RE: [virtio-comment] 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, February 6, 2024 10:32 PM
> 
> On Mon, Feb 05 2024, Parav Pandit <parav@nvidia.com> wrote:
> 
> >> From: Cornelia Huck <cohuck@redhat.com>
> >> Sent: Monday, February 5, 2024 8:50 PM
> >>
> >> On Tue, Jan 16 2024, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >>
> >> > On Tue, Jan 16, 2024 at 01:18:59PM +0000, Parav Pandit wrote:
> >> >>
> >> >> > From: Cornelia Huck <cohuck@redhat.com>
> >> >> > Sent: Tuesday, January 16, 2024 6:08 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: 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
> >>
> >> My comment here still holds.
> >>
> > It is a variable length data structure with few trailing fields as not valid.
> > The "actual size" depends on negotiated feature bit, which is what is written
> here.
> >
> > How about below?
> >
> > When calculating the size of \field{struct virtio_net_hdr}, the driver
> > must consider all the fields inclusive up to \field{padding_reserved},
> > i.e. 20 bytes if VIRTIO_NET_F_HASH_REPORT is negotiated, and 12 bytes if
> not.
> 
> It's up to padding_reserved with F_HASH_REPORT and up to num_buffers if
> not, isn't it?

Yes, shall I send v4 as?
When calculating the size of \field{struct virtio_net_hdr}, the driver must consider all the fields inclusive up to \field{padding_reserved},
i.e. 20 bytes if VIRTIO_NET_F_HASH_REPORT is negotiated, and upto \field{num_buffers}, i.e. 12 bytes if not.