---
  ctree.h     |  7 +++++-
  uuid-tree.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
  2 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/ctree.h b/ctree.h
index f9c49d6041c1..7b9e3f1cef6e 100644
--- a/ctree.h
+++ b/ctree.h

@@ -1101,6 +1101,7 @@ struct btrfs_fs_info {
  	struct btrfs_root *csum_root;
  	struct btrfs_root *quota_root;
  	struct btrfs_root *free_space_root;
+	struct btrfs_root *uuid_root;
  
  	struct rb_root fs_root_tree;
  

@@ -2774,11 +2775,15 @@ int btrfs_csum_truncate(struct btrfs_trans_handle *trans,
  			struct btrfs_root *root, struct btrfs_path *path,
  			u64 isize);
  
-/* uuid-tree.c */
+/* uuid-tree.c, mounted fs (online) interface */
  int btrfs_lookup_uuid_subvol_item(int fd, const u8 *uuid, u64 *subvol_id);
  int btrfs_lookup_uuid_received_subvol_item(int fd, const u8 *uuid,
  					   u64 *subvol_id);
  
+/* uuid-tree.c, unmounted fs (offline) interface */
+int btrfs_uuid_tree_add(struct btrfs_trans_handle *trans, u8 *uuid, u8 type,
+			u64 subid_cpu);
+
  static inline int is_fstree(u64 rootid)
  {
  	if (rootid == BTRFS_FS_TREE_OBJECTID ||

diff --git a/uuid-tree.c b/uuid-tree.c
index b9190103c355..3f547198f016 100644
--- a/uuid-tree.c
+++ b/uuid-tree.c

@@ -170,3 +170,68 @@ out:
  	btrfs_free_path(path);
  	return ret;
  }
+
+int btrfs_uuid_tree_add(struct btrfs_trans_handle *trans, u8 *uuid, u8 type,
+			u64 subid_cpu)
+{
+	struct btrfs_fs_info *fs_info = trans->fs_info;
+	struct btrfs_root *uuid_root = fs_info->uuid_root;
+	int ret;
+	struct btrfs_path *path = NULL;
+	struct btrfs_key key;
+	struct extent_buffer *eb;
+	int slot;
+	unsigned long offset;
+	__le64 subid_le;
+
+	if (!uuid_root) {
+		warning("%s: uuid root is not initialized", __func__);
+		return -EINVAL;
+	}
+
+	ret = btrfs_uuid_tree_lookup(uuid_root, uuid, type, subid_cpu);
+	if (ret != -ENOENT)
+		return ret;
+
+	key.type = type;
+	btrfs_uuid_to_key(uuid, &key.objectid, &key.offset);
+
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ret = btrfs_insert_empty_item(trans, uuid_root, path, &key,
+				      sizeof(subid_le));
+	if (ret >= 0) {
+		/* Add an item for the type for the first time */
+		eb = path->nodes[0];
+		slot = path->slots[0];
+		offset = btrfs_item_ptr_offset(eb, slot);
+	} else if (ret == -EEXIST) {
+		/*
+		 * An item with that type already exists.
+		 * Extend the item and store the new subid at the end.
+		 */
+		btrfs_extend_item(uuid_root, path, sizeof(subid_le));
+		eb = path->nodes[0];
+		slot = path->slots[0];
+		offset = btrfs_item_ptr_offset(eb, slot);
+		offset += btrfs_item_size_nr(eb, slot) - sizeof(subid_le);
+	} else if (ret < 0) {
+		warning("insert uuid item failed %d (0x%016llx, 0x%016llx) type %u!",
+			ret, (unsigned long long)key.objectid,
+			(unsigned long long)key.offset, type);
+		goto out;
+	}
+
+	ret = 0;
+	subid_le = cpu_to_le64(subid_cpu);
+	write_extent_buffer(eb, &subid_le, offset, sizeof(subid_le));
+	btrfs_mark_buffer_dirty(eb);
+
+out:
+	btrfs_free_path(path);
+	return ret;
+}