IEHINITT is a system utility used to place volume label sets onto any number of magnetic tapes mounted on one or more tape units. The IEHINITT Utility supports the REKEY function. You can use the REKEY function to replace the key label structure that is stored on a tape cartridge with a new key label structure. For details, see The Re-keying Exit.

These exits use the dynamic exits service, CSVDYNEX, which is currently described in z/OS MVS Programming: Authorized Assembler Services Reference ALE-DYNz/OS MVS Programming: Authorized Assembler Services Reference ALE-DYNz/OS MVS Programming: Authorized Assembler Services Reference ALE-DYN. By means of this facility a single exit, IEHINITT_EXIT has been defined for the INITT function, with two associated exit points, a pre-label and a post-label. For the REKEY function, a separate exit REKEY_EXIT has been defined with only one exit point, a re-keying exit point.

Using this same facility, installations can associate their own exit routines with these exits. See chapter ‘Adding an Exit Routine to an Exit’ in the z/OS MVS Programming: Authorized Assembler Services Reference ALE-DYN book for details. The Dynamic Exits Facility allows multiple exit routines to be simultaneously defined to a single exit and, as such, coordination of processing between these exit routines is critical.

The same exit routine is called at each exit point. This means that the exit must determine whether it is being entered for Pre or Post Label exit processing. A flag is set in the parameter list passed to the exit routine to indicate which exit point called the exit routine.

Although the Dynamic Exit Services Facility allows a degree of specification on order of call, that specification applies only to the last routine associated with an exit. So, in fact, there is no means of ensuring the order of call of routines. Therefore, all existing exit routines are always called for both Pre and Post label processing.