ctree.c

Go to the documentation of this file.

/*
 * 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 <linux/slab.h>
#include <linux/rbtree.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 void del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
            struct btrfs_path *path, int level, int slot,
            int tree_mod_log);
static void tree_mod_log_free_eb(struct btrfs_fs_info *fs_info,
                 struct extent_buffer *eb);
struct extent_buffer *read_old_tree_block(struct btrfs_root *root, u64 bytenr,
                      u32 blocksize, u64 parent_transid,
                      u64 time_seq);
struct extent_buffer *btrfs_find_old_tree_block(struct btrfs_root *root,
                        u64 bytenr, u32 blocksize,
                        u64 time_seq);

struct btrfs_path *btrfs_alloc_path(void)
{
    struct btrfs_path *path;
    path = kmem_cache_zalloc(btrfs_path_cachep, GFP_NOFS);
    return path;
}

/*
 * set all locked nodes in the path to blocking locks.  This should
 * be done before scheduling
 */
noinline void btrfs_set_path_blocking(struct btrfs_path *p)
{
    int i;
    for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
        if (!p->nodes[i] || !p->locks[i])
            continue;
        btrfs_set_lock_blocking_rw(p->nodes[i], p->locks[i]);
        if (p->locks[i] == BTRFS_READ_LOCK)
            p->locks[i] = BTRFS_READ_LOCK_BLOCKING;
        else if (p->locks[i] == BTRFS_WRITE_LOCK)
            p->locks[i] = BTRFS_WRITE_LOCK_BLOCKING;
    }
}

/*
 * reset all the locked nodes in the patch to spinning locks.
 *
 * held is used to keep lockdep happy, when lockdep is enabled
 * we set held to a blocking lock before we go around and
 * retake all the spinlocks in the path.  You can safely use NULL
 * for held
 */
noinline void btrfs_clear_path_blocking(struct btrfs_path *p,
                    struct extent_buffer *held, int held_rw)
{
    int i;

#ifdef CONFIG_DEBUG_LOCK_ALLOC
    /* lockdep really cares that we take all of these spinlocks
     * in the right order.  If any of the locks in the path are not
     * currently blocking, it is going to complain.  So, make really
     * really sure by forcing the path to blocking before we clear
     * the path blocking.
     */
    if (held) {
        btrfs_set_lock_blocking_rw(held, held_rw);
        if (held_rw == BTRFS_WRITE_LOCK)
            held_rw = BTRFS_WRITE_LOCK_BLOCKING;
        else if (held_rw == BTRFS_READ_LOCK)
            held_rw = BTRFS_READ_LOCK_BLOCKING;
    }
    btrfs_set_path_blocking(p);
#endif

    for (i = BTRFS_MAX_LEVEL - 1; i >= 0; i--) {
        if (p->nodes[i] && p->locks[i]) {
            btrfs_clear_lock_blocking_rw(p->nodes[i], p->locks[i]);
            if (p->locks[i] == BTRFS_WRITE_LOCK_BLOCKING)
                p->locks[i] = BTRFS_WRITE_LOCK;
            else if (p->locks[i] == BTRFS_READ_LOCK_BLOCKING)
                p->locks[i] = BTRFS_READ_LOCK;
        }
    }

#ifdef CONFIG_DEBUG_LOCK_ALLOC
    if (held)
        btrfs_clear_lock_blocking_rw(held, held_rw);
#endif
}

/* this also releases the path */
void btrfs_free_path(struct btrfs_path *p)
{
    if (!p)
        return;
    btrfs_release_path(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_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_rw(p->nodes[i], p->locks[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;

    while (1) {
        rcu_read_lock();
        eb = rcu_dereference(root->node);

        /*
         * RCU really hurts here, we could free up the root node because
         * it was cow'ed but we may not get the new root node yet so do
         * the inc_not_zero dance and if it doesn't work then
         * synchronize_rcu and try again.
         */
        if (atomic_inc_not_zero(&eb->refs)) {
            rcu_read_unlock();
            break;
        }
        rcu_read_unlock();
        synchronize_rcu();
    }
    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);
        if (eb == root->node)
            break;
        btrfs_tree_unlock(eb);
        free_extent_buffer(eb);
    }
    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_read_lock_root_node(struct btrfs_root *root)
{
    struct extent_buffer *eb;

    while (1) {
        eb = btrfs_root_node(root);
        btrfs_tree_read_lock(eb);
        if (eb == root->node)
            break;
        btrfs_tree_read_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)
{
    spin_lock(&root->fs_info->trans_lock);
    if (root->track_dirty && list_empty(&root->dirty_list)) {
        list_add(&root->dirty_list,
             &root->fs_info->dirty_cowonly_roots);
    }
    spin_unlock(&root->fs_info->trans_lock);
}

/*
 * 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;
    int ret = 0;
    int level;
    struct btrfs_disk_key disk_key;

    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);
    if (level == 0)
        btrfs_item_key(buf, &disk_key, 0);
    else
        btrfs_node_key(buf, &disk_key, 0);

    cow = btrfs_alloc_free_block(trans, root, buf->len, 0,
                     new_root_objectid, &disk_key, level,
                     buf->start, 0);
    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_backref_rev(cow, BTRFS_MIXED_BACKREF_REV);
    btrfs_clear_header_flag(cow, BTRFS_HEADER_FLAG_WRITTEN |
                     BTRFS_HEADER_FLAG_RELOC);
    if (new_root_objectid == BTRFS_TREE_RELOC_OBJECTID)
        btrfs_set_header_flag(cow, BTRFS_HEADER_FLAG_RELOC);
    else
        btrfs_set_header_owner(cow, new_root_objectid);

    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 (new_root_objectid == BTRFS_TREE_RELOC_OBJECTID)
        ret = btrfs_inc_ref(trans, root, cow, 1, 1);
    else
        ret = btrfs_inc_ref(trans, root, cow, 0, 1);

    if (ret)
        return ret;

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

enum mod_log_op {
    MOD_LOG_KEY_REPLACE,
    MOD_LOG_KEY_ADD,
    MOD_LOG_KEY_REMOVE,
    MOD_LOG_KEY_REMOVE_WHILE_FREEING,
    MOD_LOG_KEY_REMOVE_WHILE_MOVING,
    MOD_LOG_MOVE_KEYS,
    MOD_LOG_ROOT_REPLACE,
};

struct tree_mod_move {
    int dst_slot;
    int nr_items;
};

struct tree_mod_root {
    u64 logical;
    u8 level;
};

struct tree_mod_elem {
    struct rb_node node;
    u64 index;      /* shifted logical */
    u64 seq;
    enum mod_log_op op;

    /* this is used for MOD_LOG_KEY_* and MOD_LOG_MOVE_KEYS operations */
    int slot;

    /* this is used for MOD_LOG_KEY* and MOD_LOG_ROOT_REPLACE */
    u64 generation;

    /* those are used for op == MOD_LOG_KEY_{REPLACE,REMOVE} */
    struct btrfs_disk_key key;
    u64 blockptr;

    /* this is used for op == MOD_LOG_MOVE_KEYS */
    struct tree_mod_move move;

    /* this is used for op == MOD_LOG_ROOT_REPLACE */
    struct tree_mod_root old_root;
};

static inline void tree_mod_log_read_lock(struct btrfs_fs_info *fs_info)
{
    read_lock(&fs_info->tree_mod_log_lock);
}

static inline void tree_mod_log_read_unlock(struct btrfs_fs_info *fs_info)
{
    read_unlock(&fs_info->tree_mod_log_lock);
}

static inline void tree_mod_log_write_lock(struct btrfs_fs_info *fs_info)
{
    write_lock(&fs_info->tree_mod_log_lock);
}

static inline void tree_mod_log_write_unlock(struct btrfs_fs_info *fs_info)
{
    write_unlock(&fs_info->tree_mod_log_lock);
}

/*
 * This adds a new blocker to the tree mod log's blocker list if the @elem
 * passed does not already have a sequence number set. So when a caller expects
 * to record tree modifications, it should ensure to set elem->seq to zero
 * before calling btrfs_get_tree_mod_seq.
 * Returns a fresh, unused tree log modification sequence number, even if no new
 * blocker was added.
 */
u64 btrfs_get_tree_mod_seq(struct btrfs_fs_info *fs_info,
               struct seq_list *elem)
{
    u64 seq;

    tree_mod_log_write_lock(fs_info);
    spin_lock(&fs_info->tree_mod_seq_lock);
    if (!elem->seq) {
        elem->seq = btrfs_inc_tree_mod_seq(fs_info);
        list_add_tail(&elem->list, &fs_info->tree_mod_seq_list);
    }
    seq = btrfs_inc_tree_mod_seq(fs_info);
    spin_unlock(&fs_info->tree_mod_seq_lock);
    tree_mod_log_write_unlock(fs_info);

    return seq;
}

void btrfs_put_tree_mod_seq(struct btrfs_fs_info *fs_info,
                struct seq_list *elem)
{
    struct rb_root *tm_root;
    struct rb_node *node;
    struct rb_node *next;
    struct seq_list *cur_elem;
    struct tree_mod_elem *tm;
    u64 min_seq = (u64)-1;
    u64 seq_putting = elem->seq;

    if (!seq_putting)
        return;

    spin_lock(&fs_info->tree_mod_seq_lock);
    list_del(&elem->list);
    elem->seq = 0;

    list_for_each_entry(cur_elem, &fs_info->tree_mod_seq_list, list) {
        if (cur_elem->seq < min_seq) {
            if (seq_putting > cur_elem->seq) {
                /*
                 * blocker with lower sequence number exists, we
                 * cannot remove anything from the log
                 */
                spin_unlock(&fs_info->tree_mod_seq_lock);
                return;
            }
            min_seq = cur_elem->seq;
        }
    }
    spin_unlock(&fs_info->tree_mod_seq_lock);

    /*
     * anything that's lower than the lowest existing (read: blocked)
     * sequence number can be removed from the tree.
     */
    tree_mod_log_write_lock(fs_info);
    tm_root = &fs_info->tree_mod_log;
    for (node = rb_first(tm_root); node; node = next) {
        next = rb_next(node);
        tm = container_of(node, struct tree_mod_elem, node);
        if (tm->seq > min_seq)
            continue;
        rb_erase(node, tm_root);
        kfree(tm);
    }
    tree_mod_log_write_unlock(fs_info);
}

/*
 * key order of the log:
 *       index -> sequence
 *
 * the index is the shifted logical of the *new* root node for root replace
 * operations, or the shifted logical of the affected block for all other
 * operations.
 */
static noinline int
__tree_mod_log_insert(struct btrfs_fs_info *fs_info, struct tree_mod_elem *tm)
{
    struct rb_root *tm_root;
    struct rb_node **new;
    struct rb_node *parent = NULL;
    struct tree_mod_elem *cur;

    BUG_ON(!tm || !tm->seq);

    tm_root = &fs_info->tree_mod_log;
    new = &tm_root->rb_node;
    while (*new) {
        cur = container_of(*new, struct tree_mod_elem, node);
        parent = *new;
        if (cur->index < tm->index)
            new = &((*new)->rb_left);
        else if (cur->index > tm->index)
            new = &((*new)->rb_right);
        else if (cur->seq < tm->seq)
            new = &((*new)->rb_left);
        else if (cur->seq > tm->seq)
            new = &((*new)->rb_right);
        else {
            kfree(tm);
            return -EEXIST;
        }
    }

    rb_link_node(&tm->node, parent, new);
    rb_insert_color(&tm->node, tm_root);
    return 0;
}

/*
 * Determines if logging can be omitted. Returns 1 if it can. Otherwise, it
 * returns zero with the tree_mod_log_lock acquired. The caller must hold
 * this until all tree mod log insertions are recorded in the rb tree and then
 * call tree_mod_log_write_unlock() to release.
 */
static inline int tree_mod_dont_log(struct btrfs_fs_info *fs_info,
                    struct extent_buffer *eb) {
    smp_mb();
    if (list_empty(&(fs_info)->tree_mod_seq_list))
        return 1;
    if (eb && btrfs_header_level(eb) == 0)
        return 1;

    tree_mod_log_write_lock(fs_info);
    if (list_empty(&fs_info->tree_mod_seq_list)) {
        /*
         * someone emptied the list while we were waiting for the lock.
         * we must not add to the list when no blocker exists.
         */
        tree_mod_log_write_unlock(fs_info);
        return 1;
    }

    return 0;
}

/*
 * This allocates memory and gets a tree modification sequence number.
 *
 * Returns <0 on error.
 * Returns >0 (the added sequence number) on success.
 */
static inline int tree_mod_alloc(struct btrfs_fs_info *fs_info, gfp_t flags,
                 struct tree_mod_elem **tm_ret)
{
    struct tree_mod_elem *tm;

    /*
     * once we switch from spin locks to something different, we should
     * honor the flags parameter here.
     */
    tm = *tm_ret = kzalloc(sizeof(*tm), GFP_ATOMIC);
    if (!tm)
        return -ENOMEM;

    tm->seq = btrfs_inc_tree_mod_seq(fs_info);
    return tm->seq;
}

static inline int
__tree_mod_log_insert_key(struct btrfs_fs_info *fs_info,
              struct extent_buffer *eb, int slot,
              enum mod_log_op op, gfp_t flags)
{
    int ret;
    struct tree_mod_elem *tm;

    ret = tree_mod_alloc(fs_info, flags, &tm);
    if (ret < 0)
        return ret;

    tm->index = eb->start >> PAGE_CACHE_SHIFT;
    if (op != MOD_LOG_KEY_ADD) {
        btrfs_node_key(eb, &tm->key, slot);
        tm->blockptr = btrfs_node_blockptr(eb, slot);
    }
    tm->op = op;
    tm->slot = slot;
    tm->generation = btrfs_node_ptr_generation(eb, slot);

    return __tree_mod_log_insert(fs_info, tm);
}

static noinline int
tree_mod_log_insert_key_mask(struct btrfs_fs_info *fs_info,
                 struct extent_buffer *eb, int slot,
                 enum mod_log_op op, gfp_t flags)
{
    int ret;

    if (tree_mod_dont_log(fs_info, eb))
        return 0;

    ret = __tree_mod_log_insert_key(fs_info, eb, slot, op, flags);

    tree_mod_log_write_unlock(fs_info);
    return ret;
}

static noinline int
tree_mod_log_insert_key(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
            int slot, enum mod_log_op op)
{
    return tree_mod_log_insert_key_mask(fs_info, eb, slot, op, GFP_NOFS);
}

static noinline int
tree_mod_log_insert_key_locked(struct btrfs_fs_info *fs_info,
                 struct extent_buffer *eb, int slot,
                 enum mod_log_op op)
{
    return __tree_mod_log_insert_key(fs_info, eb, slot, op, GFP_NOFS);
}

static noinline int
tree_mod_log_insert_move(struct btrfs_fs_info *fs_info,
             struct extent_buffer *eb, int dst_slot, int src_slot,
             int nr_items, gfp_t flags)
{
    struct tree_mod_elem *tm;
    int ret;
    int i;

    if (tree_mod_dont_log(fs_info, eb))
        return 0;

    /*
     * When we override something during the move, we log these removals.
     * This can only happen when we move towards the beginning of the
     * buffer, i.e. dst_slot < src_slot.
     */
    for (i = 0; i + dst_slot < src_slot && i < nr_items; i++) {
        ret = tree_mod_log_insert_key_locked(fs_info, eb, i + dst_slot,
                          MOD_LOG_KEY_REMOVE_WHILE_MOVING);
        BUG_ON(ret < 0);
    }

    ret = tree_mod_alloc(fs_info, flags, &tm);
    if (ret < 0)
        goto out;

    tm->index = eb->start >> PAGE_CACHE_SHIFT;
    tm->slot = src_slot;
    tm->move.dst_slot = dst_slot;
    tm->move.nr_items = nr_items;
    tm->op = MOD_LOG_MOVE_KEYS;

    ret = __tree_mod_log_insert(fs_info, tm);
out:
    tree_mod_log_write_unlock(fs_info);
    return ret;
}

static inline void
__tree_mod_log_free_eb(struct btrfs_fs_info *fs_info, struct extent_buffer *eb)
{
    int i;
    u32 nritems;
    int ret;

    if (btrfs_header_level(eb) == 0)
        return;

    nritems = btrfs_header_nritems(eb);
    for (i = nritems - 1; i >= 0; i--) {
        ret = tree_mod_log_insert_key_locked(fs_info, eb, i,
                          MOD_LOG_KEY_REMOVE_WHILE_FREEING);
        BUG_ON(ret < 0);
    }
}

static noinline int
tree_mod_log_insert_root(struct btrfs_fs_info *fs_info,
             struct extent_buffer *old_root,
             struct extent_buffer *new_root, gfp_t flags)
{
    struct tree_mod_elem *tm;
    int ret;

    if (tree_mod_dont_log(fs_info, NULL))
        return 0;

    ret = tree_mod_alloc(fs_info, flags, &tm);
    if (ret < 0)
        goto out;

    tm->index = new_root->start >> PAGE_CACHE_SHIFT;
    tm->old_root.logical = old_root->start;
    tm->old_root.level = btrfs_header_level(old_root);
    tm->generation = btrfs_header_generation(old_root);
    tm->op = MOD_LOG_ROOT_REPLACE;

    ret = __tree_mod_log_insert(fs_info, tm);
out:
    tree_mod_log_write_unlock(fs_info);
    return ret;
}

static struct tree_mod_elem *
__tree_mod_log_search(struct btrfs_fs_info *fs_info, u64 start, u64 min_seq,
              int smallest)
{
    struct rb_root *tm_root;
    struct rb_node *node;
    struct tree_mod_elem *cur = NULL;
    struct tree_mod_elem *found = NULL;
    u64 index = start >> PAGE_CACHE_SHIFT;

    tree_mod_log_read_lock(fs_info);
    tm_root = &fs_info->tree_mod_log;
    node = tm_root->rb_node;
    while (node) {
        cur = container_of(node, struct tree_mod_elem, node);
        if (cur->index < index) {
            node = node->rb_left;
        } else if (cur->index > index) {
            node = node->rb_right;
        } else if (cur->seq < min_seq) {
            node = node->rb_left;
        } else if (!smallest) {
            /* we want the node with the highest seq */
            if (found)
                BUG_ON(found->seq > cur->seq);
            found = cur;
            node = node->rb_left;
        } else if (cur->seq > min_seq) {
            /* we want the node with the smallest seq */
            if (found)
                BUG_ON(found->seq < cur->seq);
            found = cur;
            node = node->rb_right;
        } else {
            found = cur;
            break;
        }
    }
    tree_mod_log_read_unlock(fs_info);

    return found;
}

/*
 * this returns the element from the log with the smallest time sequence
 * value that's in the log (the oldest log item). any element with a time
 * sequence lower than min_seq will be ignored.
 */
static struct tree_mod_elem *
tree_mod_log_search_oldest(struct btrfs_fs_info *fs_info, u64 start,
               u64 min_seq)
{
    return __tree_mod_log_search(fs_info, start, min_seq, 1);
}

/*
 * this returns the element from the log with the largest time sequence
 * value that's in the log (the most recent log item). any element with
 * a time sequence lower than min_seq will be ignored.
 */
static struct tree_mod_elem *
tree_mod_log_search(struct btrfs_fs_info *fs_info, u64 start, u64 min_seq)
{
    return __tree_mod_log_search(fs_info, start, min_seq, 0);
}

static noinline void
tree_mod_log_eb_copy(struct btrfs_fs_info *fs_info, struct extent_buffer *dst,
             struct extent_buffer *src, unsigned long dst_offset,
             unsigned long src_offset, int nr_items)
{
    int ret;
    int i;

    if (tree_mod_dont_log(fs_info, NULL))
        return;

    if (btrfs_header_level(dst) == 0 && btrfs_header_level(src) == 0) {
        tree_mod_log_write_unlock(fs_info);
        return;
    }

    for (i = 0; i < nr_items; i++) {
        ret = tree_mod_log_insert_key_locked(fs_info, src,
                             i + src_offset,
                             MOD_LOG_KEY_REMOVE);
        BUG_ON(ret < 0);
        ret = tree_mod_log_insert_key_locked(fs_info, dst,
                             i + dst_offset,
                             MOD_LOG_KEY_ADD);
        BUG_ON(ret < 0);
    }

    tree_mod_log_write_unlock(fs_info);
}

static inline void
tree_mod_log_eb_move(struct btrfs_fs_info *fs_info, struct extent_buffer *dst,
             int dst_offset, int src_offset, int nr_items)
{
    int ret;
    ret = tree_mod_log_insert_move(fs_info, dst, dst_offset, src_offset,
                       nr_items, GFP_NOFS);
    BUG_ON(ret < 0);
}

static noinline void
tree_mod_log_set_node_key(struct btrfs_fs_info *fs_info,
              struct extent_buffer *eb,
              struct btrfs_disk_key *disk_key, int slot, int atomic)
{
    int ret;

    ret = tree_mod_log_insert_key_mask(fs_info, eb, slot,
                       MOD_LOG_KEY_REPLACE,
                       atomic ? GFP_ATOMIC : GFP_NOFS);
    BUG_ON(ret < 0);
}

static noinline void
tree_mod_log_free_eb(struct btrfs_fs_info *fs_info, struct extent_buffer *eb)
{
    if (tree_mod_dont_log(fs_info, eb))
        return;

    __tree_mod_log_free_eb(fs_info, eb);

    tree_mod_log_write_unlock(fs_info);
}

static noinline void
tree_mod_log_set_root_pointer(struct btrfs_root *root,
                  struct extent_buffer *new_root_node)
{
    int ret;
    ret = tree_mod_log_insert_root(root->fs_info, root->node,
                       new_root_node, GFP_NOFS);
    BUG_ON(ret < 0);
}

/*
 * check if the tree block can be shared by multiple trees
 */
int btrfs_block_can_be_shared(struct btrfs_root *root,
                  struct extent_buffer *buf)
{
    /*
     * Tree blocks not in refernece counted trees and tree roots
     * are never shared. If a block was allocated after the last
     * snapshot and the block was not allocated by tree relocation,
     * we know the block is not shared.
     */
    if (root->ref_cows &&
        buf != root->node && buf != root->commit_root &&
        (btrfs_header_generation(buf) <=
         btrfs_root_last_snapshot(&root->root_item) ||
         btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)))
        return 1;
#ifdef BTRFS_COMPAT_EXTENT_TREE_V0
    if (root->ref_cows &&
        btrfs_header_backref_rev(buf) < BTRFS_MIXED_BACKREF_REV)
        return 1;
#endif
    return 0;
}

static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
                       struct btrfs_root *root,
                       struct extent_buffer *buf,
                       struct extent_buffer *cow,
                       int *last_ref)
{
    u64 refs;
    u64 owner;
    u64 flags;
    u64 new_flags = 0;
    int ret;

    /*
     * Backrefs update rules:
     *
     * Always use full backrefs for extent pointers in tree block
     * allocated by tree relocation.
     *
     * If a shared tree block is no longer referenced by its owner
     * tree (btrfs_header_owner(buf) == root->root_key.objectid),
     * use full backrefs for extent pointers in tree block.
     *
     * If a tree block is been relocating
     * (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID),
     * use full backrefs for extent pointers in tree block.
     * The reason for this is some operations (such as drop tree)
     * are only allowed for blocks use full backrefs.
     */

    if (btrfs_block_can_be_shared(root, buf)) {
        ret = btrfs_lookup_extent_info(trans, root, buf->start,
                           buf->len, &refs, &flags);
        if (ret)
            return ret;
        if (refs == 0) {
            ret = -EROFS;
            btrfs_std_error(root->fs_info, ret);
            return ret;
        }
    } else {
        refs = 1;
        if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||
            btrfs_header_backref_rev(buf) < BTRFS_MIXED_BACKREF_REV)
            flags = BTRFS_BLOCK_FLAG_FULL_BACKREF;
        else
            flags = 0;
    }

    owner = btrfs_header_owner(buf);
    BUG_ON(owner == BTRFS_TREE_RELOC_OBJECTID &&
           !(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF));

    if (refs > 1) {
        if ((owner == root->root_key.objectid ||
             root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) &&
            !(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF)) {
            ret = btrfs_inc_ref(trans, root, buf, 1, 1);
            BUG_ON(ret); /* -ENOMEM */

            if (root->root_key.objectid ==
                BTRFS_TREE_RELOC_OBJECTID) {
                ret = btrfs_dec_ref(trans, root, buf, 0, 1);
                BUG_ON(ret); /* -ENOMEM */
                ret = btrfs_inc_ref(trans, root, cow, 1, 1);
                BUG_ON(ret); /* -ENOMEM */
            }
            new_flags |= BTRFS_BLOCK_FLAG_FULL_BACKREF;
        } else {

            if (root->root_key.objectid ==
                BTRFS_TREE_RELOC_OBJECTID)
                ret = btrfs_inc_ref(trans, root, cow, 1, 1);
            else
                ret = btrfs_inc_ref(trans, root, cow, 0, 1);
            BUG_ON(ret); /* -ENOMEM */
        }
        if (new_flags != 0) {
            ret = btrfs_set_disk_extent_flags(trans, root,
                              buf->start,
                              buf->len,
                              new_flags, 0);
            if (ret)
                return ret;
        }
    } else {
        if (flags & BTRFS_BLOCK_FLAG_FULL_BACKREF) {
            if (root->root_key.objectid ==
                BTRFS_TREE_RELOC_OBJECTID)
                ret = btrfs_inc_ref(trans, root, cow, 1, 1);
            else
                ret = btrfs_inc_ref(trans, root, cow, 0, 1);
            BUG_ON(ret); /* -ENOMEM */
            ret = btrfs_dec_ref(trans, root, buf, 1, 1);
            BUG_ON(ret); /* -ENOMEM */
        }
        tree_mod_log_free_eb(root->fs_info, buf);
        clean_tree_block(trans, root, buf);
        *last_ref = 1;
    }
    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.
 */
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)
{
    struct btrfs_disk_key disk_key;
    struct extent_buffer *cow;
    int level, ret;
    int last_ref = 0;
    int unlock_orig = 0;
    u64 parent_start;

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

    btrfs_assert_tree_locked(buf);

    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);

    if (level == 0)
        btrfs_item_key(buf, &disk_key, 0);
    else
        btrfs_node_key(buf, &disk_key, 0);

    if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) {
        if (parent)
            parent_start = parent->start;
        else
            parent_start = 0;
    } else
        parent_start = 0;

    cow = btrfs_alloc_free_block(trans, root, buf->len, parent_start,
                     root->root_key.objectid, &disk_key,
                     level, search_start, empty_size);
    if (IS_ERR(cow))
        return PTR_ERR(cow);

    /* cow is set to blocking by btrfs_init_new_buffer */

    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_backref_rev(cow, BTRFS_MIXED_BACKREF_REV);
    btrfs_clear_header_flag(cow, BTRFS_HEADER_FLAG_WRITTEN |
                     BTRFS_HEADER_FLAG_RELOC);
    if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
        btrfs_set_header_flag(cow, BTRFS_HEADER_FLAG_RELOC);
    else
        btrfs_set_header_owner(cow, root->root_key.objectid);

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

    ret = update_ref_for_cow(trans, root, buf, cow, &last_ref);
    if (ret) {
        btrfs_abort_transaction(trans, root, ret);
        return ret;
    }

    if (root->ref_cows)
        btrfs_reloc_cow_block(trans, root, buf, cow);

    if (buf == root->node) {
        WARN_ON(parent && parent != buf);
        if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID ||
            btrfs_header_backref_rev(buf) < BTRFS_MIXED_BACKREF_REV)
            parent_start = buf->start;
        else
            parent_start = 0;

        extent_buffer_get(cow);
        tree_mod_log_set_root_pointer(root, cow);
        rcu_assign_pointer(root->node, cow);

        btrfs_free_tree_block(trans, root, buf, parent_start,
                      last_ref);
        free_extent_buffer(buf);
        add_root_to_dirty_list(root);
    } else {
        if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
            parent_start = parent->start;
        else
            parent_start = 0;

        WARN_ON(trans->transid != btrfs_header_generation(parent));
        tree_mod_log_insert_key(root->fs_info, parent, parent_slot,
                    MOD_LOG_KEY_REPLACE);
        btrfs_set_node_blockptr(parent, parent_slot,
                    cow->start);
        btrfs_set_node_ptr_generation(parent, parent_slot,
                          trans->transid);
        btrfs_mark_buffer_dirty(parent);
        btrfs_free_tree_block(trans, root, buf, parent_start,
                      last_ref);
    }
    if (unlock_orig)
        btrfs_tree_unlock(buf);
    free_extent_buffer_stale(buf);
    btrfs_mark_buffer_dirty(cow);
    *cow_ret = cow;
    return 0;
}

/*
 * returns the logical address of the oldest predecessor of the given root.
 * entries older than time_seq are ignored.
 */
static struct tree_mod_elem *
__tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info,
               struct btrfs_root *root, u64 time_seq)
{
    struct tree_mod_elem *tm;
    struct tree_mod_elem *found = NULL;
    u64 root_logical = root->node->start;
    int looped = 0;

    if (!time_seq)
        return 0;

    /*
     * the very last operation that's logged for a root is the replacement
     * operation (if it is replaced at all). this has the index of the *new*
     * root, making it the very first operation that's logged for this root.
     */
    while (1) {
        tm = tree_mod_log_search_oldest(fs_info, root_logical,
                        time_seq);
        if (!looped && !tm)
            return 0;
        /*
         * if there are no tree operation for the oldest root, we simply
         * return it. this should only happen if that (old) root is at
         * level 0.
         */
        if (!tm)
            break;

        /*
         * if there's an operation that's not a root replacement, we
         * found the oldest version of our root. normally, we'll find a
         * MOD_LOG_KEY_REMOVE_WHILE_FREEING operation here.
         */
        if (tm->op != MOD_LOG_ROOT_REPLACE)
            break;

        found = tm;
        root_logical = tm->old_root.logical;
        BUG_ON(root_logical == root->node->start);
        looped = 1;
    }

    /* if there's no old root to return, return what we found instead */
    if (!found)
        found = tm;

    return found;
}

/*
 * tm is a pointer to the first operation to rewind within eb. then, all
 * previous operations will be rewinded (until we reach something older than
 * time_seq).
 */
static void
__tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq,
              struct tree_mod_elem *first_tm)
{
    u32 n;
    struct rb_node *next;
    struct tree_mod_elem *tm = first_tm;
    unsigned long o_dst;
    unsigned long o_src;
    unsigned long p_size = sizeof(struct btrfs_key_ptr);

    n = btrfs_header_nritems(eb);
    while (tm && tm->seq >= time_seq) {
        /*
         * all the operations are recorded with the operator used for
         * the modification. as we're going backwards, we do the
         * opposite of each operation here.
         */
        switch (tm->op) {
        case MOD_LOG_KEY_REMOVE_WHILE_FREEING:
            BUG_ON(tm->slot < n);
        case MOD_LOG_KEY_REMOVE_WHILE_MOVING:
        case MOD_LOG_KEY_REMOVE:
            btrfs_set_node_key(eb, &tm->key, tm->slot);
            btrfs_set_node_blockptr(eb, tm->slot, tm->blockptr);
            btrfs_set_node_ptr_generation(eb, tm->slot,
                              tm->generation);
            n++;
            break;
        case MOD_LOG_KEY_REPLACE:
            BUG_ON(tm->slot >= n);
            btrfs_set_node_key(eb, &tm->key, tm->slot);
            btrfs_set_node_blockptr(eb, tm->slot, tm->blockptr);
            btrfs_set_node_ptr_generation(eb, tm->slot,
                              tm->generation);
            break;
        case MOD_LOG_KEY_ADD:
            /* if a move operation is needed it's in the log */
            n--;
            break;
        case MOD_LOG_MOVE_KEYS:
            o_dst = btrfs_node_key_ptr_offset(tm->slot);
            o_src = btrfs_node_key_ptr_offset(tm->move.dst_slot);
            memmove_extent_buffer(eb, o_dst, o_src,
                          tm->move.nr_items * p_size);
            break;
        case MOD_LOG_ROOT_REPLACE:
            /*
             * this operation is special. for roots, this must be
             * handled explicitly before rewinding.
             * for non-roots, this operation may exist if the node
             * was a root: root A -> child B; then A gets empty and
             * B is promoted to the new root. in the mod log, we'll
             * have a root-replace operation for B, a tree block
             * that is no root. we simply ignore that operation.
             */
            break;
        }
        next = rb_next(&tm->node);
        if (!next)
            break;
        tm = container_of(next, struct tree_mod_elem, node);
        if (tm->index != first_tm->index)
            break;
    }
    btrfs_set_header_nritems(eb, n);
}

static struct extent_buffer *
tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
            u64 time_seq)
{
    struct extent_buffer *eb_rewin;
    struct tree_mod_elem *tm;

    if (!time_seq)
        return eb;

    if (btrfs_header_level(eb) == 0)
        return eb;

    tm = tree_mod_log_search(fs_info, eb->start, time_seq);
    if (!tm)
        return eb;

    if (tm->op == MOD_LOG_KEY_REMOVE_WHILE_FREEING) {
        BUG_ON(tm->slot != 0);
        eb_rewin = alloc_dummy_extent_buffer(eb->start,
                        fs_info->tree_root->nodesize);
        BUG_ON(!eb_rewin);
        btrfs_set_header_bytenr(eb_rewin, eb->start);
        btrfs_set_header_backref_rev(eb_rewin,
                         btrfs_header_backref_rev(eb));
        btrfs_set_header_owner(eb_rewin, btrfs_header_owner(eb));
        btrfs_set_header_level(eb_rewin, btrfs_header_level(eb));
    } else {
        eb_rewin = btrfs_clone_extent_buffer(eb);
        BUG_ON(!eb_rewin);
    }

    extent_buffer_get(eb_rewin);
    free_extent_buffer(eb);

    __tree_mod_log_rewind(eb_rewin, time_seq, tm);
    WARN_ON(btrfs_header_nritems(eb_rewin) >
        BTRFS_NODEPTRS_PER_BLOCK(fs_info->fs_root));

    return eb_rewin;
}

/*
 * get_old_root() rewinds the state of @root's root node to the given @time_seq
 * value. If there are no changes, the current root->root_node is returned. If
 * anything changed in between, there's a fresh buffer allocated on which the
 * rewind operations are done. In any case, the returned buffer is read locked.
 * Returns NULL on error (with no locks held).
 */
static inline struct extent_buffer *
get_old_root(struct btrfs_root *root, u64 time_seq)
{
    struct tree_mod_elem *tm;
    struct extent_buffer *eb;
    struct extent_buffer *old;
    struct tree_mod_root *old_root = NULL;
    u64 old_generation = 0;
    u64 logical;
    u32 blocksize;

    eb = btrfs_read_lock_root_node(root);
    tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq);
    if (!tm)
        return root->node;

    if (tm->op == MOD_LOG_ROOT_REPLACE) {
        old_root = &tm->old_root;
        old_generation = tm->generation;
        logical = old_root->logical;
    } else {
        logical = root->node->start;
    }

    tm = tree_mod_log_search(root->fs_info, logical, time_seq);
    if (old_root && tm && tm->op != MOD_LOG_KEY_REMOVE_WHILE_FREEING) {
        btrfs_tree_read_unlock(root->node);
        free_extent_buffer(root->node);
        blocksize = btrfs_level_size(root, old_root->level);
        old = read_tree_block(root, logical, blocksize, 0);
        if (!old) {
            pr_warn("btrfs: failed to read tree block %llu from get_old_root\n",
                logical);
            WARN_ON(1);
        } else {
            eb = btrfs_clone_extent_buffer(old);
            free_extent_buffer(old);
        }
    } else if (old_root) {
        btrfs_tree_read_unlock(root->node);
        free_extent_buffer(root->node);
        eb = alloc_dummy_extent_buffer(logical, root->nodesize);
    } else {
        eb = btrfs_clone_extent_buffer(root->node);
        btrfs_tree_read_unlock(root->node);
        free_extent_buffer(root->node);
    }

    if (!eb)
        return NULL;
    extent_buffer_get(eb);
    btrfs_tree_read_lock(eb);
    if (old_root) {
        btrfs_set_header_bytenr(eb, eb->start);
        btrfs_set_header_backref_rev(eb, BTRFS_MIXED_BACKREF_REV);
        btrfs_set_header_owner(eb, root->root_key.objectid);
        btrfs_set_header_level(eb, old_root->level);
        btrfs_set_header_generation(eb, old_generation);
    }
    if (tm)
        __tree_mod_log_rewind(eb, time_seq, tm);
    else
        WARN_ON(btrfs_header_level(eb) != 0);
    WARN_ON(btrfs_header_nritems(eb) > BTRFS_NODEPTRS_PER_BLOCK(root));

    return eb;
}

int btrfs_old_root_level(struct btrfs_root *root, u64 time_seq)
{
    struct tree_mod_elem *tm;
    int level;

    tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq);
    if (tm && tm->op == MOD_LOG_ROOT_REPLACE) {
        level = tm->old_root.level;
    } else {
        rcu_read_lock();
        level = btrfs_header_level(root->node);
        rcu_read_unlock();
    }

    return level;
}

static inline int should_cow_block(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root,
                   struct extent_buffer *buf)
{
    /* ensure we can see the force_cow */
    smp_rmb();

    /*
     * We do not need to cow a block if
     * 1) this block is not created or changed in this transaction;
     * 2) this block does not belong to TREE_RELOC tree;
     * 3) the root is not forced COW.
     *
     * What is forced COW:
     *    when we create snapshot during commiting the transaction,
     *    after we've finished coping src root, we must COW the shared
     *    block to ensure the metadata consistency.
     */
    if (btrfs_header_generation(buf) == trans->transid &&
        !btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN) &&
        !(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID &&
          btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)) &&
        !root->force_cow)
        return 0;
    return 1;
}

/*
 * 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 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);
    }

    if (!should_cow_block(trans, root, buf)) {
        *cow_ret = buf;
        return 0;
    }

    search_start = buf->start & ~((u64)(1024 * 1024 * 1024) - 1);

    if (parent)
        btrfs_set_lock_blocking(parent);
    btrfs_set_lock_blocking(buf);

    ret = __btrfs_cow_block(trans, root, buf, parent,
                 parent_slot, cow_ret, search_start, 0);

    trace_btrfs_cow_block(root, buf, *cow_ret);

    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);

    return btrfs_comp_cpu_keys(&k1, k2);
}

/*
 * same as comp_keys only with two btrfs_key's
 */
int btrfs_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;

    btrfs_set_lock_blocking(parent);

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

        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;
        }

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

        btrfs_tree_lock(cur);
        btrfs_set_lock_blocking(cur);
        err = __btrfs_cow_block(trans, root, cur, parent, i,
                    &cur, search_start,
                    min(16 * blocksize,
                        (end_slot - i) * blocksize));
        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);
    }
    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);
}


/*
 * 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 *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 (!kaddr || offset < map_start ||
            (offset + sizeof(struct btrfs_disk_key)) >
            map_start + map_len) {

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

            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;
            return 0;
        }
    }
    *slot = low;
    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);
}

int btrfs_bin_search(struct extent_buffer *eb, struct btrfs_key *key,
             int level, int *slot)
{
    return bin_search(eb, key, level, slot);
}

static void root_add_used(struct btrfs_root *root, u32 size)
{
    spin_lock(&root->accounting_lock);
    btrfs_set_root_used(&root->root_item,
                btrfs_root_used(&root->root_item) + size);
    spin_unlock(&root->accounting_lock);
}

static void root_sub_used(struct btrfs_root *root, u32 size)
{
    spin_lock(&root->accounting_lock);
    btrfs_set_root_used(&root->root_item,
                btrfs_root_used(&root->root_item) - size);
    spin_unlock(&root->accounting_lock);
}

/* 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];
    u64 orig_ptr;

    if (level == 0)
        return 0;

    mid = path->nodes[level];

    WARN_ON(path->locks[level] != BTRFS_WRITE_LOCK &&
        path->locks[level] != BTRFS_WRITE_LOCK_BLOCKING);
    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);
        if (!child) {
            ret = -EROFS;
            btrfs_std_error(root->fs_info, ret);
            goto enospc;
        }

        btrfs_tree_lock(child);
        btrfs_set_lock_blocking(child);
        ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
        if (ret) {
            btrfs_tree_unlock(child);
            free_extent_buffer(child);
            goto enospc;
        }

        tree_mod_log_free_eb(root->fs_info, root->node);
        tree_mod_log_set_root_pointer(root, child);
        rcu_assign_pointer(root->node, child);

        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);

        root_sub_used(root, mid->len);
        btrfs_free_tree_block(trans, root, mid, 0, 1);
        /* once for the root ptr */
        free_extent_buffer_stale(mid);
        return 0;
    }
    if (btrfs_header_nritems(mid) >
        BTRFS_NODEPTRS_PER_BLOCK(root) / 4)
        return 0;

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

    /*
     * 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) {
            clean_tree_block(trans, root, right);
            btrfs_tree_unlock(right);
            del_ptr(trans, root, path, level + 1, pslot + 1, 1);
            root_sub_used(root, right->len);
            btrfs_free_tree_block(trans, root, right, 0, 1);
            free_extent_buffer_stale(right);
            right = NULL;
        } else {
            struct btrfs_disk_key right_key;
            btrfs_node_key(right, &right_key, 0);
            tree_mod_log_set_node_key(root->fs_info, parent,
                          &right_key, pslot + 1, 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
         */
        if (!left) {
            ret = -EROFS;
            btrfs_std_error(root->fs_info, ret);
            goto enospc;
        }
        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) {
        clean_tree_block(trans, root, mid);
        btrfs_tree_unlock(mid);
        del_ptr(trans, root, path, level + 1, pslot, 1);
        root_sub_used(root, mid->len);
        btrfs_free_tree_block(trans, root, mid, 0, 1);
        free_extent_buffer_stale(mid);
        mid = NULL;
    } else {
        /* update the parent key to reflect our changes */
        struct btrfs_disk_key mid_key;
        btrfs_node_key(mid, &mid_key, 0);
        tree_mod_log_set_node_key(root->fs_info, parent, &mid_key,
                      pslot, 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 */
    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];

    if (level == 0)
        return 1;

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

    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);
        btrfs_set_lock_blocking(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);
            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);
            tree_mod_log_set_node_key(root->fs_info, parent,
                          &disk_key, pslot, 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);
        btrfs_set_lock_blocking(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);
            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);
            tree_mod_log_set_node_key(root->fs_info, parent,
                          &disk_key, pslot + 1, 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 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;
    u64 gen;
    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)) {
            gen = btrfs_node_ptr_generation(node, nr);
            readahead_tree_block(root, search, blocksize, gen);
            nread += blocksize;
        }
        nscan++;
        if ((nread > 65536 || nscan > 32))
            break;
    }
}

/*
 * returns -EAGAIN if it had to drop the path, or zero if everything was in
 * cache
 */
static noinline int reada_for_balance(struct btrfs_root *root,
                      struct btrfs_path *path, int level)
{
    int slot;
    int nritems;
    struct extent_buffer *parent;
    struct extent_buffer *eb;
    u64 gen;
    u64 block1 = 0;
    u64 block2 = 0;
    int ret = 0;
    int blocksize;

    parent = path->nodes[level + 1];
    if (!parent)
        return 0;

    nritems = btrfs_header_nritems(parent);
    slot = path->slots[level + 1];
    blocksize = btrfs_level_size(root, level);

    if (slot > 0) {
        block1 = btrfs_node_blockptr(parent, slot - 1);
        gen = btrfs_node_ptr_generation(parent, slot - 1);
        eb = btrfs_find_tree_block(root, block1, blocksize);
        /*
         * if we get -eagain from btrfs_buffer_uptodate, we
         * don't want to return eagain here.  That will loop
         * forever
         */
        if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
            block1 = 0;
        free_extent_buffer(eb);
    }
    if (slot + 1 < nritems) {
        block2 = btrfs_node_blockptr(parent, slot + 1);
        gen = btrfs_node_ptr_generation(parent, slot + 1);
        eb = btrfs_find_tree_block(root, block2, blocksize);
        if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
            block2 = 0;
        free_extent_buffer(eb);
    }
    if (block1 || block2) {
        ret = -EAGAIN;

        /* release the whole path */
        btrfs_release_path(path);

        /* read the blocks */
        if (block1)
            readahead_tree_block(root, block1, blocksize, 0);
        if (block2)
            readahead_tree_block(root, block2, blocksize, 0);

        if (block1) {
            eb = read_tree_block(root, block1, blocksize, 0);
            free_extent_buffer(eb);
        }
        if (block2) {
            eb = read_tree_block(root, block2, blocksize, 0);
            free_extent_buffer(eb);
        }
    }
    return ret;
}


/*
 * 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 min_write_lock_level,
                   int *write_lock_level)
{
    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_rw(t, path->locks[i]);
            path->locks[i] = 0;
            if (write_lock_level &&
                i > min_write_lock_level &&
                i <= *write_lock_level) {
                *write_lock_level = i - 1;
            }
        }
    }
}

/*
 * This releases any locks held in the path starting at level and
 * going all the way up to the root.
 *
 * btrfs_search_slot will keep the lock held on higher nodes in a few
 * corner cases, such as COW of the block at slot zero in the node.  This
 * ignores those rules, and it should only be called when there are no
 * more updates to be done higher up in the tree.
 */
noinline void btrfs_unlock_up_safe(struct btrfs_path *path, int level)
{
    int i;

    if (path->keep_locks)
        return;

    for (i = level; i < BTRFS_MAX_LEVEL; i++) {
        if (!path->nodes[i])
            continue;
        if (!path->locks[i])
            continue;
        btrfs_tree_unlock_rw(path->nodes[i], path->locks[i]);
        path->locks[i] = 0;
    }
}

/*
 * helper function for btrfs_search_slot.  The goal is to find a block
 * in cache without setting the path to blocking.  If we find the block
 * we return zero and the path is unchanged.
 *
 * If we can't find the block, we set the path blocking and do some
 * reada.  -EAGAIN is returned and the search must be repeated.
 */
static int
read_block_for_search(struct btrfs_trans_handle *trans,
               struct btrfs_root *root, struct btrfs_path *p,
               struct extent_buffer **eb_ret, int level, int slot,
               struct btrfs_key *key, u64 time_seq)
{
    u64 blocknr;
    u64 gen;
    u32 blocksize;
    struct extent_buffer *b = *eb_ret;
    struct extent_buffer *tmp;
    int ret;

    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) {
        /* first we do an atomic uptodate check */
        if (btrfs_buffer_uptodate(tmp, 0, 1) > 0) {
            if (btrfs_buffer_uptodate(tmp, gen, 1) > 0) {
                /*
                 * we found an up to date block without
                 * sleeping, return
                 * right away
                 */
                *eb_ret = tmp;
                return 0;
            }
            /* the pages were up to date, but we failed
             * the generation number check.  Do a full
             * read for the generation number that is correct.
             * We must do this without dropping locks so
             * we can trust our generation number
             */
            free_extent_buffer(tmp);
            btrfs_set_path_blocking(p);

            /* now we're allowed to do a blocking uptodate check */
            tmp = read_tree_block(root, blocknr, blocksize, gen);
            if (tmp && btrfs_buffer_uptodate(tmp, gen, 0) > 0) {
                *eb_ret = tmp;
                return 0;
            }
            free_extent_buffer(tmp);
            btrfs_release_path(p);
            return -EIO;
        }
    }

    /*
     * reduce lock contention at high levels
     * of the btree by dropping locks before
     * we read.  Don't release the lock on the current
     * level because we need to walk this node to figure
     * out which blocks to read.
     */
    btrfs_unlock_up_safe(p, level + 1);
    btrfs_set_path_blocking(p);

    free_extent_buffer(tmp);
    if (p->reada)
        reada_for_search(root, p, level, slot, key->objectid);

    btrfs_release_path(p);

    ret = -EAGAIN;
    tmp = read_tree_block(root, blocknr, blocksize, 0);
    if (tmp) {
        /*
         * If the read above didn't mark this buffer up to date,
         * it will never end up being up to date.  Set ret to EIO now
         * and give up so that our caller doesn't loop forever
         * on our EAGAINs.
         */
        if (!btrfs_buffer_uptodate(tmp, 0, 0))
            ret = -EIO;
        free_extent_buffer(tmp);
    }
    return ret;
}

/*
 * helper function for btrfs_search_slot.  This does all of the checks
 * for node-level blocks and does any balancing required based on
 * the ins_len.
 *
 * If no extra work was required, zero is returned.  If we had to
 * drop the path, -EAGAIN is returned and btrfs_search_slot must
 * start over
 */
static int
setup_nodes_for_search(struct btrfs_trans_handle *trans,
               struct btrfs_root *root, struct btrfs_path *p,
               struct extent_buffer *b, int level, int ins_len,
               int *write_lock_level)
{
    int ret;
    if ((p->search_for_split || ins_len > 0) && btrfs_header_nritems(b) >=
        BTRFS_NODEPTRS_PER_BLOCK(root) - 3) {
        int sret;

        if (*write_lock_level < level + 1) {
            *write_lock_level = level + 1;
            btrfs_release_path(p);
            goto again;
        }

        sret = reada_for_balance(root, p, level);
        if (sret)
            goto again;

        btrfs_set_path_blocking(p);
        sret = split_node(trans, root, p, level);
        btrfs_clear_path_blocking(p, NULL, 0);

        BUG_ON(sret > 0);
        if (sret) {
            ret = sret;
            goto done;
        }
        b = p->nodes[level];
    } else if (ins_len < 0 && btrfs_header_nritems(b) <
           BTRFS_NODEPTRS_PER_BLOCK(root) / 2) {
        int sret;

        if (*write_lock_level < level + 1) {
            *write_lock_level = level + 1;
            btrfs_release_path(p);
            goto again;
        }

        sret = reada_for_balance(root, p, level);
        if (sret)
            goto again;

        btrfs_set_path_blocking(p);
        sret = balance_level(trans, root, p, level);
        btrfs_clear_path_blocking(p, NULL, 0);

        if (sret) {
            ret = sret;
            goto done;
        }
        b = p->nodes[level];
        if (!b) {
            btrfs_release_path(p);
            goto again;
        }
        BUG_ON(btrfs_header_nritems(b) == 1);
    }
    return 0;

again:
    ret = -EAGAIN;
done:
    return ret;
}

/*
 * 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;
    int slot;
    int ret;
    int err;
    int level;
    int lowest_unlock = 1;
    int root_lock;
    /* everything at write_lock_level or lower must be write locked */
    int write_lock_level = 0;
    u8 lowest_level = 0;
    int min_write_lock_level;

    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;

        /* when we are removing items, we might have to go up to level
         * two as we update tree pointers  Make sure we keep write
         * for those levels as well
         */
        write_lock_level = 2;
    } else if (ins_len > 0) {
        /*
         * for inserting items, make sure we have a write lock on
         * level 1 so we can update keys
         */
        write_lock_level = 1;
    }

    if (!cow)
        write_lock_level = -1;

    if (cow && (p->keep_locks || p->lowest_level))
        write_lock_level = BTRFS_MAX_LEVEL;

    min_write_lock_level = write_lock_level;

again:
    /*
     * we try very hard to do read locks on the root
     */
    root_lock = BTRFS_READ_LOCK;
    level = 0;
    if (p->search_commit_root) {
        /*
         * the commit roots are read only
         * so we always do read locks
         */
        b = root->commit_root;
        extent_buffer_get(b);
        level = btrfs_header_level(b);
        if (!p->skip_locking)
            btrfs_tree_read_lock(b);
    } else {
        if (p->skip_locking) {
            b = btrfs_root_node(root);
            level = btrfs_header_level(b);
        } else {
            /* we don't know the level of the root node
             * until we actually have it read locked
             */
            b = btrfs_read_lock_root_node(root);
            level = btrfs_header_level(b);
            if (level <= write_lock_level) {
                /* whoops, must trade for write lock */
                btrfs_tree_read_unlock(b);
                free_extent_buffer(b);
                b = btrfs_lock_root_node(root);
                root_lock = BTRFS_WRITE_LOCK;

                /* the level might have changed, check again */
                level = btrfs_header_level(b);
            }
        }
    }
    p->nodes[level] = b;
    if (!p->skip_locking)
        p->locks[level] = root_lock;

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

        /*
         * setup the path here so we can release it under lock
         * contention with the cow code
         */
        if (cow) {
            /*
             * if we don't really need to cow this block
             * then we don't want to set the path blocking,
             * so we test it here
             */
            if (!should_cow_block(trans, root, b))
                goto cow_done;

            btrfs_set_path_blocking(p);

            /*
             * must have write locks on this node and the
             * parent
             */
            if (level + 1 > write_lock_level) {
                write_lock_level = level + 1;
                btrfs_release_path(p);
                goto again;
            }

            err = btrfs_cow_block(trans, root, b,
                          p->nodes[level + 1],
                          p->slots[level + 1], &b);
            if (err) {
                ret = err;
                goto done;
            }
        }
cow_done:
        BUG_ON(!cow && ins_len);

        p->nodes[level] = b;
        btrfs_clear_path_blocking(p, NULL, 0);

        /*
         * we have a lock on b and as long as we aren't changing
         * the tree, there is no way to for the items in b to change.
         * It is safe to drop the lock on our parent before we
         * go through the expensive btree search on b.
         *
         * If cow is true, then we might be changing slot zero,
         * which may require changing the parent.  So, we can't
         * drop the lock until after we know which slot we're
         * operating on.
         */
        if (!cow)
            btrfs_unlock_up_safe(p, level + 1);

        ret = bin_search(b, key, level, &slot);

        if (level != 0) {
            int dec = 0;
            if (ret && slot > 0) {
                dec = 1;
                slot -= 1;
            }
            p->slots[level] = slot;
            err = setup_nodes_for_search(trans, root, p, b, level,
                         ins_len, &write_lock_level);
            if (err == -EAGAIN)
                goto again;
            if (err) {
                ret = err;
                goto done;
            }
            b = p->nodes[level];
            slot = p->slots[level];

            /*
             * slot 0 is special, if we change the key
             * we have to update the parent pointer
             * which means we must have a write lock
             * on the parent
             */
            if (slot == 0 && cow &&
                write_lock_level < level + 1) {
                write_lock_level = level + 1;
                btrfs_release_path(p);
                goto again;
            }

            unlock_up(p, level, lowest_unlock,
                  min_write_lock_level, &write_lock_level);

            if (level == lowest_level) {
                if (dec)
                    p->slots[level]++;
                goto done;
            }

            err = read_block_for_search(trans, root, p,
                            &b, level, slot, key, 0);
            if (err == -EAGAIN)
                goto again;
            if (err) {
                ret = err;
                goto done;
            }

            if (!p->skip_locking) {
                level = btrfs_header_level(b);
                if (level <= write_lock_level) {
                    err = btrfs_try_tree_write_lock(b);
                    if (!err) {
                        btrfs_set_path_blocking(p);
                        btrfs_tree_lock(b);
                        btrfs_clear_path_blocking(p, b,
                                  BTRFS_WRITE_LOCK);
                    }
                    p->locks[level] = BTRFS_WRITE_LOCK;
                } else {
                    err = btrfs_try_tree_read_lock(b);
                    if (!err) {
                        btrfs_set_path_blocking(p);
                        btrfs_tree_read_lock(b);
                        btrfs_clear_path_blocking(p, b,
                                  BTRFS_READ_LOCK);
                    }
                    p->locks[level] = BTRFS_READ_LOCK;
                }
                p->nodes[level] = b;
            }
        } else {
            p->slots[level] = slot;
            if (ins_len > 0 &&
                btrfs_leaf_free_space(root, b) < ins_len) {
                if (write_lock_level < 1) {
                    write_lock_level = 1;
                    btrfs_release_path(p);
                    goto again;
                }

                btrfs_set_path_blocking(p);
                err = split_leaf(trans, root, key,
                         p, ins_len, ret == 0);
                btrfs_clear_path_blocking(p, NULL, 0);

                BUG_ON(err > 0);
                if (err) {
                    ret = err;
                    goto done;
                }
            }
            if (!p->search_for_split)
                unlock_up(p, level, lowest_unlock,
                      min_write_lock_level, &write_lock_level);
            goto done;
        }
    }
    ret = 1;
done:
    /*
     * we don't really know what they plan on doing with the path
     * from here on, so for now just mark it as blocking
     */
    if (!p->leave_spinning)
        btrfs_set_path_blocking(p);
    if (ret < 0)
        btrfs_release_path(p);
    return ret;
}

/*
 * Like btrfs_search_slot, this looks for a key in the given tree. It uses the
 * current state of the tree together with the operations recorded in the tree
 * modification log to search for the key in a previous version of this tree, as
 * denoted by the time_seq parameter.
 *
 * Naturally, there is no support for insert, delete or cow operations.
 *
 * The resulting path and return value will be set up as if we called
 * btrfs_search_slot at that point in time with ins_len and cow both set to 0.
 */
int btrfs_search_old_slot(struct btrfs_root *root, struct btrfs_key *key,
              struct btrfs_path *p, u64 time_seq)
{
    struct extent_buffer *b;
    int slot;
    int ret;
    int err;
    int level;
    int lowest_unlock = 1;
    u8 lowest_level = 0;

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

    if (p->search_commit_root) {
        BUG_ON(time_seq);
        return btrfs_search_slot(NULL, root, key, p, 0, 0);
    }

again:
    b = get_old_root(root, time_seq);
    level = btrfs_header_level(b);
    p->locks[level] = BTRFS_READ_LOCK;

    while (b) {
        level = btrfs_header_level(b);
        p->nodes[level] = b;
        btrfs_clear_path_blocking(p, NULL, 0);

        /*
         * we have a lock on b and as long as we aren't changing
         * the tree, there is no way to for the items in b to change.
         * It is safe to drop the lock on our parent before we
         * go through the expensive btree search on b.
         */
        btrfs_unlock_up_safe(p, level + 1);

        ret = bin_search(b, key, level, &slot);

        if (level != 0) {
            int dec = 0;
            if (ret && slot > 0) {
                dec = 1;
                slot -= 1;
            }
            p->slots[level] = slot;
            unlock_up(p, level, lowest_unlock, 0, NULL);

            if (level == lowest_level) {
                if (dec)
                    p->slots[level]++;
                goto done;
            }

            err = read_block_for_search(NULL, root, p, &b, level,
                            slot, key, time_seq);
            if (err == -EAGAIN)
                goto again;
            if (err) {
                ret = err;
                goto done;
            }

            level = btrfs_header_level(b);
            err = btrfs_try_tree_read_lock(b);
            if (!err) {
                btrfs_set_path_blocking(p);
                btrfs_tree_read_lock(b);
                btrfs_clear_path_blocking(p, b,
                              BTRFS_READ_LOCK);
            }
            p->locks[level] = BTRFS_READ_LOCK;
            p->nodes[level] = b;
            b = tree_mod_log_rewind(root->fs_info, b, time_seq);
            if (b != p->nodes[level]) {
                btrfs_tree_unlock_rw(p->nodes[level],
                             p->locks[level]);
                p->locks[level] = 0;
                p->nodes[level] = b;
            }
        } else {
            p->slots[level] = slot;
            unlock_up(p, level, lowest_unlock, 0, NULL);
            goto done;
        }
    }
    ret = 1;
done:
    if (!p->leave_spinning)
        btrfs_set_path_blocking(p);
    if (ret < 0)
        btrfs_release_path(p);

    return ret;
}

/*
 * helper to use instead of search slot if no exact match is needed but
 * instead the next or previous item should be returned.
 * When find_higher is true, the next higher item is returned, the next lower
 * otherwise.
 * When return_any and find_higher are both true, and no higher item is found,
 * return the next lower instead.
 * When return_any is true and find_higher is false, and no lower item is found,
 * return the next higher instead.
 * It returns 0 if any item is found, 1 if none is found (tree empty), and
 * < 0 on error
 */
int btrfs_search_slot_for_read(struct btrfs_root *root,
                   struct btrfs_key *key, struct btrfs_path *p,
                   int find_higher, int return_any)
{
    int ret;
    struct extent_buffer *leaf;

again:
    ret = btrfs_search_slot(NULL, root, key, p, 0, 0);
    if (ret <= 0)
        return ret;
    /*
     * a return value of 1 means the path is at the position where the
     * item should be inserted. Normally this is the next bigger item,
     * but in case the previous item is the last in a leaf, path points
     * to the first free slot in the previous leaf, i.e. at an invalid
     * item.
     */
    leaf = p->nodes[0];

    if (find_higher) {
        if (p->slots[0] >= btrfs_header_nritems(leaf)) {
            ret = btrfs_next_leaf(root, p);
            if (ret <= 0)
                return ret;
            if (!return_any)
                return 1;
            /*
             * no higher item found, return the next
             * lower instead
             */
            return_any = 0;
            find_higher = 0;
            btrfs_release_path(p);
            goto again;
        }
    } else {
        if (p->slots[0] == 0) {
            ret = btrfs_prev_leaf(root, p);
            if (ret < 0)
                return ret;
            if (!ret) {
                p->slots[0] = btrfs_header_nritems(leaf) - 1;
                return 0;
            }
            if (!return_any)
                return 1;
            /*
             * no lower item found, return the next
             * higher instead
             */
            return_any = 0;
            find_higher = 1;
            btrfs_release_path(p);
            goto again;
        } else {
            --p->slots[0];
        }
    }
    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
 *
 */
static void 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;
    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];
        tree_mod_log_set_node_key(root->fs_info, t, key, tslot, 1);
        btrfs_set_node_key(t, key, tslot);
        btrfs_mark_buffer_dirty(path->nodes[i]);
        if (tslot != 0)
            break;
    }
}

/*
 * update item key.
 *
 * This function isn't completely safe. It's the caller's responsibility
 * that the new key won't break the order
 */
void 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);
        BUG_ON(comp_keys(&disk_key, new_key) >= 0);
    }
    if (slot < btrfs_header_nritems(eb) - 1) {
        btrfs_item_key(eb, &disk_key, slot + 1);
        BUG_ON(comp_keys(&disk_key, new_key) <= 0);
    }

    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);
}

/*
 * 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);

    tree_mod_log_eb_copy(root->fs_info, dst, src, dst_nritems, 0,
                 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) {
        /*
         * don't call tree_mod_log_eb_move here, key removal was already
         * fully logged by tree_mod_log_eb_copy above.
         */
        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);

    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;

    tree_mod_log_eb_move(root->fs_info, dst, push_items, 0, dst_nritems);
    memmove_extent_buffer(dst, btrfs_node_key_ptr_offset(push_items),
                      btrfs_node_key_ptr_offset(0),
                      (dst_nritems) *
                      sizeof(struct btrfs_key_ptr));

    tree_mod_log_eb_copy(root->fs_info, dst, src, 0,
                 src_nritems - push_items, push_items);
    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);

    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;

    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, &lower_key,
                   level, root->node->start, 0);
    if (IS_ERR(c))
        return PTR_ERR(c);

    root_add_used(root, root->nodesize);

    memset_extent_buffer(c, 0, 0, sizeof(struct btrfs_header));
    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_backref_rev(c, BTRFS_MIXED_BACKREF_REV);
    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);

    old = root->node;
    tree_mod_log_set_root_pointer(root, c);
    rcu_assign_pointer(root->node, c);

    /* 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] = BTRFS_WRITE_LOCK;
    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.
 */
static void 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;
    int ret;

    BUG_ON(!path->nodes[level]);
    btrfs_assert_tree_locked(path->nodes[level]);
    lower = path->nodes[level];
    nritems = btrfs_header_nritems(lower);
    BUG_ON(slot > nritems);
    BUG_ON(nritems == BTRFS_NODEPTRS_PER_BLOCK(root));
    if (slot != nritems) {
        if (level)
            tree_mod_log_eb_move(root->fs_info, lower, slot + 1,
                         slot, nritems - slot);
        memmove_extent_buffer(lower,
                  btrfs_node_key_ptr_offset(slot + 1),
                  btrfs_node_key_ptr_offset(slot),
                  (nritems - slot) * sizeof(struct btrfs_key_ptr));
    }
    if (level) {
        ret = tree_mod_log_insert_key(root->fs_info, lower, slot,
                          MOD_LOG_KEY_ADD);
        BUG_ON(ret < 0);
    }
    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);
}

/*
 * 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;
    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);
    mid = (c_nritems + 1) / 2;
    btrfs_node_key(c, &disk_key, mid);

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

    root_add_used(root, root->nodesize);

    memset_extent_buffer(split, 0, 0, sizeof(struct btrfs_header));
    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_backref_rev(split, BTRFS_MIXED_BACKREF_REV);
    btrfs_set_header_owner(split, root->root_key.objectid);
    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);

    tree_mod_log_eb_copy(root->fs_info, split, c, 0, mid, c_nritems - mid);
    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);

    insert_ptr(trans, root, path, &disk_key, split->start,
           path->slots[level + 1] + 1, level + 1);

    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;
}

/*
 * min slot controls the lowest index we're willing to push to the
 * right.  We'll push up to and including min_slot, but no lower
 */
static noinline 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 *right,
                      int free_space, u32 left_nritems,
                      u32 min_slot)
{
    struct extent_buffer *left = path->nodes[0];
    struct extent_buffer *upper = path->nodes[1];
    struct btrfs_map_token token;
    struct btrfs_disk_key disk_key;
    int slot;
    u32 i;
    int push_space = 0;
    int push_items = 0;
    struct btrfs_item *item;
    u32 nr;
    u32 right_nritems;
    u32 data_end;
    u32 this_item_size;

    btrfs_init_map_token(&token);

    if (empty)
        nr = 0;
    else
        nr = max_t(u32, 1, min_slot);

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

    slot = path->slots[1];
    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;

        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 (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);
        push_space -= btrfs_token_item_size(right, item, &token);
        btrfs_set_token_item_offset(right, item, push_space, &token);
    }

    left_nritems -= push_items;
    btrfs_set_header_nritems(left, left_nritems);

    if (left_nritems)
        btrfs_mark_buffer_dirty(left);
    else
        clean_tree_block(trans, root, left);

    btrfs_mark_buffer_dirty(right);

    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 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.
 *
 * this will push starting from min_slot to the end of the leaf.  It won't
 * push any slot lower than min_slot
 */
static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
               *root, struct btrfs_path *path,
               int min_data_size, int data_size,
               int empty, u32 min_slot)
{
    struct extent_buffer *left = path->nodes[0];
    struct extent_buffer *right;
    struct extent_buffer *upper;
    int slot;
    int free_space;
    u32 left_nritems;
    int ret;

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

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

    btrfs_assert_tree_locked(path->nodes[1]);

    right = read_node_slot(root, upper, slot + 1);
    if (right == NULL)
        return 1;

    btrfs_tree_lock(right);
    btrfs_set_lock_blocking(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);
    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;

    return __push_leaf_right(trans, root, path, min_data_size, empty,
                right, free_space, left_nritems, min_slot);
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
 *
 * max_slot can put a limit on how far into the leaf we'll push items.  The
 * item at 'max_slot' won't be touched.  Use (u32)-1 to make us do all the
 * items
 */
static noinline int __push_leaf_left(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     struct btrfs_path *path, int data_size,
                     int empty, struct extent_buffer *left,
                     int free_space, u32 right_nritems,
                     u32 max_slot)
{
    struct btrfs_disk_key disk_key;
    struct extent_buffer *right = path->nodes[0];
    int i;
    int push_space = 0;
    int push_items = 0;
    struct btrfs_item *item;
    u32 old_left_nritems;
    u32 nr;
    int ret = 0;
    u32 this_item_size;
    u32 old_left_item_size;
    struct btrfs_map_token token;

    btrfs_init_map_token(&token);

    if (empty)
        nr = min(right_nritems, max_slot);
    else
        nr = min(right_nritems - 1, max_slot);

    for (i = 0; i < nr; i++) {
        item = btrfs_item_nr(right, i);

        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 (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);

        ioff = btrfs_token_item_offset(left, item, &token);
        btrfs_set_token_item_offset(left, item,
              ioff - (BTRFS_LEAF_DATA_SIZE(root) - old_left_item_size),
              &token);
    }
    btrfs_set_header_nritems(left, old_left_nritems + push_items);

    /* 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);

        push_space = push_space - btrfs_token_item_size(right,
                                item, &token);
        btrfs_set_token_item_offset(right, item, push_space, &token);
    }

    btrfs_mark_buffer_dirty(left);
    if (right_nritems)
        btrfs_mark_buffer_dirty(right);
    else
        clean_tree_block(trans, root, right);

    btrfs_item_key(right, &disk_key, 0);
    fixup_low_keys(trans, root, path, &disk_key, 1);

    /* then fixup the leaf pointer in the path */
    if (path->slots[0] < push_items) {
        path->slots[0] += old_left_nritems;
        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;
}

/*
 * 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
 *
 * max_slot can put a limit on how far into the leaf we'll push items.  The
 * item at 'max_slot' won't be touched.  Use (u32)-1 to make us push all the
 * items
 */
static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
              *root, struct btrfs_path *path, int min_data_size,
              int data_size, int empty, u32 max_slot)
{
    struct extent_buffer *right = path->nodes[0];
    struct extent_buffer *left;
    int slot;
    int free_space;
    u32 right_nritems;
    int ret = 0;

    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;

    btrfs_assert_tree_locked(path->nodes[1]);

    left = read_node_slot(root, path->nodes[1], slot - 1);
    if (left == NULL)
        return 1;

    btrfs_tree_lock(left);
    btrfs_set_lock_blocking(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);
    if (ret) {
        /* we hit -ENOSPC, but it isn't fatal here */
        if (ret == -ENOSPC)
            ret = 1;
        goto out;
    }

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

    return __push_leaf_left(trans, root, path, min_data_size,
                   empty, left, free_space, right_nritems,
                   max_slot);
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.
 */
static noinline void copy_for_split(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root,
                    struct btrfs_path *path,
                    struct extent_buffer *l,
                    struct extent_buffer *right,
                    int slot, int mid, int nritems)
{
    int data_copy_size;
    int rt_data_off;
    int i;
    struct btrfs_disk_key disk_key;
    struct btrfs_map_token token;

    btrfs_init_map_token(&token);

    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;

        ioff = btrfs_token_item_offset(right, item, &token);
        btrfs_set_token_item_offset(right, item,
                        ioff + rt_data_off, &token);
    }

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

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

    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);
}

/*
 * double splits happen when we need to insert a big item in the middle
 * of a leaf.  A double split can leave us with 3 mostly empty leaves:
 * leaf: [ slots 0 - N] [ our target ] [ N + 1 - total in leaf ]
 *          A                 B                 C
 *
 * We avoid this by trying to push the items on either side of our target
 * into the adjacent leaves.  If all goes well we can avoid the double split
 * completely.
 */
static noinline int push_for_double_split(struct btrfs_trans_handle *trans,
                      struct btrfs_root *root,
                      struct btrfs_path *path,
                      int data_size)
{
    int ret;
    int progress = 0;
    int slot;
    u32 nritems;

    slot = path->slots[0];

    /*
     * try to push all the items after our slot into the
     * right leaf
     */
    ret = push_leaf_right(trans, root, path, 1, data_size, 0, slot);
    if (ret < 0)
        return ret;

    if (ret == 0)
        progress++;

    nritems = btrfs_header_nritems(path->nodes[0]);
    /*
     * our goal is to get our slot at the start or end of a leaf.  If
     * we've done so we're done
     */
    if (path->slots[0] == 0 || path->slots[0] == nritems)
        return 0;

    if (btrfs_leaf_free_space(root, path->nodes[0]) >= data_size)
        return 0;

    /* try to push all the items before our slot into the next leaf */
    slot = path->slots[0];
    ret = push_leaf_left(trans, root, path, 1, data_size, 0, slot);
    if (ret < 0)
        return ret;

    if (ret == 0)
        progress++;

    if (progress)
        return 0;
    return 1;
}

/*
 * 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 btrfs_disk_key disk_key;
    struct extent_buffer *l;
    u32 nritems;
    int mid;
    int slot;
    struct extent_buffer *right;
    int ret = 0;
    int wret;
    int split;
    int num_doubles = 0;
    int tried_avoid_double = 0;

    l = path->nodes[0];
    slot = path->slots[0];
    if (extend && data_size + btrfs_item_size_nr(l, slot) +
        sizeof(struct btrfs_item) > BTRFS_LEAF_DATA_SIZE(root))
        return -EOVERFLOW;

    /* first try to make some room by pushing left and right */
    if (data_size) {
        wret = push_leaf_right(trans, root, path, data_size,
                       data_size, 0, 0);
        if (wret < 0)
            return wret;
        if (wret) {
            wret = push_leaf_left(trans, root, path, data_size,
                          data_size, 0, (u32)-1);
            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:
    split = 1;
    l = path->nodes[0];
    slot = path->slots[0];
    nritems = btrfs_header_nritems(l);
    mid = (nritems + 1) / 2;

    if (mid <= slot) {
        if (nritems == 1 ||
            leaf_space_used(l, mid, nritems - mid) + data_size >
            BTRFS_LEAF_DATA_SIZE(root)) {
            if (slot >= nritems) {
                split = 0;
            } else {
                mid = slot;
                if (mid != nritems &&
                    leaf_space_used(l, mid, nritems - mid) +
                    data_size > BTRFS_LEAF_DATA_SIZE(root)) {
                    if (data_size && !tried_avoid_double)
                        goto push_for_double;
                    split = 2;
                }
            }
        }
    } else {
        if (leaf_space_used(l, 0, mid) + data_size >
            BTRFS_LEAF_DATA_SIZE(root)) {
            if (!extend && data_size && slot == 0) {
                split = 0;
            } 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)) {
                    if (data_size && !tried_avoid_double)
                        goto push_for_double;
                    split = 2 ;
                }
            }
        }
    }

    if (split == 0)
        btrfs_cpu_key_to_disk(&disk_key, ins_key);
    else
        btrfs_item_key(l, &disk_key, mid);

    right = btrfs_alloc_free_block(trans, root, root->leafsize, 0,
                    root->root_key.objectid,
                    &disk_key, 0, l->start, 0);
    if (IS_ERR(right))
        return PTR_ERR(right);

    root_add_used(root, root->leafsize);

    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_backref_rev(right, BTRFS_MIXED_BACKREF_REV);
    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 (split == 0) {
        if (mid <= slot) {
            btrfs_set_header_nritems(right, 0);
            insert_ptr(trans, root, path, &disk_key, right->start,
                   path->slots[1] + 1, 1);
            btrfs_tree_unlock(path->nodes[0]);
            free_extent_buffer(path->nodes[0]);
            path->nodes[0] = right;
            path->slots[0] = 0;
            path->slots[1] += 1;
        } else {
            btrfs_set_header_nritems(right, 0);
            insert_ptr(trans, root, path, &disk_key, right->start,
                      path->slots[1], 1);
            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)
                fixup_low_keys(trans, root, path,
                           &disk_key, 1);
        }
        btrfs_mark_buffer_dirty(right);
        return ret;
    }

    copy_for_split(trans, root, path, l, right, slot, mid, nritems);

    if (split == 2) {
        BUG_ON(num_doubles != 0);
        num_doubles++;
        goto again;
    }

    return 0;

push_for_double:
    push_for_double_split(trans, root, path, data_size);
    tried_avoid_double = 1;
    if (btrfs_leaf_free_space(root, path->nodes[0]) >= data_size)
        return 0;
    goto again;
}

static noinline int setup_leaf_for_split(struct btrfs_trans_handle *trans,
                     struct btrfs_root *root,
                     struct btrfs_path *path, int ins_len)
{
    struct btrfs_key key;
    struct extent_buffer *leaf;
    struct btrfs_file_extent_item *fi;
    u64 extent_len = 0;
    u32 item_size;
    int ret;

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

    BUG_ON(key.type != BTRFS_EXTENT_DATA_KEY &&
           key.type != BTRFS_EXTENT_CSUM_KEY);

    if (btrfs_leaf_free_space(root, leaf) >= ins_len)
        return 0;

    item_size = btrfs_item_size_nr(leaf, path->slots[0]);
    if (key.type == BTRFS_EXTENT_DATA_KEY) {
        fi = btrfs_item_ptr(leaf, path->slots[0],
                    struct btrfs_file_extent_item);
        extent_len = btrfs_file_extent_num_bytes(leaf, fi);
    }
    btrfs_release_path(path);

    path->keep_locks = 1;
    path->search_for_split = 1;
    ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
    path->search_for_split = 0;
    if (ret < 0)
        goto err;

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

    /* the leaf has  changed, it now has room.  return now */
    if (btrfs_leaf_free_space(root, path->nodes[0]) >= ins_len)
        goto err;

    if (key.type == BTRFS_EXTENT_DATA_KEY) {
        fi = btrfs_item_ptr(leaf, path->slots[0],
                    struct btrfs_file_extent_item);
        if (extent_len != btrfs_file_extent_num_bytes(leaf, fi))
            goto err;
    }

    btrfs_set_path_blocking(path);
    ret = split_leaf(trans, root, &key, path, ins_len, 1);
    if (ret)
        goto err;

    path->keep_locks = 0;
    btrfs_unlock_up_safe(path, 1);
    return 0;
err:
    path->keep_locks = 0;
    return ret;
}

static noinline int split_item(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root,
                   struct btrfs_path *path,
                   struct btrfs_key *new_key,
                   unsigned long split_offset)
{
    struct extent_buffer *leaf;
    struct btrfs_item *item;
    struct btrfs_item *new_item;
    int slot;
    char *buf;
    u32 nritems;
    u32 item_size;
    u32 orig_offset;
    struct btrfs_disk_key disk_key;

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

    btrfs_set_path_blocking(path);

    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);
    if (!buf)
        return -ENOMEM;

    read_extent_buffer(leaf, buf, btrfs_item_ptr_offset(leaf,
                path->slots[0]), item_size);

    slot = path->slots[0] + 1;
    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);

    BUG_ON(btrfs_leaf_free_space(root, leaf) < 0);
    kfree(buf);
    return 0;
}

/*
 * 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)
{
    int ret;
    ret = setup_leaf_for_split(trans, root, path,
                   sizeof(struct btrfs_item));
    if (ret)
        return ret;

    ret = split_item(trans, root, path, new_key, split_offset);
    return ret;
}

/*
 * This function duplicate a item, giving 'new_key' to the new item.
 * It guarantees both items live in the same tree leaf and the new item
 * is contiguous with the original item.
 *
 * This allows us to split file extent in place, keeping a lock on the
 * leaf the entire time.
 */
int btrfs_duplicate_item(struct btrfs_trans_handle *trans,
             struct btrfs_root *root,
             struct btrfs_path *path,
             struct btrfs_key *new_key)
{
    struct extent_buffer *leaf;
    int ret;
    u32 item_size;

    leaf = path->nodes[0];
    item_size = btrfs_item_size_nr(leaf, path->slots[0]);
    ret = setup_leaf_for_split(trans, root, path,
                   item_size + sizeof(struct btrfs_item));
    if (ret)
        return ret;

    path->slots[0]++;
    setup_items_for_insert(trans, root, path, new_key, &item_size,
                   item_size, item_size +
                   sizeof(struct btrfs_item), 1);
    leaf = path->nodes[0];
    memcpy_extent_buffer(leaf,
                 btrfs_item_ptr_offset(leaf, path->slots[0]),
                 btrfs_item_ptr_offset(leaf, path->slots[0] - 1),
                 item_size);
    return 0;
}

/*
 * 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.
 */
void btrfs_truncate_item(struct btrfs_trans_handle *trans,
             struct btrfs_root *root,
             struct btrfs_path *path,
             u32 new_size, int from_end)
{
    int slot;
    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;
    struct btrfs_map_token token;

    btrfs_init_map_token(&token);

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

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

    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);

        ioff = btrfs_token_item_offset(leaf, item, &token);
        btrfs_set_token_item_offset(leaf, item,
                        ioff + size_diff, &token);
    }

    /* 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);

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

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

    btrfs_init_map_token(&token);

    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);

        ioff = btrfs_token_item_offset(leaf, item, &token);
        btrfs_set_token_item_offset(leaf, item,
                        ioff - data_size, &token);
    }

    /* 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);

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

/*
 * this is a helper for btrfs_insert_empty_items, the main goal here is
 * to save stack depth by doing the bulk of the work in a function
 * that doesn't call btrfs_search_slot
 */
void setup_items_for_insert(struct btrfs_trans_handle *trans,
                struct btrfs_root *root, struct btrfs_path *path,
                struct btrfs_key *cpu_key, u32 *data_size,
                u32 total_data, u32 total_size, int nr)
{
    struct btrfs_item *item;
    int i;
    u32 nritems;
    unsigned int data_end;
    struct btrfs_disk_key disk_key;
    struct extent_buffer *leaf;
    int slot;
    struct btrfs_map_token token;

    btrfs_init_map_token(&token);

    leaf = path->nodes[0];
    slot = path->slots[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();
    }

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

            item = btrfs_item_nr(leaf, i);
            ioff = btrfs_token_item_offset(leaf, item, &token);
            btrfs_set_token_item_offset(leaf, item,
                            ioff - total_data, &token);
        }
        /* 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_token_item_offset(leaf, item,
                        data_end - data_size[i], &token);
        data_end -= data_size[i];
        btrfs_set_token_item_size(leaf, item, data_size[i], &token);
    }

    btrfs_set_header_nritems(leaf, nritems + nr);

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

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

/*
 * 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)
{
    int ret = 0;
    int slot;
    int i;
    u32 total_size = 0;
    u32 total_data = 0;

    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)
        return ret;

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

    setup_items_for_insert(trans, root, path, cpu_key, data_size,
                   total_data, total_size, nr);
    return 0;
}

/*
 * 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();
    if (!path)
        return -ENOMEM;
    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 void del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
            struct btrfs_path *path, int level, int slot,
            int tree_mod_log)
{
    struct extent_buffer *parent = path->nodes[level];
    u32 nritems;
    int ret;

    nritems = btrfs_header_nritems(parent);
    if (slot != nritems - 1) {
        if (tree_mod_log && level)
            tree_mod_log_eb_move(root->fs_info, parent, slot,
                         slot + 1, nritems - slot - 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));
    } else if (tree_mod_log && level) {
        ret = tree_mod_log_insert_key(root->fs_info, parent, slot,
                          MOD_LOG_KEY_REMOVE);
        BUG_ON(ret < 0);
    }

    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);
        fixup_low_keys(trans, root, path, &disk_key, level + 1);
    }
    btrfs_mark_buffer_dirty(parent);
}

/*
 * a helper function to delete the leaf pointed to by path->slots[1] and
 * path->nodes[1].
 *
 * 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.
 */
static noinline void btrfs_del_leaf(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root,
                    struct btrfs_path *path,
                    struct extent_buffer *leaf)
{
    WARN_ON(btrfs_header_generation(leaf) != trans->transid);
    del_ptr(trans, root, path, 1, path->slots[1], 1);

    /*
     * btrfs_free_extent is expensive, we want to make sure we
     * aren't holding any locks when we call it
     */
    btrfs_unlock_up_safe(path, 0);

    root_sub_used(root, leaf->len);

    extent_buffer_get(leaf);
    btrfs_free_tree_block(trans, root, leaf, 0, 1);
    free_extent_buffer_stale(leaf);
}
/*
 * 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;
    struct btrfs_map_token token;

    btrfs_init_map_token(&token);

    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);
            ioff = btrfs_token_item_offset(leaf, item, &token);
            btrfs_set_token_item_offset(leaf, item,
                            ioff + dsize, &token);
        }

        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 {
            btrfs_set_path_blocking(path);
            clean_tree_block(trans, root, leaf);
            btrfs_del_leaf(trans, root, path, leaf);
        }
    } 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);
            fixup_low_keys(trans, root, path, &disk_key, 1);
        }

        /* delete the leaf if it is mostly empty */
        if (used < BTRFS_LEAF_DATA_SIZE(root) / 3) {
            /* 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);

            btrfs_set_path_blocking(path);
            wret = push_leaf_left(trans, root, path, 1, 1,
                          1, (u32)-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, 1, 0);
                if (wret < 0 && wret != -ENOSPC)
                    ret = wret;
            }

            if (btrfs_header_nritems(leaf) == 0) {
                path->slots[1] = slot;
                btrfs_del_leaf(trans, root, path, leaf);
                free_extent_buffer(leaf);
                ret = 0;
            } 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(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_read_lock_root_node(root);
    level = btrfs_header_level(cur);
    WARN_ON(path->nodes[level]);
    path->nodes[level] = cur;
    path->locks[level] = BTRFS_READ_LOCK;

    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, 1) > 0) {
                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;
            btrfs_set_path_blocking(path);
            sret = btrfs_find_next_key(root, path, min_key, level,
                          cache_only, min_trans);
            if (sret == 0) {
                btrfs_release_path(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, 0, NULL);
            goto out;
        }
        btrfs_set_path_blocking(path);
        cur = read_node_slot(root, cur, slot);
        BUG_ON(!cur); /* -ENOMEM */

        btrfs_tree_read_lock(cur);

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

static void tree_move_down(struct btrfs_root *root,
               struct btrfs_path *path,
               int *level, int root_level)
{
    BUG_ON(*level == 0);
    path->nodes[*level - 1] = read_node_slot(root, path->nodes[*level],
                    path->slots[*level]);
    path->slots[*level - 1] = 0;
    (*level)--;
}

static int tree_move_next_or_upnext(struct btrfs_root *root,
                    struct btrfs_path *path,
                    int *level, int root_level)
{
    int ret = 0;
    int nritems;
    nritems = btrfs_header_nritems(path->nodes[*level]);

    path->slots[*level]++;

    while (path->slots[*level] >= nritems) {
        if (*level == root_level)
            return -1;

        /* move upnext */
        path->slots[*level] = 0;
        free_extent_buffer(path->nodes[*level]);
        path->nodes[*level] = NULL;
        (*level)++;
        path->slots[*level]++;

        nritems = btrfs_header_nritems(path->nodes[*level]);
        ret = 1;
    }
    return ret;
}

/*
 * Returns 1 if it had to move up and next. 0 is returned if it moved only next
 * or down.
 */
static int tree_advance(struct btrfs_root *root,
            struct btrfs_path *path,
            int *level, int root_level,
            int allow_down,
            struct btrfs_key *key)
{
    int ret;

    if (*level == 0 || !allow_down) {
        ret = tree_move_next_or_upnext(root, path, level, root_level);
    } else {
        tree_move_down(root, path, level, root_level);
        ret = 0;
    }
    if (ret >= 0) {
        if (*level == 0)
            btrfs_item_key_to_cpu(path->nodes[*level], key,
                    path->slots[*level]);
        else
            btrfs_node_key_to_cpu(path->nodes[*level], key,
                    path->slots[*level]);
    }
    return ret;
}

static int tree_compare_item(struct btrfs_root *left_root,
                 struct btrfs_path *left_path,
                 struct btrfs_path *right_path,
                 char *tmp_buf)
{
    int cmp;
    int len1, len2;
    unsigned long off1, off2;

    len1 = btrfs_item_size_nr(left_path->nodes[0], left_path->slots[0]);
    len2 = btrfs_item_size_nr(right_path->nodes[0], right_path->slots[0]);
    if (len1 != len2)
        return 1;

    off1 = btrfs_item_ptr_offset(left_path->nodes[0], left_path->slots[0]);
    off2 = btrfs_item_ptr_offset(right_path->nodes[0],
                right_path->slots[0]);

    read_extent_buffer(left_path->nodes[0], tmp_buf, off1, len1);

    cmp = memcmp_extent_buffer(right_path->nodes[0], tmp_buf, off2, len1);
    if (cmp)
        return 1;
    return 0;
}

#define ADVANCE 1
#define ADVANCE_ONLY_NEXT -1

/*
 * This function compares two trees and calls the provided callback for
 * every changed/new/deleted item it finds.
 * If shared tree blocks are encountered, whole subtrees are skipped, making
 * the compare pretty fast on snapshotted subvolumes.
 *
 * This currently works on commit roots only. As commit roots are read only,
 * we don't do any locking. The commit roots are protected with transactions.
 * Transactions are ended and rejoined when a commit is tried in between.
 *
 * This function checks for modifications done to the trees while comparing.
 * If it detects a change, it aborts immediately.
 */
int btrfs_compare_trees(struct btrfs_root *left_root,
            struct btrfs_root *right_root,
            btrfs_changed_cb_t changed_cb, void *ctx)
{
    int ret;
    int cmp;
    struct btrfs_trans_handle *trans = NULL;
    struct btrfs_path *left_path = NULL;
    struct btrfs_path *right_path = NULL;
    struct btrfs_key left_key;
    struct btrfs_key right_key;
    char *tmp_buf = NULL;
    int left_root_level;
    int right_root_level;
    int left_level;
    int right_level;
    int left_end_reached;
    int right_end_reached;
    int advance_left;
    int advance_right;
    u64 left_blockptr;
    u64 right_blockptr;
    u64 left_start_ctransid;
    u64 right_start_ctransid;
    u64 ctransid;

    left_path = btrfs_alloc_path();
    if (!left_path) {
        ret = -ENOMEM;
        goto out;
    }
    right_path = btrfs_alloc_path();
    if (!right_path) {
        ret = -ENOMEM;
        goto out;
    }

    tmp_buf = kmalloc(left_root->leafsize, GFP_NOFS);
    if (!tmp_buf) {
        ret = -ENOMEM;
        goto out;
    }

    left_path->search_commit_root = 1;
    left_path->skip_locking = 1;
    right_path->search_commit_root = 1;
    right_path->skip_locking = 1;

    spin_lock(&left_root->root_times_lock);
    left_start_ctransid = btrfs_root_ctransid(&left_root->root_item);
    spin_unlock(&left_root->root_times_lock);

    spin_lock(&right_root->root_times_lock);
    right_start_ctransid = btrfs_root_ctransid(&right_root->root_item);
    spin_unlock(&right_root->root_times_lock);

    trans = btrfs_join_transaction(left_root);
    if (IS_ERR(trans)) {
        ret = PTR_ERR(trans);
        trans = NULL;
        goto out;
    }

    /*
     * Strategy: Go to the first items of both trees. Then do
     *
     * If both trees are at level 0
     *   Compare keys of current items
     *     If left < right treat left item as new, advance left tree
     *       and repeat
     *     If left > right treat right item as deleted, advance right tree
     *       and repeat
     *     If left == right do deep compare of items, treat as changed if
     *       needed, advance both trees and repeat
     * If both trees are at the same level but not at level 0
     *   Compare keys of current nodes/leafs
     *     If left < right advance left tree and repeat
     *     If left > right advance right tree and repeat
     *     If left == right compare blockptrs of the next nodes/leafs
     *       If they match advance both trees but stay at the same level
     *         and repeat
     *       If they don't match advance both trees while allowing to go
     *         deeper and repeat
     * If tree levels are different
     *   Advance the tree that needs it and repeat
     *
     * Advancing a tree means:
     *   If we are at level 0, try to go to the next slot. If that's not
     *   possible, go one level up and repeat. Stop when we found a level
     *   where we could go to the next slot. We may at this point be on a
     *   node or a leaf.
     *
     *   If we are not at level 0 and not on shared tree blocks, go one
     *   level deeper.
     *
     *   If we are not at level 0 and on shared tree blocks, go one slot to
     *   the right if possible or go up and right.
     */

    left_level = btrfs_header_level(left_root->commit_root);
    left_root_level = left_level;
    left_path->nodes[left_level] = left_root->commit_root;
    extent_buffer_get(left_path->nodes[left_level]);

    right_level = btrfs_header_level(right_root->commit_root);
    right_root_level = right_level;
    right_path->nodes[right_level] = right_root->commit_root;
    extent_buffer_get(right_path->nodes[right_level]);

    if (left_level == 0)
        btrfs_item_key_to_cpu(left_path->nodes[left_level],
                &left_key, left_path->slots[left_level]);
    else
        btrfs_node_key_to_cpu(left_path->nodes[left_level],
                &left_key, left_path->slots[left_level]);
    if (right_level == 0)
        btrfs_item_key_to_cpu(right_path->nodes[right_level],
                &right_key, right_path->slots[right_level]);
    else
        btrfs_node_key_to_cpu(right_path->nodes[right_level],
                &right_key, right_path->slots[right_level]);

    left_end_reached = right_end_reached = 0;
    advance_left = advance_right = 0;

    while (1) {
        /*
         * We need to make sure the transaction does not get committed
         * while we do anything on commit roots. This means, we need to
         * join and leave transactions for every item that we process.
         */
        if (trans && btrfs_should_end_transaction(trans, left_root)) {
            btrfs_release_path(left_path);
            btrfs_release_path(right_path);

            ret = btrfs_end_transaction(trans, left_root);
            trans = NULL;
            if (ret < 0)
                goto out;
        }
        /* now rejoin the transaction */
        if (!trans) {
            trans = btrfs_join_transaction(left_root);
            if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                trans = NULL;
                goto out;
            }

            spin_lock(&left_root->root_times_lock);
            ctransid = btrfs_root_ctransid(&left_root->root_item);
            spin_unlock(&left_root->root_times_lock);
            if (ctransid != left_start_ctransid)
                left_start_ctransid = 0;

            spin_lock(&right_root->root_times_lock);
            ctransid = btrfs_root_ctransid(&right_root->root_item);
            spin_unlock(&right_root->root_times_lock);
            if (ctransid != right_start_ctransid)
                right_start_ctransid = 0;

            if (!left_start_ctransid || !right_start_ctransid) {
                WARN(1, KERN_WARNING
                    "btrfs: btrfs_compare_tree detected "
                    "a change in one of the trees while "
                    "iterating. This is probably a "
                    "bug.\n");
                ret = -EIO;
                goto out;
            }

            /*
             * the commit root may have changed, so start again
             * where we stopped
             */
            left_path->lowest_level = left_level;
            right_path->lowest_level = right_level;
            ret = btrfs_search_slot(NULL, left_root,
                    &left_key, left_path, 0, 0);
            if (ret < 0)
                goto out;
            ret = btrfs_search_slot(NULL, right_root,
                    &right_key, right_path, 0, 0);
            if (ret < 0)
                goto out;
        }

        if (advance_left && !left_end_reached) {
            ret = tree_advance(left_root, left_path, &left_level,
                    left_root_level,
                    advance_left != ADVANCE_ONLY_NEXT,
                    &left_key);
            if (ret < 0)
                left_end_reached = ADVANCE;
            advance_left = 0;
        }
        if (advance_right && !right_end_reached) {
            ret = tree_advance(right_root, right_path, &right_level,
                    right_root_level,
                    advance_right != ADVANCE_ONLY_NEXT,
                    &right_key);
            if (ret < 0)
                right_end_reached = ADVANCE;
            advance_right = 0;
        }

        if (left_end_reached && right_end_reached) {
            ret = 0;
            goto out;
        } else if (left_end_reached) {
            if (right_level == 0) {
                ret = changed_cb(left_root, right_root,
                        left_path, right_path,
                        &right_key,
                        BTRFS_COMPARE_TREE_DELETED,
                        ctx);
                if (ret < 0)
                    goto out;
            }
            advance_right = ADVANCE;
            continue;
        } else if (right_end_reached) {
            if (left_level == 0) {
                ret = changed_cb(left_root, right_root,
                        left_path, right_path,
                        &left_key,
                        BTRFS_COMPARE_TREE_NEW,
                        ctx);
                if (ret < 0)
                    goto out;
            }
            advance_left = ADVANCE;
            continue;
        }

        if (left_level == 0 && right_level == 0) {
            cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
            if (cmp < 0) {
                ret = changed_cb(left_root, right_root,
                        left_path, right_path,
                        &left_key,
                        BTRFS_COMPARE_TREE_NEW,
                        ctx);
                if (ret < 0)
                    goto out;
                advance_left = ADVANCE;
            } else if (cmp > 0) {
                ret = changed_cb(left_root, right_root,
                        left_path, right_path,
                        &right_key,
                        BTRFS_COMPARE_TREE_DELETED,
                        ctx);
                if (ret < 0)
                    goto out;
                advance_right = ADVANCE;
            } else {
                WARN_ON(!extent_buffer_uptodate(left_path->nodes[0]));
                ret = tree_compare_item(left_root, left_path,
                        right_path, tmp_buf);
                if (ret) {
                    WARN_ON(!extent_buffer_uptodate(left_path->nodes[0]));
                    ret = changed_cb(left_root, right_root,
                        left_path, right_path,
                        &left_key,
                        BTRFS_COMPARE_TREE_CHANGED,
                        ctx);
                    if (ret < 0)
                        goto out;
                }
                advance_left = ADVANCE;
                advance_right = ADVANCE;
            }
        } else if (left_level == right_level) {
            cmp = btrfs_comp_cpu_keys(&left_key, &right_key);
            if (cmp < 0) {
                advance_left = ADVANCE;
            } else if (cmp > 0) {
                advance_right = ADVANCE;
            } else {
                left_blockptr = btrfs_node_blockptr(
                        left_path->nodes[left_level],
                        left_path->slots[left_level]);
                right_blockptr = btrfs_node_blockptr(
                        right_path->nodes[right_level],
                        right_path->slots[right_level]);
                if (left_blockptr == right_blockptr) {
                    /*
                     * As we're on a shared block, don't
                     * allow to go deeper.
                     */
                    advance_left = ADVANCE_ONLY_NEXT;
                    advance_right = ADVANCE_ONLY_NEXT;
                } else {
                    advance_left = ADVANCE;
                    advance_right = ADVANCE;
                }
            }
        } else if (left_level < right_level) {
            advance_right = ADVANCE;
        } else {
            advance_left = ADVANCE;
        }
    }

out:
    btrfs_free_path(left_path);
    btrfs_free_path(right_path);
    kfree(tmp_buf);

    if (trans) {
        if (!ret)
            ret = btrfs_end_transaction(trans, left_root);
        else
            btrfs_end_transaction(trans, left_root);
    }

    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 level,
            int cache_only, u64 min_trans)
{
    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)) {
            int ret;
            int orig_lowest;
            struct btrfs_key cur_key;
            if (level + 1 >= BTRFS_MAX_LEVEL ||
                !path->nodes[level + 1])
                return 1;

            if (path->locks[level + 1]) {
                level++;
                continue;
            }

            slot = btrfs_header_nritems(c) - 1;
            if (level == 0)
                btrfs_item_key_to_cpu(c, &cur_key, slot);
            else
                btrfs_node_key_to_cpu(c, &cur_key, slot);

            orig_lowest = path->lowest_level;
            btrfs_release_path(path);
            path->lowest_level = level;
            ret = btrfs_search_slot(NULL, root, &cur_key, path,
                        0, 0);
            path->lowest_level = orig_lowest;
            if (ret < 0)
                return ret;

            c = path->nodes[level];
            slot = path->slots[level];
            if (ret == 0)
                slot++;
            goto next;
        }

        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, 1) <= 0) {
                    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)
{
    return btrfs_next_old_leaf(root, path, 0);
}

int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
            u64 time_seq)
{
    int slot;
    int level;
    struct extent_buffer *c;
    struct extent_buffer *next;
    struct btrfs_key key;
    u32 nritems;
    int ret;
    int old_spinning = path->leave_spinning;
    int next_rw_lock = 0;

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

    btrfs_item_key_to_cpu(path->nodes[0], &key, nritems - 1);
again:
    level = 1;
    next = NULL;
    next_rw_lock = 0;
    btrfs_release_path(path);

    path->keep_locks = 1;
    path->leave_spinning = 1;

    if (time_seq)
        ret = btrfs_search_old_slot(root, &key, path, time_seq);
    else
        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) {
        if (ret == 0)
            path->slots[0]++;
        ret = 0;
        goto done;
    }

    while (level < BTRFS_MAX_LEVEL) {
        if (!path->nodes[level]) {
            ret = 1;
            goto done;
        }

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

        if (next) {
            btrfs_tree_unlock_rw(next, next_rw_lock);
            free_extent_buffer(next);
        }

        next = c;
        next_rw_lock = path->locks[level];
        ret = read_block_for_search(NULL, root, path, &next, level,
                        slot, &key, 0);
        if (ret == -EAGAIN)
            goto again;

        if (ret < 0) {
            btrfs_release_path(path);
            goto done;
        }

        if (!path->skip_locking) {
            ret = btrfs_try_tree_read_lock(next);
            if (!ret && time_seq) {
                /*
                 * If we don't get the lock, we may be racing
                 * with push_leaf_left, holding that lock while
                 * itself waiting for the leaf we've currently
                 * locked. To solve this situation, we give up
                 * on our lock and cycle.
                 */
                free_extent_buffer(next);
                btrfs_release_path(path);
                cond_resched();
                goto again;
            }
            if (!ret) {
                btrfs_set_path_blocking(path);
                btrfs_tree_read_lock(next);
                btrfs_clear_path_blocking(path, next,
                              BTRFS_READ_LOCK);
            }
            next_rw_lock = BTRFS_READ_LOCK;
        }
        break;
    }
    path->slots[level] = slot;
    while (1) {
        level--;
        c = path->nodes[level];
        if (path->locks[level])
            btrfs_tree_unlock_rw(c, path->locks[level]);

        free_extent_buffer(c);
        path->nodes[level] = next;
        path->slots[level] = 0;
        if (!path->skip_locking)
            path->locks[level] = next_rw_lock;
        if (!level)
            break;

        ret = read_block_for_search(NULL, root, path, &next, level,
                        0, &key, 0);
        if (ret == -EAGAIN)
            goto again;

        if (ret < 0) {
            btrfs_release_path(path);
            goto done;
        }

        if (!path->skip_locking) {
            ret = btrfs_try_tree_read_lock(next);
            if (!ret) {
                btrfs_set_path_blocking(path);
                btrfs_tree_read_lock(next);
                btrfs_clear_path_blocking(path, next,
                              BTRFS_READ_LOCK);
            }
            next_rw_lock = BTRFS_READ_LOCK;
        }
    }
    ret = 0;
done:
    unlock_up(path, 0, 1, 0, NULL);
    path->leave_spinning = old_spinning;
    if (!old_spinning)
        btrfs_set_path_blocking(path);

    return ret;
}

/*
 * 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) {
            btrfs_set_path_blocking(path);
            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.objectid < min_objectid)
            break;
        if (found_key.type == type)
            return 0;
        if (found_key.objectid == min_objectid &&
            found_key.type < type)
            break;
    }
    return 1;
}