BT_TYPE_SPAN_STATIC
vmem_add1(vm, addr, size, BT_TYPE_SPAN_STATIC);
case BT_TYPE_SPAN_STATIC:
#define BT_ISSPAN_P(bt) ((bt)->bt_type <= BT_TYPE_SPAN_STATIC)
MPASS(type == BT_TYPE_SPAN || type == BT_TYPE_SPAN_STATIC);