pg_autovacuum start-script

I'm about to try to implement a simple pg_autovacuum script that can be
used in conjunction with or integrated entirely with the contrib
start-scripts for postgres. I just want to check that what I'm doing
has the appropriate sanity checks.

The behavior I'm considering is:

if pg_ctl status returns a good value then
if pg_autovacuum is not running then
start pg_autovacuum
else
error
else
error

Based on what I (think I) know, this covers the cases where:

1. There is not a valid instance of postgres running.
2. There is already a valid instance of pg_autovacuum running (which
can still run as a daemon even in the event that postgres is stopped,
IIRC).
3. It is safe to start pg_autovacuum because neither of the above cases
holds.

Is this logic sufficiently sane?

In a subsequent iteration, I could even warn, I suppose, if the script
discovered any vacuums (whether initiated by pg_autovacuum or no)
already running.

-tfo