text: /*
   * 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 <linux/mm.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,
  		      const 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_fs_info *fs_info,
  			  struct extent_buffer *dst,
  			  struct extent_buffer *src, int empty);
  static int balance_node_right(struct btrfs_trans_handle *trans,
  			      struct btrfs_fs_info *fs_info,
  			      struct extent_buffer *dst_buf,
  			      struct extent_buffer *src_buf);
  static void del_ptr(struct btrfs_root *root, struct btrfs_path *path,
  		    int level, int slot);
  static int tree_mod_log_free_eb(struct btrfs_fs_info *fs_info,
  				 struct extent_buffer *eb);
  
  struct btrfs_path *btrfs_alloc_path(void)
  {
  	return kmem_cache_zalloc(btrfs_path_cachep, GFP_NOFS);
  }
  
  /*
   * 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;
  
  	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);
  
  	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;
  		}
  	}
  
  	if (held)
  		btrfs_clear_lock_blocking_rw(held, held_rw);
  }
  
  /* 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 COWed 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.
   */
  static 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)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  
  	if (test_bit(BTRFS_ROOT_DIRTY, &root->state) ||
  	    !test_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state))
  		return;
  
  	spin_lock(&fs_info->trans_lock);
  	if (!test_and_set_bit(BTRFS_ROOT_DIRTY, &root->state)) {
  		/* Want the extent tree to be the last on the list */
  		if (root->objectid == BTRFS_EXTENT_TREE_OBJECTID)
  			list_move_tail(&root->dirty_list,
  				       &fs_info->dirty_cowonly_roots);
  		else
  			list_move(&root->dirty_list,
  				  &fs_info->dirty_cowonly_roots);
  	}
  	spin_unlock(&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 btrfs_fs_info *fs_info = root->fs_info;
  	struct extent_buffer *cow;
  	int ret = 0;
  	int level;
  	struct btrfs_disk_key disk_key;
  
  	WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
  		trans->transid != fs_info->running_transaction->transid);
  	WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
  		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_tree_block(trans, root, 0, new_root_objectid,
  			&disk_key, level, buf->start, 0);
  	if (IS_ERR(cow))
  		return PTR_ERR(cow);
  
  	copy_extent_buffer_full(cow, buf);
  	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_fsid(cow, fs_info->fsid);
  
  	WARN_ON(btrfs_header_generation(buf) > trans->transid);
  	if (new_root_objectid == BTRFS_TREE_RELOC_OBJECTID)
  		ret = btrfs_inc_ref(trans, root, cow, 1);
  	else
  		ret = btrfs_inc_ref(trans, root, cow, 0);
  
  	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 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);
  }
  
  /*
   * Pull a new tree mod seq number for our operation.
   */
  static inline u64 btrfs_inc_tree_mod_seq(struct btrfs_fs_info *fs_info)
  {
  	return atomic64_inc_return(&fs_info->tree_mod_seq);
  }
  
  /*
   * 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)
  {
  	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);
  	}
  	spin_unlock(&fs_info->tree_mod_seq_lock);
  	tree_mod_log_write_unlock(fs_info);
  
  	return elem->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 = rb_entry(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:
   *       node/leaf start address -> sequence
   *
   * The 'start address' is the logical address of the *new* root node
   * for root replace operations, or the logical address of the affected
   * block for all other operations.
   *
   * Note: must be called with write lock (tree_mod_log_write_lock).
   */
  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;
  
  	tm->seq = btrfs_inc_tree_mod_seq(fs_info);
  
  	tm_root = &fs_info->tree_mod_log;
  	new = &tm_root->rb_node;
  	while (*new) {
  		cur = rb_entry(*new, struct tree_mod_elem, node);
  		parent = *new;
  		if (cur->logical < tm->logical)
  			new = &((*new)->rb_left);
  		else if (cur->logical > tm->logical)
  			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
  			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)) {
  		tree_mod_log_write_unlock(fs_info);
  		return 1;
  	}
  
  	return 0;
  }
  
  /* Similar to tree_mod_dont_log, but doesn't acquire any locks. */
  static inline int tree_mod_need_log(const struct btrfs_fs_info *fs_info,
  				    struct extent_buffer *eb)
  {
  	smp_mb();
  	if (list_empty(&(fs_info)->tree_mod_seq_list))
  		return 0;
  	if (eb && btrfs_header_level(eb) == 0)
  		return 0;
  
  	return 1;
  }
  
  static struct tree_mod_elem *
  alloc_tree_mod_elem(struct extent_buffer *eb, int slot,
  		    enum mod_log_op op, gfp_t flags)
  {
  	struct tree_mod_elem *tm;
  
  	tm = kzalloc(sizeof(*tm), flags);
  	if (!tm)
  		return NULL;
  
  	tm->logical = eb->start;
  	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);
  	RB_CLEAR_NODE(&tm->node);
  
  	return tm;
  }
  
  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, gfp_t flags)
  {
  	struct tree_mod_elem *tm;
  	int ret;
  
  	if (!tree_mod_need_log(fs_info, eb))
  		return 0;
  
  	tm = alloc_tree_mod_elem(eb, slot, op, flags);
  	if (!tm)
  		return -ENOMEM;
  
  	if (tree_mod_dont_log(fs_info, eb)) {
  		kfree(tm);
  		return 0;
  	}
  
  	ret = __tree_mod_log_insert(fs_info, tm);
  	tree_mod_log_write_unlock(fs_info);
  	if (ret)
  		kfree(tm);
  
  	return ret;
  }
  
  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)
  {
  	struct tree_mod_elem *tm = NULL;
  	struct tree_mod_elem **tm_list = NULL;
  	int ret = 0;
  	int i;
  	int locked = 0;
  
  	if (!tree_mod_need_log(fs_info, eb))
  		return 0;
  
  	tm_list = kcalloc(nr_items, sizeof(struct tree_mod_elem *), GFP_NOFS);
  	if (!tm_list)
  		return -ENOMEM;
  
  	tm = kzalloc(sizeof(*tm), GFP_NOFS);
  	if (!tm) {
  		ret = -ENOMEM;
  		goto free_tms;
  	}
  
  	tm->logical = eb->start;
  	tm->slot = src_slot;
  	tm->move.dst_slot = dst_slot;
  	tm->move.nr_items = nr_items;
  	tm->op = MOD_LOG_MOVE_KEYS;
  
  	for (i = 0; i + dst_slot < src_slot && i < nr_items; i++) {
  		tm_list[i] = alloc_tree_mod_elem(eb, i + dst_slot,
  		    MOD_LOG_KEY_REMOVE_WHILE_MOVING, GFP_NOFS);
  		if (!tm_list[i]) {
  			ret = -ENOMEM;
  			goto free_tms;
  		}
  	}
  
  	if (tree_mod_dont_log(fs_info, eb))
  		goto free_tms;
  	locked = 1;
  
  	/*
  	 * 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(fs_info, tm_list[i]);
  		if (ret)
  			goto free_tms;
  	}
  
  	ret = __tree_mod_log_insert(fs_info, tm);
  	if (ret)
  		goto free_tms;
  	tree_mod_log_write_unlock(fs_info);
  	kfree(tm_list);
  
  	return 0;
  free_tms:
  	for (i = 0; i < nr_items; i++) {
  		if (tm_list[i] && !RB_EMPTY_NODE(&tm_list[i]->node))
  			rb_erase(&tm_list[i]->node, &fs_info->tree_mod_log);
  		kfree(tm_list[i]);
  	}
  	if (locked)
  		tree_mod_log_write_unlock(fs_info);
  	kfree(tm_list);
  	kfree(tm);
  
  	return ret;
  }
  
  static inline int
  __tree_mod_log_free_eb(struct btrfs_fs_info *fs_info,
  		       struct tree_mod_elem **tm_list,
  		       int nritems)
  {
  	int i, j;
  	int ret;
  
  	for (i = nritems - 1; i >= 0; i--) {
  		ret = __tree_mod_log_insert(fs_info, tm_list[i]);
  		if (ret) {
  			for (j = nritems - 1; j > i; j--)
  				rb_erase(&tm_list[j]->node,
  					 &fs_info->tree_mod_log);
  			return ret;
  		}
  	}
  
  	return 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,
  			 int log_removal)
  {
  	struct tree_mod_elem *tm = NULL;
  	struct tree_mod_elem **tm_list = NULL;
  	int nritems = 0;
  	int ret = 0;
  	int i;
  
  	if (!tree_mod_need_log(fs_info, NULL))
  		return 0;
  
  	if (log_removal && btrfs_header_level(old_root) > 0) {
  		nritems = btrfs_header_nritems(old_root);
  		tm_list = kcalloc(nritems, sizeof(struct tree_mod_elem *),
  				  GFP_NOFS);
  		if (!tm_list) {
  			ret = -ENOMEM;
  			goto free_tms;
  		}
  		for (i = 0; i < nritems; i++) {
  			tm_list[i] = alloc_tree_mod_elem(old_root, i,
  			    MOD_LOG_KEY_REMOVE_WHILE_FREEING, GFP_NOFS);
  			if (!tm_list[i]) {
  				ret = -ENOMEM;
  				goto free_tms;
  			}
  		}
  	}
  
  	tm = kzalloc(sizeof(*tm), GFP_NOFS);
  	if (!tm) {
  		ret = -ENOMEM;
  		goto free_tms;
  	}
  
  	tm->logical = new_root->start;
  	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;
  
  	if (tree_mod_dont_log(fs_info, NULL))
  		goto free_tms;
  
  	if (tm_list)
  		ret = __tree_mod_log_free_eb(fs_info, tm_list, nritems);
  	if (!ret)
  		ret = __tree_mod_log_insert(fs_info, tm);
  
  	tree_mod_log_write_unlock(fs_info);
  	if (ret)
  		goto free_tms;
  	kfree(tm_list);
  
  	return ret;
  
  free_tms:
  	if (tm_list) {
  		for (i = 0; i < nritems; i++)
  			kfree(tm_list[i]);
  		kfree(tm_list);
  	}
  	kfree(tm);
  
  	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;
  
  	tree_mod_log_read_lock(fs_info);
  	tm_root = &fs_info->tree_mod_log;
  	node = tm_root->rb_node;
  	while (node) {
  		cur = rb_entry(node, struct tree_mod_elem, node);
  		if (cur->logical < start) {
  			node = node->rb_left;
  		} else if (cur->logical > start) {
  			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 int
  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 = 0;
  	struct tree_mod_elem **tm_list = NULL;
  	struct tree_mod_elem **tm_list_add, **tm_list_rem;
  	int i;
  	int locked = 0;
  
  	if (!tree_mod_need_log(fs_info, NULL))
  		return 0;
  
  	if (btrfs_header_level(dst) == 0 && btrfs_header_level(src) == 0)
  		return 0;
  
  	tm_list = kcalloc(nr_items * 2, sizeof(struct tree_mod_elem *),
  			  GFP_NOFS);
  	if (!tm_list)
  		return -ENOMEM;
  
  	tm_list_add = tm_list;
  	tm_list_rem = tm_list + nr_items;
  	for (i = 0; i < nr_items; i++) {
  		tm_list_rem[i] = alloc_tree_mod_elem(src, i + src_offset,
  		    MOD_LOG_KEY_REMOVE, GFP_NOFS);
  		if (!tm_list_rem[i]) {
  			ret = -ENOMEM;
  			goto free_tms;
  		}
  
  		tm_list_add[i] = alloc_tree_mod_elem(dst, i + dst_offset,
  		    MOD_LOG_KEY_ADD, GFP_NOFS);
  		if (!tm_list_add[i]) {
  			ret = -ENOMEM;
  			goto free_tms;
  		}
  	}
  
  	if (tree_mod_dont_log(fs_info, NULL))
  		goto free_tms;
  	locked = 1;
  
  	for (i = 0; i < nr_items; i++) {
  		ret = __tree_mod_log_insert(fs_info, tm_list_rem[i]);
  		if (ret)
  			goto free_tms;
  		ret = __tree_mod_log_insert(fs_info, tm_list_add[i]);
  		if (ret)
  			goto free_tms;
  	}
  
  	tree_mod_log_write_unlock(fs_info);
  	kfree(tm_list);
  
  	return 0;
  
  free_tms:
  	for (i = 0; i < nr_items * 2; i++) {
  		if (tm_list[i] && !RB_EMPTY_NODE(&tm_list[i]->node))
  			rb_erase(&tm_list[i]->node, &fs_info->tree_mod_log);
  		kfree(tm_list[i]);
  	}
  	if (locked)
  		tree_mod_log_write_unlock(fs_info);
  	kfree(tm_list);
  
  	return ret;
  }
  
  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);
  	BUG_ON(ret < 0);
  }
  
  static noinline void
  tree_mod_log_set_node_key(struct btrfs_fs_info *fs_info,
  			  struct extent_buffer *eb, int slot, int atomic)
  {
  	int ret;
  
  	ret = tree_mod_log_insert_key(fs_info, eb, slot,
  					MOD_LOG_KEY_REPLACE,
  					atomic ? GFP_ATOMIC : GFP_NOFS);
  	BUG_ON(ret < 0);
  }
  
  static noinline int
  tree_mod_log_free_eb(struct btrfs_fs_info *fs_info, struct extent_buffer *eb)
  {
  	struct tree_mod_elem **tm_list = NULL;
  	int nritems = 0;
  	int i;
  	int ret = 0;
  
  	if (btrfs_header_level(eb) == 0)
  		return 0;
  
  	if (!tree_mod_need_log(fs_info, NULL))
  		return 0;
  
  	nritems = btrfs_header_nritems(eb);
  	tm_list = kcalloc(nritems, sizeof(struct tree_mod_elem *), GFP_NOFS);
  	if (!tm_list)
  		return -ENOMEM;
  
  	for (i = 0; i < nritems; i++) {
  		tm_list[i] = alloc_tree_mod_elem(eb, i,
  		    MOD_LOG_KEY_REMOVE_WHILE_FREEING, GFP_NOFS);
  		if (!tm_list[i]) {
  			ret = -ENOMEM;
  			goto free_tms;
  		}
  	}
  
  	if (tree_mod_dont_log(fs_info, eb))
  		goto free_tms;
  
  	ret = __tree_mod_log_free_eb(fs_info, tm_list, nritems);
  	tree_mod_log_write_unlock(fs_info);
  	if (ret)
  		goto free_tms;
  	kfree(tm_list);
  
  	return 0;
  
  free_tms:
  	for (i = 0; i < nritems; i++)
  		kfree(tm_list[i]);
  	kfree(tm_list);
  
  	return ret;
  }
  
  static noinline void
  tree_mod_log_set_root_pointer(struct btrfs_root *root,
  			      struct extent_buffer *new_root_node,
  			      int log_removal)
  {
  	int ret;
  	ret = tree_mod_log_insert_root(root->fs_info, root->node,
  				       new_root_node, log_removal);
  	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 reference 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 (test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
  	    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 (test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
  	    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)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	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, fs_info, buf->start,
  					       btrfs_header_level(buf), 1,
  					       &refs, &flags);
  		if (ret)
  			return ret;
  		if (refs == 0) {
  			ret = -EROFS;
  			btrfs_handle_fs_error(fs_info, ret, NULL);
  			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);
  			if (ret)
  				return ret;
  
  			if (root->root_key.objectid ==
  			    BTRFS_TREE_RELOC_OBJECTID) {
  				ret = btrfs_dec_ref(trans, root, buf, 0);
  				if (ret)
  					return ret;
  				ret = btrfs_inc_ref(trans, root, cow, 1);
  				if (ret)
  					return ret;
  			}
  			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);
  			else
  				ret = btrfs_inc_ref(trans, root, cow, 0);
  			if (ret)
  				return ret;
  		}
  		if (new_flags != 0) {
  			int level = btrfs_header_level(buf);
  
  			ret = btrfs_set_disk_extent_flags(trans, fs_info,
  							  buf->start,
  							  buf->len,
  							  new_flags, level, 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);
  			else
  				ret = btrfs_inc_ref(trans, root, cow, 0);
  			if (ret)
  				return ret;
  			ret = btrfs_dec_ref(trans, root, buf, 1);
  			if (ret)
  				return ret;
  		}
  		clean_tree_block(fs_info, 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_fs_info *fs_info = root->fs_info;
  	struct btrfs_disk_key disk_key;
  	struct extent_buffer *cow;
  	int level, ret;
  	int last_ref = 0;
  	int unlock_orig = 0;
  	u64 parent_start = 0;
  
  	if (*cow_ret == buf)
  		unlock_orig = 1;
  
  	btrfs_assert_tree_locked(buf);
  
  	WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
  		trans->transid != fs_info->running_transaction->transid);
  	WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
  		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) && parent)
  		parent_start = parent->start;
  
  	cow = btrfs_alloc_tree_block(trans, root, 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_full(cow, buf);
  	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_fsid(cow, fs_info->fsid);
  
  	ret = update_ref_for_cow(trans, root, buf, cow, &last_ref);
  	if (ret) {
  		btrfs_abort_transaction(trans, ret);
  		return ret;
  	}
  
  	if (test_bit(BTRFS_ROOT_REF_COWS, &root->state)) {
  		ret = btrfs_reloc_cow_block(trans, root, buf, cow);
  		if (ret) {
  			btrfs_abort_transaction(trans, ret);
  			return ret;
  		}
  	}
  
  	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;
  
  		extent_buffer_get(cow);
  		tree_mod_log_set_root_pointer(root, cow, 1);
  		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 {
  		WARN_ON(trans->transid != btrfs_header_generation(parent));
  		tree_mod_log_insert_key(fs_info, parent, parent_slot,
  					MOD_LOG_KEY_REPLACE, GFP_NOFS);
  		btrfs_set_node_blockptr(parent, parent_slot,
  					cow->start);
  		btrfs_set_node_ptr_generation(parent, parent_slot,
  					      trans->transid);
  		btrfs_mark_buffer_dirty(parent);
  		if (last_ref) {
  			ret = tree_mod_log_free_eb(fs_info, buf);
  			if (ret) {
  				btrfs_abort_transaction(trans, ret);
  				return ret;
  			}
  		}
  		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 extent_buffer *eb_root, u64 time_seq)
  {
  	struct tree_mod_elem *tm;
  	struct tree_mod_elem *found = NULL;
  	u64 root_logical = eb_root->start;
  	int looped = 0;
  
  	if (!time_seq)
  		return NULL;
  
  	/*
  	 * the very last operation that's logged for a root is the
  	 * replacement operation (if it is replaced at all). this has
  	 * the logical address 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 NULL;
  		/*
  		 * 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;
  		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 rewound (until we reach something older than
   * time_seq).
   */
  static void
  __tree_mod_log_rewind(struct btrfs_fs_info *fs_info, 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);
  	tree_mod_log_read_lock(fs_info);
  	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);
  			/* Fallthrough */
  		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 = rb_entry(next, struct tree_mod_elem, node);
  		if (tm->logical != first_tm->logical)
  			break;
  	}
  	tree_mod_log_read_unlock(fs_info);
  	btrfs_set_header_nritems(eb, n);
  }
  
  /*
   * Called with eb read locked. If the buffer cannot be rewound, the same buffer
   * is returned. If rewind operations happen, a fresh buffer is returned. The
   * returned buffer is always read-locked. If the returned buffer is not the
   * input buffer, the lock on the input buffer is released and the input buffer
   * is freed (its refcount is decremented).
   */
  static struct extent_buffer *
  tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct btrfs_path *path,
  		    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;
  
  	btrfs_set_path_blocking(path);
  	btrfs_set_lock_blocking_rw(eb, BTRFS_READ_LOCK);
  
  	if (tm->op == MOD_LOG_KEY_REMOVE_WHILE_FREEING) {
  		BUG_ON(tm->slot != 0);
  		eb_rewin = alloc_dummy_extent_buffer(fs_info, eb->start);
  		if (!eb_rewin) {
  			btrfs_tree_read_unlock_blocking(eb);
  			free_extent_buffer(eb);
  			return NULL;
  		}
  		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);
  		if (!eb_rewin) {
  			btrfs_tree_read_unlock_blocking(eb);
  			free_extent_buffer(eb);
  			return NULL;
  		}
  	}
  
  	btrfs_clear_path_blocking(path, NULL, BTRFS_READ_LOCK);
  	btrfs_tree_read_unlock_blocking(eb);
  	free_extent_buffer(eb);
  
  	extent_buffer_get(eb_rewin);
  	btrfs_tree_read_lock(eb_rewin);
  	__tree_mod_log_rewind(fs_info, eb_rewin, time_seq, tm);
  	WARN_ON(btrfs_header_nritems(eb_rewin) >
  		BTRFS_NODEPTRS_PER_BLOCK(fs_info));
  
  	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 btrfs_fs_info *fs_info = root->fs_info;
  	struct tree_mod_elem *tm;
  	struct extent_buffer *eb = NULL;
  	struct extent_buffer *eb_root;
  	struct extent_buffer *old;
  	struct tree_mod_root *old_root = NULL;
  	u64 old_generation = 0;
  	u64 logical;
  
  	eb_root = btrfs_read_lock_root_node(root);
  	tm = __tree_mod_log_oldest_root(fs_info, eb_root, time_seq);
  	if (!tm)
  		return eb_root;
  
  	if (tm->op == MOD_LOG_ROOT_REPLACE) {
  		old_root = &tm->old_root;
  		old_generation = tm->generation;
  		logical = old_root->logical;
  	} else {
  		logical = eb_root->start;
  	}
  
  	tm = tree_mod_log_search(fs_info, logical, time_seq);
  	if (old_root && tm && tm->op != MOD_LOG_KEY_REMOVE_WHILE_FREEING) {
  		btrfs_tree_read_unlock(eb_root);
  		free_extent_buffer(eb_root);
  		old = read_tree_block(fs_info, logical, 0);
  		if (WARN_ON(IS_ERR(old) || !extent_buffer_uptodate(old))) {
  			if (!IS_ERR(old))
  				free_extent_buffer(old);
  			btrfs_warn(fs_info,
  				   "failed to read tree block %llu from get_old_root",
  				   logical);
  		} else {
  			eb = btrfs_clone_extent_buffer(old);
  			free_extent_buffer(old);
  		}
  	} else if (old_root) {
  		btrfs_tree_read_unlock(eb_root);
  		free_extent_buffer(eb_root);
  		eb = alloc_dummy_extent_buffer(fs_info, logical);
  	} else {
  		btrfs_set_lock_blocking_rw(eb_root, BTRFS_READ_LOCK);
  		eb = btrfs_clone_extent_buffer(eb_root);
  		btrfs_tree_read_unlock_blocking(eb_root);
  		free_extent_buffer(eb_root);
  	}
  
  	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, btrfs_header_owner(eb_root));
  		btrfs_set_header_level(eb, old_root->level);
  		btrfs_set_header_generation(eb, old_generation);
  	}
  	if (tm)
  		__tree_mod_log_rewind(fs_info, eb, time_seq, tm);
  	else
  		WARN_ON(btrfs_header_level(eb) != 0);
  	WARN_ON(btrfs_header_nritems(eb) > BTRFS_NODEPTRS_PER_BLOCK(fs_info));
  
  	return eb;
  }
  
  int btrfs_old_root_level(struct btrfs_root *root, u64 time_seq)
  {
  	struct tree_mod_elem *tm;
  	int level;
  	struct extent_buffer *eb_root = btrfs_root_node(root);
  
  	tm = __tree_mod_log_oldest_root(root->fs_info, eb_root, time_seq);
  	if (tm && tm->op == MOD_LOG_ROOT_REPLACE) {
  		level = tm->old_root.level;
  	} else {
  		level = btrfs_header_level(eb_root);
  	}
  	free_extent_buffer(eb_root);
  
  	return level;
  }
  
  static inline int should_cow_block(struct btrfs_trans_handle *trans,
  				   struct btrfs_root *root,
  				   struct extent_buffer *buf)
  {
  	if (btrfs_is_testing(root->fs_info))
  		return 0;
  
  	/* 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 committing 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)) &&
  	    !test_bit(BTRFS_ROOT_FORCE_COW, &root->state))
  		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 COWed 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)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	u64 search_start;
  	int ret;
  
  	if (trans->transaction != fs_info->running_transaction)
  		WARN(1, KERN_CRIT "trans %llu running %llu\n",
  		       trans->transid,
  		       fs_info->running_transaction->transid);
  
  	if (trans->transid != fs_info->generation)
  		WARN(1, KERN_CRIT "trans %llu running %llu\n",
  		       trans->transid, fs_info->generation);
  
  	if (!should_cow_block(trans, root, buf)) {
  		trans->dirty = true;
  		*cow_ret = buf;
  		return 0;
  	}
  
  	search_start = buf->start & ~((u64)SZ_1G - 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(const struct btrfs_disk_key *disk,
  		     const 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(const struct btrfs_key *k1, const 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, u64 *last_ret,
  		       struct btrfs_key *progress)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	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);
  
  	WARN_ON(trans->transaction != fs_info->running_transaction);
  	WARN_ON(trans->transid != fs_info->generation);
  
  	parent_nritems = btrfs_header_nritems(parent);
  	blocksize = fs_info->nodesize;
  	end_slot = parent_nritems - 1;
  
  	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) {
  			other = btrfs_node_blockptr(parent, i + 1);
  			close = close_blocks(blocknr, other, blocksize);
  		}
  		if (close) {
  			last_block = blocknr;
  			continue;
  		}
  
  		cur = find_extent_buffer(fs_info, blocknr);
  		if (cur)
  			uptodate = btrfs_buffer_uptodate(cur, gen, 0);
  		else
  			uptodate = 0;
  		if (!cur || !uptodate) {
  			if (!cur) {
  				cur = read_tree_block(fs_info, blocknr, gen);
  				if (IS_ERR(cur)) {
  					return PTR_ERR(cur);
  				} else if (!extent_buffer_uptodate(cur)) {
  					free_extent_buffer(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;
  }
  
  /*
   * 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,
  				       const 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;
  
  	if (low > high) {
  		btrfs_err(eb->fs_info,
  		 "%s: low (%d) > high (%d) eb %llu owner %llu level %d",
  			  __func__, low, high, eb->start,
  			  btrfs_header_owner(eb), btrfs_header_level(eb));
  		return -EINVAL;
  	}
  
  	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 if (err == 1) {
  				read_extent_buffer(eb, &unaligned,
  						   offset, sizeof(unaligned));
  				tmp = &unaligned;
  			} else {
  				return err;
  			}
  
  		} 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, const 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, const 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).
   */
  static noinline struct extent_buffer *
  read_node_slot(struct btrfs_fs_info *fs_info, struct extent_buffer *parent,
  	       int slot)
  {
  	int level = btrfs_header_level(parent);
  	struct extent_buffer *eb;
  
  	if (slot < 0 || slot >= btrfs_header_nritems(parent))
  		return ERR_PTR(-ENOENT);
  
  	BUG_ON(level == 0);
  
  	eb = read_tree_block(fs_info, btrfs_node_blockptr(parent, slot),
  			     btrfs_node_ptr_generation(parent, slot));
  	if (!IS_ERR(eb) && !extent_buffer_uptodate(eb)) {
  		free_extent_buffer(eb);
  		eb = ERR_PTR(-EIO);
  	}
  
  	return eb;
  }
  
  /*
   * 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 btrfs_fs_info *fs_info = root->fs_info;
  	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(fs_info, mid, 0);
  		if (IS_ERR(child)) {
  			ret = PTR_ERR(child);
  			btrfs_handle_fs_error(fs_info, ret, NULL);
  			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_set_root_pointer(root, child, 1);
  		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(fs_info, 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(fs_info) / 4)
  		return 0;
  
  	left = read_node_slot(fs_info, parent, pslot - 1);
  	if (IS_ERR(left))
  		left = NULL;
  
  	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(fs_info, parent, pslot + 1);
  	if (IS_ERR(right))
  		right = NULL;
  
  	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, fs_info, 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, fs_info, mid, right, 1);
  		if (wret < 0 && wret != -ENOSPC)
  			ret = wret;
  		if (btrfs_header_nritems(right) == 0) {
  			clean_tree_block(fs_info, right);
  			btrfs_tree_unlock(right);
  			del_ptr(root, path, level + 1, pslot + 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(fs_info, parent,
  						  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_handle_fs_error(fs_info, ret, NULL);
  			goto enospc;
  		}
  		wret = balance_node_right(trans, fs_info, mid, left);
  		if (wret < 0) {
  			ret = wret;
  			goto enospc;
  		}
  		if (wret == 1) {
  			wret = push_node_left(trans, fs_info, left, mid, 1);
  			if (wret < 0)
  				ret = wret;
  		}
  		BUG_ON(wret == 1);
  	}
  	if (btrfs_header_nritems(mid) == 0) {
  		clean_tree_block(fs_info, mid);
  		btrfs_tree_unlock(mid);
  		del_ptr(root, path, level + 1, pslot);
  		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(fs_info, parent, 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 btrfs_fs_info *fs_info = root->fs_info;
  	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(fs_info, parent, pslot - 1);
  	if (IS_ERR(left))
  		left = NULL;
  
  	/* 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(fs_info) - 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, fs_info,
  						      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(fs_info, parent, 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(fs_info, parent, pslot + 1);
  	if (IS_ERR(right))
  		right = NULL;
  
  	/*
  	 * 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(fs_info) - 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, fs_info,
  							  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(fs_info, parent,
  						  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_fs_info *fs_info,
  			     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;
  	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 = fs_info->nodesize;
  	eb = find_extent_buffer(fs_info, search);
  	if (eb) {
  		free_extent_buffer(eb);
  		return;
  	}
  
  	target = search;
  
  	nritems = btrfs_header_nritems(node);
  	nr = slot;
  
  	while (1) {
  		if (path->reada == READA_BACK) {
  			if (nr == 0)
  				break;
  			nr--;
  		} else if (path->reada == READA_FORWARD) {
  			nr++;
  			if (nr >= nritems)
  				break;
  		}
  		if (path->reada == READA_BACK && objectid) {
  			btrfs_node_key(node, &disk_key, nr);
  			if (btrfs_disk_key_objectid(&disk_key) != objectid)
  				break;
  		}
  		search = btrfs_node_blockptr(node, nr);
  		if ((search <= target && target - search <= 65536) ||
  		    (search > target && search - target <= 65536)) {
  			readahead_tree_block(fs_info, search);
  			nread += blocksize;
  		}
  		nscan++;
  		if ((nread > 65536 || nscan > 32))
  			break;
  	}
  }
  
  static noinline void reada_for_balance(struct btrfs_fs_info *fs_info,
  				       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;
  
  	parent = path->nodes[level + 1];
  	if (!parent)
  		return;
  
  	nritems = btrfs_header_nritems(parent);
  	slot = path->slots[level + 1];
  
  	if (slot > 0) {
  		block1 = btrfs_node_blockptr(parent, slot - 1);
  		gen = btrfs_node_ptr_generation(parent, slot - 1);
  		eb = find_extent_buffer(fs_info, block1);
  		/*
  		 * 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 = find_extent_buffer(fs_info, block2);
  		if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
  			block2 = 0;
  		free_extent_buffer(eb);
  	}
  
  	if (block1)
  		readahead_tree_block(fs_info, block1);
  	if (block2)
  		readahead_tree_block(fs_info, block2);
  }
  
  
  /*
   * 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_root *root, struct btrfs_path *p,
  		      struct extent_buffer **eb_ret, int level, int slot,
  		      const struct btrfs_key *key)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	u64 blocknr;
  	u64 gen;
  	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);
  
  	tmp = find_extent_buffer(fs_info, blocknr);
  	if (tmp) {
  		/* first we do an atomic uptodate check */
  		if (btrfs_buffer_uptodate(tmp, gen, 1) > 0) {
  			*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
  		 */
  		btrfs_set_path_blocking(p);
  
  		/* now we're allowed to do a blocking uptodate check */
  		ret = btrfs_read_buffer(tmp, gen);
  		if (!ret) {
  			*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_NONE)
  		reada_for_search(fs_info, p, level, slot, key->objectid);
  
  	ret = -EAGAIN;
  	tmp = read_tree_block(fs_info, blocknr, gen);
  	if (!IS_ERR(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);
  	} else {
  		ret = PTR_ERR(tmp);
  	}
  
  	btrfs_release_path(p);
  	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)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	int ret;
  
  	if ((p->search_for_split || ins_len > 0) && btrfs_header_nritems(b) >=
  	    BTRFS_NODEPTRS_PER_BLOCK(fs_info) - 3) {
  		int sret;
  
  		if (*write_lock_level < level + 1) {
  			*write_lock_level = level + 1;
  			btrfs_release_path(p);
  			goto again;
  		}
  
  		btrfs_set_path_blocking(p);
  		reada_for_balance(fs_info, p, level);
  		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(fs_info) / 2) {
  		int sret;
  
  		if (*write_lock_level < level + 1) {
  			*write_lock_level = level + 1;
  			btrfs_release_path(p);
  			goto again;
  		}
  
  		btrfs_set_path_blocking(p);
  		reada_for_balance(fs_info, p, level);
  		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;
  }
  
  static void key_search_validate(struct extent_buffer *b,
  				const struct btrfs_key *key,
  				int level)
  {
  #ifdef CONFIG_BTRFS_ASSERT
  	struct btrfs_disk_key disk_key;
  
  	btrfs_cpu_key_to_disk(&disk_key, key);
  
  	if (level == 0)
  		ASSERT(!memcmp_extent_buffer(b, &disk_key,
  		    offsetof(struct btrfs_leaf, items[0].key),
  		    sizeof(disk_key)));
  	else
  		ASSERT(!memcmp_extent_buffer(b, &disk_key,
  		    offsetof(struct btrfs_node, ptrs[0].key),
  		    sizeof(disk_key)));
  #endif
  }
  
  static int key_search(struct extent_buffer *b, const struct btrfs_key *key,
  		      int level, int *prev_cmp, int *slot)
  {
  	if (*prev_cmp != 0) {
  		*prev_cmp = bin_search(b, key, level, slot);
  		return *prev_cmp;
  	}
  
  	key_search_validate(b, key, level);
  	*slot = 0;
  
  	return 0;
  }
  
  int btrfs_find_item(struct btrfs_root *fs_root, struct btrfs_path *path,
  		u64 iobjectid, u64 ioff, u8 key_type,
  		struct btrfs_key *found_key)
  {
  	int ret;
  	struct btrfs_key key;
  	struct extent_buffer *eb;
  
  	ASSERT(path);
  	ASSERT(found_key);
  
  	key.type = key_type;
  	key.objectid = iobjectid;
  	key.offset = ioff;
  
  	ret = btrfs_search_slot(NULL, fs_root, &key, path, 0, 0);
  	if (ret < 0)
  		return ret;
  
  	eb = path->nodes[0];
  	if (ret && path->slots[0] >= btrfs_header_nritems(eb)) {
  		ret = btrfs_next_leaf(fs_root, path);
  		if (ret)
  			return ret;
  		eb = path->nodes[0];
  	}
  
  	btrfs_item_key_to_cpu(eb, found_key, path->slots[0]);
  	if (found_key->type != key.type ||
  			found_key->objectid != key.objectid)
  		return 1;
  
  	return 0;
  }
  
  /*
   * look for key in the tree.  path is filled in with nodes along the way
   * if key is found, we return zero and you can find the item in the leaf
   * level of the path (level 0)
   *
   * If the key isn't found, the path points to the slot where it should
   * be inserted, and 1 is returned.  If there are other errors during the
   * search a negative error number is returned.
   *
   * if ins_len > 0, nodes and leaves will be split as we walk down the
   * tree.  if ins_len < 0, nodes will be merged as we walk down the tree (if
   * possible)
   */
  int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
  		      const struct btrfs_key *key, struct btrfs_path *p,
  		      int ins_len, int cow)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	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;
  	int prev_cmp;
  
  	lowest_level = p->lowest_level;
  	WARN_ON(lowest_level && ins_len > 0);
  	WARN_ON(p->nodes[0] != NULL);
  	BUG_ON(!cow && ins_len);
  
  	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:
  	prev_cmp = -1;
  	/*
  	 * 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
  		 */
  		if (p->need_commit_sem)
  			down_read(&fs_info->commit_root_sem);
  		b = root->commit_root;
  		extent_buffer_get(b);
  		level = btrfs_header_level(b);
  		if (p->need_commit_sem)
  			up_read(&fs_info->commit_root_sem);
  		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) {
  			bool last_level = (level == (BTRFS_MAX_LEVEL - 1));
  
  			/*
  			 * 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)) {
  				trans->dirty = true;
  				goto cow_done;
  			}
  
  			/*
  			 * must have write locks on this node and the
  			 * parent
  			 */
  			if (level > write_lock_level ||
  			    (level + 1 > write_lock_level &&
  			    level + 1 < BTRFS_MAX_LEVEL &&
  			    p->nodes[level + 1])) {
  				write_lock_level = level + 1;
  				btrfs_release_path(p);
  				goto again;
  			}
  
  			btrfs_set_path_blocking(p);
  			if (last_level)
  				err = btrfs_cow_block(trans, root, b, NULL, 0,
  						      &b);
  			else
  				err = btrfs_cow_block(trans, root, b,
  						      p->nodes[level + 1],
  						      p->slots[level + 1], &b);
  			if (err) {
  				ret = err;
  				goto done;
  			}
  		}
  cow_done:
  		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 we're inserting or deleting (ins_len != 0), 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 (!ins_len && !p->keep_locks) {
  			int u = level + 1;
  
  			if (u < BTRFS_MAX_LEVEL && p->locks[u]) {
  				btrfs_tree_unlock_rw(p->nodes[u], p->locks[u]);
  				p->locks[u] = 0;
  			}
  		}
  
  		ret = key_search(b, key, level, &prev_cmp, &slot);
  		if (ret < 0)
  			goto done;
  
  		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 && ins_len &&
  			    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(root, p, &b, level,
  						    slot, key);
  			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_tree_read_lock_atomic(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(fs_info, 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 && !p->skip_release_on_error)
  		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, const struct btrfs_key *key,
  			  struct btrfs_path *p, u64 time_seq)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	struct extent_buffer *b;
  	int slot;
  	int ret;
  	int err;
  	int level;
  	int lowest_unlock = 1;
  	u8 lowest_level = 0;
  	int prev_cmp = -1;
  
  	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);
  
  		/*
  		 * Since we can unwind ebs we want to do a real search every
  		 * time.
  		 */
  		prev_cmp = -1;
  		ret = key_search(b, key, level, &prev_cmp, &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(root, p, &b, level,
  						    slot, key);
  			if (err == -EAGAIN)
  				goto again;
  			if (err) {
  				ret = err;
  				goto done;
  			}
  
  			level = btrfs_header_level(b);
  			err = btrfs_tree_read_lock_atomic(b);
  			if (!err) {
  				btrfs_set_path_blocking(p);
  				btrfs_tree_read_lock(b);
  				btrfs_clear_path_blocking(p, b,
  							  BTRFS_READ_LOCK);
  			}
  			b = tree_mod_log_rewind(fs_info, p, b, time_seq);
  			if (!b) {
  				ret = -ENOMEM;
  				goto done;
  			}
  			p->locks[level] = BTRFS_READ_LOCK;
  			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,
  			       const 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) {
  				leaf = p->nodes[0];
  				if (p->slots[0] == btrfs_header_nritems(leaf))
  					p->slots[0]--;
  				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_fs_info *fs_info,
  			   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(fs_info, t, 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_fs_info *fs_info,
  			     struct btrfs_path *path,
  			     const 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(fs_info, 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_fs_info *fs_info,
  			  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(fs_info) - 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);
  
  	ret = tree_mod_log_eb_copy(fs_info, dst, src, dst_nritems, 0,
  				   push_items);
  	if (ret) {
  		btrfs_abort_transaction(trans, ret);
  		return ret;
  	}
  	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_fs_info *fs_info,
  			      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(fs_info) - 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(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));
  
  	ret = tree_mod_log_eb_copy(fs_info, dst, src, 0,
  				   src_nritems - push_items, push_items);
  	if (ret) {
  		btrfs_abort_transaction(trans, ret);
  		return ret;
  	}
  	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)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	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_tree_block(trans, root, 0, root->root_key.objectid,
  				   &lower_key, level, root->node->start, 0);
  	if (IS_ERR(c))
  		return PTR_ERR(c);
  
  	root_add_used(root, fs_info->nodesize);
  
  	memzero_extent_buffer(c, 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_fsid(c, fs_info->fsid);
  	write_extent_buffer_chunk_tree_uuid(c, fs_info->chunk_tree_uuid);
  
  	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, 0);
  	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_BLOCKING;
  	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_fs_info *fs_info, 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(fs_info));
  	if (slot != nritems) {
  		if (level)
  			tree_mod_log_eb_move(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(fs_info, lower, slot,
  					      MOD_LOG_KEY_ADD, GFP_NOFS);
  		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 btrfs_fs_info *fs_info = root->fs_info;
  	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
  		 *
  		 * tree mod log: We don't log_removal old root in
  		 * insert_new_root, because that root buffer will be kept as a
  		 * normal node. We are going to log removal of half of the
  		 * elements below with tree_mod_log_eb_copy. We're holding a
  		 * tree lock on the buffer, which is why we cannot race with
  		 * other tree_mod_log users.
  		 */
  		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(fs_info) - 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_tree_block(trans, root, 0, root->root_key.objectid,
  			&disk_key, level, c->start, 0);
  	if (IS_ERR(split))
  		return PTR_ERR(split);
  
  	root_add_used(root, fs_info->nodesize);
  
  	memzero_extent_buffer(split, 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_fsid(split, fs_info->fsid);
  	write_extent_buffer_chunk_tree_uuid(split, fs_info->chunk_tree_uuid);
  
  	ret = tree_mod_log_eb_copy(fs_info, split, c, 0, mid, c_nritems - mid);
  	if (ret) {
  		btrfs_abort_transaction(trans, ret);
  		return ret;
  	}
  	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, fs_info, 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)
  {
  	struct btrfs_item *start_item;
  	struct btrfs_item *end_item;
  	struct btrfs_map_token token;
  	int data_len;
  	int nritems = btrfs_header_nritems(l);
  	int end = min(nritems, start + nr) - 1;
  
  	if (!nr)
  		return 0;
  	btrfs_init_map_token(&token);
  	start_item = btrfs_item_nr(start);
  	end_item = btrfs_item_nr(end);
  	data_len = btrfs_token_item_offset(l, start_item, &token) +
  		btrfs_token_item_size(l, start_item, &token);
  	data_len = data_len - btrfs_token_item_offset(l, end_item, &token);
  	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_fs_info *fs_info,
  				   struct extent_buffer *leaf)
  {
  	int nritems = btrfs_header_nritems(leaf);
  	int ret;
  
  	ret = BTRFS_LEAF_DATA_SIZE(fs_info) - leaf_space_used(leaf, 0, nritems);
  	if (ret < 0) {
  		btrfs_crit(fs_info,
  			   "leaf free space ret %d, leaf data size %lu, used %d nritems %d",
  			   ret,
  			   (unsigned long) BTRFS_LEAF_DATA_SIZE(fs_info),
  			   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_fs_info *fs_info,
  				      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(i);
  
  		if (!empty && push_items > 0) {
  			if (path->slots[0] > i)
  				break;
  			if (path->slots[0] == i) {
  				int space = btrfs_leaf_free_space(fs_info, 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;
  
  	WARN_ON(!empty && push_items == left_nritems);
  
  	/* 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(fs_info, left);
  
  	/* make room in the right data area */
  	data_end = leaf_data_end(fs_info, right);
  	memmove_extent_buffer(right,
  			      BTRFS_LEAF_DATA_OFFSET + data_end - push_space,
  			      BTRFS_LEAF_DATA_OFFSET + data_end,
  			      BTRFS_LEAF_DATA_SIZE(fs_info) - data_end);
  
  	/* copy from the left data area */
  	copy_extent_buffer(right, left, BTRFS_LEAF_DATA_OFFSET +
  		     BTRFS_LEAF_DATA_SIZE(fs_info) - push_space,
  		     BTRFS_LEAF_DATA_OFFSET + leaf_data_end(fs_info, 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(fs_info);
  	for (i = 0; i < right_nritems; i++) {
  		item = btrfs_item_nr(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(fs_info, 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(fs_info, 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 btrfs_fs_info *fs_info = root->fs_info;
  	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(fs_info, upper, slot + 1);
  	/*
  	 * slot + 1 is not valid or we fail to read the right node,
  	 * no big deal, just return.
  	 */
  	if (IS_ERR(right))
  		return 1;
  
  	btrfs_tree_lock(right);
  	btrfs_set_lock_blocking(right);
  
  	free_space = btrfs_leaf_free_space(fs_info, 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(fs_info, right);
  	if (free_space < data_size)
  		goto out_unlock;
  
  	left_nritems = btrfs_header_nritems(left);
  	if (left_nritems == 0)
  		goto out_unlock;
  
  	if (path->slots[0] == left_nritems && !empty) {
  		/* Key greater than all keys in the leaf, right neighbor has
  		 * enough room for it and we're not emptying our leaf to delete
  		 * it, therefore use right neighbor to insert the new item and
  		 * no need to touch/dirty our left leaft. */
  		btrfs_tree_unlock(left);
  		free_extent_buffer(left);
  		path->nodes[0] = right;
  		path->slots[0] = 0;
  		path->slots[1]++;
  		return 0;
  	}
  
  	return __push_leaf_right(fs_info, 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_fs_info *fs_info,
  				     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(i);
  
  		if (!empty && push_items > 0) {
  			if (path->slots[0] < i)
  				break;
  			if (path->slots[0] == i) {
  				int space = btrfs_leaf_free_space(fs_info, 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;
  	}
  	WARN_ON(!empty && push_items == btrfs_header_nritems(right));
  
  	/* 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(fs_info) -
  		     btrfs_item_offset_nr(right, push_items - 1);
  
  	copy_extent_buffer(left, right, BTRFS_LEAF_DATA_OFFSET +
  		     leaf_data_end(fs_info, left) - push_space,
  		     BTRFS_LEAF_DATA_OFFSET +
  		     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(i);
  
  		ioff = btrfs_token_item_offset(left, item, &token);
  		btrfs_set_token_item_offset(left, item,
  		      ioff - (BTRFS_LEAF_DATA_SIZE(fs_info) - old_left_item_size),
  		      &token);
  	}
  	btrfs_set_header_nritems(left, old_left_nritems + push_items);
  
  	/* fixup right node */
  	if (push_items > right_nritems)
  		WARN(1, KERN_CRIT "push items %d nr %u\n", push_items,
  		       right_nritems);
  
  	if (push_items < right_nritems) {
  		push_space = btrfs_item_offset_nr(right, push_items - 1) -
  						  leaf_data_end(fs_info, right);
  		memmove_extent_buffer(right, BTRFS_LEAF_DATA_OFFSET +
  				      BTRFS_LEAF_DATA_SIZE(fs_info) - push_space,
  				      BTRFS_LEAF_DATA_OFFSET +
  				      leaf_data_end(fs_info, 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(fs_info);
  	for (i = 0; i < right_nritems; i++) {
  		item = btrfs_item_nr(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(fs_info, right);
  
  	btrfs_item_key(right, &disk_key, 0);
  	fixup_low_keys(fs_info, 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 btrfs_fs_info *fs_info = root->fs_info;
  	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(fs_info, path->nodes[1], slot - 1);
  	/*
  	 * slot - 1 is not valid or we fail to read the left node,
  	 * no big deal, just return.
  	 */
  	if (IS_ERR(left))
  		return 1;
  
  	btrfs_tree_lock(left);
  	btrfs_set_lock_blocking(left);
  
  	free_space = btrfs_leaf_free_space(fs_info, 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(fs_info, left);
  	if (free_space < data_size) {
  		ret = 1;
  		goto out;
  	}
  
  	return __push_leaf_left(fs_info, 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_fs_info *fs_info,
  				    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(fs_info, 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_OFFSET + BTRFS_LEAF_DATA_SIZE(fs_info) -
  		     data_copy_size, BTRFS_LEAF_DATA_OFFSET +
  		     leaf_data_end(fs_info, l), data_copy_size);
  
  	rt_data_off = BTRFS_LEAF_DATA_SIZE(fs_info) - btrfs_item_end_nr(l, mid);
  
  	for (i = 0; i < nritems; i++) {
  		struct btrfs_item *item = btrfs_item_nr(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, fs_info, 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)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	int ret;
  	int progress = 0;
  	int slot;
  	u32 nritems;
  	int space_needed = data_size;
  
  	slot = path->slots[0];
  	if (slot < btrfs_header_nritems(path->nodes[0]))
  		space_needed -= btrfs_leaf_free_space(fs_info, path->nodes[0]);
  
  	/*
  	 * try to push all the items after our slot into the
  	 * right leaf
  	 */
  	ret = push_leaf_right(trans, root, path, 1, space_needed, 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(fs_info, path->nodes[0]) >= data_size)
  		return 0;
  
  	/* try to push all the items before our slot into the next leaf */
  	slot = path->slots[0];
  	space_needed = data_size;
  	if (slot > 0)
  		space_needed -= btrfs_leaf_free_space(fs_info, path->nodes[0]);
  	ret = push_leaf_left(trans, root, path, 1, space_needed, 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,
  			       const 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;
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	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(fs_info))
  		return -EOVERFLOW;
  
  	/* first try to make some room by pushing left and right */
  	if (data_size && path->nodes[1]) {
  		int space_needed = data_size;
  
  		if (slot < btrfs_header_nritems(l))
  			space_needed -= btrfs_leaf_free_space(fs_info, l);
  
  		wret = push_leaf_right(trans, root, path, space_needed,
  				       space_needed, 0, 0);
  		if (wret < 0)
  			return wret;
  		if (wret) {
  			space_needed = data_size;
  			if (slot > 0)
  				space_needed -= btrfs_leaf_free_space(fs_info,
  								      l);
  			wret = push_leaf_left(trans, root, path, space_needed,
  					      space_needed, 0, (u32)-1);
  			if (wret < 0)
  				return wret;
  		}
  		l = path->nodes[0];
  
  		/* did the pushes work? */
  		if (btrfs_leaf_free_space(fs_info, 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(fs_info)) {
  			if (slot >= nritems) {
  				split = 0;
  			} else {
  				mid = slot;
  				if (mid != nritems &&
  				    leaf_space_used(l, mid, nritems - mid) +
  				    data_size > BTRFS_LEAF_DATA_SIZE(fs_info)) {
  					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(fs_info)) {
  			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(fs_info)) {
  					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_tree_block(trans, root, 0, root->root_key.objectid,
  			&disk_key, 0, l->start, 0);
  	if (IS_ERR(right))
  		return PTR_ERR(right);
  
  	root_add_used(root, fs_info->nodesize);
  
  	memzero_extent_buffer(right, 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_fsid(right, fs_info->fsid);
  	write_extent_buffer_chunk_tree_uuid(right, fs_info->chunk_tree_uuid);
  
  	if (split == 0) {
  		if (mid <= slot) {
  			btrfs_set_header_nritems(right, 0);
  			insert_ptr(trans, fs_info, 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, fs_info, 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(fs_info, path, &disk_key, 1);
  		}
  		/*
  		 * We create a new leaf 'right' for the required ins_len and
  		 * we'll do btrfs_mark_buffer_dirty() on this leaf after copying
  		 * the content of ins_len to 'right'.
  		 */
  		return ret;
  	}
  
  	copy_for_split(trans, fs_info, 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(fs_info, 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_fs_info *fs_info = root->fs_info;
  	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(fs_info, 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)
  		ret = -EAGAIN;
  	if (ret < 0)
  		goto err;
  
  	ret = -EAGAIN;
  	leaf = path->nodes[0];
  	/* if our item isn't there, return now */
  	if (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(fs_info, 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_fs_info *fs_info,
  			       struct btrfs_path *path,
  			       const 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(fs_info, leaf) < sizeof(struct btrfs_item));
  
  	btrfs_set_path_blocking(path);
  
  	item = btrfs_item_nr(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(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(fs_info, 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,
  		     const 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(root->fs_info, 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,
  			 const 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(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_fs_info *fs_info,
  			 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(fs_info, 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(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_OFFSET +
  			      data_end + size_diff, BTRFS_LEAF_DATA_OFFSET +
  			      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,
  				      BTRFS_FILE_EXTENT_INLINE_DATA_START);
  			}
  		}
  
  		memmove_extent_buffer(leaf, BTRFS_LEAF_DATA_OFFSET +
  			      data_end + size_diff, BTRFS_LEAF_DATA_OFFSET +
  			      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(fs_info, path, &disk_key, 1);
  	}
  
  	item = btrfs_item_nr(slot);
  	btrfs_set_item_size(leaf, item, new_size);
  	btrfs_mark_buffer_dirty(leaf);
  
  	if (btrfs_leaf_free_space(fs_info, leaf) < 0) {
  		btrfs_print_leaf(leaf);
  		BUG();
  	}
  }
  
  /*
   * make the item pointed to by the path bigger, data_size is the added size.
   */
  void btrfs_extend_item(struct btrfs_fs_info *fs_info, 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(fs_info, leaf);
  
  	if (btrfs_leaf_free_space(fs_info, leaf) < data_size) {
  		btrfs_print_leaf(leaf);
  		BUG();
  	}
  	slot = path->slots[0];
  	old_data = btrfs_item_end_nr(leaf, slot);
  
  	BUG_ON(slot < 0);
  	if (slot >= nritems) {
  		btrfs_print_leaf(leaf);
  		btrfs_crit(fs_info, "slot %d too large, nritems %d",
  			   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(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_OFFSET +
  		      data_end - data_size, BTRFS_LEAF_DATA_OFFSET +
  		      data_end, old_data - data_end);
  
  	data_end = old_data;
  	old_size = btrfs_item_size_nr(leaf, slot);
  	item = btrfs_item_nr(slot);
  	btrfs_set_item_size(leaf, item, old_size + data_size);
  	btrfs_mark_buffer_dirty(leaf);
  
  	if (btrfs_leaf_free_space(fs_info, leaf) < 0) {
  		btrfs_print_leaf(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_root *root, struct btrfs_path *path,
  			    const struct btrfs_key *cpu_key, u32 *data_size,
  			    u32 total_data, u32 total_size, int nr)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	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;
  
  	if (path->slots[0] == 0) {
  		btrfs_cpu_key_to_disk(&disk_key, cpu_key);
  		fixup_low_keys(fs_info, path, &disk_key, 1);
  	}
  	btrfs_unlock_up_safe(path, 1);
  
  	btrfs_init_map_token(&token);
  
  	leaf = path->nodes[0];
  	slot = path->slots[0];
  
  	nritems = btrfs_header_nritems(leaf);
  	data_end = leaf_data_end(fs_info, leaf);
  
  	if (btrfs_leaf_free_space(fs_info, leaf) < total_size) {
  		btrfs_print_leaf(leaf);
  		btrfs_crit(fs_info, "not enough freespace need %u have %d",
  			   total_size, btrfs_leaf_free_space(fs_info, leaf));
  		BUG();
  	}
  
  	if (slot != nritems) {
  		unsigned int old_data = btrfs_item_end_nr(leaf, slot);
  
  		if (old_data < data_end) {
  			btrfs_print_leaf(leaf);
  			btrfs_crit(fs_info, "slot %d old_data %d data_end %d",
  				   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(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_OFFSET +
  			      data_end - total_data, BTRFS_LEAF_DATA_OFFSET +
  			      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(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);
  	btrfs_mark_buffer_dirty(leaf);
  
  	if (btrfs_leaf_free_space(fs_info, leaf) < 0) {
  		btrfs_print_leaf(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,
  			    const 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(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,
  		      const 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_root *root, struct btrfs_path *path,
  		    int level, int slot)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	struct extent_buffer *parent = path->nodes[level];
  	u32 nritems;
  	int ret;
  
  	nritems = btrfs_header_nritems(parent);
  	if (slot != nritems - 1) {
  		if (level)
  			tree_mod_log_eb_move(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 (level) {
  		ret = tree_mod_log_insert_key(fs_info, parent, slot,
  					      MOD_LOG_KEY_REMOVE, GFP_NOFS);
  		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(fs_info, 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(root, path, 1, path->slots[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 btrfs_fs_info *fs_info = root->fs_info;
  	struct extent_buffer *leaf;
  	struct btrfs_item *item;
  	u32 last_off;
  	u32 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(fs_info, leaf);
  
  		memmove_extent_buffer(leaf, BTRFS_LEAF_DATA_OFFSET +
  			      data_end + dsize,
  			      BTRFS_LEAF_DATA_OFFSET + data_end,
  			      last_off - data_end);
  
  		for (i = slot + nr; i < nritems; i++) {
  			u32 ioff;
  
  			item = btrfs_item_nr(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(fs_info, 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(fs_info, path, &disk_key, 1);
  		}
  
  		/* delete the leaf if it is mostly empty */
  		if (used < BTRFS_LEAF_DATA_SIZE(fs_info) / 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--;
  		key.offset = (u64)-1;
  	} else if (key.objectid > 0) {
  		key.objectid--;
  		key.type = (u8)-1;
  		key.offset = (u64)-1;
  	} 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);
  	/*
  	 * We might have had an item with the previous key in the tree right
  	 * before we released our path. And after we released our path, that
  	 * item might have been pushed to the first slot (0) of the leaf we
  	 * were holding due to a tree balance. Alternatively, an item with the
  	 * previous key can exist as the only element of a leaf (big fat item).
  	 * Therefore account for these 2 cases, so that our callers (like
  	 * btrfs_previous_item) don't miss an existing item with a key matching
  	 * the previous key we computed above.
  	 */
  	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 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_path *path,
  			 u64 min_trans)
  {
  	struct btrfs_fs_info *fs_info = root->fs_info;
  	struct extent_buffer *cur;
  	struct btrfs_key found_key;
  	int slot;
  	int sret;
  	u32 nritems;
  	int level;
  	int ret = 1;
  	int keep_locks = path->keep_locks;
  
  	path->keep_locks = 1;
  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 min_trans parameters.
  		 * If it is too old, old, skip to the next one.
  		 */
  		while (slot < nritems) {
  			u64 gen;
  
  			gen = btrfs_node_ptr_generation(cur, slot);
  			if (gen < min_trans) {
  				slot++;
  				continue;
  			}
  			break;
  		}
  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,
  						  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;
  			goto out;
  		}
  		btrfs_set_path_blocking(path);
  		cur = read_node_slot(fs_info, cur, slot);
  		if (IS_ERR(cur)) {
  			ret = PTR_ERR(cur);
  			goto out;
  		}
  
  		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:
  	path->keep_locks = keep_locks;
  	if (ret == 0) {
  		btrfs_unlock_up_safe(path, path->lowest_level + 1);
  		btrfs_set_path_blocking(path);
  		memcpy(min_key, &found_key, sizeof(found_key));
  	}
  	return ret;
  }
  
  static int tree_move_down(struct btrfs_fs_info *fs_info,
  			   struct btrfs_path *path,
  			   int *level)
  {
  	struct extent_buffer *eb;
  
  	BUG_ON(*level == 0);
  	eb = read_node_slot(fs_info, path->nodes[*level], path->slots[*level]);
  	if (IS_ERR(eb))
  		return PTR_ERR(eb);
  
  	path->nodes[*level - 1] = eb;
  	path->slots[*level - 1] = 0;
  	(*level)--;
  	return 0;
  }
  
  static int tree_move_next_or_upnext(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_fs_info *fs_info,
  			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(path, level, root_level);
  	} else {
  		ret = tree_move_down(fs_info, path, level);
  	}
  	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_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)
  {
  	struct btrfs_fs_info *fs_info = left_root->fs_info;
  	int ret;
  	int cmp;
  	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_gen;
  	u64 right_gen;
  
  	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 = kvmalloc(fs_info->nodesize, GFP_KERNEL);
  	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;
  
  	/*
  	 * 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.
  	 */
  
  	down_read(&fs_info->commit_root_sem);
  	left_level = btrfs_header_level(left_root->commit_root);
  	left_root_level = left_level;
  	left_path->nodes[left_level] =
  			btrfs_clone_extent_buffer(left_root->commit_root);
  	if (!left_path->nodes[left_level]) {
  		up_read(&fs_info->commit_root_sem);
  		ret = -ENOMEM;
  		goto out;
  	}
  	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] =
  			btrfs_clone_extent_buffer(right_root->commit_root);
  	if (!right_path->nodes[right_level]) {
  		up_read(&fs_info->commit_root_sem);
  		ret = -ENOMEM;
  		goto out;
  	}
  	extent_buffer_get(right_path->nodes[right_level]);
  	up_read(&fs_info->commit_root_sem);
  
  	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) {
  		if (advance_left && !left_end_reached) {
  			ret = tree_advance(fs_info, left_path, &left_level,
  					left_root_level,
  					advance_left != ADVANCE_ONLY_NEXT,
  					&left_key);
  			if (ret == -1)
  				left_end_reached = ADVANCE;
  			else if (ret < 0)
  				goto out;
  			advance_left = 0;
  		}
  		if (advance_right && !right_end_reached) {
  			ret = tree_advance(fs_info, right_path, &right_level,
  					right_root_level,
  					advance_right != ADVANCE_ONLY_NEXT,
  					&right_key);
  			if (ret == -1)
  				right_end_reached = ADVANCE;
  			else if (ret < 0)
  				goto out;
  			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 {
  				enum btrfs_compare_tree_result result;
  
  				WARN_ON(!extent_buffer_uptodate(left_path->nodes[0]));
  				ret = tree_compare_item(left_path, right_path,
  							tmp_buf);
  				if (ret)
  					result = BTRFS_COMPARE_TREE_CHANGED;
  				else
  					result = BTRFS_COMPARE_TREE_SAME;
  				ret = changed_cb(left_root, right_root,
  						 left_path, right_path,
  						 &left_key, result, 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]);
  				left_gen = btrfs_node_ptr_generation(
  						left_path->nodes[left_level],
  						left_path->slots[left_level]);
  				right_gen = btrfs_node_ptr_generation(
  						right_path->nodes[right_level],
  						right_path->slots[right_level]);
  				if (left_blockptr == right_blockptr &&
  				    left_gen == right_gen) {
  					/*
  					 * 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);
  	kvfree(tmp_buf);
  	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 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, 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 gen = btrfs_node_ptr_generation(c, slot);
  
  			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;
  	}
  	/*
  	 * So the above check misses one case:
  	 * - after releasing the path above, someone has removed the item that
  	 *   used to be at the very end of the block, and balance between leafs
  	 *   gets another one with bigger key.offset to replace it.
  	 *
  	 * This one should be returned as well, or we can get leaf corruption
  	 * later(esp. in __btrfs_drop_extents()).
  	 *
  	 * And a bit more explanation about this check,
  	 * with ret > 0, the key isn't found, the path points to the slot
  	 * where it should be inserted, so the path->slots[0] item must be the
  	 * bigger one.
  	 */
  	if (nritems > 0 && ret > 0 && path->slots[0] == nritems - 1) {
  		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(root, path, &next, level,
  					    slot, &key);
  		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(root, path, &next, level,
  					    0, &key);
  		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;
  }
  
  /*
   * search in extent tree to find a previous Metadata/Data extent item with
   * min objecitd.
   *
   * returns 0 if something is found, 1 if nothing was found and < 0 on error
   */
  int btrfs_previous_extent_item(struct btrfs_root *root,
  			struct btrfs_path *path, u64 min_objectid)
  {
  	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 == BTRFS_EXTENT_ITEM_KEY ||
  		    found_key.type == BTRFS_METADATA_ITEM_KEY)
  			return 0;
  		if (found_key.objectid == min_objectid &&
  		    found_key.type < BTRFS_EXTENT_ITEM_KEY)
  			break;
  	}
  	return 1;
  }
  