Callable services

To use IMS callable services, an exit routine must invoke one of two IMS callable services entry points in AMODE 31. The exit routine will receive a control block and a callable services parameter list.

The callable services interface module DFSCSI00 contains two entry points that your exit routine can invoke: DFSCSII0 and DFSCSIF0.

Entry point DFSCSII0 initializes callable services. To begin initialization, issue CALL DFSCSII0 with the appropriate registers initialized. DFSCSII0 returns a callable services token and a parameter list address. The callable services token must be passed to IMS when you invoke one of the callable services. The parameter list address directs reentrant programs to a storage area in which to build parameter lists needed to invoke callable services.

Entry point DFSCSIF0 invokes one of the callable services. To invoke a callable service, issue CALL DFSCSIF0 with the appropriate information specified. You must tell IMS which service to invoke. You do this by initializing two parameter lists. The first list, the callable services parameter list, contains information needed by callable services to route the request to the appropriate service. The second list, the function-specific parameter list, defines which service is to be used and provides information required by that service.

When your exit routine receives control back from callable services, register 15 contains a return code indicating whether the call was successful. The callable services parameter list contains a return code and a reason code if the call did not complete successfully. The function-specific parameter list can contain data from a specific callable service.