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

[Parav Pandit <parav@nvidia.com>]

> From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Sent: Wednesday, December 13, 2023 12:13 PM
> 
> On Fri, 10 Nov 2023 14:40:39 +0200, Parav Pandit <parav@nvidia.com>
> wrote:
> > Receive buffer size calculation is based on the following negotiated
> > features.
> >
> > The text has wrong calculation for IPv6 and also it has missed
> > VIRTIO_NET_F_HASH_REPORT.
> >
> > The problem of igorance of VIRTIO_NET_F_HASH_REPORT is reported in
> > [1], however fix for ipv6 payload length must also be considered.
> >
> > Since for the both the fixes touching same requirements, a new issue
> > is created as [2].
> >
> > This patch brings following fixes.
> >
> > 1. Fix annotating struct virtio_net_hdr as field 2. Fix receive buffer
> > calculation for guest GSO cases to consider
> >    ipv6 payload length
> > 3. small grammar corrections for article 4. reword the requirement to
> > consider the virtio_ndr_hdr which is
> >    depends on the negotiated feature, hence first clarify the
> >    struct virtio_net_hdr size
> >
> > [1] https://github.com/oasis-tcs/virtio-spec/issues/170
> > [2] https://github.com/oasis-tcs/virtio-spec/issues/183
> >
> > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/170
> > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/183
> > Signed-off-by: Parav Pandit <parav@nvidia.com>
> > ---
> >  device-types/net/description.tex | 25 ++++++++++++++++++-------
> >  1 file changed, 18 insertions(+), 7 deletions(-)
> >
> > diff --git a/device-types/net/description.tex
> > b/device-types/net/description.tex
> > index 96f7dc5..f5647d4 100644
> > --- a/device-types/net/description.tex
> > +++ b/device-types/net/description.tex
> > @@ -660,24 +660,35 @@ \subsubsection{Setting Up Receive
> > Buffers}\label{sec:Device Types / Network Devi  If the
> > VIRTIO_NET_F_GUEST_TSO4, VIRTIO_NET_F_GUEST_TSO6,
> > VIRTIO_NET_F_GUEST_UFO, VIRTIO_NET_F_GUEST_USO4 or
> > VIRTIO_NET_F_GUEST_USO6  features are used, the maximum incoming
> > packet -will be to 65550 bytes long (the maximum size of a -TCP or UDP
> > packet, plus the 14 byte ethernet header), otherwise
> > -1514 bytes.  The 12-byte struct virtio_net_hdr is prepended to this,
> > -making for 65562 or 1526 bytes.
> > +will of size 65589 bytes long (14 bytes of Ethernet header, plus 40
> > +bytes of the IPv6 header, plus 65535 bytes of maximum IPv6 payload
> > +including any extension header) otherwise 1514 bytes.
> > +When VIRTIO_NET_F_HASH_REPORT is not negotiated, the required receive
> > +buffer size is either 65601 or 1526 bytes.
> > +When VIRTIO_NET_F_HASH_REPORT is negotiated, the required receive
> > +buffer size is either 65609 or 1534 bytes.
> >
> >  \drivernormative{\paragraph}{Setting Up Receive Buffers}{Device Types
> > / Network Device / Device Operation / Setting Up Receive Buffers}
> >
> > +If VIRTIO_NET_F_HASH_REPORT is not negotiated, the size of the field
> > +\field{struct virtio_net_hdr} is 12 bytes.
> > +
I realized just now, that above normative is incorrect due to optional VIRTIO_NET_F_MRG_RXBUF.
I will remove/reword it.

> > +If VIRTIO_NET_F_HASH_REPORT is negotiated, the size of the field
> > +\field{struct virtio_net_hdr} is 20 bytes.
> 
> For the receive side, is these needed?
> 
For uniformity between tx and rx I thought it is useful as it is not covered anywhere else in the normative.

> Other is ok to me.
> 
> Thanks