tcp: add tcp_can_forward_retransmit

Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

@@ -1992,6 +1992,33 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
 	return err;
 }
 
+static int tcp_can_forward_retransmit(struct sock *sk)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	/* Forward retransmissions are possible only during Recovery. */
+	if (icsk->icsk_ca_state != TCP_CA_Recovery)
+		return 0;
+
+	/* No forward retransmissions in Reno are possible. */
+	if (tcp_is_reno(tp))
+		return 0;
+
+	/* Yeah, we have to make difficult choice between forward transmission
+	 * and retransmission... Both ways have their merits...
+	 *
+	 * For now we do not retransmit anything, while we have some new
+	 * segments to send. In the other cases, follow rule 3 for
+	 * NextSeg() specified in RFC3517.
+	 */
+
+	if (tcp_may_send_now(sk))
+		return 0;
+
+	return 1;
+}
+
 /* This gets called after a retransmit timeout, and the initially
  * retransmitted data is acknowledged.  It tries to continue
  * resending the rest of the retransmit queue, until either
@@ -2057,24 +2084,7 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 	}
 
 	/* OK, demanded retransmission is finished. */
-
-	/* Forward retransmissions are possible only during Recovery. */
-	if (icsk->icsk_ca_state != TCP_CA_Recovery)
-		return;
-
-	/* No forward retransmissions in Reno are possible. */
-	if (tcp_is_reno(tp))
-		return;
-
-	/* Yeah, we have to make difficult choice between forward transmission
-	 * and retransmission... Both ways have their merits...
-	 *
-	 * For now we do not retransmit anything, while we have some new
-	 * segments to send. In the other cases, follow rule 3 for
-	 * NextSeg() specified in RFC3517.
-	 */
-
-	if (tcp_may_send_now(sk))
+	if (!tcp_can_forward_retransmit(sk))
 		return;
 
 	/* If nothing is SACKed, highest_sack in the loop won't be valid */