Considerations for User Label Processing

To process ANSI or IBM standard user labels in OS simulation, you must do the following:

  1. Specify the file as AUL or SUL in a FILEDEF command.
  2. Provide routines to process the user standard labels in your program.
  3. Specify the address of the user label routines using the EXLST parameter in the DCB for the file. See the MVS/XA Data Administration Guide for information on how to establish a DCB EXLST and the exact linkage for communication between user label routines and the operating system. This exact linkage should be used under CMS with the following exceptions:
    1. There is no support for code X'06' EOV EXIT routine.
    2. For input labels, return codes 8 and 12 from the user routine are not supported. If an input return code is not 0, it is treated as if it were 4.
  4. Note that your standard user label routines do not perform any I/O. They set up an output label for writing, but the CMS tape label processing routines actually write out the label. For input, the CMS label processing routines read in your user standard label but then give control to your routine to check the label.