RE: [PATCH v2 1/2] virtio-net: Fix receive buffer size calculation text

[Parav Pandit <parav@nvidia.com>]

> From: Cornelia Huck <cohuck@redhat.com>
> Sent: Tuesday, January 16, 2024 4:33 PM
> To: Parav Pandit <parav@nvidia.com>; virtio-comment@lists.oasis-open.org;
> mst@redhat.com
> Cc: Shahaf Shuler <shahafs@nvidia.com>; xuanzhuo@linux.alibaba.com;
> yuri.benditovich@daynix.com
> Subject: RE: [PATCH v2 1/2] virtio-net: Fix receive buffer size calculation text
> 
> On Tue, Jan 16 2024, Parav Pandit <parav@nvidia.com> wrote:
> 
> >> From: Cornelia Huck <cohuck@redhat.com>
> >> Sent: Monday, January 15, 2024 10:14 PM
> >
> >> On Mon, Jan 15 2024, Parav Pandit <parav@nvidia.com> wrote:
> >> > +The driver MUST consider size of field \field{struct
> >> > +virtio_net_hdr}
> >> > +20 bytes if VIRTIO_NET_F_HASH_REPORT is negotiated, and 12 bytes
> >> > +if
> >> not.
> >> > +
> >>
> >> Requiring the driver to consider the size of something to be its
> >> actual size seems a bit odd :) I don't think we need this, as the
> >> length can be derived from looking at the definitions, and is already
> >> spelled out explicitly, if you consider my suggestion above.
> > We need this because tx side also needs to refer to the virtio_net_hdr in
> patch 2 to be same as that of the rx side.
> > And hence, this normative sets base line for tx side too. Relying on rest of the
> receive packet normative is not enough.
> 
> Hm, why? If struct virtio_net_hdr is well-defined, its size is well-defined as
> well, and we do not need to state it explictly?
Because, 
the size of virtio_net_hdr is derived from the rx side features.
Today there is no normative line that says that even though you are using A, B, C Rx features, due to which your tx side virtio_net_hdr also changes.
The 2nd patch in this series adds this explicit normative as explained in the cover letter.