char *file_name;
const char *file_name;
truncate (file_name, length)     char *file_name;     off_t length;{  error_t err;  file_t file = __file_name_lookup (file_name, O_WRITE, 0);  if (file == MACH_PORT_NULL)    return -1;  err = __file_set_size (file, length);  __mach_port_deallocate (__mach_task_self (), file);  if (err)    return __hurd_fail (err);  return 0;}