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      | 44 ++++++++++++++++++++++++++++++++++++++++++++
 net/mptcp/protocol.h |  7 +++++++
 2 files changed, 51 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index 1611dbe63eb2..b0b9376ffcee 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -157,6 +157,23 @@ 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_array)
+BTF_ID(func, bpf_mptcp_put_subflows_array)
+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 +182,30 @@ struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
 	return NULL;
 }
 EXPORT_SYMBOL(bpf_mptcp_sock_from_subflow);
+
+struct mptcp_subflows_array *bpf_mptcp_get_subflows_array(struct mptcp_sock *msk)
+{
+	struct mptcp_subflow_context *subflow;
+	struct mptcp_subflows_array *array;
+
+	array = kzalloc(sizeof(*array), GFP_KERNEL);
+	if (!array)
+		return array;
+
+	mptcp_for_each_subflow(msk, subflow)
+		array->subflows[array->nr++] = subflow;
+
+	return array;
+}
+EXPORT_SYMBOL(bpf_mptcp_get_subflows_array);
+
+void bpf_mptcp_put_subflows_array(struct mptcp_subflows_array *array)
+{
+	int i;
+
+	for (i = 0; i < MPTCP_SUBFLOWS_MAX; i++)
+		array->subflows[i] = NULL;
+	array->nr = 0;
+	kfree(array);
+}
+EXPORT_SYMBOL(bpf_mptcp_put_subflows_array);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 13c6ad5fbade..9eb15caa94f9 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -501,6 +501,13 @@ struct mptcp_subflow_context {
 	struct	rcu_head rcu;
 };
 
+#define MPTCP_SUBFLOWS_MAX	8
+
+struct mptcp_subflows_array {
+	u8 nr;
+	struct mptcp_subflow_context *subflows[MPTCP_SUBFLOWS_MAX];
+};
+
 static inline struct mptcp_subflow_context *
 mptcp_subflow_ctx(const struct sock *sk)
 {
-- 
2.34.1