[libvirt-users] Device lease hot unplug and events

[Milan Zamazal]

Peter Krempa <pkrempa at redhat.com> writes:

> On Mon, Oct 15, 2018 at 09:56:39 +0200, Milan Zamazal wrote:
>> Peter Krempa <pkrempa at 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.

OK, done: https://bugzilla.redhat.com/1639228