core: add Unit.Markers property

The property is never set by systemd, only reset after a stop or restart or
reload. It may externally be set to mark the unit for a later restart/reload.

I wasn't sure whether to configure the property only for the types where this
makes sense (Service, Swap, etc). But Restart() method is defined on the unit,
and also having this always under the same property name is more convenient.

src/basic/unit-def.c

@@ -117,6 +117,13 @@ static const char* const freezer_state_table[_FREEZER_STATE_MAX] = {
 
 DEFINE_STRING_TABLE_LOOKUP(freezer_state, FreezerState);
 
+static const char* const unit_marker_table[_UNIT_MARKER_MAX] = {
+        [UNIT_MARKER_NEEDS_RELOAD]  = "needs-reload",
+        [UNIT_MARKER_NEEDS_RESTART] = "needs-restart",
+};
+
+DEFINE_STRING_TABLE_LOOKUP(unit_marker, UnitMarker);
+
 static const char* const automount_state_table[_AUTOMOUNT_STATE_MAX] = {
         [AUTOMOUNT_DEAD] = "dead",
         [AUTOMOUNT_WAITING] = "waiting",

src/basic/unit-def.h

@@ -58,6 +58,13 @@ typedef enum FreezerState {
         _FREEZER_STATE_INVALID = -EINVAL,
 } FreezerState;
 
+typedef enum UnitMarker {
+        UNIT_MARKER_NEEDS_RELOAD,
+        UNIT_MARKER_NEEDS_RESTART,
+        _UNIT_MARKER_MAX,
+        _UNIT_MARKER_INVALID = -1
+} UnitMarker;
+
 typedef enum AutomountState {
         AUTOMOUNT_DEAD,
         AUTOMOUNT_WAITING,
@@ -267,6 +274,9 @@ UnitActiveState unit_active_state_from_string(const char *s) _pure_;
 const char *freezer_state_to_string(FreezerState i) _const_;
 FreezerState freezer_state_from_string(const char *s) _pure_;
 
+const char *unit_marker_to_string(UnitMarker m) _const_;
+UnitMarker unit_marker_from_string(const char *s) _pure_;
+
 const char* automount_state_to_string(AutomountState i) _const_;
 AutomountState automount_state_from_string(const char *s) _pure_;