DFSEWAL macro

The work areas that IMS is to create for the external subsystem must be defined by including DFSEWAL macro statements along with the DFSEMODL statements provided for ESMT generation.

The DFSEWAL statements, one for each work area defined, follow the DFSEMODL statements, except that the last statement in the series must be a DFSEMODL statement specifying END=LAST. The DFSEWAL statements cause a table of work area definitions to be built in the generated ESMT.

Work areas can be defined in each subtable generated in the ESMT. At least one module must be defined in each subtable. If a subtable is generated containing only work area definitions, an error occurs during IMS processing of the ESMT.

IMS creates the work areas defined in a subtable after loading the modules defined in the subtable. IMS stores the addresses of the created work areas in a work area list control block. This control block is also defined by the DFSEWAL macro and can either be contained in the module address control block for the subtable or be created as a separate control block. For this discussion, EWAL is used to refer to the external subsystem work area list control block.

Figure 1. EWAL, EEVTP, and EEVT relationship

If the external subsystem wants IMS to create work areas for its ESAP, it should define two (possibly three) subtables in the ESMT. Modules definitions would be contained in one subtable. The module address control block for this subtable is the EEVT. The second subtable would contain work area definitions. The module address control block for this subtable would either contain the EWAL or be used as the EWAL, and would be anchored in the EEVTP along with the EEVT. Modules could be defined in two subtables: one for exit routines and one for other external subsystem modules that are activated by exit routines.

The second larger block of example code below illustrates how the external subsystem might specify work area definitions.

DFSEWAL DSNAME,SOURCE=,WALSP=,NAME=,DSLABEL=,
        SUBPOOL=,LV=,OPTION=

Mapping DSECTs for all referenced control blocks must be included in the ESMT generation source, otherwise the assembly will fail.

The source control block DSECT name and label must be specified. However, IMS does not store the EWAL address into this control block.

If the size for the EWAL is specified, IMS obtains storage for the EWAL without checking if the module address control block was specified as the EWAL source. If the EWAL size is not specified and the module address and EWAL source control block DSECT names do not match, IMS does not create the work areas. (IMS does not know the address of the source control block. IMS does not indicate that the work areas were not created.)

IMS reserves the EEVPEWA field in the EEVTP control block for the address of an EWAL. The following code illustrates how definitions can be specified by an external subsystem to anchor a work area list in this field. What really happens is that a module address control block is created, anchored at EEVPEWA, and used as the EWAL.

      DFSEMODL DSNAME=(DFSEEVT,68,230),SOURCE=(DFSEEVTP,EEVPEEA),
                  MODNAME=INITEXIT,DSLABEL=EEVTINIT,SUBPOOL=230
         DFSEMODL MODNAME=IDEXIT,DSLABEL=EEVTID,SUBPOOL=230
         DFSEMODL MODNAME=RIDEXIT,DSLABEL=EEVTRID,SUBPOOL=230,
                  OPTION=NODEP
                       .       .       .
                       .       .       .
                       .       .       .
         DFSEMODL MODNAME=CMDEXIT,DSLABEL=EEVTCMD,SUBPOOL=230,
                  OPTION=NODEP
         DFSEMODL END=YES
         DFSEMODL DSNAME=(ESSEWAL,40,230),SOURCE=(DFSEEVTP,EEVPEWA),
                  MODNAME=MODX,LABEL=MODXADDR,SUBPOOL=230
         DFSEWAL  DSNAME=(ESSEWAL),SOURCE=(ESSEWAL,ESSEWAL),WALSP=230,
                  NAME=WKA1,DSLABEL=WKA1ADDR,SUBPOOL=230,LV=200
         DFSEWAL  NAME=WKA2,DSLABEL=WKA2ADDR,SUBPOOL=230,LV=100
         DFSEWAL  NAME=WKA3,DSLABEL=WKA3ADDR,SUBPOOL=230,LV=100
         DFSEMODL END=LAST