At Major Call 4, DFSORT supplies your EFS program with fields in the EFS interface containing:

• An action code indicating that Major Call 4 is in effect.
• An EFS Program Context Area (a private communication area for the EFS program).

When the EFS program returns control to DFSORT, it can supply fields in the EFS interface containing:

• A message list containing messages for printing to the message data set.
• A return code (in general register 15).