Re: [Qemu-devel] [libvirt] [PULL 25/26] block: Remove deprecated -drive option serial

[Eric Blake]

On 06/22/2018 09:30 AM, Daniel P. Berrangé wrote:
> > > Perhaps we could use a more structured notification, to make detecting
> > > use of deprecated features programmatically trivial.  A QMP event might
> > > do.
> >
> > Libvirt currently has CI that is largely focused on unit testing. We
> > recently did some work, however, to get our functional test suite
> > working properly again (Sys-Virt-TCK) and are trying to get some
> > new CI hardware. So if we get that running, we coud run tests on real
> > QEMU versions and check the /var/log/libvirt/qemu/$GUEST.logs to
> > make sure we're not triggering unexpected warnings from QEMU
>
> This could be even easier if there was a --no-deprecations flag to
> QEMU which triggered abort() whenever mgmt app uses a deprecated
> feature.

Yes, a QMP event (which libvirt could then turn into a hard error if it 
ever receives the event) or a qemu command line option to make 
deprecated usage fatal (which libvirt would choose to enable) would both 
be pragmatic approaches to quickly vetting whether libvirt is using 
something that qemu has marked deprecated - provided that we are careful 
to always wire up the event/abort into qemu at each location where we 
also add a deprecation message.  An event might be more flexible than 
qemu aborting (as libvirt could make programmatic decisions on whether 
to keep going in spite of the event, rather than the guest 
unconditionally being lost).

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org