/*
 * 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 <linux/percpu_counter.h>
#include "hash.h"
#include "tree-log.h"
#include "disk-io.h"
#include "print-tree.h"
#include "volumes.h"
#include "raid56.h"
#include "locking.h"
#include "free-space-cache.h"
#include "free-space-tree.h"
#include "math.h"
#include "sysfs.h"
#include "qgroup.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,
                                struct btrfs_delayed_ref_node *node, 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,
                                       int delalloc);
static int block_rsv_use_bytes(struct btrfs_block_rsv *block_rsv,
                               u64 num_bytes);
int btrfs_pin_extent(struct btrfs_root *root,
                     u64 bytenr, u64 num_bytes, int reserved);

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

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

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);

        if (info->first_logical_byte > block_group->key.objectid)
                info->first_logical_byte = block_group->key.objectid;

        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);
                if (bytenr == 0 && info->first_logical_byte > ret->key.objectid)
                        info->first_logical_byte = ret->key.objectid;
        }
        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);
        set_extent_bits(&root->fs_info->freed_extents[1],
                        start, end, EXTENT_UPTODATE);
        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);
        clear_extent_bits(&root->fs_info->freed_extents[1],
                          start, end, EXTENT_UPTODATE);
}

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);
                if (ret)
                        return ret;
        }

        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);
                if (ret)
                        return ret;

                while (nr--) {
                        u64 start, len;

                        if (logical[nr] > cache->key.objectid +
                            cache->key.offset)
                                continue;

                        if (logical[nr] + stripe_len <= cache->key.objectid)
                                continue;

                        start = logical[nr];
                        if (start < cache->key.objectid) {
                                start = cache->key.objectid;
                                len = (logical[nr] + stripe_len) - start;
                        } else {
                                len = min_t(u64, stripe_len,
                                            cache->key.objectid +
                                            cache->key.offset - start);
                        }

                        cache->bytes_super += len;
                        ret = add_excluded_extent(root, start, len);
                        if (ret) {
                                kfree(logical);
                                return ret;
                        }
                }

                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->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);
}

#ifdef CONFIG_BTRFS_DEBUG
static void fragment_free_space(struct btrfs_root *root,
                                struct btrfs_block_group_cache *block_group)
{
        u64 start = block_group->key.objectid;
        u64 len = block_group->key.offset;
        u64 chunk = block_group->flags & BTRFS_BLOCK_GROUP_METADATA ?
                root->nodesize : root->sectorsize;
        u64 step = chunk << 1;

        while (len > chunk) {
                btrfs_remove_free_space(block_group, start, chunk);
                start += step;
                if (len < step)
                        len = 0;
                else
                        len -= step;
        }
}
#endif

/*
 * 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.
 */
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 int load_extent_tree_free(struct btrfs_caching_control *caching_ctl)
{
        struct btrfs_block_group_cache *block_group;
        struct btrfs_fs_info *fs_info;
        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;
        bool wakeup = true;

        block_group = caching_ctl->block_group;
        fs_info = block_group->fs_info;
        extent_root = fs_info->extent_root;

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

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

#ifdef CONFIG_BTRFS_DEBUG
        /*
         * If we're fragmenting we don't want to make anybody think we can
         * allocate from this block group until we've had a chance to fragment
         * the free space.
         */
        if (btrfs_should_fragment_free_space(extent_root, block_group))
                wakeup = false;
#endif
        /*
         * 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 = READA_FORWARD;

        key.objectid = last;
        key.offset = 0;
        key.type = BTRFS_EXTENT_ITEM_KEY;

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

        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() ||
                            rwsem_is_contended(&fs_info->commit_root_sem)) {
                                if (wakeup)
                                        caching_ctl->progress = last;
                                btrfs_release_path(path);
                                up_read(&fs_info->commit_root_sem);
                                mutex_unlock(&caching_ctl->mutex);
                                cond_resched();
                                mutex_lock(&caching_ctl->mutex);
                                down_read(&fs_info->commit_root_sem);
                                goto next;
                        }

                        ret = btrfs_next_leaf(extent_root, path);
                        if (ret < 0)
                                goto out;
                        if (ret)
                                break;
                        leaf = path->nodes[0];
                        nritems = btrfs_header_nritems(leaf);
                        continue;
                }

                if (key.objectid < last) {
                        key.objectid = last;
                        key.offset = 0;
                        key.type = BTRFS_EXTENT_ITEM_KEY;

                        if (wakeup)
                                caching_ctl->progress = last;
                        btrfs_release_path(path);
                        goto next;
                }

                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 ||
                    key.type == BTRFS_METADATA_ITEM_KEY) {
                        total_found += add_new_free_space(block_group,
                                                          fs_info, last,
                                                          key.objectid);
                        if (key.type == BTRFS_METADATA_ITEM_KEY)
                                last = key.objectid +
                                        fs_info->tree_root->nodesize;
                        else
                                last = key.objectid + key.offset;

                        if (total_found > CACHING_CTL_WAKE_UP) {
                                total_found = 0;
                                if (wakeup)
                                        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;

out:
        btrfs_free_path(path);
        return ret;
}

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;
        int ret;

        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;

        mutex_lock(&caching_ctl->mutex);
        down_read(&fs_info->commit_root_sem);

        if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE))
                ret = load_free_space_tree(caching_ctl);
        else
                ret = load_extent_tree_free(caching_ctl);

        spin_lock(&block_group->lock);
        block_group->caching_ctl = NULL;
        block_group->cached = ret ? BTRFS_CACHE_ERROR : BTRFS_CACHE_FINISHED;
        spin_unlock(&block_group->lock);

#ifdef CONFIG_BTRFS_DEBUG
        if (btrfs_should_fragment_free_space(extent_root, block_group)) {
                u64 bytes_used;

                spin_lock(&block_group->space_info->lock);
                spin_lock(&block_group->lock);
                bytes_used = block_group->key.offset -
                        btrfs_block_group_used(&block_group->item);
                block_group->space_info->bytes_used += bytes_used >> 1;
                spin_unlock(&block_group->lock);
                spin_unlock(&block_group->space_info->lock);
                fragment_free_space(extent_root, block_group);
        }
#endif

        caching_ctl->progress = (u64)-1;

        up_read(&fs_info->commit_root_sem);
        free_excluded_extents(fs_info->extent_root, block_group);
        mutex_unlock(&caching_ctl->mutex);

        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,
                             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);
        btrfs_init_work(&caching_ctl->work, btrfs_cache_helper,
                        caching_thread, NULL, NULL);

        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);

        if (fs_info->mount_opt & BTRFS_MOUNT_SPACE_CACHE) {
                mutex_lock(&caching_ctl->mutex);
                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;
                        caching_ctl->progress = (u64)-1;
                } else {
                        if (load_cache_only) {
                                cache->caching_ctl = NULL;
                                cache->cached = BTRFS_CACHE_NO;
                        } else {
                                cache->cached = BTRFS_CACHE_STARTED;
                                cache->has_caching_ctl = 1;
                        }
                }
                spin_unlock(&cache->lock);
#ifdef CONFIG_BTRFS_DEBUG
                if (ret == 1 &&
                    btrfs_should_fragment_free_space(fs_info->extent_root,
                                                     cache)) {
                        u64 bytes_used;

                        spin_lock(&cache->space_info->lock);
                        spin_lock(&cache->lock);
                        bytes_used = cache->key.offset -
                                btrfs_block_group_used(&cache->item);
                        cache->space_info->bytes_used += bytes_used >> 1;
                        spin_unlock(&cache->lock);
                        spin_unlock(&cache->space_info->lock);
                        fragment_free_space(fs_info->extent_root, cache);
                }
#endif
                mutex_unlock(&caching_ctl->mutex);

                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're either using the free space tree or no caching at all.
                 * 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;
                        cache->has_caching_ctl = 1;
                }
                spin_unlock(&cache->lock);
                wake_up(&caching_ctl->wait);
        }

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

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

        btrfs_get_block_group(cache);

        btrfs_queue_work(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();
}

/* simple helper to search for an existing data extent at a given offset */
int btrfs_lookup_data_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;
        key.type = 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 a tree block.
 *
 * 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 offset, int metadata, 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;

        /*
         * If we don't have skinny metadata, don't bother doing anything
         * different
         */
        if (metadata && !btrfs_fs_incompat(root->fs_info, SKINNY_METADATA)) {
                offset = root->nodesize;
                metadata = 0;
        }

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

        if (!trans) {
                path->skip_locking = 1;
                path->search_commit_root = 1;
        }

search_again:
        key.objectid = bytenr;
        key.offset = offset;
        if (metadata)
                key.type = BTRFS_METADATA_ITEM_KEY;
        else
                key.type = BTRFS_EXTENT_ITEM_KEY;

        ret = btrfs_search_slot(trans, root->fs_info->extent_root,
                                &key, path, 0, 0);
        if (ret < 0)
                goto out_free;

        if (ret > 0 && metadata && key.type == BTRFS_METADATA_ITEM_KEY) {
                if (path->slots[0]) {
                        path->slots[0]--;
                        btrfs_item_key_to_cpu(path->nodes[0], &key,
                                              path->slots[0]);
                        if (key.objectid == bytenr &&
                            key.type == BTRFS_EXTENT_ITEM_KEY &&
                            key.offset == root->nodesize)
                                ret = 0;
                }
        }

        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 search_again;
                }
                spin_lock(&head->lock);
                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;
                spin_unlock(&head->lock);
                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 COWed 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(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 = btrfs_crc32c(high_crc, &lenum, sizeof(lenum));
        lenum = cpu_to_le64(owner);
        low_crc = btrfs_crc32c(low_crc, &lenum, sizeof(lenum));
        lenum = cpu_to_le64(offset);
        low_crc = btrfs_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, int *last_ref)
{
        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);
                *last_ref = 1;
        } 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_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;
        bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
                                                 SKINNY_METADATA);

        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;

        /*
         * Owner is our parent level, so we can just add one to get the level
         * for the block we are interested in.
         */
        if (skinny_metadata && owner < BTRFS_FIRST_FREE_OBJECTID) {
                key.type = BTRFS_METADATA_ITEM_KEY;
                key.offset = owner;
        }

again:
        ret = btrfs_search_slot(trans, root, &key, path, extra_size, 1);
        if (ret < 0) {
                err = ret;
                goto out;
        }

        /*
         * We may be a newly converted file system which still has the old fat
         * extent entries for metadata, so try and see if we have one of those.
         */
        if (ret > 0 && skinny_metadata) {
                skinny_metadata = false;
                if (path->slots[0]) {
                        path->slots[0]--;
                        btrfs_item_key_to_cpu(path->nodes[0], &key,
                                              path->slots[0]);
                        if (key.objectid == bytenr &&
                            key.type == BTRFS_EXTENT_ITEM_KEY &&
                            key.offset == num_bytes)
                                ret = 0;
                }
                if (ret) {
                        key.objectid = bytenr;
                        key.type = BTRFS_EXTENT_ITEM_KEY;
                        key.offset = num_bytes;
                        btrfs_release_path(path);
                        goto again;
                }
        }

        if (ret && !insert) {
                err = -ENOENT;
                goto out;
        } else if (WARN_ON(ret)) {
                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)) {
                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 && !skinny_metadata) {
                ptr += sizeof(struct btrfs_tree_block_info);
                BUG_ON(ptr > end);
        }

        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_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(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_root *root,
                                  struct btrfs_path *path,
                                  struct btrfs_extent_inline_ref *iref,
                                  int refs_to_mod,
                                  struct btrfs_delayed_extent_op *extent_op,
                                  int *last_ref)
{
        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 {
                *last_ref = 1;
                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(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(root, path, iref,
                                             refs_to_add, extent_op, NULL);
        } else if (ret == -ENOENT) {
                setup_inline_extent_backref(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 *last_ref)
{
        int ret = 0;

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

#define in_range(b, first, len)        ((b) >= (first) && (b) < (first) + (len))
static int btrfs_issue_discard(struct block_device *bdev, u64 start, u64 len,
                               u64 *discarded_bytes)
{
        int j, ret = 0;
        u64 bytes_left, end;
        u64 aligned_start = ALIGN(start, 1 << 9);

        if (WARN_ON(start != aligned_start)) {
                len -= aligned_start - start;
                len = round_down(len, 1 << 9);
                start = aligned_start;
        }

        *discarded_bytes = 0;

        if (!len)
                return 0;

        end = start + len;
        bytes_left = len;

        /* Skip any superblocks on this device. */
        for (j = 0; j < BTRFS_SUPER_MIRROR_MAX; j++) {
                u64 sb_start = btrfs_sb_offset(j);
                u64 sb_end = sb_start + BTRFS_SUPER_INFO_SIZE;
                u64 size = sb_start - start;

                if (!in_range(sb_start, start, bytes_left) &&
                    !in_range(sb_end, start, bytes_left) &&
                    !in_range(start, sb_start, BTRFS_SUPER_INFO_SIZE))
                        continue;

                /*
                 * Superblock spans beginning of range.  Adjust start and
                 * try again.
                 */

                if (sb_start <= start) {
                        start += sb_end - start;
                        if (start > end) {
                                bytes_left = 0;
                                break;
                        }
                        bytes_left = end - start;
                        continue;
                }

                if (size) {
                        ret = blkdev_issue_discard(bdev, start >> 9, size >> 9,
                                                   GFP_NOFS, 0);
                        if (!ret)
                                *discarded_bytes += size;
                        else if (ret != -EOPNOTSUPP)
                                return ret;
                }

                start = sb_end;
                if (start > end) {
                        bytes_left = 0;
                        break;
                }
                bytes_left = end - start;
        }

        if (bytes_left) {
                ret = blkdev_issue_discard(bdev, start >> 9, bytes_left >> 9,
                                           GFP_NOFS, 0);
                if (!ret)
                        *discarded_bytes += bytes_left;
        }
        return ret;
}

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;


        /*
         * Avoid races with device replace and make sure our bbio has devices
         * associated to its stripes that don't go away while we are discarding.
         */
        btrfs_bio_counter_inc_blocked(root->fs_info);
        /* Tell the block device(s) that the sectors can be discarded */
        ret = btrfs_map_block(root->fs_info, 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++) {
                        u64 bytes;
                        if (!stripe->dev->can_discard)
                                continue;

                        ret = btrfs_issue_discard(stripe->dev->bdev,
                                                  stripe->physical,
                                                  stripe->length,
                                                  &bytes);
                        if (!ret)
                                discarded_bytes += bytes;
                        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;
                }
                btrfs_put_bbio(bbio);
        }
        btrfs_bio_counter_dec(root->fs_info);

        if (actual_bytes)
                *actual_bytes = discarded_bytes;


        if (ret == -EOPNOTSUPP)
                ret = 0;
        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 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);
        } else {
                ret = btrfs_add_delayed_data_ref(fs_info, trans, bytenr,
                                        num_bytes, parent, root_objectid,
                                        owner, offset, 0,
                                        BTRFS_ADD_DELAYED_REF, NULL);
        }
        return ret;
}

static int __btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
                                  struct btrfs_root *root,
                                  struct btrfs_delayed_ref_node *node,
                                  u64 parent, u64 root_objectid,
                                  u64 owner, u64 offset, int refs_to_add,
                                  struct btrfs_delayed_extent_op *extent_op)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_extent_item *item;
        struct btrfs_key key;
        u64 bytenr = node->bytenr;
        u64 num_bytes = node->num_bytes;
        u64 refs;
        int ret;

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

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

        /*
         * Ok we had -EAGAIN which means we didn't have space to insert and
         * inline extent ref, so just update the reference count and add a
         * normal backref.
         */
        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &key, path->slots[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 = READA_FORWARD;
        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 ret;
}

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);
        trace_run_delayed_data_ref(node, ref, node->action);

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

        if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
                if (extent_op)
                        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, 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, 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;
        int metadata = !extent_op->is_data;

        if (trans->aborted)
                return 0;

        if (metadata && !btrfs_fs_incompat(root->fs_info, SKINNY_METADATA))
                metadata = 0;

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

        key.objectid = node->bytenr;

        if (metadata) {
                key.type = BTRFS_METADATA_ITEM_KEY;
                key.offset = extent_op->level;
        } else {
                key.type = BTRFS_EXTENT_ITEM_KEY;
                key.offset = node->num_bytes;
        }

again:
        path->reada = READA_FORWARD;
        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) {
                if (metadata) {
                        if (path->slots[0] > 0) {
                                path->slots[0]--;
                                btrfs_item_key_to_cpu(path->nodes[0], &key,
                                                      path->slots[0]);
                                if (key.objectid == node->bytenr &&
                                    key.type == BTRFS_EXTENT_ITEM_KEY &&
                                    key.offset == node->num_bytes)
                                        ret = 0;
                        }
                        if (ret > 0) {
                                btrfs_release_path(path);
                                metadata = 0;

                                key.objectid = node->bytenr;
                                key.offset = node->num_bytes;
                                key.type = BTRFS_EXTENT_ITEM_KEY;
                                goto again;
                        }
                } else {
                        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;
        bool skinny_metadata = btrfs_fs_incompat(root->fs_info,
                                                 SKINNY_METADATA);

        ref = btrfs_delayed_node_to_tree_ref(node);
        trace_run_delayed_tree_ref(node, ref, node->action);

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

        ins.objectid = node->bytenr;
        if (skinny_metadata) {
                ins.offset = ref->level;
                ins.type = BTRFS_METADATA_ITEM_KEY;
        } else {
                ins.offset = node->num_bytes;
                ins.type = BTRFS_EXTENT_ITEM_KEY;
        }

        BUG_ON(node->ref_mod != 1);
        if (node->action == BTRFS_ADD_DELAYED_REF && insert_reserved) {
                BUG_ON(!extent_op || !extent_op->update_flags);
                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,
                                             parent, ref_root,
                                             ref->level, 0, 1,
                                             extent_op);
        } else if (node->action == BTRFS_DROP_DELAYED_REF) {
                ret = __btrfs_free_extent(trans, root, node,
                                          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) {
                if (insert_reserved)
                        btrfs_pin_extent(root, node->bytenr,
                                         node->num_bytes, 1);
                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);
                trace_run_delayed_ref_head(node, head, node->action);

                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);
                        }
                }

                /* Also free its reserved qgroup space */
                btrfs_qgroup_free_delayed_ref(root->fs_info,
                                              head->qgroup_ref_root,
                                              head->qgroup_reserved);
                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 inline struct btrfs_delayed_ref_node *
select_delayed_ref(struct btrfs_delayed_ref_head *head)
{
        struct btrfs_delayed_ref_node *ref;

        if (list_empty(&head->ref_list))
                return NULL;

        /*
         * Select a delayed ref of type BTRFS_ADD_DELAYED_REF first.
         * This is to prevent a ref count from going down to zero, which deletes
         * the extent item from the extent tree, when there still are references
         * to add, which would fail because they would not find the extent item.
         */
        list_for_each_entry(ref, &head->ref_list, list) {
                if (ref->action == BTRFS_ADD_DELAYED_REF)
                        return ref;
        }

        return list_entry(head->ref_list.next, struct btrfs_delayed_ref_node,
                          list);
}

/*
 * 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 __btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                                             struct btrfs_root *root,
                                             unsigned long nr)
{
        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;
        ktime_t start = ktime_get();
        int ret;
        unsigned long count = 0;
        unsigned long actual_count = 0;
        int must_insert_reserved = 0;

        delayed_refs = &trans->transaction->delayed_refs;
        while (1) {
                if (!locked_ref) {
                        if (count >= nr)
                                break;

                        spin_lock(&delayed_refs->lock);
                        locked_ref = btrfs_select_ref_head(trans);
                        if (!locked_ref) {
                                spin_unlock(&delayed_refs->lock);
                                break;
                        }

                        /* grab the lock that says we are going to process
                         * all the refs for this head */
                        ret = btrfs_delayed_ref_lock(trans, locked_ref);
                        spin_unlock(&delayed_refs->lock);
                        /*
                         * 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.
                 * Or we can get node references of the same type that weren't
                 * merged when created due to bumps in the tree mod seq, and
                 * we need to merge them to prevent adding an inline extent
                 * backref before dropping it (triggering a BUG_ON at
                 * insert_inline_extent_backref()).
                 */
                spin_lock(&locked_ref->lock);
                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)) {
                        spin_unlock(&locked_ref->lock);
                        btrfs_delayed_ref_unlock(locked_ref);
                        spin_lock(&delayed_refs->lock);
                        locked_ref->processing = 0;
                        delayed_refs->num_heads_ready++;
                        spin_unlock(&delayed_refs->lock);
                        locked_ref = NULL;
                        cond_resched();
                        count++;
                        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) {
                                btrfs_free_delayed_extent_op(extent_op);
                                extent_op = NULL;
                        }

                        if (extent_op) {
                                spin_unlock(&locked_ref->lock);
                                ret = run_delayed_extent_op(trans, root,
                                                            ref, extent_op);
                                btrfs_free_delayed_extent_op(extent_op);

                                if (ret) {
                                        /*
                                         * Need to reset must_insert_reserved if
                                         * there was an error so the abort stuff
                                         * can cleanup the reserved space
                                         * properly.
                                         */
                                        if (must_insert_reserved)
                                                locked_ref->must_insert_reserved = 1;
                                        locked_ref->processing = 0;
                                        btrfs_debug(fs_info, "run_delayed_extent_op returned %d", ret);
                                        btrfs_delayed_ref_unlock(locked_ref);
                                        return ret;
                                }
                                continue;
                        }

                        /*
                         * Need to drop our head ref lock and re-acquire the
                         * delayed ref lock and then re-check to make sure
                         * nobody got added.
                         */
                        spin_unlock(&locked_ref->lock);
                        spin_lock(&delayed_refs->lock);
                        spin_lock(&locked_ref->lock);
                        if (!list_empty(&locked_ref->ref_list) ||
                            locked_ref->extent_op) {
                                spin_unlock(&locked_ref->lock);
                                spin_unlock(&delayed_refs->lock);
                                continue;
                        }
                        ref->in_tree = 0;
                        delayed_refs->num_heads--;
                        rb_erase(&locked_ref->href_node,
                                 &delayed_refs->href_root);
                        spin_unlock(&delayed_refs->lock);
                } else {
                        actual_count++;
                        ref->in_tree = 0;
                        list_del(&ref->list);
                }
                atomic_dec(&delayed_refs->num_entries);

                if (!btrfs_delayed_ref_is_head(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(&locked_ref->lock);

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

                btrfs_free_delayed_extent_op(extent_op);
                if (ret) {
                        locked_ref->processing = 0;
                        btrfs_delayed_ref_unlock(locked_ref);
                        btrfs_put_delayed_ref(ref);
                        btrfs_debug(fs_info, "run_one_delayed_ref returned %d", ret);
                        return ret;
                }

                /*
                 * If this node is a head, that means all the refs in this head
                 * have been dealt with, and we will pick the next head to deal
                 * with, so we must unlock the head and drop it from the cluster
                 * list before we release it.
                 */
                if (btrfs_delayed_ref_is_head(ref)) {
                        if (locked_ref->is_data &&
                            locked_ref->total_ref_mod < 0) {
                                spin_lock(&delayed_refs->lock);
                                delayed_refs->pending_csums -= ref->num_bytes;
                                spin_unlock(&delayed_refs->lock);
                        }
                        btrfs_delayed_ref_unlock(locked_ref);
                        locked_ref = NULL;
                }
                btrfs_put_delayed_ref(ref);
                count++;
                cond_resched();
        }

        /*
         * We don't want to include ref heads since we can have empty ref heads
         * and those will drastically skew our runtime down since we just do
         * accounting, no actual extent tree updates.
         */
        if (actual_count > 0) {
                u64 runtime = ktime_to_ns(ktime_sub(ktime_get(), start));
                u64 avg;

                /*
                 * We weigh the current average higher than our current runtime
                 * to avoid large swings in the average.
                 */
                spin_lock(&delayed_refs->lock);
                avg = fs_info->avg_delayed_ref_runtime * 3 + runtime;
                fs_info->avg_delayed_ref_runtime = avg >> 2;    /* div by 4 */
                spin_unlock(&delayed_refs->lock);
        }
        return 0;
}

#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

static inline u64 heads_to_leaves(struct btrfs_root *root, u64 heads)
{
        u64 num_bytes;

        num_bytes = heads * (sizeof(struct btrfs_extent_item) +
                             sizeof(struct btrfs_extent_inline_ref));
        if (!btrfs_fs_incompat(root->fs_info, SKINNY_METADATA))
                num_bytes += heads * sizeof(struct btrfs_tree_block_info);

        /*
         * We don't ever fill up leaves all the way so multiply by 2 just to be
         * closer to what we're really going to want to use.
         */
        return div_u64(num_bytes, BTRFS_LEAF_DATA_SIZE(root));
}

/*
 * Takes the number of bytes to be csumm'ed and figures out how many leaves it
 * would require to store the csums for that many bytes.
 */
u64 btrfs_csum_bytes_to_leaves(struct btrfs_root *root, u64 csum_bytes)
{
        u64 csum_size;
        u64 num_csums_per_leaf;
        u64 num_csums;

        csum_size = BTRFS_LEAF_DATA_SIZE(root) - sizeof(struct btrfs_item);
        num_csums_per_leaf = div64_u64(csum_size,
                        (u64)btrfs_super_csum_size(root->fs_info->super_copy));
        num_csums = div64_u64(csum_bytes, root->sectorsize);
        num_csums += num_csums_per_leaf - 1;
        num_csums = div64_u64(num_csums, num_csums_per_leaf);
        return num_csums;
}

int btrfs_check_space_for_delayed_refs(struct btrfs_trans_handle *trans,
                                       struct btrfs_root *root)
{
        struct btrfs_block_rsv *global_rsv;
        u64 num_heads = trans->transaction->delayed_refs.num_heads_ready;
        u64 csum_bytes = trans->transaction->delayed_refs.pending_csums;
        u64 num_dirty_bgs = trans->transaction->num_dirty_bgs;
        u64 num_bytes, num_dirty_bgs_bytes;
        int ret = 0;

        num_bytes = btrfs_calc_trans_metadata_size(root, 1);
        num_heads = heads_to_leaves(root, num_heads);
        if (num_heads > 1)
                num_bytes += (num_heads - 1) * root->nodesize;
        num_bytes <<= 1;
        num_bytes += btrfs_csum_bytes_to_leaves(root, csum_bytes) * root->nodesize;
        num_dirty_bgs_bytes = btrfs_calc_trans_metadata_size(root,
                                                             num_dirty_bgs);
        global_rsv = &root->fs_info->global_block_rsv;

        /*
         * If we can't allocate any more chunks lets make sure we have _lots_ of
         * wiggle room since running delayed refs can create more delayed refs.
         */
        if (global_rsv->space_info->full) {
                num_dirty_bgs_bytes <<= 1;
                num_bytes <<= 1;
        }

        spin_lock(&global_rsv->lock);
        if (global_rsv->reserved <= num_bytes + num_dirty_bgs_bytes)
                ret = 1;
        spin_unlock(&global_rsv->lock);
        return ret;
}

int btrfs_should_throttle_delayed_refs(struct btrfs_trans_handle *trans,
                                       struct btrfs_root *root)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        u64 num_entries =
                atomic_read(&trans->transaction->delayed_refs.num_entries);
        u64 avg_runtime;
        u64 val;

        smp_mb();
        avg_runtime = fs_info->avg_delayed_ref_runtime;
        val = num_entries * avg_runtime;
        if (num_entries * avg_runtime >= NSEC_PER_SEC)
                return 1;
        if (val >= NSEC_PER_SEC / 2)
                return 2;

        return btrfs_check_space_for_delayed_refs(trans, root);
}

struct async_delayed_refs {
        struct btrfs_root *root;
        u64 transid;
        int count;
        int error;
        int sync;
        struct completion wait;
        struct btrfs_work work;
};

static void delayed_ref_async_start(struct btrfs_work *work)
{
        struct async_delayed_refs *async;
        struct btrfs_trans_handle *trans;
        int ret;

        async = container_of(work, struct async_delayed_refs, work);

        /* if the commit is already started, we don't need to wait here */
        if (btrfs_transaction_blocked(async->root->fs_info))
                goto done;

        trans = btrfs_join_transaction(async->root);
        if (IS_ERR(trans)) {
                async->error = PTR_ERR(trans);
                goto done;
        }

        /*
         * trans->sync means that when we call end_transaction, we won't
         * wait on delayed refs
         */
        trans->sync = true;

        /* Don't bother flushing if we got into a different transaction */
        if (trans->transid > async->transid)
                goto end;

        ret = btrfs_run_delayed_refs(trans, async->root, async->count);
        if (ret)
                async->error = ret;
end:
        ret = btrfs_end_transaction(trans, async->root);
        if (ret && !async->error)
                async->error = ret;
done:
        if (async->sync)
                complete(&async->wait);
        else
                kfree(async);
}

int btrfs_async_run_delayed_refs(struct btrfs_root *root,
                                 unsigned long count, u64 transid, int wait)
{
        struct async_delayed_refs *async;
        int ret;

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

        async->root = root->fs_info->tree_root;
        async->count = count;
        async->error = 0;
        async->transid = transid;
        if (wait)
                async->sync = 1;
        else
                async->sync = 0;
        init_completion(&async->wait);

        btrfs_init_work(&async->work, btrfs_extent_refs_helper,
                        delayed_ref_async_start, NULL, NULL);

        btrfs_queue_work(root->fs_info->extent_workers, &async->work);

        if (wait) {
                wait_for_completion(&async->wait);
                ret = async->error;
                kfree(async);
                return ret;
        }
        return 0;
}

/*
 * 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_head *head;
        int ret;
        int run_all = count == (unsigned long)-1;
        bool can_flush_pending_bgs = trans->can_flush_pending_bgs;

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

        if (root->fs_info->creating_free_space_tree)
                return 0;

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

        delayed_refs = &trans->transaction->delayed_refs;
        if (count == 0)
                count = atomic_read(&delayed_refs->num_entries) * 2;

again:
#ifdef SCRAMBLE_DELAYED_REFS
        delayed_refs->run_delayed_start = find_middle(&delayed_refs->root);
#endif
        trans->can_flush_pending_bgs = false;
        ret = __btrfs_run_delayed_refs(trans, root, count);
        if (ret < 0) {
                btrfs_abort_transaction(trans, root, ret);
                return ret;
        }

        if (run_all) {
                if (!list_empty(&trans->new_bgs))
                        btrfs_create_pending_block_groups(trans, root);

                spin_lock(&delayed_refs->lock);
                node = rb_first(&delayed_refs->href_root);
                if (!node) {
                        spin_unlock(&delayed_refs->lock);
                        goto out;
                }
                count = (unsigned long)-1;

                while (node) {
                        head = rb_entry(node, struct btrfs_delayed_ref_head,
                                        href_node);
                        if (btrfs_delayed_ref_is_head(&head->node)) {
                                struct btrfs_delayed_ref_node *ref;

                                ref = &head->node;
                                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;
                        } else {
                                WARN_ON(1);