[libvirt] [PATCH 1/2] qemu: make sure capability probing process can start

[Jiri Denemark]

On Thu, Oct 09, 2014 at 10:14:48 +0100, Daniel Berrange wrote:
> On Thu, Oct 09, 2014 at 09:58:30AM +0200, Martin Kletzander wrote:
> > When daemon is killed right in the middle of probing a qemu binary for
> > its capabilities, the VM is left running.  Next time the daemon is
> > starting, it cannot start qemu process because the one that's already
> > running does have the pidfile flock()'d.
> 
> I was wondering if there's anything we can easily change in the way
> we launch the QEMU binary so that it automatically dies when libvirtd
> exits, rather than us needing to manually kill it.
> 
> The comments say we have to use daemonize to synchronize with the
> monitor socket creation and I recall we've tried other approaches
> to that before which failed.
> 
> Another idea would be to play with adding '-serial stdio' and then
> when libvirt died stdio would get a broken pipe but I don't think
> it is safe to use -serial when we have -M none so that's out.
> 
> So I guss we don't have much choice but to manually kill.

It would be cool if we could tell QEMU to die when the monitor
connection gets closed. Configuring some predefined actions to be taken
when monitor is closed would be useful in general... we could use that
to automatically cancel migration if QEMU loses connection with libvirt,
for example. I'm not sure how this idea would be taken by QEMU
community, though. I'll try to get opinions on it during KVM Forum. But
even if this is something that could be done, we'd still need Martin's
solution.

Jirka