tcp: add TCPWinProbe and TCPKeepAlive SNMP counters

Diagnosing problems related to Window Probes has been hard because
we lack a counter.

TCPWinProbe counts the number of ACK packets a sender has to send
at regular intervals to make sure a reverse ACK packet opening back
a window had not been lost.

TCPKeepAlive counts the number of ACK packets sent to keep TCP
flows alive (SO_KEEPALIVE)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Nandita Dukkipati <nanditad@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 13 insertions, 8 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 7a2248a35b13..b8ea12880fd9 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -527,7 +527,7 @@ int tcp_fragment(struct sock *, struct sk_buff *, u32, unsigned int, gfp_t);
 
 void tcp_send_probe0(struct sock *);
 void tcp_send_partial(struct sock *);
-int tcp_write_wakeup(struct sock *);
+int tcp_write_wakeup(struct sock *, int mib);
 void tcp_send_fin(struct sock *sk);
 void tcp_send_active_reset(struct sock *sk, gfp_t priority);
 int tcp_send_synack(struct sock *);
diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index 6a6fb747c78d..eee8968407f0 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -276,6 +276,8 @@ enum
         LINUX_MIB_TCPACKSKIPPEDFINWAIT2,        /* TCPACKSkippedFinWait2 */
         LINUX_MIB_TCPACKSKIPPEDTIMEWAIT,        /* TCPACKSkippedTimeWait */
         LINUX_MIB_TCPACKSKIPPEDCHALLENGE,       /* TCPACKSkippedChallenge */
+        LINUX_MIB_TCPWINPROBE,                  /* TCPWinProbe */
+        LINUX_MIB_TCPKEEPALIVE,                 /* TCPKeepAlive */
         __LINUX_MIB_MAX
 };
 
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index e1f3b911dd1e..da5d483e236a 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -298,6 +298,8 @@ static const struct snmp_mib snmp4_net_list[] = {
         SNMP_MIB_ITEM("TCPACKSkippedFinWait2", LINUX_MIB_TCPACKSKIPPEDFINWAIT2),
         SNMP_MIB_ITEM("TCPACKSkippedTimeWait", LINUX_MIB_TCPACKSKIPPEDTIMEWAIT),
         SNMP_MIB_ITEM("TCPACKSkippedChallenge", LINUX_MIB_TCPACKSKIPPEDCHALLENGE),
+        SNMP_MIB_ITEM("TCPWinProbe", LINUX_MIB_TCPWINPROBE),
+        SNMP_MIB_ITEM("TCPKeepAlive", LINUX_MIB_TCPKEEPALIVE),
         SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b76c719e1979..7386d32cd670 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3382,7 +3382,7 @@ EXPORT_SYMBOL_GPL(tcp_send_ack);
  * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
  * out-of-date with SND.UNA-1 to probe window.
  */
-static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
+static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *skb;
@@ -3400,6 +3400,7 @@ static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
          */
         tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
         skb_mstamp_get(&skb->skb_mstamp);
+        NET_INC_STATS_BH(sock_net(sk), mib);
         return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
 }
 
@@ -3407,12 +3408,12 @@ void tcp_send_window_probe(struct sock *sk)
 {
         if (sk->sk_state == TCP_ESTABLISHED) {
                 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
-                tcp_xmit_probe_skb(sk, 0);
+                tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
         }
 }
 
 /* Initiate keepalive or window probe from timer. */
-int tcp_write_wakeup(struct sock *sk)
+int tcp_write_wakeup(struct sock *sk, int mib)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *skb;
@@ -3449,8 +3450,8 @@ int tcp_write_wakeup(struct sock *sk)
                 return err;
         } else {
                 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
-                        tcp_xmit_probe_skb(sk, 1);
-                return tcp_xmit_probe_skb(sk, 0);
+                        tcp_xmit_probe_skb(sk, 1, mib);
+                return tcp_xmit_probe_skb(sk, 0, mib);
         }
 }
 
@@ -3464,7 +3465,7 @@ void tcp_send_probe0(struct sock *sk)
         unsigned long probe_max;
         int err;
 
-        err = tcp_write_wakeup(sk);
+        err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
 
         if (tp->packets_out || !tcp_send_head(sk)) {
                 /* Cancel probe timer, if it is not required. */
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 8c65dc147d8b..65bf670e8714 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -616,7 +616,7 @@ static void tcp_keepalive_timer (unsigned long data)
                         tcp_write_err(sk);
                         goto out;
                 }
-                if (tcp_write_wakeup(sk) <= 0) {
+                if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
                         icsk->icsk_probes_out++;
                         elapsed = keepalive_intvl_when(tp);
                 } else {