Open system files total

Hi,

I'd like to know how many total system files Postgresql has open at any
one time.

Is this the easiest way ??

a) Find out how many Postgres process's - `ps aux | grep postgres`
b) For each Postgres process find out which files it has open - `ls
/proc/*postgres_process_id*/fd | wc -l`
c) Add up each Postgres process file open total to work out grand total
of open files for user Postgres.

I know I can get the total for the whole machine using
/proc/user_beancounters but I'd like to know
just for Postgres.

Many thanks
Best regards
Rudi.