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

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Message-ID: <3bc02b33-421e-4c95-8f69-33ec89782621@gmail.com>
Date: Wed, 30 Oct 2024 19:12:54 +0800
From: Tao Chen <chen.dylane@...il.com>
To: Matthieu Baerts <matttbe@...nel.org>, 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

在 2024/10/30 18:49, Matthieu Baerts 写道:
> 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?
>

Hi Matt, thank you for your reply, as you said, i did not use 
tools/testing/selftests/bpf/config to compile kernel, i will use this 
helpful
feature.

> 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.
> 

If i use the kernel not support MPTCP, the compile error still exists, 
and i can not build the bpf test successfully. Maybe skill the test case 
seems better when kernel not support. Now that bpf_core_field_exists 
check already used in the code, i think it is better to use new 
definition mode.

> 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


-- 
Best Regards
Dylane Chen