def copy_qcow2_image(base, target, size):
            # TODO(pbrady): Consider copying the cow image here
            # with preallocation=metadata set for performance reasons.
            # This would be keyed on a 'preallocate_images' setting.
            libvirt_utils.create_cow_image(base, target)
            if size:
                image = imgmodel.LocalFileImage(target, imgmodel.FORMAT_QCOW2)
                disk.extend(image, size)