Re: [PATCH v3 0/6] TUN/VirtioNet USO features support.

[Andrew Melnichenko]

Hi all,

On Thu, Sep 8, 2022 at 3:44 AM David Ahern <dsahern@xxxxxxxxxx> wrote:
>
> On 9/7/22 6:50 AM, Andrew Melnychenko wrote:
> > Added new offloads for TUN devices TUN_F_USO4 and TUN_F_USO6.
> > Technically they enable NETIF_F_GSO_UDP_L4
> > (and only if USO4 & USO6 are set simultaneously).
> > It allows the transmission of large UDP packets.
>
> Please spell out USO at least once in the cover letter to make sure the
> acronym is clear.

USO - UDP Segmentation Offload. Ability to split UDP packets into
several segments.
Allows sending/receiving big UDP packets. At some point, it looks like
UFO(fragmentation),
but each segment contains a UDP header.

>
> >
> > Different features USO4 and USO6 are required for qemu where Windows guests can
> > enable disable USO receives for IPv4 and IPv6 separately.
> > On the other side, Linux can't really differentiate USO4 and USO6, for now.
>
> Why is that and what is needed for Linux to differentiate between the 2
> protocols?

Well, this feature requires for Windows VM guest interaction. Windows may have
a separate configuration for USO4/USO6. Currently, we support Windows guests
with enabled USO4 and USO6 simultaneously.
To implement this on Linux host, will require at least one additional
netdev feature
and changes in Linux network stack. Discussion about that will be in
the future after
some research.

>
> > For now, to enable USO for TUN it requires enabling USO4 and USO6 together.
> > In the future, there would be a mechanism to control UDP_L4 GSO separately.
> >
> > New types for virtio-net already in virtio-net specification:
> > https://github.com/oasis-tcs/virtio-spec/issues/120
> >
> > Test it WIP Qemu https://github.com/daynix/qemu/tree/USOv3
> >
> > Andrew (5):
> >   uapi/linux/if_tun.h: Added new offload types for USO4/6.
> >   driver/net/tun: Added features for USO.
> >   uapi/linux/virtio_net.h: Added USO types.
> >   linux/virtio_net.h: Support USO offload in vnet header.
> >   drivers/net/virtio_net.c: Added USO support.
> >
> > Andrew Melnychenko (1):
> >   udp: allow header check for dodgy GSO_UDP_L4 packets.
> >
> >  drivers/net/tap.c               | 10 ++++++++--
> >  drivers/net/tun.c               |  8 +++++++-
> >  drivers/net/virtio_net.c        | 19 +++++++++++++++----
> >  include/linux/virtio_net.h      |  9 +++++++++
> >  include/uapi/linux/if_tun.h     |  2 ++
> >  include/uapi/linux/virtio_net.h |  5 +++++
> >  net/ipv4/udp_offload.c          |  2 +-
> >  7 files changed, 47 insertions(+), 8 deletions(-)
> >
>