Dealing with table names in functions

Is there a safe way to deal with tables being passed into a function,
specifically in terms of what schema they're in? I can just blindly
accept a text string and hope that it's always evaluated in the
correct search_path context, but that doesn't seem so good. OTOH, if
I accept an OID, there's no great way to pass that to most of the
rest of the system... I can cast the OID to regclass, but that
doesn't get me a fully-qualified name.

It would be nice if there was a way to convert an OID into a fully-
qualified name.

I'm working on some partitioning stuff, and I'm currently writing a
function that will return the name of a partition given the parent
table and what period to partition on (ie: day, month, year, etc).

Originally, I thought I'd just accept an OID for the table name, but
I can't think of a safe way to look up that tables schema name
(because I want to return a fully qualified name). Obviously, I can
look in pg_class and pg_namespace, but someone could do a DROP TABLE
between when I do that lookup and when I actually use the name. So I
thought I'd just do a LOCK TABLE... except I need the table name to
do that. Catch-22.
--
Jim Nasby                                            jim@nasby.net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)