Fix peer polling with shorter remote poll

If the remote peer uses a polling interval shorter than the local
minimum, the local peer will be unable to send any packets as the
timeout will be updated on every received valid packet and will never
expire.

Modify the delay calculation to aim at poll interval away since the last
transmit.

Also, share the delay calculation code with transmit_timeout().

diff --git a/ntp_core.c b/ntp_core.c
index 4e17d2625b2710800351d54a0e83aa835b03ae8c..0dd8524d7bc8f26d3295760aea5b913b64685ead 100644 (file)
--- a/ntp_core.c
+++ b/ntp_core.c
@@ -330,6 +330,7 @@ NCR_GetInstance(NTP_Remote_Address *remote_addr, NTP_Source_Type type, SourcePar
   result->auto_offline = params->auto_offline;
   
   result->local_poll = params->minpoll;
+  result->remote_poll = 0;
 
   /* Create a source instance for this NTP source */
   result->source = SRC_CreateNewInstance(UTI_IPToRefid(&remote_addr->ip_addr), SRC_NTP, params->sel_option, &result->remote_addr.ip_addr);
@@ -438,7 +439,7 @@ get_poll_adj(NCR_Instance inst, double error_in_estimate, double peer_distance)
 /* ================================================== */
 
 static double
-get_transmit_delay(NCR_Instance inst)
+get_transmit_delay(NCR_Instance inst, int on_tx, double last_tx)
 {
   int poll_to_use;
   double delay_time;
@@ -475,7 +476,7 @@ get_transmit_delay(NCR_Instance inst)
 
         case MODE_ACTIVE:
           /* Symmetric active association - aim at some randomised time approx
-             half the poll interval away, to interleave 50-50 with the peer */
+             the poll interval away since the last transmit */
 
           /* Use shorter of the local and remote poll interval, but not shorter
              than the allowed minimum */
@@ -485,7 +486,12 @@ get_transmit_delay(NCR_Instance inst)
           if (poll_to_use < inst->minpoll)
             poll_to_use = inst->minpoll;
 
-          delay_time = (double) (1UL<<poll_to_use) / 2.0;
+          delay_time = (double) (1UL<<poll_to_use);
+
+          if (last_tx > 0.0)
+            delay_time -= last_tx;
+          if (delay_time < 0.0)
+            delay_time = 0.0;
 
           break;
         default:
@@ -496,7 +502,9 @@ get_transmit_delay(NCR_Instance inst)
 
     case MD_BURST_WAS_ONLINE:
     case MD_BURST_WAS_OFFLINE:
-      delay_time = BURST_INTERVAL;
+      /* With burst, the timeout for new transmit after valid reply is shorter
+         than the timeout without reply */
+      delay_time = on_tx ? BURST_TIMEOUT : BURST_INTERVAL;
       break;
     default:
       assert(0);
@@ -635,7 +643,7 @@ static void
 transmit_timeout(void *arg)
 {
   NCR_Instance inst = (NCR_Instance) arg;
-  double timeout_delay=0.0;
+  double timeout_delay;
   int do_auth;
 
   inst->timer_running = 0;
@@ -719,21 +727,17 @@ transmit_timeout(void *arg)
                   &inst->local_rx, &inst->local_tx, &inst->local_ntp_tx,
                   &inst->remote_addr);
 
-  /* Restart timer for this message */
   switch (inst->opmode) {
-    case MD_ONLINE:
-      timeout_delay = (double)(1 << inst->local_poll);
-      break;
-    case MD_OFFLINE:
-      assert(0);
-      return;
     case MD_BURST_WAS_ONLINE:
     case MD_BURST_WAS_OFFLINE:
       --inst->burst_total_samples_to_go;
-      timeout_delay = BURST_TIMEOUT;
+      break;
+    default:
       break;
   }
 
+  /* Restart timer for this message */
+  timeout_delay = get_transmit_delay(inst, 1, 0.0);
   inst->timer_running = 1;
   inst->timeout_id = SCH_AddTimeoutInClass(timeout_delay, SAMPLING_SEPARATION,
                                            SAMPLING_RANDOMNESS,
@@ -1171,7 +1175,7 @@ receive_packet(NTP_Packet *message, struct timeval *now, double now_err, NCR_Ins
 
   /* And now, requeue the timer. */
   if (requeue_transmit && inst->opmode != MD_OFFLINE) {
-    delay_time = get_transmit_delay(inst);
+    delay_time = get_transmit_delay(inst, 0, local_interval);
 
     if (kod_rate) {
       /* Back off for a while */