Btrfs: Add backrefs and forward refs for subvols and snapshots

Subvols and snapshots can now be referenced from any point in the directory
tree.  We need to maintain back refs for them so we can find lost
subvols.

Forward refs are added so that we know all of the subvols and
snapshots referenced anywhere in the directory tree of a single subvol.  This
can be used to do recursive snapshotting (but they aren't yet) and it is
also used to detect and prevent directory loops when creating new snapshots.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 75 insertions, 1 deletions

diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
index eb7f765..e9be3ab 100644
--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -84,7 +84,7 @@ int btrfs_find_last_root(struct btrfs_root *root, u64 objectid,
 	int slot;
 
 	search_key.objectid = objectid;
-	search_key.type = (u8)-1;
+	search_key.type = BTRFS_ROOT_ITEM_KEY;
 	search_key.offset = (u64)-1;
 
 	path = btrfs_alloc_path();
@@ -275,3 +275,77 @@ 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, u8 type, u64 ref_id)
+{
+	struct btrfs_key key;
+	int ret;
+	struct btrfs_path *path;
+
+	path = btrfs_alloc_path();
+
+	key.objectid = root_id;
+	key.type = type;
+	key.offset = ref_id;
+
+	ret = btrfs_search_slot(trans, tree_root, &key, path, -1, 1);
+	BUG_ON(ret);
+
+	ret = btrfs_del_item(trans, tree_root, path);
+	BUG_ON(ret);
+
+	btrfs_free_path(path);
+	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, u8 type, 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();
+
+	key.objectid = root_id;
+	key.type = type;
+	key.offset = ref_id;
+
+	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);
+
+	btrfs_free_path(path);
+	return ret;
+}