Added TCP high-water statistics variable

This variable will report the maximum number of simultaneous tcp clients
that BIND has served while running.

It can be verified by running rndc status, then inspect "tcp high-water:
count", or by generating statistics file, rndc stats, then inspect the
line with "TCP connection high-water" text.

The tcp-highwater variable is atomically updated based on an existing
tcp-quota system handled in ns/client.c.

bin/named/server.c

@@ -11447,6 +11447,11 @@ named_server_status(named_server_t *server, isc_buffer_t **text) {
 		     isc_quota_getmax(&server->sctx->tcpquota));
 	CHECK(putstr(text, line));
 
+	snprintf(line, sizeof(line), "TCP high-water: %u\n",
+		     (unsigned)ns_stats_get_counter(server->sctx->nsstats,
+					  ns_statscounter_tcphighwater));
+	CHECK(putstr(text, line));
+
 	if (server->reload_status != NAMED_RELOAD_DONE) {
 		snprintf(line, sizeof(line), "reload/reconfig %s\n",
 			 server->reload_status == NAMED_RELOAD_FAILED

bin/named/statschannel.c

@@ -241,6 +241,8 @@ init_desc(void) {
 	SET_NSSTATDESC(invalidsig, "requests with invalid signature",
 		       "ReqBadSIG");
 	SET_NSSTATDESC(requesttcp, "TCP requests received", "ReqTCP");
+	SET_NSSTATDESC(tcphighwater, "TCP connection high-water",
+		       "TCPConnHighWater");
 	SET_NSSTATDESC(authrej, "auth queries rejected", "AuthQryRej");
 	SET_NSSTATDESC(recurserej, "recursive queries rejected", "RecQryRej");
 	SET_NSSTATDESC(xfrrej, "transfer requests rejected", "XfrRej");
@@ -322,6 +324,7 @@ init_desc(void) {
 		       "QryUsedStale");
 	SET_NSSTATDESC(prefetch, "queries triggered prefetch", "Prefetch");
 	SET_NSSTATDESC(keytagopt, "Keytag option received", "KeyTagOpt");
+
 	INSIST(i == ns_statscounter_max);
 
 	/* Initialize resolver statistics */

lib/isc/stats.c

@@ -29,17 +29,17 @@
 #define ISC_STATS_VALID(x)		ISC_MAGIC_VALID(x, ISC_STATS_MAGIC)
 
 #if defined(_WIN32) && !defined(_WIN64)
-typedef atomic_int_fast32_t isc_stat_t;
+	typedef atomic_int_fast32_t isc__atomic_statcounter_t;
 #else
-typedef atomic_int_fast64_t isc_stat_t;
+	typedef atomic_int_fast64_t isc__atomic_statcounter_t;
 #endif
 
 struct isc_stats {
-	unsigned int		magic;
-	isc_mem_t		*mctx;
-	isc_refcount_t		references;
-	int			ncounters;
-	isc_stat_t		*counters;
+	unsigned int			magic;
+	isc_mem_t			*mctx;
+	isc_refcount_t			references;
+	int				ncounters;
+	isc__atomic_statcounter_t	*counters;
 };
 
 static isc_result_t

lib/ns/client.c

@@ -3400,7 +3400,6 @@ client_accept(ns_client_t *client) {
 	isc_result_t result;
 
 	CTRACE("accept");
-
 	/*
 	 * Set up a new TCP connection. This means try to attach to the
 	 * TCP client quota (tcp-clients), but fail if we're over quota.
@@ -3451,6 +3450,12 @@ client_accept(ns_client_t *client) {
 		RUNTIME_CHECK(result == ISC_R_SUCCESS);
 	}
 
+	/* TCP high-water stats update. */
+	unsigned int curr_tcpquota = isc_quota_getused(&client->sctx->tcpquota);
+	ns_stats_update_if_greater(client->sctx->nsstats,
+				   ns_statscounter_tcphighwater,
+				   curr_tcpquota);
+
 	/*
 	 * If this client was set up using get_client() or get_worker(),
 	 * then TCP is already marked active. However, if it was restarted

lib/ns/include/ns/stats.h

@@ -102,7 +102,9 @@ enum {
 	ns_statscounter_prefetch = 63,
 	ns_statscounter_keytagopt = 64,
 
-	ns_statscounter_max = 65
+	ns_statscounter_tcphighwater = 65,
+
+	ns_statscounter_max = 66,
 };
 
 void