The EFS interface consists of a variable-length parameter list and is used to communicate between DFSORT and your EFS program. DFSORT initializes the parameter list to zeros during the initialization phase, except that the list end indicator is set to X'FFFFFFFF'.

The parameter list resides below 16MB virtual, and remains accessible while the EFS program is active, although DFSORT might change its storage location during run-time to optimize use of storage. The actual address in register 1 (used to pass the interface parameter list address) can therefore change while DFSORT is running.

Figure 1 illustrates the structure of the EFS interface parameter list. The illustrated portions of the list are explained in order in the following pages. EXEC PARMs are not described in the figure, but are included in processing.

Figure 1. EFS Interface Parameter List