On Fri, 06 Jan 2012 14:09:41 -0600 Michael Roth <mdr...@linux.vnet.ibm.com> wrote:
> On 01/06/2012 01:06 PM, Luiz Capitulino wrote: > > On Fri, 6 Jan 2012 17:05:53 +0000 > > "Daniel P. Berrange"<berra...@redhat.com> wrote: > > > >> On Fri, Jan 06, 2012 at 11:00:42AM -0600, Michael Roth wrote: > >>> On 01/06/2012 04:56 AM, Daniel P. Berrange wrote: > >>>> On Thu, Jan 05, 2012 at 06:18:26PM -0600, Michael Roth wrote: > >>>>> On 01/05/2012 04:26 PM, MATSUDA, Daiki wrote: > >>>>>> Hi, all. > >>>>>> > >>>>>> I am trying QEMU Guest Agent and encountered a small bug. It is that > >>>>>> the > >>>>>> PIDFILE remains when daemon start fails. And maybe forgotton to > >>>>>> g_free(). > >>>>>> > >>>>>> MATSUDA, Daiki > >>>>>> > >>>>> > >>>>> Thanks for the patch. There was some contention in the past about > >>>>> whether or not to clean up pidfiles when there was abnormal > >>>>> termination, but personally I like this approach better. > > > > Ok, but can't we use atexit() instead then? > > I guess I prefer it to this patch, but I don't believe that covers > segfaults and the like, so maybe a combination of atexit() and F_SETLK > would be best (as F_SETLK can still leave stale PID files, they just > wouldn't obstruct subsequent instances, but we should still clean them > up whenever we can) Agreed. > > > > >>>> > >>>> Yep, this still leaves open the problem of pidfile cleanup when the > >>>> daemon crashes. For libvirtd we recently switched over to a crash-safe > >>>> pidfile acquisition design, that uses fcntl(F_SETLK) to maintain > >>>> exclusive access over the pidfile. With this you don't need to worry > >>>> about forgetting to unlink() on termination, since the POSIX lock is > >>>> automatically released when process exits (or crashes). > >>> > >>> Yup, we did the same at some point via lockf(). An argument was made > >>> that stale PID files from unresolved crashes should stick around, so > >>> we dropped it. I think we should re-evaluate that decision...libvirt > >>> taking the same approach is pretty good precedence for me. I don't > >>> expect to have state from crashed programs interrupting attempts to > >>> restart them, it's more an unpleasant surprise than a feature, I > >>> think. > > > > Ok, I'll agree with you this time. Let's do it. > > > >> > >> Yeah, I think that is rather unpleasant, particularly for something > >> like qemu guest agent, which we want to try to ensure is reliably > >> running. In any case, if qemu guest agent is being launched by > >> something like SystemD, then you can configure whether systemd > >> will auto-restart it when it dies with non-zero exit status, so > >> I don't think we should delibrately leave stale pidfiles for that > >> scenario. > >> > >> Regards, > >> Daniel > > >
