netdev - Re: [PATCH bpf 3/3] bpf, selftests: Adapt cls_redirect to call csum

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Message-ID: <65cde627-96af-b99e-7a6f-a688c2c6dbdd@iogearbox.net>
Date:   Tue, 2 Jun 2020 17:48:54 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alan Maguire <alan.maguire@...cle.com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf 3/3] bpf, selftests: Adapt cls_redirect to call
 csum_level helper

On 6/2/20 5:13 PM, Lorenz Bauer wrote:
> On Tue, 2 Jun 2020 at 15:58, Daniel Borkmann <daniel@...earbox.net> wrote:
>>
>> Adapt bpf_skb_adjust_room() to pass in BPF_F_ADJ_ROOM_NO_CSUM_RESET flag and
>> use the new bpf_csum_level() helper to inc/dec the checksum level by one after
>> the encap/decap.
> 
> Just to be on the safe side: we go from
>      | ETH | IP | UDP | GUE | IP | TCP |
> to
>      | ETH | IP | TCP |
> by cutting | IP | UDP | GUE | after the Ethernet header.
> 
> Since IP is never included in csum_level and because GUE is not eligible for
> CHECKSUM_UNNECESSARY we only need to do csum_level-- once, not twice.

Yes, that is correct.