virtio: link the rng backend through an alias property

The virtio-rng backend is currently linked twice, once in the proxy
device (e.g. virtio-rng-pci) and once in virtio-rng-device.  This causes
a double unref of the backend when the parent device is unplugged.

To fix this, make the proxy device use an alias, similar to what is
already being done for the iothread link.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NGonglei <arei.gonglei@huawei.com>
Message-id: 1414577839-18695-1-git-send-email-pbonzini@redhat.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/s390x/s390-virtio-bus.c

@@ -311,10 +311,8 @@ static void s390_virtio_rng_instance_init(Object *obj)
 
     virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
                                 TYPE_VIRTIO_RNG);
-    object_property_add_link(obj, "rng", TYPE_RNG_BACKEND,
-                             (Object **)&dev->vdev.conf.rng,
-                             qdev_prop_allow_set_link_before_realize,
-                             OBJ_PROP_LINK_UNREF_ON_RELEASE, NULL);
+    object_property_add_alias(obj, "rng", OBJECT(&dev->vdev),
+                              "rng", &error_abort);
 }
 
 static uint64_t s390_virtio_device_vq_token(VirtIOS390Device *dev, int vq)

hw/s390x/virtio-ccw.c

@@ -1544,10 +1544,8 @@ static void virtio_ccw_rng_instance_init(Object *obj)
 
     virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
                                 TYPE_VIRTIO_RNG);
-    object_property_add_link(obj, "rng", TYPE_RNG_BACKEND,
-                             (Object **)&dev->vdev.conf.rng,
-                             qdev_prop_allow_set_link_before_realize,
-                             OBJ_PROP_LINK_UNREF_ON_RELEASE, NULL);
+    object_property_add_alias(obj, "rng", OBJECT(&dev->vdev),
+                              "rng", &error_abort);
 }
 
 static Property virtio_ccw_rng_properties[] = {

hw/virtio/virtio-pci.c

@@ -1525,11 +1525,8 @@ static void virtio_rng_initfn(Object *obj)
 
     virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
                                 TYPE_VIRTIO_RNG);
-    object_property_add_link(obj, "rng", TYPE_RNG_BACKEND,
-                             (Object **)&dev->vdev.conf.rng,
-                             qdev_prop_allow_set_link_before_realize,
-                             OBJ_PROP_LINK_UNREF_ON_RELEASE, NULL);
-
+    object_property_add_alias(obj, "rng", OBJECT(&dev->vdev), "rng",
+                              &error_abort);
 }
 
 static const TypeInfo virtio_rng_pci_info = {