Re: [Qemu-devel] Re: [PATCH 10/15] virtio-serial: Add QMP events for failed port/device add

[Amit Shah]

On (Fri) Mar 26 2010 [01:17:49], Jamie Lokier wrote:
> Luiz Capitulino wrote:
> > On Thu, 25 Mar 2010 09:17:17 +0530
> > Amit Shah <address@hidden> wrote:
> > 
> > > On (Wed) Mar 24 2010 [17:34:15], Luiz Capitulino wrote:
> > > > On Wed, 24 Mar 2010 20:19:28 +0530
> > > > Amit Shah <address@hidden> wrote:
> > > > 
> > > > > When adding a port or a device to the guest fails, management software
> > > > > might be interested in knowing and then cleaning up the host-side of 
> > > > > the
> > > > > port. Introduce QMP events to signal such errors.
> > > > 
> > > >  I'm completely unfamiliar with virtio-serial, so let me ask: how are 
> > > > ports
> > > > added? I'd expect the command performing this operation to fail in this 
> > > > case.
> > > 
> > > If adding the port fails in qemu, then the command will fail. However if
> > > adding the port in the guest fails, we raise this QMP event. Adding in
> > > the guest could fail because of several reasons, like ENOMEM. In this
> > > case, the mgmt might want to hot-unplug the port from qemu so that
> > > resources are freed and also apps are notified of guest side not ready.
> > 
> >  Ok, what about a disconnect? Does virtio-serial have this kind of action?
> 
> Disconnect would be valuable.  E.g. if the guest app dies (but not the
> guest kernel), it won't get a chance to send an "I'm going away"
> message.

That's something applications should be able to handle: If an app on the
guest dies, the app on the host should be able to discover this.

In any case, we have 'open' and 'close' notifications where we trigger
callbacks for the applications if they're interested in such events.
This only works for in-qemu apps, though, so I'm OK with adding a QMP
event for this as well.

> Machine reboot, PCI reset and so on, should probably trigger a

All these messages belong to other subsystems, not virtio-serial. Eg,
libvirt or other mgmt app should know that a reset event, when received,
affects virtio ports as well. Similar for pci events.

                Amit