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

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Date:   Wed, 7 Sep 2022 18:44:16 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Andrew Melnychenko <andrew@...nix.com>, edumazet@...gle.com,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        jasowang@...hat.com, mst@...hat.com, pabeni@...hat.com,
        yoshfuji@...ux-ipv6.org
Cc:     yan@...nix.com, yuri.benditovich@...nix.com
Subject: Re: [PATCH v3 0/6] TUN/VirtioNet USO features support.

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.

> 
> 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?

> 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(-)
>