net/tcp-fastopen: refactor cookie check logic

Refactor the cookie check logic in tcp_send_syn_data() into a function.
This function will be called else where in later changes.

Signed-off-by: Wei Wang <weiwan@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -1493,6 +1493,8 @@ struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
 			      struct tcp_fastopen_cookie *foc,
 			      struct dst_entry *dst);
 void tcp_fastopen_init_key_once(bool publish);
+bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
+			     struct tcp_fastopen_cookie *cookie);
 #define TCP_FASTOPEN_KEY_LENGTH 16
 
 /* Fastopen key context */

net/ipv4/tcp_fastopen.c

@@ -325,3 +325,24 @@ fastopen:
 	*foc = valid_foc;
 	return NULL;
 }
+
+bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
+			       struct tcp_fastopen_cookie *cookie)
+{
+	unsigned long last_syn_loss = 0;
+	int syn_loss = 0;
+
+	tcp_fastopen_cache_get(sk, mss, cookie, &syn_loss, &last_syn_loss);
+
+	/* Recurring FO SYN losses: no cookie or data in SYN */
+	if (syn_loss > 1 &&
+	    time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
+		cookie->len = -1;
+		return false;
+	}
+	if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE) {
+		cookie->len = -1;
+		return true;
+	}
+	return cookie->len > 0;
+}

net/ipv4/tcp_output.c

@@ -3267,23 +3267,11 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_fastopen_request *fo = tp->fastopen_req;
-	int syn_loss = 0, space, err = 0;
-	unsigned long last_syn_loss = 0;
+	int space, err = 0;
 	struct sk_buff *syn_data;
 
 	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
-	tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
-			       &syn_loss, &last_syn_loss);
-	/* Recurring FO SYN losses: revert to regular handshake temporarily */
-	if (syn_loss > 1 &&
-	    time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
-		fo->cookie.len = -1;
-		goto fallback;
-	}
-
-	if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
-		fo->cookie.len = -1;
-	else if (fo->cookie.len <= 0)
+	if (!tcp_fastopen_cookie_check(sk, &tp->rx_opt.mss_clamp, &fo->cookie))
 		goto fallback;
 
 	/* MSS for SYN-data is based on cached MSS and bounded by PMTU and