From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:49153) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RjGFj-0004MH-70 for qemu-devel@nongnu.org; Fri, 06 Jan 2012 15:19:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RjGFh-0001HA-NV for qemu-devel@nongnu.org; Fri, 06 Jan 2012 15:19:03 -0500 Received: from mx1.redhat.com ([209.132.183.28]:3535) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RjGFh-0001H3-FH for qemu-devel@nongnu.org; Fri, 06 Jan 2012 15:19:01 -0500 Date: Fri, 6 Jan 2012 18:18:32 -0200 From: Luiz Capitulino Message-ID: <20120106181832.74e0163f@doriath> In-Reply-To: <4F075505.3000100@linux.vnet.ibm.com> References: <4F062390.6070007@intellilink.co.jp> <4F063DD2.3080104@linux.vnet.ibm.com> <20120106105619.GG14293@redhat.com> <4F0728BA.6020106@linux.vnet.ibm.com> <20120106170553.GA15223@redhat.com> <20120106170637.6f4b25fd@doriath> <4F075505.3000100@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] GuestAgent: PIDFILE remains when daemon start fails List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michael Roth Cc: Kazuo Tanaka , "MATSUDA, Daiki" , qemu-devel@nongnu.org On Fri, 06 Jan 2012 14:09:41 -0600 Michael Roth wrote: > On 01/06/2012 01:06 PM, Luiz Capitulino wrote: > > On Fri, 6 Jan 2012 17:05:53 +0000 > > "Daniel P. Berrange" 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 > > >