SMF allows an installation to pass up to 60 characters of information (such as accounting information) to a user-defined subsystem. A user-defined subsystem is any subsystem other than TSO/E, ASCH, STC, JES2, or JES3. You specify the information to be passed in the SUBPARM parameter of the SMFPRMxx parmlib member, and it can be changed by an IPL or by the SET or SETSMF operator command.
To use the information, the subsystem issues the SMFSUBP macro during its initialization to determine if any SUBPARM information is present or if the values have been changed by a subsequent IPL. (See z/OS MVS Programming: Authorized Assembler Services Reference SET-WTO for more information.)
In response to a SET command, SMF issues a subsystem interface (SSI) call to all user-defined subsystems that have a SUBSYS or SUBPARM option specified. In response to a SETSMF command, SMF issues an SSI call only to the subsystem specified in the SETSMF command.
When each subsystem receives the SSI call, it must issue the SMFSUBP macro instruction to determine if any values that affect its operation have been changed. If the subsystem determines that the information string passed to it is incorrect, it uses the SMFCHSUB macro instruction to change the information. (See z/OS MVS Programming: Authorized Assembler Services Reference SET-WTO for more information.)