RE: [virtio-comment] Re: [PATCH v1 3/8] device-context: Define the device context fields for device migration

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Wednesday, October 25, 2023 3:59 PM
> 
> On Wed, Oct 25, 2023 at 10:22:03AM +0000, Parav Pandit wrote:
> > > From: Michael S. Tsirkin <mst@redhat.com>
> > > Sent: Wednesday, October 25, 2023 3:50 PM
> > >
> > > On Wed, Oct 25, 2023 at 09:50:02AM +0000, Parav Pandit wrote:
> > > > Hence, I believe device context as defined now is still reusable
> > > > as common
> > > building block.
> > > > For non-passthrough, such hypervisor can simply ignore the fields
> > > > which it is
> > > not interested in.
> > >
> > > Interesting. So a hypervisor encounters a field it does not
> > > recognize. How does hypervisor know that a field is safe to ignore?
> >
> > In v2 all the supported fields are published in a query command.
> > If hypervisor wants to know the precise fields of interest, when the device
> reports unknown field, it can make its decision to ignore or fail to work.
> 
> It really can't make any decisions here. Some fields are safe to ignore, some are
> not but how can you tell?
If there are unknown fields that can appear, hypervisor can avoid operating this device.
It does not have to be attributed as mandatory/optional fields.