machine: introduce MACHINE_CLASS_CAN_REGISTER

Follow-up for 6df5f80bd3

Similar to SESSION_CAN_* macros in logind-session.h

src/machine/machine-varlink.c

@@ -155,7 +155,7 @@ int vl_method_register(sd_varlink *link, sd_json_variant *parameters, sd_varlink
         if (r != 0)
                 return r;
 
-        if (!IN_SET(machine->class, MACHINE_CONTAINER, MACHINE_VM))
+        if (!MACHINE_CLASS_CAN_REGISTER(machine->class))
                 return sd_varlink_error_invalid_parameter_name(link, "class");
 
         if (manager->runtime_scope != RUNTIME_SCOPE_USER) {

src/machine/machine.h

@@ -25,6 +25,8 @@ typedef enum MachineClass {
         _MACHINE_CLASS_INVALID = -EINVAL,
 } MachineClass;
 
+#define MACHINE_CLASS_CAN_REGISTER(class) IN_SET((class), MACHINE_CONTAINER, MACHINE_VM)
+
 typedef enum KillWhom {
         KILL_LEADER,
         KILL_SUPERVISOR,

src/machine/machined-dbus.c

@@ -256,6 +256,7 @@ static int machine_add_from_params(
         assert(manager);
         assert(message);
         assert(name);
+        assert(c == _MACHINE_CLASS_INVALID || MACHINE_CLASS_CAN_REGISTER(c));
         assert(ret);
 
         if (leader_pidref->pid == 1)
@@ -433,7 +434,7 @@ static int method_create_or_register_machine(
                 c = _MACHINE_CLASS_INVALID;
         else {
                 c = machine_class_from_string(class);
-                if (c < 0 || !IN_SET(c, MACHINE_CONTAINER, MACHINE_VM))
+                if (c < 0 || !MACHINE_CLASS_CAN_REGISTER(c))
                         return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid machine class parameter");
         }
 
@@ -608,7 +609,7 @@ static int method_create_or_register_machine_ex(
                 c = _MACHINE_CLASS_INVALID;
         else {
                 c = machine_class_from_string(class);
-                if (c < 0 || !IN_SET(c, MACHINE_CONTAINER, MACHINE_VM))
+                if (c < 0 || !MACHINE_CLASS_CAN_REGISTER(c))
                         return sd_bus_error_set(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid machine class parameter");
         }