qdev: Have qdev_set_parent_bus() handle devices already on a bus

Instead of qdev_set_parent_bus() silently doing the wrong
thing if it's handed a device that's already on a bus,
have it remove the device from the old bus and add it to
the new one. This is useful for the raspi2 sdcard.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Message-id: 1488293711-14195-2-git-send-email-peter.maydell@linaro.org

hw/core/qdev.c

@@ -102,9 +102,23 @@ static void bus_add_child(BusState *bus, DeviceState *child)
 
 void qdev_set_parent_bus(DeviceState *dev, BusState *bus)
 {
+    bool replugging = dev->parent_bus != NULL;
+
+    if (replugging) {
+        /* Keep a reference to the device while it's not plugged into
+         * any bus, to avoid it potentially evaporating when it is
+         * dereffed in bus_remove_child().
+         */
+        object_ref(OBJECT(dev));
+        bus_remove_child(dev->parent_bus, dev);
+        object_unref(OBJECT(dev->parent_bus));
+    }
     dev->parent_bus = bus;
     object_ref(OBJECT(bus));
     bus_add_child(bus, dev);
+    if (replugging) {
+        object_unref(OBJECT(dev));
+    }
 }
 
 /* Create a new device.  This only initializes the device state