Re: [PATCH v6 11/21] virtio-net: Return an error when vhost cannot enable RSS

[Michael S. Tsirkin]

On Wed, Nov 01, 2023 at 05:35:50PM +0900, Akihiko Odaki wrote:
> On 2023/11/01 15:38, Michael S. Tsirkin wrote:
> > On Wed, Nov 01, 2023 at 01:50:00PM +0900, Akihiko Odaki wrote:
> > > We had another discussion regarding migration for patch "virtio-net: Do 
> > > not
> > > clear VIRTIO_NET_F_HASH_REPORT". It does change the runtime behavior so we
> > > need to take migration into account. I still think the patch does not
> > > require a compatibility flag since it only exposes a new feature and does
> > > not prevent migrating from old QEMU that exposes less features. It instead
> > > fixes the case where migrating between hosts with different tap feature
> > > sets.
> > 
> > When in doubt, add a compat flag.
> 
> Personally I'm confident about the migration compatibility with patch
> "virtio-net: Do not clear VIRTIO_NET_F_HASH_REPORT". virtio-net already does
> the same thing when the tap implementation on the destination implements
> virtio-net header support while the counterpart of the source does not.

Trust me there's been so many times where we were very sure and
problems come up later. Just don't enable new functionality for
old machine types, problem solved. Why is this hard?

-- 
MST