tcp: add generic netlink support for tcp_metrics

Add support for genl "tcp_metrics". No locking
is changed, only that now we can unlink and delete
entries after grace period. We implement get/del for
single entry and dump to support show/flush filtering
in user space. Del without address attribute causes
flush for all addresses, sadly under genl_mutex.

v2:
- remove rcu_assign_pointer as suggested by Eric Dumazet,
it is not needed because there are no other writes under lock
- move the flushing code in tcp_metrics_flush_all

v3:
- remove synchronize_rcu on flush as suggested by Eric Dumazet

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/Kbuild

@@ -363,6 +363,7 @@ header-y += sysctl.h
 header-y += sysinfo.h
 header-y += taskstats.h
 header-y += tcp.h
+header-y += tcp_metrics.h
 header-y += telephony.h
 header-y += termios.h
 header-y += time.h

include/linux/tcp_metrics.h

@@ -0,0 +1,54 @@
+/* tcp_metrics.h - TCP Metrics Interface */
+
+#ifndef _LINUX_TCP_METRICS_H
+#define _LINUX_TCP_METRICS_H
+
+#include <linux/types.h>
+
+/* NETLINK_GENERIC related info
+ */
+#define TCP_METRICS_GENL_NAME		"tcp_metrics"
+#define TCP_METRICS_GENL_VERSION	0x1
+
+enum tcp_metric_index {
+	TCP_METRIC_RTT,
+	TCP_METRIC_RTTVAR,
+	TCP_METRIC_SSTHRESH,
+	TCP_METRIC_CWND,
+	TCP_METRIC_REORDERING,
+
+	/* Always last.  */
+	__TCP_METRIC_MAX,
+};
+
+#define TCP_METRIC_MAX	(__TCP_METRIC_MAX - 1)
+
+enum {
+	TCP_METRICS_ATTR_UNSPEC,
+	TCP_METRICS_ATTR_ADDR_IPV4,		/* u32 */
+	TCP_METRICS_ATTR_ADDR_IPV6,		/* binary */
+	TCP_METRICS_ATTR_AGE,			/* msecs */
+	TCP_METRICS_ATTR_TW_TSVAL,		/* u32, raw, rcv tsval */
+	TCP_METRICS_ATTR_TW_TS_STAMP,		/* s32, sec age */
+	TCP_METRICS_ATTR_VALS,			/* nested +1, u32 */
+	TCP_METRICS_ATTR_FOPEN_MSS,		/* u16 */
+	TCP_METRICS_ATTR_FOPEN_SYN_DROPS,	/* u16, count of drops */
+	TCP_METRICS_ATTR_FOPEN_SYN_DROP_TS,	/* msecs age */
+	TCP_METRICS_ATTR_FOPEN_COOKIE,		/* binary */
+
+	__TCP_METRICS_ATTR_MAX,
+};
+
+#define TCP_METRICS_ATTR_MAX	(__TCP_METRICS_ATTR_MAX - 1)
+
+enum {
+	TCP_METRICS_CMD_UNSPEC,
+	TCP_METRICS_CMD_GET,
+	TCP_METRICS_CMD_DEL,
+
+	__TCP_METRICS_CMD_MAX,
+};
+
+#define TCP_METRICS_CMD_MAX	(__TCP_METRICS_CMD_MAX - 1)
+
+#endif /* _LINUX_TCP_METRICS_H */