From: Geliang Tang <tanggeliang@kylinos.cn>

This patch introduces a dedicated MPTCP helper, sock_set_reuseaddr, which
sets the address reuse flag on the first subflow socket of an MPTCP
connection, and it will be applied to the target side in the 'NVMe over
MPTCP' implementation.

Co-developed-by: zhenwei pi <zhenwei.pi@linux.dev>
Signed-off-by: zhenwei pi <zhenwei.pi@linux.dev>
Co-developed-by: Hui Zhu <zhuhui@kylinos.cn>
Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>
Co-developed-by: Gang Yan <yangang@kylinos.cn>
Signed-off-by: Gang Yan <yangang@kylinos.cn>
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 include/net/mptcp.h  |  4 ++++
 net/mptcp/protocol.c | 16 ++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 60cbf29448b0..63b64b7699e3 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -246,6 +246,8 @@ static inline __be32 mptcp_reset_option(const struct sk_buff *skb)
 void mptcp_active_detect_blackhole(struct sock *sk, bool expired);
 
 void mptcp_sock_set_nodelay(struct sock *sk);
+
+void mptcp_sock_set_reuseaddr(struct sock *sk);
 #else
 
 static inline void mptcp_init(void)
@@ -339,6 +341,8 @@ static inline __be32 mptcp_reset_option(const struct sk_buff *skb)  { return hto
 static inline void mptcp_active_detect_blackhole(struct sock *sk, bool expired) { }
 
 static inline void mptcp_sock_set_nodelay(struct sock *sk) { }
+
+static inline void mptcp_sock_set_reuseaddr(struct sock *sk) { }
 #endif /* CONFIG_MPTCP */
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 692111941808..bb923c4fabd1 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3818,6 +3818,22 @@ void mptcp_sock_set_nodelay(struct sock *sk)
 }
 EXPORT_SYMBOL(mptcp_sock_set_nodelay);
 
+void mptcp_sock_set_reuseaddr(struct sock *sk)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct sock *ssk;
+
+	lock_sock(sk);
+	ssk = __mptcp_nmpc_sk(msk);
+	if (IS_ERR(ssk))
+		goto unlock;
+	ssk->sk_reuse = SK_CAN_REUSE;
+	sk->sk_reuse = ssk->sk_reuse;
+unlock:
+	release_sock(sk);
+}
+EXPORT_SYMBOL(mptcp_sock_set_reuseaddr);
+
 bool mptcp_finish_join(struct sock *ssk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
-- 
2.53.0