Special Considerations for Multiprogramming
Systems under VM/370 When a multiprogramming operating system such as OS/VS or DOS/VS is run
in a virtual machine, its resource-management algorithms interact with
those of VM/370 -- especially when the virtual operating system has a page wait or an I/O wait. Multiprogramming operating systems use these
two methods to interact with VM/310: • VM/VS handshaking • The diagnose interface
This topic discusses these methods and
an operating system under VM/370 that
situations. VM/VS HANDSHAKING also those aspects of running
apply only in certain unique VM/VS handshaking permits instructions issued by an operating system in
a virtual machine to be processed directly by the processor. It also permits VM/310 to simulate privileged instructions. VM/VS handshaking
is available for these operating systems running in virtual machines
under VM/370: • DOS/VS Release 34 with the Advanced Functions-DOS/VS Program Product (S746-XE2) • DOS/VSE with the VSE/Advanced Functions Program Product (5746-XES) • VS1 Release 4 and subsequent releases DOS/VS Release 34 with the Advanced Functions-DOS/VS program Product (S746-XE2) uses handshaking. The use and efficiency of DOS/VS with handshaking is similar to VS1. For further details, refer to the
appropriate DOS/VS program product publications. DOS/VSE with the VSE/Advanced Functions program Product (5146-XES) uses VM/VS handshaking (also known as the DOS/VSE-VM/370 linkage
facility). The use and efficiency of DOS/VSE with handshaking is similar to VS1. For further details, refer to GC33-6106. Although handshaking is a system generation feature for 'Sl, it is
active only when VS1 is under the control of VM/370. It is disabled
when that same iS1 operating system is run on a real machine. For
details about VM/yS handshaking for VS1, refer to the "OS/VS in a
virtual Machine" section in this publication. Section 1. General Considerations 9

THE DIAGNOSE INTERFACE
The diagnose interface, by use of the DIAGNOSE instruction, permits
operating systems running in virtual aachines under VM/310 to
communicate easily and efficiently with VM/310. While this topic provides a summary of the diagnose interface
functions, details about how to use the DIAGNOSE instruction to request
these functions are in the !!LJIQ By inserting DIAGNOSE instructions where appropriate in the operating system's code, the following functions can be requested by a virtual machine: Diagnose
Code • Examine the processor's extended identification code. -----0-- • Examine the contents of real storage. 4 • Invoke a virtual console function (that is, a CP command) 8 from the virtual machine operating system. • Obtain, from CP's pseudo timer: C
- Today's date (aa/dd/yy) - The time-of-day (hh:mm:ss) - Virtual and total processor time used by the virtual
machine • Release pages of virtual storage (but not discontiguous 10 storage) • Manipulate an input spool file in one of the following 14
ways:
- Read the next reader, punch, or printer spool data
- Select a new file for processing
- Repeat the active file n times - Restart the current file at the beginning
- Backspace one record
- Retrieve the subsequent file descriptor • Perform a standard DASD I/O operation. 18 • Clear the VM/310 I/O error recording area on disk. 1C • Perform a general I/O operation for tape or disk. 20 • Interrogate CP's device type and features control blocks. 24 • Notify CP that a dynamically modified channel program is to
be executed. 28 • Locate the start DASD address of the I/O error 2C
recording area (LOGREC). • Read one page of LOGREC data. 30 • Read the VM/310 system dump spool file. 34 10 IBM VM/370 Operating Systems in a Virtual Machine