usage_skip
result = __bfs_forwards(root, &usage_mask, usage_match, usage_skip, target_entry);
result = __bfs_backwards(root, &usage_mask, usage_match, usage_skip, target_entry);
ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, usage_skip, NULL);
ret = check_path(target, &src_entry, hlock_equal, usage_skip, &target_entry);