virtio: Allow virtio to be modular and used by modules

This is needed for the virtio PCI device to be compiled as a module.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/virtio/Kconfig

 # Virtio always gets selected by whoever wants it.
 config VIRTIO
-	bool
+	tristate
 
 # Similarly the virtio ring implementation.
 config VIRTIO_RING
-	bool
+	tristate
 	depends on VIRTIO

drivers/virtio/virtio.c

@@ -162,4 +162,12 @@ static int virtio_init(void)
 		panic("virtio bus registration failed");
 	return 0;
 }
+
+static void __exit virtio_exit(void)
+{
+	bus_unregister(&virtio_bus);
+}
 core_initcall(virtio_init);
+module_exit(virtio_exit);
+
+MODULE_LICENSE("GPL");

drivers/virtio/virtio_ring.c

@@ -266,6 +266,7 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 
 	return IRQ_HANDLED;
 }
+EXPORT_SYMBOL_GPL(vring_interrupt);
 
 static struct virtqueue_ops vring_vq_ops = {
 	.add_buf = vring_add_buf,
@@ -318,9 +319,12 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
 
 	return &vq->vq;
 }
+EXPORT_SYMBOL_GPL(vring_new_virtqueue);
 
 void vring_del_virtqueue(struct virtqueue *vq)
 {
 	kfree(to_vvq(vq));
 }
+EXPORT_SYMBOL_GPL(vring_del_virtqueue);
 
+MODULE_LICENSE("GPL");