The exit receives a parameter block that describes the CKDS or PKDS record and the action occurring to the record. By setting a return code in the parameter block, the exit may affect the processing of the record. Depending on the return code, one of these actions occurs:

• ICSF continues to read the record.
• ICSF does not read or write the record.
• ICSF does not read or write the entire CKDS or PKDS.

The parameter block contains the address of the CKDS or PKDS record. The exit can add information into the installation data field of the record. For integrity reasons, ICSF receives only changes to this particular field. If the exit sets a return code to continue processing, ICSF processes the record with this information.

The KGUP exit, the PCF conversion program exit, and the single-record, read-write exit can add information to the installation data field of the CKDS or PKDS header record to identify the data set. If the header record installation data field contains information identifying the CKDS or PKDS, the single-record, read-write exit can check the field to ensure that it is processing the correct data set. If the exit finds that it is processing the wrong CKDS or PKDS, the exit can set a return code to stop the processing of the entire data set.

You can use the exit to prevent processing of a record. You can check certain fields in the record and specify that the record not be processed. For example, during postprocessing conversion, you can prevent the processing of any record of a certain key type. However, the exit should never prevent processing of a record containing a system key because ICSF uses these keys in its processing. You differentiate a system key record from other key records by its key label. A system key record label contains all binary zeros. All other key labels contain an alphabetic first character with the remaining characters as either alphabetic or numeric.