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Re: [libvirt] [PATCH] qemu: Try multiple times to open unix monitor socket



On Wed, Jul 15, 2009 at 09:49:03AM -0400, Jim Paris wrote:
> Daniel P. Berrange wrote:
> > On Wed, Jul 15, 2009 at 11:40:42AM +0200, Daniel Veillard wrote:
> > > On Tue, Jul 14, 2009 at 06:22:42PM -0400, Cole Robinson wrote:
> > > > Unlike the pty monitor (which we know exists since we scrape its path from
> > > > stdout), we have no way of knowing that the unix monitor socket should exist/
> > > > be initialized. As a result, some of my KVM guests randomly fail to start on
> > > > F10 host.
> > > > 
> > > > Try to open the unix socket in a 3 second timeout loop. Ignore EACCES (path
> > > > does not exist if a first time run) and ECONNREFUSED (leftover socket from
> > > > a previous run hasn't been removed yet). Fixes things for me.
> > > 
> > >   It's always a bit annoying to end up with heuristics like this
> > > but if we don't have any other way, okay, ACK
> > 
> > I don't like it much either, but this is no worse than what we had todo
> > to find the /dev/pts/XXX path where we waited ina  loop for 3 seconds.
> > ACK to this patch
> > 
> > 
> > Long term we'll need to discuss with QEMU developers to find a better
> > way todo this without needing a timeout.  One idea is actually instead
> > of passing a UNIX domain socket path to QEMU, actually create & bind
> > the socket in libvirt and then pass the pre-opened FD to QEMU. This
> > would guarentee that we can instantly connect to the monitor. Of course
> > then the job of waiting passes to the code that sends monitor commands.
> 
> What about qemu's -daemonize option:
> 
> -daemonize 
>    Daemonize the QEMU process after initialization.  QEMU will not
>    detach from standard IO until it is ready to receive connections on
>    any of its devices.  This option is a useful way for external
>    programs to launch QEMU without having to cope with initialization
>    race conditions.
> 
> It looks like it was introduced in 0.9.0.

Hmm, that's a possibility. I'l have to take a look what it does and
whether it wil have any interactions with stuff that libvirt does
in between daemonizing & exec'ing QEMU

Daniel
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