tcp: Add SNMP counters for backlog and min_ttl drops

Commit 6b03a53a (tcp: use limited socket backlog) added the possibility
of dropping frames when backlog queue is full.

Commit d218d111 (tcp: Generalized TTL Security Mechanism) added the
possibility of dropping frames when TTL is under a given limit.

This patch adds new SNMP MIB entries, named TCPBacklogDrop and
TCPMinTTLDrop, published in /proc/net/netstat in TcpExt: line

netstat -s | egrep "TCPBacklogDrop|TCPMinTTLDrop"
    TCPBacklogDrop: 0
    TCPMinTTLDrop: 0

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

2 files changed, 7 insertions, 2 deletions

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 242ed2307370..4f1f337f4337 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -249,6 +249,8 @@ static const struct snmp_mib snmp4_net_list[] = {
         SNMP_MIB_ITEM("TCPSackShifted", LINUX_MIB_SACKSHIFTED),
         SNMP_MIB_ITEM("TCPSackMerged", LINUX_MIB_SACKMERGED),
         SNMP_MIB_ITEM("TCPSackShiftFallback", LINUX_MIB_SACKSHIFTFALLBACK),
+        SNMP_MIB_ITEM("TCPBacklogDrop", LINUX_MIB_TCPBACKLOGDROP),
+        SNMP_MIB_ITEM("TCPMinTTLDrop", LINUX_MIB_TCPMINTTLDROP),
         SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 1915f7dc30e6..8d51d39ad1bb 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1651,8 +1651,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
         if (!sk)
                 goto no_tcp_socket;
 
-        if (iph->ttl < inet_sk(sk)->min_ttl)
+        if (unlikely(iph->ttl < inet_sk(sk)->min_ttl)) {
+                NET_INC_STATS_BH(net, LINUX_MIB_TCPMINTTLDROP);
                 goto discard_and_relse;
+        }
 
 process:
         if (sk->sk_state == TCP_TIME_WAIT)
@@ -1682,8 +1684,9 @@ process:
                         if (!tcp_prequeue(sk, skb))
                                 ret = tcp_v4_do_rcv(sk, skb);
                 }
-        } else if (sk_add_backlog(sk, skb)) {
+        } else if (unlikely(sk_add_backlog(sk, skb))) {
                 bh_unlock_sock(sk);
+                NET_INC_STATS_BH(net, LINUX_MIB_TCPBACKLOGDROP);
                 goto discard_and_relse;
         }
         bh_unlock_sock(sk);