From: Geliang Tang <tanggeliang@kylinos.cn>

This patch introduces a dedicated MPTCP helper, sock_set_syncnt, which sets
the SYN retransmission count on the first subflow socket and it will be
applied to the host 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  |  7 +++++++
 net/mptcp/protocol.c | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 63b64b7699e3..d6bb67a55f24 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -248,6 +248,8 @@ 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);
+
+int mptcp_sock_set_syncnt(struct sock *sk, int val);
 #else
 
 static inline void mptcp_init(void)
@@ -343,6 +345,11 @@ 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) { }
+
+static inline int mptcp_sock_set_syncnt(struct sock *sk, int val)
+{
+	return 0;
+}
 #endif /* CONFIG_MPTCP */
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index bb923c4fabd1..961f11a24277 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3834,6 +3834,25 @@ void mptcp_sock_set_reuseaddr(struct sock *sk)
 }
 EXPORT_SYMBOL(mptcp_sock_set_reuseaddr);
 
+int mptcp_sock_set_syncnt(struct sock *sk, int val)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct sock *ssk;
+
+	if (val < 1 || val > MAX_TCP_SYNCNT)
+		return -EINVAL;
+
+	lock_sock(sk);
+	ssk = __mptcp_nmpc_sk(msk);
+	if (IS_ERR(ssk))
+		goto unlock;
+	WRITE_ONCE(inet_csk(ssk)->icsk_syn_retries, val);
+unlock:
+	release_sock(sk);
+	return 0;
+}
+EXPORT_SYMBOL(mptcp_sock_set_syncnt);
+
 bool mptcp_finish_join(struct sock *ssk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
-- 
2.53.0