netdev - Re: [PATCH bpf-next/net v3 2/5] bpf: Add mptcp_subflow bpf

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Message-ID: <0d6a0d05-f8e7-4626-9899-02ef1fdd8d0d@kernel.org>
Date: Mon, 19 May 2025 12:05:06 +0200
From: Matthieu Baerts <matttbe@...nel.org>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>,
 Geliang Tang <geliang@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
 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@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>,
 Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Martin KaFai Lau <martin.lau@...nel.org>
Subject: Re: [PATCH bpf-next/net v3 2/5] bpf: Add mptcp_subflow bpf_iter

Hi Martin,

Thank you for your reply!

On 17/05/2025 00:34, Martin KaFai Lau wrote:
> On 3/20/25 10:48 AM, Matthieu Baerts (NGI0) wrote:

(...)

>> @BPF maintainers: we would like to allow this new mptcp_subflow bpf_iter
>> to be used with struct_ops, but only with the two new ones we are going
>> to introduce that are specific to MPTCP, and with not others struct_ops
>> (TCP CC, sched_ext, etc.). We are not sure how to do that. By chance, do
>> you have examples or doc you could point to us to have this restriction
>> in place, please?
> 
> The bpf_qdisc.c has done that. Take a look at the
> "bpf_qdisc_kfunc_filter()".
> 
> It is in net-next and bpf-next/net.
Many thanks for the pointer! I see, some operations have specific kfunc,
similar to our needs!

>> Also, for one of the two future MPTCP struct_ops, not all callbacks
>> should be allowed to use this new bpf_iter, because they are called from
>> different contexts. How can we ensure such callbacks from a struct_ops
>> cannot call mptcp_subflow bpf_iter without adding new dedicated checks
>> looking if some locks are held for all callbacks? We understood that
>> they wanted to have something similar with sched_ext, but we are not
>> sure if this code is ready nor if it is going to be accepted.
> 
> Same. Take a look at "bpf_qdisc_kfunc_filter()".
Excellent, thank you, we will look at that!

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