linux-kernel - Re: [PATCH bpf-next/net v2 7/7] selftests/bpf: Add mptcp_subflow bpf

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Message-ID: <5313b129-72b1-4fdc-954e-e2d0a141a99c@linux.dev>
Date: Thu, 23 Jan 2025 17:38:28 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Geliang Tang <geliang@...nel.org>
Cc: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>, mptcp@...ts.linux.dev,
 Mat Martineau <martineau@...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
Subject: Re: [PATCH bpf-next/net v2 7/7] selftests/bpf: Add mptcp_subflow
 bpf_iter subtest

On 12/19/24 7:46 AM, Matthieu Baerts (NGI0) wrote:
> +SEC("cgroup/getsockopt")
> +int iters_subflow(struct bpf_sockopt *ctx)
> +{
> +	struct mptcp_subflow_context *subflow;
> +	struct bpf_sock *sk = ctx->sk;
> +	struct sock *ssk = NULL;
> +	struct mptcp_sock *msk;
> +	int local_ids = 0;
> +
> +	if (ctx->level != SOL_TCP || ctx->optname != TCP_IS_MPTCP)
> +		return 1;
> +
> +	msk = bpf_skc_to_mptcp_sock(sk);
> +	if (!msk || msk->pm.server_side || !msk->pm.subflows)
> +		return 1;
> +
> +	msk = bpf_mptcp_sock_acquire(msk);
> +	if (!msk)
> +		return 1;
> +	bpf_for_each(mptcp_subflow, subflow, msk) {
> +		/* Here MPTCP-specific packet scheduler kfunc can be called:
> +		 * this test is not doing anything really useful, only to
> +		 * verify the iteration works.
> +		 */
> +
> +		local_ids += subflow->subflow_id;
> +
> +		/* only to check the following kfunc works */
> +		ssk = mptcp_subflow_tcp_sock(subflow);

It is good to have test cases to exercise the new iter and kfunc. Thanks.

However, it seems not useful to show how it will be used in the future 
packet/subflow scheduler. iiuc, the core piece is in bpf_struct_ops. Without it, 
it is hard to comment. Any RFC patches ready to be posted?

> +	}
> +
> +	if (!ssk)
> +		goto out;
> +
> +	/* assert: if not OK, something wrong on the kernel side */
> +	if (ssk->sk_dport != ((struct sock *)msk)->sk_dport)
> +		goto out;
> +
> +	/* only to check the following kfunc works */
> +	subflow = bpf_mptcp_subflow_ctx(ssk);
> +	if (!subflow || subflow->token != msk->token)
> +		goto out;
> +
> +	ids = local_ids;
> +
> +out:
> +	bpf_mptcp_sock_release(msk);
> +	return 1;
> +}