Re: [virtio-dev] [PATCH] virtio-net: use mtu size as buffer length for big packets

[Jason Wang <jasowang@redhat.com>]

On Tue, Aug 9, 2022 at 5:22 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Tue, Aug 09, 2022 at 03:44:22PM +0800, Jason Wang wrote:
> > > @@ -3571,8 +3581,10 @@ static int virtnet_probe(struct virtio_device
> > > *vdev)
> > >       if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> > >           virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> > >           virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_ECN) ||
> > > -         virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO))
> > > +         virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_UFO)) {
> > >               vi->big_packets = true;
> > > +             vi->gso_is_supported = true;
> > >
> > > Please do the same for virtnet_clear_guest_offloads(), and
> > > correspondingly virtnet_restore_guest_offloads() as well. Not sure why
> > > virtnet_clear_guest_offloads() or the caller doesn't unset big_packet on
> > > successful return, seems like a bug to me.
> >
> > It is fine as long as
> >
> > 1) we don't implement ethtool API for changing guest offloads
> > 2) big mode XDP is not enabled
> >
> > So that code works only for XDP but we forbid big packets in the case
> > of XDP right now.
> >
> > Thanks
>
> To put it another way, changing big_packets after probe requires a bunch
> of work as current code assumes this flag never changes.
> Adding a TODO to handle dynamic offload config is fine but
> I don't think it should block this.

Yes, this is what I mean.

Thanks

>
> --
> MST
>