tcp: snmp stats for Fast Open, SYN rtx, and data pkts

Add the following snmp stats:

TCPFastOpenActiveFail: Fast Open attempts (SYN/data) failed beacuse
the remote does not accept it or the attempts timed out.

TCPSynRetrans: number of SYN and SYN/ACK retransmits to break down
retransmissions into SYN, fast-retransmits, timeout retransmits, etc.

TCPOrigDataSent: number of outgoing packets with original data (excluding
retransmission but including data-in-SYN). This counter is different from
TcpOutSegs because TcpOutSegs also tracks pure ACKs. TCPOrigDataSent is
more useful to track the TCP retransmission rate.

Change TCPFastOpenActive to track only successful Fast Opens to be symmetric to
TCPFastOpenPassive.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Nandita Dukkipati <nanditad@google.com>
Signed-off-by: Lawrence Brakmo <brakmo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 17c0fb172fba..c4f1d9a76c44 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -854,8 +854,10 @@ static int tcp_v4_rtx_synack(struct sock *sk, struct request_sock *req)
 {
         int res = tcp_v4_send_synack(sk, NULL, req, 0);
 
-        if (!res)
+        if (!res) {
                 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
+                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
+        }
         return res;
 }