[NETFILTER]: add sysctl to read out the number of current connections

Apparently a lot of scripts use a construct like
	cat /proc/net/ip_conntrack | wc -l
which has a negative impact on system performance due to all the locking
required.
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/sysctl.h

@@ -424,6 +424,7 @@ enum
  	NET_IPV4_NF_CONNTRACK_SCTP_TIMEOUT_SHUTDOWN_SENT=24,
  	NET_IPV4_NF_CONNTRACK_SCTP_TIMEOUT_SHUTDOWN_RECD=25,
  	NET_IPV4_NF_CONNTRACK_SCTP_TIMEOUT_SHUTDOWN_ACK_SENT=26,
+	NET_IPV4_NF_CONNTRACK_COUNT=27,
 };
  
 /* /proc/sys/net/ipv6 */

net/ipv4/netfilter/ip_conntrack_standalone.c

@@ -515,6 +515,14 @@ static ctl_table ip_ct_sysctl_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+	{
+		.ctl_name	= NET_IPV4_NF_CONNTRACK_COUNT,
+		.procname	= "ip_conntrack_count",
+		.data		= &ip_conntrack_count,
+		.maxlen		= sizeof(int),
+		.mode		= 0444,
+		.proc_handler	= &proc_dointvec,
+	},
 	{
 		.ctl_name	= NET_IPV4_NF_CONNTRACK_BUCKETS,
 		.procname	= "ip_conntrack_buckets",