# From this point we have a VDI on Xen host;
        # If anything goes wrong, we need to remember its uuid.
        try:
            filename = None
            vdi_uuid = session.get_xenapi().VDI.get_uuid(vdi_ref)
            with_vdi_attached_here(session, vdi_ref, False,
                                   lambda dev:
                                   _stream_disk(dev, image_type,
                                                virtual_size, image_file))
            if image_type in (ImageType.KERNEL, ImageType.RAMDISK):
                # We need to invoke a plugin for copying the
                # content of the VDI into the proper path.
                LOG.debug(_("Copying VDI %s to /boot/guest on dom0"), vdi_ref)
                fn = "copy_kernel_vdi"
                args = {}
                args['vdi-ref'] = vdi_ref
                # Let the plugin copy the correct number of bytes.
                args['image-size'] = str(vdi_size)
                task = session.async_call_plugin('glance', fn, args)
                filename = session.wait_for_task(task, instance_id)
                # Remove the VDI as it is not needed anymore.
                session.get_xenapi().VDI.destroy(vdi_ref)
                LOG.debug(_("Kernel/Ramdisk VDI %s destroyed"), vdi_ref)
                return [dict(vdi_type=ImageType.to_string(image_type),
                             vdi_uuid=None,
                             file=filename)]
            else:
                return [dict(vdi_type=ImageType.to_string(image_type),
                             vdi_uuid=vdi_uuid,
                             file=None)]
        except (cls.XenAPI.Failure, IOError, OSError) as e:
            # We look for XenAPI and OS failures.
            LOG.exception(_("instance %s: Failed to fetch glance image"),
                          instance_id, exc_info=sys.exc_info())
            e.args = e.args + ([dict(vdi_type=ImageType.
                                              to_string(image_type),
                                    vdi_uuid=vdi_uuid,
                                    file=filename)],)
            raise e