Chapter 11: Your Mfextmap File

In Workbench, you use the file mfextmap.dat file to map the DD names used by programs to the associated PC files. When you migrate to Mainframe Express, you can define your existing mfextmap.dat file to the MFEXTMAP migration tool. Then you can run a program and let Mainframe Express allocate the data sets for you and optionally generate a TSO CLIST, REXX exec, and/or JCL jobstream that you can use next time you run the program.

11.1 Enabling the MFEXTMAP Migration Tool

You must enable the MFEXTMAP migration tool in each project that you want to use it.

With the project loaded, click Project Settings on the Project menu.
Click the Execution tab and Migration subtab.
Select Use MFEXTMAP to map data set allocations.
Specify the folder containing your mfextmap.dat in the Folder containing mfextmap.dat field.
Click OK.

11.2 Using Your Mfextmap File

The simplest way to use the mfextmap.dat file is in a TSO session.

With the project loaded, start a TSO session in the normal way, ensuring that the Clist or REXX Exec to execute field is empty.
In the Application Output window, execute a CALL statement for your program, for example:
```
call myprog
```
If the called program opens a file that does not have a DD name allocated for it in the TSO session, Mainframe Express uses the mfextmap.dat file to map the DD name to the associated PC file.

You can also use the mfextmap.dat file in a JCL job. In that case, to run the program, you must include at least a JOB statement and an EXEC statement in the jobstream.

Note that you must be running the program from the TSO or JCL tab on the Start Debugging dialog box. Support for the mfextmap.dat file is not available when running a non-mainframe program.

When the program finishes (or you click Stop Debugging), Mainframe Express displays the MFEXTMAP migration tool dialog box. For each file that was mapped from the mfextmap.dat file, it lists the DD name, the PC filename, and a suggested MVS data set name that you could use when you run the program again. For these data set names, it uses the convention: userid.programname.ddname.MFEXTMAP.DATA

For a DD name that is mapped to a special PC name such as nul (for null), lpt1 (for printer), or con (for console), the MFEXTMAP migration tool generates the equivalent MVS allocation. For example:

DD Name	Special Name	TSO Command	JCL Statement
MYDD1	nul	ALLOC F(MYDD1) DUMMY SHR REU	//MYDD1 DD DUMMY
MYDD2	lpt1	ALLOC F(MYDD2) SYSOUT(A) SHR REU	//MYDD2 DD SYSOUT=*
MYDD3	con	ALLOC F(MYDD3) DA(*) SHR REU	//MYDD3 DD SYSOUT=*

In the MFEXTMAP migration tool dialog box, you can:

Change any of the data set allocations, if necessary.
Optionally, ask Mainframe Express to create one or more of the following:
- A CLIST to run the program, containing a CALL command and an ALLOCATE command for each DD name.
- A REXX exec to run the program, containing a CALL command and an ALLOCATE command for each DD name.
- A JCL jobstream to run the program, containing a JOB statement, an EXEC statement, and a DD statement for each DD name.

Click OK to exit from the dialog box. Mainframe Express allocates the data sets to the catalog and, if requested, creates the CLIST, REXX exec, and/or JCL jobstream.

If the CLIST, REXX exec, or jobstream exists (perhaps from a previous run), you are given the option of overwriting or updating it.

If you select Overwrite, a new CLIST, REXX exec, or jobstream is generated from the current list of DD names that were displayed in the MFEXTMAP migration tool dialog box.
If you select Update, new ALLOCATE commands or DD statements are added to the existing commands or statements. This might be necessary if the program was only partially executed during the previous run.

Mainframe Express also writes the mfextmap.log file to the listing subfolder for the project.

After the program has completed, you can edit, if necessary, any CLIST, REXX exec, or jobstream that was created (to change the JOB information, for example) and use it next time you run the program.