btrfs_free_space_test_bit
bit_set = btrfs_free_space_test_bit(block_group, path, offset);
prev_bit_set = btrfs_free_space_test_bit(block_group, path, prev_block);
next_bit_set = btrfs_free_space_test_bit(block_group, path, end);
bool btrfs_free_space_test_bit(struct btrfs_block_group *block_group,
bit = btrfs_free_space_test_bit(cache, path, offset);