virtio-bus: cleanup plug/unplug interface

Right now we have these pairs:

- virtio_bus_plug_device/virtio_bus_destroy_device.  The first
  takes a VirtIODevice, the second takes a VirtioBusState

- device_plugged/device_unplug callbacks in the VirtioBusClass
  (here it's just the naming that is inconsistent)

- virtio_bus_destroy_device is not called by anyone (and since
  it calls qdev_free, it would be called by the proxies---but
  then the callback is useless since the proxies can do whatever
  they want before calling virtio_bus_destroy_device)

And there is a k->init but no k->exit, hence virtio_device_exit is
overwritten by subclasses (except virtio-9p).  This cleans it up by:

- renaming the device_unplug callback to device_unplugged

- renaming virtio_bus_plug_device to virtio_bus_device_plugged,
  matching the callback name

- renaming virtio_bus_destroy_device to virtio_bus_device_unplugged,
  removing the qdev_free, making it take a VirtIODevice and calling it
  from virtio_device_exit

- adding a k->exit callback

virtio_device_exit is still overwritten, the next patches will fix that.

Cc: qemu-stable@nongnu.org
Acked-by: Andreas Faerber <afaerber@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/hw/virtio/virtio-bus.h

@@ -61,7 +61,7 @@ typedef struct VirtioBusClass {
      * transport independent exit function.
      * This is called by virtio-bus just before the device is unplugged.
      */
-    void (*device_unplug)(DeviceState *d);
+    void (*device_unplugged)(DeviceState *d);
     /*
      * Does the transport have variable vring alignment?
      * (ie can it ever call virtio_queue_set_align()?)
@@ -74,9 +74,9 @@ struct VirtioBusState {
     BusState parent_obj;
 };
 
-int virtio_bus_plug_device(VirtIODevice *vdev);
+int virtio_bus_device_plugged(VirtIODevice *vdev);
 void virtio_bus_reset(VirtioBusState *bus);
-void virtio_bus_destroy_device(VirtioBusState *bus);
+void virtio_bus_device_unplugged(VirtIODevice *bus);
 /* Get the device id of the plugged device. */
 uint16_t virtio_bus_get_vdev_id(VirtioBusState *bus);
 /* Get the config_len field of the plugged device. */