Except when opening a VTOC, if you change the data set name in the JFCB and your job step is APF-authorized, you should do a system enqueue on the major name of "SYSDSN" for the substituted data set name. Issuing an ENQ macro for a major name of SYSDSN requires authorization.

If your program changes the data set name or the volume serial number and is not authorized, OPEN TYPE=J calls dynamic allocation for the new name. CLOSE will automatically unallocate the data set.

To use the correct interface with other system functions (for example, partial release), the ENQ macro should include the TCB of the initiator and the length of the data set name (with no trailing blanks). When you complete processing of the data set, you should use the DEQ macro to release the resources. If your program is not authorized and issues an OPEN TYPE=J macro, and the substituted data set name is already enqueued by another job step, an ABEND 913 occurs with a return code of X'1C'.

To open a VTOC data set to change its contents (that is, open it for OUTPUT, OUTIN, INOUT, UPDAT, OUTINX, or EXTEND), your program must be authorized under the Authorized Program Facility (APF). APF provides security and integrity for your data sets and programs. Details on how to authorize your program are provided in z/OS MVS Programming: Assembler Services Guide, z/OS MVS Programming: Authorized Assembler Services Guide, and z/OS MVS Programming: Assembler Services Reference ABE-HSP.

You cannot extend a VTOC by this means.