dm_pool_get_free_block_count
int dm_pool_get_free_block_count(struct dm_pool_metadata *pmd,
r = dm_pool_get_free_block_count(pool->pmd, &nr_free);
r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
r = dm_pool_get_free_block_count(pool->pmd, &nr_free_blocks_data);