linux-kernel - Re: [PATCH bpf-next] selftests/bpf: Fix compile error when MPTCP not support

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Message-ID: <abb72d1b-3347-4493-9a18-43c1655b7449@kernel.org>
Date: Wed, 30 Oct 2024 11:49:58 +0100
From: Matthieu Baerts <matttbe@...nel.org>
To: Tao Chen <chen.dylane@...il.com>, Mat Martineau <martineau@...nel.org>,
 Geliang Tang <geliang@...nel.org>, Andrii Nakryiko <andrii@...nel.org>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Martin KaFai Lau <martin.lau@...ux.dev>,
 Yonghong Song <yonghong.song@...ux.dev>, Jiri Olsa <jolsa@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, mptcp@...ts.linux.dev
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix compile error when MPTCP not
 support

Hi Tao Chen,

Thank you for having shared this patch.

On 30/10/2024 11:01, Tao Chen wrote:
> Fix compile error when MPTCP feature not support, though eBPF core check
> already done which seems invalid in this situation, the error info like:
> progs/mptcp_sock.c:49:40: error: no member named 'is_mptcp' in 'struct
> tcp_sock'
>    49 |         is_mptcp = bpf_core_field_exists(tsk->is_mptcp) ?
> 
> The filed created in new definitions with eBPF core feature to solve
> this build problem, and test case result still ok in MPTCP kernel.
> 
> 176/1   mptcp/base:OK
> 176/2   mptcp/mptcpify:OK
> 176     mptcp:OK
> Summary: 1/2 PASSED, 0 SKIPPED, 0 FAILED
> 
> Fixes: 8039d353217c ("selftests/bpf: Add MPTCP test base")

The commit you mentioned here is more than 2 years old, and as far as I
can see, nobody else reported this compilation issue. I guess that's
because people used tools/testing/selftests/bpf/config file as expected
to populate the kernel config, and I suppose you didn't, right?

I don't think other BPF selftests check for missing kernel config if
they are specified in the 'config' file, but even if it is the case, I
think it would be better to skip all the MPTCP tests, and not try to
have them checking something that doesn't exist: no need to validate
these tests if the expected kernel config has not been enabled.

But again, please correct me if I'm wrong, but I don't think there is
anything to change here to fix your compilation issue: simply make sure
to use this tools/testing/selftests/bpf/config file to generate your
kernel config, no?

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.