[libvirt] [PATCH 0/3] Emit event on lease attach/detach

[Daniel P. Berrangé]

On Tue, Apr 23, 2019 at 03:06:22PM +0200, Michal Privoznik wrote:
> On 4/16/19 1:39 AM, Cole Robinson wrote:
> > On 4/5/19 3:57 AM, Michal Privoznik wrote:
> > > Unfortunately, we can't emit VIR_DOMAIN_EVENT_ID_DEVICE_ADDED or
> > > VIR_DOMAIN_EVENT_ID_DEVICE_REMOVED event because that carries device
> > > alias within itself and leases don't have one.
> > > 
> > 
> > Hmm. I understand that <leases> aren't really devices so it doesn't have
> > any direct reason to give it an info structure and assign it an alias.
> > But that's really an argument for why they shouldn't have been  a device
> > to begin with. I presume we did it that way to take advantage of the
> > existing hotplug APIs. But then adding a special purpose event seems
> > like going in the opposite direction.
> > 
> > How invasive is it to add an 'info' bit to lease devices, allocate
> > aliases with the rest of qemu devices, maybe add an ADDRESS_TYPE_LEASE
> > or something that is just an explicit no op for the ADDRESS consumers.
> > My guess is it's not too bad but there could be dragons lurking
> > 
> > There's already places internally where this would simplify things: it's
> > annoying that device iterator code already needs to play games like
> > 'check the address of all devices, oh except leases and graphics which
> > don't have info, oh and hostdev info is a pointer for some reason'
> 
> Yeah, it's annoying, but I remember discussion from when I was introducing
> user aliases. I wanted to just have some dummy element that would not mean
> anything to libvirt but users could set it and then match devices using it
> as a mark. It was rejected because it doesn't map onto anything in qemu.
> Well, nor do leases, nor would their address.
> 
> I don't have a preference here really. But if we wanted to invent addresees
> for leases then I guess we would have to do it for already running domains
> too (when daemon restarts).

My preference is for the new event as this series does. We shouldn't try
to force something to be more like a device when it clearly isn't.


Regards,
Daniel
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