Begin logical file locking (INT 21h, C8h - Novell NetWare 4.0)

        Entry:
          AH = C8h
            if function C6h lock mode 00h:
                 DL = mode
                         00h no wait
                         01h wait
            if function C6h lock mode 01h:
                 BP = timeout in timer ticks (1/18 sec)
        Return:
          AL = error code