net: tcp: add mib counters to track zero window transitions

Three counters are added:
- one to track when we went from non-zero to zero window
- one to track the reverse
- one counter incremented when we want to announce zero window,
  but can't because we would shrink current window.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 14 insertions, 1 deletions

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index a6c8a80ec9d6..99d2e9b6fac9 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -280,6 +280,9 @@ static const struct snmp_mib snmp4_net_list[] = {
         SNMP_MIB_ITEM("TCPSpuriousRtxHostQueues", LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES),
         SNMP_MIB_ITEM("BusyPollRxPackets", LINUX_MIB_BUSYPOLLRXPACKETS),
         SNMP_MIB_ITEM("TCPAutoCorking", LINUX_MIB_TCPAUTOCORKING),
+        SNMP_MIB_ITEM("TCPFromZeroWindowAdv", LINUX_MIB_TCPFROMZEROWINDOWADV),
+        SNMP_MIB_ITEM("TCPToZeroWindowAdv", LINUX_MIB_TCPTOZEROWINDOWADV),
+        SNMP_MIB_ITEM("TCPWantZeroWindowAdv", LINUX_MIB_TCPWANTZEROWINDOWADV),
         SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 21e8a9f33287..c5eadec001c1 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -269,6 +269,7 @@ EXPORT_SYMBOL(tcp_select_initial_window);
 static u16 tcp_select_window(struct sock *sk)
 {
         struct tcp_sock *tp = tcp_sk(sk);
+        u32 old_win = tp->rcv_wnd;
         u32 cur_win = tcp_receive_window(tp);
         u32 new_win = __tcp_select_window(sk);
 
@@ -281,6 +282,9 @@ static u16 tcp_select_window(struct sock *sk)
                  *
                  * Relax Will Robinson.
                  */
+                if (new_win == 0)
+                        NET_INC_STATS(sock_net(sk),
+                                      LINUX_MIB_TCPWANTZEROWINDOWADV);
                 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
         }
         tp->rcv_wnd = new_win;
@@ -298,8 +302,14 @@ static u16 tcp_select_window(struct sock *sk)
         new_win >>= tp->rx_opt.rcv_wscale;
 
         /* If we advertise zero window, disable fast path. */
-        if (new_win == 0)
+        if (new_win == 0) {
                 tp->pred_flags = 0;
+                if (old_win)
+                        NET_INC_STATS(sock_net(sk),
+                                      LINUX_MIB_TCPTOZEROWINDOWADV);
+        } else if (old_win == 0) {
+                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
+        }
 
         return new_win;
 }