Re: [PATCH 1/1] softmmu: fix device deletion events with -device JSON syntax

[Daniel P . Berrangé]

On Wed, Jan 05, 2022 at 04:00:54PM +0100, Laurent Vivier wrote:
> On 05/01/2022 15:55, Daniel P. Berrangé wrote:
> > On Wed, Jan 05, 2022 at 03:49:12PM +0100, Laurent Vivier wrote:
> > > On 05/01/2022 13:38, Daniel P. Berrangé wrote:
> > > > The -device JSON syntax impl leaks a reference on the created
> > > > DeviceState instance. As a result when you hot-unplug the
> > > > device, the device_finalize method won't be called and thus
> > > > it will fail to emit the required DEVICE_DELETED event.
> > > > 
> > > > A 'json-cli' feature was previously added against the
> > > > 'device_add' QMP command QAPI schema to indicated to mgmt
> > > > apps that -device supported JSON syntax. Given the hotplug
> > > > bug that feature flag is no unusable for its purpose, so
> > > 
> > > Not sure to understand: do you mean "now unusable"?
> > 
> > An application wants to known whether QEMU can support JSON
> > syntax with -device. If they look for the 'json-cli' feature
> > as a witness, they'll end up using JSON with QEMU 6.2 which
> > is giving them broken hotplug. This is unusable for any
> > non-trivial use cases. So we need a new witness to indicate
> > whether JSON is viable with -device, that only the newly
> > fixed QEMU will report.
> 
> I understand that, my problem was with your sentence:
> 
> "Given the hotplug bug that feature flag is no unusable for its purpose"

What's the problem with that ? It is reasonabled to say a -device impl
which is broken for hotplug is not usable for non-toy use cases.

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 :|