Move serve-stale logging to its own category, so that its verbosity can be curtailed.

doc/arm/logging-categories.xml

@@ -315,6 +315,17 @@
 	  </para>
 	</entry>
       </row>
+      <row rowsep="0">
+	<entry colname="1">
+	  <para><command>serve-stale</command></para>
+	</entry>
+	<entry colname="2">
+	  <para>
+	    Whether or not a stale answer is used
+	    following a resolver failure.
+	  </para>
+	</entry>
+      </row>
       <row rowsep="0">
 	<entry colname="1">
 	  <para><command>spill</command></para>

lib/ns/include/ns/log.h

@@ -28,6 +28,7 @@ LIBNS_EXTERNAL_DATA extern isc_logmodule_t ns_modules[];
 #define NS_LOGCATEGORY_UPDATE_SECURITY	(&ns_categories[4])
 #define NS_LOGCATEGORY_QUERY_ERRORS	(&ns_categories[5])
 #define NS_LOGCATEGORY_TAT		(&ns_categories[6])
+#define NS_LOGCATEGORY_SERVE_STALE	(&ns_categories[7])
 
 /*
  * Backwards compatibility.

lib/ns/log.c

@@ -34,6 +34,7 @@ LIBNS_EXTERNAL_DATA isc_logcategory_t ns_categories[] = {
 	{ "update-security",            0 },
 	{ "query-errors",               0 },
 	{ "trust-anchor-telemetry",     0 },
+	{ "serve-stale",                0 },
 	{ NULL, 			0 }
 };
 

lib/ns/query.c

@@ -5493,7 +5493,7 @@ query_lookup(query_ctx_t *qctx) {
 
 		dns_name_format(qctx->client->query.qname,
 				namebuf, sizeof(namebuf));
-		isc_log_write(ns_lctx, NS_LOGCATEGORY_GENERAL,
+		isc_log_write(ns_lctx, NS_LOGCATEGORY_SERVE_STALE,
 			      NS_LOGMODULE_QUERY, ISC_LOG_INFO,
 			      "%s resolver failure, stale answer %s",
 			      namebuf, success ? "used" : "unavailable");