Merge branch 'tcp_delack_max'

Eric Dumazet says:

====================
tcp: add tcp_delack_max()

First patches are adding const qualifiers to four existing helpers.

Third patch adds a much needed companion feature to RTAX_RTO_MIN.
====================

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

1 files changed, 15 insertions, 1 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 1fc1f879cfd6..2d1e4b5ac1ca 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3977,6 +3977,20 @@ int tcp_connect(struct sock *sk)
 }
 EXPORT_SYMBOL(tcp_connect);
 
+u32 tcp_delack_max(const struct sock *sk)
+{
+	const struct dst_entry *dst = __sk_dst_get(sk);
+	u32 delack_max = inet_csk(sk)->icsk_delack_max;
+
+	if (dst && dst_metric_locked(dst, RTAX_RTO_MIN)) {
+		u32 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
+		u32 delack_from_rto_min = max_t(int, 1, rto_min - 1);
+
+		delack_max = min_t(u32, delack_max, delack_from_rto_min);
+	}
+	return delack_max;
+}
+
 /* Send out a delayed ack, the caller does the policy checking
  * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
  * for details.
@@ -4012,7 +4026,7 @@ void tcp_send_delayed_ack(struct sock *sk)
 		ato = min(ato, max_ato);
 	}
 
-	ato = min_t(u32, ato, inet_csk(sk)->icsk_delack_max);
+	ato = min_t(u32, ato, tcp_delack_max(sk));
 
 	/* Stay within the limit we were given */
 	timeout = jiffies + ato;