This patch implements a new helper bpf_mptcp_get_next_subflow() to get the
next available subflow of msk.

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

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/bpf.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index a3c41c079fe4..94671d5e80d1 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -114,6 +114,22 @@ 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_next_subflow)
+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))
@@ -122,3 +138,21 @@ struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
 	return NULL;
 }
 EXPORT_SYMBOL(bpf_mptcp_sock_from_subflow);
+
+struct mptcp_subflow_context *bpf_mptcp_get_next_subflow(struct mptcp_sock *msk)
+{
+	struct mptcp_subflow_context *subflow, *next;
+
+	next = list_first_entry_or_null(&msk->conn_list, typeof(*subflow), node);
+	mptcp_for_each_subflow(msk, subflow) {
+		if (msk->last_snd && subflow->tcp_sock == msk->last_snd) {
+			if (!list_is_last(&subflow->node, &msk->conn_list)) {
+				next = list_next_entry(subflow, node);
+				break;
+			}
+		}
+	}
+
+	return next;
+}
+EXPORT_SYMBOL(bpf_mptcp_get_next_subflow);
-- 
2.34.1