RE: [virtio-dev] Re: [PATCH v3] virtio-net: Mention VIRTIO_NET_F_HASH_REPORT dependency on VIRTIO_NET_F_CTRL_VQ

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Sunday, February 12, 2023 4:39 AM

[..]
> > This is even better.
> > > Ideally we'll add a "MUST", but since we can't,
> > Lets hear Michael's view, why MUST cannot be done.
> > Based on our discussion here, I think MUST is possible and cleaner without
> breaking any existing sw or device.
> 
> 1.2 is out without this requirement. Making this a MUST at this point would
> declare such previously conformant devices non-conformant.
> So I'm afraid our hands are tied.
> 
Technically yes, I agree it make non conformant.
The device that offered HASH_REPORT without offering CVQ, is extremely rare/narrow case.
I am not sure if anyone would have ever built such a thing just because such description was missing from the spec.
So, I am inclined towards a practical part than purely technical.

But I can live with SHOULD here if you want to stick to strict compliance here.

> It might be a good idea to start building out a charter documenting all kind of
> compat hacks like this such that new devices are not tempted to do the wrong
> thing. I am not sure how this will look exactly though.
> 
We should write a line along with device requirements something like below.

Even though CVQ is not mandatory for HASH_REPORT, it is strong advised the device to NOT report this feature when CTRL_VQ is not advertised.

Once there is better section, more generic table etc can be created.
Since you created the ballot already, I will supply the short patch to add above description later.