Re: VIRTIO_NET_HDR_F_RSC_INFO in virtio-net vs headers update

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Apr 27, 2020 at 11:10:29AM +0200, Cornelia Huck wrote:
> On Mon, 27 Apr 2020 16:41:30 +0800
> Jason Wang <jasowang@redhat.com> wrote:
> 
> > 
> > On 2020/4/27 下午3:33, Cornelia Huck wrote:
> > > Hi,
> > >
> > > I'm currently trying to prepare a linux-headers update to 5.7-rc3,
> > > which adds the definition of VIRTIO_NET_HDR_F_RSC_INFO.
> > >
> > > Unfortunately, this breaks the build of virtio-net, because now
> > > virtio_net_rsc_ext_num_{packets,dupacks} are undefined (they are
> > > guarded by existence of VIRTIO_NET_HDR_F_RSC_INFO).
> > >
> > > What is the right way to fix this? Remove the constants that are now
> > > provided by the header and keep the definitions of
> > > virtio_net_rsc_ext_num_{packets,dupacks}?
> > 
> > 
> > We probably need to add a version of the above function when 
> > VIRTIO_NET_HDR_F_RSC_INFO is defined as attached.
> > 
> > But I fail to understand why we need a fallback when 
> > VIRTIO_NET_HDR_F_RSC_INFO is not defined.
> 
> Yes, the current code in virtio-net looks a bit odd, which is why I
> asked.
> 
> I see two options:
> - do the change you proposed, do the headers update, and then rip out
>    the compat handling
> - do the above in a single step
> 
> I'd prefer the second option.

Slight preference for 1st one but both are ok.

> > 
> > Thanks
> > 
> > 
> > >
> > > [I'd like to queue a headers update as soon as possible, as the whole
> > > s390 protected virt stuff depends on it...]
> > >
> > >