tcp: Change possible SYN flooding messages

"Possible SYN flooding on port xxxx " messages can fill logs on servers.

Change logic to log the message only once per listener, and add two new
SNMP counters to track :

TCPReqQFullDoCookies : number of times a SYNCOOKIE was replied to client

TCPReqQFullDrop : number of times a SYN request was dropped because
syncookies were not enabled.

Based on a prior patch from Tom Herbert, and suggestions from David.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index 99e6e19b57c2..4c0766e201e3 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -96,7 +96,8 @@ extern int sysctl_max_syn_backlog;
  */
 struct listen_sock {
         u8                      max_qlen_log;
-        /* 3 bytes hole, try to use */
+        u8                      synflood_warned;
+        /* 2 bytes hole, try to use */
         int                     qlen;
         int                     qlen_young;
         int                     clock_hand;