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Description of CP1STLVL

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The essential files in this package are

  • CP1STL ASSEMBLE -- Source code for CP exit.
  • CP1STLVL DESCRIPT -- This file, a description and explanation.
  • CP1STL TXTBX0 -- Assembled CP1STL ASSEMBLE (for z/VM 6.3.0)
  • CP1STL TXTBW0 -- Assembled CP1STL ASSEMBLE (for z/VM 6.2.0)
  • CP1STL TXTBU0 -- Assembled CP1STL ASSEMBLE (for z/VM 5.3.0-6.1.0)
  • CP1STL TXTBT0 -- Assembled CP1STL ASSEMBLE (for z/VM 5.2.0)
  • CP1STL TXTBQ0 -- Assembled CP1STL ASSEMBLE (for z/VM 4.3.0)
  • CP1STL TXTBG0 -- Assembled CP1STL ASSEMBLE (for VM/ESA 2.4.0)
There are also other files that might be useful to a few people:
  • CP1STL ASSPRE52 -- Source code for CP exit, pre-5.2.0 version.
  • CP1STL ASSBT0 -- Source code for 5.2.0 version, CP1STL TXTBT0
  • CP1STL EXEC -- Crude EXEC to do all the CPXLOAD stuff.
  • CP1STLVL IAGREE -- Agreement File for VM Download Library
  • CP1STLVL ABSTRACT -- One line description for VM Download Library
The author of the program and documentation is Tim Greer.

The CP1STLVL package helps users of VM second-level systems (guests) execute a CP command on the first level system, and receive the response, without interrupting the second-level system. This is done by loading and enabling the CP exit CP1STL. To the second-level user, the appearance is that a new CP command exists.

I created this tool as a convenience in testing. Often I am using a VM guest operating system running on a first-level VM system, and have a need to invoke a first-level command. For example, I may wish to define a temporary disk, define and couple a virtual CTC, or invoke a trace. In the past, I would do this by pressing PA1 to get thrown into first-level CP READ, do the command, and then PA1 back to second level. That method has some disadvantages. In particular, you freeze the second-level system while you are doing your first-level stuff, leaving any dialed-in users looking at the x-clock, and potentially causing timeout errors for links to other systems (e.g. via ISFC). Also, you must be on the first-level logon session. If you are dialed in to the second-level system, you can't even invoke a first-level command. Finally, in order to automate my testing, I sometimes need to be able to include this first-level activity in a REXX EXEC I am running second-level. The CP1STL CP exit is a means of getting around these problems.

The files included in this package allow a class A user to add the CP command CP1STLVL to the second-level system. (Of course, you can choose to name the command something else.) For those interested in seeing how it works or adding to it, I include the source code. You may also need the source code so that you can compile for the appropriate CP level. (Use QUERY CPLEVEL to verify what level you are running.) I have provided CP1STL TXTs for several VM release levels. If your second-level system is at some other CP level, recompile of CP1STL ASSEMBLE is recommended. That said, I would expect CP1STL TXTBQ0 to work ok for z/VM 3.1.0 through 5.1.0, and CP1STL TXTBU0 may well work beyond z/VM 5.3.0. Here are the instructions, copied out of CP1STL ASSEMBLE:

                                                                           
  To use, once you have assembled CP1STL TXTBG0, put these files on             
  some Class A user's A (191) disk and invoke the following commands            
  (Subsequent lines assume you chose filemode B on the first line):             
                                                                                
    CPACCESS userid 191 filemode RR                                             
    CPXLOAD CP1STL TXTBG0 B NOCONTROL TEMP                                      
    DEF COM CP1STLVL ANYTIME EPNAME CP1STLIN PRIVCLASSANY                       
    ENABLE CMD CP1STLVL                                                         
                                                                                
  In order to undo some of your handiwork, you may want to be aware             
  of a few other commands:                                                      
    DISABLE CMD CP1STLVL -- to disable the CP1STLVL command                     
    QUERY CPXLOAD        -- find the identifier number of CP1STLVL TXTBG0       
    CPXUNLOAD ID nn      -- unload CP1STLVL TXTBG0 (nn is the identifier)       

(In the above, replace TXTBG0 with TXTBQ0, TXTBT0, etc. as appropriate.) You can invoke the above commands one at a time from the command line, from within a REXX EXEC, or put them in SYSTEM CONFIG so that the function is available as soon as the system comes up. You may want to modify some of the above instructions. In particular, notice that I have defined the CP1STLVL command to be usable ANYTIME (including before logon) and by everyone (PRIVCLASSANY). Obviously you should do something different if security is a concern. For more information, see VM/ESA CP Exit Customization. The first edition of this is for VM Version 2, Release 1.0, October 1995, IBM publication number SC24-5672-00. This book also contains more examples of CP exits.

This tool is for VM guests running on a VM first-level system. It is possible to do a similar thing on other guest operating systems, and source code for an OS/390 version is available on VM's web pages as well. Also available is CPHOST, a version of CP1STLVL to which Shimon Lebowitz and Kris Buelens added some functionality.