Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 5704 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
new file mode 100644
index 000000000..814f2f07e
--- /dev/null
+++ b/fs/btrfs/ctree.c
@@ -0,0 +1,5704 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2007,2008 Oracle.  All rights reserved.
+ */
+
+#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"
+#include "volumes.h"
+#include "qgroup.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 extent_buffer *dst,
+			  struct extent_buffer *src, int empty);
+static int balance_node_right(struct btrfs_trans_handle *trans,
+			      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 const struct btrfs_csums {
+	u16		size;
+	const char	name[10];
+	const char	driver[12];
+} btrfs_csums[] = {
+	[BTRFS_CSUM_TYPE_CRC32] = { .size = 4, .name = "crc32c" },
+	[BTRFS_CSUM_TYPE_XXHASH] = { .size = 8, .name = "xxhash64" },
+	[BTRFS_CSUM_TYPE_SHA256] = { .size = 32, .name = "sha256" },
+	[BTRFS_CSUM_TYPE_BLAKE2] = { .size = 32, .name = "blake2b",
+				     .driver = "blake2b-256" },
+};
+
+int btrfs_super_csum_size(const struct btrfs_super_block *s)
+{
+	u16 t = btrfs_super_csum_type(s);
+	/*
+	 * csum type is validated at mount time
+	 */
+	return btrfs_csums[t].size;
+}
+
+const char *btrfs_super_csum_name(u16 csum_type)
+{
+	/* csum type is validated at mount time */
+	return btrfs_csums[csum_type].name;
+}
+
+/*
+ * Return driver name if defined, otherwise the name that's also a valid driver
+ * name
+ */
+const char *btrfs_super_csum_driver(u16 csum_type)
+{
+	/* csum type is validated at mount time */
+	return btrfs_csums[csum_type].driver[0] ?
+		btrfs_csums[csum_type].driver :
+		btrfs_csums[csum_type].name;
+}
+
+size_t __attribute_const__ btrfs_get_num_csums(void)
+{
+	return ARRAY_SIZE(btrfs_csums);
+}
+
+struct btrfs_path *btrfs_alloc_path(void)
+{
+	return kmem_cache_zalloc(btrfs_path_cachep, GFP_NOFS);
+}
+
+/* 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;
+}
+
+/*
+ * Cowonly root (not-shareable trees, everything not subvolume or reloc roots),
+ * just get put onto a simple dirty list.  Transaction walks this list 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->root_key.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_SHAREABLE, &root->state) &&
+		trans->transid != fs_info->running_transaction->transid);
+	WARN_ON(test_bit(BTRFS_ROOT_SHAREABLE, &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,
+				     BTRFS_NESTING_NEW_ROOT);
+	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->fs_devices->metadata_uuid);
+
+	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) {
+		btrfs_tree_unlock(cow);
+		free_extent_buffer(cow);
+		btrfs_abort_transaction(trans, 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_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 {
+		int dst_slot;
+		int nr_items;
+	} move;
+
+	/* this is used for op == MOD_LOG_ROOT_REPLACE */
+	struct tree_mod_root old_root;
+};
+
+/*
+ * 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)
+{
+	write_lock(&fs_info->tree_mod_log_lock);
+	if (!elem->seq) {
+		elem->seq = btrfs_inc_tree_mod_seq(fs_info);
+		list_add_tail(&elem->list, &fs_info->tree_mod_seq_list);
+	}
+	write_unlock(&fs_info->tree_mod_log_lock);
+
+	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 tree_mod_elem *tm;
+	u64 min_seq = (u64)-1;
+	u64 seq_putting = elem->seq;
+
+	if (!seq_putting)
+		return;
+
+	write_lock(&fs_info->tree_mod_log_lock);
+	list_del(&elem->list);
+	elem->seq = 0;
+
+	if (!list_empty(&fs_info->tree_mod_seq_list)) {
+		struct seq_list *first;
+
+		first = list_first_entry(&fs_info->tree_mod_seq_list,
+					 struct seq_list, list);
+		if (seq_putting > first->seq) {
+			/*
+			 * Blocker with lower sequence number exists, we
+			 * cannot remove anything from the log.
+			 */
+			write_unlock(&fs_info->tree_mod_log_lock);
+			return;
+		}
+		min_seq = first->seq;
+	}
+
+	/*
+	 * anything that's lower than the lowest existing (read: blocked)
+	 * sequence number can be removed from the tree.
+	 */
+	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);
+	}
+	write_unlock(&fs_info->tree_mod_log_lock);
+}
+
+/*
+ * 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.
+ */
+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;
+
+	lockdep_assert_held_write(&fs_info->tree_mod_log_lock);
+
+	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
+ * write unlock fs_info::tree_mod_log_lock.
+ */
+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;
+
+	write_lock(&fs_info->tree_mod_log_lock);
+	if (list_empty(&(fs_info)->tree_mod_seq_list)) {
+		write_unlock(&fs_info->tree_mod_log_lock);
+		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 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(eb->fs_info, eb))
+		return 0;
+
+	tm = alloc_tree_mod_elem(eb, slot, op, flags);
+	if (!tm)
+		return -ENOMEM;
+
+	if (tree_mod_dont_log(eb->fs_info, eb)) {
+		kfree(tm);
+		return 0;
+	}
+
+	ret = __tree_mod_log_insert(eb->fs_info, tm);
+	write_unlock(&eb->fs_info->tree_mod_log_lock);
+	if (ret)
+		kfree(tm);
+
+	return ret;
+}
+
+static noinline int tree_mod_log_insert_move(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(eb->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(eb->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(eb->fs_info, tm_list[i]);
+		if (ret)
+			goto free_tms;
+	}
+
+	ret = __tree_mod_log_insert(eb->fs_info, tm);
+	if (ret)
+		goto free_tms;
+	write_unlock(&eb->fs_info->tree_mod_log_lock);
+	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, &eb->fs_info->tree_mod_log);
+		kfree(tm_list[i]);
+	}
+	if (locked)
+		write_unlock(&eb->fs_info->tree_mod_log_lock);
+	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 extent_buffer *old_root,
+			 struct extent_buffer *new_root, int log_removal)
+{
+	struct btrfs_fs_info *fs_info = old_root->fs_info;
+	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);
+
+	write_unlock(&fs_info->tree_mod_log_lock);
+	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;
+
+	read_lock(&fs_info->tree_mod_log_lock);
+	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;
+		}
+	}
+	read_unlock(&fs_info->tree_mod_log_lock);
+
+	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 extent_buffer *dst,
+		     struct extent_buffer *src, unsigned long dst_offset,
+		     unsigned long src_offset, int nr_items)
+{
+	struct btrfs_fs_info *fs_info = dst->fs_info;
+	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;
+	}
+
+	write_unlock(&fs_info->tree_mod_log_lock);
+	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)
+		write_unlock(&fs_info->tree_mod_log_lock);
+	kfree(tm_list);
+
+	return ret;
+}
+
+static noinline int tree_mod_log_free_eb(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(eb->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(eb->fs_info, eb))
+		goto free_tms;
+
+	ret = __tree_mod_log_free_eb(eb->fs_info, tm_list, nritems);
+	write_unlock(&eb->fs_info->tree_mod_log_lock);
+	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;
+}
+
+/*
+ * 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 shareable 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_SHAREABLE, &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;
+
+	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, buf,
+							  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;
+		}
+		btrfs_clean_tree_block(buf);
+		*last_ref = 1;
+	}
+	return 0;
+}
+
+static struct extent_buffer *alloc_tree_block_no_bg_flush(
+					  struct btrfs_trans_handle *trans,
+					  struct btrfs_root *root,
+					  u64 parent_start,
+					  const struct btrfs_disk_key *disk_key,
+					  int level,
+					  u64 hint,
+					  u64 empty_size,
+					  enum btrfs_lock_nesting nest)
+{
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct extent_buffer *ret;
+
+	/*
+	 * If we are COWing a node/leaf from the extent, chunk, device or free
+	 * space trees, make sure that we do not finish block group creation of
+	 * pending block groups. We do this to avoid a deadlock.
+	 * COWing can result in allocation of a new chunk, and flushing pending
+	 * block groups (btrfs_create_pending_block_groups()) can be triggered
+	 * when finishing allocation of a new chunk. Creation of a pending block
+	 * group modifies the extent, chunk, device and free space trees,
+	 * therefore we could deadlock with ourselves since we are holding a
+	 * lock on an extent buffer that btrfs_create_pending_block_groups() may
+	 * try to COW later.
+	 * For similar reasons, we also need to delay flushing pending block
+	 * groups when splitting a leaf or node, from one of those trees, since
+	 * we are holding a write lock on it and its parent or when inserting a
+	 * new root node for one of those trees.
+	 */
+	if (root == fs_info->extent_root ||
+	    root == fs_info->chunk_root ||
+	    root == fs_info->dev_root ||
+	    root == fs_info->free_space_root)
+		trans->can_flush_pending_bgs = false;
+
+	ret = btrfs_alloc_tree_block(trans, root, parent_start,
+				     root->root_key.objectid, disk_key, level,
+				     hint, empty_size, nest);
+	trans->can_flush_pending_bgs = true;
+
+	return ret;
+}
+
+/*
+ * 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,
+			     enum btrfs_lock_nesting nest)
+{
+	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_SHAREABLE, &root->state) &&
+		trans->transid != fs_info->running_transaction->transid);
+	WARN_ON(test_bit(BTRFS_ROOT_SHAREABLE, &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 = alloc_tree_block_no_bg_flush(trans, root, parent_start, &disk_key,
+					   level, search_start, empty_size, nest);
+	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->fs_devices->metadata_uuid);
+
+	ret = update_ref_for_cow(trans, root, buf, cow, &last_ref);
+	if (ret) {
+		btrfs_tree_unlock(cow);
+		free_extent_buffer(cow);
+		btrfs_abort_transaction(trans, ret);
+		return ret;
+	}
+
+	if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state)) {
+		ret = btrfs_reloc_cow_block(trans, root, buf, cow);
+		if (ret) {
+			btrfs_tree_unlock(cow);
+			free_extent_buffer(cow);
+			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;
+
+		atomic_inc(&cow->refs);
+		ret = tree_mod_log_insert_root(root->node, cow, 1);
+		BUG_ON(ret < 0);
+		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(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(buf);
+			if (ret) {
+				btrfs_tree_unlock(cow);
+				free_extent_buffer(cow);
+				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 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(eb_root->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);
+	read_lock(&fs_info->tree_mod_log_lock);
+	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;
+	}
+	read_unlock(&fs_info->tree_mod_log_lock);
+	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_read(eb);
+
+	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_tree_read_unlock_blocking(eb);
+	free_extent_buffer(eb);
+
+	btrfs_set_buffer_lockdep_class(btrfs_header_owner(eb_rewin),
+				       eb_rewin, btrfs_header_level(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;
+	u64 eb_root_owner = 0;
+	struct extent_buffer *old;
+	struct tree_mod_root *old_root = NULL;
+	u64 old_generation = 0;
+	u64 logical;
+	int level;
+
+	eb_root = btrfs_read_lock_root_node(root);
+	tm = __tree_mod_log_oldest_root(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;
+		level = old_root->level;
+	} else {
+		logical = eb_root->start;
+		level = btrfs_header_level(eb_root);
+	}
+
+	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, level, NULL);
+		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 {
+			struct tree_mod_elem *tm2;
+
+			btrfs_tree_read_lock(old);
+			eb = btrfs_clone_extent_buffer(old);
+			/*
+			 * After the lookup for the most recent tree mod operation
+			 * above and before we locked and cloned the extent buffer
+			 * 'old', a new tree mod log operation may have been added.
+			 * So lookup for a more recent one to make sure the number
+			 * of mod log operations we replay is consistent with the
+			 * number of items we have in the cloned extent buffer,
+			 * otherwise we can hit a BUG_ON when rewinding the extent
+			 * buffer.
+			 */
+			tm2 = tree_mod_log_search(fs_info, logical, time_seq);
+			btrfs_tree_read_unlock(old);
+			free_extent_buffer(old);
+			ASSERT(tm2);
+			ASSERT(tm2 == tm || tm2->seq > tm->seq);
+			if (!tm2 || tm2->seq < tm->seq) {
+				free_extent_buffer(eb);
+				return NULL;
+			}
+			tm = tm2;
+		}
+	} else if (old_root) {
+		eb_root_owner = btrfs_header_owner(eb_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_read(eb_root);
+		eb = btrfs_clone_extent_buffer(eb_root);
+		btrfs_tree_read_unlock_blocking(eb_root);
+		free_extent_buffer(eb_root);
+	}
+
+	if (!eb)
+		return NULL;
+	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, eb_root_owner);
+		btrfs_set_header_level(eb, old_root->level);
+		btrfs_set_header_generation(eb, old_generation);
+	}
+	btrfs_set_buffer_lockdep_class(btrfs_header_owner(eb), eb,
+				       btrfs_header_level(eb));
+	btrfs_tree_read_lock(eb);
+	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(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 bit */
+	smp_mb__before_atomic();
+
+	/*
+	 * 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 copying 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,
+		    enum btrfs_lock_nesting nest)
+{
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	u64 search_start;
+	int ret;
+
+	if (test_bit(BTRFS_ROOT_DELETING, &root->state))
+		btrfs_err(fs_info,
+			"COW'ing blocks on a fs root that's being dropped");
+
+	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_write(parent);
+	btrfs_set_lock_blocking_write(buf);
+
+	/*
+	 * Before CoWing this block for later modification, check if it's
+	 * the subtree root and do the delayed subtree trace if needed.
+	 *
+	 * Also We don't care about the error, as it's handled internally.
+	 */
+	btrfs_qgroup_trace_subtree_after_cow(trans, root, buf);
+	ret = __btrfs_cow_block(trans, root, buf, parent,
+				 parent_slot, cow_ret, search_start, 0, nest);
+
+	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;
+}
+
+#ifdef __LITTLE_ENDIAN
+
+/*
+ * Compare two keys, on little-endian the disk order is same as CPU order and
+ * we can avoid the conversion.
+ */
+static int comp_keys(const struct btrfs_disk_key *disk_key,
+		     const struct btrfs_key *k2)
+{
+	const struct btrfs_key *k1 = (const struct btrfs_key *)disk_key;
+
+	return btrfs_comp_cpu_keys(k1, k2);
+}
+
+#else
+
+/*
+ * 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);
+}
+#endif
+
+/*
+ * same as comp_keys only with two btrfs_key's
+ */
+int __pure 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_write(parent);
+
+	for (i = start_slot; i <= end_slot; i++) {
+		struct btrfs_key first_key;
+		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);
+		btrfs_node_key_to_cpu(parent, &first_key, 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,
+						      parent_level - 1,
+						      &first_key);
+				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,
+						parent_level - 1,&first_key);
+				if (err) {
+					free_extent_buffer(cur);
+					return err;
+				}
+			}
+		}
+		if (search_start == 0)
+			search_start = last_block;
+
+		btrfs_tree_lock(cur);
+		btrfs_set_lock_blocking_write(cur);
+		err = __btrfs_cow_block(trans, root, cur, parent, i,
+					&cur, search_start,
+					min(16 * blocksize,
+					    (end_slot - i) * blocksize),
+					BTRFS_NESTING_COW);
+		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 ret;
+	const int key_size = sizeof(struct btrfs_disk_key);
+
+	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) {
+		unsigned long oip;
+		unsigned long offset;
+		struct btrfs_disk_key *tmp;
+		struct btrfs_disk_key unaligned;
+		int mid;
+
+		mid = (low + high) / 2;
+		offset = p + mid * item_size;
+		oip = offset_in_page(offset);
+
+		if (oip + key_size <= PAGE_SIZE) {
+			const unsigned long idx = offset >> PAGE_SHIFT;
+			char *kaddr = page_address(eb->pages[idx]);
+
+			tmp = (struct btrfs_disk_key *)(kaddr + oip);
+		} else {
+			read_extent_buffer(eb, &unaligned, offset, key_size);
+			tmp = &unaligned;
+		}
+
+		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
+ */
+int btrfs_bin_search(struct extent_buffer *eb, const struct btrfs_key *key,
+		     int *slot)
+{
+	if (btrfs_header_level(eb) == 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);
+}
+
+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).
+ */
+struct extent_buffer *btrfs_read_node_slot(struct extent_buffer *parent,
+					   int slot)
+{
+	int level = btrfs_header_level(parent);
+	struct extent_buffer *eb;
+	struct btrfs_key first_key;
+
+	if (slot < 0 || slot >= btrfs_header_nritems(parent))
+		return ERR_PTR(-ENOENT);
+
+	BUG_ON(level == 0);
+
+	btrfs_node_key_to_cpu(parent, &first_key, slot);
+	eb = read_tree_block(parent->fs_info, btrfs_node_blockptr(parent, slot),
+			     btrfs_node_ptr_generation(parent, slot),
+			     level - 1, &first_key);
+	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;
+
+	ASSERT(level > 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 = btrfs_read_node_slot(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_write(child);
+		ret = btrfs_cow_block(trans, root, child, mid, 0, &child,
+				      BTRFS_NESTING_COW);
+		if (ret) {
+			btrfs_tree_unlock(child);
+			free_extent_buffer(child);
+			goto enospc;
+		}
+
+		ret = tree_mod_log_insert_root(root->node, child, 1);
+		BUG_ON(ret < 0);
+		rcu_assign_pointer(root->node, child);
+
+		add_root_to_dirty_list(root);
+		btrfs_tree_unlock(child);
+
+		path->locks[level] = 0;
+		path->nodes[level] = NULL;
+		btrfs_clean_tree_block(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 = btrfs_read_node_slot(parent, pslot - 1);
+	if (IS_ERR(left))
+		left = NULL;
+
+	if (left) {
+		__btrfs_tree_lock(left, BTRFS_NESTING_LEFT);
+		btrfs_set_lock_blocking_write(left);
+		wret = btrfs_cow_block(trans, root, left,
+				       parent, pslot - 1, &left,
+				       BTRFS_NESTING_LEFT_COW);
+		if (wret) {
+			ret = wret;
+			goto enospc;
+		}
+	}
+
+	right = btrfs_read_node_slot(parent, pslot + 1);
+	if (IS_ERR(right))
+		right = NULL;
+
+	if (right) {
+		__btrfs_tree_lock(right, BTRFS_NESTING_RIGHT);
+		btrfs_set_lock_blocking_write(right);
+		wret = btrfs_cow_block(trans, root, right,
+				       parent, pslot + 1, &right,
+				       BTRFS_NESTING_RIGHT_COW);
+		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, 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, mid, right, 1);
+		if (wret < 0 && wret != -ENOSPC)
+			ret = wret;
+		if (btrfs_header_nritems(right) == 0) {
+			btrfs_clean_tree_block(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);
+			ret = tree_mod_log_insert_key(parent, pslot + 1,
+					MOD_LOG_KEY_REPLACE, GFP_NOFS);
+			BUG_ON(ret < 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, mid, left);
+		if (wret < 0) {
+			ret = wret;
+			goto enospc;
+		}
+		if (wret == 1) {
+			wret = push_node_left(trans, left, mid, 1);
+			if (wret < 0)
+				ret = wret;
+		}
+		BUG_ON(wret == 1);
+	}
+	if (btrfs_header_nritems(mid) == 0) {
+		btrfs_clean_tree_block(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);
+		ret = tree_mod_log_insert_key(parent, pslot,
+				MOD_LOG_KEY_REPLACE, GFP_NOFS);
+		BUG_ON(ret < 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) {
+			atomic_inc(&left->refs);
+			/* 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 = btrfs_read_node_slot(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_NESTING_LEFT);
+		btrfs_set_lock_blocking_write(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,
+					      BTRFS_NESTING_LEFT_COW);
+			if (ret)
+				wret = 1;
+			else {
+				wret = push_node_left(trans, 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);
+			ret = tree_mod_log_insert_key(parent, pslot,
+					MOD_LOG_KEY_REPLACE, GFP_NOFS);
+			BUG_ON(ret < 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 = btrfs_read_node_slot(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_NESTING_RIGHT);
+		btrfs_set_lock_blocking_write(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, BTRFS_NESTING_RIGHT_COW);
+			if (ret)
+				wret = 1;
+			else {
+				wret = balance_node_right(trans, right, mid);
+			}
+		}
+		if (wret < 0)
+			ret = wret;
+		if (wret == 0) {
+			struct btrfs_disk_key disk_key;
+
+			btrfs_node_key(right, &disk_key, 0);
+			ret = tree_mod_log_insert_key(parent, pslot + 1,
+					MOD_LOG_KEY_REPLACE, GFP_NOFS);
+			BUG_ON(ret < 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) {
+			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;
+			}
+		}
+	}
+}
+
+/*
+ * 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 *tmp;
+	struct btrfs_key first_key;
+	int ret;
+	int parent_level;
+
+	blocknr = btrfs_node_blockptr(*eb_ret, slot);
+	gen = btrfs_node_ptr_generation(*eb_ret, slot);
+	parent_level = btrfs_header_level(*eb_ret);
+	btrfs_node_key_to_cpu(*eb_ret, &first_key, 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) {
+			/*
+			 * Do extra check for first_key, eb can be stale due to
+			 * being cached, read from scrub, or have multiple
+			 * parents (shared tree blocks).
+			 */
+			if (btrfs_verify_level_key(tmp,
+					parent_level - 1, &first_key, gen)) {
+				free_extent_buffer(tmp);
+				return -EUCLEAN;
+			}
+			*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, parent_level - 1, &first_key);
+		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);
+
+	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, parent_level - 1,
+			      &first_key);
+	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 (!extent_buffer_uptodate(tmp))
+			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);
+
+		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);
+
+		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;
+}
+
+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;
+}
+
+static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root,
+							struct btrfs_path *p,
+							int write_lock_level)
+{
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct extent_buffer *b;
+	int root_lock = 0;
+	int level = 0;
+
+	if (p->search_commit_root) {
+		/*
+		 * The commit roots are read only so we always do read locks,
+		 * and we always must hold the commit_root_sem when doing
+		 * searches on them, the only exception is send where we don't
+		 * want to block transaction commits for a long time, so
+		 * we need to clone the commit root in order to avoid races
+		 * with transaction commits that create a snapshot of one of
+		 * the roots used by a send operation.
+		 */
+		if (p->need_commit_sem) {
+			down_read(&fs_info->commit_root_sem);
+			b = btrfs_clone_extent_buffer(root->commit_root);
+			up_read(&fs_info->commit_root_sem);
+			if (!b)
+				return ERR_PTR(-ENOMEM);
+
+		} else {
+			b = root->commit_root;
+			atomic_inc(&b->refs);
+		}
+		level = btrfs_header_level(b);
+		/*
+		 * Ensure that all callers have set skip_locking when
+		 * p->search_commit_root = 1.
+		 */
+		ASSERT(p->skip_locking == 1);
+
+		goto out;
+	}
+
+	if (p->skip_locking) {
+		b = btrfs_root_node(root);
+		level = btrfs_header_level(b);
+		goto out;
+	}
+
+	/* We try very hard to do read locks on the root */
+	root_lock = BTRFS_READ_LOCK;
+
+	/*
+	 * If the level is set to maximum, we can skip trying to get the read
+	 * lock.
+	 */
+	if (write_lock_level < BTRFS_MAX_LEVEL) {
+		/*
+		 * We don't know the level of the root node until we actually
+		 * have it read locked
+		 */
+		b = __btrfs_read_lock_root_node(root, p->recurse);
+		level = btrfs_header_level(b);
+		if (level > write_lock_level)
+			goto out;
+
+		/* 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);
+
+out:
+	/*
+	 * The root may have failed to write out at some point, and thus is no
+	 * longer valid, return an error in this case.
+	 */
+	if (!extent_buffer_uptodate(b)) {
+		if (root_lock)
+			btrfs_tree_unlock_rw(b, root_lock);
+		free_extent_buffer(b);
+		return ERR_PTR(-EIO);
+	}
+
+	p->nodes[level] = b;
+	if (!p->skip_locking)
+		p->locks[level] = root_lock;
+	/*
+	 * Callers are responsible for dropping b's references.
+	 */
+	return b;
+}
+
+
+/*
+ * btrfs_search_slot - look for a key in a tree and perform necessary
+ * modifications to preserve tree invariants.
+ *
+ * @trans:	Handle of transaction, used when modifying the tree
+ * @p:		Holds all btree nodes along the search path
+ * @root:	The root node of the tree
+ * @key:	The key we are looking for
+ * @ins_len:	Indicates purpose of search, for inserts it is 1, for
+ *		deletions it's -1. 0 for plain searches
+ * @cow:	boolean should CoW operations be performed. Must always be 1
+ *		when modifying the tree.
+ *
+ * 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)
+ *
+ * If @key is found, 0 is returned and you can find the item in the leaf level
+ * of the path (level 0)
+ *
+ * If @key isn't found, 1 is returned and the leaf level of the path (level 0)
+ * points to the slot where it should be inserted
+ *
+ * If an error is encountered while searching the tree a negative error number
+ * is returned
+ */
+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 extent_buffer *b;
+	int slot;
+	int ret;
+	int err;
+	int level;
+	int lowest_unlock = 1;
+	/* 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;
+	b = btrfs_search_slot_get_root(root, p, write_lock_level);
+	if (IS_ERR(b)) {
+		ret = PTR_ERR(b);
+		goto done;
+	}
+
+	while (b) {
+		int dec = 0;
+
+		level = btrfs_header_level(b);
+
+		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,
+						      BTRFS_NESTING_COW);
+			else
+				err = btrfs_cow_block(trans, root, b,
+						      p->nodes[level + 1],
+						      p->slots[level + 1], &b,
+						      BTRFS_NESTING_COW);
+			if (err) {
+				ret = err;
+				goto done;
+			}
+		}
+cow_done:
+		p->nodes[level] = b;
+		/*
+		 * Leave path with blocking locks to avoid massive
+		 * lock context switch, this is made on purpose.
+		 */
+
+		/*
+		 * 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;
+			}
+		}
+
+		/*
+		 * If btrfs_bin_search returns an exact match (prev_cmp == 0)
+		 * we can safely assume the target key will always be in slot 0
+		 * on lower levels due to the invariants BTRFS' btree provides,
+		 * namely that a btrfs_key_ptr entry always points to the
+		 * lowest key in the child node, thus we can skip searching
+		 * lower levels
+		 */
+		if (prev_cmp == 0) {
+			slot = 0;
+			ret = 0;
+		} else {
+			ret = btrfs_bin_search(b, key, &slot);
+			prev_cmp = ret;
+			if (ret < 0)
+				goto done;
+		}
+
+		if (level == 0) {
+			p->slots[level] = slot;
+			if (ins_len > 0 &&
+			    btrfs_leaf_free_space(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);
+
+				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, NULL);
+			goto done;
+		}
+		if (ret && slot > 0) {
+			dec = 1;
+			slot--;
+		}
+		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) {
+				if (!btrfs_try_tree_write_lock(b)) {
+					btrfs_set_path_blocking(p);
+					btrfs_tree_lock(b);
+				}
+				p->locks[level] = BTRFS_WRITE_LOCK;
+			} else {
+				if (!btrfs_tree_read_lock_atomic(b)) {
+					btrfs_set_path_blocking(p);
+					__btrfs_tree_read_lock(b, BTRFS_NESTING_NORMAL,
+							       p->recurse);
+				}
+				p->locks[level] = BTRFS_READ_LOCK;
+			}
+			p->nodes[level] = b;
+		}
+	}
+	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;
+
+	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);
+	if (!b) {
+		ret = -EIO;
+		goto done;
+	}
+	level = btrfs_header_level(b);
+	p->locks[level] = BTRFS_READ_LOCK;
+
+	while (b) {
+		int dec = 0;
+
+		level = btrfs_header_level(b);
+		p->nodes[level] = b;
+
+		/*
+		 * we have a lock on b and as long as we aren't changing
+		 * the tree, there is no way to for the items in b to change.
+		 * It is safe to drop the lock on our parent before we
+		 * go through the expensive btree search on b.
+		 */
+		btrfs_unlock_up_safe(p, level + 1);
+
+		ret = btrfs_bin_search(b, key, &slot);
+		if (ret < 0)
+			goto done;
+
+		if (level == 0) {
+			p->slots[level] = slot;
+			unlock_up(p, level, lowest_unlock, 0, NULL);
+			goto done;
+		}
+
+		if (ret && slot > 0) {
+			dec = 1;
+			slot--;
+		}
+		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);
+		if (!btrfs_tree_read_lock_atomic(b)) {
+			btrfs_set_path_blocking(p);
+			btrfs_tree_read_lock(b);
+		}
+		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;
+	}
+	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_path *path,
+			   struct btrfs_disk_key *key, int level)
+{
+	int i;
+	struct extent_buffer *t;
+	int ret;
+
+	for (i = level; i < BTRFS_MAX_LEVEL; i++) {
+		int tslot = path->slots[i];
+
+		if (!path->nodes[i])
+			break;
+		t = path->nodes[i];
+		ret = tree_mod_log_insert_key(t, tslot, MOD_LOG_KEY_REPLACE,
+				GFP_ATOMIC);
+		BUG_ON(ret < 0);
+		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);
+		if (unlikely(comp_keys(&disk_key, new_key) >= 0)) {
+			btrfs_crit(fs_info,
+		"slot %u key (%llu %u %llu) new key (%llu %u %llu)",
+				   slot, btrfs_disk_key_objectid(&disk_key),
+				   btrfs_disk_key_type(&disk_key),
+				   btrfs_disk_key_offset(&disk_key),
+				   new_key->objectid, new_key->type,
+				   new_key->offset);
+			btrfs_print_leaf(eb);
+			BUG();
+		}
+	}
+	if (slot < btrfs_header_nritems(eb) - 1) {
+		btrfs_item_key(eb, &disk_key, slot + 1);
+		if (unlikely(comp_keys(&disk_key, new_key) <= 0)) {
+			btrfs_crit(fs_info,
+		"slot %u key (%llu %u %llu) new key (%llu %u %llu)",
+				   slot, btrfs_disk_key_objectid(&disk_key),
+				   btrfs_disk_key_type(&disk_key),
+				   btrfs_disk_key_offset(&disk_key),
+				   new_key->objectid, new_key->type,
+				   new_key->offset);
+			btrfs_print_leaf(eb);
+			BUG();
+		}
+	}
+
+	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(path, &disk_key, 1);
+}
+
+/*
+ * Check key order of two sibling extent buffers.
+ *
+ * Return true if something is wrong.
+ * Return false if everything is fine.
+ *
+ * Tree-checker only works inside one tree block, thus the following
+ * corruption can not be detected by tree-checker:
+ *
+ * Leaf @left			| Leaf @right
+ * --------------------------------------------------------------
+ * | 1 | 2 | 3 | 4 | 5 | f6 |   | 7 | 8 |
+ *
+ * Key f6 in leaf @left itself is valid, but not valid when the next
+ * key in leaf @right is 7.
+ * This can only be checked at tree block merge time.
+ * And since tree checker has ensured all key order in each tree block
+ * is correct, we only need to bother the last key of @left and the first
+ * key of @right.
+ */
+static bool check_sibling_keys(struct extent_buffer *left,
+			       struct extent_buffer *right)
+{
+	struct btrfs_key left_last;
+	struct btrfs_key right_first;
+	int level = btrfs_header_level(left);
+	int nr_left = btrfs_header_nritems(left);
+	int nr_right = btrfs_header_nritems(right);
+
+	/* No key to check in one of the tree blocks */
+	if (!nr_left || !nr_right)
+		return false;
+
+	if (level) {
+		btrfs_node_key_to_cpu(left, &left_last, nr_left - 1);
+		btrfs_node_key_to_cpu(right, &right_first, 0);
+	} else {
+		btrfs_item_key_to_cpu(left, &left_last, nr_left - 1);
+		btrfs_item_key_to_cpu(right, &right_first, 0);
+	}
+
+	if (btrfs_comp_cpu_keys(&left_last, &right_first) >= 0) {
+		btrfs_crit(left->fs_info,
+"bad key order, sibling blocks, left last (%llu %u %llu) right first (%llu %u %llu)",
+			   left_last.objectid, left_last.type,
+			   left_last.offset, right_first.objectid,
+			   right_first.type, right_first.offset);
+		return true;
+	}
+	return false;
+}
+
+/*
+ * 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 extent_buffer *dst,
+			  struct extent_buffer *src, int empty)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	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);
+
+	/* dst is the left eb, src is the middle eb */
+	if (check_sibling_keys(dst, src)) {
+		ret = -EUCLEAN;
+		btrfs_abort_transaction(trans, ret);
+		return ret;
+	}
+	ret = tree_mod_log_eb_copy(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_insert_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 extent_buffer *dst,
+			      struct extent_buffer *src)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	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;
+
+	/* dst is the right eb, src is the middle eb */
+	if (check_sibling_keys(src, dst)) {
+		ret = -EUCLEAN;
+		btrfs_abort_transaction(trans, ret);
+		return ret;
+	}
+	ret = tree_mod_log_insert_move(dst, push_items, 0, dst_nritems);
+	BUG_ON(ret < 0);
+	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(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;
+	int ret;
+
+	BUG_ON(path->nodes[level]);
+	BUG_ON(path->nodes[level-1] != root->node);
+
+	lower = path->nodes[level-1];
+	if (level == 1)
+		btrfs_item_key(lower, &lower_key, 0);
+	else
+		btrfs_node_key(lower, &lower_key, 0);
+
+	c = alloc_tree_block_no_bg_flush(trans, root, 0, &lower_key, level,
+					 root->node->start, 0,
+					 BTRFS_NESTING_NEW_ROOT);
+	if (IS_ERR(c))
+		return PTR_ERR(c);
+
+	root_add_used(root, fs_info->nodesize);
+
+	btrfs_set_header_nritems(c, 1);
+	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;
+	ret = tree_mod_log_insert_root(root->node, c, 0);
+	BUG_ON(ret < 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);
+	atomic_inc(&c->refs);
+	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_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(trans->fs_info));
+	if (slot != nritems) {
+		if (level) {
+			ret = tree_mod_log_insert_move(lower, slot + 1, slot,
+					nritems - slot);
+			BUG_ON(ret < 0);
+		}
+		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(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 = alloc_tree_block_no_bg_flush(trans, root, 0, &disk_key, level,
+					     c->start, 0, BTRFS_NESTING_SPLIT);
+	if (IS_ERR(split))
+		return PTR_ERR(split);
+
+	root_add_used(root, fs_info->nodesize);
+	ASSERT(btrfs_header_level(c) == level);
+
+	ret = tree_mod_log_eb_copy(split, c, 0, mid, c_nritems - mid);
+	if (ret) {
+		btrfs_tree_unlock(split);
+		free_extent_buffer(split);
+		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, 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;
+	int data_len;
+	int nritems = btrfs_header_nritems(l);
+	int end = min(nritems, start + nr) - 1;
+
+	if (!nr)
+		return 0;
+	start_item = btrfs_item_nr(start);
+	end_item = btrfs_item_nr(end);
+	data_len = btrfs_item_offset(l, start_item) +
+		   btrfs_item_size(l, start_item);
+	data_len = data_len - btrfs_item_offset(l, end_item);
+	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 extent_buffer *leaf)
+{
+	struct btrfs_fs_info *fs_info = leaf->fs_info;
+	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_path *path,
+				      int data_size, int empty,
+				      struct extent_buffer *right,
+				      int free_space, u32 left_nritems,
+				      u32 min_slot)
+{
+	struct btrfs_fs_info *fs_info = right->fs_info;
+	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;
+
+	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(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(left);
+
+	/* make room in the right data area */
+	data_end = leaf_data_end(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(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 */
+	btrfs_init_map_token(&token, right);
+	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(&token, item);
+		btrfs_set_token_item_offset(&token, item, push_space);
+	}
+
+	left_nritems -= push_items;
+	btrfs_set_header_nritems(left, left_nritems);
+
+	if (left_nritems)
+		btrfs_mark_buffer_dirty(left);
+	else
+		btrfs_clean_tree_block(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)
+			btrfs_clean_tree_block(path->nodes[0]);
+		btrfs_tree_unlock(path->nodes[0]);
+		free_extent_buffer(path->nodes[0]);
+		path->nodes[0] = right;
+		path->slots[1] += 1;
+	} else {
+		btrfs_tree_unlock(right);
+		free_extent_buffer(right);
+	}
+	return 0;
+
+out_unlock:
+	btrfs_tree_unlock(right);
+	free_extent_buffer(right);
+	return 1;
+}
+
+/*
+ * push some data in the path leaf to the right, trying to free up at
+ * least data_size bytes.  returns zero if the push worked, nonzero otherwise
+ *
+ * returns 1 if the push failed because the other node didn't have enough
+ * room, 0 if everything worked out and < 0 if there were major errors.
+ *
+ * this will push starting from min_slot to the end of the leaf.  It won't
+ * push any slot lower than min_slot
+ */
+static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
+			   *root, struct btrfs_path *path,
+			   int min_data_size, int data_size,
+			   int empty, u32 min_slot)
+{
+	struct extent_buffer *left = path->nodes[0];
+	struct extent_buffer *right;
+	struct extent_buffer *upper;
+	int slot;
+	int free_space;
+	u32 left_nritems;
+	int ret;
+
+	if (!path->nodes[1])
+		return 1;
+
+	slot = path->slots[1];
+	upper = path->nodes[1];
+	if (slot >= btrfs_header_nritems(upper) - 1)
+		return 1;
+
+	btrfs_assert_tree_locked(path->nodes[1]);
+
+	right = btrfs_read_node_slot(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_NESTING_RIGHT);
+	btrfs_set_lock_blocking_write(right);
+
+	free_space = btrfs_leaf_free_space(right);
+	if (free_space < data_size)
+		goto out_unlock;
+
+	/* cow and double check */
+	ret = btrfs_cow_block(trans, root, right, upper,
+			      slot + 1, &right, BTRFS_NESTING_RIGHT_COW);
+	if (ret)
+		goto out_unlock;
+
+	free_space = btrfs_leaf_free_space(right);
+	if (free_space < data_size)
+		goto out_unlock;
+
+	left_nritems = btrfs_header_nritems(left);
+	if (left_nritems == 0)
+		goto out_unlock;
+
+	if (check_sibling_keys(left, right)) {
+		ret = -EUCLEAN;
+		btrfs_abort_transaction(trans, ret);
+		btrfs_tree_unlock(right);
+		free_extent_buffer(right);
+		return ret;
+	}
+	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 leaf. */
+		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(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_path *path, int data_size,
+				     int empty, struct extent_buffer *left,
+				     int free_space, u32 right_nritems,
+				     u32 max_slot)
+{
+	struct btrfs_fs_info *fs_info = left->fs_info;
+	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;
+
+	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(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(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);
+
+	btrfs_init_map_token(&token, left);
+	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(&token, item);
+		btrfs_set_token_item_offset(&token, item,
+		      ioff - (BTRFS_LEAF_DATA_SIZE(fs_info) - old_left_item_size));
+	}
+	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(right);
+		memmove_extent_buffer(right, BTRFS_LEAF_DATA_OFFSET +
+				      BTRFS_LEAF_DATA_SIZE(fs_info) - push_space,
+				      BTRFS_LEAF_DATA_OFFSET +
+				      leaf_data_end(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));
+	}
+
+	btrfs_init_map_token(&token, right);
+	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(&token, item);
+		btrfs_set_token_item_offset(&token, item, push_space);
+	}
+
+	btrfs_mark_buffer_dirty(left);
+	if (right_nritems)
+		btrfs_mark_buffer_dirty(right);
+	else
+		btrfs_clean_tree_block(right);
+
+	btrfs_item_key(right, &disk_key, 0);
+	fixup_low_keys(path, &disk_key, 1);
+
+	/* then fixup the leaf pointer in the path */
+	if (path->slots[0] < push_items) {
+		path->slots[0] += old_left_nritems;
+		btrfs_tree_unlock(path->nodes[0]);
+		free_extent_buffer(path->nodes[0]);
+		path->nodes[0] = left;
+		path->slots[1] -= 1;
+	} else {
+		btrfs_tree_unlock(left);
+		free_extent_buffer(left);
+		path->slots[0] -= push_items;
+	}
+	BUG_ON(path->slots[0] < 0);
+	return ret;
+out:
+	btrfs_tree_unlock(left);
+	free_extent_buffer(left);
+	return ret;
+}
+
+/*
+ * push some data in the path leaf to the left, trying to free up at
+ * least data_size bytes.  returns zero if the push worked, nonzero otherwise
+ *
+ * max_slot can put a limit on how far into the leaf we'll push items.  The
+ * item at 'max_slot' won't be touched.  Use (u32)-1 to make us push all the
+ * items
+ */
+static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
+			  *root, struct btrfs_path *path, int min_data_size,
+			  int data_size, int empty, u32 max_slot)
+{
+	struct extent_buffer *right = path->nodes[0];
+	struct extent_buffer *left;
+	int slot;
+	int free_space;
+	u32 right_nritems;
+	int ret = 0;
+
+	slot = path->slots[1];
+	if (slot == 0)
+		return 1;
+	if (!path->nodes[1])
+		return 1;
+
+	right_nritems = btrfs_header_nritems(right);
+	if (right_nritems == 0)
+		return 1;
+
+	btrfs_assert_tree_locked(path->nodes[1]);
+
+	left = btrfs_read_node_slot(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_NESTING_LEFT);
+	btrfs_set_lock_blocking_write(left);
+
+	free_space = btrfs_leaf_free_space(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,
+			      BTRFS_NESTING_LEFT_COW);
+	if (ret) {
+		/* we hit -ENOSPC, but it isn't fatal here */
+		if (ret == -ENOSPC)
+			ret = 1;
+		goto out;
+	}
+
+	free_space = btrfs_leaf_free_space(left);
+	if (free_space < data_size) {
+		ret = 1;
+		goto out;
+	}
+
+	if (check_sibling_keys(left, right)) {
+		ret = -EUCLEAN;
+		btrfs_abort_transaction(trans, ret);
+		goto out;
+	}
+	return __push_leaf_left(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_path *path,
+				    struct extent_buffer *l,
+				    struct extent_buffer *right,
+				    int slot, int mid, int nritems)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	int data_copy_size;
+	int rt_data_off;
+	int i;
+	struct btrfs_disk_key disk_key;
+	struct btrfs_map_token token;
+
+	nritems = nritems - mid;
+	btrfs_set_header_nritems(right, nritems);
+	data_copy_size = btrfs_item_end_nr(l, mid) - leaf_data_end(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(l), data_copy_size);
+
+	rt_data_off = BTRFS_LEAF_DATA_SIZE(fs_info) - btrfs_item_end_nr(l, mid);
+
+	btrfs_init_map_token(&token, right);
+	for (i = 0; i < nritems; i++) {
+		struct btrfs_item *item = btrfs_item_nr(i);
+		u32 ioff;
+
+		ioff = btrfs_token_item_offset(&token, item);
+		btrfs_set_token_item_offset(&token, item, ioff + rt_data_off);
+	}
+
+	btrfs_set_header_nritems(l, mid);
+	btrfs_item_key(right, &disk_key, 0);
+	insert_ptr(trans, path, &disk_key, right->start, path->slots[1] + 1, 1);
+
+	btrfs_mark_buffer_dirty(right);
+	btrfs_mark_buffer_dirty(l);
+	BUG_ON(path->slots[0] != slot);
+
+	if (mid <= slot) {
+		btrfs_tree_unlock(path->nodes[0]);
+		free_extent_buffer(path->nodes[0]);
+		path->nodes[0] = right;
+		path->slots[0] -= mid;
+		path->slots[1] += 1;
+	} else {
+		btrfs_tree_unlock(right);
+		free_extent_buffer(right);
+	}
+
+	BUG_ON(path->slots[0] < 0);
+}
+
+/*
+ * double splits happen when we need to insert a big item in the middle
+ * of a leaf.  A double split can leave us with 3 mostly empty leaves:
+ * leaf: [ slots 0 - N] [ our target ] [ N + 1 - total in leaf ]
+ *          A                 B                 C
+ *
+ * We avoid this by trying to push the items on either side of our target
+ * into the adjacent leaves.  If all goes well we can avoid the double split
+ * completely.
+ */
+static noinline int push_for_double_split(struct btrfs_trans_handle *trans,
+					  struct btrfs_root *root,
+					  struct btrfs_path *path,
+					  int data_size)
+{
+	int ret;
+	int progress = 0;
+	int slot;
+	u32 nritems;
+	int space_needed = data_size;
+
+	slot = path->slots[0];
+	if (slot < btrfs_header_nritems(path->nodes[0]))
+		space_needed -= btrfs_leaf_free_space(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(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(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(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(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(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);
+
+	/*
+	 * We have to about BTRFS_NESTING_NEW_ROOT here if we've done a double
+	 * split, because we're only allowed to have MAX_LOCKDEP_SUBCLASSES
+	 * subclasses, which is 8 at the time of this patch, and we've maxed it
+	 * out.  In the future we could add a
+	 * BTRFS_NESTING_SPLIT_THE_SPLITTENING if we need to, but for now just
+	 * use BTRFS_NESTING_NEW_ROOT.
+	 */
+	right = alloc_tree_block_no_bg_flush(trans, root, 0, &disk_key, 0,
+					     l->start, 0, num_doubles ?
+					     BTRFS_NESTING_NEW_ROOT :
+					     BTRFS_NESTING_SPLIT);
+	if (IS_ERR(right))
+		return PTR_ERR(right);
+
+	root_add_used(root, fs_info->nodesize);
+
+	if (split == 0) {
+		if (mid <= slot) {
+			btrfs_set_header_nritems(right, 0);
+			insert_ptr(trans, 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, 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(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, 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(path->nodes[0]) >= data_size)
+		return 0;
+	goto again;
+}
+
+static noinline int setup_leaf_for_split(struct btrfs_trans_handle *trans,
+					 struct btrfs_root *root,
+					 struct btrfs_path *path, int ins_len)
+{
+	struct btrfs_key key;
+	struct extent_buffer *leaf;
+	struct btrfs_file_extent_item *fi;
+	u64 extent_len = 0;
+	u32 item_size;
+	int ret;
+
+	leaf = path->nodes[0];
+	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
+
+	BUG_ON(key.type != BTRFS_EXTENT_DATA_KEY &&
+	       key.type != BTRFS_EXTENT_CSUM_KEY);
+
+	if (btrfs_leaf_free_space(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(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_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(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(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(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, 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_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;
+
+	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(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 */
+	btrfs_init_map_token(&token, leaf);
+	for (i = slot; i < nritems; i++) {
+		u32 ioff;
+		item = btrfs_item_nr(i);
+
+		ioff = btrfs_token_item_offset(&token, item);
+		btrfs_set_token_item_offset(&token, item, ioff + size_diff);
+	}
+
+	/* 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(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(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_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;
+
+	leaf = path->nodes[0];
+
+	nritems = btrfs_header_nritems(leaf);
+	data_end = leaf_data_end(leaf);
+
+	if (btrfs_leaf_free_space(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(leaf->fs_info, "slot %d too large, nritems %d",
+			   slot, nritems);
+		BUG();
+	}
+
+	/*
+	 * item0..itemN ... dataN.offset..dataN.size .. data0.size
+	 */
+	/* first correct the data pointers */
+	btrfs_init_map_token(&token, leaf);
+	for (i = slot; i < nritems; i++) {
+		u32 ioff;
+		item = btrfs_item_nr(i);
+
+		ioff = btrfs_token_item_offset(&token, item);
+		btrfs_set_token_item_offset(&token, item, ioff - data_size);
+	}
+
+	/* 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(leaf) < 0) {
+		btrfs_print_leaf(leaf);
+		BUG();
+	}
+}
+
+/**
+ * setup_items_for_insert - Helper called before inserting one or more items
+ * to a leaf. Main purpose is to save stack depth by doing the bulk of the work
+ * in a function that doesn't call btrfs_search_slot
+ *
+ * @root:	root we are inserting items to
+ * @path:	points to the leaf/slot where we are going to insert new items
+ * @cpu_key:	array of keys for items to be inserted
+ * @data_size:	size of the body of each item we are going to insert
+ * @nr:		size of @cpu_key/@data_size arrays
+ */
+void setup_items_for_insert(struct btrfs_root *root, struct btrfs_path *path,
+			    const struct btrfs_key *cpu_key, u32 *data_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;
+	u32 total_size;
+	u32 total_data = 0;
+
+	for (i = 0; i < nr; i++)
+		total_data += data_size[i];
+	total_size = total_data + (nr * sizeof(struct btrfs_item));
+
+	if (path->slots[0] == 0) {
+		btrfs_cpu_key_to_disk(&disk_key, cpu_key);
+		fixup_low_keys(path, &disk_key, 1);
+	}
+	btrfs_unlock_up_safe(path, 1);
+
+	leaf = path->nodes[0];
+	slot = path->slots[0];
+
+	nritems = btrfs_header_nritems(leaf);
+	data_end = leaf_data_end(leaf);
+
+	if (btrfs_leaf_free_space(leaf) < total_size) {
+		btrfs_print_leaf(leaf);
+		btrfs_crit(fs_info, "not enough freespace need %u have %d",
+			   total_size, btrfs_leaf_free_space(leaf));
+		BUG();
+	}
+
+	btrfs_init_map_token(&token, leaf);
+	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,
+		"item at slot %d with data offset %u beyond data end of leaf %u",
+				   slot, old_data, data_end);
+			BUG();
+		}
+		/*
+		 * 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(&token, item);
+			btrfs_set_token_item_offset(&token, item,
+						    ioff - total_data);
+		}
+		/* 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);
+		data_end -= data_size[i];
+		btrfs_set_token_item_offset(&token, item, data_end);
+		btrfs_set_token_item_size(&token, item, data_size[i]);
+	}
+
+	btrfs_set_header_nritems(leaf, nritems + nr);
+	btrfs_mark_buffer_dirty(leaf);
+
+	if (btrfs_leaf_free_space(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, 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 extent_buffer *parent = path->nodes[level];
+	u32 nritems;
+	int ret;
+
+	nritems = btrfs_header_nritems(parent);
+	if (slot != nritems - 1) {
+		if (level) {
+			ret = tree_mod_log_insert_move(parent, slot, slot + 1,
+					nritems - slot - 1);
+			BUG_ON(ret < 0);
+		}
+		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(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(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);
+
+	atomic_inc(&leaf->refs);
+	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;
+
+	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(leaf);
+		struct btrfs_map_token token;
+
+		memmove_extent_buffer(leaf, BTRFS_LEAF_DATA_OFFSET +
+			      data_end + dsize,
+			      BTRFS_LEAF_DATA_OFFSET + data_end,
+			      last_off - data_end);
+
+		btrfs_init_map_token(&token, leaf);
+		for (i = slot + nr; i < nritems; i++) {
+			u32 ioff;
+
+			item = btrfs_item_nr(i);
+			ioff = btrfs_token_item_offset(&token, item);
+			btrfs_set_token_item_offset(&token, item, ioff + dsize);
+		}
+
+		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);
+			btrfs_clean_tree_block(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(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];
+			atomic_inc(&leaf->refs);
+
+			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_key orig_key;
+	struct btrfs_disk_key found_key;
+	int ret;
+
+	btrfs_item_key_to_cpu(path->nodes[0], &key, 0);
+	orig_key = key;
+
+	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;
+
+	/*
+	 * Previous key not found. Even if we were at slot 0 of the leaf we had
+	 * before releasing the path and calling btrfs_search_slot(), we now may
+	 * be in a slot pointing to the same original key - this can happen if
+	 * after we released the path, one of more items were moved from a
+	 * sibling leaf into the front of the leaf we had due to an insertion
+	 * (see push_leaf_right()).
+	 * If we hit this case and our slot is > 0 and just decrement the slot
+	 * so that the caller does not process the same key again, which may or
+	 * may not break the caller, depending on its logic.
+	 */
+	if (path->slots[0] < btrfs_header_nritems(path->nodes[0])) {
+		btrfs_item_key(path->nodes[0], &found_key, path->slots[0]);
+		ret = comp_keys(&found_key, &orig_key);
+		if (ret == 0) {
+			if (path->slots[0] > 0) {
+				path->slots[0]--;
+				return 0;
+			}
+			/*
+			 * At slot 0, same key as before, it means orig_key is
+			 * the lowest, leftmost, key in the tree. We're done.
+			 */
+			return 1;
+		}
+	}
+
+	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 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 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 = btrfs_bin_search(cur, min_key, &slot);
+		if (sret < 0) {
+			ret = sret;
+			goto out;
+		}
+
+		/* 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, 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 = btrfs_read_node_slot(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);
+	}
+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;
+}
+
+/*
+ * 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 && !path->skip_locking);
+	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] || path->skip_locking) {
+				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_NESTING_RIGHT,
+						       path->recurse);
+			}
+			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_NESTING_RIGHT,
+						       path->recurse);
+			}
+			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;
+}