ctree.c

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

#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "print-tree.h"

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

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

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

void btrfs_free_path(struct btrfs_path *p)
{
	btrfs_release_path(NULL, p);
	kmem_cache_free(btrfs_path_cachep, p);
}

void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p)
{
	int i;
	for (i = 0; i < BTRFS_MAX_LEVEL; i++) {
		if (!p->nodes[i])
			break;
		free_extent_buffer(p->nodes[i]);
	}
	memset(p, 0, sizeof(*p));
}

static int __btrfs_cow_block(struct btrfs_trans_handle *trans,
			     struct btrfs_root *root,
			     struct extent_buffer *buf,
			     struct extent_buffer *parent, int parent_slot,
			     struct extent_buffer **cow_ret,
			     u64 search_start, u64 empty_size)
{
	struct extent_buffer *cow;
	int ret = 0;
	int different_trans = 0;

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

	cow = btrfs_alloc_free_block(trans, root, buf->len,
				     search_start, empty_size);
	if (IS_ERR(cow))
		return PTR_ERR(cow);

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

	WARN_ON(btrfs_header_generation(buf) > trans->transid);
	if (btrfs_header_generation(buf) != trans->transid) {
		different_trans = 1;
		ret = btrfs_inc_ref(trans, root, buf);
		if (ret)
			return ret;
	} else {
		clean_tree_block(trans, root, buf);
	}

	if (buf == root->node) {
		root->node = cow;
		extent_buffer_get(cow);
		if (buf != root->commit_root) {
			btrfs_free_extent(trans, root, buf->start,
					  buf->len, 1);
		}
		free_extent_buffer(buf);
	} else {
		btrfs_set_node_blockptr(parent, parent_slot,
					cow->start);
		btrfs_mark_buffer_dirty(parent);
		WARN_ON(btrfs_header_generation(parent) != trans->transid);
		btrfs_free_extent(trans, root, buf->start, buf->len, 1);
	}
	free_extent_buffer(buf);
	btrfs_mark_buffer_dirty(cow);
	*cow_ret = cow;
	return 0;
}

int btrfs_cow_block(struct btrfs_trans_handle *trans,
		    struct btrfs_root *root, struct extent_buffer *buf,
		    struct extent_buffer *parent, int parent_slot,
		    struct extent_buffer **cow_ret)
{
	u64 search_start;
	int ret;
	if (trans->transaction != root->fs_info->running_transaction) {
		printk(KERN_CRIT "trans %Lu running %Lu\n", trans->transid,
		       root->fs_info->running_transaction->transid);
		WARN_ON(1);
	}
	if (trans->transid != root->fs_info->generation) {
		printk(KERN_CRIT "trans %Lu running %Lu\n", trans->transid,
		       root->fs_info->generation);
		WARN_ON(1);
	}
	if (btrfs_header_generation(buf) == trans->transid) {
		*cow_ret = buf;
		return 0;
	}

	search_start = buf->start & ~((u64)BTRFS_BLOCK_GROUP_SIZE - 1);
	ret = __btrfs_cow_block(trans, root, buf, parent,
				 parent_slot, cow_ret, search_start, 0);
	return ret;
}

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;
}

static int should_defrag_leaf(struct extent_buffer *leaf)
{
	struct btrfs_key key;
	u32 nritems;

	if (btrfs_buffer_defrag(leaf))
		return 1;

	nritems = btrfs_header_nritems(leaf);
	if (nritems == 0)
		return 0;

	btrfs_item_key_to_cpu(leaf, &key, 0);
	if (key.type == BTRFS_DIR_ITEM_KEY)
		return 1;


	btrfs_item_key_to_cpu(leaf, &key, nritems - 1);
	if (key.type == BTRFS_DIR_ITEM_KEY)
		return 1;
	if (nritems > 4) {
		btrfs_item_key_to_cpu(leaf, &key, nritems / 2);
		if (key.type == BTRFS_DIR_ITEM_KEY)
			return 1;
	}
	return 0;
}

int btrfs_realloc_node(struct btrfs_trans_handle *trans,
		       struct btrfs_root *root, struct extent_buffer *parent,
		       int cache_only, u64 *last_ret)
{
	struct extent_buffer *cur;
	struct extent_buffer *tmp;
	u64 blocknr;
	u64 search_start = *last_ret;
	u64 last_block = 0;
	u64 other;
	u32 parent_nritems;
	int start_slot;
	int end_slot;
	int i;
	int err = 0;
	int parent_level;
	int uptodate;
	u32 blocksize;

	if (trans->transaction != root->fs_info->running_transaction) {
		printk(KERN_CRIT "trans %Lu running %Lu\n", trans->transid,
		       root->fs_info->running_transaction->transid);
		WARN_ON(1);
	}
	if (trans->transid != root->fs_info->generation) {
		printk(KERN_CRIT "trans %Lu running %Lu\n", trans->transid,
		       root->fs_info->generation);
		WARN_ON(1);
	}
	parent_level = btrfs_header_level(parent);

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

	start_slot = 0;
	end_slot = parent_nritems;

	if (parent_nritems == 1)
		return 0;

	for (i = start_slot; i < end_slot; i++) {
		int close = 1;
		blocknr = btrfs_node_blockptr(parent, i);
		if (last_block == 0)
			last_block = blocknr;
		if (i > 0) {
			other = btrfs_node_blockptr(parent, i - 1);
			close = close_blocks(blocknr, other, blocksize);
		}
		if (close && i < end_slot - 1) {
			other = btrfs_node_blockptr(parent, i + 1);
			close = close_blocks(blocknr, other, blocksize);
		}
		if (close) {
			last_block = blocknr;
			continue;
		}

		cur = btrfs_find_tree_block(root, blocknr, blocksize);
		if (cur)
			uptodate = btrfs_buffer_uptodate(cur);
		else
			uptodate = 0;
		if (!cur || !uptodate ||
		    (parent_level != 1 && !btrfs_buffer_defrag(cur)) ||
		    (parent_level == 1 && !should_defrag_leaf(cur))) {
			if (cache_only) {
				free_extent_buffer(cur);
				continue;
			}
			if (!cur) {
				cur = read_tree_block(root, blocknr,
							 blocksize);
			} else if (!uptodate) {
				btrfs_read_buffer(cur);
			}
		}
		if (search_start == 0)
			search_start = last_block;

		err = __btrfs_cow_block(trans, root, cur, parent, i,
					&tmp, search_start,
					min(16 * blocksize,
					    (end_slot - i) * blocksize));
		if (err) {
			free_extent_buffer(cur);
			break;
		}
		search_start = tmp->start;
		*last_ret = search_start;
		if (parent_level == 1)
			btrfs_clear_buffer_defrag(tmp);
		free_extent_buffer(tmp);
	}
	return err;
}

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

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

	btrfs_disk_key_to_cpu(&k1, disk);

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

static int check_node(struct btrfs_root *root, struct btrfs_path *path,
		      int level)
{
	struct extent_buffer *parent = NULL;
	struct extent_buffer *node = path->nodes[level];
	struct btrfs_disk_key parent_key;
	struct btrfs_disk_key node_key;
	int parent_slot;
	int slot;
	struct btrfs_key cpukey;
	u32 nritems = btrfs_header_nritems(node);

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

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

static int check_leaf(struct btrfs_root *root, struct btrfs_path *path,
		      int level)
{
	struct extent_buffer *leaf = path->nodes[level];
	struct extent_buffer *parent = NULL;
	int parent_slot;
	struct btrfs_key cpukey;
	struct btrfs_disk_key parent_key;
	struct btrfs_disk_key leaf_key;
	int slot = path->slots[0];

	u32 nritems = btrfs_header_nritems(leaf);

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

	if (nritems == 0)
		return 0;

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

		BUG_ON(memcmp(&parent_key, &leaf_key,
		       sizeof(struct btrfs_disk_key)));
		BUG_ON(btrfs_node_blockptr(parent, parent_slot) !=
		       btrfs_header_bytenr(leaf));
	}
#if 0
	for (i = 0; nritems > 1 && i < nritems - 2; i++) {
		btrfs_item_key_to_cpu(leaf, &cpukey, i + 1);
		btrfs_item_key(leaf, &leaf_key, i);
		if (comp_keys(&leaf_key, &cpukey) >= 0) {
			btrfs_print_leaf(root, leaf);
			printk("slot %d offset bad key\n", i);
			BUG_ON(1);
		}
		if (btrfs_item_offset_nr(leaf, i) !=
			btrfs_item_end_nr(leaf, i + 1)) {
			btrfs_print_leaf(root, leaf);
			printk("slot %d offset bad\n", i);
			BUG_ON(1);
		}
		if (i == 0) {
			if (btrfs_item_offset_nr(leaf, i) +
			       btrfs_item_size_nr(leaf, i) !=
			       BTRFS_LEAF_DATA_SIZE(root)) {
				btrfs_print_leaf(root, leaf);
				printk("slot %d first offset bad\n", i);
				BUG_ON(1);
			}
		}
	}
	if (nritems > 0) {
		if (btrfs_item_size_nr(leaf, nritems - 1) > 4096) {
				btrfs_print_leaf(root, leaf);
				printk("slot %d bad size \n", nritems - 1);
				BUG_ON(1);
		}
	}
#endif
	if (slot != 0 && slot < nritems - 1) {
		btrfs_item_key(leaf, &leaf_key, slot);
		btrfs_item_key_to_cpu(leaf, &cpukey, slot - 1);
		if (comp_keys(&leaf_key, &cpukey) <= 0) {
			btrfs_print_leaf(root, leaf);
			printk("slot %d offset bad key\n", slot);
			BUG_ON(1);
		}
		if (btrfs_item_offset_nr(leaf, slot - 1) !=
		       btrfs_item_end_nr(leaf, slot)) {
			btrfs_print_leaf(root, leaf);
			printk("slot %d offset bad\n", slot);
			BUG_ON(1);
		}
	}
	if (slot < nritems - 1) {
		btrfs_item_key(leaf, &leaf_key, slot);
		btrfs_item_key_to_cpu(leaf, &cpukey, slot + 1);
		BUG_ON(comp_keys(&leaf_key, &cpukey) >= 0);
		if (btrfs_item_offset_nr(leaf, slot) !=
			btrfs_item_end_nr(leaf, slot + 1)) {
			btrfs_print_leaf(root, leaf);
			printk("slot %d offset bad\n", slot);
			BUG_ON(1);
		}
	}
	BUG_ON(btrfs_item_offset_nr(leaf, 0) +
	       btrfs_item_size_nr(leaf, 0) != BTRFS_LEAF_DATA_SIZE(root));
	return 0;
}

static int check_block(struct btrfs_root *root, struct btrfs_path *path,
			int level)
{
	return 0;
#if 0
	struct extent_buffer *buf = path->nodes[level];

	if (memcmp_extent_buffer(buf, root->fs_info->fsid,
				 (unsigned long)btrfs_header_fsid(buf),
				 BTRFS_FSID_SIZE)) {
		printk("warning bad block %Lu\n", buf->start);
		return 1;
	}
#endif
	if (level == 0)
		return check_leaf(root, path, level);
	return check_node(root, path, level);
}

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

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

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

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

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

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

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

static struct extent_buffer *read_node_slot(struct btrfs_root *root,
				   struct extent_buffer *parent, int slot)
{
	if (slot < 0)
		return NULL;
	if (slot >= btrfs_header_nritems(parent))
		return NULL;
	return read_tree_block(root, btrfs_node_blockptr(parent, slot),
		       btrfs_level_size(root, btrfs_header_level(parent) - 1));
}

static int balance_level(struct btrfs_trans_handle *trans, struct btrfs_root
			 *root, struct btrfs_path *path, int level)
{
	struct extent_buffer *right = NULL;
	struct extent_buffer *mid;
	struct extent_buffer *left = NULL;
	struct extent_buffer *parent = NULL;
	int ret = 0;
	int wret;
	int pslot;
	int orig_slot = path->slots[level];
	int err_on_enospc = 0;
	u64 orig_ptr;

	if (level == 0)
		return 0;

	mid = path->nodes[level];
	orig_ptr = btrfs_node_blockptr(mid, orig_slot);

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

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

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

		/* promote the child to a root */
		child = read_node_slot(root, mid, 0);
		BUG_ON(!child);
		root->node = child;
		path->nodes[level] = NULL;
		clean_tree_block(trans, root, mid);
		wait_on_tree_block_writeback(root, mid);
		/* once for the path */
		free_extent_buffer(mid);
		ret = btrfs_free_extent(trans, root, mid->start, mid->len, 1);
		/* once for the root ptr */
		free_extent_buffer(mid);
		return ret;
	}
	if (btrfs_header_nritems(mid) >
	    BTRFS_NODEPTRS_PER_BLOCK(root) / 4)
		return 0;

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

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

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

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

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

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

/* returns zero if the push worked, non-zero otherwise */
static int push_nodes_for_insert(struct btrfs_trans_handle *trans,
				struct btrfs_root *root,
				struct btrfs_path *path, int level)
{
	struct extent_buffer *right = NULL;
	struct extent_buffer *mid;
	struct extent_buffer *left = NULL;
	struct extent_buffer *parent = NULL;
	int ret = 0;
	int wret;
	int pslot;
	int orig_slot = path->slots[level];
	u64 orig_ptr;

	if (level == 0)
		return 1;

	mid = path->nodes[level];
	orig_ptr = btrfs_node_blockptr(mid, orig_slot);

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

	if (!parent)
		return 1;

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

	/* first, try to make some room in the middle buffer */
	if (left) {
		u32 left_nr;
		left_nr = btrfs_header_nritems(left);
		if (left_nr >= BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
			wret = 1;
		} else {
			ret = btrfs_cow_block(trans, root, left, parent,
					      pslot - 1, &left);
			if (ret)
				wret = 1;
			else {
				wret = push_node_left(trans, root,
						      left, mid);
			}
		}
		if (wret < 0)
			ret = wret;
		if (wret == 0) {
			struct btrfs_disk_key disk_key;
			orig_slot += left_nr;
			btrfs_node_key(mid, &disk_key, 0);
			btrfs_set_node_key(parent, &disk_key, pslot);
			btrfs_mark_buffer_dirty(parent);
			if (btrfs_header_nritems(left) > orig_slot) {
				path->nodes[level] = left;
				path->slots[level + 1] -= 1;
				path->slots[level] = orig_slot;
				free_extent_buffer(mid);
			} else {
				orig_slot -=
					btrfs_header_nritems(left);
				path->slots[level] = orig_slot;
				free_extent_buffer(left);
			}
			return 0;
		}
		free_extent_buffer(left);
	}
	right= read_node_slot(root, parent, pslot + 1);

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

			btrfs_node_key(right, &disk_key, 0);
			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);
				free_extent_buffer(mid);
			} else {
				free_extent_buffer(right);
			}
			return 0;
		}
		free_extent_buffer(right);
	}
	return 1;
}

/*
 * readahead one full node of leaves
 */
static void reada_for_search(struct btrfs_root *root, struct btrfs_path *path,
			     int level, int slot)
{
	struct extent_buffer *node;
	u32 nritems;
	u64 search;
	u64 lowest_read;
	u64 highest_read;
	u64 nread = 0;
	int direction = path->reada;
	struct extent_buffer *eb;
	u32 nr;
	u32 blocksize;
	u32 nscan = 0;

	if (level == 0)
		return;

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

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

	highest_read = search;
	lowest_read = search;

	nritems = btrfs_header_nritems(node);
	nr = slot;
	while(1) {
		if (direction < 0) {
			if (nr == 0)
				break;
			nr--;
		} else if (direction > 0) {
			nr++;
			if (nr >= nritems)
				break;
		}
		search = btrfs_node_blockptr(node, nr);
		if ((search >= lowest_read && search <= highest_read) ||
		    (search < lowest_read && lowest_read - search <= 32768) ||
		    (search > highest_read && search - highest_read <= 32768)) {
			readahead_tree_block(root, search, blocksize);
			nread += blocksize;
		}
		nscan++;
		if (path->reada < 2 && (nread > (256 * 1024) || nscan > 32))
			break;
		if(nread > (1024 * 1024) || nscan > 128)
			break;

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

	lowest_level = p->lowest_level;
	WARN_ON(lowest_level && ins_len);
	WARN_ON(p->nodes[0] != NULL);
	WARN_ON(!mutex_is_locked(&root->fs_info->fs_mutex));
again:
	b = root->node;
	extent_buffer_get(b);
	while (b) {
		level = btrfs_header_level(b);
		if (cow) {
			int wret;
			wret = btrfs_cow_block(trans, root, b,
					       p->nodes[level + 1],
					       p->slots[level + 1],
					       &b);
			if (wret) {
				free_extent_buffer(b);
				return wret;
			}
		}
		BUG_ON(!cow && ins_len);
		if (level != btrfs_header_level(b))
			WARN_ON(1);
		level = btrfs_header_level(b);
		p->nodes[level] = b;
		ret = check_block(root, p, level);
		if (ret)
			return -1;
		ret = bin_search(b, key, level, &slot);
		if (level != 0) {
			if (ret && slot > 0)
				slot -= 1;
			p->slots[level] = slot;
			if (ins_len > 0 && btrfs_header_nritems(b) >=
			    BTRFS_NODEPTRS_PER_BLOCK(root) - 1) {
				int sret = split_node(trans, root, p, level);
				BUG_ON(sret > 0);
				if (sret)
					return sret;
				b = p->nodes[level];
				slot = p->slots[level];
			} else if (ins_len < 0) {
				int sret = balance_level(trans, root, p,
							 level);
				if (sret)
					return sret;
				b = p->nodes[level];
				if (!b) {
					btrfs_release_path(NULL, p);
					goto again;
				}
				slot = p->slots[level];
				BUG_ON(btrfs_header_nritems(b) == 1);
			}
			/* this is only true while dropping a snapshot */
			if (level == lowest_level)
				break;
			bytenr = btrfs_node_blockptr(b, slot);
			if (should_reada)
				reada_for_search(root, p, level, slot);
			b = read_tree_block(root, bytenr,
					    btrfs_level_size(root, level - 1));
		} else {
			p->slots[level] = slot;
			if (ins_len > 0 && btrfs_leaf_free_space(root, b) <
			    sizeof(struct btrfs_item) + ins_len) {
				int sret = split_leaf(trans, root, key,
						      p, ins_len);
				BUG_ON(sret > 0);
				if (sret)
					return sret;
			}
			return ret;
		}
	}
	return 1;
}

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

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

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

	src_nritems = btrfs_header_nritems(src);
	dst_nritems = btrfs_header_nritems(dst);
	push_items = BTRFS_NODEPTRS_PER_BLOCK(root) - dst_nritems;

	if (push_items <= 0) {
		return 1;
	}

	if (src_nritems < push_items)
		push_items = src_nritems;

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

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

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

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

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

	if (max_push < push_items)
		push_items = max_push;

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

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

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

	btrfs_mark_buffer_dirty(src);
	btrfs_mark_buffer_dirty(dst);
	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 int insert_new_root(struct btrfs_trans_handle *trans,
			   struct btrfs_root *root,
			   struct btrfs_path *path, int level)
{
	struct extent_buffer *lower;
	struct extent_buffer *c;
	struct btrfs_disk_key lower_key;

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

	c = btrfs_alloc_free_block(trans, root, root->nodesize,
				   root->node->start, 0);
	if (IS_ERR(c))
		return PTR_ERR(c);
	memset_extent_buffer(c, 0, 0, root->nodesize);
	btrfs_set_header_nritems(c, 1);
	btrfs_set_header_level(c, level);
	btrfs_set_header_bytenr(c, c->start);
	btrfs_set_header_generation(c, trans->transid);
	btrfs_set_header_owner(c, root->root_key.objectid);
	lower = path->nodes[level-1];

	write_extent_buffer(c, root->fs_info->fsid,
			    (unsigned long)btrfs_header_fsid(c),
			    BTRFS_FSID_SIZE);
	if (level == 1)
		btrfs_item_key(lower, &lower_key, 0);
	else
		btrfs_node_key(lower, &lower_key, 0);
	btrfs_set_node_key(c, &lower_key, 0);
	btrfs_set_node_blockptr(c, 0, lower->start);

	btrfs_mark_buffer_dirty(c);

	/* the super has an extra ref to root->node */
	free_extent_buffer(root->node);
	root->node = c;
	extent_buffer_get(c);
	path->nodes[level] = c;
	path->slots[level] = 0;
	return 0;
}

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

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

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

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

	c_nritems = btrfs_header_nritems(c);
	split = btrfs_alloc_free_block(trans, root, root->nodesize,
				       c->start, 0);
	if (IS_ERR(split))
		return PTR_ERR(split);

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

	mid = (c_nritems + 1) / 2;

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

	btrfs_mark_buffer_dirty(c);
	btrfs_mark_buffer_dirty(split);

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

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

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

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

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

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

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

	right = read_tree_block(root, btrfs_node_blockptr(upper, slot + 1),
				root->leafsize);
	free_space = btrfs_leaf_free_space(root, right);
	if (free_space < data_size + sizeof(struct btrfs_item)) {
		free_extent_buffer(right);
		return 1;
	}

	/* cow and double check */
	ret = btrfs_cow_block(trans, root, right, upper,
			      slot + 1, &right);
	if (ret) {
		free_extent_buffer(right);
		return 1;
	}
	free_space = btrfs_leaf_free_space(root, right);
	if (free_space < data_size + sizeof(struct btrfs_item)) {
		free_extent_buffer(right);
		return 1;
	}

	left_nritems = btrfs_header_nritems(left);
	if (left_nritems == 0) {
		free_extent_buffer(right);
		return 1;
	}

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

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

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

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

	if (push_items == 0) {
		free_extent_buffer(right);
		return 1;
	}

	if (push_items == left_nritems)
		WARN_ON(1);

	/* push left to right */
	right_nritems = btrfs_header_nritems(right);
	push_space = btrfs_item_end_nr(left, left_nritems - push_items);
	push_space -= leaf_data_end(root, left);

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

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

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

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

	/* update the item pointers */
	right_nritems += push_items;
	btrfs_set_header_nritems(right, right_nritems);
	push_space = BTRFS_LEAF_DATA_SIZE(root);

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

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

	btrfs_mark_buffer_dirty(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;
		free_extent_buffer(path->nodes[0]);
		path->nodes[0] = right;
		path->slots[1] += 1;
	} else {
		free_extent_buffer(right);
	}
	return 0;
}
/*
 * push some data in the path leaf to the left, trying to free up at
 * least data_size bytes.  returns zero if the push worked, nonzero otherwise
 */
static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
			  *root, struct btrfs_path *path, int data_size)
{
	struct btrfs_disk_key disk_key;
	struct extent_buffer *right = path->nodes[0];
	struct extent_buffer *left;
	int slot;
	int i;
	int free_space;
	int push_space = 0;
	int push_items = 0;
	struct btrfs_item *item;
	u32 old_left_nritems;
	u32 right_nritems;
	int ret = 0;
	int wret;
	u32 this_item_size;
	u32 old_left_item_size;

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

	left = read_tree_block(root, btrfs_node_blockptr(path->nodes[1],
			       slot - 1), root->leafsize);
	free_space = btrfs_leaf_free_space(root, left);
	if (free_space < data_size + sizeof(struct btrfs_item)) {
		free_extent_buffer(left);
		return 1;
	}

	/* cow and double check */
	ret = btrfs_cow_block(trans, root, left,
			      path->nodes[1], slot - 1, &left);
	if (ret) {
		/* we hit -ENOSPC, but it isn't fatal here */
		free_extent_buffer(left);
		return 1;
	}
	free_space = btrfs_leaf_free_space(root, left);
	if (free_space < data_size + sizeof(struct btrfs_item)) {
		free_extent_buffer(left);
		return 1;
	}

	right_nritems = btrfs_header_nritems(right);
	if (right_nritems == 0) {
		free_extent_buffer(left);
		return 1;
	}

	for (i = 0; i < right_nritems - 1; i++) {
		item = btrfs_item_nr(right, i);
		if (!right->map_token) {
			map_extent_buffer(right, (unsigned long)item,
					sizeof(struct btrfs_item),
					&right->map_token, &right->kaddr,
					&right->map_start, &right->map_len,
					KM_USER1);
		}

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

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

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

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

	if (push_items == 0) {
		free_extent_buffer(left);
		return 1;
	}
	if (push_items == btrfs_header_nritems(right))
		WARN_ON(1);

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

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

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

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

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

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

	/* fixup right node */
	push_space = btrfs_item_offset_nr(right, push_items - 1) -
					  leaf_data_end(root, right);
	memmove_extent_buffer(right, btrfs_leaf_data(right) +
			      BTRFS_LEAF_DATA_SIZE(root) - push_space,
			      btrfs_leaf_data(right) +
			      leaf_data_end(root, right), push_space);

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

	right_nritems = btrfs_header_nritems(right) - push_items;
	btrfs_set_header_nritems(right, right_nritems);
	push_space = BTRFS_LEAF_DATA_SIZE(root);

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

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

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

	btrfs_mark_buffer_dirty(left);
	btrfs_mark_buffer_dirty(right);

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

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

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

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

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

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

	right = btrfs_alloc_free_block(trans, root, root->leafsize,
				       l->start, 0);
	if (IS_ERR(right))
		return PTR_ERR(right);

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

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

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

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

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

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

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

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

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

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

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

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

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

	if (!double_split) {
		return ret;
	}

	right = btrfs_alloc_free_block(trans, root, root->leafsize,
				       l->start, 0);
	if (IS_ERR(right))
		return PTR_ERR(right);

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

	btrfs_cpu_key_to_disk(&disk_key, ins_key);
	btrfs_set_header_nritems(right, 0);
	wret = insert_ptr(trans, root, path,
			  &disk_key, right->start,
			  path->slots[1], 1);
	if (wret)
		ret = wret;
	if (path->slots[1] == 0) {
		wret = fixup_low_keys(trans, root, path, &disk_key, 1);
		if (wret)
			ret = wret;
	}
	free_extent_buffer(path->nodes[0]);
	path->nodes[0] = right;
	path->slots[0] = 0;
	return ret;
}

int btrfs_truncate_item(struct btrfs_trans_handle *trans,
			struct btrfs_root *root,
			struct btrfs_path *path,
			u32 new_size)
{
	int ret = 0;
	int slot;
	int slot_orig;
	struct extent_buffer *leaf;
	struct btrfs_item *item;
	u32 nritems;
	unsigned int data_end;
	unsigned int old_data_start;
	unsigned int old_size;
	unsigned int size_diff;
	int i;

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

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

	slot = path->slots[0];
	old_data_start = btrfs_item_offset_nr(leaf, slot);
	old_size = btrfs_item_size_nr(leaf, slot);
	BUG_ON(old_size <= new_size);
	size_diff = old_size - new_size;

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

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

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

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

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

	/* shift the data */
	memmove_extent_buffer(leaf, btrfs_leaf_data(leaf) +
		      data_end + size_diff, btrfs_leaf_data(leaf) +
		      data_end, old_data_start + new_size - data_end);

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

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

int btrfs_extend_item(struct btrfs_trans_handle *trans,
		      struct btrfs_root *root, struct btrfs_path *path,
		      u32 data_size)
{
	int ret = 0;
	int slot;
	int slot_orig;
	struct extent_buffer *leaf;
	struct btrfs_item *item;
	u32 nritems;
	unsigned int data_end;
	unsigned int old_data;
	unsigned int old_size;
	int i;

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

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

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

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

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

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

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

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

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

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

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

	btrfs_cpu_key_to_disk(&disk_key, cpu_key);

	/* create a root if there isn't one */
	if (!root->node)
		BUG();

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

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

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

	if (btrfs_leaf_free_space(root, leaf) <
	    sizeof(struct btrfs_item) + data_size) {
		btrfs_print_leaf(root, leaf);
		printk("not enough freespace need %u have %d\n",
		       data_size, btrfs_leaf_free_space(root, leaf));
		BUG();
	}

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

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

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

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

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

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

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

	/* setup the item for the new data */
	btrfs_set_item_key(leaf, &disk_key, slot);
	item = btrfs_item_nr(leaf, slot);
	btrfs_set_item_offset(leaf, item, data_end - data_size);
	btrfs_set_item_size(leaf, item, data_size);
	btrfs_set_header_nritems(leaf, nritems + 1);
	btrfs_mark_buffer_dirty(leaf);

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

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

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

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

/*
 * delete the pointer from a given node.
 *
 * If the delete empties a node, the node is removed from the tree,
 * continuing all the way the root if required.  The root is converted into
 * a leaf if all the nodes are emptied.
 */
static int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
		   struct btrfs_path *path, int level, int slot)
{
	struct extent_buffer *parent = path->nodes[level];
	u32 nritems;
	int ret = 0;
	int wret;

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

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

/*
 * delete the item at the leaf level in path.  If that empties
 * the leaf, remove it from the tree
 */
int btrfs_del_item(struct btrfs_trans_handle *trans, struct btrfs_root *root,
		   struct btrfs_path *path)
{
	int slot;
	struct extent_buffer *leaf;
	struct btrfs_item *item;
	int doff;
	int dsize;
	int ret = 0;
	int wret;
	u32 nritems;

	leaf = path->nodes[0];
	slot = path->slots[0];
	doff = btrfs_item_offset_nr(leaf, slot);
	dsize = btrfs_item_size_nr(leaf, slot);
	nritems = btrfs_header_nritems(leaf);

	if (slot != nritems - 1) {
		int i;
		int data_end = leaf_data_end(root, leaf);

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

		for (i = slot + 1; i < nritems; i++) {
			u32 ioff;

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

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

		memmove_extent_buffer(leaf, btrfs_item_nr_offset(slot),
			      btrfs_item_nr_offset(slot + 1),
			      sizeof(struct btrfs_item) *
			      (nritems - slot - 1));
	}
	btrfs_set_header_nritems(leaf, nritems - 1);
	nritems--;

	/* delete the leaf if we've emptied it */
	if (nritems == 0) {
		if (leaf == root->node) {
			btrfs_set_header_level(leaf, 0);
		} else {
			clean_tree_block(trans, root, leaf);
			wait_on_tree_block_writeback(root, leaf);
			wret = del_ptr(trans, root, path, 1, path->slots[1]);
			if (wret)
				ret = wret;
			wret = btrfs_free_extent(trans, root,
						 leaf->start, leaf->len, 1);
			if (wret)
				ret = wret;
		}
	} else {
		int used = leaf_space_used(leaf, 0, nritems);
		if (slot == 0) {
			struct btrfs_disk_key disk_key;

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

		/* delete the leaf if it is mostly empty */
		if (used < BTRFS_LEAF_DATA_SIZE(root) / 3) {
			/* push_leaf_left fixes the path.
			 * make sure the path still points to our leaf
			 * for possible call to del_ptr below
			 */
			slot = path->slots[1];
			extent_buffer_get(leaf);

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

			if (btrfs_header_nritems(leaf) == 0) {
				u64 bytenr = leaf->start;
				u32 blocksize = leaf->len;

				clean_tree_block(trans, root, leaf);
				wait_on_tree_block_writeback(root, leaf);

				wret = del_ptr(trans, root, path, 1, slot);
				if (wret)
					ret = wret;

				free_extent_buffer(leaf);
				wret = btrfs_free_extent(trans, root, bytenr,
							 blocksize, 1);
				if (wret)
					ret = wret;
			} else {
				btrfs_mark_buffer_dirty(leaf);
				free_extent_buffer(leaf);
			}
		} else {
			btrfs_mark_buffer_dirty(leaf);
		}
	}
	return ret;
}

/*
 * walk up the tree as far as required to find the next leaf.
 * returns 0 if it found something or 1 if there are no greater leaves.
 * returns < 0 on io errors.
 */
int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
{
	int slot;
	int level = 1;
	u64 bytenr;
	struct extent_buffer *c;
	struct extent_buffer *next = NULL;

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

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

		bytenr = btrfs_node_blockptr(c, slot);
		if (next)
			free_extent_buffer(next);

		if (path->reada)
			reada_for_search(root, path, level, slot);

		next = read_tree_block(root, bytenr,
				       btrfs_level_size(root, level -1));
		break;
	}
	path->slots[level] = slot;
	while(1) {
		level--;
		c = path->nodes[level];
		free_extent_buffer(c);
		path->nodes[level] = next;
		path->slots[level] = 0;
		if (!level)
			break;
		if (path->reada)
			reada_for_search(root, path, level, 0);
		next = read_tree_block(root, btrfs_node_blockptr(next, 0),
				       btrfs_level_size(root, level - 1));
	}
	return 0;
}