tablespace_oid alias?

Hi all,

I want to get the databases that correspond to a certain tablespace
through a call to pg_tablespace_databases(tablespace_oid)

Which would be the OID alias type for tablespace_oid?

I've tried:
# select pg_tablespace_databases('pg_default'::XXX);

with XXΧ as any of the OID aliases mentioned in the manual's chapter 8
section on "Object Iddentifier Types", but without success.

Any hints? Missing something?


TIA,
Thalis K.