[PATCH net-next] tcp: add SNMP counter for zero-window drops

[Yafang Shao]

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.s...@gmail.com>
---
 include/uapi/linux/snmp.h | 1 +
 net/ipv4/proc.c           | 1 +
 net/ipv4/tcp_input.c      | 8 ++++++--
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index 750d891..97517f3 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -279,6 +279,7 @@ enum
        LINUX_MIB_TCPDELIVERED,                 /* TCPDelivered */
        LINUX_MIB_TCPDELIVEREDCE,               /* TCPDeliveredCE */
        LINUX_MIB_TCPACKCOMPRESSED,             /* TCPAckCompressed */
+       LINUX_MIB_TCPZEROWINDOWDROP,            /* TCPZeroWindowDrop */
        __LINUX_MIB_MAX
 };
 
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 77350c1..225ef34 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -287,6 +287,7 @@ static int sockstat_seq_show(struct seq_file *seq, void *v)
        SNMP_MIB_ITEM("TCPDelivered", LINUX_MIB_TCPDELIVERED),
        SNMP_MIB_ITEM("TCPDeliveredCE", LINUX_MIB_TCPDELIVEREDCE),
        SNMP_MIB_ITEM("TCPAckCompressed", LINUX_MIB_TCPACKCOMPRESSED),
+       SNMP_MIB_ITEM("TCPZeroWindowDrop", LINUX_MIB_TCPZEROWINDOWDROP),
        SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 76ca88f..9c5b341 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 @@ static void tcp_data_queue(struct sock *sk, struct 
sk_buff *skb)
                /* 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;
        }
 
-- 
1.8.3.1