tcp: add SNMP counter for zero-window drops

It will be helpful if we could display the drops due to zero window or no
enough window space.
So a new SNMP MIB entry is added to track this behavior.
This entry is named LINUX_MIB_TCPZEROWINDOWDROP and published in
/proc/net/netstat in TcpExt line as TCPZeroWindowDrop.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 76ca88f63b70..9c5b3415413f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4668,8 +4668,10 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
          *  Out of sequence packets to the out_of_order_queue.
          */
         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
-                if (tcp_receive_window(tp) == 0)
+                if (tcp_receive_window(tp) == 0) {
+                        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
                         goto out_of_window;
+                }
 
                 /* Ok. In sequence. In window. */
 queue_and_out:
@@ -4735,8 +4737,10 @@ drop:
                 /* If window is closed, drop tail of packet. But after
                  * remembering D-SACK for its head made in previous line.
                  */
-                if (!tcp_receive_window(tp))
+                if (!tcp_receive_window(tp)) {
+                        NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
                         goto out_of_window;
+                }
                 goto queue_and_out;
         }