vd_backend_ioctl
VD_EFI_DEV_SET(edev, vd, (vd_efi_ioctl_func)vd_backend_ioctl);
VD_EFI_DEV_SET(edev, vd, (vd_efi_ioctl_func)vd_backend_ioctl);
request->status = vd_backend_ioctl(vd, ioctl->cmd, ioctl->arg);
static int vd_backend_ioctl(vd_t *vd, int cmd, caddr_t arg);