new: usr: Implement the ForwardOnlyFail statistics channel counter

The new ForwardOnlyFail statistics channel counter indicates the
number of queries failed due to bad forwarders for 'forward only'
zones.

Related to #1793

Merge branch 'aram/add-new-stats-channel-counter-forwardonlyfail' into 'main'

See merge request isc-projects/bind9!9498

bin/named/statschannel.c

@@ -472,6 +472,8 @@ init_desc(void) {
 			"ClientQuota");
 	SET_RESSTATDESC(nextitem, "waited for next item", "NextItem");
 	SET_RESSTATDESC(priming, "priming queries", "Priming");
+	SET_RESSTATDESC(forwardonlyfail, "all forwarders failed",
+			"ForwardOnlyFail");
 
 	INSIST(i == dns_resstatscounter_max);
 

bin/tests/system/forward/tests.sh

@@ -166,10 +166,11 @@ status=$((status + ret))
 
 # GL#1793
 n=$((n + 1))
-echo_i "checking that the 'serverquota' counter isn't increased because of the SERVFAIL in the previous check ($n)"
+echo_i "checking that the correct counter is increased because of the SERVFAIL in the previous check ($n)"
 ret=0
 "${CURL}" "http://10.53.0.4:${EXTRAPORT1}/json/v1" 2>/dev/null >statschannel.out.$n
-grep -F "ServerQuota" statschannel.out.$n >/dev/null && ret=1
+grep -F '"ServerQuota"' statschannel.out.$n >/dev/null && ret=1
+grep -F '"ForwardOnlyFail":1' statschannel.out.$n >/dev/null || ret=1
 if [ $ret != 0 ]; then echo_i "failed"; fi
 status=$((status + ret))
 

doc/arm/reference.rst

@@ -8236,6 +8236,9 @@ Resolver Statistics Counters
 ``ClientQuota``
     This indicates the number of queries spilled for exceeding the :any:`clients-per-query` quota.
 
+``ForwardOnlyFail``
+    This indicates the number of queries failed due to bad forwarders for ``forward only`` zones.
+
 ``NextItem``
     This indicates the number of times the server waited for the next item after receiving an invalid response.
 

lib/dns/include/dns/stats.h

@@ -74,7 +74,8 @@ enum {
 	dns_resstatscounter_clientquota = 43,
 	dns_resstatscounter_nextitem = 44,
 	dns_resstatscounter_priming = 45,
-	dns_resstatscounter_max = 46,
+	dns_resstatscounter_forwardonlyfail = 46,
+	dns_resstatscounter_max = 47,
 
 	/*
 	 * DNSSEC stats.

lib/dns/resolver.c

@@ -3715,13 +3715,23 @@ out:
 
 			/*
 			 * If all of the addresses found were over the
-			 * fetches-per-server quota, return the
-			 * configured response.
+			 * fetches-per-server quota, increase the ServerQuota
+			 * counter and return the configured response.
 			 */
 			if (all_spilled) {
 				result = res->quotaresp[dns_quotatype_server];
 				inc_stats(res, dns_resstatscounter_serverquota);
 			}
+
+			/*
+			 * If we are using a 'forward only' policy, and all
+			 * the forwarders are bad, increase the ForwardOnlyFail
+			 * counter.
+			 */
+			if (fctx->fwdpolicy == dns_fwdpolicy_only) {
+				inc_stats(res,
+					  dns_resstatscounter_forwardonlyfail);
+			}
 		}
 	} else {
 		/*