Setting TCP keepalive for Cyrus daemons

[Bron Gondwana]

On Sat, Feb 13, 2010 at 10:00:52AM -0600, Gary Mills wrote:
> On Sat, Feb 13, 2010 at 09:09:05PM +1100, Bron Gondwana wrote:
> > On Fri, Feb 12, 2010 at 09:45:02AM -0600, Gary Mills wrote:
> > > I'm willing to add a `keepalive' option to Cyrus master along with the
> > > setsockopt() system call to enable that setting.  This option could be
> > > added to the cyrus.conf file for any services that could benefit from
> > > it. Would this be a reasonable addition to Cyrus?
> > 
> > How does this look?
> 
> Wow, you beat me to it!  You even covered all of the settings.

:)

> > +{ "tcp_keepalive", 0, SWITCH }
> > +/* Enable keepalive on TCP connections */
> > +
> > +{ "tcp_keepalive_cnt", 0, INT }
> > +/* Number of TCP keepalive probes to send before declaring the 
> > +   connection dead (0 == system default) */
> > +
> > +{ "tcp_keepalive_idle", 0, INT }
> > +/* Number of seconds a connection must be idle before keepalive
> > +   probes are sent (0 == system default) */
> > +
> > +{ "tcp_keepalive_intvl", 0, INT }
> > +/* Number of seconds between keepalive probes (0 == system default) */
> > 
> > A switch to enable keepalive, plus options to edit each of the
> > tunables.  The full patch is attached - not tested except for
> > a compile yet.
> 
> I can't comment on imap/sync_client.c because I don't use that
> technique.  In master.c, I would have put my changes into
> spawn_service(), just before master exec'ed the daemon.  However,
> putting them where the connection was first accepted should be fine
> too.

I considered that - but I wanted it to be after:

cyrus_init(alt_config, service, 0);

So that you could control options per service.

> One thing to watch is that only SO_KEEPALIVE is standard.  The other
> three symbols: TCP_KEEPCNT, TCP_KEEPIDLE, and TCP_KEEPINTVL only exist
> in some operating systems.  They have global settings but don't have
> per-socket options.  For these, the setsockopt() function calls need
> to be conditional on the symbols.

Hmm - yeah, OK.  I'll protect them with #ifdefs.

> For which Cyrus version is your patch intended.  I'm still running
> cyrus-imapd-2.3.8 .

It's roughly against 2.3-tail (I have a couple more patches in between
that build debian packages and add a .gitignore file, but otherwise it's
2.3-tail).  I'm pretty sure it will backport to 2.3.8 though, that area
of the code hasn't been changed in a while.

Bron.
that far OK.