Re: [Qemu-devel] [PATCH 0/1] add exit-script option to qemu

[Daniel P . Berrangé]

On Fri, Oct 05, 2018 at 08:56:27AM +0200, Dominik Csapak wrote:
> On 10/4/18 3:51 PM, Daniel P. Berrangé wrote:
> > On Wed, Oct 03, 2018 at 11:13:43AM +0200, Dominik Csapak wrote:
> > > this patch aims to execute a script when qemu exits
> > > so that one can do cleanups when using --daemonize without
> > > having to use the qmp monitor
> > 
> > IMHO the idea of cleanup scripts run by QEMU itself is flawed.
> > QEMU will inevitably crash before cleanup scripts can be run,
> > so whatever mgmt app is using QEMU needs to be able to do
> > cleanup without QEMU's help.
> > 
> > I think this can be done more reliably with a wrapper script,
> > that spawns QEMU, waits for it to exit and then calls the
> > cleanup script. On Linux at least you can use prctl() with
> > PR_SET_CHILD_SUBREAPER so you can detect exit'ing of QEMU
> > even after it has daemonized.
> > 
> > Perhaps we could have such a wrapper script put in the
> > contrib directory
> > 
> > Regards,
> > Daniel
> > 
> Hi,
> 
> for cleaning up after qemu crashes, you are completely right,
> (ignoring that the downscript for tap devices also never gets executed
> then), but this series has another use.
> 
> With it, a user can determine the reason of a graceful shutdown
> (e.g., if it was by a signal, qmp or from inside) of qemu,
> especially when using -no-reboot without using qmp
> 
> and using qmp for that is not very practical for everyone,
> or is there another way for that which i am missing?

Honestly QMP *is* the right answer. We've put alot of effort into QMP
and I don't think it is sensible to start adding new mechanisms to
provide the same information in an adhoc manner.

What makes you think QMP isn't practical to use ?  We have client
impls that talk to QMP in scripts/qmp that are just a few 100 lines
of pretty simple python code.

Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|