UDYEX1 is a user-written exit which can control allocation and deallocation of datasets using the utility UDYN. A default exit is provided on the distributed source and load datasest which only allows control users to allocate and deallocate datasets.

This document covers the following topics:

• How to use UDYEX1

• UDYEX1 Conventions

---

How to use UDYEX1

When called, R1 points to a parameter list which contains the address of three parameters as follows:

Parm1 ->	One byte code indicating the function to be performed: A: Dataset allocation D: Dataset deallocation
Parm2 ->	44 byte field containing the name of the dataset being allocated or deallocated.
Parm3 ->	6 byte field containing the volser of the dataset being allocated or deallocated if provided by the user. Please note that for a deallocate request, this is not required and therefore may not be filled out.

Based on the above information, the exit can decide whether this request should be allowed or not. To allow the request, the user must simply return "0" in RF; to disallow the request return "4" in RF.

UDYEX1 Conventions

The following table summarises the UDYEX1 linkage conventions:

Feature	Convention
Attributes	None required
Type	Online
Registers at entry	R1 points to the parameter list as described above RD points to a 18F savearea which can be used by the exit
Registers at return	All registers must be returned unchanged with the exception of RF which contains the return code.
Return codes	0 Allow request 4 Disallow request
Considerations	Will be loaded by UDYN.