On 2023/11/01 18:09, Michael S. Tsirkin wrote:
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?
I see. I'll add a compatibility flag for VIRTIO_NET_F_HASH_REPORT
exposure; it should be quite easy.
