Writing the DESERV Exit

A DESERV exit gets control once prior to any DESERV GET, PUT, RENAME, UPDATE or DELETE function processing, and once immediately prior to DESERV's return to the caller. A DESERV exit receives control in key 0 and supervisor state. Register 13 points to an 18-word key 0 register save area.

The DESX DSECT maps the input to the exit routines and is defined in the IGWDES macro. Register 1 points to the DESX on entry to the exit routine. The DESX structure is shown in Table 1.

Table 1. DESX Structure Mapping DESERV Exit Parameter List
Offset	Length or Bit Pattern	Name	Description
0 (X'0')	36	DESX	(structure)
0 (X'0')	16	DESX_HEADER	(character)
0 (X'0')	8	DESX_ID	Eyecatcher - IGWDESX (character)
08 (X'08')	4	DESX_LEN	Length of DESX (signed)
08 (X'08')	X'24'	DESX_LEN_IV	Constant to be used with DESX_LEN
12 (X'0C')	1	DESX_LEV	Control block level (character)
12 (X'0C')	X'01'	DESX_LEV_IV	Constant to be used with DESX_LEV
13 (X'0D')	3	-	Reserved
16 (X'10')	4	DESX_DESP_PTR	Address of caller's DESP (address)
20 (X'14')	4	DESX_DST	Address of DESERV screen table (address)
24 (X'18')	1	DESX_CALLER_KEY	Key of DESERV caller in bits 0-3 (unsigned)
25 (X'19')	1	DESX_FLAGS	(bitstring)
	1... ....	DESX_BLDL_BIT	DESERV issues BLDL to process this GET request
	.1.. ....	DESX_PREV_BIT	EXIT called before DESERV PUT or GET function
	..1. ....	DESX_POST_BIT	EXIT called after DESERV PUT or GET function
26 (X'1A')	2	-	Reserved
28 (X'1C')	4	DESX_RETURN_CODE	Return code to be returned to DESERV caller (unsigned)
32 (X'20')	4	DESX_REASON_CODE	Reason code to be returned to DESERV caller (unsigned)

Note that the DESERV return and reason codes, with the exception of the PUT codes, can be found in z/OS DFSMS Using Data Sets. See Figure 1 for the PUT return and reason codes.