netdev - Re: mptcp splat

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Date: Thu, 28 Mar 2024 18:35:00 +0100
From: Matthieu Baerts <matttbe@...nel.org>
To: Martin KaFai Lau <martin.lau@...ux.dev>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>,
 Paolo Abeni <pabeni@...hat.com>
Cc: Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
 MPTCP Upstream <mptcp@...ts.linux.dev>, Mat Martineau
 <martineau@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
 Martin KaFai Lau <martin.lau@...nel.org>, Geliang Tang <geliang@...nel.org>
Subject: Re: mptcp splat

Hi Martin,

On 27/03/2024 23:16, Martin KaFai Lau wrote:

(...)

> Unrelated, is there a way to tell if a tcp_sock is a subflow?

Yes, you can use "sk_is_mptcp(sk)". Please note that this 'sk' *has* to
be a tcp_sock, this is not checked by the helper.

That's what is used with bpf_mptcp_sock_from_subflow()

https://elixir.bootlin.com/linux/latest/source/net/mptcp/bpf.c#L15

> bpf prog
> can use it to decide if it wants to setsockopt on a subflow or not.
I think it is important to keep the possibility to set socket options
per subflow. If the original issue discussed here is limited to
set_rcvlowat(), best to address it there.

Cheers,
Matt
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