netdev - Re: [PATCH net v2 3/4] udp: do not transition UDP fraglist to unnecessary checksum

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Date: Thu, 21 Mar 2024 18:22:59 +0100
From: Antoine Tenart <atenart@...nel.org>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Cc: steffen.klassert@...unet.com, willemdebruijn.kernel@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net v2 3/4] udp: do not transition UDP fraglist to unnecessary checksum

Quoting Willem de Bruijn (2024-03-21 15:58:17)
> Antoine Tenart wrote:
> > 
> > If I sum up our discussion CHECKSUM_NONE conversion is wanted,
> > CHECKSUM_UNNECESSARY conversion is a no-op and CHECKSUM_PARTIAL
> > conversion breaks things. What about we just convert CHECKSUM_NONE to
> > CHECKSUM_UNNECESSARY?
> 
> CHECKSUM_NONE cannot be converted to CHECKSUM_UNNECESSARY in the
> receive path. Unless it is known to have been locally generated,
> this means that the packet has not been verified yet.

I'm not sure to follow, non-partial checksums are being verified by
skb_gro_checksum_validate_zero_check in udp4/6_gro_receive before ending
up in udp4/6_gro_complete. That's also probably what the original commit
msg refers to: "After validating the csum, we mark ip_summed as
CHECKSUM_UNNECESSARY for fraglist GRO packets".

With fraglist, the csum can then be converted to CHECKSUM_UNNECESSARY.
Except for CHECKSUM_PARTIAL, as we discussed.

Does that make sense? Anything we can do to help moving this forward?

Thanks!
Antoine