- Clear documentation for interactivity between the subnet module and

the serve-expired and prefetch configuration options.

doc/Changelog

@@ -1,5 +1,7 @@
 30 November 2022: George
 	- Add SVCB and HTTPS to the types removed by 'unbound-control flush'.
+	- Clear documentation for interactivity between the subnet module and
+	  the serve-expired and prefetch configuration options.
 
 30 November 2022: Wouter
 	- Fix #782: Segmentation fault in stats.c:404.

doc/unbound.conf.5.in

@@ -2358,6 +2358,9 @@ The maximum size of the ECS cache is controlled by 'msg-cache-size' in the
 configuration file. On top of that, for each query only 100 different subnets
 are allowed to be stored for each address family. Exceeding that number, older
 entries will be purged from cache.
+.LP
+This module does not interact with the \fBserve\-expired*\fR and
+\fBprefetch:\fR options.
 .TP
 .B send\-client\-subnet: \fI<IP address>\fR
 Send client source address to this authority. Append /num to indicate a

edns-subnet/subnetmod.c

@@ -204,6 +204,17 @@ subnetmod_init(struct module_env *env, int id)
 	}
 	alloc_init(&sn_env->alloc, NULL, 0);
 	env->modinfo[id] = (void*)sn_env;
+
+	/* Warn that serve-expired and prefetch do not work with the subnet
+	 * module cache. */
+	if(env->cfg->serve_expired)
+		log_warn(
+			"subnetcache: serve-expired is set but not working "
+			"for data originating from the subnet module cache.");
+	if(env->cfg->prefetch)
+		log_warn(
+			"subnetcache: prefetch is set but not working "
+			"for data originating from the subnet module cache.");
 	/* Copy msg_cache settings */
 	sn_env->subnet_msg_cache = slabhash_create(env->cfg->msg_cache_slabs,
 		HASH_DEFAULT_STARTARRAY, env->cfg->msg_cache_size,