1 06/24/86  discard_
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 3 
 4 Syntax for attach description:       discard_
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 6    Any options are ignored.
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 8 
 9 Function: The discard_ I/O module provides a sink for output and a no-op for
10 input.  All output operations are supported and return a 0 error code, but
11 discard any data.  All input operations are supported and return either
12 error_table_$end_of_info or error_table_$no_record as described below.  The
13 control and modes operations are also supported as no-op's.
14 
15 Entries in the module are not called directly by users; rather the
16 module is accessed through the I/O system.
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18 
19 List of opening modes:
20    This module supports all opening modes:
21 stream_input
22 stream_output
23 stream_inpt_output
24 sequential_input
25 sequential_output
26 sequential_input_output
27 sequential_update
28 keyed_sequential_input
29 keyed_sequential_output
30 keyed_sequential_update
31 direct_input
32 direct_output
33 direct_update
34 
35 
36 Control Operation:
37 This module supports the control operation in all opening modes.  All orders
38 are accepted; but they have no effect.  A 0 error code is always returned, and
39 the structure pointed to by the info pointer argument is not changed.
40 
41 Modes Operation:
42 This module supports modes operation in all opening modes.  It always returns
43 a null string for the old modes and a 0 error code.
44 
45 
46 Get Chars, Get Line, and Read Record Operation:
47 These operations always set the returned length to 0 and the error code to
48 error_table_$end_of_info.
49 
50 Put Chars, and Write Record Operation:
51 These operations simply set the error code to 0 and return.
52 
53 Position Operation:
54 This operation simply sets the error code to 0 and returns.
55 
56 
57 Delete Operation:
58 This operation sets the error code to error_table_$no_record and returns.
59 
60 Read Key, and Seek Key Operations:
61 These operations set the returned length to 0 and the error code
62 error_table_$no_record.
63 
64 Read Length Operation:
65 This operation sets the returned length to 0 and the error code to
66 error_table_$no_record.
67 
68 
69 Note:
70 Table 5-1 in the Multics Programmer's Reference Manual (AG91) describes which
71 operations are allowed in which opening modes.  This IO module implements all
72 of the indicated operations in each opening mode (including those operations
73 qualified by notes in the table).