s390x: add helper get_machine_class

We will need the machine class at machine initialization time, so the
usual way via qdev won't do. Let's cache the machine class and also use
the default values of the base machine for capability discovery.
Signed-off-by: NHalil Pasic <pasic@linux.vnet.ibm.com>
Acked-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Message-Id: <20170711145441.33925-2-pasic@linux.vnet.ibm.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>

hw/s390x/s390-virtio-ccw.c

@@ -255,36 +255,35 @@ static inline void machine_set_dea_key_wrap(Object *obj, bool value,
     ms->dea_key_wrap = value;
 }
 
-bool ri_allowed(void)
-{
-    if (kvm_enabled()) {
-        MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
-        if (object_class_dynamic_cast(OBJECT_CLASS(mc),
-                                      TYPE_S390_CCW_MACHINE)) {
-            S390CcwMachineClass *s390mc = S390_MACHINE_CLASS(mc);
+static S390CcwMachineClass *current_mc;
 
-            return s390mc->ri_allowed;
-        }
+static S390CcwMachineClass *get_machine_class(void)
+{
+    if (unlikely(!current_mc)) {
         /*
-         * Make sure the "none" machine can have ri, otherwise it won't * be
-         * unlocked in KVM and therefore the host CPU model might be wrong.
-         */
-        return true;
+        * No s390 ccw machine was instantiated, we are likely to
+        * be called for the 'none' machine. The properties will
+        * have their after-initialization values.
+        */
+        current_mc = S390_MACHINE_CLASS(
+                     object_class_by_name(TYPE_S390_CCW_MACHINE));
     }
-    return 0;
+    return current_mc;
 }
 
-bool cpu_model_allowed(void)
+bool ri_allowed(void)
 {
-    MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
-    if (object_class_dynamic_cast(OBJECT_CLASS(mc),
-                                  TYPE_S390_CCW_MACHINE)) {
-        S390CcwMachineClass *s390mc = S390_MACHINE_CLASS(mc);
-
-        return s390mc->cpu_model_allowed;
+    if (!kvm_enabled()) {
+        return false;
     }
-    /* allow CPU model qmp queries with the "none" machine */
-    return true;
+    /* for "none" machine this results in true */
+    return get_machine_class()->ri_allowed;
+}
+
+bool cpu_model_allowed(void)
+{
+    /* for "none" machine this results in true */
+    return get_machine_class()->cpu_model_allowed;
 }
 
 static char *machine_get_loadparm(Object *obj, Error **errp)
@@ -394,6 +393,7 @@ static const TypeInfo ccw_machine_info = {
     static void ccw_machine_##suffix##_instance_init(Object *obj)             \
     {                                                                         \
         MachineState *machine = MACHINE(obj);                                 \
+        current_mc = S390_MACHINE_CLASS(MACHINE_GET_CLASS(machine));          \
         ccw_machine_##suffix##_instance_options(machine);                     \
     }                                                                         \
     static const TypeInfo ccw_machine_##suffix##_info = {                     \