tcp: Abstract back handling peer aliveness test into helper function.

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -389,6 +389,7 @@ extern void tcp_enter_loss(struct sock *sk, int how);
 extern void tcp_clear_retrans(struct tcp_sock *tp);
 extern void tcp_update_metrics(struct sock *sk);
 extern void tcp_init_metrics(struct sock *sk);
+extern bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst);
 extern void tcp_disable_fack(struct tcp_sock *tp);
 extern void tcp_close(struct sock *sk, long timeout);
 extern void tcp_init_sock(struct sock *sk);

net/ipv4/tcp_ipv4.c

@@ -1405,7 +1405,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 			 (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
 			  (sysctl_max_syn_backlog >> 2)) &&
 			 (!peer || !peer->tcp_ts_stamp) &&
-			 (!dst || !dst_metric(dst, RTAX_RTT))) {
+			 !tcp_peer_is_proven(req, dst)) {
 			/* Without syncookies last quarter of
 			 * backlog is filled with destinations,
 			 * proven to be alive.

net/ipv4/tcp_metrics.c

+#include <linux/module.h>
 #include <linux/cache.h>
 #include <linux/tcp.h>
 
 #include <net/inet_connection_sock.h>
+#include <net/request_sock.h>
 #include <net/sock.h>
 #include <net/dst.h>
 #include <net/tcp.h>
@@ -190,3 +192,11 @@ void tcp_init_metrics(struct sock *sk)
 		tp->snd_cwnd = tcp_init_cwnd(tp, dst);
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 }
+
+bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst)
+{
+	if (!dst)
+		return false;
+	return dst_metric(dst, RTAX_RTT) ? true : false;
+}
+EXPORT_SYMBOL_GPL(tcp_peer_is_proven);

net/ipv6/tcp_ipv6.c

@@ -1177,7 +1177,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
 			 (sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
 			  (sysctl_max_syn_backlog >> 2)) &&
 			 (!peer || !peer->tcp_ts_stamp) &&
-			 (!dst || !dst_metric(dst, RTAX_RTT))) {
+			 !tcp_peer_is_proven(req, dst)) {
 			/* Without syncookies last quarter of
 			 * backlog is filled with destinations,
 			 * proven to be alive.