Tablespace OID, database OID, relfilenode

Hi!
Quick and to the point:

If i execute
select pg_relation_filepath('pgbench_accounts');

I get
pg_relation_filepath
----------------------
base/5/16398

where "base" is tablespace, but not tablespace OID, nor tablespace name.
How do I link it to get from "base" the tablespace OID?

Or, in other words, given table pgbench_accounts, how do I get tablespace
OID, database OID and relfilenode so that I can use this info to filter
output of pg_waldump?

Thanks a ton!