block_map_tree_slot
struct block_map_tree_slot slot = lock->tree_slots[lock->height];
struct block_map_tree_slot tree_slot = lock->tree_slots[height];
struct block_map_tree_slot tree_slot;
tree_slot = (struct block_map_tree_slot) {
struct block_map_tree_slot *tree_slot;
struct block_map_tree_slot tree_slots[VDO_BLOCK_MAP_TREE_HEIGHT + 1];