(OMODVOL1, EMODVOL1)

If you state that an input or output tape has a standard label, the operating system checks for the standard volume label at the beginning of the tape. For ISO/ANSI tapes, the system checks for the correct version. If you specify that the tape has nonstandard labels or no labels, the system attempts to verify that the first record is not a standard volume label.

Because of conflicting label types or conflicting tape characteristics, various error conditions can occur during this verification of the first record. Under some error conditions, the tape is accepted for use. Under other error conditions, the tape is not accepted and the system issues another mount message. For certain other error conditions, the system gives control to a label anomaly exit and under certain conditions to a volume label editor routine. Your installation can use routines supplied by IBM or you can supply your own routines. The system calls the label anomaly exit, IFG019LA, before a possible call to a volume label editor routine. The type of anomaly and the actions taken by the label anomaly exit determine whether the system calls the volume label editor. IBM recommends using the label anomaly exit instead of the volume label editor because the label anomaly exit can handle more situations, its interface is cleaner and it is expected to be easier to write. IBM does not plan to enhance the label editor function.

The IBM-supplied volume label editor routines find the discrepancies between the requested tape and the mounted tape and, if necessary, pass control to the appropriate data management routine to create or destroy labels, as required. Installation-supplied routines can perform other functions.