fs/btrfs/ctree.c

/*
 * Copyright (C) 2007,2008 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/rbtree.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "print-tree.h"
#include "locking.h"

static int split_node(struct btrfs_trans_handle *trans, struct btrfs_root
		      *root, struct btrfs_path *path, int level);
static int split_leaf(struct btrfs_trans_handle *trans, struct btrfs_root
		      *root, struct btrfs_key *ins_key,
		      struct btrfs_path *path, int data_size, int extend);
static int push_node_left(struct btrfs_trans_handle *trans,
			  struct btrfs_root *root, struct extent_buffer *dst,
			  struct extent_buffer *src, int empty);
static int balance_node_right(struct btrfs_trans_handle *trans,
			      struct btrfs_root *root,
			      struct extent_buffer *dst_buf,
			      struct extent_buffer *src_buf);
static void del_ptr(struct btrfs_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)
{
	struct btrfs_path *path;
	path = kmem_cache_zalloc(btrfs_path_cachep, GFP_NOFS);
	return path;
}

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

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

	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 cow'ed but we may not get the new root node yet so do
		 * the inc_not_zero dance and if it doesn't work then
		 * synchronize_rcu and try again.
		 */
		if (atomic_inc_not_zero(&eb->refs)) {
			rcu_read_unlock();
			break;
		}
		rcu_read_unlock();
		synchronize_rcu();
	}
	return eb;
}

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

	while (1) {
		eb = btrfs_root_node(root);
		btrfs_tree_lock(eb);
		if (eb == root->node)
			break;
		btrfs_tree_unlock(eb);
		free_extent_buffer(eb);
	}
	return eb;
}

/* loop around taking references on and locking the root node of the
 * tree until you end up with a lock on the root.  A locked buffer
 * is returned, with a reference held.
 */
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)
{
	if (test_bit(BTRFS_ROOT_DIRTY, &root->state) ||
	    !test_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state))
		return;

	spin_lock(&root->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,
				       &root->fs_info->dirty_cowonly_roots);
		else
			list_move(&root->dirty_list,
				  &root->fs_info->dirty_cowonly_roots);
	}
	spin_unlock(&root->fs_info->trans_lock);
}

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

	WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
		trans->transid != root->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(cow, buf, 0, 0, cow->len);
	btrfs_set_header_bytenr(cow, cow->start);
	btrfs_set_header_generation(cow, trans->transid);
	btrfs_set_header_backref_rev(cow, BTRFS_MIXED_BACKREF_REV);
	btrfs_clear_header_flag(cow, BTRFS_HEADER_FLAG_WRITTEN |
				     BTRFS_HEADER_FLAG_RELOC);
	if (new_root_objectid == BTRFS_TREE_RELOC_OBJECTID)
		btrfs_set_header_flag(cow, BTRFS_HEADER_FLAG_RELOC);
	else
		btrfs_set_header_owner(cow, new_root_objectid);

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

	WARN_ON(btrfs_header_generation(buf) > trans->transid);
	if (new_root_objectid == BTRFS_TREE_RELOC_OBJECTID)
		ret = btrfs_inc_ref(trans, root, cow, 1);
	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 index;		/* shifted logical */
	u64 seq;
	enum mod_log_op op;

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

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

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

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

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

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

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

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

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

/*
 * 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 = container_of(node, struct tree_mod_elem, node);
		if (tm->seq > min_seq)
			continue;
		rb_erase(node, tm_root);
		kfree(tm);
	}
	tree_mod_log_write_unlock(fs_info);
}

/*
 * key order of the log:
 *       index -> sequence
 *
 * the index is the shifted logical of the *new* root node for root replace
 * operations, or the shifted logical of the affected block for all other
 * operations.
 *
 * 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;

	BUG_ON(!tm);

	tm->seq = btrfs_inc_tree_mod_seq(fs_info);

	tm_root = &fs_info->tree_mod_log;
	new = &tm_root->rb_node;
	while (*new) {
		cur = container_of(*new, struct tree_mod_elem, node);
		parent = *new;
		if (cur->index < tm->index)
			new = &((*new)->rb_left);
		else if (cur->index > tm->index)
			new = &((*new)->rb_right);
		else if (cur->seq < tm->seq)
			new = &((*new)->rb_left);
		else if (cur->seq > tm->seq)
			new = &((*new)->rb_right);
		else
			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->index = eb->start >> PAGE_CACHE_SHIFT;
	if (op != MOD_LOG_KEY_ADD) {
		btrfs_node_key(eb, &tm->key, slot);
		tm->blockptr = btrfs_node_blockptr(eb, slot);
	}
	tm->op = op;
	tm->slot = slot;
	tm->generation = btrfs_node_ptr_generation(eb, slot);
	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, gfp_t flags)
{
	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 *), flags);
	if (!tm_list)
		return -ENOMEM;

	tm = kzalloc(sizeof(*tm), flags);
	if (!tm) {
		ret = -ENOMEM;
		goto free_tms;
	}

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

	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, flags);
		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, gfp_t flags,
			 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 *),
				  flags);
		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, flags);
			if (!tm_list[i]) {
				ret = -ENOMEM;
				goto free_tms;
			}
		}
	}

	tm = kzalloc(sizeof(*tm), flags);
	if (!tm) {
		ret = -ENOMEM;
		goto free_tms;
	}

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

	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;
	u64 index = start >> PAGE_CACHE_SHIFT;

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

	return found;
}

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

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

static noinline 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, GFP_NOFS);
	BUG_ON(ret < 0);
}

static noinline void
tree_mod_log_set_node_key(struct btrfs_fs_info *fs_info,
			  struct extent_buffer *eb, 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, GFP_NOFS, 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 refernece counted trees and tree roots
	 * are never shared. If a block was allocated after the last
	 * snapshot and the block was not allocated by tree relocation,
	 * we know the block is not shared.
	 */
	if (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)
{
	u64 refs;
	u64 owner;
	u64 flags;
	u64 new_flags = 0;
	int ret;

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

	if (btrfs_block_can_be_shared(root, buf)) {
		ret = btrfs_lookup_extent_info(trans, root, buf->start,
					       btrfs_header_level(buf), 1,
					       &refs, &flags);
		if (ret)
			return ret;
		if (refs == 0) {
			ret = -EROFS;
			btrfs_std_error(root->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);
			BUG_ON(ret); /* -ENOMEM */

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

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

			ret = btrfs_set_disk_extent_flags(trans, root,
							  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);
			BUG_ON(ret); /* -ENOMEM */
			ret = btrfs_dec_ref(trans, root, buf, 1);
			BUG_ON(ret); /* -ENOMEM */
		}
		clean_tree_block(trans, root->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_disk_key disk_key;
	struct extent_buffer *cow;
	int level, ret;
	int last_ref = 0;
	int unlock_orig = 0;
	u64 parent_start;

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

	btrfs_assert_tree_locked(buf);

	WARN_ON(test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
		trans->transid != root->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) {
		if (parent)
			parent_start = parent->start;
		else
			parent_start = 0;
	} else
		parent_start = 0;

	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(cow, buf, 0, 0, cow->len);
	btrfs_set_header_bytenr(cow, cow->start);
	btrfs_set_header_generation(cow, trans->transid);
	btrfs_set_header_backref_rev(cow, BTRFS_MIXED_BACKREF_REV);
	btrfs_clear_header_flag(cow, BTRFS_HEADER_FLAG_WRITTEN |
				     BTRFS_HEADER_FLAG_RELOC);
	if (root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID)
		btrfs_set_header_flag(cow, BTRFS_HEADER_FLAG_RELOC);
	else
		btrfs_set_header_owner(cow, root->root_key.objectid);

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

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

	if (test_bit(BTRFS_ROOT_REF_COWS, &root->state)) {
		ret = btrfs_reloc_cow_block(trans, root, buf, cow);
		if (ret) {
			btrfs_abort_transaction(trans, root, 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;
		else
			parent_start = 0;

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

		WARN_ON(trans->transid != btrfs_header_generation(parent));
		tree_mod_log_insert_key(root->fs_info, parent, parent_slot,
					MOD_LOG_KEY_REPLACE, 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(root->fs_info, buf);
			if (ret) {
				btrfs_abort_transaction(trans, root, 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 index of the *new*
	 * root, making it the very first operation that's logged for this root.
	 */
	while (1) {
		tm = tree_mod_log_search_oldest(fs_info, root_logical,
						time_seq);
		if (!looped && !tm)
			return 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 rewinded (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 = container_of(next, struct tree_mod_elem, node);
		if (tm->index != first_tm->index)
			break;
	}
	tree_mod_log_read_unlock(fs_info);
	btrfs_set_header_nritems(eb, n);
}

/*
 * Called with eb read locked. If the buffer cannot be rewinded, 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->tree_root));

	return eb_rewin;
}

/*
 * get_old_root() rewinds the state of @root's root node to the given @time_seq
 * value. If there are no changes, the current root->root_node is returned. If
 * anything changed in between, there's a fresh buffer allocated on which the
 * rewind operations are done. In any case, the returned buffer is read locked.
 * Returns NULL on error (with no locks held).
 */
static inline struct extent_buffer *
get_old_root(struct btrfs_root *root, u64 time_seq)
{
	struct tree_mod_elem *tm;
	struct extent_buffer *eb = 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(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(root->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(root, logical, 0);
		if (WARN_ON(IS_ERR(old) || !extent_buffer_uptodate(old))) {
			if (!IS_ERR(old))
				free_extent_buffer(old);
			btrfs_warn(root->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(root->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(root->fs_info, eb, time_seq, tm);
	else
		WARN_ON(btrfs_header_level(eb) != 0);
	WARN_ON(btrfs_header_nritems(eb) > BTRFS_NODEPTRS_PER_BLOCK(root));

	return eb;
}

int btrfs_old_root_level(struct btrfs_root *root, u64 time_seq)
{
	struct tree_mod_elem *tm;
	int level;
	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_test_is_dummy_root(root))
		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 commiting the transaction,
	 *    after we've finished coping src root, we must COW the shared
	 *    block to ensure the metadata consistency.
	 */
	if (btrfs_header_generation(buf) == trans->transid &&
	    !btrfs_header_flag(buf, BTRFS_HEADER_FLAG_WRITTEN) &&
	    !(root->root_key.objectid != BTRFS_TREE_RELOC_OBJECTID &&
	      btrfs_header_flag(buf, BTRFS_HEADER_FLAG_RELOC)) &&
	    !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 cow'd more than
 * once per transaction, as long as it hasn't been written yet
 */
noinline int btrfs_cow_block(struct btrfs_trans_handle *trans,
		    struct btrfs_root *root, struct extent_buffer *buf,
		    struct extent_buffer *parent, int parent_slot,
		    struct extent_buffer **cow_ret)
{
	u64 search_start;
	int ret;

	if (trans->transaction != root->fs_info->running_transaction)
		WARN(1, KERN_CRIT "trans %llu running %llu\n",
		       trans->transid,
		       root->fs_info->running_transaction->transid);

	if (trans->transid != root->fs_info->generation)
		WARN(1, KERN_CRIT "trans %llu running %llu\n",
		       trans->transid, root->fs_info->generation);

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

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

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

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

	trace_btrfs_cow_block(root, buf, *cow_ret);

	return ret;
}

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

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

	btrfs_disk_key_to_cpu(&k1, disk);

	return btrfs_comp_cpu_keys(&k1, k2);
}

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

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

	parent_level = btrfs_header_level(parent);

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

	parent_nritems = btrfs_header_nritems(parent);
	blocksize = root->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 = btrfs_find_tree_block(root->fs_info, blocknr);
		if (cur)
			uptodate = btrfs_buffer_uptodate(cur, gen, 0);
		else
			uptodate = 0;
		if (!cur || !uptodate) {
			if (!cur) {
				cur = read_tree_block(root, 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;
}

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


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

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

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

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

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

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

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

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

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

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

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

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

	if (slot < 0)
		return NULL;
	if (slot >= btrfs_header_nritems(parent))
		return NULL;

	BUG_ON(level == 0);

	eb = read_tree_block(root, btrfs_node_blockptr(parent, slot),
			     btrfs_node_ptr_generation(parent, slot));
	if (IS_ERR(eb) || !extent_buffer_uptodate(eb)) {
		if (!IS_ERR(eb))
			free_extent_buffer(eb);
		eb = NULL;
	}

	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 extent_buffer *right = NULL;
	struct extent_buffer *mid;
	struct extent_buffer *left = NULL;
	struct extent_buffer *parent = NULL;
	int ret = 0;
	int wret;
	int pslot;
	int orig_slot = path->slots[level];
	u64 orig_ptr;

	if (level == 0)
		return 0;

	mid = path->nodes[level];

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

	orig_ptr = btrfs_node_blockptr(mid, orig_slot);

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

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

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

		/* promote the child to a root */
		child = read_node_slot(root, mid, 0);
		if (!child) {
			ret = -EROFS;
			btrfs_std_error(root->fs_info, ret, 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(trans, root->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(root) / 4)
		return 0;

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

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

	/*
	 * then try to empty the right most buffer into the middle
	 */
	if (right) {
		wret = push_node_left(trans, root, mid, right, 1);
		if (wret < 0 && wret != -ENOSPC)
			ret = wret;
		if (btrfs_header_nritems(right) == 0) {
			clean_tree_block(trans, root->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(root->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_std_error(root->fs_info, ret, NULL);
			goto enospc;
		}
		wret = balance_node_right(trans, root, mid, left);
		if (wret < 0) {
			ret = wret;
			goto enospc;
		}
		if (wret == 1) {
			wret = push_node_left(trans, root, left, mid, 1);
			if (wret < 0)
				ret = wret;
		}
		BUG_ON(wret == 1);
	}
	if (btrfs_header_nritems(mid) == 0) {
		clean_tree_block(trans, root->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(root->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 extent_buffer *right = NULL;
	struct extent_buffer *mid;
	struct extent_buffer *left = NULL;
	struct extent_buffer *parent = NULL;
	int ret = 0;
	int wret;
	int pslot;
	int orig_slot = path->slots[level];

	if (level == 0)
		return 1;

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

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

	if (!parent)
		return 1;

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

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

		btrfs_tree_lock(left);
		btrfs_set_lock_blocking(left);

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

	/*
	 * then try to empty the right most buffer into the middle
	 */
	if (right) {
		u32 right_nr;

		btrfs_tree_lock(right);
		btrfs_set_lock_blocking(right);

		right_nr = btrfs_header_nritems(right);
		if (right_nr >= BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
			wret = 1;
		} else {
			ret = btrfs_cow_block(trans, root, right,
					      parent, pslot + 1,
					      &right);
			if (ret)
				wret = 1;
			else {
				wret = balance_node_right(trans, root,
							  right, mid);
			}
		}
		if (wret < 0)
			ret = wret;
		if (wret == 0) {
			struct btrfs_disk_key disk_key;

			btrfs_node_key(right, &disk_key, 0);
			tree_mod_log_set_node_key(root->fs_info, parent,
						  pslot + 1, 0);
			btrfs_set_node_key(parent, &disk_key, pslot + 1);
			btrfs_mark_buffer_dirty(parent);

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

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

	if (level != 1)
		return;

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

	node = path->nodes[level];

	search = btrfs_node_blockptr(node, slot);
	blocksize = root->nodesize;
	eb = btrfs_find_tree_block(root->fs_info, search);
	if (eb) {
		free_extent_buffer(eb);
		return;
	}

	target = search;

	nritems = btrfs_header_nritems(node);
	nr = slot;

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

static noinline void reada_for_balance(struct btrfs_root *root,
				       struct btrfs_path *path, int level)
{
	int slot;
	int nritems;
	struct extent_buffer *parent;
	struct extent_buffer *eb;
	u64 gen;
	u64 block1 = 0;
	u64 block2 = 0;

	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 = btrfs_find_tree_block(root->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 = btrfs_find_tree_block(root->fs_info, block2);
		if (eb && btrfs_buffer_uptodate(eb, gen, 1) != 0)
			block2 = 0;
		free_extent_buffer(eb);
	}

	if (block1)
		readahead_tree_block(root, block1);
	if (block2)
		readahead_tree_block(root, 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_trans_handle *trans,
		       struct btrfs_root *root, struct btrfs_path *p,
		       struct extent_buffer **eb_ret, int level, int slot,
		       struct btrfs_key *key, u64 time_seq)
{
	u64 blocknr;
	u64 gen;
	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 = btrfs_find_tree_block(root->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_for_search(root, p, level, slot, key->objectid);

	btrfs_release_path(p);

	ret = -EAGAIN;
	tmp = read_tree_block(root, blocknr, 0);
	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);
	}
	return ret;
}

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

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

		btrfs_set_path_blocking(p);
		reada_for_balance(root, 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(root) / 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(root, 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,
				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, 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, struct btrfs_key *key, struct btrfs_path *p, int
		      ins_len, int cow)
{
	struct extent_buffer *b;
	int slot;
	int ret;
	int err;
	int level;
	int lowest_unlock = 1;
	int root_lock;
	/* everything at write_lock_level or lower must be write locked */
	int write_lock_level = 0;
	u8 lowest_level = 0;
	int min_write_lock_level;
	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(&root->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(&root->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) {
			/*
			 * if we don't really need to cow this block
			 * then we don't want to set the path blocking,
			 * so we test it here
			 */
			if (!should_cow_block(trans, root, b))
				goto cow_done;

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

			if (!p->skip_locking) {
				level = btrfs_header_level(b);
				if (level <= write_lock_level) {
					err = btrfs_try_tree_write_lock(b);
					if (!err) {
						btrfs_set_path_blocking(p);
						btrfs_tree_lock(b);
						btrfs_clear_path_blocking(p, b,
								  BTRFS_WRITE_LOCK);
					}
					p->locks[level] = BTRFS_WRITE_LOCK;
				} else {
					err = btrfs_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(root, b) < ins_len) {
				if (write_lock_level < 1) {
					write_lock_level = 1;
					btrfs_release_path(p);
					goto again;
				}

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

				BUG_ON(err > 0);
				if (err) {
					ret = err;
					goto done;
				}
			}
			if (!p->search_for_split)
				unlock_up(p, level, lowest_unlock,
					  min_write_lock_level, &write_lock_level);
			goto done;
		}
	}
	ret = 1;
done:
	/*
	 * we don't really know what they plan on doing with the path
	 * from here on, so for now just mark it as blocking
	 */
	if (!p->leave_spinning)
		btrfs_set_path_blocking(p);
	if (ret < 0 && !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, struct btrfs_key *key,
			  struct btrfs_path *p, u64 time_seq)
{
	struct extent_buffer *b;
	int slot;
	int ret;
	int err;
	int level;
	int lowest_unlock = 1;
	u8 lowest_level = 0;
	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 eb's 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(NULL, root, p, &b, level,
						    slot, key, time_seq);
			if (err == -EAGAIN)
				goto again;
			if (err) {
				ret = err;
				goto done;
			}

			level = btrfs_header_level(b);
			err = btrfs_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(root->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,
			       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)