Merge 48317bfc4b03957632ea3fbcfdd2060b4cdd7ffb into fdab24bf6acc62d3011f9b5abdf834b4886642b2

src/resolve/resolved-dns-cache.c

@@ -171,6 +171,17 @@ void dns_cache_flush(DnsCache *c) {
         c->by_expiry = prioq_free(c->by_expiry);
 }
 
+void dns_cache_force_stale(DnsCache *c) {
+        DnsCacheItem *item;
+
+        assert(c);
+        
+        /* Force all entries to be stale; they will be cleaned out properly as appropriate*/
+        HASHMAP_FOREACH(item, c->by_key) {
+                item->until_valid=1;
+        }
+}
+
 static void dns_cache_make_space(DnsCache *c, unsigned add) {
         assert(c);
 

src/resolve/resolved-dns-cache.h

@@ -22,6 +22,7 @@ typedef struct DnsCache {
 
 void dns_cache_flush(DnsCache *c);
 void dns_cache_prune(DnsCache *c);
+void dns_cache_force_stale(DnsCache *c);
 
 int dns_cache_put(
                 DnsCache *c,

src/resolve/resolved-manager.c

@@ -379,11 +379,19 @@ static int on_clock_change(sd_event_source *source, int fd, uint32_t revents, vo
          *
          * (Also, this is triggered after system suspend, which is also a good reason to drop caches, since
          * we might be connected to a different network now without this being visible in a dropped link
-         * carrier or so.) */
-
-        log_info("Clock change detected. Flushing caches.");
-        manager_flush_caches(m, LOG_DEBUG /* downgrade the functions own log message, since we already logged here at LOG_INFO level */);
-
+         * carrier or so.) 
+         * 
+         * That being said, old data isn't neccessarily invalid; so if we can't reach upstream DNS immediately,
+         * provide stale data if configured to.  */
+        
+        if(m->stale_retention_usec == 0){
+                log_info("Clock change detected. Flushing caches.");
+                manager_flush_caches(m, LOG_DEBUG /* downgrade the functions own log message, since we already logged here at LOG_INFO level */);
+        } else {
+                log_info("Clock change detected. Marking caches as stale.");
+                manager_force_caches_stale(m, LOG_DEBUG /* downgrade the functions own log message, since we already logged here at LOG_INFO level */);
+        }
+        
         /* The clock change timerfd is unusable after it triggered once, create a new one. */
         return manager_clock_change_listen(m);
 }
@@ -1763,6 +1771,17 @@ void manager_flush_caches(Manager *m, int log_level) {
         log_full(log_level, "Flushed all caches.");
 }
 
+void manager_force_caches_stale(Manager *m, int log_level) {
+        assert(m);
+
+        LIST_FOREACH(scopes, scope, m->dns_scopes) {
+                dns_cache_force_stale(&scope->cache);
+                dns_cache_prune(&scope->cache); /* it is likley that pruning is needed*/
+        }
+
+        log_full(log_level, "All cached data marked stale.");
+}
+
 void manager_reset_server_features(Manager *m) {
         Link *l;
 

src/resolve/resolved-manager.h

@@ -221,6 +221,7 @@ void manager_dnssec_verdict(Manager *m, DnssecVerdict verdict, const DnsResource
 bool manager_routable(Manager *m);
 
 void manager_flush_caches(Manager *m, int log_level);
+void manager_force_caches_stale(Manager *m, int log_level);
 void manager_reset_server_features(Manager *m);
 
 void manager_cleanup_saved_user(Manager *m);