linux-kernel - Re: [PATCH bpf-next 3/4] selftests/bpf: Add mptcp subflow example

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Date: Tue, 7 May 2024 07:49:36 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Cc: MPTCP Upstream <mptcp@...ts.linux.dev>, Mat Martineau <martineau@...nel.org>, 
	Geliang Tang <geliang@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, Mykola Lysenko <mykolal@...com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, 
	Nicolas Rybowski <nicolas.rybowski@...sares.net>, Geliang Tang <tanggeliang@...inos.cn>
Subject: Re: [PATCH bpf-next 3/4] selftests/bpf: Add mptcp subflow example

On Tue, May 7, 2024 at 3:53 AM Matthieu Baerts (NGI0)
<matttbe@...nel.org> wrote:
>
> From: Nicolas Rybowski <nicolas.rybowski@...sares.net>
>
> Move Nicolas's patch into bpf selftests directory. This example added a
> test that was adding a different mark (SO_MARK) on each subflow, and
> changing the TCP CC only on the first subflow.
>
> This example shows how it is possible to:
>
>     Identify the parent msk of an MPTCP subflow.
>     Put different sockopt for each subflow of a same MPTCP connection.
>
> Here especially, we implemented two different behaviours:
>
>     A socket mark (SOL_SOCKET SO_MARK) is put on each subflow of a same
>     MPTCP connection. The order of creation of the current subflow defines
>     its mark.

> The TCP CC algorithm of the very first subflow of an MPTCP
>     connection is set to "reno".

why?
What does it test?
That bpf_setsockopt() can actually do it?
But the next patch doesn't check that it's reno.

It looks to me that dropping this "set to reno" part
won't change the purpose of the rest of selftest.

pw-bot: cr