timesyncd: emit signal when timesyncd NTPServers property changes

Emit signal when timesyncd LinkNTPServers property changes

Tested:
```
 Monitoring bus message stream.
```
```
> Type=signal  Endian=l  Flags=1  Version=1 Cookie=21  Timestamp="Fri 2023-05-19 07:50:47.427051 UT"
  Sender=:1.623  Path=/org/freedesktop/timesync1  Interface=org.freedesktop.DBus.Properties  Memberd
  UniqueName=:1.623
  MESSAGE "sa{sv}as" {
          STRING "org.freedesktop.timesync1.Manager";
          ARRAY "{sv}" {
                  DICT_ENTRY "sv" {
                          STRING "LinkNTPServers";
                          VARIANT "as" {
                                  ARRAY "s" {
                                          STRING "10.8.8.18";
                                          STRING "10.8.8.19";
                                  };
                          };
                  };
          };
          ARRAY "s" {
          };
  };
```
```
> Type=signal  Endian=l  Flags=1  Version=1 Cookie=28  Timestamp="Fri 2023-05-19 07:53:22.609416 UT"
  Sender=:1.623  Path=/org/freedesktop/timesync1  Interface=org.freedesktop.DBus.Properties  Memberd
  UniqueName=:1.623
  MESSAGE "sa{sv}as" {
          STRING "org.freedesktop.timesync1.Manager";
          ARRAY "{sv}" {
                  DICT_ENTRY "sv" {
                          STRING "LinkNTPServers";
                          VARIANT "as" {
                                  ARRAY "s" {
                                          STRING "10.8.8.18";
                                          STRING "10.8.8.20";
                                  };
                          };
                  };
          };
          ARRAY "s" {
          };
  };
```
```
> Type=signal  Endian=l  Flags=1  Version=1 Cookie=6  Timestamp="Fri 2023-05-19 08:12:26.964666 UTC"
  Sender=:1.627  Path=/org/freedesktop/timesync1  Interface=org.freedesktop.DBus.Properties  Memberd
  UniqueName=:1.627
  MESSAGE "sa{sv}as" {
          STRING "org.freedesktop.timesync1.Manager";
          ARRAY "{sv}" {
                  DICT_ENTRY "sv" {
                          STRING "LinkNTPServers";
                          VARIANT "as" {
                                  ARRAY "s" {
                                          STRING "10.8.8.18";
                                  };
                          };
                  };
          };
          ARRAY "s" {
          };
  };
```
```
> Type=signal  Endian=l  Flags=1  Version=1 Cookie=162  Timestamp="Mon 2023-07-10 09:06:18.865654 UTC"
  Sender=:1.1  Path=/org/freedesktop/timesync1  Interface=org.freedesktop.DBus.Properties  Member=PropertiesChanged
  UniqueName=:1.1
  MESSAGE "sa{sv}as" {
          STRING "org.freedesktop.timesync1.Manager";
          ARRAY "{sv}" {
                  DICT_ENTRY "sv" {
                          STRING "RuntimeNTPServers";
                          VARIANT "as" {
                                  ARRAY "s" {
                                          STRING "10.2.16.10";
                                  };
                          };
                  };
          };
          ARRAY "s" {
          };
  };
```

Signed-off-by: Kingbom Dou <doujinbao@bytedance.com>

4 files changed, 110 insertions, 5 deletions

diff --git a/src/timesync/timesyncd-bus.c b/src/timesync/timesyncd-bus.c
index 1c33f3fbd2..7237080f32 100644
--- a/src/timesync/timesyncd-bus.c
+++ b/src/timesync/timesyncd-bus.c
@@ -210,10 +210,10 @@ static int property_get_ntp_message(
 static const sd_bus_vtable manager_vtable[] = {
         SD_BUS_VTABLE_START(0),
 
-        SD_BUS_PROPERTY("LinkNTPServers", "as", property_get_servers, offsetof(Manager, link_servers), 0),
-        SD_BUS_PROPERTY("SystemNTPServers", "as", property_get_servers, offsetof(Manager, system_servers), SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("RuntimeNTPServers", "as", property_get_servers, offsetof(Manager, runtime_servers), 0),
-        SD_BUS_PROPERTY("FallbackNTPServers", "as", property_get_servers, offsetof(Manager, fallback_servers), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("LinkNTPServers", "as", property_get_servers, offsetof(Manager, link_servers), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("SystemNTPServers", "as", property_get_servers, offsetof(Manager, system_servers), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("RuntimeNTPServers", "as", property_get_servers, offsetof(Manager, runtime_servers), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
+        SD_BUS_PROPERTY("FallbackNTPServers", "as", property_get_servers, offsetof(Manager, fallback_servers), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("ServerName", "s", property_get_current_server_name, offsetof(Manager, current_server_name), 0),
         SD_BUS_PROPERTY("ServerAddress", "(iay)", property_get_current_server_address, offsetof(Manager, current_server_address), 0),
         SD_BUS_PROPERTY("RootDistanceMaxUSec", "t", bus_property_get_usec, offsetof(Manager, root_distance_max_usec), SD_BUS_VTABLE_PROPERTY_CONST),
diff --git a/src/timesync/timesyncd-manager.c b/src/timesync/timesyncd-manager.c
index 74ac20ac7c..21825f1165 100644
--- a/src/timesync/timesyncd-manager.c
+++ b/src/timesync/timesyncd-manager.c
@@ -955,6 +955,8 @@ Manager* manager_free(Manager *m) {
 
         sd_event_source_unref(m->event_save_time);
 
+        sd_event_source_unref(m->deferred_ntp_server_event_source);
+
         sd_resolve_unref(m->resolve);
         sd_event_unref(m->event);
 
@@ -1221,3 +1223,71 @@ static int manager_save_time_and_rearm(Manager *m, usec_t t) {
 
         return 0;
 }
+
+static const char* ntp_server_property_name[_SERVER_TYPE_MAX] = {
+        [SERVER_SYSTEM]   = "SystemNTPServers",
+        [SERVER_FALLBACK] = "FallbackNTPServers",
+        [SERVER_LINK] = "LinkNTPServers",
+        [SERVER_RUNTIME] = "RuntimeNTPServers",
+};
+
+static int ntp_server_emit_changed_strv(Manager *manager, char **properties) {
+        assert(manager);
+        assert(properties);
+
+        if (sd_bus_is_ready(manager->bus) <= 0)
+                return 0;
+
+        return sd_bus_emit_properties_changed_strv(
+                        manager->bus,
+                        "/org/freedesktop/timesync1",
+                        "org.freedesktop.timesync1.Manager",
+                        properties);
+}
+
+static int on_deferred_ntp_server(sd_event_source *s, void *userdata) {
+        int r;
+        _cleanup_strv_free_ char **p = NULL;
+        Manager *m = ASSERT_PTR(userdata);
+
+        m->deferred_ntp_server_event_source = sd_event_source_disable_unref(m->deferred_ntp_server_event_source);
+
+        for (int type = SERVER_SYSTEM; type < _SERVER_TYPE_MAX; type++)
+                if (m->ntp_server_change_mask & (1U << type))
+                        if (strv_extend(&p, ntp_server_property_name[type]) < 0)
+                                log_oom();
+
+        m->ntp_server_change_mask = 0;
+
+        if (strv_isempty(p))
+                return log_error_errno(SYNTHETIC_ERRNO(ENOMEM), "Failed to build ntp server event strv!");
+
+        r = ntp_server_emit_changed_strv(m, p);
+        if (r < 0)
+                log_warning_errno(r, "Could not emit ntp server changed properties, ignoring: %m");
+
+        return 0;
+}
+
+int bus_manager_emit_ntp_server_changed(Manager *m) {
+        int r;
+
+        assert(m);
+
+        if (m->deferred_ntp_server_event_source)
+                return 0;
+
+        if (!m->event)
+                return 0;
+
+        if (IN_SET(sd_event_get_state(m->event), SD_EVENT_FINISHED, SD_EVENT_EXITING))
+                return 0;
+
+        r = sd_event_add_defer(m->event, &m->deferred_ntp_server_event_source, on_deferred_ntp_server, m);
+        if (r < 0)
+                return log_error_errno(r, "Failed to allocate ntp server event source: %m");
+
+        (void) sd_event_source_set_description(m->deferred_ntp_server_event_source, "deferred-ntp-server");
+
+        return 1;
+}
diff --git a/src/timesync/timesyncd-manager.h b/src/timesync/timesyncd-manager.h
index e595c7ddfc..8cbb91d907 100644
--- a/src/timesync/timesyncd-manager.h
+++ b/src/timesync/timesyncd-manager.h
@@ -116,6 +116,10 @@ struct Manager {
         sd_event_source *event_save_time;
         usec_t save_time_interval_usec;
         bool save_on_exit;
+
+        /* Used to coalesce bus PropertiesChanged events */
+        sd_event_source *deferred_ntp_server_event_source;
+        unsigned ntp_server_change_mask;
 };
 
 int manager_new(Manager **ret);
@@ -133,3 +137,5 @@ void manager_disconnect(Manager *m);
 bool manager_is_connected(Manager *m);
 
 int manager_setup_save_time_event(Manager *m);
+
+int bus_manager_emit_ntp_server_changed(Manager *m);
diff --git a/src/timesync/timesyncd-server.c b/src/timesync/timesyncd-server.c
index 7aa1551baf..fc9bca8c5a 100644
--- a/src/timesync/timesyncd-server.c
+++ b/src/timesync/timesyncd-server.c
@@ -60,12 +60,31 @@ ServerAddress* server_address_free(ServerAddress *a) {
         return mfree(a);
 }
 
+static int enable_ntp_server_defer_event(Manager *m, ServerType type) {
+        int r;
+
+        assert(m);
+        assert((type >= 0) && (type < _SERVER_TYPE_MAX));
+
+        r = sd_event_source_set_enabled(m->deferred_ntp_server_event_source, SD_EVENT_ONESHOT);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to reenable system ntp server change event source!");
+
+        r = bus_manager_emit_ntp_server_changed(m);
+        if (r < 0)
+                return r;
+
+        m->ntp_server_change_mask |= 1U << type;
+
+        return 1;
+}
+
 int server_name_new(
                 Manager *m,
                 ServerName **ret,
                 ServerType type,
                 const char *string) {
-
+        int r;
         ServerName *n;
 
         assert(m);
@@ -103,6 +122,10 @@ int server_name_new(
                 assert_not_reached();
         }
 
+        r = enable_ntp_server_defer_event(m, type);
+        if (r < 0)
+                log_debug_errno(r, "Failed to enable ntp server defer event, ignoring: %m");
+
         if (type != SERVER_FALLBACK &&
             m->current_server_name &&
             m->current_server_name->type == SERVER_FALLBACK)
@@ -117,6 +140,8 @@ int server_name_new(
 }
 
 ServerName *server_name_free(ServerName *n) {
+        int r;
+
         if (!n)
                 return NULL;
 
@@ -134,6 +159,10 @@ ServerName *server_name_free(ServerName *n) {
                 else
                         assert_not_reached();
 
+                r = enable_ntp_server_defer_event(n->manager, n->type);
+                if (r < 0)
+                        log_debug_errno(r, "Failed to enable ntp server defer event, ignoring: %m");
+
                 if (n->manager->current_server_name == n)
                         manager_set_server_name(n->manager, NULL);
         }