netdev - Re: [PATCH net 0/2] Lift UDP_SEGMENT restriction for egress via device w/o csum offload

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Date: Sun, 23 Jun 2024 04:18:35 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jakub Sitnicki <jakub@...udflare.com>, 
 netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Willem de Bruijn <willemb@...gle.com>, 
 kernel-team@...udflare.com
Subject: Re: [PATCH net 0/2] Lift UDP_SEGMENT restriction for egress via
 device w/o csum offload

Jakub Sitnicki wrote:
> This is a follow-up to an earlier question [1] if we can make UDP GSO work with
> any egress device, even those with no checksum offload capability. That's the
> default setup for TUN/TAP.
> 
> I leave it to the maintainers to decide if it qualifies as a fix. We plan to
> backport it to our v6.6 either way, hence the submission to -net.
> 
> [1] https://lore.kernel.org/netdev/87jzqsld6q.fsf@cloudflare.com/

Agreed with the change to allow UDP_SEGMENT to work regardless of
device capabilities.

In my opinion this is a new feature with sufficient risk of unintended
side effects to be net-next material.

Maybe worth recording in patch 1 the reason for the original check:
that UDP_SEGMENT with software checksumming in the GSO stack may be
a regression vs copy_and_checksum in the send syscall.

> 
> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> ---
> Jakub Sitnicki (2):
>       udp: Allow GSO transmit from devices with no checksum offload
>       selftests/net: Add test coverage for UDP GSO software fallback
> 
>  net/ipv4/udp.c                        |  3 +--
>  net/ipv4/udp_offload.c                |  8 +++++++
>  net/ipv6/udp.c                        |  3 +--
>  tools/testing/selftests/net/udpgso.c  | 15 +++++++++---
>  tools/testing/selftests/net/udpgso.sh | 43 +++++++++++++++++++++++++++++++++++
>  5 files changed, 65 insertions(+), 7 deletions(-)
>