timedate: defer the property changed signal until job of starting/stopping NTP service is finished

Before this, the property changed signal is emitted immediately after
StartUnit/StopUnit method is called. So, the running state of the NTP
client service may not updated.
This makes the timing of emitting property changed signal is deferred
until job of starting/stopping NTP client service is completed.

Fixes #9672.

src/timedate/timedated.c

@@ -46,6 +46,9 @@ typedef struct Context {
         Hashmap *polkit_registry;
         sd_bus_message *cache;
 
+        sd_bus_slot *slot_job_removed;
+        char *path_ntp_unit;
+
         LIST_HEAD(UnitStatusInfo, units);
 } Context;
 
@@ -74,6 +77,9 @@ static void context_free(Context *c) {
         bus_verify_polkit_async_registry_free(c->polkit_registry);
         sd_bus_message_unref(c->cache);
 
+        sd_bus_slot_unref(c->slot_job_removed);
+        free(c->path_ntp_unit);
+
         while ((p = c->units)) {
                 LIST_REMOVE(units, c->units, p);
                 unit_status_info_free(p);
@@ -345,17 +351,55 @@ static int context_update_ntp_status(Context *c, sd_bus *bus, sd_bus_message *m)
         return 0;
 }
 
-static int unit_start_or_stop(UnitStatusInfo *u, sd_bus *bus, sd_bus_error *error, bool start) {
+static int match_job_removed(sd_bus_message *m, void *userdata, sd_bus_error *error) {
+        const char *path;
+        Context *c = userdata;
         int r;
 
+        assert(c);
+        assert(m);
+
+        r = sd_bus_message_read(m, "uoss", NULL, &path, NULL, NULL);
+        if (r < 0) {
+                bus_log_parse_error(r);
+                return 0;
+        }
+
+        if (!streq_ptr(path, c->path_ntp_unit))
+                return 0;
+
+        (void) sd_bus_emit_properties_changed(sd_bus_message_get_bus(m), "/org/freedesktop/timedate1", "org.freedesktop.timedate1", "NTP", NULL);
+
+        c->slot_job_removed = sd_bus_slot_unref(c->slot_job_removed);
+        c->path_ntp_unit = mfree(c->path_ntp_unit);
+
+        return 0;
+}
+
+static int unit_start_or_stop(Context *c, UnitStatusInfo *u, sd_bus *bus, sd_bus_error *error, bool start) {
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+        _cleanup_(sd_bus_slot_unrefp) sd_bus_slot *slot = NULL;
+        const char *path;
+        int r;
+
+        assert(c);
         assert(u);
         assert(bus);
         assert(error);
 
-        /* Call context_update_ntp_status() to update UnitStatusInfo before calling this. */
+        /* This method may be called frequently. Forget the previous job if it has not completed yet. */
+        c->slot_job_removed = sd_bus_slot_unref(c->slot_job_removed);
 
-        if (streq(u->active_state, "active") == start)
-                return 0;
+        r = sd_bus_match_signal_async(
+                        bus,
+                        &slot,
+                        "org.freedesktop.systemd1",
+                        "/org/freedesktop/systemd1",
+                        "org.freedesktop.systemd1.Manager",
+                        "JobRemoved",
+                        match_job_removed, NULL, c);
+        if (r < 0)
+                return r;
 
         r = sd_bus_call_method(
                 bus,
@@ -364,13 +408,22 @@ static int unit_start_or_stop(UnitStatusInfo *u, sd_bus *bus, sd_bus_error *erro
                 "org.freedesktop.systemd1.Manager",
                 start ? "StartUnit" : "StopUnit",
                 error,
-                NULL,
+                &reply,
                 "ss",
                 u->name,
                 "replace");
         if (r < 0)
                 return r;
 
+        r = sd_bus_message_read(reply, "o", &path);
+        if (r < 0)
+                return bus_log_parse_error(r);
+
+        r = free_and_strdup(&c->path_ntp_unit, path);
+        if (r < 0)
+                return log_oom();
+
+        c->slot_job_removed = TAKE_PTR(slot);
         return 0;
 }
 
@@ -422,8 +475,9 @@ static int unit_enable_or_disable(UnitStatusInfo *u, sd_bus *bus, sd_bus_error *
                         error,
                         NULL,
                         NULL);
-         if (r < 0)
-                 return r;
+        if (r < 0)
+                return r;
+
         return 0;
 }
 
@@ -813,7 +867,7 @@ static int method_set_ntp(sd_bus_message *m, void *userdata, sd_bus_error *error
                         if (q < 0)
                                 r = q;
 
-                        q = unit_start_or_stop(u, bus, error, enable);
+                        q = unit_start_or_stop(c, u, bus, error, enable);
                         if (q < 0)
                                 r = q;
                 }
@@ -827,17 +881,17 @@ static int method_set_ntp(sd_bus_message *m, void *userdata, sd_bus_error *error
                         if (r < 0)
                                 continue;
 
-                        r = unit_start_or_stop(u, bus, error, enable);
+                        r = unit_start_or_stop(c, u, bus, error, enable);
                         break;
                 }
 
-        else if (context_ntp_service_is_active(c) <= 0)
+        else
                 LIST_FOREACH(units, u, c->units) {
                         if (!streq(u->load_state, "loaded") ||
                             !streq(u->unit_file_state, "enabled"))
                                 continue;
 
-                        r = unit_start_or_stop(u, bus, error, enable);
+                        r = unit_start_or_stop(c, u, bus, error, enable);
                         break;
                 }
 
@@ -846,8 +900,6 @@ static int method_set_ntp(sd_bus_message *m, void *userdata, sd_bus_error *error
 
         log_info("Set NTP to %sd", enable_disable(enable));
 
-        (void) sd_bus_emit_properties_changed(bus, "/org/freedesktop/timedate1", "org.freedesktop.timedate1", "NTP", NULL);
-
         return sd_bus_reply_method_return(m, NULL);
 }