350 	/* List of upper level edges, which link this node to its parents */
351 	struct list_head upper;  member
372 	 * 1 if corresponding block has been COWed but some upper level block
387 #define UPPER	1  macro
390  * Represent an edge connecting upper and lower backref nodes.
394 	 * list[LOWER] is linked to btrfs_backref_node::upper of lower level
395 	 * node, and list[UPPER] is linked to btrfs_backref_node::lower of
396 	 * upper level node.
398 	 * Also, build_backref_tree() uses list[UPPER] for pending edges, before
399 	 * linking list[UPPER] to its upper level nodes.
413 	 * List of blocks that have been COWed but some block pointers in upper
457 					   struct btrfs_backref_node *upper,  in btrfs_backref_link_edge()  argument
460 	ASSERT(upper && lower && upper->level == lower->level + 1);  in btrfs_backref_link_edge()
462 	edge->node[UPPER] = upper;  in btrfs_backref_link_edge()
464 		list_add_tail(&edge->list[LOWER], &lower->upper);  in btrfs_backref_link_edge()
466 		list_add_tail(&edge->list[UPPER], &upper->lower);  in btrfs_backref_link_edge()
520 	ASSERT(list_empty(&node->upper));  in btrfs_backref_drop_node()