core: emit changes for NFailedUnits property

By notifying the clients when this property is changed it's possible to
allow "system health monitor" tools to get transitions like
running<->degraded. This is an alternative to send changes on the
SystemState property since the latter is more difficult to derive.

src/core/dbus-manager.c

@@ -1985,7 +1985,7 @@ const sd_bus_vtable bus_manager_vtable[] = {
         SD_BUS_WRITABLE_PROPERTY("LogLevel", "s", property_get_log_level, property_set_log_level, 0, 0),
         SD_BUS_WRITABLE_PROPERTY("LogTarget", "s", property_get_log_target, property_set_log_target, 0, 0),
         SD_BUS_PROPERTY("NNames", "u", property_get_n_names, 0, 0),
-        SD_BUS_PROPERTY("NFailedUnits", "u", property_get_n_failed_units, 0, 0),
+        SD_BUS_PROPERTY("NFailedUnits", "u", property_get_n_failed_units, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("NJobs", "u", property_get_n_jobs, 0, 0),
         SD_BUS_PROPERTY("NInstalledJobs", "u", bus_property_get_unsigned, offsetof(Manager, n_installed_jobs), 0),
         SD_BUS_PROPERTY("NFailedJobs", "u", bus_property_get_unsigned, offsetof(Manager, n_failed_jobs), 0),
@@ -2138,5 +2138,23 @@ void bus_manager_send_reloading(Manager *m, bool active) {
         r = bus_foreach_bus(m, NULL, send_reloading, INT_TO_PTR(active));
         if (r < 0)
                 log_debug_errno(r, "Failed to send reloading signal: %m");
-
+}
+
+static int send_changed_signal(sd_bus *bus, void *userdata) {
+        assert(bus);
+
+        return sd_bus_emit_properties_changed_strv(bus,
+                                                   "/org/freedesktop/systemd1",
+                                                   "org.freedesktop.systemd1.Manager",
+                                                   NULL);
+}
+
+void bus_manager_send_change_signal(Manager *m) {
+        int r;
+
+        assert(m);
+
+        r = bus_foreach_bus(m, NULL, send_changed_signal, NULL);
+        if (r < 0)
+                log_debug_errno(r, "Failed to send manager change signal: %m");
 }

src/core/dbus-manager.h

@@ -27,3 +27,4 @@ extern const sd_bus_vtable bus_manager_vtable[];
 
 void bus_manager_send_finished(Manager *m, usec_t firmware_usec, usec_t loader_usec, usec_t kernel_usec, usec_t initrd_usec, usec_t userspace_usec, usec_t total_usec);
 void bus_manager_send_reloading(Manager *m, bool active);
+void bus_manager_send_change_signal(Manager *m);

src/core/manager.c

@@ -3053,6 +3053,23 @@ const char *manager_get_runtime_prefix(Manager *m) {
                getenv("XDG_RUNTIME_DIR");
 }
 
+void manager_update_failed_units(Manager *m, Unit *u, bool failed) {
+        unsigned size;
+
+        assert(m);
+        assert(u->manager == m);
+
+        size = set_size(m->failed_units);
+
+        if (failed)
+                set_put(m->failed_units, u);
+        else
+                set_remove(m->failed_units, u);
+
+        if (set_size(m->failed_units) != size)
+                bus_manager_send_change_signal(m);
+}
+
 ManagerState manager_state(Manager *m) {
         Unit *u;
 

src/core/manager.h

@@ -362,5 +362,7 @@ const char *manager_get_runtime_prefix(Manager *m);
 
 ManagerState manager_state(Manager *m);
 
+void manager_update_failed_units(Manager *m, Unit *u, bool failed);
+
 const char *manager_state_to_string(ManagerState m) _const_;
 ManagerState manager_state_from_string(const char *s) _pure_;

src/core/unit.c

@@ -516,7 +516,7 @@ void unit_free(Unit *u) {
                 free(u->cgroup_path);
         }
 
-        set_remove(u->manager->failed_units, u);
+        manager_update_failed_units(u->manager, u, false);
         set_remove(u->manager->startup_units, u);
 
         free(u->description);
@@ -1797,10 +1797,7 @@ void unit_notify(Unit *u, UnitActiveState os, UnitActiveState ns, bool reload_su
         }
 
         /* Keep track of failed units */
-        if (ns == UNIT_FAILED)
-                set_put(u->manager->failed_units, u);
-        else
-                set_remove(u->manager->failed_units, u);
+        manager_update_failed_units(u->manager, u, ns == UNIT_FAILED);
 
         /* Make sure the cgroup is always removed when we become inactive */
         if (UNIT_IS_INACTIVE_OR_FAILED(ns))