Btrfs: do less aggressive btree readahead

[linux-2.6] / fs / btrfs / ctree.c

/*
 * Copyright (C) 2007,2008 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 "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "print-tree.h"
#include "locking.h"

static int split_node(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_path *path, int level);
static int split_leaf(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_key *ins_key,
                      struct btrfs_path *path, int data_size, int extend);
static int push_node_left(struct btrfs_trans_handle *trans,
                          struct btrfs_root *root, struct extent_buffer *dst,
                          struct extent_buffer *src, int empty);
static int balance_node_right(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root,
                              struct extent_buffer *dst_buf,
                              struct extent_buffer *src_buf);
static int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                   struct btrfs_path *path, int level, int slot);

inline void btrfs_init_path(struct btrfs_path *p)
{
        memset(p, 0, sizeof(*p));
}

struct btrfs_path *btrfs_alloc_path(void)
{
        struct btrfs_path *path;
        path = kmem_cache_alloc(btrfs_path_cachep, GFP_NOFS);
        if (path) {
                btrfs_init_path(path);
                path->reada = 1;
        }
        return path;
}

/* this also releases the path */
void btrfs_free_path(struct btrfs_path *p)
{
        btrfs_release_path(NULL, p);
        kmem_cache_free(btrfs_path_cachep, p);
}

/*
 * path release drops references on the extent buffers in the path
 * and it drops any locks held by this path
 *
 * It is safe to call this on paths that no locks or extent buffers held.
 */
noinline void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p)
{
        int i;

        for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
                p->slots[i] = 0;
                if (!p->nodes[i])
                        continue;
                if (p->locks[i]) {
                        btrfs_tree_unlock(p->nodes[i]);
                        p->locks[i] = 0;
                }
                free_extent_buffer(p->nodes[i]);
                p->nodes[i] = NULL;
        }
}

/*
 * safely gets a reference on the root node of a tree.  A lock
 * is not taken, so a concurrent writer may put a different node
 * at the root of the tree.  See btrfs_lock_root_node for the
 * looping required.
 *
 * The extent buffer returned by this has a reference taken, so
 * it won't disappear.  It may stop being the root of the tree
 * at any time because there are no locks held.
 */
struct extent_buffer *btrfs_root_node(struct btrfs_root *root)
{
        struct extent_buffer *eb;
        spin_lock(&root->node_lock);
        eb = root->node;
        extent_buffer_get(eb);
        spin_unlock(&root->node_lock);
        return eb;
}

/* loop around taking references on and locking the root node of the
 * tree until you end up with a lock on the root.  A locked buffer
 * is returned, with a reference held.
 */
struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root)
{
        struct extent_buffer *eb;

        while (1) {
                eb = btrfs_root_node(root);
                btrfs_tree_lock(eb);

                spin_lock(&root->node_lock);
                if (eb == root->node) {
                        spin_unlock(&root->node_lock);
                        break;
                }
                spin_unlock(&root->node_lock);

                btrfs_tree_unlock(eb);
                free_extent_buffer(eb);
        }
        return eb;
}

/* cowonly root (everything not a reference counted cow subvolume), just get
 * put onto a simple dirty list.  transaction.c walks this to make sure they
 * get properly updated on disk.
 */
static void add_root_to_dirty_list(struct btrfs_root *root)
{
        if (root->track_dirty && list_empty(&root->dirty_list)) {
                list_add(&root->dirty_list,
                         &root->fs_info->dirty_cowonly_roots);
        }
}

/*
 * used by snapshot creation to make a copy of a root for a tree with
 * a given objectid.  The buffer with the new root node is returned in
 * cow_ret, and this func returns zero on success or a negative error code.
 */
int btrfs_copy_root(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      struct extent_buffer *buf,
                      struct extent_buffer **cow_ret, u64 new_root_objectid)
{
        struct extent_buffer *cow;
        u32 nritems;
        int ret = 0;
        int level;
        struct btrfs_root *new_root;

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

        memcpy(new_root, root, sizeof(*new_root));
        new_root->root_key.objectid = new_root_objectid;

        WARN_ON(root->ref_cows && trans->transid !=
                root->fs_info->running_transaction->transid);
        WARN_ON(root->ref_cows && trans->transid != root->last_trans);

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

        cow = btrfs_alloc_free_block(trans, new_root, buf->len, 0,
                                     new_root_objectid, trans->transid,
                                     level, buf->start, 0);
        if (IS_ERR(cow)) {
                kfree(new_root);
                return PTR_ERR(cow);
        }

        copy_extent_buffer(cow, buf, 0, 0, cow->len);
        btrfs_set_header_bytenr(cow, cow->start);
        btrfs_set_header_generation(cow, trans->transid);
        btrfs_set_header_owner(cow, new_root_objectid);
        btrfs_clear_header_flag(cow, BTRFS_HEADER_FLAG_WRITTEN);

        write_extent_buffer(cow, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(cow),
                            BTRFS_FSID_SIZE);

        WARN_ON(btrfs_header_generation(buf) > trans->transid);
        ret = btrfs_inc_ref(trans, new_root, buf, cow, NULL);
        kfree(new_root);

        if (ret)
                return ret;

        btrfs_mark_buffer_dirty(cow);
        *cow_ret = cow;
        return 0;
}

/*
 * does the dirty work in cow of a single block.  The parent block (if
 * supplied) is updated to point to the new cow copy.  The new buffer is marked
 * dirty and returned locked.  If you modify the block it needs to be marked
 * dirty again.
 *
 * search_start -- an allocation hint for the new block
 *
 * empty_size -- a hint that you plan on doing more cow.  This is the size in
 * bytes the allocator should try to find free next to the block it returns.
 * This is just a hint and may be ignored by the allocator.
 *
 * prealloc_dest -- if you have already reserved a destination for the cow,
 * this uses that block instead of allocating a new one.
 * btrfs_alloc_reserved_extent is used to finish the allocation.
 */
static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root,
                             struct extent_buffer *buf,
                             struct extent_buffer *parent, int parent_slot,
                             struct extent_buffer **cow_ret,
                             u64 search_start, u64 empty_size,
                             u64 prealloc_dest)
{
        u64 parent_start;
        struct extent_buffer *cow;
        u32 nritems;
        int ret = 0;
        int level;
        int unlock_orig = 0;

        if (*cow_ret == buf)
                unlock_orig = 1;

        WARN_ON(!btrfs_tree_locked(buf));

        if (parent)
                parent_start = parent->start;
        else
                parent_start = 0;

        WARN_ON(root->ref_cows && trans->transid !=
                root->fs_info->running_transaction->transid);
        WARN_ON(root->ref_cows && trans->transid != root->last_trans);

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

        if (prealloc_dest) {
                struct btrfs_key ins;

                ins.objectid = prealloc_dest;
                ins.offset = buf->len;
                ins.type = BTRFS_EXTENT_ITEM_KEY;

                ret = btrfs_alloc_reserved_extent(trans, root, parent_start,
                                                  root->root_key.objectid,
                                                  trans->transid, level, &ins);
                BUG_ON(ret);
                cow = btrfs_init_new_buffer(trans, root, prealloc_dest,
                                            buf->len);
        } else {
                cow = btrfs_alloc_free_block(trans, root, buf->len,
                                             parent_start,
                                             root->root_key.objectid,
                                             trans->transid, level,
                                             search_start, empty_size);
        }
        if (IS_ERR(cow))
                return PTR_ERR(cow);

        copy_extent_buffer(cow, buf, 0, 0, cow->len);
        btrfs_set_header_bytenr(cow, cow->start);
        btrfs_set_header_generation(cow, trans->transid);
        btrfs_set_header_owner(cow, root->root_key.objectid);
        btrfs_clear_header_flag(cow, BTRFS_HEADER_FLAG_WRITTEN);

        write_extent_buffer(cow, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(cow),
                            BTRFS_FSID_SIZE);

        WARN_ON(btrfs_header_generation(buf) > trans->transid);
        if (btrfs_header_generation(buf) != trans->transid) {
                u32 nr_extents;
                ret = btrfs_inc_ref(trans, root, buf, cow, &nr_extents);
                if (ret)
                        return ret;

                ret = btrfs_cache_ref(trans, root, buf, nr_extents);
                WARN_ON(ret);
        } else if (btrfs_header_owner(buf) == BTRFS_TREE_RELOC_OBJECTID) {
                /*
                 * There are only two places that can drop reference to
                 * tree blocks owned by living reloc trees, one is here,
                 * the other place is btrfs_drop_subtree. In both places,
                 * we check reference count while tree block is locked.
                 * Furthermore, if reference count is one, it won't get
                 * increased by someone else.
                 */
                u32 refs;
                ret = btrfs_lookup_extent_ref(trans, root, buf->start,
                                              buf->len, &refs);
                BUG_ON(ret);
                if (refs == 1) {
                        ret = btrfs_update_ref(trans, root, buf, cow,
                                               0, nritems);
                        clean_tree_block(trans, root, buf);
                } else {
                        ret = btrfs_inc_ref(trans, root, buf, cow, NULL);
                }
                BUG_ON(ret);
        } else {
                ret = btrfs_update_ref(trans, root, buf, cow, 0, nritems);
                if (ret)
                        return ret;
                clean_tree_block(trans, root, buf);
        }

        if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) {
                ret = btrfs_reloc_tree_cache_ref(trans, root, cow, buf->start);
                WARN_ON(ret);
        }

        if (buf == root->node) {
                WARN_ON(parent && parent != buf);

                spin_lock(&root->node_lock);
                root->node = cow;
                extent_buffer_get(cow);
                spin_unlock(&root->node_lock);

                if (buf != root->commit_root) {
                        btrfs_free_extent(trans, root, buf->start,
                                          buf->len, buf->start,
                                          root->root_key.objectid,
                                          btrfs_header_generation(buf),
                                          level, 1);
                }
                free_extent_buffer(buf);
                add_root_to_dirty_list(root);
        } else {
                btrfs_set_node_blockptr(parent, parent_slot,
                                        cow->start);
                WARN_ON(trans->transid == 0);
                btrfs_set_node_ptr_generation(parent, parent_slot,
                                              trans->transid);
                btrfs_mark_buffer_dirty(parent);
                WARN_ON(btrfs_header_generation(parent) != trans->transid);
                btrfs_free_extent(trans, root, buf->start, buf->len,
                                  parent_start, btrfs_header_owner(parent),
                                  btrfs_header_generation(parent), level, 1);
        }
        if (unlock_orig)
                btrfs_tree_unlock(buf);
        free_extent_buffer(buf);
        btrfs_mark_buffer_dirty(cow);
        *cow_ret = cow;
        return 0;
}

/*
 * cows a single block, see __btrfs_cow_block for the real work.
 * This version of it has extra checks so that a block isn't cow'd more than
 * once per transaction, as long as it hasn't been written yet
 */
noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root, struct extent_buffer *buf,
                    struct extent_buffer *parent, int parent_slot,
                    struct extent_buffer **cow_ret, u64 prealloc_dest)
{
        u64 search_start;
        int ret;

        if (trans->transaction != root->fs_info->running_transaction) {
                printk(KERN_CRIT "trans %llu running %llu\n",
                       (unsigned long long)trans->transid,
                       (unsigned long long)
                       root->fs_info->running_transaction->transid);
                WARN_ON(1);
        }
        if (trans->transid != root->fs_info->generation) {
                printk(KERN_CRIT "trans %llu running %llu\n",
                       (unsigned long long)trans->transid,
                       (unsigned long long)root->fs_info->generation);
                WARN_ON(1);
        }

        spin_lock(&root->fs_info->hash_lock);
        if (btrfs_header_generation(buf) == trans->transid &&
            btrfs_header_owner(buf) == root->root_key.objectid &&
            !btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN)) {
                *cow_ret = buf;
                spin_unlock(&root->fs_info->hash_lock);
                WARN_ON(prealloc_dest);
                return 0;
        }
        spin_unlock(&root->fs_info->hash_lock);
        search_start = buf->start & ~((u64)(1024 * 1024 * 1024) - 1);
        ret = __btrfs_cow_block(trans, root, buf, parent,
                                 parent_slot, cow_ret, search_start, 0,
                                 prealloc_dest);
        return ret;
}

/*
 * helper function for defrag to decide if two blocks pointed to by a
 * node are actually close by
 */
static int close_blocks(u64 blocknr, u64 other, u32 blocksize)
{
        if (blocknr < other && other - (blocknr + blocksize) < 32768)
                return 1;
        if (blocknr > other && blocknr - (other + blocksize) < 32768)
                return 1;
        return 0;
}

/*
 * compare two keys in a memcmp fashion
 */
static int comp_keys(struct btrfs_disk_key *disk, struct btrfs_key *k2)
{
        struct btrfs_key k1;

        btrfs_disk_key_to_cpu(&k1, disk);

        if (k1.objectid > k2->objectid)
                return 1;
        if (k1.objectid < k2->objectid)
                return -1;
        if (k1.type > k2->type)
                return 1;
        if (k1.type < k2->type)
                return -1;
        if (k1.offset > k2->offset)
                return 1;
        if (k1.offset < k2->offset)
                return -1;
        return 0;
}

/*
 * same as comp_keys only with two btrfs_key's
 */
static int comp_cpu_keys(struct btrfs_key *k1, struct btrfs_key *k2)
{
        if (k1->objectid > k2->objectid)
                return 1;
        if (k1->objectid < k2->objectid)
                return -1;
        if (k1->type > k2->type)
                return 1;
        if (k1->type < k2->type)
                return -1;
        if (k1->offset > k2->offset)
                return 1;
        if (k1->offset < k2->offset)
                return -1;
        return 0;
}

/*
 * this is used by the defrag code to go through all the
 * leaves pointed to by a node and reallocate them so that
 * disk order is close to key order
 */
int btrfs_realloc_node(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root, struct extent_buffer *parent,
                       int start_slot, int cache_only, u64 *last_ret,
                       struct btrfs_key *progress)
{
        struct extent_buffer *cur;
        u64 blocknr;
        u64 gen;
        u64 search_start = *last_ret;
        u64 last_block = 0;
        u64 other;
        u32 parent_nritems;
        int end_slot;
        int i;
        int err = 0;
        int parent_level;
        int uptodate;
        u32 blocksize;
        int progress_passed = 0;
        struct btrfs_disk_key disk_key;

        parent_level = btrfs_header_level(parent);
        if (cache_only && parent_level != 1)
                return 0;

        if (trans->transaction != root->fs_info->running_transaction)
                WARN_ON(1);
        if (trans->transid != root->fs_info->generation)
                WARN_ON(1);

        parent_nritems = btrfs_header_nritems(parent);
        blocksize = btrfs_level_size(root, parent_level - 1);
        end_slot = parent_nritems;

        if (parent_nritems == 1)
                return 0;

        for (i = start_slot; i < end_slot; i++) {
                int close = 1;

                if (!parent->map_token) {
                        map_extent_buffer(parent,
                                        btrfs_node_key_ptr_offset(i),
                                        sizeof(struct btrfs_key_ptr),
                                        &parent->map_token, &parent->kaddr,
                                        &parent->map_start, &parent->map_len,
                                        KM_USER1);
                }
                btrfs_node_key(parent, &disk_key, i);
                if (!progress_passed && comp_keys(&disk_key, progress) < 0)
                        continue;

                progress_passed = 1;
                blocknr = btrfs_node_blockptr(parent, i);
                gen = btrfs_node_ptr_generation(parent, i);
                if (last_block == 0)
                        last_block = blocknr;

                if (i > 0) {
                        other = btrfs_node_blockptr(parent, i - 1);
                        close = close_blocks(blocknr, other, blocksize);
                }
                if (!close && i < end_slot - 2) {
                        other = btrfs_node_blockptr(parent, i + 1);
                        close = close_blocks(blocknr, other, blocksize);
                }
                if (close) {
                        last_block = blocknr;
                        continue;
                }
                if (parent->map_token) {
                        unmap_extent_buffer(parent, parent->map_token,
                                            KM_USER1);
                        parent->map_token = NULL;
                }

                cur = btrfs_find_tree_block(root, blocknr, blocksize);
                if (cur)
                        uptodate = btrfs_buffer_uptodate(cur, gen);
                else
                        uptodate = 0;
                if (!cur || !uptodate) {
                        if (cache_only) {
                                free_extent_buffer(cur);
                                continue;
                        }
                        if (!cur) {
                                cur = read_tree_block(root, blocknr,
                                                         blocksize, gen);
                        } else if (!uptodate) {
                                btrfs_read_buffer(cur, gen);
                        }
                }
                if (search_start == 0)
                        search_start = last_block;

                btrfs_tree_lock(cur);
                err = __btrfs_cow_block(trans, root, cur, parent, i,
                                        &cur, search_start,
                                        min(16 * blocksize,
                                            (end_slot - i) * blocksize), 0);
                if (err) {
                        btrfs_tree_unlock(cur);
                        free_extent_buffer(cur);
                        break;
                }
                search_start = cur->start;
                last_block = cur->start;
                *last_ret = search_start;
                btrfs_tree_unlock(cur);
                free_extent_buffer(cur);
        }
        if (parent->map_token) {
                unmap_extent_buffer(parent, parent->map_token,
                                    KM_USER1);
                parent->map_token = NULL;
        }
        return err;
}

/*
 * The leaf data grows from end-to-front in the node.
 * this returns the address of the start of the last item,
 * which is the stop of the leaf data stack
 */
static inline unsigned int leaf_data_end(struct btrfs_root *root,
                                         struct extent_buffer *leaf)
{
        u32 nr = btrfs_header_nritems(leaf);
        if (nr == 0)
                return BTRFS_LEAF_DATA_SIZE(root);
        return btrfs_item_offset_nr(leaf, nr - 1);
}

/*
 * extra debugging checks to make sure all the items in a key are
 * well formed and in the proper order
 */
static int check_node(struct btrfs_root *root, struct btrfs_path *path,
                      int level)
{
        struct extent_buffer *parent = NULL;
        struct extent_buffer *node = path->nodes[level];
        struct btrfs_disk_key parent_key;
        struct btrfs_disk_key node_key;
        int parent_slot;
        int slot;
        struct btrfs_key cpukey;
        u32 nritems = btrfs_header_nritems(node);

        if (path->nodes[level + 1])
                parent = path->nodes[level + 1];

        slot = path->slots[level];
        BUG_ON(nritems == 0);
        if (parent) {
                parent_slot = path->slots[level + 1];
                btrfs_node_key(parent, &parent_key, parent_slot);
                btrfs_node_key(node, &node_key, 0);
                BUG_ON(memcmp(&parent_key, &node_key,
                              sizeof(struct btrfs_disk_key)));
                BUG_ON(btrfs_node_blockptr(parent, parent_slot) !=
                       btrfs_header_bytenr(node));
        }
        BUG_ON(nritems > BTRFS_NODEPTRS_PER_BLOCK(root));
        if (slot != 0) {
                btrfs_node_key_to_cpu(node, &cpukey, slot - 1);
                btrfs_node_key(node, &node_key, slot);
                BUG_ON(comp_keys(&node_key, &cpukey) <= 0);
        }
        if (slot < nritems - 1) {
                btrfs_node_key_to_cpu(node, &cpukey, slot + 1);
                btrfs_node_key(node, &node_key, slot);
                BUG_ON(comp_keys(&node_key, &cpukey) >= 0);
        }
        return 0;
}

/*
 * extra checking to make sure all the items in a leaf are
 * well formed and in the proper order
 */
static int check_leaf(struct btrfs_root *root, struct btrfs_path *path,
                      int level)
{
        struct extent_buffer *leaf = path->nodes[level];
        struct extent_buffer *parent = NULL;
        int parent_slot;
        struct btrfs_key cpukey;
        struct btrfs_disk_key parent_key;
        struct btrfs_disk_key leaf_key;
        int slot = path->slots[0];

        u32 nritems = btrfs_header_nritems(leaf);

        if (path->nodes[level + 1])
                parent = path->nodes[level + 1];

        if (nritems == 0)
                return 0;

        if (parent) {
                parent_slot = path->slots[level + 1];
                btrfs_node_key(parent, &parent_key, parent_slot);
                btrfs_item_key(leaf, &leaf_key, 0);

                BUG_ON(memcmp(&parent_key, &leaf_key,
                       sizeof(struct btrfs_disk_key)));
                BUG_ON(btrfs_node_blockptr(parent, parent_slot) !=
                       btrfs_header_bytenr(leaf));
        }
        if (slot != 0 && slot < nritems - 1) {
                btrfs_item_key(leaf, &leaf_key, slot);
                btrfs_item_key_to_cpu(leaf, &cpukey, slot - 1);
                if (comp_keys(&leaf_key, &cpukey) <= 0) {
                        btrfs_print_leaf(root, leaf);
                        printk(KERN_CRIT "slot %d offset bad key\n", slot);
                        BUG_ON(1);
                }
                if (btrfs_item_offset_nr(leaf, slot - 1) !=
                       btrfs_item_end_nr(leaf, slot)) {
                        btrfs_print_leaf(root, leaf);
                        printk(KERN_CRIT "slot %d offset bad\n", slot);
                        BUG_ON(1);
                }
        }
        if (slot < nritems - 1) {
                btrfs_item_key(leaf, &leaf_key, slot);
                btrfs_item_key_to_cpu(leaf, &cpukey, slot + 1);
                BUG_ON(comp_keys(&leaf_key, &cpukey) >= 0);
                if (btrfs_item_offset_nr(leaf, slot) !=
                        btrfs_item_end_nr(leaf, slot + 1)) {
                        btrfs_print_leaf(root, leaf);
                        printk(KERN_CRIT "slot %d offset bad\n", slot);
                        BUG_ON(1);
                }
        }
        BUG_ON(btrfs_item_offset_nr(leaf, 0) +
               btrfs_item_size_nr(leaf, 0) != BTRFS_LEAF_DATA_SIZE(root));
        return 0;
}

static noinline int check_block(struct btrfs_root *root,
                                struct btrfs_path *path, int level)
{
        return 0;
        if (level == 0)
                return check_leaf(root, path, level);
        return check_node(root, path, level);
}

/*
 * search for key in the extent_buffer.  The items start at offset p,
 * and they are item_size apart.  There are 'max' items in p.
 *
 * the slot in the array is returned via slot, and it points to
 * the place where you would insert key if it is not found in
 * the array.
 *
 * slot may point to max if the key is bigger than all of the keys
 */
static noinline int generic_bin_search(struct extent_buffer *eb,
                                       unsigned long p,
                                       int item_size, struct btrfs_key *key,
                                       int max, int *slot)
{
        int low = 0;
        int high = max;
        int mid;
        int ret;
        struct btrfs_disk_key *tmp = NULL;
        struct btrfs_disk_key unaligned;
        unsigned long offset;
        char *map_token = NULL;
        char *kaddr = NULL;
        unsigned long map_start = 0;
        unsigned long map_len = 0;
        int err;

        while (low < high) {
                mid = (low + high) / 2;
                offset = p + mid * item_size;

                if (!map_token || offset < map_start ||
                    (offset + sizeof(struct btrfs_disk_key)) >
                    map_start + map_len) {
                        if (map_token) {
                                unmap_extent_buffer(eb, map_token, KM_USER0);
                                map_token = NULL;
                        }

                        err = map_private_extent_buffer(eb, offset,
                                                sizeof(struct btrfs_disk_key),
                                                &map_token, &kaddr,
                                                &map_start, &map_len, KM_USER0);

                        if (!err) {
                                tmp = (struct btrfs_disk_key *)(kaddr + offset -
                                                        map_start);
                        } else {
                                read_extent_buffer(eb, &unaligned,
                                                   offset, sizeof(unaligned));
                                tmp = &unaligned;
                        }

                } else {
                        tmp = (struct btrfs_disk_key *)(kaddr + offset -
                                                        map_start);
                }
                ret = comp_keys(tmp, key);

                if (ret < 0)
                        low = mid + 1;
                else if (ret > 0)
                        high = mid;
                else {
                        *slot = mid;
                        if (map_token)
                                unmap_extent_buffer(eb, map_token, KM_USER0);
                        return 0;
                }
        }
        *slot = low;
        if (map_token)
                unmap_extent_buffer(eb, map_token, KM_USER0);
        return 1;
}

/*
 * simple bin_search frontend that does the right thing for
 * leaves vs nodes
 */
static int bin_search(struct extent_buffer *eb, struct btrfs_key *key,
                      int level, int *slot)
{
        if (level == 0) {
                return generic_bin_search(eb,
                                          offsetof(struct btrfs_leaf, items),
                                          sizeof(struct btrfs_item),
                                          key, btrfs_header_nritems(eb),
                                          slot);
        } else {
                return generic_bin_search(eb,
                                          offsetof(struct btrfs_node, ptrs),
                                          sizeof(struct btrfs_key_ptr),
                                          key, btrfs_header_nritems(eb),
                                          slot);
        }
        return -1;
}

/* given a node and slot number, this reads the blocks it points to.  The
 * extent buffer is returned with a reference taken (but unlocked).
 * NULL is returned on error.
 */
static noinline struct extent_buffer *read_node_slot(struct btrfs_root *root,
                                   struct extent_buffer *parent, int slot)
{
        int level = btrfs_header_level(parent);
        if (slot < 0)
                return NULL;
        if (slot >= btrfs_header_nritems(parent))
                return NULL;

        BUG_ON(level == 0);

        return read_tree_block(root, btrfs_node_blockptr(parent, slot),
                       btrfs_level_size(root, level - 1),
                       btrfs_node_ptr_generation(parent, slot));
}

/*
 * node level balancing, used to make sure nodes are in proper order for
 * item deletion.  We balance from the top down, so we have to make sure
 * that a deletion won't leave an node completely empty later on.
 */
static noinline int balance_level(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root,
                         struct btrfs_path *path, int level)
{
        struct extent_buffer *right = NULL;
        struct extent_buffer *mid;
        struct extent_buffer *left = NULL;
        struct extent_buffer *parent = NULL;
        int ret = 0;
        int wret;
        int pslot;
        int orig_slot = path->slots[level];
        int err_on_enospc = 0;
        u64 orig_ptr;

        if (level == 0)
                return 0;

        mid = path->nodes[level];
        WARN_ON(!path->locks[level]);
        WARN_ON(btrfs_header_generation(mid) != trans->transid);

        orig_ptr = btrfs_node_blockptr(mid, orig_slot);

        if (level < BTRFS_MAX_LEVEL - 1)
                parent = path->nodes[level + 1];
        pslot = path->slots[level + 1];

        /*
         * deal with the case where there is only one pointer in the root
         * by promoting the node below to a root
         */
        if (!parent) {
                struct extent_buffer *child;

                if (btrfs_header_nritems(mid) != 1)
                        return 0;

                /* promote the child to a root */
                child = read_node_slot(root, mid, 0);
                btrfs_tree_lock(child);
                BUG_ON(!child);
                ret = btrfs_cow_block(trans, root, child, mid, 0, &child, 0);
                BUG_ON(ret);

                spin_lock(&root->node_lock);
                root->node = child;
                spin_unlock(&root->node_lock);

                ret = btrfs_update_extent_ref(trans, root, child->start,
                                              mid->start, child->start,
                                              root->root_key.objectid,
                                              trans->transid, level - 1);
                BUG_ON(ret);

                add_root_to_dirty_list(root);
                btrfs_tree_unlock(child);
                path->locks[level] = 0;
                path->nodes[level] = NULL;
                clean_tree_block(trans, root, mid);
                btrfs_tree_unlock(mid);
                /* once for the path */
                free_extent_buffer(mid);
                ret = btrfs_free_extent(trans, root, mid->start, mid->len,
                                        mid->start, root->root_key.objectid,
                                        btrfs_header_generation(mid),
                                        level, 1);
                /* once for the root ptr */
                free_extent_buffer(mid);
                return ret;
        }
        if (btrfs_header_nritems(mid) >
            BTRFS_NODEPTRS_PER_BLOCK(root) / 4)
                return 0;

        if (btrfs_header_nritems(mid) < 2)
                err_on_enospc = 1;

        left = read_node_slot(root, parent, pslot - 1);
        if (left) {
                btrfs_tree_lock(left);
                wret = btrfs_cow_block(trans, root, left,
                                       parent, pslot - 1, &left, 0);
                if (wret) {
                        ret = wret;
                        goto enospc;
                }
        }
        right = read_node_slot(root, parent, pslot + 1);
        if (right) {
                btrfs_tree_lock(right);
                wret = btrfs_cow_block(trans, root, right,
                                       parent, pslot + 1, &right, 0);
                if (wret) {
                        ret = wret;
                        goto enospc;
                }
        }

        /* first, try to make some room in the middle buffer */
        if (left) {
                orig_slot += btrfs_header_nritems(left);
                wret = push_node_left(trans, root, left, mid, 1);
                if (wret < 0)
                        ret = wret;
                if (btrfs_header_nritems(mid) < 2)
                        err_on_enospc = 1;
        }

        /*
         * then try to empty the right most buffer into the middle
         */
        if (right) {
                wret = push_node_left(trans, root, mid, right, 1);
                if (wret < 0 && wret != -ENOSPC)
                        ret = wret;
                if (btrfs_header_nritems(right) == 0) {
                        u64 bytenr = right->start;
                        u64 generation = btrfs_header_generation(parent);
                        u32 blocksize = right->len;

                        clean_tree_block(trans, root, right);
                        btrfs_tree_unlock(right);
                        free_extent_buffer(right);
                        right = NULL;
                        wret = del_ptr(trans, root, path, level + 1, pslot +
                                       1);
                        if (wret)
                                ret = wret;
                        wret = btrfs_free_extent(trans, root, bytenr,
                                                 blocksize, parent->start,
                                                 btrfs_header_owner(parent),
                                                 generation, level, 1);
                        if (wret)
                                ret = wret;
                } else {
                        struct btrfs_disk_key right_key;
                        btrfs_node_key(right, &right_key, 0);
                        btrfs_set_node_key(parent, &right_key, pslot + 1);
                        btrfs_mark_buffer_dirty(parent);
                }
        }
        if (btrfs_header_nritems(mid) == 1) {
                /*
                 * we're not allowed to leave a node with one item in the
                 * tree during a delete.  A deletion from lower in the tree
                 * could try to delete the only pointer in this node.
                 * So, pull some keys from the left.
                 * There has to be a left pointer at this point because
                 * otherwise we would have pulled some pointers from the
                 * right
                 */
                BUG_ON(!left);
                wret = balance_node_right(trans, root, mid, left);
                if (wret < 0) {
                        ret = wret;
                        goto enospc;
                }
                if (wret == 1) {
                        wret = push_node_left(trans, root, left, mid, 1);
                        if (wret < 0)
                                ret = wret;
                }
                BUG_ON(wret == 1);
        }
        if (btrfs_header_nritems(mid) == 0) {
                /* we've managed to empty the middle node, drop it */
                u64 root_gen = btrfs_header_generation(parent);
                u64 bytenr = mid->start;
                u32 blocksize = mid->len;

                clean_tree_block(trans, root, mid);
                btrfs_tree_unlock(mid);
                free_extent_buffer(mid);
                mid = NULL;
                wret = del_ptr(trans, root, path, level + 1, pslot);
                if (wret)
                        ret = wret;
                wret = btrfs_free_extent(trans, root, bytenr, blocksize,
                                         parent->start,
                                         btrfs_header_owner(parent),
                                         root_gen, level, 1);
                if (wret)
                        ret = wret;
        } else {
                /* update the parent key to reflect our changes */
                struct btrfs_disk_key mid_key;
                btrfs_node_key(mid, &mid_key, 0);
                btrfs_set_node_key(parent, &mid_key, pslot);
                btrfs_mark_buffer_dirty(parent);
        }

        /* update the path */
        if (left) {
                if (btrfs_header_nritems(left) > orig_slot) {
                        extent_buffer_get(left);
                        /* left was locked after cow */
                        path->nodes[level] = left;
                        path->slots[level + 1] -= 1;
                        path->slots[level] = orig_slot;
                        if (mid) {
                                btrfs_tree_unlock(mid);
                                free_extent_buffer(mid);
                        }
                } else {
                        orig_slot -= btrfs_header_nritems(left);
                        path->slots[level] = orig_slot;
                }
        }
        /* double check we haven't messed things up */
        check_block(root, path, level);
        if (orig_ptr !=
            btrfs_node_blockptr(path->nodes[level], path->slots[level]))
                BUG();
enospc:
        if (right) {
                btrfs_tree_unlock(right);
                free_extent_buffer(right);
        }
        if (left) {
                if (path->nodes[level] != left)
                        btrfs_tree_unlock(left);
                free_extent_buffer(left);
        }
        return ret;
}

/* Node balancing for insertion.  Here we only split or push nodes around
 * when they are completely full.  This is also done top down, so we
 * have to be pessimistic.
 */
static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
                                          struct btrfs_root *root,
                                          struct btrfs_path *path, int level)
{
        struct extent_buffer *right = NULL;
        struct extent_buffer *mid;
        struct extent_buffer *left = NULL;
        struct extent_buffer *parent = NULL;
        int ret = 0;
        int wret;
        int pslot;
        int orig_slot = path->slots[level];
        u64 orig_ptr;

        if (level == 0)
                return 1;

        mid = path->nodes[level];
        WARN_ON(btrfs_header_generation(mid) != trans->transid);
        orig_ptr = btrfs_node_blockptr(mid, orig_slot);

        if (level < BTRFS_MAX_LEVEL - 1)
                parent = path->nodes[level + 1];
        pslot = path->slots[level + 1];

        if (!parent)
                return 1;

        left = read_node_slot(root, parent, pslot - 1);

        /* first, try to make some room in the middle buffer */
        if (left) {
                u32 left_nr;

                btrfs_tree_lock(left);
                left_nr = btrfs_header_nritems(left);
                if (left_nr >= BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
                        wret = 1;
                } else {
                        ret = btrfs_cow_block(trans, root, left, parent,
                                              pslot - 1, &left, 0);
                        if (ret)
                                wret = 1;
                        else {
                                wret = push_node_left(trans, root,
                                                      left, mid, 0);
                        }
                }
                if (wret < 0)
                        ret = wret;
                if (wret == 0) {
                        struct btrfs_disk_key disk_key;
                        orig_slot += left_nr;
                        btrfs_node_key(mid, &disk_key, 0);
                        btrfs_set_node_key(parent, &disk_key, pslot);
                        btrfs_mark_buffer_dirty(parent);
                        if (btrfs_header_nritems(left) > orig_slot) {
                                path->nodes[level] = left;
                                path->slots[level + 1] -= 1;
                                path->slots[level] = orig_slot;
                                btrfs_tree_unlock(mid);
                                free_extent_buffer(mid);
                        } else {
                                orig_slot -=
                                        btrfs_header_nritems(left);
                                path->slots[level] = orig_slot;
                                btrfs_tree_unlock(left);
                                free_extent_buffer(left);
                        }
                        return 0;
                }
                btrfs_tree_unlock(left);
                free_extent_buffer(left);
        }
        right = read_node_slot(root, parent, pslot + 1);

        /*
         * then try to empty the right most buffer into the middle
         */
        if (right) {
                u32 right_nr;
                btrfs_tree_lock(right);
                right_nr = btrfs_header_nritems(right);
                if (right_nr >= BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
                        wret = 1;
                } else {
                        ret = btrfs_cow_block(trans, root, right,
                                              parent, pslot + 1,
                                              &right, 0);
                        if (ret)
                                wret = 1;
                        else {
                                wret = balance_node_right(trans, root,
                                                          right, mid);
                        }
                }
                if (wret < 0)
                        ret = wret;
                if (wret == 0) {
                        struct btrfs_disk_key disk_key;

                        btrfs_node_key(right, &disk_key, 0);
                        btrfs_set_node_key(parent, &disk_key, pslot + 1);
                        btrfs_mark_buffer_dirty(parent);

                        if (btrfs_header_nritems(mid) <= orig_slot) {
                                path->nodes[level] = right;
                                path->slots[level + 1] += 1;
                                path->slots[level] = orig_slot -
                                        btrfs_header_nritems(mid);
                                btrfs_tree_unlock(mid);
                                free_extent_buffer(mid);
                        } else {
                                btrfs_tree_unlock(right);
                                free_extent_buffer(right);
                        }
                        return 0;
                }
                btrfs_tree_unlock(right);
                free_extent_buffer(right);
        }
        return 1;
}

/*
 * readahead one full node of leaves, finding things that are close
 * to the block in 'slot', and triggering ra on them.
 */
static noinline void reada_for_search(struct btrfs_root *root,
                                      struct btrfs_path *path,
                                      int level, int slot, u64 objectid)
{
        struct extent_buffer *node;
        struct btrfs_disk_key disk_key;
        u32 nritems;
        u64 search;
        u64 target;
        u64 nread = 0;
        int direction = path->reada;
        struct extent_buffer *eb;
        u32 nr;
        u32 blocksize;
        u32 nscan = 0;

        if (level != 1)
                return;

        if (!path->nodes[level])
                return;

        node = path->nodes[level];

        search = btrfs_node_blockptr(node, slot);
        blocksize = btrfs_level_size(root, level - 1);
        eb = btrfs_find_tree_block(root, search, blocksize);
        if (eb) {
                free_extent_buffer(eb);
                return;
        }

        target = search;

        nritems = btrfs_header_nritems(node);
        nr = slot;
        while (1) {
                if (direction < 0) {
                        if (nr == 0)
                                break;
                        nr--;
                } else if (direction > 0) {
                        nr++;
                        if (nr >= nritems)
                                break;
                }
                if (path->reada < 0 && objectid) {
                        btrfs_node_key(node, &disk_key, nr);
                        if (btrfs_disk_key_objectid(&disk_key) != objectid)
                                break;
                }
                search = btrfs_node_blockptr(node, nr);
                if ((search <= target && target - search <= 65536) ||
                    (search > target && search - target <= 65536)) {
                        readahead_tree_block(root, search, blocksize,
                                     btrfs_node_ptr_generation(node, nr));
                        nread += blocksize;
                }
                nscan++;
                if ((nread > 65536 || nscan > 32))
                        break;
        }
}

/*
 * when we walk down the tree, it is usually safe to unlock the higher layers
 * in the tree.  The exceptions are when our path goes through slot 0, because
 * operations on the tree might require changing key pointers higher up in the
 * tree.
 *
 * callers might also have set path->keep_locks, which tells this code to keep
 * the lock if the path points to the last slot in the block.  This is part of
 * walking through the tree, and selecting the next slot in the higher block.
 *
 * lowest_unlock sets the lowest level in the tree we're allowed to unlock.  so
 * if lowest_unlock is 1, level 0 won't be unlocked
 */
static noinline void unlock_up(struct btrfs_path *path, int level,
                               int lowest_unlock)
{
        int i;
        int skip_level = level;
        int no_skips = 0;
        struct extent_buffer *t;

        for (i = level; i < BTRFS_MAX_LEVEL; i++) {
                if (!path->nodes[i])
                        break;
                if (!path->locks[i])
                        break;
                if (!no_skips && path->slots[i] == 0) {
                        skip_level = i + 1;
                        continue;
                }
                if (!no_skips && path->keep_locks) {
                        u32 nritems;
                        t = path->nodes[i];
                        nritems = btrfs_header_nritems(t);
                        if (nritems < 1 || path->slots[i] >= nritems - 1) {
                                skip_level = i + 1;
                                continue;
                        }
                }
                if (skip_level < i && i >= lowest_unlock)
                        no_skips = 1;

                t = path->nodes[i];
                if (i >= lowest_unlock && i > skip_level && path->locks[i]) {
                        btrfs_tree_unlock(t);
                        path->locks[i] = 0;
                }
        }
}

/*
 * look for key in the tree.  path is filled in with nodes along the way
 * if key is found, we return zero and you can find the item in the leaf
 * level of the path (level 0)
 *
 * If the key isn't found, the path points to the slot where it should
 * be inserted, and 1 is returned.  If there are other errors during the
 * search a negative error number is returned.
 *
 * if ins_len > 0, nodes and leaves will be split as we walk down the
 * tree.  if ins_len < 0, nodes will be merged as we walk down the tree (if
 * possible)
 */
int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_key *key, struct btrfs_path *p, int
                      ins_len, int cow)
{
        struct extent_buffer *b;
        struct extent_buffer *tmp;
        int slot;
        int ret;
        int level;
        int should_reada = p->reada;
        int lowest_unlock = 1;
        int blocksize;
        u8 lowest_level = 0;
        u64 blocknr;
        u64 gen;
        struct btrfs_key prealloc_block;

        lowest_level = p->lowest_level;
        WARN_ON(lowest_level && ins_len > 0);
        WARN_ON(p->nodes[0] != NULL);

        if (ins_len < 0)
                lowest_unlock = 2;

        prealloc_block.objectid = 0;

again:
        if (p->skip_locking)
                b = btrfs_root_node(root);
        else
                b = btrfs_lock_root_node(root);

        while (b) {
                level = btrfs_header_level(b);

                /*
                 * setup the path here so we can release it under lock
                 * contention with the cow code
                 */
                p->nodes[level] = b;
                if (!p->skip_locking)
                        p->locks[level] = 1;

                if (cow) {
                        int wret;

                        /* is a cow on this block not required */
                        spin_lock(&root->fs_info->hash_lock);
                        if (btrfs_header_generation(b) == trans->transid &&
                            btrfs_header_owner(b) == root->root_key.objectid &&
                            !btrfs_header_flag(b, BTRFS_HEADER_FLAG_WRITTEN)) {
                                spin_unlock(&root->fs_info->hash_lock);
                                goto cow_done;
                        }
                        spin_unlock(&root->fs_info->hash_lock);

                        /* ok, we have to cow, is our old prealloc the right
                         * size?
                         */
                        if (prealloc_block.objectid &&
                            prealloc_block.offset != b->len) {
                                btrfs_free_reserved_extent(root,
                                           prealloc_block.objectid,
                                           prealloc_block.offset);
                                prealloc_block.objectid = 0;
                        }

                        /*
                         * for higher level blocks, try not to allocate blocks
                         * with the block and the parent locks held.
                         */
                        if (level > 1 && !prealloc_block.objectid &&
                            btrfs_path_lock_waiting(p, level)) {
                                u32 size = b->len;
                                u64 hint = b->start;

                                btrfs_release_path(root, p);
                                ret = btrfs_reserve_extent(trans, root,
                                                           size, size, 0,
                                                           hint, (u64)-1,
                                                           &prealloc_block, 0);
                                BUG_ON(ret);
                                goto again;
                        }

                        wret = btrfs_cow_block(trans, root, b,
                                               p->nodes[level + 1],
                                               p->slots[level + 1],
                                               &b, prealloc_block.objectid);
                        prealloc_block.objectid = 0;
                        if (wret) {
                                free_extent_buffer(b);
                                ret = wret;
                                goto done;
                        }
                }
cow_done:
                BUG_ON(!cow && ins_len);
                if (level != btrfs_header_level(b))
                        WARN_ON(1);
                level = btrfs_header_level(b);

                p->nodes[level] = b;
                if (!p->skip_locking)
                        p->locks[level] = 1;

                ret = check_block(root, p, level);
                if (ret) {
                        ret = -1;
                        goto done;
                }

                ret = bin_search(b, key, level, &slot);
                if (level != 0) {
                        if (ret && slot > 0)
                                slot -= 1;
                        p->slots[level] = slot;
                        if ((p->search_for_split || ins_len > 0) &&
                            btrfs_header_nritems(b) >=
                            BTRFS_NODEPTRS_PER_BLOCK(root) - 3) {
                                int sret = split_node(trans, root, p, level);
                                BUG_ON(sret > 0);
                                if (sret) {
                                        ret = sret;
                                        goto done;
                                }
                                b = p->nodes[level];
                                slot = p->slots[level];
                        } else if (ins_len < 0) {
                                int sret = balance_level(trans, root, p,
                                                         level);
                                if (sret) {
                                        ret = sret;
                                        goto done;
                                }
                                b = p->nodes[level];
                                if (!b) {
                                        btrfs_release_path(NULL, p);
                                        goto again;
                                }
                                slot = p->slots[level];
                                BUG_ON(btrfs_header_nritems(b) == 1);
                        }
                        unlock_up(p, level, lowest_unlock);

                        /* this is only true while dropping a snapshot */
                        if (level == lowest_level) {
                                ret = 0;
                                goto done;
                        }

                        blocknr = btrfs_node_blockptr(b, slot);
                        gen = btrfs_node_ptr_generation(b, slot);
                        blocksize = btrfs_level_size(root, level - 1);

                        tmp = btrfs_find_tree_block(root, blocknr, blocksize);
                        if (tmp && btrfs_buffer_uptodate(tmp, gen)) {
                                b = tmp;
                        } else {
                                /*
                                 * reduce lock contention at high levels
                                 * of the btree by dropping locks before
                                 * we read.
                                 */
                                if (level > 1) {
                                        btrfs_release_path(NULL, p);
                                        if (tmp)
                                                free_extent_buffer(tmp);
                                        if (should_reada)
                                                reada_for_search(root, p,
                                                                 level, slot,
                                                                 key->objectid);

                                        tmp = read_tree_block(root, blocknr,
                                                         blocksize, gen);
                                        if (tmp)
                                                free_extent_buffer(tmp);
                                        goto again;
                                } else {
                                        if (tmp)
                                                free_extent_buffer(tmp);
                                        if (should_reada)
                                                reada_for_search(root, p,
                                                                 level, slot,
                                                                 key->objectid);
                                        b = read_node_slot(root, b, slot);
                                }
                        }
                        if (!p->skip_locking)
                                btrfs_tree_lock(b);
                } else {
                        p->slots[level] = slot;
                        if (ins_len > 0 &&
                            btrfs_leaf_free_space(root, b) < ins_len) {
                                int sret = split_leaf(trans, root, key,
                                                      p, ins_len, ret == 0);
                                BUG_ON(sret > 0);
                                if (sret) {
                                        ret = sret;
                                        goto done;
                                }
                        }
                        if (!p->search_for_split)
                                unlock_up(p, level, lowest_unlock);
                        goto done;
                }
        }
        ret = 1;
done:
        if (prealloc_block.objectid) {
                btrfs_free_reserved_extent(root,
                           prealloc_block.objectid,
                           prealloc_block.offset);
        }

        return ret;
}

int btrfs_merge_path(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     struct btrfs_key *node_keys,
                     u64 *nodes, int lowest_level)
{
        struct extent_buffer *eb;
        struct extent_buffer *parent;
        struct btrfs_key key;
        u64 bytenr;
        u64 generation;
        u32 blocksize;
        int level;
        int slot;
        int key_match;
        int ret;

        eb = btrfs_lock_root_node(root);
        ret = btrfs_cow_block(trans, root, eb, NULL, 0, &eb, 0);
        BUG_ON(ret);

        parent = eb;
        while (1) {
                level = btrfs_header_level(parent);
                if (level == 0 || level <= lowest_level)
                        break;

                ret = bin_search(parent, &node_keys[lowest_level], level,
                                 &slot);
                if (ret && slot > 0)
                        slot--;

                bytenr = btrfs_node_blockptr(parent, slot);
                if (nodes[level - 1] == bytenr)
                        break;

                blocksize = btrfs_level_size(root, level - 1);
                generation = btrfs_node_ptr_generation(parent, slot);
                btrfs_node_key_to_cpu(eb, &key, slot);
                key_match = !memcmp(&key, &node_keys[level - 1], sizeof(key));

                if (generation == trans->transid) {
                        eb = read_tree_block(root, bytenr, blocksize,
                                             generation);
                        btrfs_tree_lock(eb);
                }

                /*
                 * if node keys match and node pointer hasn't been modified
                 * in the running transaction, we can merge the path. for
                 * blocks owened by reloc trees, the node pointer check is
                 * skipped, this is because these blocks are fully controlled
                 * by the space balance code, no one else can modify them.
                 */
                if (!nodes[level - 1] || !key_match ||
                    (generation == trans->transid &&
                     btrfs_header_owner(eb) != BTRFS_TREE_RELOC_OBJECTID)) {
                        if (level == 1 || level == lowest_level + 1) {
                                if (generation == trans->transid) {
                                        btrfs_tree_unlock(eb);
                                        free_extent_buffer(eb);
                                }
                                break;
                        }

                        if (generation != trans->transid) {
                                eb = read_tree_block(root, bytenr, blocksize,
                                                generation);
                                btrfs_tree_lock(eb);
                        }

                        ret = btrfs_cow_block(trans, root, eb, parent, slot,
                                              &eb, 0);
                        BUG_ON(ret);

                        if (root->root_key.objectid ==
                            BTRFS_TREE_RELOC_OBJECTID) {
                                if (!nodes[level - 1]) {
                                        nodes[level - 1] = eb->start;
                                        memcpy(&node_keys[level - 1], &key,
                                               sizeof(node_keys[0]));
                                } else {
                                        WARN_ON(1);
                                }
                        }

                        btrfs_tree_unlock(parent);
                        free_extent_buffer(parent);
                        parent = eb;
                        continue;
                }

                btrfs_set_node_blockptr(parent, slot, nodes[level - 1]);
                btrfs_set_node_ptr_generation(parent, slot, trans->transid);
                btrfs_mark_buffer_dirty(parent);

                ret = btrfs_inc_extent_ref(trans, root,
                                        nodes[level - 1],
                                        blocksize, parent->start,
                                        btrfs_header_owner(parent),
                                        btrfs_header_generation(parent),
                                        level - 1);
                BUG_ON(ret);

                /*
                 * If the block was created in the running transaction,
                 * it's possible this is the last reference to it, so we
                 * should drop the subtree.
                 */
                if (generation == trans->transid) {
                        ret = btrfs_drop_subtree(trans, root, eb, parent);
                        BUG_ON(ret);
                        btrfs_tree_unlock(eb);
                        free_extent_buffer(eb);
                } else {
                        ret = btrfs_free_extent(trans, root, bytenr,
                                        blocksize, parent->start,
                                        btrfs_header_owner(parent),
                                        btrfs_header_generation(parent),
                                        level - 1, 1);
                        BUG_ON(ret);
                }
                break;
        }
        btrfs_tree_unlock(parent);
        free_extent_buffer(parent);
        return 0;
}

/*
 * adjust the pointers going up the tree, starting at level
 * making sure the right key of each node is points to 'key'.
 * This is used after shifting pointers to the left, so it stops
 * fixing up pointers when a given leaf/node is not in slot 0 of the
 * higher levels
 *
 * If this fails to write a tree block, it returns -1, but continues
 * fixing up the blocks in ram so the tree is consistent.
 */
static int fixup_low_keys(struct btrfs_trans_handle *trans,
                          struct btrfs_root *root, struct btrfs_path *path,
                          struct btrfs_disk_key *key, int level)
{
        int i;
        int ret = 0;
        struct extent_buffer *t;

        for (i = level; i < BTRFS_MAX_LEVEL; i++) {
                int tslot = path->slots[i];
                if (!path->nodes[i])
                        break;
                t = path->nodes[i];
                btrfs_set_node_key(t, key, tslot);
                btrfs_mark_buffer_dirty(path->nodes[i]);
                if (tslot != 0)
                        break;
        }
        return ret;
}

/*
 * update item key.
 *
 * This function isn't completely safe. It's the caller's responsibility
 * that the new key won't break the order
 */
int btrfs_set_item_key_safe(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root, struct btrfs_path *path,
                            struct btrfs_key *new_key)
{
        struct btrfs_disk_key disk_key;
        struct extent_buffer *eb;
        int slot;

        eb = path->nodes[0];
        slot = path->slots[0];
        if (slot > 0) {
                btrfs_item_key(eb, &disk_key, slot - 1);
                if (comp_keys(&disk_key, new_key) >= 0)
                        return -1;
        }
        if (slot < btrfs_header_nritems(eb) - 1) {
                btrfs_item_key(eb, &disk_key, slot + 1);
                if (comp_keys(&disk_key, new_key) <= 0)
                        return -1;
        }

        btrfs_cpu_key_to_disk(&disk_key, new_key);
        btrfs_set_item_key(eb, &disk_key, slot);
        btrfs_mark_buffer_dirty(eb);
        if (slot == 0)
                fixup_low_keys(trans, root, path, &disk_key, 1);
        return 0;
}

/*
 * try to push data from one node into the next node left in the
 * tree.
 *
 * returns 0 if some ptrs were pushed left, < 0 if there was some horrible
 * error, and > 0 if there was no room in the left hand block.
 */
static int push_node_left(struct btrfs_trans_handle *trans,
                          struct btrfs_root *root, struct extent_buffer *dst,
                          struct extent_buffer *src, int empty)
{
        int push_items = 0;
        int src_nritems;
        int dst_nritems;
        int ret = 0;

        src_nritems = btrfs_header_nritems(src);
        dst_nritems = btrfs_header_nritems(dst);
        push_items = BTRFS_NODEPTRS_PER_BLOCK(root) - dst_nritems;
        WARN_ON(btrfs_header_generation(src) != trans->transid);
        WARN_ON(btrfs_header_generation(dst) != trans->transid);

        if (!empty && src_nritems <= 8)
                return 1;

        if (push_items <= 0)
                return 1;

        if (empty) {
                push_items = min(src_nritems, push_items);
                if (push_items < src_nritems) {
                        /* leave at least 8 pointers in the node if
                         * we aren't going to empty it
                         */
                        if (src_nritems - push_items < 8) {
                                if (push_items <= 8)
                                        return 1;
                                push_items -= 8;
                        }
                }
        } else
                push_items = min(src_nritems - 8, push_items);

        copy_extent_buffer(dst, src,
                           btrfs_node_key_ptr_offset(dst_nritems),
                           btrfs_node_key_ptr_offset(0),
                           push_items * sizeof(struct btrfs_key_ptr));

        if (push_items < src_nritems) {
                memmove_extent_buffer(src, btrfs_node_key_ptr_offset(0),
                                      btrfs_node_key_ptr_offset(push_items),
                                      (src_nritems - push_items) *
                                      sizeof(struct btrfs_key_ptr));
        }
        btrfs_set_header_nritems(src, src_nritems - push_items);
        btrfs_set_header_nritems(dst, dst_nritems + push_items);
        btrfs_mark_buffer_dirty(src);
        btrfs_mark_buffer_dirty(dst);

        ret = btrfs_update_ref(trans, root, src, dst, dst_nritems, push_items);
        BUG_ON(ret);

        return ret;
}

/*
 * try to push data from one node into the next node right in the
 * tree.
 *
 * returns 0 if some ptrs were pushed, < 0 if there was some horrible
 * error, and > 0 if there was no room in the right hand block.
 *
 * this will  only push up to 1/2 the contents of the left node over
 */
static int balance_node_right(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root,
                              struct extent_buffer *dst,
                              struct extent_buffer *src)
{
        int push_items = 0;
        int max_push;
        int src_nritems;
        int dst_nritems;
        int ret = 0;

        WARN_ON(btrfs_header_generation(src) != trans->transid);
        WARN_ON(btrfs_header_generation(dst) != trans->transid);

        src_nritems = btrfs_header_nritems(src);
        dst_nritems = btrfs_header_nritems(dst);
        push_items = BTRFS_NODEPTRS_PER_BLOCK(root) - dst_nritems;
        if (push_items <= 0)
                return 1;

        if (src_nritems < 4)
                return 1;

        max_push = src_nritems / 2 + 1;
        /* don't try to empty the node */
        if (max_push >= src_nritems)
                return 1;

        if (max_push < push_items)
                push_items = max_push;

        memmove_extent_buffer(dst, btrfs_node_key_ptr_offset(push_items),
                                      btrfs_node_key_ptr_offset(0),
                                      (dst_nritems) *
                                      sizeof(struct btrfs_key_ptr));

        copy_extent_buffer(dst, src,
                           btrfs_node_key_ptr_offset(0),
                           btrfs_node_key_ptr_offset(src_nritems - push_items),
                           push_items * sizeof(struct btrfs_key_ptr));

        btrfs_set_header_nritems(src, src_nritems - push_items);
        btrfs_set_header_nritems(dst, dst_nritems + push_items);

        btrfs_mark_buffer_dirty(src);
        btrfs_mark_buffer_dirty(dst);

        ret = btrfs_update_ref(trans, root, src, dst, 0, push_items);
        BUG_ON(ret);

        return ret;
}

/*
 * helper function to insert a new root level in the tree.
 * A new node is allocated, and a single item is inserted to
 * point to the existing root
 *
 * returns zero on success or < 0 on failure.
 */
static noinline int insert_new_root(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct btrfs_path *path, int level)
{
        u64 lower_gen;
        struct extent_buffer *lower;
        struct extent_buffer *c;
        struct extent_buffer *old;
        struct btrfs_disk_key lower_key;
        int ret;

        BUG_ON(path->nodes[level]);
        BUG_ON(path->nodes[level-1] != root->node);

        lower = path->nodes[level-1];
        if (level == 1)
                btrfs_item_key(lower, &lower_key, 0);
        else
                btrfs_node_key(lower, &lower_key, 0);

        c = btrfs_alloc_free_block(trans, root, root->nodesize, 0,
                                   root->root_key.objectid, trans->transid,
                                   level, root->node->start, 0);
        if (IS_ERR(c))
                return PTR_ERR(c);

        memset_extent_buffer(c, 0, 0, root->nodesize);
        btrfs_set_header_nritems(c, 1);
        btrfs_set_header_level(c, level);
        btrfs_set_header_bytenr(c, c->start);
        btrfs_set_header_generation(c, trans->transid);
        btrfs_set_header_owner(c, root->root_key.objectid);

        write_extent_buffer(c, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(c),
                            BTRFS_FSID_SIZE);

        write_extent_buffer(c, root->fs_info->chunk_tree_uuid,
                            (unsigned long)btrfs_header_chunk_tree_uuid(c),
                            BTRFS_UUID_SIZE);

        btrfs_set_node_key(c, &lower_key, 0);
        btrfs_set_node_blockptr(c, 0, lower->start);
        lower_gen = btrfs_header_generation(lower);
        WARN_ON(lower_gen != trans->transid);

        btrfs_set_node_ptr_generation(c, 0, lower_gen);

        btrfs_mark_buffer_dirty(c);

        spin_lock(&root->node_lock);
        old = root->node;
        root->node = c;
        spin_unlock(&root->node_lock);

        ret = btrfs_update_extent_ref(trans, root, lower->start,
                                      lower->start, c->start,
                                      root->root_key.objectid,
                                      trans->transid, level - 1);
        BUG_ON(ret);

        /* the super has an extra ref to root->node */
        free_extent_buffer(old);

        add_root_to_dirty_list(root);
        extent_buffer_get(c);
        path->nodes[level] = c;
        path->locks[level] = 1;
        path->slots[level] = 0;
        return 0;
}

/*
 * worker function to insert a single pointer in a node.
 * the node should have enough room for the pointer already
 *
 * slot and level indicate where you want the key to go, and
 * blocknr is the block the key points to.
 *
 * returns zero on success and < 0 on any error
 */
static int insert_ptr(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_path *path, struct btrfs_disk_key
                      *key, u64 bytenr, int slot, int level)
{
        struct extent_buffer *lower;
        int nritems;

        BUG_ON(!path->nodes[level]);
        lower = path->nodes[level];
        nritems = btrfs_header_nritems(lower);
        if (slot > nritems)
                BUG();
        if (nritems == BTRFS_NODEPTRS_PER_BLOCK(root))
                BUG();
        if (slot != nritems) {
                memmove_extent_buffer(lower,
                              btrfs_node_key_ptr_offset(slot + 1),
                              btrfs_node_key_ptr_offset(slot),
                              (nritems - slot) * sizeof(struct btrfs_key_ptr));
        }
        btrfs_set_node_key(lower, key, slot);
        btrfs_set_node_blockptr(lower, slot, bytenr);
        WARN_ON(trans->transid == 0);
        btrfs_set_node_ptr_generation(lower, slot, trans->transid);
        btrfs_set_header_nritems(lower, nritems + 1);
        btrfs_mark_buffer_dirty(lower);
        return 0;
}

/*
 * split the node at the specified level in path in two.
 * The path is corrected to point to the appropriate node after the split
 *
 * Before splitting this tries to make some room in the node by pushing
 * left and right, if either one works, it returns right away.
 *
 * returns 0 on success and < 0 on failure
 */
static noinline int split_node(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               struct btrfs_path *path, int level)
{
        struct extent_buffer *c;
        struct extent_buffer *split;
        struct btrfs_disk_key disk_key;
        int mid;
        int ret;
        int wret;
        u32 c_nritems;

        c = path->nodes[level];
        WARN_ON(btrfs_header_generation(c) != trans->transid);
        if (c == root->node) {
                /* trying to split the root, lets make a new one */
                ret = insert_new_root(trans, root, path, level + 1);
                if (ret)
                        return ret;
        } else {
                ret = push_nodes_for_insert(trans, root, path, level);
                c = path->nodes[level];
                if (!ret && btrfs_header_nritems(c) <
                    BTRFS_NODEPTRS_PER_BLOCK(root) - 3)
                        return 0;
                if (ret < 0)
                        return ret;
        }

        c_nritems = btrfs_header_nritems(c);

        split = btrfs_alloc_free_block(trans, root, root->nodesize,
                                        path->nodes[level + 1]->start,
                                        root->root_key.objectid,
                                        trans->transid, level, c->start, 0);
        if (IS_ERR(split))
                return PTR_ERR(split);

        btrfs_set_header_flags(split, btrfs_header_flags(c));
        btrfs_set_header_level(split, btrfs_header_level(c));
        btrfs_set_header_bytenr(split, split->start);
        btrfs_set_header_generation(split, trans->transid);
        btrfs_set_header_owner(split, root->root_key.objectid);
        btrfs_set_header_flags(split, 0);
        write_extent_buffer(split, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(split),
                            BTRFS_FSID_SIZE);
        write_extent_buffer(split, root->fs_info->chunk_tree_uuid,
                            (unsigned long)btrfs_header_chunk_tree_uuid(split),
                            BTRFS_UUID_SIZE);

        mid = (c_nritems + 1) / 2;

        copy_extent_buffer(split, c,
                           btrfs_node_key_ptr_offset(0),
                           btrfs_node_key_ptr_offset(mid),
                           (c_nritems - mid) * sizeof(struct btrfs_key_ptr));
        btrfs_set_header_nritems(split, c_nritems - mid);
        btrfs_set_header_nritems(c, mid);
        ret = 0;

        btrfs_mark_buffer_dirty(c);
        btrfs_mark_buffer_dirty(split);

        btrfs_node_key(split, &disk_key, 0);
        wret = insert_ptr(trans, root, path, &disk_key, split->start,
                          path->slots[level + 1] + 1,
                          level + 1);
        if (wret)
                ret = wret;

        ret = btrfs_update_ref(trans, root, c, split, 0, c_nritems - mid);
        BUG_ON(ret);

        if (path->slots[level] >= mid) {
                path->slots[level] -= mid;
                btrfs_tree_unlock(c);
                free_extent_buffer(c);
                path->nodes[level] = split;
                path->slots[level + 1] += 1;
        } else {
                btrfs_tree_unlock(split);
                free_extent_buffer(split);
        }
        return ret;
}

/*
 * how many bytes are required to store the items in a leaf.  start
 * and nr indicate which items in the leaf to check.  This totals up the
 * space used both by the item structs and the item data
 */
static int leaf_space_used(struct extent_buffer *l, int start, int nr)
{
        int data_len;
        int nritems = btrfs_header_nritems(l);
        int end = min(nritems, start + nr) - 1;

        if (!nr)
                return 0;
        data_len = btrfs_item_end_nr(l, start);
        data_len = data_len - btrfs_item_offset_nr(l, end);
        data_len += sizeof(struct btrfs_item) * nr;
        WARN_ON(data_len < 0);
        return data_len;
}

/*
 * The space between the end of the leaf items and
 * the start of the leaf data.  IOW, how much room
 * the leaf has left for both items and data
 */
noinline int btrfs_leaf_free_space(struct btrfs_root *root,
                                   struct extent_buffer *leaf)
{
        int nritems = btrfs_header_nritems(leaf);
        int ret;
        ret = BTRFS_LEAF_DATA_SIZE(root) - leaf_space_used(leaf, 0, nritems);
        if (ret < 0) {
                printk(KERN_CRIT "leaf free space ret %d, leaf data size %lu, "
                       "used %d nritems %d\n",
                       ret, (unsigned long) BTRFS_LEAF_DATA_SIZE(root),
                       leaf_space_used(leaf, 0, nritems), nritems);
        }
        return ret;
}

/*
 * push some data in the path leaf to the right, trying to free up at
 * least data_size bytes.  returns zero if the push worked, nonzero otherwise
 *
 * returns 1 if the push failed because the other node didn't have enough
 * room, 0 if everything worked out and < 0 if there were major errors.
 */
static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
                           *root, struct btrfs_path *path, int data_size,
                           int empty)
{
        struct extent_buffer *left = path->nodes[0];
        struct extent_buffer *right;
        struct extent_buffer *upper;
        struct btrfs_disk_key disk_key;
        int slot;
        u32 i;
        int free_space;
        int push_space = 0;
        int push_items = 0;
        struct btrfs_item *item;
        u32 left_nritems;
        u32 nr;
        u32 right_nritems;
        u32 data_end;
        u32 this_item_size;
        int ret;

        slot = path->slots[1];
        if (!path->nodes[1])
                return 1;

        upper = path->nodes[1];
        if (slot >= btrfs_header_nritems(upper) - 1)
                return 1;

        WARN_ON(!btrfs_tree_locked(path->nodes[1]));

        right = read_node_slot(root, upper, slot + 1);
        btrfs_tree_lock(right);
        free_space = btrfs_leaf_free_space(root, right);
        if (free_space < data_size)
                goto out_unlock;

        /* cow and double check */
        ret = btrfs_cow_block(trans, root, right, upper,
                              slot + 1, &right, 0);
        if (ret)
                goto out_unlock;

        free_space = btrfs_leaf_free_space(root, right);
        if (free_space < data_size)
                goto out_unlock;

        left_nritems = btrfs_header_nritems(left);
        if (left_nritems == 0)
                goto out_unlock;

        if (empty)
                nr = 0;
        else
                nr = 1;

        if (path->slots[0] >= left_nritems)
                push_space += data_size;

        i = left_nritems - 1;
        while (i >= nr) {
                item = btrfs_item_nr(left, i);

                if (!empty && push_items > 0) {
                        if (path->slots[0] > i)
                                break;
                        if (path->slots[0] == i) {
                                int space = btrfs_leaf_free_space(root, left);
                                if (space + push_space * 2 > free_space)
                                        break;
                        }
                }

                if (path->slots[0] == i)
                        push_space += data_size;

                if (!left->map_token) {
                        map_extent_buffer(left, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &left->map_token, &left->kaddr,
                                        &left->map_start, &left->map_len,
                                        KM_USER1);
                }

                this_item_size = btrfs_item_size(left, item);
                if (this_item_size + sizeof(*item) + push_space > free_space)
                        break;

                push_items++;
                push_space += this_item_size + sizeof(*item);
                if (i == 0)
                        break;
                i--;
        }
        if (left->map_token) {
                unmap_extent_buffer(left, left->map_token, KM_USER1);
                left->map_token = NULL;
        }

        if (push_items == 0)
                goto out_unlock;

        if (!empty && push_items == left_nritems)
                WARN_ON(1);

        /* push left to right */
        right_nritems = btrfs_header_nritems(right);

        push_space = btrfs_item_end_nr(left, left_nritems - push_items);
        push_space -= leaf_data_end(root, left);

        /* make room in the right data area */
        data_end = leaf_data_end(root, right);
        memmove_extent_buffer(right,
                              btrfs_leaf_data(right) + data_end - push_space,
                              btrfs_leaf_data(right) + data_end,
                              BTRFS_LEAF_DATA_SIZE(root) - data_end);

        /* copy from the left data area */
        copy_extent_buffer(right, left, btrfs_leaf_data(right) +
                     BTRFS_LEAF_DATA_SIZE(root) - push_space,
                     btrfs_leaf_data(left) + leaf_data_end(root, left),
                     push_space);

        memmove_extent_buffer(right, btrfs_item_nr_offset(push_items),
                              btrfs_item_nr_offset(0),
                              right_nritems * sizeof(struct btrfs_item));

        /* copy the items from left to right */
        copy_extent_buffer(right, left, btrfs_item_nr_offset(0),
                   btrfs_item_nr_offset(left_nritems - push_items),
                   push_items * sizeof(struct btrfs_item));

        /* update the item pointers */
        right_nritems += push_items;
        btrfs_set_header_nritems(right, right_nritems);
        push_space = BTRFS_LEAF_DATA_SIZE(root);
        for (i = 0; i < right_nritems; i++) {
                item = btrfs_item_nr(right, i);
                if (!right->map_token) {
                        map_extent_buffer(right, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &right->map_token, &right->kaddr,
                                        &right->map_start, &right->map_len,
                                        KM_USER1);
                }
                push_space -= btrfs_item_size(right, item);
                btrfs_set_item_offset(right, item, push_space);
        }

        if (right->map_token) {
                unmap_extent_buffer(right, right->map_token, KM_USER1);
                right->map_token = NULL;
        }
        left_nritems -= push_items;
        btrfs_set_header_nritems(left, left_nritems);

        if (left_nritems)
                btrfs_mark_buffer_dirty(left);
        btrfs_mark_buffer_dirty(right);

        ret = btrfs_update_ref(trans, root, left, right, 0, push_items);
        BUG_ON(ret);

        btrfs_item_key(right, &disk_key, 0);
        btrfs_set_node_key(upper, &disk_key, slot + 1);
        btrfs_mark_buffer_dirty(upper);

        /* then fixup the leaf pointer in the path */
        if (path->slots[0] >= left_nritems) {
                path->slots[0] -= left_nritems;
                if (btrfs_header_nritems(path->nodes[0]) == 0)
                        clean_tree_block(trans, root, path->nodes[0]);
                btrfs_tree_unlock(path->nodes[0]);
                free_extent_buffer(path->nodes[0]);
                path->nodes[0] = right;
                path->slots[1] += 1;
        } else {
                btrfs_tree_unlock(right);
                free_extent_buffer(right);
        }
        return 0;

out_unlock:
        btrfs_tree_unlock(right);
        free_extent_buffer(right);
        return 1;
}

/*
 * push some data in the path leaf to the left, trying to free up at
 * least data_size bytes.  returns zero if the push worked, nonzero otherwise
 */
static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
                          *root, struct btrfs_path *path, int data_size,
                          int empty)
{
        struct btrfs_disk_key disk_key;
        struct extent_buffer *right = path->nodes[0];
        struct extent_buffer *left;
        int slot;
        int i;
        int free_space;
        int push_space = 0;
        int push_items = 0;
        struct btrfs_item *item;
        u32 old_left_nritems;
        u32 right_nritems;
        u32 nr;
        int ret = 0;
        int wret;
        u32 this_item_size;
        u32 old_left_item_size;

        slot = path->slots[1];
        if (slot == 0)
                return 1;
        if (!path->nodes[1])
                return 1;

        right_nritems = btrfs_header_nritems(right);
        if (right_nritems == 0)
                return 1;

        WARN_ON(!btrfs_tree_locked(path->nodes[1]));

        left = read_node_slot(root, path->nodes[1], slot - 1);
        btrfs_tree_lock(left);
        free_space = btrfs_leaf_free_space(root, left);
        if (free_space < data_size) {
                ret = 1;
                goto out;
        }

        /* cow and double check */
        ret = btrfs_cow_block(trans, root, left,
                              path->nodes[1], slot - 1, &left, 0);
        if (ret) {
                /* we hit -ENOSPC, but it isn't fatal here */
                ret = 1;
                goto out;
        }

        free_space = btrfs_leaf_free_space(root, left);
        if (free_space < data_size) {
                ret = 1;
                goto out;
        }

        if (empty)
                nr = right_nritems;
        else
                nr = right_nritems - 1;

        for (i = 0; i < nr; i++) {
                item = btrfs_item_nr(right, i);
                if (!right->map_token) {
                        map_extent_buffer(right, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &right->map_token, &right->kaddr,
                                        &right->map_start, &right->map_len,
                                        KM_USER1);
                }

                if (!empty && push_items > 0) {
                        if (path->slots[0] < i)
                                break;
                        if (path->slots[0] == i) {
                                int space = btrfs_leaf_free_space(root, right);
                                if (space + push_space * 2 > free_space)
                                        break;
                        }
                }

                if (path->slots[0] == i)
                        push_space += data_size;

                this_item_size = btrfs_item_size(right, item);
                if (this_item_size + sizeof(*item) + push_space > free_space)
                        break;

                push_items++;
                push_space += this_item_size + sizeof(*item);
        }

        if (right->map_token) {
                unmap_extent_buffer(right, right->map_token, KM_USER1);
                right->map_token = NULL;
        }

        if (push_items == 0) {
                ret = 1;
                goto out;
        }
        if (!empty && push_items == btrfs_header_nritems(right))
                WARN_ON(1);

        /* push data from right to left */
        copy_extent_buffer(left, right,
                           btrfs_item_nr_offset(btrfs_header_nritems(left)),
                           btrfs_item_nr_offset(0),
                           push_items * sizeof(struct btrfs_item));

        push_space = BTRFS_LEAF_DATA_SIZE(root) -
                     btrfs_item_offset_nr(right, push_items - 1);

        copy_extent_buffer(left, right, btrfs_leaf_data(left) +
                     leaf_data_end(root, left) - push_space,
                     btrfs_leaf_data(right) +
                     btrfs_item_offset_nr(right, push_items - 1),
                     push_space);
        old_left_nritems = btrfs_header_nritems(left);
        BUG_ON(old_left_nritems <= 0);

        old_left_item_size = btrfs_item_offset_nr(left, old_left_nritems - 1);
        for (i = old_left_nritems; i < old_left_nritems + push_items; i++) {
                u32 ioff;

                item = btrfs_item_nr(left, i);
                if (!left->map_token) {
                        map_extent_buffer(left, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &left->map_token, &left->kaddr,
                                        &left->map_start, &left->map_len,
                                        KM_USER1);
                }

                ioff = btrfs_item_offset(left, item);
                btrfs_set_item_offset(left, item,
                      ioff - (BTRFS_LEAF_DATA_SIZE(root) - old_left_item_size));
        }
        btrfs_set_header_nritems(left, old_left_nritems + push_items);
        if (left->map_token) {
                unmap_extent_buffer(left, left->map_token, KM_USER1);
                left->map_token = NULL;
        }

        /* fixup right node */
        if (push_items > right_nritems) {
                printk(KERN_CRIT "push items %d nr %u\n", push_items,
                       right_nritems);
                WARN_ON(1);
        }

        if (push_items < right_nritems) {
                push_space = btrfs_item_offset_nr(right, push_items - 1) -
                                                  leaf_data_end(root, right);
                memmove_extent_buffer(right, btrfs_leaf_data(right) +
                                      BTRFS_LEAF_DATA_SIZE(root) - push_space,
                                      btrfs_leaf_data(right) +
                                      leaf_data_end(root, right), push_space);

                memmove_extent_buffer(right, btrfs_item_nr_offset(0),
                              btrfs_item_nr_offset(push_items),
                             (btrfs_header_nritems(right) - push_items) *
                             sizeof(struct btrfs_item));
        }
        right_nritems -= push_items;
        btrfs_set_header_nritems(right, right_nritems);
        push_space = BTRFS_LEAF_DATA_SIZE(root);
        for (i = 0; i < right_nritems; i++) {
                item = btrfs_item_nr(right, i);

                if (!right->map_token) {
                        map_extent_buffer(right, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &right->map_token, &right->kaddr,
                                        &right->map_start, &right->map_len,
                                        KM_USER1);
                }

                push_space = push_space - btrfs_item_size(right, item);
                btrfs_set_item_offset(right, item, push_space);
        }
        if (right->map_token) {
                unmap_extent_buffer(right, right->map_token, KM_USER1);
                right->map_token = NULL;
        }

        btrfs_mark_buffer_dirty(left);
        if (right_nritems)
                btrfs_mark_buffer_dirty(right);

        ret = btrfs_update_ref(trans, root, right, left,
                               old_left_nritems, push_items);
        BUG_ON(ret);

        btrfs_item_key(right, &disk_key, 0);
        wret = fixup_low_keys(trans, root, path, &disk_key, 1);
        if (wret)
                ret = wret;

        /* then fixup the leaf pointer in the path */
        if (path->slots[0] < push_items) {
                path->slots[0] += old_left_nritems;
                if (btrfs_header_nritems(path->nodes[0]) == 0)
                        clean_tree_block(trans, root, path->nodes[0]);
                btrfs_tree_unlock(path->nodes[0]);
                free_extent_buffer(path->nodes[0]);
                path->nodes[0] = left;
                path->slots[1] -= 1;
        } else {
                btrfs_tree_unlock(left);
                free_extent_buffer(left);
                path->slots[0] -= push_items;
        }
        BUG_ON(path->slots[0] < 0);
        return ret;
out:
        btrfs_tree_unlock(left);
        free_extent_buffer(left);
        return ret;
}

/*
 * split the path's leaf in two, making sure there is at least data_size
 * available for the resulting leaf level of the path.
 *
 * returns 0 if all went well and < 0 on failure.
 */
static noinline int split_leaf(struct btrfs_trans_handle *trans,
                               struct btrfs_root *root,
                               struct btrfs_key *ins_key,
                               struct btrfs_path *path, int data_size,
                               int extend)
{
        struct extent_buffer *l;
        u32 nritems;
        int mid;
        int slot;
        struct extent_buffer *right;
        int data_copy_size;
        int rt_data_off;
        int i;
        int ret = 0;
        int wret;
        int double_split;
        int num_doubles = 0;
        struct btrfs_disk_key disk_key;

        /* first try to make some room by pushing left and right */
        if (data_size && ins_key->type != BTRFS_DIR_ITEM_KEY) {
                wret = push_leaf_right(trans, root, path, data_size, 0);
                if (wret < 0)
                        return wret;
                if (wret) {
                        wret = push_leaf_left(trans, root, path, data_size, 0);
                        if (wret < 0)
                                return wret;
                }
                l = path->nodes[0];

                /* did the pushes work? */
                if (btrfs_leaf_free_space(root, l) >= data_size)
                        return 0;
        }

        if (!path->nodes[1]) {
                ret = insert_new_root(trans, root, path, 1);
                if (ret)
                        return ret;
        }
again:
        double_split = 0;
        l = path->nodes[0];
        slot = path->slots[0];
        nritems = btrfs_header_nritems(l);
        mid = (nritems + 1) / 2;

        right = btrfs_alloc_free_block(trans, root, root->leafsize,
                                        path->nodes[1]->start,
                                        root->root_key.objectid,
                                        trans->transid, 0, l->start, 0);
        if (IS_ERR(right)) {
                BUG_ON(1);
                return PTR_ERR(right);
        }

        memset_extent_buffer(right, 0, 0, sizeof(struct btrfs_header));
        btrfs_set_header_bytenr(right, right->start);
        btrfs_set_header_generation(right, trans->transid);
        btrfs_set_header_owner(right, root->root_key.objectid);
        btrfs_set_header_level(right, 0);
        write_extent_buffer(right, root->fs_info->fsid,
                            (unsigned long)btrfs_header_fsid(right),
                            BTRFS_FSID_SIZE);

        write_extent_buffer(right, root->fs_info->chunk_tree_uuid,
                            (unsigned long)btrfs_header_chunk_tree_uuid(right),
                            BTRFS_UUID_SIZE);
        if (mid <= slot) {
                if (nritems == 1 ||
                    leaf_space_used(l, mid, nritems - mid) + data_size >
                        BTRFS_LEAF_DATA_SIZE(root)) {
                        if (slot >= nritems) {
                                btrfs_cpu_key_to_disk(&disk_key, ins_key);
                                btrfs_set_header_nritems(right, 0);
                                wret = insert_ptr(trans, root, path,
                                                  &disk_key, right->start,
                                                  path->slots[1] + 1, 1);
                                if (wret)
                                        ret = wret;

                                btrfs_tree_unlock(path->nodes[0]);
                                free_extent_buffer(path->nodes[0]);
                                path->nodes[0] = right;
                                path->slots[0] = 0;
                                path->slots[1] += 1;
                                btrfs_mark_buffer_dirty(right);
                                return ret;
                        }
                        mid = slot;
                        if (mid != nritems &&
                            leaf_space_used(l, mid, nritems - mid) +
                            data_size > BTRFS_LEAF_DATA_SIZE(root)) {
                                double_split = 1;
                        }
                }
        } else {
                if (leaf_space_used(l, 0, mid) + data_size >
                        BTRFS_LEAF_DATA_SIZE(root)) {
                        if (!extend && data_size && slot == 0) {
                                btrfs_cpu_key_to_disk(&disk_key, ins_key);
                                btrfs_set_header_nritems(right, 0);
                                wret = insert_ptr(trans, root, path,
                                                  &disk_key,
                                                  right->start,
                                                  path->slots[1], 1);
                                if (wret)
                                        ret = wret;
                                btrfs_tree_unlock(path->nodes[0]);
                                free_extent_buffer(path->nodes[0]);
                                path->nodes[0] = right;
                                path->slots[0] = 0;
                                if (path->slots[1] == 0) {
                                        wret = fixup_low_keys(trans, root,
                                                      path, &disk_key, 1);
                                        if (wret)
                                                ret = wret;
                                }
                                btrfs_mark_buffer_dirty(right);
                                return ret;
                        } else if ((extend || !data_size) && slot == 0) {
                                mid = 1;
                        } else {
                                mid = slot;
                                if (mid != nritems &&
                                    leaf_space_used(l, mid, nritems - mid) +
                                    data_size > BTRFS_LEAF_DATA_SIZE(root)) {
                                        double_split = 1;
                                }
                        }
                }
        }
        nritems = nritems - mid;
        btrfs_set_header_nritems(right, nritems);
        data_copy_size = btrfs_item_end_nr(l, mid) - leaf_data_end(root, l);

        copy_extent_buffer(right, l, btrfs_item_nr_offset(0),
                           btrfs_item_nr_offset(mid),
                           nritems * sizeof(struct btrfs_item));

        copy_extent_buffer(right, l,
                     btrfs_leaf_data(right) + BTRFS_LEAF_DATA_SIZE(root) -
                     data_copy_size, btrfs_leaf_data(l) +
                     leaf_data_end(root, l), data_copy_size);

        rt_data_off = BTRFS_LEAF_DATA_SIZE(root) -
                      btrfs_item_end_nr(l, mid);

        for (i = 0; i < nritems; i++) {
                struct btrfs_item *item = btrfs_item_nr(right, i);
                u32 ioff;

                if (!right->map_token) {
                        map_extent_buffer(right, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &right->map_token, &right->kaddr,
                                        &right->map_start, &right->map_len,
                                        KM_USER1);
                }

                ioff = btrfs_item_offset(right, item);
                btrfs_set_item_offset(right, item, ioff + rt_data_off);
        }

        if (right->map_token) {
                unmap_extent_buffer(right, right->map_token, KM_USER1);
                right->map_token = NULL;
        }

        btrfs_set_header_nritems(l, mid);
        ret = 0;
        btrfs_item_key(right, &disk_key, 0);
        wret = insert_ptr(trans, root, path, &disk_key, right->start,
                          path->slots[1] + 1, 1);
        if (wret)
                ret = wret;

        btrfs_mark_buffer_dirty(right);
        btrfs_mark_buffer_dirty(l);
        BUG_ON(path->slots[0] != slot);

        ret = btrfs_update_ref(trans, root, l, right, 0, nritems);
        BUG_ON(ret);

        if (mid <= slot) {
                btrfs_tree_unlock(path->nodes[0]);
                free_extent_buffer(path->nodes[0]);
                path->nodes[0] = right;
                path->slots[0] -= mid;
                path->slots[1] += 1;
        } else {
                btrfs_tree_unlock(right);
                free_extent_buffer(right);
        }

        BUG_ON(path->slots[0] < 0);

        if (double_split) {
                BUG_ON(num_doubles != 0);
                num_doubles++;
                goto again;
        }
        return ret;
}

/*
 * This function splits a single item into two items,
 * giving 'new_key' to the new item and splitting the
 * old one at split_offset (from the start of the item).
 *
 * The path may be released by this operation.  After
 * the split, the path is pointing to the old item.  The
 * new item is going to be in the same node as the old one.
 *
 * Note, the item being split must be smaller enough to live alone on
 * a tree block with room for one extra struct btrfs_item
 *
 * This allows us to split the item in place, keeping a lock on the
 * leaf the entire time.
 */
int btrfs_split_item(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     struct btrfs_path *path,
                     struct btrfs_key *new_key,
                     unsigned long split_offset)
{
        u32 item_size;
        struct extent_buffer *leaf;
        struct btrfs_key orig_key;
        struct btrfs_item *item;
        struct btrfs_item *new_item;
        int ret = 0;
        int slot;
        u32 nritems;
        u32 orig_offset;
        struct btrfs_disk_key disk_key;
        char *buf;

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &orig_key, path->slots[0]);
        if (btrfs_leaf_free_space(root, leaf) >= sizeof(struct btrfs_item))
                goto split;

        item_size = btrfs_item_size_nr(leaf, path->slots[0]);
        btrfs_release_path(root, path);

        path->search_for_split = 1;
        path->keep_locks = 1;

        ret = btrfs_search_slot(trans, root, &orig_key, path, 0, 1);
        path->search_for_split = 0;

        /* if our item isn't there or got smaller, return now */
        if (ret != 0 || item_size != btrfs_item_size_nr(path->nodes[0],
                                                        path->slots[0])) {
                path->keep_locks = 0;
                return -EAGAIN;
        }

        ret = split_leaf(trans, root, &orig_key, path,
                         sizeof(struct btrfs_item), 1);
        path->keep_locks = 0;
        BUG_ON(ret);

        leaf = path->nodes[0];
        BUG_ON(btrfs_leaf_free_space(root, leaf) < sizeof(struct btrfs_item));

split:
        item = btrfs_item_nr(leaf, path->slots[0]);
        orig_offset = btrfs_item_offset(leaf, item);
        item_size = btrfs_item_size(leaf, item);


        buf = kmalloc(item_size, GFP_NOFS);
        read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf,
                            path->slots[0]), item_size);
        slot = path->slots[0] + 1;
        leaf = path->nodes[0];

        nritems = btrfs_header_nritems(leaf);

        if (slot != nritems) {
                /* shift the items */
                memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot + 1),
                              btrfs_item_nr_offset(slot),
                              (nritems - slot) * sizeof(struct btrfs_item));

        }

        btrfs_cpu_key_to_disk(&disk_key, new_key);
        btrfs_set_item_key(leaf, &disk_key, slot);

        new_item = btrfs_item_nr(leaf, slot);

        btrfs_set_item_offset(leaf, new_item, orig_offset);
        btrfs_set_item_size(leaf, new_item, item_size - split_offset);

        btrfs_set_item_offset(leaf, item,
                              orig_offset + item_size - split_offset);
        btrfs_set_item_size(leaf, item, split_offset);

        btrfs_set_header_nritems(leaf, nritems + 1);

        /* write the data for the start of the original item */
        write_extent_buffer(leaf, buf,
                            btrfs_item_ptr_offset(leaf, path->slots[0]),
                            split_offset);

        /* write the data for the new item */
        write_extent_buffer(leaf, buf + split_offset,
                            btrfs_item_ptr_offset(leaf, slot),
                            item_size - split_offset);
        btrfs_mark_buffer_dirty(leaf);

        ret = 0;
        if (btrfs_leaf_free_space(root, leaf) < 0) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
        kfree(buf);
        return ret;
}

/*
 * make the item pointed to by the path smaller.  new_size indicates
 * how small to make it, and from_end tells us if we just chop bytes
 * off the end of the item or if we shift the item to chop bytes off
 * the front.
 */
int btrfs_truncate_item(struct btrfs_trans_handle *trans,
                        struct btrfs_root *root,
                        struct btrfs_path *path,
                        u32 new_size, int from_end)
{
        int ret = 0;
        int slot;
        int slot_orig;
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        u32 nritems;
        unsigned int data_end;
        unsigned int old_data_start;
        unsigned int old_size;
        unsigned int size_diff;
        int i;

        slot_orig = path->slots[0];
        leaf = path->nodes[0];
        slot = path->slots[0];

        old_size = btrfs_item_size_nr(leaf, slot);
        if (old_size == new_size)
                return 0;

        nritems = btrfs_header_nritems(leaf);
        data_end = leaf_data_end(root, leaf);

        old_data_start = btrfs_item_offset_nr(leaf, slot);

        size_diff = old_size - new_size;

        BUG_ON(slot < 0);
        BUG_ON(slot >= nritems);

        /*
         * item0..itemN ... dataN.offset..dataN.size .. data0.size
         */
        /* first correct the data pointers */
        for (i = slot; i < nritems; i++) {
                u32 ioff;
                item = btrfs_item_nr(leaf, i);

                if (!leaf->map_token) {
                        map_extent_buffer(leaf, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &leaf->map_token, &leaf->kaddr,
                                        &leaf->map_start, &leaf->map_len,
                                        KM_USER1);
                }

                ioff = btrfs_item_offset(leaf, item);
                btrfs_set_item_offset(leaf, item, ioff + size_diff);
        }

        if (leaf->map_token) {
                unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
                leaf->map_token = NULL;
        }

        /* shift the data */
        if (from_end) {
                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end + size_diff, btrfs_leaf_data(leaf) +
                              data_end, old_data_start + new_size - data_end);
        } else {
                struct btrfs_disk_key disk_key;
                u64 offset;

                btrfs_item_key(leaf, &disk_key, slot);

                if (btrfs_disk_key_type(&disk_key) == BTRFS_EXTENT_DATA_KEY) {
                        unsigned long ptr;
                        struct btrfs_file_extent_item *fi;

                        fi = btrfs_item_ptr(leaf, slot,
                                            struct btrfs_file_extent_item);
                        fi = (struct btrfs_file_extent_item *)(
                             (unsigned long)fi - size_diff);

                        if (btrfs_file_extent_type(leaf, fi) ==
                            BTRFS_FILE_EXTENT_INLINE) {
                                ptr = btrfs_item_ptr_offset(leaf, slot);
                                memmove_extent_buffer(leaf, ptr,
                                      (unsigned long)fi,
                                      offsetof(struct btrfs_file_extent_item,
                                                 disk_bytenr));
                        }
                }

                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end + size_diff, btrfs_leaf_data(leaf) +
                              data_end, old_data_start - data_end);

                offset = btrfs_disk_key_offset(&disk_key);
                btrfs_set_disk_key_offset(&disk_key, offset + size_diff);
                btrfs_set_item_key(leaf, &disk_key, slot);
                if (slot == 0)
                        fixup_low_keys(trans, root, path, &disk_key, 1);
        }

        item = btrfs_item_nr(leaf, slot);
        btrfs_set_item_size(leaf, item, new_size);
        btrfs_mark_buffer_dirty(leaf);

        ret = 0;
        if (btrfs_leaf_free_space(root, leaf) < 0) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
        return ret;
}

/*
 * make the item pointed to by the path bigger, data_size is the new size.
 */
int btrfs_extend_item(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root, struct btrfs_path *path,
                      u32 data_size)
{
        int ret = 0;
        int slot;
        int slot_orig;
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        u32 nritems;
        unsigned int data_end;
        unsigned int old_data;
        unsigned int old_size;
        int i;

        slot_orig = path->slots[0];
        leaf = path->nodes[0];

        nritems = btrfs_header_nritems(leaf);
        data_end = leaf_data_end(root, leaf);

        if (btrfs_leaf_free_space(root, leaf) < data_size) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
        slot = path->slots[0];
        old_data = btrfs_item_end_nr(leaf, slot);

        BUG_ON(slot < 0);
        if (slot >= nritems) {
                btrfs_print_leaf(root, leaf);
                printk(KERN_CRIT "slot %d too large, nritems %d\n",
                       slot, nritems);
                BUG_ON(1);
        }

        /*
         * item0..itemN ... dataN.offset..dataN.size .. data0.size
         */
        /* first correct the data pointers */
        for (i = slot; i < nritems; i++) {
                u32 ioff;
                item = btrfs_item_nr(leaf, i);

                if (!leaf->map_token) {
                        map_extent_buffer(leaf, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &leaf->map_token, &leaf->kaddr,
                                        &leaf->map_start, &leaf->map_len,
                                        KM_USER1);
                }
                ioff = btrfs_item_offset(leaf, item);
                btrfs_set_item_offset(leaf, item, ioff - data_size);
        }

        if (leaf->map_token) {
                unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
                leaf->map_token = NULL;
        }

        /* shift the data */
        memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                      data_end - data_size, btrfs_leaf_data(leaf) +
                      data_end, old_data - data_end);

        data_end = old_data;
        old_size = btrfs_item_size_nr(leaf, slot);
        item = btrfs_item_nr(leaf, slot);
        btrfs_set_item_size(leaf, item, old_size + data_size);
        btrfs_mark_buffer_dirty(leaf);

        ret = 0;
        if (btrfs_leaf_free_space(root, leaf) < 0) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
        return ret;
}

/*
 * Given a key and some data, insert items into the tree.
 * This does all the path init required, making room in the tree if needed.
 * Returns the number of keys that were inserted.
 */
int btrfs_insert_some_items(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root,
                            struct btrfs_path *path,
                            struct btrfs_key *cpu_key, u32 *data_size,
                            int nr)
{
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        int ret = 0;
        int slot;
        int i;
        u32 nritems;
        u32 total_data = 0;
        u32 total_size = 0;
        unsigned int data_end;
        struct btrfs_disk_key disk_key;
        struct btrfs_key found_key;

        for (i = 0; i < nr; i++) {
                if (total_size + data_size[i] + sizeof(struct btrfs_item) >
                    BTRFS_LEAF_DATA_SIZE(root)) {
                        break;
                        nr = i;
                }
                total_data += data_size[i];
                total_size += data_size[i] + sizeof(struct btrfs_item);
        }
        BUG_ON(nr == 0);

        ret = btrfs_search_slot(trans, root, cpu_key, path, total_size, 1);
        if (ret == 0)
                return -EEXIST;
        if (ret < 0)
                goto out;

        leaf = path->nodes[0];

        nritems = btrfs_header_nritems(leaf);
        data_end = leaf_data_end(root, leaf);

        if (btrfs_leaf_free_space(root, leaf) < total_size) {
                for (i = nr; i >= 0; i--) {
                        total_data -= data_size[i];
                        total_size -= data_size[i] + sizeof(struct btrfs_item);
                        if (total_size < btrfs_leaf_free_space(root, leaf))
                                break;
                }
                nr = i;
        }

        slot = path->slots[0];
        BUG_ON(slot < 0);

        if (slot != nritems) {
                unsigned int old_data = btrfs_item_end_nr(leaf, slot);

                item = btrfs_item_nr(leaf, slot);
                btrfs_item_key_to_cpu(leaf, &found_key, slot);

                /* figure out how many keys we can insert in here */
                total_data = data_size[0];
                for (i = 1; i < nr; i++) {
                        if (comp_cpu_keys(&found_key, cpu_key + i) <= 0)
                                break;
                        total_data += data_size[i];
                }
                nr = i;

                if (old_data < data_end) {
                        btrfs_print_leaf(root, leaf);
                        printk(KERN_CRIT "slot %d old_data %d data_end %d\n",
                               slot, old_data, data_end);
                        BUG_ON(1);
                }
                /*
                 * item0..itemN ... dataN.offset..dataN.size .. data0.size
                 */
                /* first correct the data pointers */
                WARN_ON(leaf->map_token);
                for (i = slot; i < nritems; i++) {
                        u32 ioff;

                        item = btrfs_item_nr(leaf, i);
                        if (!leaf->map_token) {
                                map_extent_buffer(leaf, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &leaf->map_token, &leaf->kaddr,
                                        &leaf->map_start, &leaf->map_len,
                                        KM_USER1);
                        }

                        ioff = btrfs_item_offset(leaf, item);
                        btrfs_set_item_offset(leaf, item, ioff - total_data);
                }
                if (leaf->map_token) {
                        unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
                        leaf->map_token = NULL;
                }

                /* shift the items */
                memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot + nr),
                              btrfs_item_nr_offset(slot),
                              (nritems - slot) * sizeof(struct btrfs_item));

                /* shift the data */
                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end - total_data, btrfs_leaf_data(leaf) +
                              data_end, old_data - data_end);
                data_end = old_data;
        } else {
                /*
                 * this sucks but it has to be done, if we are inserting at
                 * the end of the leaf only insert 1 of the items, since we
                 * have no way of knowing whats on the next leaf and we'd have
                 * to drop our current locks to figure it out
                 */
                nr = 1;
        }

        /* setup the item for the new data */
        for (i = 0; i < nr; i++) {
                btrfs_cpu_key_to_disk(&disk_key, cpu_key + i);
                btrfs_set_item_key(leaf, &disk_key, slot + i);
                item = btrfs_item_nr(leaf, slot + i);
                btrfs_set_item_offset(leaf, item, data_end - data_size[i]);
                data_end -= data_size[i];
                btrfs_set_item_size(leaf, item, data_size[i]);
        }
        btrfs_set_header_nritems(leaf, nritems + nr);
        btrfs_mark_buffer_dirty(leaf);

        ret = 0;
        if (slot == 0) {
                btrfs_cpu_key_to_disk(&disk_key, cpu_key);
                ret = fixup_low_keys(trans, root, path, &disk_key, 1);
        }

        if (btrfs_leaf_free_space(root, leaf) < 0) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
out:
        if (!ret)
                ret = nr;
        return ret;
}

/*
 * Given a key and some data, insert items into the tree.
 * This does all the path init required, making room in the tree if needed.
 */
int btrfs_insert_empty_items(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root,
                            struct btrfs_path *path,
                            struct btrfs_key *cpu_key, u32 *data_size,
                            int nr)
{
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        int ret = 0;
        int slot;
        int slot_orig;
        int i;
        u32 nritems;
        u32 total_size = 0;
        u32 total_data = 0;
        unsigned int data_end;
        struct btrfs_disk_key disk_key;

        for (i = 0; i < nr; i++)
                total_data += data_size[i];

        total_size = total_data + (nr * sizeof(struct btrfs_item));
        ret = btrfs_search_slot(trans, root, cpu_key, path, total_size, 1);
        if (ret == 0)
                return -EEXIST;
        if (ret < 0)
                goto out;

        slot_orig = path->slots[0];
        leaf = path->nodes[0];

        nritems = btrfs_header_nritems(leaf);
        data_end = leaf_data_end(root, leaf);

        if (btrfs_leaf_free_space(root, leaf) < total_size) {
                btrfs_print_leaf(root, leaf);
                printk(KERN_CRIT "not enough freespace need %u have %d\n",
                       total_size, btrfs_leaf_free_space(root, leaf));
                BUG();
        }

        slot = path->slots[0];
        BUG_ON(slot < 0);

        if (slot != nritems) {
                unsigned int old_data = btrfs_item_end_nr(leaf, slot);

                if (old_data < data_end) {
                        btrfs_print_leaf(root, leaf);
                        printk(KERN_CRIT "slot %d old_data %d data_end %d\n",
                               slot, old_data, data_end);
                        BUG_ON(1);
                }
                /*
                 * item0..itemN ... dataN.offset..dataN.size .. data0.size
                 */
                /* first correct the data pointers */
                WARN_ON(leaf->map_token);
                for (i = slot; i < nritems; i++) {
                        u32 ioff;

                        item = btrfs_item_nr(leaf, i);
                        if (!leaf->map_token) {
                                map_extent_buffer(leaf, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &leaf->map_token, &leaf->kaddr,
                                        &leaf->map_start, &leaf->map_len,
                                        KM_USER1);
                        }

                        ioff = btrfs_item_offset(leaf, item);
                        btrfs_set_item_offset(leaf, item, ioff - total_data);
                }
                if (leaf->map_token) {
                        unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
                        leaf->map_token = NULL;
                }

                /* shift the items */
                memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot + nr),
                              btrfs_item_nr_offset(slot),
                              (nritems - slot) * sizeof(struct btrfs_item));

                /* shift the data */
                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end - total_data, btrfs_leaf_data(leaf) +
                              data_end, old_data - data_end);
                data_end = old_data;
        }

        /* setup the item for the new data */
        for (i = 0; i < nr; i++) {
                btrfs_cpu_key_to_disk(&disk_key, cpu_key + i);
                btrfs_set_item_key(leaf, &disk_key, slot + i);
                item = btrfs_item_nr(leaf, slot + i);
                btrfs_set_item_offset(leaf, item, data_end - data_size[i]);
                data_end -= data_size[i];
                btrfs_set_item_size(leaf, item, data_size[i]);
        }
        btrfs_set_header_nritems(leaf, nritems + nr);
        btrfs_mark_buffer_dirty(leaf);

        ret = 0;
        if (slot == 0) {
                btrfs_cpu_key_to_disk(&disk_key, cpu_key);
                ret = fixup_low_keys(trans, root, path, &disk_key, 1);
        }

        if (btrfs_leaf_free_space(root, leaf) < 0) {
                btrfs_print_leaf(root, leaf);
                BUG();
        }
out:
        return ret;
}

/*
 * Given a key and some data, insert an item into the tree.
 * This does all the path init required, making room in the tree if needed.
 */
int btrfs_insert_item(struct btrfs_trans_handle *trans, struct btrfs_root
                      *root, struct btrfs_key *cpu_key, void *data, u32
                      data_size)
{
        int ret = 0;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        unsigned long ptr;

        path = btrfs_alloc_path();
        BUG_ON(!path);
        ret = btrfs_insert_empty_item(trans, root, path, cpu_key, data_size);
        if (!ret) {
                leaf = path->nodes[0];
                ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
                write_extent_buffer(leaf, data, ptr, data_size);
                btrfs_mark_buffer_dirty(leaf);
        }
        btrfs_free_path(path);
        return ret;
}

/*
 * delete the pointer from a given node.
 *
 * the tree should have been previously balanced so the deletion does not
 * empty a node.
 */
static int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                   struct btrfs_path *path, int level, int slot)
{
        struct extent_buffer *parent = path->nodes[level];
        u32 nritems;
        int ret = 0;
        int wret;

        nritems = btrfs_header_nritems(parent);
        if (slot != nritems - 1) {
                memmove_extent_buffer(parent,
                              btrfs_node_key_ptr_offset(slot),
                              btrfs_node_key_ptr_offset(slot + 1),
                              sizeof(struct btrfs_key_ptr) *
                              (nritems - slot - 1));
        }
        nritems--;
        btrfs_set_header_nritems(parent, nritems);
        if (nritems == 0 && parent == root->node) {
                BUG_ON(btrfs_header_level(root->node) != 1);
                /* just turn the root into a leaf and break */
                btrfs_set_header_level(root->node, 0);
        } else if (slot == 0) {
                struct btrfs_disk_key disk_key;

                btrfs_node_key(parent, &disk_key, 0);
                wret = fixup_low_keys(trans, root, path, &disk_key, level + 1);
                if (wret)
                        ret = wret;
        }
        btrfs_mark_buffer_dirty(parent);
        return ret;
}

/*
 * a helper function to delete the leaf pointed to by path->slots[1] and
 * path->nodes[1].  bytenr is the node block pointer, but since the callers
 * already know it, it is faster to have them pass it down than to
 * read it out of the node again.
 *
 * This deletes the pointer in path->nodes[1] and frees the leaf
 * block extent.  zero is returned if it all worked out, < 0 otherwise.
 *
 * The path must have already been setup for deleting the leaf, including
 * all the proper balancing.  path->nodes[1] must be locked.
 */
noinline int btrfs_del_leaf(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root,
                            struct btrfs_path *path, u64 bytenr)
{
        int ret;
        u64 root_gen = btrfs_header_generation(path->nodes[1]);

        ret = del_ptr(trans, root, path, 1, path->slots[1]);
        if (ret)
                return ret;

        ret = btrfs_free_extent(trans, root, bytenr,
                                btrfs_level_size(root, 0),
                                path->nodes[1]->start,
                                btrfs_header_owner(path->nodes[1]),
                                root_gen, 0, 1);
        return ret;
}
/*
 * delete the item at the leaf level in path.  If that empties
 * the leaf, remove it from the tree
 */
int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
                    struct btrfs_path *path, int slot, int nr)
{
        struct extent_buffer *leaf;
        struct btrfs_item *item;
        int last_off;
        int dsize = 0;
        int ret = 0;
        int wret;
        int i;
        u32 nritems;

        leaf = path->nodes[0];
        last_off = btrfs_item_offset_nr(leaf, slot + nr - 1);

        for (i = 0; i < nr; i++)
                dsize += btrfs_item_size_nr(leaf, slot + i);

        nritems = btrfs_header_nritems(leaf);

        if (slot + nr != nritems) {
                int data_end = leaf_data_end(root, leaf);

                memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
                              data_end + dsize,
                              btrfs_leaf_data(leaf) + data_end,
                              last_off - data_end);

                for (i = slot + nr; i < nritems; i++) {
                        u32 ioff;

                        item = btrfs_item_nr(leaf, i);
                        if (!leaf->map_token) {
                                map_extent_buffer(leaf, (unsigned long)item,
                                        sizeof(struct btrfs_item),
                                        &leaf->map_token, &leaf->kaddr,
                                        &leaf->map_start, &leaf->map_len,
                                        KM_USER1);
                        }
                        ioff = btrfs_item_offset(leaf, item);
                        btrfs_set_item_offset(leaf, item, ioff + dsize);
                }

                if (leaf->map_token) {
                        unmap_extent_buffer(leaf, leaf->map_token, KM_USER1);
                        leaf->map_token = NULL;
                }

                memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot),
                              btrfs_item_nr_offset(slot + nr),
                              sizeof(struct btrfs_item) *
                              (nritems - slot - nr));
        }
        btrfs_set_header_nritems(leaf, nritems - nr);
        nritems -= nr;

        /* delete the leaf if we've emptied it */
        if (nritems == 0) {
                if (leaf == root->node) {
                        btrfs_set_header_level(leaf, 0);
                } else {
                        ret = btrfs_del_leaf(trans, root, path, leaf->start);
                        BUG_ON(ret);
                }
        } else {
                int used = leaf_space_used(leaf, 0, nritems);
                if (slot == 0) {
                        struct btrfs_disk_key disk_key;

                        btrfs_item_key(leaf, &disk_key, 0);
                        wret = fixup_low_keys(trans, root, path,
                                              &disk_key, 1);
                        if (wret)
                                ret = wret;
                }

                /* delete the leaf if it is mostly empty */
                if (used < BTRFS_LEAF_DATA_SIZE(root) / 4) {
                        /* push_leaf_left fixes the path.
                         * make sure the path still points to our leaf
                         * for possible call to del_ptr below
                         */
                        slot = path->slots[1];
                        extent_buffer_get(leaf);

                        wret = push_leaf_left(trans, root, path, 1, 1);
                        if (wret < 0 && wret != -ENOSPC)
                                ret = wret;

                        if (path->nodes[0] == leaf &&
                            btrfs_header_nritems(leaf)) {
                                wret = push_leaf_right(trans, root, path, 1, 1);
                                if (wret < 0 && wret != -ENOSPC)
                                        ret = wret;
                        }

                        if (btrfs_header_nritems(leaf) == 0) {
                                path->slots[1] = slot;
                                ret = btrfs_del_leaf(trans, root, path,
                                                     leaf->start);
                                BUG_ON(ret);
                                free_extent_buffer(leaf);
                        } else {
                                /* if we're still in the path, make sure
                                 * we're dirty.  Otherwise, one of the
                                 * push_leaf functions must have already
                                 * dirtied this buffer
                                 */
                                if (path->nodes[0] == leaf)
                                        btrfs_mark_buffer_dirty(leaf);
                                free_extent_buffer(leaf);
                        }
                } else {
                        btrfs_mark_buffer_dirty(leaf);
                }
        }
        return ret;
}

/*
 * search the tree again to find a leaf with lesser keys
 * returns 0 if it found something or 1 if there are no lesser leaves.
 * returns < 0 on io errors.
 *
 * This may release the path, and so you may lose any locks held at the
 * time you call it.
 */
int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path)
{
        struct btrfs_key key;
        struct btrfs_disk_key found_key;
        int ret;

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

        if (key.offset > 0)
                key.offset--;
        else if (key.type > 0)
                key.type--;
        else if (key.objectid > 0)
                key.objectid--;
        else
                return 1;

        btrfs_release_path(root, path);
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                return ret;
        btrfs_item_key(path->nodes[0], &found_key, 0);
        ret = comp_keys(&found_key, &key);
        if (ret < 0)
                return 0;
        return 1;
}

/*
 * A helper function to walk down the tree starting at min_key, and looking
 * for nodes or leaves that are either in cache or have a minimum
 * transaction id.  This is used by the btree defrag code, and tree logging
 *
 * This does not cow, but it does stuff the starting key it finds back
 * into min_key, so you can call btrfs_search_slot with cow=1 on the
 * key and get a writable path.
 *
 * This does lock as it descends, and path->keep_locks should be set
 * to 1 by the caller.
 *
 * This honors path->lowest_level to prevent descent past a given level
 * of the tree.
 *
 * min_trans indicates the oldest transaction that you are interested
 * in walking through.  Any nodes or leaves older than min_trans are
 * skipped over (without reading them).
 *
 * returns zero if something useful was found, < 0 on error and 1 if there
 * was nothing in the tree that matched the search criteria.
 */
int btrfs_search_forward(struct btrfs_root *root, struct btrfs_key *min_key,
                         struct btrfs_key *max_key,
                         struct btrfs_path *path, int cache_only,
                         u64 min_trans)
{
        struct extent_buffer *cur;
        struct btrfs_key found_key;
        int slot;
        int sret;
        u32 nritems;
        int level;
        int ret = 1;

        WARN_ON(!path->keep_locks);
again:
        cur = btrfs_lock_root_node(root);
        level = btrfs_header_level(cur);
        WARN_ON(path->nodes[level]);
        path->nodes[level] = cur;
        path->locks[level] = 1;

        if (btrfs_header_generation(cur) < min_trans) {
                ret = 1;
                goto out;
        }
        while (1) {
                nritems = btrfs_header_nritems(cur);
                level = btrfs_header_level(cur);
                sret = bin_search(cur, min_key, level, &slot);

                /* at the lowest level, we're done, setup the path and exit */
                if (level == path->lowest_level) {
                        if (slot >= nritems)
                                goto find_next_key;
                        ret = 0;
                        path->slots[level] = slot;
                        btrfs_item_key_to_cpu(cur, &found_key, slot);
                        goto out;
                }
                if (sret && slot > 0)
                        slot--;
                /*
                 * check this node pointer against the cache_only and
                 * min_trans parameters.  If it isn't in cache or is too
                 * old, skip to the next one.
                 */
                while (slot < nritems) {
                        u64 blockptr;
                        u64 gen;
                        struct extent_buffer *tmp;
                        struct btrfs_disk_key disk_key;

                        blockptr = btrfs_node_blockptr(cur, slot);
                        gen = btrfs_node_ptr_generation(cur, slot);
                        if (gen < min_trans) {
                                slot++;
                                continue;
                        }
                        if (!cache_only)
                                break;

                        if (max_key) {
                                btrfs_node_key(cur, &disk_key, slot);
                                if (comp_keys(&disk_key, max_key) >= 0) {
                                        ret = 1;
                                        goto out;
                                }
                        }

                        tmp = btrfs_find_tree_block(root, blockptr,
                                            btrfs_level_size(root, level - 1));

                        if (tmp && btrfs_buffer_uptodate(tmp, gen)) {
                                free_extent_buffer(tmp);
                                break;
                        }
                        if (tmp)
                                free_extent_buffer(tmp);
                        slot++;
                }
find_next_key:
                /*
                 * we didn't find a candidate key in this node, walk forward
                 * and find another one
                 */
                if (slot >= nritems) {
                        path->slots[level] = slot;
                        sret = btrfs_find_next_key(root, path, min_key, level,
                                                  cache_only, min_trans);
                        if (sret == 0) {
                                btrfs_release_path(root, path);
                                goto again;
                        } else {
                                goto out;
                        }
                }
                /* save our key for returning back */
                btrfs_node_key_to_cpu(cur, &found_key, slot);
                path->slots[level] = slot;
                if (level == path->lowest_level) {
                        ret = 0;
                        unlock_up(path, level, 1);
                        goto out;
                }
                cur = read_node_slot(root, cur, slot);

                btrfs_tree_lock(cur);
                path->locks[level - 1] = 1;
                path->nodes[level - 1] = cur;
                unlock_up(path, level, 1);
        }
out:
        if (ret == 0)
                memcpy(min_key, &found_key, sizeof(found_key));
        return ret;
}

/*
 * this is similar to btrfs_next_leaf, but does not try to preserve
 * and fixup the path.  It looks for and returns the next key in the
 * tree based on the current path and the cache_only and min_trans
 * parameters.
 *
 * 0 is returned if another key is found, < 0 if there are any errors
 * and 1 is returned if there are no higher keys in the tree
 *
 * path->keep_locks should be set to 1 on the search made before
 * calling this function.
 */
int btrfs_find_next_key(struct btrfs_root *root, struct btrfs_path *path,
                        struct btrfs_key *key, int lowest_level,
                        int cache_only, u64 min_trans)
{
        int level = lowest_level;
        int slot;
        struct extent_buffer *c;

        WARN_ON(!path->keep_locks);
        while (level < BTRFS_MAX_LEVEL) {
                if (!path->nodes[level])
                        return 1;

                slot = path->slots[level] + 1;
                c = path->nodes[level];
next:
                if (slot >= btrfs_header_nritems(c)) {
                        level++;
                        if (level == BTRFS_MAX_LEVEL)
                                return 1;
                        continue;
                }
                if (level == 0)
                        btrfs_item_key_to_cpu(c, key, slot);
                else {
                        u64 blockptr = btrfs_node_blockptr(c, slot);
                        u64 gen = btrfs_node_ptr_generation(c, slot);

                        if (cache_only) {
                                struct extent_buffer *cur;
                                cur = btrfs_find_tree_block(root, blockptr,
                                            btrfs_level_size(root, level - 1));
                                if (!cur || !btrfs_buffer_uptodate(cur, gen)) {
                                        slot++;
                                        if (cur)
                                                free_extent_buffer(cur);
                                        goto next;
                                }
                                free_extent_buffer(cur);
                        }
                        if (gen < min_trans) {
                                slot++;
                                goto next;
                        }
                        btrfs_node_key_to_cpu(c, key, slot);
                }
                return 0;
        }
        return 1;
}

/*
 * search the tree again to find a leaf with greater keys
 * returns 0 if it found something or 1 if there are no greater leaves.
 * returns < 0 on io errors.
 */
int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
{
        int slot;
        int level = 1;
        struct extent_buffer *c;
        struct extent_buffer *next = NULL;
        struct btrfs_key key;
        u32 nritems;
        int ret;

        nritems = btrfs_header_nritems(path->nodes[0]);
        if (nritems == 0)
                return 1;

        btrfs_item_key_to_cpu(path->nodes[0], &key, nritems - 1);

        btrfs_release_path(root, path);
        path->keep_locks = 1;
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        path->keep_locks = 0;

        if (ret < 0)
                return ret;

        nritems = btrfs_header_nritems(path->nodes[0]);
        /*
         * by releasing the path above we dropped all our locks.  A balance
         * could have added more items next to the key that used to be
         * at the very end of the block.  So, check again here and
         * advance the path if there are now more items available.
         */
        if (nritems > 0 && path->slots[0] < nritems - 1) {
                path->slots[0]++;
                goto done;
        }

        while (level < BTRFS_MAX_LEVEL) {
                if (!path->nodes[level])
                        return 1;

                slot = path->slots[level] + 1;
                c = path->nodes[level];
                if (slot >= btrfs_header_nritems(c)) {
                        level++;
                        if (level == BTRFS_MAX_LEVEL)
                                return 1;
                        continue;
                }

                if (next) {
                        btrfs_tree_unlock(next);
                        free_extent_buffer(next);
                }

                if (level == 1 && (path->locks[1] || path->skip_locking) &&
                    path->reada)
                        reada_for_search(root, path, level, slot, 0);

                next = read_node_slot(root, c, slot);
                if (!path->skip_locking) {
                        WARN_ON(!btrfs_tree_locked(c));
                        btrfs_tree_lock(next);
                }
                break;
        }
        path->slots[level] = slot;
        while (1) {
                level--;
                c = path->nodes[level];
                if (path->locks[level])
                        btrfs_tree_unlock(c);
                free_extent_buffer(c);
                path->nodes[level] = next;
                path->slots[level] = 0;
                if (!path->skip_locking)
                        path->locks[level] = 1;
                if (!level)
                        break;
                if (level == 1 && path->locks[1] && path->reada)
                        reada_for_search(root, path, level, slot, 0);
                next = read_node_slot(root, next, 0);
                if (!path->skip_locking) {
                        WARN_ON(!btrfs_tree_locked(path->nodes[level]));
                        btrfs_tree_lock(next);
                }
        }
done:
        unlock_up(path, 0, 1);
        return 0;
}

/*
 * this uses btrfs_prev_leaf to walk backwards in the tree, and keeps
 * searching until it gets past min_objectid or finds an item of 'type'
 *
 * returns 0 if something is found, 1 if nothing was found and < 0 on error
 */
int btrfs_previous_item(struct btrfs_root *root,
                        struct btrfs_path *path, u64 min_objectid,
                        int type)
{
        struct btrfs_key found_key;
        struct extent_buffer *leaf;
        u32 nritems;
        int ret;

        while (1) {
                if (path->slots[0] == 0) {
                        ret = btrfs_prev_leaf(root, path);
                        if (ret != 0)
                                return ret;
                } else {
                        path->slots[0]--;
                }
                leaf = path->nodes[0];
                nritems = btrfs_header_nritems(leaf);
                if (nritems == 0)
                        return 1;
                if (path->slots[0] == nritems)
                        path->slots[0]--;

                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
                if (found_key.type == type)
                        return 0;
                if (found_key.objectid < min_objectid)
                        break;
                if (found_key.objectid == min_objectid &&
                    found_key.type < type)
                        break;
        }
        return 1;
}