VHOST_VDPA_DEV_MAX
minor = ida_alloc_max(&vhost_vdpa_ida, VHOST_VDPA_DEV_MAX - 1,
r = alloc_chrdev_region(&vhost_vdpa_major, 0, VHOST_VDPA_DEV_MAX,
unregister_chrdev_region(vhost_vdpa_major, VHOST_VDPA_DEV_MAX);
unregister_chrdev_region(vhost_vdpa_major, VHOST_VDPA_DEV_MAX);