/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */
#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/sort.h>
#include <linux/rcupdate.h>
#include <linux/kthread.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include "compat.h"
#include "hash.h"
#include "ctree.h"
#include "disk-io.h"
#include "print-tree.h"
#include "transaction.h"
#include "volumes.h"
#include "locking.h"
#include "free-space-cache.h"

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

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

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

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

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

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

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

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

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

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

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

        return 0;
}

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

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

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

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

        return ret;
}

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

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

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

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

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

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

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

                while (nr--) {
                        cache->bytes_super += stripe_len;
                        ret = add_excluded_extent(root, logical[nr],
                                                  stripe_len);
                        BUG_ON(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->cached != BTRFS_CACHE_STARTED) {
                spin_unlock(&cache->lock);
                return NULL;
        }

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

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

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

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

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

        return total_added;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        free_excluded_extents(extent_root, block_group);

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

        put_caching_control(caching_ctl);
        btrfs_put_block_group(block_group);
}

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

        caching_ctl = kzalloc(sizeof(*caching_ctl), GFP_NOFS);
        BUG_ON(!caching_ctl);

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

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

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

                schedule();

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

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

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

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

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

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

        btrfs_get_block_group(cache);

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

        return ret;
}

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

        cache = block_group_cache_tree_search(info, bytenr, 0);

        return cache;
}

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

        cache = block_group_cache_tree_search(info, bytenr, 1);

        return cache;
}

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

        flags &= BTRFS_BLOCK_GROUP_TYPE_MASK;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        if (!trans)
                goto out;

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

                        btrfs_release_path(path);

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

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

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

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

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

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

        if (owner == (u64)-1) {
                while (1) {
                        if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                                ret = btrfs_next_leaf(root, path);
                                if (ret < 0)
                                        return ret;
                                BUG_ON(ret > 0);
                                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);

        ret = btrfs_extend_item(trans, root, path, new_size);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        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);

        ret = btrfs_extend_item(trans, root, path, size);

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

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

        iref = (struct btrfs_extent_inline_ref *)ptr;
        btrfs_set_extent_inline_ref_type(leaf, iref, type);
        if (type == BTRFS_EXTENT_DATA_REF_KEY) {
                struct btrfs_extent_data_ref *dref;
                dref = (struct btrfs_extent_data_ref *)(&iref->offset);
                btrfs_set_extent_data_ref_root(leaf, dref, root_objectid);
                btrfs_set_extent_data_ref_objectid(leaf, dref, owner);
                btrfs_set_extent_data_ref_offset(leaf, dref, offset);
                btrfs_set_extent_data_ref_count(leaf, dref, refs_to_add);
        } else if (type == BTRFS_SHARED_DATA_REF_KEY) {
                struct btrfs_shared_data_ref *sref;
                sref = (struct btrfs_shared_data_ref *)(iref + 1);
                btrfs_set_shared_data_ref_count(leaf, sref, refs_to_add);
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
        } else if (type == BTRFS_SHARED_BLOCK_REF_KEY) {
                btrfs_set_extent_inline_ref_offset(leaf, iref, parent);
        } else {
                btrfs_set_extent_inline_ref_offset(leaf, iref, root_objectid);
        }
        btrfs_mark_buffer_dirty(leaf);
        return 0;
}

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
int update_inline_extent_backref(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root,
                                 struct btrfs_path *path,
                                 struct btrfs_extent_inline_ref *iref,
                                 int refs_to_mod,
                                 struct btrfs_delayed_extent_op *extent_op)
{
        struct extent_buffer *leaf;
        struct btrfs_extent_item *ei;
        struct btrfs_extent_data_ref *dref = NULL;
        struct btrfs_shared_data_ref *sref = NULL;
        unsigned long ptr;
        unsigned long end;
        u32 item_size;
        int size;
        int type;
        int ret;
        u64 refs;

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

        type = btrfs_extent_inline_ref_type(leaf, iref);

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

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

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

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);
                ret = update_inline_extent_backref(trans, root, path, iref,
                                                   refs_to_add, extent_op);
        } else if (ret == -ENOENT) {
                ret = setup_inline_extent_backref(trans, root, path, iref,
                                                  parent, root_objectid,
                                                  owner, offset, refs_to_add,
                                                  extent_op);
        }
        return ret;
}

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

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

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

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

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


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


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

                        ret = btrfs_issue_discard(stripe->dev->bdev,
                                                  stripe->physical,
                                                  stripe->length);
                        if (!ret)
                                discarded_bytes += stripe->length;
                        else if (ret != -EOPNOTSUPP)
                                break;

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

        if (actual_bytes)
                *actual_bytes = discarded_bytes;


        return ret;
}

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

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

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

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

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

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

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

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

        btrfs_mark_buffer_dirty(leaf);
        btrfs_release_path(path);

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

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

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

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

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

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

}

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

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

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

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

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

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

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

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

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

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

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

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

/* helper function to actually process a single delayed ref entry */
static int run_one_delayed_ref(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               struct btrfs_delayed_ref_node *node,
                               struct btrfs_delayed_extent_op *extent_op,
                               int insert_reserved)
{
        int ret;
        if (btrfs_delayed_ref_is_head(node)) {
                struct btrfs_delayed_ref_head *head;
                /*
                 * we've hit the end of the chain and we were supposed
                 * to insert this extent into the tree.  But, it got
                 * deleted before we ever needed to insert it, so all
                 * we have to do is clean up the accounting
                 */
                BUG_ON(extent_op);
                head = btrfs_delayed_node_to_head(node);
                if (insert_reserved) {
                        btrfs_pin_extent(root, node->bytenr,
                                         node->num_bytes, 1);
                        if (head->is_data) {
                                ret = btrfs_del_csums(trans, root,
                                                      node->bytenr,
                                                      node->num_bytes);
                                BUG_ON(ret);
                        }
                }
                mutex_unlock(&head->mutex);
                return 0;
        }

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

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

static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
                                       struct btrfs_root *root,
                                       struct list_head *cluster)
{
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_ref_node *ref;
        struct btrfs_delayed_ref_head *locked_ref = NULL;
        struct btrfs_delayed_extent_op *extent_op;
        int ret;
        int count = 0;
        int must_insert_reserved = 0;

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

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

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

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

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

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

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

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

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

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

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

                                goto next;
                        }

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

                ref->in_tree = 0;
                rb_erase(&ref->rb_node, &delayed_refs->root);
                delayed_refs->num_entries--;
                /*
                 * we modified num_entries, but as we're currently running
                 * delayed refs, skip
                 *     wake_up(&delayed_refs->seq_wait);
                 * here.
                 */
                spin_unlock(&delayed_refs->lock);

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

                btrfs_put_delayed_ref(ref);
                kfree(extent_op);
                count++;
next:
                do_chunk_alloc(trans, root->fs_info->extent_root,
                               2 * 1024 * 1024,
                               btrfs_get_alloc_profile(root, 0),
                               CHUNK_ALLOC_NO_FORCE);
                cond_resched();
                spin_lock(&delayed_refs->lock);
        }
        return count;
}


static void wait_for_more_refs(struct btrfs_delayed_ref_root *delayed_refs,
                        unsigned long num_refs)
{
        struct list_head *first_seq = delayed_refs->seq_head.next;

        spin_unlock(&delayed_refs->lock);
        pr_debug("waiting for more refs (num %ld, first %p)\n",
                 num_refs, first_seq);
        wait_event(delayed_refs->seq_wait,
                   num_refs != delayed_refs->num_entries ||
                   delayed_refs->seq_head.next != first_seq);
        pr_debug("done waiting for more refs (num %ld, first %p)\n",
                 delayed_refs->num_entries, delayed_refs->seq_head.next);
        spin_lock(&delayed_refs->lock);
}

/*
 * 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.
 */
int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root, unsigned long count)
{
        struct rb_node *node;
        struct btrfs_delayed_ref_root *delayed_refs;
        struct btrfs_delayed_ref_node *ref;
        struct list_head cluster;
        int ret;
        u64 delayed_start;
        int run_all = count == (unsigned long)-1;
        int run_most = 0;
        unsigned long num_refs = 0;
        int consider_waiting;

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

        do_chunk_alloc(trans, root->fs_info->extent_root,
                       2 * 1024 * 1024, btrfs_get_alloc_profile(root, 0),
                       CHUNK_ALLOC_NO_FORCE);

        delayed_refs = &trans->transaction->delayed_refs;
        INIT_LIST_HEAD(&cluster);
again:
        consider_waiting = 0;
        spin_lock(&delayed_refs->lock);
        if (count == 0) {
                count = delayed_refs->num_entries * 2;
                run_most = 1;
        }
        while (1) {
                if (!(run_all || run_most) &&
                    delayed_refs->num_heads_ready < 64)
                        break;

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

                if (delayed_start >= delayed_refs->run_delayed_start) {
                        if (consider_waiting == 0) {
                                /*
                                 * btrfs_find_ref_cluster looped. let's do one
                                 * more cycle. if we don't run any delayed ref
                                 * during that cycle (because we can't because
                                 * all of them are blocked) and if the number of
                                 * refs doesn't change, we avoid busy waiting.
                                 */
                                consider_waiting = 1;
                                num_refs = delayed_refs->num_entries;
                        } else {
                                wait_for_more_refs(delayed_refs, num_refs);
                                /*
                                 * after waiting, things have changed. we
                                 * dropped the lock and someone else might have
                                 * run some refs, built new clusters and so on.
                                 * therefore, we restart staleness detection.
                                 */
                                consider_waiting = 0;
                        }
                }

                ret = run_clustered_refs(trans, root, &cluster);
                BUG_ON(ret < 0);

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

                if (count == 0)
                        break;

                if (ret || delayed_refs->run_delayed_start == 0) {
                        /* refs were run, let's reset staleness detection */
                        consider_waiting = 0;
                }
        }

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

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

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

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

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

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

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

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

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

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

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

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

                btrfs_release_path(path);

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

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

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

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

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

        data_ref = btrfs_delayed_node_to_data_ref(ref);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        ret = 0;
out:
        return ret;
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

}

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

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

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

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

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

                if (block_group->ro)
                        goto out_free;

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

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

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

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

        spin_lock(&block_group->lock);
        if (block_group->cached != BTRFS_CACHE_FINISHED) {
                /* We're not cached, don't bother trying to write stuff out */
                dcs = BTRFS_DC_WRITTEN;
                spin_unlock(&block_group->lock);
                goto out_put;
        }
        spin_unlock(&block_group->lock);

        num_pages = (int)div64_u64(block_group->key.offset, 1024 * 1024 * 1024);
        if (!num_pages)
                num_pages = 1;

        /*
         * Just to make absolutely sure we have enough space, we're going to
         * preallocate 12 pages worth of space for each block group.  In
         * practice we ought to use at most 8, but we need extra space so we can
         * add our header and have a terminator between the extents and the
         * bitmaps.
         */
        num_pages *= 16;
        num_pages *= PAGE_CACHE_SIZE;

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

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

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

        return ret;
}

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

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

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

        while (1) {
                if (last == 0) {
                        err = btrfs_run_delayed_refs(trans, root,
                                                     (unsigned long)-1);
                        BUG_ON(err);
                }

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

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

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

                err = write_one_cache_group(trans, root, path, cache);
                BUG_ON(err);
                btrfs_put_block_group(cache);
        }

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

                cache = btrfs_lookup_first_block_group(root->fs_info, last);
                while (cache) {
                        /*
                         * Really this shouldn't happen, but it could if we
                         * couldn't write the entire preallocated extent and
                         * splitting the extent resulted in a new block.