netdev - Re: [PATCH net-next 12/16] selftests: forwarding: lib: Add helpers for checksum handling

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Date:   Sun, 29 Jan 2023 12:10:22 +0200
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     Petr Machata <petrm@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>, netdev@...r.kernel.org
Cc:     bridge@...ts.linux-foundation.org, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 12/16] selftests: forwarding: lib: Add helpers
 for checksum handling

On 26/01/2023 19:01, Petr Machata wrote:
> In order to generate IGMPv3 and MLDv2 packets on the fly, we will need
> helpers to calculate the packet checksum.
> 
> The approach presented in this patch revolves around payload templates
> for mausezahn. These are mausezahn-like payload strings (01:23:45:...)
> with possibly one 2-byte sequence replaced with the word PAYLOAD. The
> main function is payload_template_calc_checksum(), which calculates
> RFC 1071 checksum of the message. There are further helpers to then
> convert the checksum to the payload format, and to expand it.
> 
> For IPv6, MLDv2 message checksum is computed using a pseudoheader that
> differs from the header used in the payload itself. The fact that the
> two messages are different means that the checksum needs to be
> returned as a separate quantity, instead of being expanded in-place in
> the payload itself. Furthermore, the pseudoheader includes a length of
> the message. Much like the checksum, this needs to be expanded in
> mausezahn format. And likewise for number of addresses for (S,G)
> entries. Thus we have several places where a computed quantity needs
> to be presented in the payload format. Add a helper u16_to_bytes(),
> which will be used in all these cases.
> 
> Signed-off-by: Petr Machata <petrm@...dia.com>
> ---
>  tools/testing/selftests/net/forwarding/lib.sh | 56 +++++++++++++++++++
>  1 file changed, 56 insertions(+)
> 

Acked-by: Nikolay Aleksandrov <razor@...ckwall.org>