HYPERVISOR_xen_version
(void)HYPERVISOR_xen_version(0, (void*)0);
if (HYPERVISOR_xen_version(XENVER_version, NULL) < 0) {
xen_version = HYPERVISOR_xen_version(XENVER_version, NULL);
HYPERVISOR_xen_version(XENVER_extraversion, xen_extra_version);
if (HYPERVISOR_xen_version(XENVER_get_features, &features) < 0)