sources: improve no majority log message

Add the number of sources that form an agreement (overlapping
intervals), if at least two agree with each other, and number of
reachable sources to the "Can't synchronize: no majority" log message to
better explain why synchronization is failing and hint that adding more
sources might help.

Author: mlichvar

sources.c

@@ -1222,12 +1222,23 @@ SRC_SelectSource(SRC_Instance updated_inst)
   assert(depth == 0 && trust_depth == 0);
   assert(2 * n_sel_sources == n_endpoints);
 
-  if ((best_trust_depth == 0 && best_depth <= n_sel_sources / 2) ||
-      (best_trust_depth > 0 && best_trust_depth <= n_sel_trust_sources / 2)) {
+  if (best_trust_depth > 0) {
+    best_depth = best_trust_depth;
+    n_sel_sources = n_sel_trust_sources;
+  }
+
+  if (best_depth <= n_sel_sources / 2) {
     /* Could not even get half the reachable (trusted) sources to agree */
 
     if (!reported_no_majority) {
-      log_selection_message(LOGS_WARN, "Can't synchronise: no majority");
+      if (best_depth < 2)
+        log_selection_message(LOGS_WARN, "%s (no agreement among %d %ssources)",
+                              "Can't synchronise: no majority", n_sel_sources,
+                              best_trust_depth > 0 ? "trusted " : "");
+      else
+        log_selection_message(LOGS_WARN, "%s (only %d of %d %ssources agree)",
+                              "Can't synchronise: no majority", best_depth,
+                              n_sel_sources, best_trust_depth > 0 ? "trusted " : "");
       reported_no_majority = 1;
       report_selection_loss = 0;
     }

test/simulation/009-sourceselection

@@ -24,6 +24,12 @@ for falsetickers in 3 4; do
 	# These check are expected to fail
 	check_source_selection && test_fail
 	check_sync && test_fail
+
+	if [ $falsetickers = 3 ]; then
+		check_log_messages "Can't synchronise: no majority (only 2 of 5 sources agree)" 1 1 || test_fail
+	else
+		check_log_messages "Can't synchronise: no majority (no agreement among 5 sources)" 1 1 || test_fail
+	fi
 done
 
 # Sources with large asymmetric delay should be excluded

test/simulation/148-replacement

@@ -68,7 +68,7 @@ check_source_selection && test_fail
 check_packet_interval || test_fail
 check_sync || test_fail
 
-check_log_messages "Can't synchronise: no majority" 1 1 || test_fail
+check_log_messages "Can't synchronise: no majority (no agreement among 2 sources)" 1 1 || test_fail
 check_log_messages "Detected falseticker" 0 2 || test_fail
 check_log_messages "Source 192.168.123.. replaced with" 3 60 || test_fail
 check_log_messages "Source 192.168.123.1 replaced with" 1 25 || test_fail