init so people can check to see if they
     * are still on the list after taking the semaphore
     */
    list_del_init(&block_group->list);
    if (list_empty(&block_group->space_info->block_groups[index]))
        clear_avail_alloc_bits(root->fs_info, block_group->flags);
    up_write(&block_group->space_info->groups_sem);

    if (block_group->cached == BTRFS_CACHE_STARTED)
        wait_block_group_cache_done(block_group);

    btrfs_remove_free_space_cache(block_group);

    spin_lock(&block_group->space_info->lock);
    block_group->space_info->total_bytes -= block_group->key.offset;
    block_group->space_info->bytes_readonly -= block_group->key.offset;
    block_group->space_info->disk_total -= block_group->key.offset * factor;
    spin_unlock(&block_group->space_info->lock);

    memcpy(&key, &block_group->key, sizeof(key));

    btrfs_clear_space_info_full(root->fs_info);

    btrfs_put_block_group(block_group);
    btrfs_put_block_group(block_group);

    ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
    if (ret > 0)
        ret = -EIO;
    if (ret < 0)
        goto out;

    ret = btrfs_del_item(trans, root, path);
out:
    btrfs_free_path(path);
    return ret;
}

int btrfs_init_space_info(struct btrfs_fs_info *fs_info)
{
    struct btrfs_space_info *space_info;
    struct btrfs_super_block *disk_super;
    u64 features;
    u64 flags;
    int mixed = 0;
    int ret;

    disk_super = fs_info->super_copy;
    if (!btrfs_super_root(disk_super))
        return 1;

    features = btrfs_super_incompat_flags(disk_super);
    if (features & BTRFS_FEATURE_INCOMPAT_MIXED_GROUPS)
        mixed = 1;

    flags = BTRFS_BLOCK_GROUP_SYSTEM;
    ret = update_space_info(fs_info, flags, 0, 0, &space_info);
    if (ret)
        goto out;

    if (mixed) {
        flags = BTRFS_BLOCK_GROUP_METADATA | BTRFS_BLOCK_GROUP_DATA;
        ret = update_space_info(fs_info, flags, 0, 0, &space_info);
    } else {
        flags = BTRFS_BLOCK_GROUP_METADATA;
        ret = update_space_info(fs_info, flags, 0, 0, &space_info);
        if (ret)
            goto out;

        flags = BTRFS_BLOCK_GROUP_DATA;
        ret = update_space_info(fs_info, flags, 0, 0, &space_info);
    }
out:
    return ret;
}

int btrfs_error_unpin_extent_range(struct btrfs_root *root, u64 start, u64 end)
{
    return unpin_extent_range(root, start, end);
}

int btrfs_error_discard_extent(struct btrfs_root *root, u64 bytenr,
                   u64 num_bytes, u64 *actual_bytes)
{
    return btrfs_discard_extent(root, bytenr, num_bytes, actual_bytes);
}

int btrfs_trim_fs(struct btrfs_root *root, struct fstrim_range *range)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct btrfs_block_group_cache *cache = NULL;
    u64 group_trimmed;
    u64 start;
    u64 end;
    u64 trimmed = 0;
    u64 total_bytes = btrfs_super_total_bytes(fs_info->super_copy);
    int ret = 0;

    /*
     * try to trim all FS space, our block group may start from non-zero.
     */
    if (range->len == total_bytes)
        cache = btrfs_lookup_first_block_group(fs_info, range->start);
    else
        cache = btrfs_lookup_block_group(fs_info, range->start);

    while (cache) {
        if (cache->key.objectid >= (range->start + range->len)) {
            btrfs_put_block_group(cache);
            break;
        }

        start = max(range->start, cache->key.objectid);
        end = min(range->start + range->len,
                cache->key.objectid + cache->key.offset);

        if (end - start >= range->minlen) {
            if (!block_group_cache_done(cache)) {
                ret = cache_block_group(cache, NULL, root, 0);
                if (!ret)
                    wait_block_group_cache_done(cache);
            }
            ret = btrfs_trim_block_group(cache,
                             &group_trimmed,
                             start,
                             end,
                             range->minlen);

            trimmed += group_trimmed;
            if (ret) {
                btrfs_put_block_group(cache);
                break;
            }
        }

        cache = next_block_group(fs_info->tree_root, cache);
    }

    range->len = trimmed;
    return ret;
}