06/24/86  discard_


Syntax for attach description:       discard_

   Any options are ignored.


Function: The discard_ I/O module provides a sink for output and a no-op for
input.  All output operations are supported and return a 0 error code, but
discard any data.  All input operations are supported and return either
error_table_$end_of_info or error_table_$no_record as described below.  The
control and modes operations are also supported as no-op's.

Entries in the module are not called directly by users; rather the
module is accessed through the I/O system.


List of opening modes:
   This module supports all opening modes:
stream_input
stream_output
stream_inpt_output
sequential_input
sequential_output
sequential_input_output
sequential_update
keyed_sequential_input
keyed_sequential_output
keyed_sequential_update
direct_input
direct_output
direct_update


Control Operation:
This module supports the control operation in all opening modes.  All orders
are accepted; but they have no effect.  A 0 error code is always returned, and
the structure pointed to by the info pointer argument is not changed.

Modes Operation:
This module supports modes operation in all opening modes.  It always returns
a null string for the old modes and a 0 error code.


Get Chars, Get Line, and Read Record Operation:
These operations always set the returned length to 0 and the error code to
error_table_$end_of_info.

Put Chars, and Write Record Operation:
These operations simply set the error code to 0 and return.

Position Operation:
This operation simply sets the error code to 0 and returns.


Delete Operation:
This operation sets the error code to error_table_$no_record and returns.

Read Key, and Seek Key Operations:
These operations set the returned length to 0 and the error code
error_table_$no_record.

Read Length Operation:
This operation sets the returned length to 0 and the error code to
error_table_$no_record.


Note:
Table 5-1 in the Multics Programmer's Reference Manual (AG91) describes which
operations are allowed in which opening modes.  This IO module implements all
of the indicated operations in each opening mode (including those operations
qualified by notes in the table).


                                          -----------------------------------------------------------


Historical Background

This edition of the Multics software materials and documentation is provided and donated
to Massachusetts Institute of Technology by Group BULL including BULL HN Information Systems Inc. 
as a contribution to computer science knowledge.  
This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
Bell Laboratories, General Electric, Honeywell Information Systems Inc., Honeywell BULL Inc., Groupe BULL
and BULL HN Information Systems Inc. to the development of this operating system. 
Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
incorporated Multics principles.
Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

                                          -----------------------------------------------------------

Permission to use, copy, modify, and distribute these programs and their documentation for any purpose and without
fee is hereby granted,provided that the below copyright notice and historical background appear in all copies
and that both the copyright notice and historical background and this permission notice appear in supporting
documentation, and that the names of MIT, HIS, BULL or BULL HN not be used in advertising or publicity pertaining
to distribution of the programs without specific prior written permission.
    Copyright 1972 by Massachusetts Institute of Technology and Honeywell Information Systems Inc.
    Copyright 2006 by BULL HN Information Systems Inc.
    Copyright 2006 by Bull SAS
    All Rights Reserved