code: def sys_close(self, fd):
          
          if self._is_fd_open(fd):
              self._close(fd)
          else:
              return -errno.EBADF
          logger.debug(f'sys_close({fd})')
          return 0
docs: Closes a file descriptor
          :rtype: int
          :param fd: the file descriptor to close.
          :return: C{0} on success.