Re: [PATCH v4 14/16] qapi: deprecate "device" field of DEVICE_* events

[Vladimir Sementsov-Ogievskiy]

On 14.02.23 14:57, Markus Armbruster wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
>
> > On Tue, Feb 14, 2023 at 09:54:22AM +0100, Markus Armbruster wrote:
> > > Daniel P. Berrangé <berrange@redhat.com> writes:
> > >
> > > > On Mon, Feb 13, 2023 at 05:01:01PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> > > > > The device field is redundant, because QOM path always include device
> > > > > ID when this ID exist.
> > > >
> > > > The flipside to that view is that applications configuring QEMU are
> > > > specifying the device ID for -device (CLI) / device_add (QMP) and
> > > > not the QOM path. IOW, the device ID is the more interesting field
> > > > than QOM path, so feels like the wrong one to be dropping.
> > >
> > > QOM path is a reliable way to identify a device.  Device ID isn't:
> > > devices need not have one.  Therefore, dropping the QOM path would be
> > > wrong.
> > >
> > > > Is there any real benefit to dropping this ?
> > >
> > > The device ID is a trap for the unwary: relying on it is fine until you
> > > run into a scenario where you have to deal with devices lacking IDs.
> >
> > When a mgmt app is configuring QEMU though, it does it exclusively
> > with device ID values. If I add a device "-device foo,id=dev0",
> > and then later hot-unplug it "device_del dev0", it is pretty
> > reasonable to then expect that the DEVICE_DELETED even will then
> > include the ID value the app has been using elsewhere.
>
> The management application would be well advised to use QOM paths with
> device_del, because only that works even for devices created by default
> (which have no ID), and devices the user created behind the management
> application's back.
>
> > If the mgmt app is using IDs everywhere when dealing with a device,
> > then trap effectively doesn't exist for their usage scenario.

What if we go one step further and deprecate "id" in device_add / device_del as 
well?

So that user will have to use qom path also in device_add. We may return an error if user 
don't specify "machine/peripheral/" prefix.. Or allow to create device with any 
QOM path?

--
Best regards,
Vladimir