fs/btrfs/root-tree.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2007 Oracle.  All rights reserved.
  */

 #include <linux/err.h>
 #include <linux/uuid.h>
 #include "ctree.h"
 #include "transaction.h"
 #include "disk-io.h"
 #include "print-tree.h"

 /*
  * Read a root item from the tree. In case we detect a root item smaller then
  * sizeof(root_item), we know it's an old version of the root structure and
  * initialize all new fields to zero. The same happens if we detect mismatching
  * generation numbers as then we know the root was once mounted with an older
  * kernel that was not aware of the root item structure change.
  */
 static void btrfs_read_root_item(struct extent_buffer *eb, int slot,
 				struct btrfs_root_item *item)
 {
 	uuid_le uuid;
 	u32 len;
 	int need_reset = 0;

 	len = btrfs_item_size_nr(eb, slot);
 	read_extent_buffer(eb, item, btrfs_item_ptr_offset(eb, slot),
 			   min_t(u32, len, sizeof(*item)));
 	if (len < sizeof(*item))
 		need_reset = 1;
 	if (!need_reset && btrfs_root_generation(item)
 		!= btrfs_root_generation_v2(item)) {
 		if (btrfs_root_generation_v2(item) != 0) {
 			btrfs_warn(eb->fs_info,
 					"mismatching generation and generation_v2 found in root item. This root was probably mounted with an older kernel. Resetting all new fields.");
 		}
 		need_reset = 1;
 	}
 	if (need_reset) {
 		memset(&item->generation_v2, 0,
 			sizeof(*item) - offsetof(struct btrfs_root_item,
 					generation_v2));

 		uuid_le_gen(&uuid);
 		memcpy(item->uuid, uuid.b, BTRFS_UUID_SIZE);
 	}
 }

 /*
  * btrfs_find_root - lookup the root by the key.
  * root: the root of the root tree
  * search_key: the key to search
  * path: the path we search
  * root_item: the root item of the tree we look for
  * root_key: the root key of the tree we look for
  *
  * If ->offset of 'search_key' is -1ULL, it means we are not sure the offset
  * of the search key, just lookup the root with the highest offset for a
  * given objectid.
  *
  * If we find something return 0, otherwise > 0, < 0 on error.
  */
 int btrfs_find_root(struct btrfs_root *root, const struct btrfs_key *search_key,
 		    struct btrfs_path *path, struct btrfs_root_item *root_item,
 		    struct btrfs_key *root_key)
 {
 	struct btrfs_key found_key;
 	struct extent_buffer *l;
 	int ret;
 	int slot;

 	ret = btrfs_search_slot(NULL, root, search_key, path, 0, 0);
 	if (ret < 0)
 		return ret;

 	if (search_key->offset != -1ULL) {	/* the search key is exact */
 		if (ret > 0)
 			goto out;
 	} else {
 		BUG_ON(ret == 0);		/* Logical error */
 		if (path->slots[0] == 0)
 			goto out;
 		path->slots[0]--;
 		ret = 0;
 	}

 	l = path->nodes[0];
 	slot = path->slots[0];

 	btrfs_item_key_to_cpu(l, &found_key, slot);
 	if (found_key.objectid != search_key->objectid ||
 	    found_key.type != BTRFS_ROOT_ITEM_KEY) {
 		ret = 1;
 		goto out;
 	}

 	if (root_item)
 		btrfs_read_root_item(l, slot, root_item);
 	if (root_key)
 		memcpy(root_key, &found_key, sizeof(found_key));
 out:
 	btrfs_release_path(path);
 	return ret;
 }

 void 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));
 }

 /*
  * 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_fs_info *fs_info = root->fs_info;
 	struct btrfs_path *path;
 	struct extent_buffer *l;
 	int ret;
 	int slot;
 	unsigned long ptr;
 	u32 old_len;

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

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

 	if (ret > 0) {
 		btrfs_crit(fs_info,
 			"unable to find root key (%llu %u %llu) in tree %llu",
 			key->objectid, key->type, key->offset,
 			root->root_key.objectid);
 		ret = -EUCLEAN;
 		btrfs_abort_transaction(trans, ret);
 		goto out;
 	}

 	l = path->nodes[0];
 	slot = path->slots[0];
 	ptr = btrfs_item_ptr_offset(l, slot);
 	old_len = btrfs_item_size_nr(l, slot);

 	/*
 	 * If this is the first time we update the root item which originated
 	 * from an older kernel, we need to enlarge the item size to make room
 	 * for the added fields.
 	 */
 	if (old_len < sizeof(*item)) {
 		btrfs_release_path(path);
 		ret = btrfs_search_slot(trans, root, key, path,
 				-1, 1);
 		if (ret < 0) {
 			btrfs_abort_transaction(trans, ret);
 			goto out;
 		}

 		ret = btrfs_del_item(trans, root, path);
 		if (ret < 0) {
 			btrfs_abort_transaction(trans, ret);
 			goto out;
 		}
 		btrfs_release_path(path);
 		ret = btrfs_insert_empty_item(trans, root, path,
 				key, sizeof(*item));
 		if (ret < 0) {
 			btrfs_abort_transaction(trans, ret);
 			goto out;
 		}
 		l = path->nodes[0];
 		slot = path->slots[0];
 		ptr = btrfs_item_ptr_offset(l, slot);
 	}

 	/*
 	 * Update generation_v2 so at the next mount we know the new root
 	 * fields are valid.
 	 */
 	btrfs_set_root_generation_v2(item, btrfs_root_generation(item));

 	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,
 		      const struct btrfs_key *key, struct btrfs_root_item *item)
 {
 	/*
 	 * Make sure generation v1 and v2 match. See update_root for details.
 	 */
 	btrfs_set_root_generation_v2(item, btrfs_root_generation(item));
 	return btrfs_insert_item(trans, root, key, item, sizeof(*item));
 }

 int btrfs_find_orphan_roots(struct btrfs_fs_info *fs_info)
 {
 	struct btrfs_root *tree_root = fs_info->tree_root;
 	struct extent_buffer *leaf;
 	struct btrfs_path *path;
 	struct btrfs_key key;
 	struct btrfs_key root_key;
 	struct btrfs_root *root;
 	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;

 	root_key.type = BTRFS_ROOT_ITEM_KEY;
 	root_key.offset = (u64)-1;

 	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(path);

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

 		root_key.objectid = key.offset;
 		key.offset++;

 		/*
 		 * The root might have been inserted already, as before we look
 		 * for orphan roots, log replay might have happened, which
 		 * triggers a transaction commit and qgroup accounting, which
 		 * in turn reads and inserts fs roots while doing backref
 		 * walking.
 		 */
 		root = btrfs_lookup_fs_root(fs_info, root_key.objectid);
 		if (root) {
 			WARN_ON(!test_bit(BTRFS_ROOT_ORPHAN_ITEM_INSERTED,
 					  &root->state));
 			if (btrfs_root_refs(&root->root_item) == 0) {
 				set_bit(BTRFS_ROOT_DEAD_TREE, &root->state);
 				btrfs_add_dead_root(root);
 			}
 			continue;
 		}

 		root = btrfs_read_fs_root(tree_root, &root_key);
 		err = PTR_ERR_OR_ZERO(root);
 		if (err && err != -ENOENT) {
 			break;
 		} else if (err == -ENOENT) {
 			struct btrfs_trans_handle *trans;

 			btrfs_release_path(path);

 			trans = btrfs_join_transaction(tree_root);
 			if (IS_ERR(trans)) {
 				err = PTR_ERR(trans);
 				btrfs_handle_fs_error(fs_info, err,
 					    "Failed to start trans to delete orphan item");
 				break;
 			}
 			err = btrfs_del_orphan_item(trans, tree_root,
 						    root_key.objectid);
 			btrfs_end_transaction(trans);
 			if (err) {
 				btrfs_handle_fs_error(fs_info, err,
 					    "Failed to delete root orphan item");
 				break;
 			}
 			continue;
 		}

 		err = btrfs_init_fs_root(root);
 		if (err) {
 			btrfs_free_fs_root(root);
 			break;
 		}

 		set_bit(BTRFS_ROOT_ORPHAN_ITEM_INSERTED, &root->state);

 		err = btrfs_insert_fs_root(fs_info, root);
 		if (err) {
 			BUG_ON(err == -EEXIST);
 			btrfs_free_fs_root(root);
 			break;
 		}

 		if (btrfs_root_refs(&root->root_item) == 0) {
 			set_bit(BTRFS_ROOT_DEAD_TREE, &root->state);
 			btrfs_add_dead_root(root);
 		}
 	}

 	btrfs_free_path(path);
 	return err;
 }

 /* drop the root item for 'key' from the tree root */
 int btrfs_del_root(struct btrfs_trans_handle *trans,
 		   const struct btrfs_key *key)
 {
 	struct btrfs_root *root = trans->fs_info->tree_root;
 	struct btrfs_path *path;
 	int ret;

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

 	BUG_ON(ret != 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, u64 root_id,
 		       u64 ref_id, u64 dirid, u64 *sequence, const char *name,
 		       int name_len)

 {
 	struct btrfs_root *tree_root = trans->fs_info->tree_root;
 	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);
 		if (ret) {
 			err = ret;
 			goto out;
 		}
 	} else
 		err = -ENOENT;

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

 out:
 	btrfs_free_path(path);
 	return err;
 }

 /*
  * 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.
  *
  * Will return 0, -ENOMEM, or anything from the CoW path
  */
 int btrfs_add_root_ref(struct btrfs_trans_handle *trans, u64 root_id,
 		       u64 ref_id, u64 dirid, u64 sequence, const char *name,
 		       int name_len)
 {
 	struct btrfs_root *tree_root = trans->fs_info->tree_root;
 	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);
 	if (ret) {
 		btrfs_abort_transaction(trans, ret);
 		btrfs_free_path(path);
 		return 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(path);
 		key.objectid = ref_id;
 		key.type = BTRFS_ROOT_REF_KEY;
 		key.offset = root_id;
 		goto again;
 	}

 	btrfs_free_path(path);
 	return 0;
 }

 /*
  * Old btrfs forgets to init root_item->flags and root_item->byte_limit
  * for subvolumes. To work around this problem, we steal a bit from
  * root_item->inode_item->flags, and use it to indicate if those fields
  * have been properly initialized.
  */
 void btrfs_check_and_init_root_item(struct btrfs_root_item *root_item)
 {
 	u64 inode_flags = btrfs_stack_inode_flags(&root_item->inode);

 	if (!(inode_flags & BTRFS_INODE_ROOT_ITEM_INIT)) {
 		inode_flags |= BTRFS_INODE_ROOT_ITEM_INIT;
 		btrfs_set_stack_inode_flags(&root_item->inode, inode_flags);
 		btrfs_set_root_flags(root_item, 0);
 		btrfs_set_root_limit(root_item, 0);
 	}
 }

 void btrfs_update_root_times(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *root)
 {
 	struct btrfs_root_item *item = &root->root_item;
 	struct timespec64 ct;

 	ktime_get_real_ts64(&ct);
 	spin_lock(&root->root_item_lock);
 	btrfs_set_root_ctransid(item, trans->transid);
 	btrfs_set_stack_timespec_sec(&item->ctime, ct.tv_sec);
 	btrfs_set_stack_timespec_nsec(&item->ctime, ct.tv_nsec);
 	spin_unlock(&root->root_item_lock);
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Copyright (C) 2007 Oracle. All rights reserved.
	*/

	#include <linux/err.h>
	#include <linux/uuid.h>
	#include "ctree.h"
	#include "transaction.h"
	#include "disk-io.h"
	#include "print-tree.h"

	/*
	* Read a root item from the tree. In case we detect a root item smaller then
	* sizeof(root_item), we know it's an old version of the root structure and
	* initialize all new fields to zero. The same happens if we detect mismatching
	* generation numbers as then we know the root was once mounted with an older
	* kernel that was not aware of the root item structure change.
	*/
	static void btrfs_read_root_item(struct extent_buffer *eb, int slot,
	struct btrfs_root_item *item)
	{
	uuid_le uuid;
	u32 len;
	int need_reset = 0;

	len = btrfs_item_size_nr(eb, slot);
	read_extent_buffer(eb, item, btrfs_item_ptr_offset(eb, slot),
	min_t(u32, len, sizeof(*item)));
	if (len < sizeof(*item))
	need_reset = 1;
	if (!need_reset && btrfs_root_generation(item)
	!= btrfs_root_generation_v2(item)) {
	if (btrfs_root_generation_v2(item) != 0) {
	btrfs_warn(eb->fs_info,
	"mismatching generation and generation_v2 found in root item. This root was probably mounted with an older kernel. Resetting all new fields.");
	}
	need_reset = 1;
	}
	if (need_reset) {
	memset(&item->generation_v2, 0,
	sizeof(*item) - offsetof(struct btrfs_root_item,
	generation_v2));

	uuid_le_gen(&uuid);
	memcpy(item->uuid, uuid.b, BTRFS_UUID_SIZE);
	}
	}

	/*
	* btrfs_find_root - lookup the root by the key.
	* root: the root of the root tree
	* search_key: the key to search
	* path: the path we search
	* root_item: the root item of the tree we look for
	* root_key: the root key of the tree we look for
	*
	* If ->offset of 'search_key' is -1ULL, it means we are not sure the offset
	* of the search key, just lookup the root with the highest offset for a
	* given objectid.
	*
	* If we find something return 0, otherwise > 0, < 0 on error.
	*/
	int btrfs_find_root(struct btrfs_root root, const struct btrfs_key search_key,
	struct btrfs_path path, struct btrfs_root_item root_item,
	struct btrfs_key *root_key)
	{
	struct btrfs_key found_key;
	struct extent_buffer *l;
	int ret;
	int slot;

	ret = btrfs_search_slot(NULL, root, search_key, path, 0, 0);
	if (ret < 0)
	return ret;

	if (search_key->offset != -1ULL) { /* the search key is exact */
	if (ret > 0)
	goto out;
	} else {
	BUG_ON(ret == 0); /* Logical error */
	if (path->slots[0] == 0)
	goto out;
	path->slots[0]--;
	ret = 0;
	}

	l = path->nodes[0];
	slot = path->slots[0];

	btrfs_item_key_to_cpu(l, &found_key, slot);
	if (found_key.objectid != search_key->objectid \|\|
	found_key.type != BTRFS_ROOT_ITEM_KEY) {
	ret = 1;
	goto out;
	}

	if (root_item)
	btrfs_read_root_item(l, slot, root_item);
	if (root_key)
	memcpy(root_key, &found_key, sizeof(found_key));
	out:
	btrfs_release_path(path);
	return ret;
	}

	void 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));
	}

	/*
	* 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_fs_info *fs_info = root->fs_info;
	struct btrfs_path *path;
	struct extent_buffer *l;
	int ret;
	int slot;
	unsigned long ptr;
	u32 old_len;

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

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

	if (ret > 0) {
	btrfs_crit(fs_info,
	"unable to find root key (%llu %u %llu) in tree %llu",
	key->objectid, key->type, key->offset,
	root->root_key.objectid);
	ret = -EUCLEAN;
	btrfs_abort_transaction(trans, ret);
	goto out;
	}

	l = path->nodes[0];
	slot = path->slots[0];
	ptr = btrfs_item_ptr_offset(l, slot);
	old_len = btrfs_item_size_nr(l, slot);

	/*
	* If this is the first time we update the root item which originated
	* from an older kernel, we need to enlarge the item size to make room
	* for the added fields.
	*/
	if (old_len < sizeof(*item)) {
	btrfs_release_path(path);
	ret = btrfs_search_slot(trans, root, key, path,
	-1, 1);
	if (ret < 0) {
	btrfs_abort_transaction(trans, ret);
	goto out;
	}

	ret = btrfs_del_item(trans, root, path);
	if (ret < 0) {
	btrfs_abort_transaction(trans, ret);
	goto out;
	}
	btrfs_release_path(path);
	ret = btrfs_insert_empty_item(trans, root, path,
	key, sizeof(*item));
	if (ret < 0) {
	btrfs_abort_transaction(trans, ret);
	goto out;
	}
	l = path->nodes[0];
	slot = path->slots[0];
	ptr = btrfs_item_ptr_offset(l, slot);
	}

	/*
	* Update generation_v2 so at the next mount we know the new root
	* fields are valid.
	*/
	btrfs_set_root_generation_v2(item, btrfs_root_generation(item));

	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,
	const struct btrfs_key key, struct btrfs_root_item item)
	{
	/*
	* Make sure generation v1 and v2 match. See update_root for details.
	*/
	btrfs_set_root_generation_v2(item, btrfs_root_generation(item));
	return btrfs_insert_item(trans, root, key, item, sizeof(*item));
	}

	int btrfs_find_orphan_roots(struct btrfs_fs_info *fs_info)
	{
	struct btrfs_root *tree_root = fs_info->tree_root;
	struct extent_buffer *leaf;
	struct btrfs_path *path;
	struct btrfs_key key;
	struct btrfs_key root_key;
	struct btrfs_root *root;
	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;

	root_key.type = BTRFS_ROOT_ITEM_KEY;
	root_key.offset = (u64)-1;

	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(path);

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

	root_key.objectid = key.offset;
	key.offset++;

	/*
	* The root might have been inserted already, as before we look
	* for orphan roots, log replay might have happened, which
	* triggers a transaction commit and qgroup accounting, which
	* in turn reads and inserts fs roots while doing backref
	* walking.
	*/
	root = btrfs_lookup_fs_root(fs_info, root_key.objectid);
	if (root) {
	WARN_ON(!test_bit(BTRFS_ROOT_ORPHAN_ITEM_INSERTED,
	&root->state));
	if (btrfs_root_refs(&root->root_item) == 0) {
	set_bit(BTRFS_ROOT_DEAD_TREE, &root->state);
	btrfs_add_dead_root(root);
	}
	continue;
	}

	root = btrfs_read_fs_root(tree_root, &root_key);
	err = PTR_ERR_OR_ZERO(root);
	if (err && err != -ENOENT) {
	break;
	} else if (err == -ENOENT) {
	struct btrfs_trans_handle *trans;

	btrfs_release_path(path);

	trans = btrfs_join_transaction(tree_root);
	if (IS_ERR(trans)) {
	err = PTR_ERR(trans);
	btrfs_handle_fs_error(fs_info, err,
	"Failed to start trans to delete orphan item");
	break;
	}
	err = btrfs_del_orphan_item(trans, tree_root,
	root_key.objectid);
	btrfs_end_transaction(trans);
	if (err) {
	btrfs_handle_fs_error(fs_info, err,
	"Failed to delete root orphan item");
	break;
	}
	continue;
	}

	err = btrfs_init_fs_root(root);
	if (err) {
	btrfs_free_fs_root(root);
	break;
	}

	set_bit(BTRFS_ROOT_ORPHAN_ITEM_INSERTED, &root->state);

	err = btrfs_insert_fs_root(fs_info, root);
	if (err) {
	BUG_ON(err == -EEXIST);
	btrfs_free_fs_root(root);
	break;
	}

	if (btrfs_root_refs(&root->root_item) == 0) {
	set_bit(BTRFS_ROOT_DEAD_TREE, &root->state);
	btrfs_add_dead_root(root);
	}
	}

	btrfs_free_path(path);
	return err;
	}

	/* drop the root item for 'key' from the tree root */
	int btrfs_del_root(struct btrfs_trans_handle *trans,
	const struct btrfs_key *key)
	{
	struct btrfs_root *root = trans->fs_info->tree_root;
	struct btrfs_path *path;
	int ret;

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

	BUG_ON(ret != 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, u64 root_id,
	u64 ref_id, u64 dirid, u64 sequence, const char name,
	int name_len)

	{
	struct btrfs_root *tree_root = trans->fs_info->tree_root;
	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);
	if (ret) {
	err = ret;
	goto out;
	}
	} else
	err = -ENOENT;

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

	out:
	btrfs_free_path(path);
	return err;
	}

	/*
	* 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.
	*
	* Will return 0, -ENOMEM, or anything from the CoW path
	*/
	int btrfs_add_root_ref(struct btrfs_trans_handle *trans, u64 root_id,
	u64 ref_id, u64 dirid, u64 sequence, const char *name,
	int name_len)
	{
	struct btrfs_root *tree_root = trans->fs_info->tree_root;
	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);
	if (ret) {
	btrfs_abort_transaction(trans, ret);
	btrfs_free_path(path);
	return 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(path);
	key.objectid = ref_id;
	key.type = BTRFS_ROOT_REF_KEY;
	key.offset = root_id;
	goto again;
	}

	btrfs_free_path(path);
	return 0;
	}

	/*
	* Old btrfs forgets to init root_item->flags and root_item->byte_limit
	* for subvolumes. To work around this problem, we steal a bit from
	* root_item->inode_item->flags, and use it to indicate if those fields
	* have been properly initialized.
	*/
	void btrfs_check_and_init_root_item(struct btrfs_root_item *root_item)
	{
	u64 inode_flags = btrfs_stack_inode_flags(&root_item->inode);

	if (!(inode_flags & BTRFS_INODE_ROOT_ITEM_INIT)) {
	inode_flags \|= BTRFS_INODE_ROOT_ITEM_INIT;
	btrfs_set_stack_inode_flags(&root_item->inode, inode_flags);
	btrfs_set_root_flags(root_item, 0);
	btrfs_set_root_limit(root_item, 0);
	}
	}

	void btrfs_update_root_times(struct btrfs_trans_handle *trans,
	struct btrfs_root *root)
	{
	struct btrfs_root_item *item = &root->root_item;
	struct timespec64 ct;

	ktime_get_real_ts64(&ct);
	spin_lock(&root->root_item_lock);
	btrfs_set_root_ctransid(item, trans->transid);
	btrfs_set_stack_timespec_sec(&item->ctime, ct.tv_sec);
	btrfs_set_stack_timespec_nsec(&item->ctime, ct.tv_nsec);
	spin_unlock(&root->root_item_lock);
	}