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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