From e8206972be6a7ebeb198cd0d400bc7a94a6a5fc5 Mon Sep 17 00:00:00 2001

From: Miroslav Lichvar <mlichvar@redhat.com>

Date: Tue, 2 Sep 2014 14:29:51 +0200

Subject: [PATCH] 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.

---

 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 19a28f37e2..a66852d7d2 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 0ac0e179c1..8296d41295 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;