This patch implements a new helper bpf_mptcp_get_subflows() to get all the
subflows of the given mptcp_sock, it returns the number of suflows. Add
a new member subflows in struct mptcp_sock as a pointers array of all the
subflows.

Register this helper in bpf_mptcp_sched_kfunc_init() to make sure it can
be accessed from the BPF context.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/bpf.c      | 28 ++++++++++++++++++++++++++++
 net/mptcp/protocol.h |  3 +++
 2 files changed, 31 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index bd3c50b07ab2..7f8782dbfa6d 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -157,6 +157,22 @@ struct bpf_struct_ops bpf_mptcp_sched_ops = {
 	.name		= "mptcp_sched_ops",
 };
 
+BTF_SET_START(bpf_mptcp_sched_kfunc_ids)
+BTF_ID(func, bpf_mptcp_get_subflows)
+BTF_SET_END(bpf_mptcp_sched_kfunc_ids)
+
+static const struct btf_kfunc_id_set bpf_mptcp_sched_kfunc_set = {
+	.owner		= THIS_MODULE,
+	.check_set	= &bpf_mptcp_sched_kfunc_ids,
+};
+
+static int __init bpf_mptcp_sched_kfunc_init(void)
+{
+	return register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					 &bpf_mptcp_sched_kfunc_set);
+}
+late_initcall(bpf_mptcp_sched_kfunc_init);
+
 struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
 {
 	if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
@@ -165,3 +181,15 @@ struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
 	return NULL;
 }
 EXPORT_SYMBOL(bpf_mptcp_sock_from_subflow);
+
+u8 bpf_mptcp_get_subflows(struct mptcp_sock *msk)
+{
+	struct mptcp_subflow_context *subflow;
+	u8 nr = 0;
+
+	mptcp_for_each_subflow(msk, subflow)
+		msk->subflows[nr++] = subflow;
+
+	return nr;
+}
+EXPORT_SYMBOL(bpf_mptcp_get_subflows);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 60d6ee54a899..5000f9db4913 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -238,6 +238,8 @@ struct mptcp_data_frag {
 	struct page *page;
 };
 
+#define MPTCP_SUBFLOWS_MAX	8
+
 /* MPTCP connection sock */
 struct mptcp_sock {
 	/* inet_connection_sock must be the first member */
@@ -298,6 +300,7 @@ struct mptcp_sock {
 
 	u32 setsockopt_seq;
 	char		ca_name[TCP_CA_NAME_MAX];
+	struct mptcp_subflow_context *subflows[MPTCP_SUBFLOWS_MAX];
 };
 
 #define mptcp_data_lock(sk) spin_lock_bh(&(sk)->sk_lock.slock)
-- 
2.34.1