From 715afa9c5771ca5b483aad77fe21906685d63889 Mon Sep 17 00:00:00 2001
From: Evan Hunt <each@isc.org>
Date: Mon, 25 Nov 2019 21:28:10 -0800
Subject: [PATCH] add a stats counter for clients dropped due to
 recursive-clients limit

---
 CHANGES                              |  4 ++++
 bin/named/statschannel.c             |  3 +++
 bin/tests/system/fetchlimit/tests.sh | 12 ++++++++++++
 lib/ns/client.c                      |  5 ++++-
 lib/ns/include/ns/stats.h            |  4 +++-
 5 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/CHANGES b/CHANGES
index 1cd85378c7..b0d9930766 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+5327.	[func]		Added a statistics counter to track queries
+			dropped because the recursive-clients quota was
+			exceeded. [GL #1399]
+
 5326.	[bug]		Add python dependancy on 'distutils.core' to configure.
 			'distutils.core' is required for installation.
 			[GL #1397]
diff --git a/bin/named/statschannel.c b/bin/named/statschannel.c
index a955d7b207..c125b659cf 100644
--- a/bin/named/statschannel.c
+++ b/bin/named/statschannel.c
@@ -324,6 +324,9 @@ init_desc(void) {
 		       "QryUsedStale");
 	SET_NSSTATDESC(prefetch, "queries triggered prefetch", "Prefetch");
 	SET_NSSTATDESC(keytagopt, "Keytag option received", "KeyTagOpt");
+	SET_NSSTATDESC(reclimitdropped,
+		       "queries dropped due to recursive client limit",
+		       "RecLimitDropped");
 
 	INSIST(i == ns_statscounter_max);
 
diff --git a/bin/tests/system/fetchlimit/tests.sh b/bin/tests/system/fetchlimit/tests.sh
index 747ae07dfc..3065060d06 100644
--- a/bin/tests/system/fetchlimit/tests.sh
+++ b/bin/tests/system/fetchlimit/tests.sh
@@ -179,5 +179,17 @@ echo_i "clients count exceeded 380 on $exceeded trials (expected 0)"
 if [ $ret != 0 ]; then echo_i "failed"; fi
 status=`expr $status + $ret`
 
+echo_i "checking drop statistics"
+rm -f ns3/named.stats
+$RNDCCMD stats
+for try in 1 2 3 4 5; do
+    [ -f ns3/named.stats ] && break
+    sleep 1
+done
+drops=`grep 'queries dropped due to recursive client limit' ns3/named.stats | sed 's/\([0-9][0-9]*\) queries.*/\1/'`
+[ "${drops:-0}" -ne 0 ] || ret=1
+if [ $ret != 0 ]; then echo_i "failed"; fi
+status=`expr $status + $ret`
+
 echo_i "exit status: $status"
 [ $status -eq 0 ] || exit 1
diff --git a/lib/ns/client.c b/lib/ns/client.c
index 8cd8226549..cf8467316f 100644
--- a/lib/ns/client.c
+++ b/lib/ns/client.c
@@ -155,8 +155,11 @@ ns_client_killoldestquery(ns_client_t *client) {
 		ISC_LIST_UNLINK(client->manager->recursing, oldest, rlink);
 		UNLOCK(&client->manager->reclock);
 		ns_query_cancel(oldest);
-	} else
+		ns_stats_increment(client->sctx->nsstats,
+				   ns_statscounter_reclimitdropped);
+	} else {
 		UNLOCK(&client->manager->reclock);
+	}
 }
 
 void
diff --git a/lib/ns/include/ns/stats.h b/lib/ns/include/ns/stats.h
index 175813113e..8afe14260f 100644
--- a/lib/ns/include/ns/stats.h
+++ b/lib/ns/include/ns/stats.h
@@ -104,7 +104,9 @@ enum {
 
 	ns_statscounter_tcphighwater = 65,
 
-	ns_statscounter_max = 66,
+	ns_statscounter_reclimitdropped = 66,
+
+	ns_statscounter_max = 67,
 };
 
 void