April 1, 1981 • Have the VM/370 system operator attach the DOS/VS system residence
directly to a userid, for that user's exclusive use. When the
operator (or another user with Class B command privileges) attaches
the disk to one user, no one else may access the volume. All of the console logs and command examples in this section
assume that a DOS/VS system residence is attached to the virtual machine
at virtual address 250. SHARING THE DOS/VS SYSTEM RESIDENCE VOLUME If VSAM is used, only one user at a time may access the DOS/VS system
residence volume in read/write status. This requirement is necessary
because only one user can update the VSAM catalog and the label
information cylinder. DOS/VS uses this cylinder to keep a record of
volumes and files needed by programs that are running.
However, if VSAM is not used and a user wants to share the DOS/VS system residence volume, set up a read/write core image library for
link-editing. Then, share the SYSRES libraries in read-only status with
other users. This method is acceptable under one of these two
conditions: • Some action has been taken by the installation to provide individual
standard label cylinders for each userid that accesses DOS/VS. • --or--
Different virtual machines use
one virtual machine uses BG and
F1, F2, and F3.
different partitions. For example,
F4, and another virtual machine uses
Another method for sharing DOS/VS is for a user to have his own
read/write copy of the system residence volume. Then, this user can
share this volume with others in read-only status and share the private
libraries with other users. STANDARD LABEL CYLINDER To share DOS/VS among virtual machines when unique partitions are DQ! assigned to each virtual machine, a user must provide a unique standard
label cylinder for each such virtual DOS/VS user. When using DOS/VSE with the VSE/Advanced Functions Program Product (5746-XE8), a user can separate label information areas and use a name
to access each area. While users must create these areas on the system
residence volume, they don't have to (as in DOS/VS Release 34 and
earlier releases): • Place label information areas at the end of the volume, following the
normal standard label cylinder • Modify the IPL communication routines • Bypass the $JOBCTLA procedure
section 3. DOS/VS in a Virtual Machine 83

Page of GC20-1821-3 As Updated April 1, 1981 by TNL GN25-0840 For DOS/VS Release 34 (or earlier), the individual standard label
cylinders should be placed at the end of the system residence volume
(following the normal standard label cylinder). To support unique
standard label cylinders, modify DOS/VS as follows: • The communication region in each DOS/VS virtual machine must point to
the appropriate label cylinder for each user. Do this by modifying
the IPL communication routines. • Bypass the procedure $JOBCTLA. This procedure updates the
communication region pointer to the normal standard label cylinder at
the end of each job. , • Bypass the label cylinder reset code in the $$BSYSWR procedure. I $$BSYSWR resets the normal standard label pointer whenever a condense I function (CONDS) of the MAINT program is requested. As an I alternative, never condense a library in any virtual machine using a I non-standard label cylinder.
Using Virtual Unit Record Devices When using DOS/VS in a virtual machine,
unit record devices, which are normally
en try:
a user must have the following
defined in the VM/370 directory • A victual card reader, from which DOS/VS reads the job input stream. • A victual printer, which receives all the SYSLST output generated
during DOS/VS operation. • A victual card punch, which receives SYSPCH output generated during DOS/VS operation.
Depending upon how DOS/VS was generated, a user may need to determine
a virtual device address. For example: If DOS/VS expects a 3211
printer at address 002 and no printer is at this address in the virtual
machine configuration, define one with the CP DEFINE command:
define 3211 002 When using CMS to prepare jobs for a DOS/VS virtual machine, use
the virtual card punch to spool jobs to the DOS/VS virtual machine.
Before using DOS/VS, find out (from the programmer at the
installation responsible for generating and maintaining DOS/VS) what
are the virtual device requirements.
A user can control virtual unit record devices with the CP SPOOL command. However, printed or punched output need not have to be printed
or punched. For example: When using a technique for alternating between
operatinq systems, a user can spool the virtual printer to the card
reader, as follows:
spool printer to *
This command reads printed output onto a CMS disk so that it can be
examined. Also, use the SPOOL command to change the output spooling
class of the virtual machine's spooled printer or punch files.
84 IBM VM/370 o?erating Systems in a Virtual Machine