From e558311df376973727c9924c1416a2101e55673d Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Tue, 2 Sep 2014 14:29:51 +0200
Subject: [PATCH 09/12] timesyncd: allow two missed replies before reselecting
 server

After receiving a reply from the server, allow two missed replies before
switching to another server to avoid unnecessary clock hopping when
packets are getting lost in the network.

(cherry picked from commit e8206972be6a7ebeb198cd0d400bc7a94a6a5fc5)
---
 src/timesync/timesyncd-manager.c | 27 ++++++++++++++++++---------
 src/timesync/timesyncd-manager.h |  1 +
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/src/timesync/timesyncd-manager.c b/src/timesync/timesyncd-manager.c
index 19a28f3..a66852d 100644
--- a/src/timesync/timesyncd-manager.c
+++ b/src/timesync/timesyncd-manager.c
@@ -92,6 +92,9 @@
 /* Maximum acceptable root distance in seconds. */
 #define NTP_MAX_ROOT_DISTANCE           5.0
 
+/* Maximum number of missed replies before selecting another source. */
+#define NTP_MAX_MISSED_REPLIES          2
+
 /*
  * "NTP timestamps are represented as a 64-bit unsigned fixed-point number,
  * in seconds relative to 0h on 1 January 1900."
@@ -206,15 +209,18 @@ static int manager_send_request(Manager *m) {
                 return manager_connect(m);
         }
 
-        r = sd_event_add_time(
-                        m->event,
-                        &m->event_timeout,
-                        clock_boottime_or_monotonic(),
-                        now(clock_boottime_or_monotonic()) + TIMEOUT_USEC, 0,
-                        manager_timeout, m);
-        if (r < 0) {
-                log_error("Failed to arm timeout timer: %s", strerror(-r));
-                return r;
+        m->missed_replies++;
+        if (m->missed_replies > NTP_MAX_MISSED_REPLIES) {
+                r = sd_event_add_time(
+                                m->event,
+                                &m->event_timeout,
+                                clock_boottime_or_monotonic(),
+                                now(clock_boottime_or_monotonic()) + TIMEOUT_USEC, 0,
+                                manager_timeout, m);
+                if (r < 0) {
+                        log_error("Failed to arm timeout timer: %s", strerror(-r));
+                        return r;
+                }
         }
 
         return 0;
@@ -549,6 +555,8 @@ static int manager_receive_response(sd_event_source *source, int fd, uint32_t re
                 return 0;
         }
 
+        m->missed_replies = 0;
+
         /* check our "time cookie" (we just stored nanoseconds in the fraction field) */
         if (be32toh(ntpmsg.origin_time.sec) != m->trans_time.tv_sec + OFFSET_1900_1970 ||
             be32toh(ntpmsg.origin_time.frac) != m->trans_time.tv_nsec) {
@@ -712,6 +720,7 @@ static int manager_begin(Manager *m) {
         assert_return(m->current_server_name, -EHOSTUNREACH);
         assert_return(m->current_server_address, -EHOSTUNREACH);
 
+        m->missed_replies = NTP_MAX_MISSED_REPLIES;
         m->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
 
         server_address_pretty(m->current_server_address, &pretty);
diff --git a/src/timesync/timesyncd-manager.h b/src/timesync/timesyncd-manager.h
index 0ac0e17..8296d41 100644
--- a/src/timesync/timesyncd-manager.h
+++ b/src/timesync/timesyncd-manager.h
@@ -53,6 +53,7 @@ struct Manager {
         ServerName *current_server_name;
         ServerAddress *current_server_address;
         int server_socket;
+        int missed_replies;
         uint64_t packet_count;
         sd_event_source *event_timeout;
 
-- 
2.1.0