dm_bitset_empty
r = dm_bitset_empty(&cmd->dirty_info, &cmd->dirty_root);
r = dm_bitset_empty(&cmd->discard_info, &cmd->discard_root);
r = dm_bitset_empty(&cmd->bitset_info, &cmd->bitset_root);
r = dm_bitset_empty(info, root);
EXPORT_SYMBOL_GPL(dm_bitset_empty);
int dm_bitset_empty(struct dm_disk_bitset *info, dm_block_t *new_root);