fs/btrfs/root-tree.c - kernel/prism - Git at Google

 /*
  * 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 "transaction.h"
 #include "disk-io.h"
 #include "print-tree.h"

 /*
  *  search forward for a root, starting with objectid 'search_start'
  *  if a root key is found, the objectid we find is filled into 'found_objectid'
  *  and 0 is returned.  < 0 is returned on error, 1 if there is nothing
  *  left in the tree.
  */
 int btrfs_search_root(struct btrfs_root *root, u64 search_start,
 		      u64 *found_objectid)
 {
 	struct btrfs_path *path;
 	struct btrfs_key search_key;
 	int ret;

 	root = root->fs_info->tree_root;
 	search_key.objectid = search_start;
 	search_key.type = (u8)-1;
 	search_key.offset = (u64)-1;

 	path = btrfs_alloc_path();
 	BUG_ON(!path);
 again:
 	ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
 	if (ret < 0)
 		goto out;
 	if (ret == 0) {
 		ret = 1;
 		goto out;
 	}
 	if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
 		ret = btrfs_next_leaf(root, path);
 		if (ret)
 			goto out;
 	}
 	btrfs_item_key_to_cpu(path->nodes[0], &search_key, path->slots[0]);
 	if (search_key.type != BTRFS_ROOT_ITEM_KEY) {
 		search_key.offset++;
 		btrfs_release_path(root, path);
 		goto again;
 	}
 	ret = 0;
 	*found_objectid = search_key.objectid;

 out:
 	btrfs_free_path(path);
 	return ret;
 }

 /*
  * lookup the root with the highest offset for a given objectid.  The key we do
  * find is copied into 'key'.  If we find something return 0, otherwise 1, < 0
  * on error.
  */
 int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
 			struct btrfs_root_item *item, struct btrfs_key *key)
 {
 	struct btrfs_path *path;
 	struct btrfs_key search_key;
 	struct btrfs_key found_key;
 	struct extent_buffer *l;
 	int ret;
 	int slot;

 	search_key.objectid = objectid;
 	search_key.type = BTRFS_ROOT_ITEM_KEY;
 	search_key.offset = (u64)-1;

 	path = btrfs_alloc_path();
 	BUG_ON(!path);
 	ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
 	if (ret < 0)
 		goto out;

 	BUG_ON(ret == 0);
 	if (path->slots[0] == 0) {
 		ret = 1;
 		goto out;
 	}
 	l = path->nodes[0];
 	slot = path->slots[0] - 1;
 	btrfs_item_key_to_cpu(l, &found_key, slot);
 	if (found_key.objectid != objectid ||
 	    found_key.type != BTRFS_ROOT_ITEM_KEY) {
 		ret = 1;
 		goto out;
 	}
 	if (item)
 		read_extent_buffer(l, item, btrfs_item_ptr_offset(l, slot),
 				   sizeof(*item));
 	if (key)
 		memcpy(key, &found_key, sizeof(found_key));
 	ret = 0;
 out:
 	btrfs_free_path(path);
 	return ret;
 }

 int btrfs_set_root_node(struct btrfs_root_item *item,
 			struct extent_buffer *node)
 {
 	btrfs_set_root_bytenr(item, node->start);
 	btrfs_set_root_level(item, btrfs_header_level(node));
 	btrfs_set_root_generation(item, btrfs_header_generation(node));
 	return 0;
 }

 /*
  * copy the data in 'item' into the btree
  */
 int btrfs_update_root(struct btrfs_trans_handle *trans, struct btrfs_root
 		      *root, struct btrfs_key *key, struct btrfs_root_item
 		      *item)
 {
 	struct btrfs_path *path;
 	struct extent_buffer *l;
 	int ret;
 	int slot;
 	unsigned long ptr;

 	path = btrfs_alloc_path();
 	BUG_ON(!path);
 	ret = btrfs_search_slot(trans, root, key, path, 0, 1);
 	if (ret < 0)
 		goto out;

 	if (ret != 0) {
 		btrfs_print_leaf(root, path->nodes[0]);
 		printk(KERN_CRIT "unable to update root key %llu %u %llu\n",
 		       (unsigned long long)key->objectid, key->type,
 		       (unsigned long long)key->offset);
 		BUG_ON(1);
 	}

 	l = path->nodes[0];
 	slot = path->slots[0];
 	ptr = btrfs_item_ptr_offset(l, slot);
 	write_extent_buffer(l, item, ptr, sizeof(*item));
 	btrfs_mark_buffer_dirty(path->nodes[0]);
 out:
 	btrfs_free_path(path);
 	return ret;
 }

 int btrfs_insert_root(struct btrfs_trans_handle *trans, struct btrfs_root
 		      *root, struct btrfs_key *key, struct btrfs_root_item
 		      *item)
 {
 	int ret;
 	ret = btrfs_insert_item(trans, root, key, item, sizeof(*item));
 	return ret;
 }

 /*
  * at mount time we want to find all the old transaction snapshots that were in
  * the process of being deleted if we crashed.  This is any root item with an
  * offset lower than the latest root.  They need to be queued for deletion to
  * finish what was happening when we crashed.
  */
 int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid)
 {
 	struct btrfs_root *dead_root;
 	struct btrfs_item *item;
 	struct btrfs_root_item *ri;
 	struct btrfs_key key;
 	struct btrfs_key found_key;
 	struct btrfs_path *path;
 	int ret;
 	u32 nritems;
 	struct extent_buffer *leaf;
 	int slot;

 	key.objectid = objectid;
 	btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
 	key.offset = 0;
 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;

 again:
 	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
 	if (ret < 0)
 		goto err;
 	while (1) {
 		leaf = path->nodes[0];
 		nritems = btrfs_header_nritems(leaf);
 		slot = path->slots[0];
 		if (slot >= nritems) {
 			ret = btrfs_next_leaf(root, path);
 			if (ret)
 				break;
 			leaf = path->nodes[0];
 			nritems = btrfs_header_nritems(leaf);
 			slot = path->slots[0];
 		}
 		item = btrfs_item_nr(leaf, slot);
 		btrfs_item_key_to_cpu(leaf, &key, slot);
 		if (btrfs_key_type(&key) != BTRFS_ROOT_ITEM_KEY)
 			goto next;

 		if (key.objectid < objectid)
 			goto next;

 		if (key.objectid > objectid)
 			break;

 		ri = btrfs_item_ptr(leaf, slot, struct btrfs_root_item);
 		if (btrfs_disk_root_refs(leaf, ri) != 0)
 			goto next;

 		memcpy(&found_key, &key, sizeof(key));
 		key.offset++;
 		btrfs_release_path(root, path);
 		dead_root =
 			btrfs_read_fs_root_no_radix(root->fs_info->tree_root,
 						    &found_key);
 		if (IS_ERR(dead_root)) {
 			ret = PTR_ERR(dead_root);
 			goto err;
 		}

 		ret = btrfs_add_dead_root(dead_root);
 		if (ret)
 			goto err;
 		goto again;
 next:
 		slot++;
 		path->slots[0]++;
 	}
 	ret = 0;
 err:
 	btrfs_free_path(path);
 	return ret;
 }

 int btrfs_find_orphan_roots(struct btrfs_root *tree_root)
 {
 	struct extent_buffer *leaf;
 	struct btrfs_path *path;
 	struct btrfs_key key;
 	int err = 0;
 	int ret;

 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;

 	key.objectid = BTRFS_ORPHAN_OBJECTID;
 	key.type = BTRFS_ORPHAN_ITEM_KEY;
 	key.offset = 0;

 	while (1) {
 		ret = btrfs_search_slot(NULL, tree_root, &key, path, 0, 0);
 		if (ret < 0) {
 			err = ret;
 			break;
 		}

 		leaf = path->nodes[0];
 		if (path->slots[0] >= btrfs_header_nritems(leaf)) {
 			ret = btrfs_next_leaf(tree_root, path);
 			if (ret < 0)
 				err = ret;
 			if (ret != 0)
 				break;
 			leaf = path->nodes[0];
 		}

 		btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
 		btrfs_release_path(tree_root, path);

 		if (key.objectid != BTRFS_ORPHAN_OBJECTID ||
 		    key.type != BTRFS_ORPHAN_ITEM_KEY)
 			break;

 		ret = btrfs_find_dead_roots(tree_root, key.offset);
 		if (ret) {
 			err = ret;
 			break;
 		}

 		key.offset++;
 	}

 	btrfs_free_path(path);
 	return err;
 }

 /* drop the root item for 'key' from 'root' */
 int btrfs_del_root(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		   struct btrfs_key *key)
 {
 	struct btrfs_path *path;
 	int ret;
 	u32 refs;
 	struct btrfs_root_item *ri;
 	struct extent_buffer *leaf;

 	path = btrfs_alloc_path();
 	BUG_ON(!path);
 	ret = btrfs_search_slot(trans, root, key, path, -1, 1);
 	if (ret < 0)
 		goto out;

 	BUG_ON(ret != 0);
 	leaf = path->nodes[0];
 	ri = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_root_item);

 	refs = btrfs_disk_root_refs(leaf, ri);
 	BUG_ON(refs != 0);
 	ret = btrfs_del_item(trans, root, path);
 out:
 	btrfs_free_path(path);
 	return ret;
 }

 int btrfs_del_root_ref(struct btrfs_trans_handle *trans,
 		       struct btrfs_root *tree_root,
 		       u64 root_id, u64 ref_id, u64 dirid, u64 *sequence,
 		       const char *name, int name_len)

 {
 	struct btrfs_path *path;
 	struct btrfs_root_ref *ref;
 	struct extent_buffer *leaf;
 	struct btrfs_key key;
 	unsigned long ptr;
 	int err = 0;
 	int ret;

 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;

 	key.objectid = root_id;
 	key.type = BTRFS_ROOT_BACKREF_KEY;
 	key.offset = ref_id;
 again:
 	ret = btrfs_search_slot(trans, tree_root, &key, path, -1, 1);
 	BUG_ON(ret < 0);
 	if (ret == 0) {
 		leaf = path->nodes[0];
 		ref = btrfs_item_ptr(leaf, path->slots[0],
 				     struct btrfs_root_ref);

 		WARN_ON(btrfs_root_ref_dirid(leaf, ref) != dirid);
 		WARN_ON(btrfs_root_ref_name_len(leaf, ref) != name_len);
 		ptr = (unsigned long)(ref + 1);
 		WARN_ON(memcmp_extent_buffer(leaf, name, ptr, name_len));
 		*sequence = btrfs_root_ref_sequence(leaf, ref);

 		ret = btrfs_del_item(trans, tree_root, path);
 		BUG_ON(ret);
 	} else
 		err = -ENOENT;

 	if (key.type == BTRFS_ROOT_BACKREF_KEY) {
 		btrfs_release_path(tree_root, path);
 		key.objectid = ref_id;
 		key.type = BTRFS_ROOT_REF_KEY;
 		key.offset = root_id;
 		goto again;
 	}

 	btrfs_free_path(path);
 	return err;
 }

 int btrfs_find_root_ref(struct btrfs_root *tree_root,
 		   struct btrfs_path *path,
 		   u64 root_id, u64 ref_id)
 {
 	struct btrfs_key key;
 	int ret;

 	key.objectid = root_id;
 	key.type = BTRFS_ROOT_REF_KEY;
 	key.offset = ref_id;

 	ret = btrfs_search_slot(NULL, tree_root, &key, path, 0, 0);
 	return ret;
 }

 /*
  * add a btrfs_root_ref item.  type is either BTRFS_ROOT_REF_KEY
  * or BTRFS_ROOT_BACKREF_KEY.
  *
  * The dirid, sequence, name and name_len refer to the directory entry
  * that is referencing the root.
  *
  * For a forward ref, the root_id is the id of the tree referencing
  * the root and ref_id is the id of the subvol  or snapshot.
  *
  * For a back ref the root_id is the id of the subvol or snapshot and
  * ref_id is the id of the tree referencing it.
  */
 int btrfs_add_root_ref(struct btrfs_trans_handle *trans,
 		       struct btrfs_root *tree_root,
 		       u64 root_id, u64 ref_id, u64 dirid, u64 sequence,
 		       const char *name, int name_len)
 {
 	struct btrfs_key key;
 	int ret;
 	struct btrfs_path *path;
 	struct btrfs_root_ref *ref;
 	struct extent_buffer *leaf;
 	unsigned long ptr;

 	path = btrfs_alloc_path();
 	if (!path)
 		return -ENOMEM;

 	key.objectid = root_id;
 	key.type = BTRFS_ROOT_BACKREF_KEY;
 	key.offset = ref_id;
 again:
 	ret = btrfs_insert_empty_item(trans, tree_root, path, &key,
 				      sizeof(*ref) + name_len);
 	BUG_ON(ret);

 	leaf = path->nodes[0];
 	ref = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_root_ref);
 	btrfs_set_root_ref_dirid(leaf, ref, dirid);
 	btrfs_set_root_ref_sequence(leaf, ref, sequence);
 	btrfs_set_root_ref_name_len(leaf, ref, name_len);
 	ptr = (unsigned long)(ref + 1);
 	write_extent_buffer(leaf, name, ptr, name_len);
 	btrfs_mark_buffer_dirty(leaf);

 	if (key.type == BTRFS_ROOT_BACKREF_KEY) {
 		btrfs_release_path(tree_root, path);
 		key.objectid = ref_id;
 		key.type = BTRFS_ROOT_REF_KEY;
 		key.offset = root_id;
 		goto again;
 	}

 	btrfs_free_path(path);
 	return 0;
 }
	/*
	* 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 "transaction.h"
	#include "disk-io.h"
	#include "print-tree.h"

	/*
	* search forward for a root, starting with objectid 'search_start'
	* if a root key is found, the objectid we find is filled into 'found_objectid'
	* and 0 is returned. < 0 is returned on error, 1 if there is nothing
	* left in the tree.
	*/
	int btrfs_search_root(struct btrfs_root *root, u64 search_start,
	u64 *found_objectid)
	{
	struct btrfs_path *path;
	struct btrfs_key search_key;
	int ret;

	root = root->fs_info->tree_root;
	search_key.objectid = search_start;
	search_key.type = (u8)-1;
	search_key.offset = (u64)-1;

	path = btrfs_alloc_path();
	BUG_ON(!path);
	again:
	ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
	if (ret < 0)
	goto out;
	if (ret == 0) {
	ret = 1;
	goto out;
	}
	if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
	ret = btrfs_next_leaf(root, path);
	if (ret)
	goto out;
	}
	btrfs_item_key_to_cpu(path->nodes[0], &search_key, path->slots[0]);
	if (search_key.type != BTRFS_ROOT_ITEM_KEY) {
	search_key.offset++;
	btrfs_release_path(root, path);
	goto again;
	}
	ret = 0;
	*found_objectid = search_key.objectid;

	out:
	btrfs_free_path(path);
	return ret;
	}

	/*
	* lookup the root with the highest offset for a given objectid. The key we do
	* find is copied into 'key'. If we find something return 0, otherwise 1, < 0
	* on error.
	*/
	int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
	struct btrfs_root_item item, struct btrfs_key key)
	{
	struct btrfs_path *path;
	struct btrfs_key search_key;
	struct btrfs_key found_key;
	struct extent_buffer *l;
	int ret;
	int slot;

	search_key.objectid = objectid;
	search_key.type = BTRFS_ROOT_ITEM_KEY;
	search_key.offset = (u64)-1;

	path = btrfs_alloc_path();
	BUG_ON(!path);
	ret = btrfs_search_slot(NULL, root, &search_key, path, 0, 0);
	if (ret < 0)
	goto out;

	BUG_ON(ret == 0);
	if (path->slots[0] == 0) {
	ret = 1;
	goto out;
	}
	l = path->nodes[0];
	slot = path->slots[0] - 1;
	btrfs_item_key_to_cpu(l, &found_key, slot);
	if (found_key.objectid != objectid \|\|
	found_key.type != BTRFS_ROOT_ITEM_KEY) {
	ret = 1;
	goto out;
	}
	if (item)
	read_extent_buffer(l, item, btrfs_item_ptr_offset(l, slot),
	sizeof(*item));
	if (key)
	memcpy(key, &found_key, sizeof(found_key));
	ret = 0;
	out:
	btrfs_free_path(path);
	return ret;
	}

	int btrfs_set_root_node(struct btrfs_root_item *item,
	struct extent_buffer *node)
	{
	btrfs_set_root_bytenr(item, node->start);
	btrfs_set_root_level(item, btrfs_header_level(node));
	btrfs_set_root_generation(item, btrfs_header_generation(node));
	return 0;
	}

	/*
	* copy the data in 'item' into the btree
	*/
	int btrfs_update_root(struct btrfs_trans_handle *trans, struct btrfs_root
	root, struct btrfs_key key, struct btrfs_root_item
	*item)
	{
	struct btrfs_path *path;
	struct extent_buffer *l;
	int ret;
	int slot;
	unsigned long ptr;

	path = btrfs_alloc_path();
	BUG_ON(!path);
	ret = btrfs_search_slot(trans, root, key, path, 0, 1);
	if (ret < 0)
	goto out;

	if (ret != 0) {
	btrfs_print_leaf(root, path->nodes[0]);
	printk(KERN_CRIT "unable to update root key %llu %u %llu\n",
	(unsigned long long)key->objectid, key->type,
	(unsigned long long)key->offset);
	BUG_ON(1);
	}

	l = path->nodes[0];
	slot = path->slots[0];
	ptr = btrfs_item_ptr_offset(l, slot);
	write_extent_buffer(l, item, ptr, sizeof(*item));
	btrfs_mark_buffer_dirty(path->nodes[0]);
	out:
	btrfs_free_path(path);
	return ret;
	}

	int btrfs_insert_root(struct btrfs_trans_handle *trans, struct btrfs_root
	root, struct btrfs_key key, struct btrfs_root_item
	*item)
	{
	int ret;
	ret = btrfs_insert_item(trans, root, key, item, sizeof(*item));
	return ret;
	}

	/*
	* at mount time we want to find all the old transaction snapshots that were in
	* the process of being deleted if we crashed. This is any root item with an
	* offset lower than the latest root. They need to be queued for deletion to
	* finish what was happening when we crashed.
	*/
	int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid)
	{
	struct btrfs_root *dead_root;
	struct btrfs_item *item;
	struct btrfs_root_item *ri;
	struct btrfs_key key;
	struct btrfs_key found_key;
	struct btrfs_path *path;
	int ret;
	u32 nritems;
	struct extent_buffer *leaf;
	int slot;

	key.objectid = objectid;
	btrfs_set_key_type(&key, BTRFS_ROOT_ITEM_KEY);
	key.offset = 0;
	path = btrfs_alloc_path();
	if (!path)
	return -ENOMEM;

	again:
	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
	if (ret < 0)
	goto err;
	while (1) {
	leaf = path->nodes[0];
	nritems = btrfs_header_nritems(leaf);
	slot = path->slots[0];
	if (slot >= nritems) {
	ret = btrfs_next_leaf(root, path);
	if (ret)
	break;
	leaf = path->nodes[0];
	nritems = btrfs_header_nritems(leaf);
	slot = path->slots[0];
	}
	item = btrfs_item_nr(leaf, slot);
	btrfs_item_key_to_cpu(leaf, &key, slot);
	if (btrfs_key_type(&key) != BTRFS_ROOT_ITEM_KEY)
	goto next;

	if (key.objectid < objectid)
	goto next;

	if (key.objectid > objectid)
	break;

	ri = btrfs_item_ptr(leaf, slot, struct btrfs_root_item);
	if (btrfs_disk_root_refs(leaf, ri) != 0)
	goto next;

	memcpy(&found_key, &key, sizeof(key));
	key.offset++;
	btrfs_release_path(root, path);
	dead_root =
	btrfs_read_fs_root_no_radix(root->fs_info->tree_root,
	&found_key);
	if (IS_ERR(dead_root)) {
	ret = PTR_ERR(dead_root);
	goto err;
	}

	ret = btrfs_add_dead_root(dead_root);
	if (ret)
	goto err;
	goto again;
	next:
	slot++;
	path->slots[0]++;
	}
	ret = 0;
	err:
	btrfs_free_path(path);
	return ret;
	}

	int btrfs_find_orphan_roots(struct btrfs_root *tree_root)
	{
	struct extent_buffer *leaf;
	struct btrfs_path *path;
	struct btrfs_key key;
	int err = 0;
	int ret;

	path = btrfs_alloc_path();
	if (!path)
	return -ENOMEM;

	key.objectid = BTRFS_ORPHAN_OBJECTID;
	key.type = BTRFS_ORPHAN_ITEM_KEY;
	key.offset = 0;

	while (1) {
	ret = btrfs_search_slot(NULL, tree_root, &key, path, 0, 0);
	if (ret < 0) {
	err = ret;
	break;
	}

	leaf = path->nodes[0];
	if (path->slots[0] >= btrfs_header_nritems(leaf)) {
	ret = btrfs_next_leaf(tree_root, path);
	if (ret < 0)
	err = ret;
	if (ret != 0)
	break;
	leaf = path->nodes[0];
	}

	btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
	btrfs_release_path(tree_root, path);

	if (key.objectid != BTRFS_ORPHAN_OBJECTID \|\|
	key.type != BTRFS_ORPHAN_ITEM_KEY)
	break;

	ret = btrfs_find_dead_roots(tree_root, key.offset);
	if (ret) {
	err = ret;
	break;
	}

	key.offset++;
	}

	btrfs_free_path(path);
	return err;
	}

	/* drop the root item for 'key' from 'root' */
	int btrfs_del_root(struct btrfs_trans_handle trans, struct btrfs_root root,
	struct btrfs_key *key)
	{
	struct btrfs_path *path;
	int ret;
	u32 refs;
	struct btrfs_root_item *ri;
	struct extent_buffer *leaf;

	path = btrfs_alloc_path();
	BUG_ON(!path);
	ret = btrfs_search_slot(trans, root, key, path, -1, 1);
	if (ret < 0)
	goto out;

	BUG_ON(ret != 0);
	leaf = path->nodes[0];
	ri = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_root_item);

	refs = btrfs_disk_root_refs(leaf, ri);
	BUG_ON(refs != 0);
	ret = btrfs_del_item(trans, root, path);
	out:
	btrfs_free_path(path);
	return ret;
	}

	int btrfs_del_root_ref(struct btrfs_trans_handle *trans,
	struct btrfs_root *tree_root,
	u64 root_id, u64 ref_id, u64 dirid, u64 *sequence,
	const char *name, int name_len)

	{
	struct btrfs_path *path;
	struct btrfs_root_ref *ref;
	struct extent_buffer *leaf;
	struct btrfs_key key;
	unsigned long ptr;
	int err = 0;
	int ret;

	path = btrfs_alloc_path();
	if (!path)
	return -ENOMEM;

	key.objectid = root_id;
	key.type = BTRFS_ROOT_BACKREF_KEY;
	key.offset = ref_id;
	again:
	ret = btrfs_search_slot(trans, tree_root, &key, path, -1, 1);
	BUG_ON(ret < 0);
	if (ret == 0) {
	leaf = path->nodes[0];
	ref = btrfs_item_ptr(leaf, path->slots[0],
	struct btrfs_root_ref);

	WARN_ON(btrfs_root_ref_dirid(leaf, ref) != dirid);
	WARN_ON(btrfs_root_ref_name_len(leaf, ref) != name_len);
	ptr = (unsigned long)(ref + 1);
	WARN_ON(memcmp_extent_buffer(leaf, name, ptr, name_len));
	*sequence = btrfs_root_ref_sequence(leaf, ref);

	ret = btrfs_del_item(trans, tree_root, path);
	BUG_ON(ret);
	} else
	err = -ENOENT;

	if (key.type == BTRFS_ROOT_BACKREF_KEY) {
	btrfs_release_path(tree_root, path);
	key.objectid = ref_id;
	key.type = BTRFS_ROOT_REF_KEY;
	key.offset = root_id;
	goto again;
	}

	btrfs_free_path(path);
	return err;
	}

	int btrfs_find_root_ref(struct btrfs_root *tree_root,
	struct btrfs_path *path,
	u64 root_id, u64 ref_id)
	{
	struct btrfs_key key;
	int ret;

	key.objectid = root_id;
	key.type = BTRFS_ROOT_REF_KEY;
	key.offset = ref_id;

	ret = btrfs_search_slot(NULL, tree_root, &key, path, 0, 0);
	return ret;
	}

	/*
	* add a btrfs_root_ref item. type is either BTRFS_ROOT_REF_KEY
	* or BTRFS_ROOT_BACKREF_KEY.
	*
	* The dirid, sequence, name and name_len refer to the directory entry
	* that is referencing the root.
	*
	* For a forward ref, the root_id is the id of the tree referencing
	* the root and ref_id is the id of the subvol or snapshot.
	*
	* For a back ref the root_id is the id of the subvol or snapshot and
	* ref_id is the id of the tree referencing it.
	*/
	int btrfs_add_root_ref(struct btrfs_trans_handle *trans,
	struct btrfs_root *tree_root,
	u64 root_id, u64 ref_id, u64 dirid, u64 sequence,
	const char *name, int name_len)
	{
	struct btrfs_key key;
	int ret;
	struct btrfs_path *path;
	struct btrfs_root_ref *ref;
	struct extent_buffer *leaf;
	unsigned long ptr;

	path = btrfs_alloc_path();
	if (!path)
	return -ENOMEM;

	key.objectid = root_id;
	key.type = BTRFS_ROOT_BACKREF_KEY;
	key.offset = ref_id;
	again:
	ret = btrfs_insert_empty_item(trans, tree_root, path, &key,
	sizeof(*ref) + name_len);
	BUG_ON(ret);

	leaf = path->nodes[0];
	ref = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_root_ref);
	btrfs_set_root_ref_dirid(leaf, ref, dirid);
	btrfs_set_root_ref_sequence(leaf, ref, sequence);
	btrfs_set_root_ref_name_len(leaf, ref, name_len);
	ptr = (unsigned long)(ref + 1);
	write_extent_buffer(leaf, name, ptr, name_len);
	btrfs_mark_buffer_dirty(leaf);

	if (key.type == BTRFS_ROOT_BACKREF_KEY) {
	btrfs_release_path(tree_root, path);
	key.objectid = ref_id;
	key.type = BTRFS_ROOT_REF_KEY;
	key.offset = root_id;
	goto again;
	}

	btrfs_free_path(path);
	return 0;
	}