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Re: [libvirt-users] Device lease hot unplug and events



On Mon, Oct 15, 2018 at 09:56:39 +0200, Milan Zamazal wrote:
> Peter Krempa <pkrempa redhat com> writes:
> 
> > On Fri, Oct 12, 2018 at 19:33:54 +0200, Milan Zamazal wrote:
> >> Hi, when working on hot unplugs of various devices, I've found out that
> >> hot unplugging <lease> device doesn't generate
> >> VIR_DOMAIN_EVENT_ID_DEVICE_REMOVED event.  <lease> also doesn't have an
> >> alias, so it wouldn't be identifiable in the corresponding callback.
> >> 
> >> Is this difference from other hotpluggable devices intentional?  If yes,
> >
> > Well a "lease" is not a device per-se. It's just libvirt putting it with
> > devices. Currently the "lease" is always successfully removed/unplugged
> > if the API returns success as there is no cooperation with qemu
> > necessary so the semantics of asking the guest OS to do something don't
> > apply.
> 
> I see, thank you for explanation.  Can we rely on the fact that lease
> removal is and remains synchronous or is it a property that can change
> in the future?

In case of the current implementation I don't see a reason why we'd have
to change it. If so it would be for a different "model".

Generally we can't guarantee that some usage will not eventually need it
but we should not change this behaviour, or at least I don't expect us
to.

> 
> >> is there any better way of checking that <lease> removal is completed
> >> than querying and examining the domain XML?  From user's point of view,
> >> it would be best if I could simply handle the device removal event the
> >> same way as with other devices.
> >
> > Yes, we probably should add the event and synthetize it for "lease"
> > since we will not get one from qemu. Also we'll need to add alias for
> > the lease so that the event can be used.
> 
> Since this is what an uninformed user expects (and I believe libvirt
> documentation doesn't contradict), I'd like to have the event + alias.
> Should I file a corresponding bug or RFE?

Yes please.

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