Ceph » CephFS

    int64_t pool;
    try {
      pool = boost::lexical_cast<unsigned>(tmp);
      if (!osdmap->have_pg_pool(pool))
        return -ENOENT;
    } catch (boost::bad_lexical_cast const&) {
      pool = osdmap->lookup_pg_pool_name(tmp);
      if (pool < 0) {
        return -ENOENT;
      }
    }

Client and MDS will check data pool based on the above code.
If pool name is a positive integer and can be cast to unsigned.
And then, use this name as id to ckeck the pool in osdmap.
If there is no pool with this id, it will return -ENOENT and no longer check as a pool name.