qdev: add helpers to be more explicit when using abstract QOM parent functions

QOM API learning curve is quite hard, in particular when devices inherit from
abstract parent.
To be more explicit about when a device class change the parent hooks, add few
helpers hoping a device class_init() will be easier to understand.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180114020412.26160-3-f4bug@amsat.org>
Reviewed-by: NLaurent Vivier <laurent@vivier.eu>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/core/qdev.c

@@ -1075,6 +1075,30 @@ static void device_class_init(ObjectClass *class, void *data)
     dc->user_creatable = true;
 }
 
+void device_class_set_parent_reset(DeviceClass *dc,
+                                   DeviceReset dev_reset,
+                                   DeviceReset *parent_reset)
+{
+    *parent_reset = dc->reset;
+    dc->reset = dev_reset;
+}
+
+void device_class_set_parent_realize(DeviceClass *dc,
+                                     DeviceRealize dev_realize,
+                                     DeviceRealize *parent_realize)
+{
+    *parent_realize = dc->realize;
+    dc->realize = dev_realize;
+}
+
+void device_class_set_parent_unrealize(DeviceClass *dc,
+                                       DeviceUnrealize dev_unrealize,
+                                       DeviceUnrealize *parent_unrealize)
+{
+    *parent_unrealize = dc->unrealize;
+    dc->unrealize = dev_unrealize;
+}
+
 void device_reset(DeviceState *dev)
 {
     DeviceClass *klass = DEVICE_GET_CLASS(dev);

include/hw/qdev-core.h

@@ -382,6 +382,16 @@ void qdev_machine_init(void);
  */
 void device_reset(DeviceState *dev);
 
+void device_class_set_parent_reset(DeviceClass *dc,
+                                   DeviceReset dev_reset,
+                                   DeviceReset *parent_reset);
+void device_class_set_parent_realize(DeviceClass *dc,
+                                     DeviceRealize dev_realize,
+                                     DeviceRealize *parent_realize);
+void device_class_set_parent_unrealize(DeviceClass *dc,
+                                       DeviceUnrealize dev_unrealize,
+                                       DeviceUnrealize *parent_unrealize);
+
 const struct VMStateDescription *qdev_get_vmsd(DeviceState *dev);
 
 const char *qdev_fw_name(DeviceState *dev);