[TCP]: Add sysctl to turn off matrics caching.

include/linux/sysctl.h

@@ -326,6 +326,7 @@ enum
 	NET_IPV4_IPFRAG_SECRET_INTERVAL=94,
 	NET_TCP_WESTWOOD=95,
 	NET_IPV4_IGMP_MAX_MSF=96,
+	NET_TCP_NO_METRICS_SAVE=97,
 };
 
 enum {

include/net/tcp.h

@@ -583,6 +583,7 @@ extern int sysctl_tcp_tw_reuse;
 extern int sysctl_tcp_frto;
 extern int sysctl_tcp_low_latency;
 extern int sysctl_tcp_westwood;
+extern int sysctl_tcp_nometrics_save;
 
 extern atomic_t tcp_memory_allocated;
 extern atomic_t tcp_sockets_allocated;

net/ipv4/sysctl_net_ipv4.c

@@ -593,6 +593,14 @@ ctl_table ipv4_table[] = {
 		.proc_handler	= &proc_dointvec_jiffies,
 		.strategy	= &sysctl_jiffies
 	},
+	{
+		.ctl_name	= NET_TCP_NO_METRICS_SAVE,
+		.procname	= "tcp_no_metrics_save",
+		.data		= &sysctl_tcp_nometrics_save,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
 	{
 		.ctl_name	= NET_TCP_WESTWOOD, 
 		.procname	= "tcp_westwood",
@@ -601,6 +609,7 @@ ctl_table ipv4_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+
 	{ .ctl_name = 0 }
 };
 

net/ipv4/tcp_input.c

@@ -87,6 +87,7 @@ int sysctl_tcp_rfc1337;
 int sysctl_tcp_max_orphans = NR_FILE;
 int sysctl_tcp_frto;
 int sysctl_tcp_westwood;
+int sysctl_tcp_nometrics_save;
 
 #define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
 #define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
@@ -518,6 +519,9 @@ void tcp_update_metrics(struct sock *sk)
 	struct tcp_opt *tp = tcp_sk(sk);
 	struct dst_entry *dst = __sk_dst_get(sk);
 
+	if (sysctl_tcp_nometrics_save)
+		return;
+
 	dst_confirm(dst);
 
 	if (dst && (dst->flags&DST_HOST)) {