linux-kernel - [PATCH bpf-next/net v3 1/5] bpf: Register mptcp common kfunc set

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Message-Id: <20250320-bpf-next-net-mptcp-bpf_iter-subflows-v3-1-9abd22c2a7fd@kernel.org>
Date: Thu, 20 Mar 2025 18:48:40 +0100
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: 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>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 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>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>, 
 Geliang Tang <geliang@...nel.org>
Subject: [PATCH bpf-next/net v3 1/5] bpf: Register mptcp common kfunc set

From: Geliang Tang <tanggeliang@...inos.cn>

MPTCP helper mptcp_sk() is used to convert struct sock to mptcp_sock.
Helpers mptcp_subflow_ctx() and mptcp_subflow_tcp_sock() are used to
convert between struct mptcp_subflow_context and sock. They all will
be used in MPTCP BPF programs too.

This patch defines corresponding wrappers of them, and put the
wrappers into mptcp common kfunc set and register the set with the
flag BPF_PROG_TYPE_UNSPEC to let them accessible to all types of BPF
programs.

Signed-off-by: Geliang Tang <tanggeliang@...inos.cn>
Reviewed-by: Mat Martineau <martineau@...nel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
Notes:
 - v2:
   - Thanks to the two new previous patches, bpf_mptcp_sk() and
     bpf_mptcp_subflow_tcp_sock() are no longer needed.
   - bpf_mptcp_subflow_ctx(): make sure the socket is an MPTCP subflow,
     and add KF_RET_NULL (Martin).
   - Restrict this kfunc to BPF_PROG_TYPE_CGROUP_SOCKOPT for the moment.
---
 net/mptcp/bpf.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index 8a16672b94e2384f5263e1432296cbca1236bb30..2e4b8ddf81ab0bb9dc547ea8783b73767d553a18 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -29,8 +29,37 @@ static const struct btf_kfunc_id_set bpf_mptcp_fmodret_set = {
 	.set   = &bpf_mptcp_fmodret_ids,
 };

+__bpf_kfunc_start_defs();
+
+__bpf_kfunc static struct mptcp_subflow_context *
+bpf_mptcp_subflow_ctx(const struct sock *sk)
+{
+	if (sk && sk_fullsock(sk) &&
+	    sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
+		return mptcp_subflow_ctx(sk);
+
+	return NULL;
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(bpf_mptcp_common_kfunc_ids)
+BTF_ID_FLAGS(func, bpf_mptcp_subflow_ctx, KF_RET_NULL)
+BTF_KFUNCS_END(bpf_mptcp_common_kfunc_ids)
+
+static const struct btf_kfunc_id_set bpf_mptcp_common_kfunc_set = {
+	.owner	= THIS_MODULE,
+	.set	= &bpf_mptcp_common_kfunc_ids,
+};
+
 static int __init bpf_mptcp_kfunc_init(void)
 {
-	return register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);
+	int ret;
+
+	ret = register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);
+	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCKOPT,
+					       &bpf_mptcp_common_kfunc_set);
+
+	return ret;
 }
 late_initcall(bpf_mptcp_kfunc_init);

-- 
2.48.1