Language interface entry points unique to external subsystems

The IMS language interface module provides three entry points that application calls directed to an external subsystem can exclusively use.

Two of the entry points are associated with an implied LIT value specified with the DFSLI macro. (The language interface module, generated by the DFSLI macro, contains the specified LIT value as a hard-coded constant.) The third entry point is not associated with an implied LIT value; it allows the application program to specify the LIT value when it makes the application call. For all entry points, register 1 contains the address of the parameter list which IMS passes to the external subsystem. The following are language interface entry points to external subsystems:

DSNHLI: Entry point associated with an implied LIT value.
The application program does not need to know which subsystem provides access to the external resources it uses. (If the external subsystem is Db2 for z/OS®, this entry point is used for SQL calls.)
DSNWLI: Entry point associated with an implied LIT value.
The application program does not need to know which subsystem provides access to the external resources it uses. (If the external subsystem is Db2 for z/OS, this entry point is used for Instrument Facility calls.)
DFSESS: Entry point allowing an application program to specify an LIT value.
The application program must know which subsystem provides access to the external resources it uses. The application program must specify the address of the LIT value as the first parameter in the application call list. Before it passes control to the external subsystem, IMS increments the address of the application call list by four to skip over the LIT value parameter.

Restriction: Do not use the DFSESS entry point to communicate with a Db2 for z/OS subsystem.