tcp: Expose tcp_sock_set_keepidle_locked

This is preparation for usage in bpf_setsockopt.

v2:
  - remove redundant EXPORT_SYMBOL (Alexei Starovoitov)
Signed-off-by: Dmitry Yakunin <zeil@yandex-team.ru>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200620153052.9439-2-zeil@yandex-team.ru

include/linux/tcp.h

@@ -499,6 +499,7 @@ int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from, int pcount,
 
 void tcp_sock_set_cork(struct sock *sk, bool on);
 int tcp_sock_set_keepcnt(struct sock *sk, int val);
+int tcp_sock_set_keepidle_locked(struct sock *sk, int val);
 int tcp_sock_set_keepidle(struct sock *sk, int val);
 int tcp_sock_set_keepintvl(struct sock *sk, int val);
 void tcp_sock_set_nodelay(struct sock *sk);

net/ipv4/tcp.c

@@ -2957,7 +2957,7 @@ void tcp_sock_set_user_timeout(struct sock *sk, u32 val)
 }
 EXPORT_SYMBOL(tcp_sock_set_user_timeout);
 
-static int __tcp_sock_set_keepidle(struct sock *sk, int val)
+int tcp_sock_set_keepidle_locked(struct sock *sk, int val)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
@@ -2984,7 +2984,7 @@ int tcp_sock_set_keepidle(struct sock *sk, int val)
 	int err;
 
 	lock_sock(sk);
-	err = __tcp_sock_set_keepidle(sk, val);
+	err = tcp_sock_set_keepidle_locked(sk, val);
 	release_sock(sk);
 	return err;
 }
@@ -3183,7 +3183,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 		break;
 
 	case TCP_KEEPIDLE:
-		err = __tcp_sock_set_keepidle(sk, val);
+		err = tcp_sock_set_keepidle_locked(sk, val);
 		break;
 	case TCP_KEEPINTVL:
 		if (val < 1 || val > MAX_TCP_KEEPINTVL)