Installing DFSMShsm Exits

To use a DFSMShsm installation exit, you must link edit the exit into a load library, such as SYS1.LINKLIB. To request that DFSMShsm use the exit, issue the SETSYS EXITON command. If there are different versions of the exits that you want to use with different DFSMShsm hosts in an MVS image, you have at least the following two options:

Define each startup procedure using a STEPLIB that consists of 1) a library that contains exits that are unique to that procedure, followed by 2) a library that contains DFSMSdss and other modules (including other exits) that are common to all hosts.
Design each exit such that it determines the ASCB address for the address space in which it is running, and then scans the QCT’s linked list of DFSMShsm host entries for the DFSMShsm host that is running under that ASCB. See ARCINEXT: Initialization Installation Exit.

Normally, you can activate DFSMShsm installation exits during DFSMShsm startup by including the SETSYS EXITON command in the DFSMShsm startup PARMLIB member. However, you can also activate an inactive exit or dynamically refresh an active exit, even while DFSMShsm is running, by link-editing the desired version of the exit into a load library and then issuing the SETSYS EXITON command. The SETSYS EXITON command causes DFSMShsm to reload the exit using the standard search sequence.

The ARCINEXT, ARCSDEXT, and ARCRPEXT exits, whether link-edited in 24-bit or 31-bit mode, are each passed parameters that are in 31-bit storage (above the 16MB line).

See Adding a New Exit.