Calling lo_open within user defined C function

I am trying to create a user defined C function that will
be called within  PL/pgSQL

Namely, I need a function that will create a new Large Object and copy
the data
of an existing Large Object into the new Large Object.

This is the way the function would be registered

CREATE FUNCTION copyoid(oid) RETURNS oid  AS '/copyoid.so'  LANGUAGE
'C';

I notice that the lo_create and lo_open functions require a postgres
connection (PGConn)

Oid lo_creat(PGconn *conn, int mode)
int lo_open(PGconn *conn, Oid lobjId, int mode)

Since the function I wish to create will be executed within the backend,

how do I handle the conn (PGconn) variable?

I realize I will need to open the original large object , create a new
large object and then
read the old and write the new until done, and then close both.

Every example I can find opens a connection and then uses the new
connection for these functions.

Is it necessary to create/"open" a connection for code that executes
within the backend ?
.......
Thanks