Re: RE: [virtio-comment] [PATCH 2/2] virtio-net: Clarify the size of the struct virtio_net_hdr for tx

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Wed, 13 Dec 2023 06:23:35 +0000, Parav Pandit <parav@nvidia.com> wrote:
>
> > From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > Sent: Wednesday, December 13, 2023 11:33 AM
> >
> > On Fri, 10 Nov 2023 14:40:40 +0200, Parav Pandit <parav@nvidia.com>
> > wrote:
> > > The feature VIRTIO_NET_F_HASH_REPORT only applies to the receive side.
> > > However, when VIRTIO_NET_F_HASH_REPORT feature was introduced, it
> > was
> > > not clarified that the size of the struct virtio_net_hdr on the packet
> > > transmission also uses higher size when VIRTIO_NET_F_HASH_REPORT is
> > > negotiated.
> > >
> > > Explicitly clarify this.
> > >
> > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/183
> > > Signed-off-by: Parav Pandit <parav@nvidia.com>
> > > ---
> > >  device-types/net/description.tex | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/device-types/net/description.tex
> > > b/device-types/net/description.tex
> > > index f5647d4..00ea58d 100644
> > > --- a/device-types/net/description.tex
> > > +++ b/device-types/net/description.tex
> > > @@ -531,6 +531,12 @@ \subsubsection{Packet
> > > Transmission}\label{sec:Device Types / Network Device / De
> > >
> > >  \drivernormative{\paragraph}{Packet Transmission}{Device Types /
> > > Network Device / Device Operation / Packet Transmission}
> > >
> > > +If VIRTIO_NET_F_HASH_REPORT is not negotiated, the size of the field
> > > +\field{struct virtio_net_hdr} is 12 bytes.
> > > +
> > > +If VIRTIO_NET_F_HASH_REPORT is negotiated, the size of the field
> > > +\field{struct virtio_net_hdr} is 20 bytes.
> > > +
> >
> > If we need a new feature, because that the implement of the current linux
> > kernel has the same size on the tx patch.
>
> I didn't understand your comment -  "if we need a new feature" part.
>
> Current Linux kernel has same size for tx and rx, snippet below.
>
>         if (vi->has_rss_hash_report)
>                 vi->hdr_len = sizeof(struct virtio_net_hdr_v1_hash);
>
> So if you are asking if we need a new feature bit? I believe, we don't need a new feature bit for current implementations and behavior.
>
> We will new feature bit in future to have shorter virtio_net_hdr on tx, however we better consume it as part of new inline descriptor format.

Sorry, I missed something.

One question, for "If VIRTIO_NET_F_HASH_REPORT is not negotiated", should we
consider the legacy mode.

Thanks.