Apr il 1, 1981
The Virtual Machine Communication Facility The Virtual Machine communication Facility (VMCF) is part of the CP component of VM/370. VKCF provides virtual machines with the ability to
send data to and receive data from any other virtual machine. VMCF is made up of five data transfer subfunctions, seven control
subfunctions, a special external interrupt (code X'4001') to
asynchronously alert virtual machines to pending messages, and an
external interrupt message header to pass control information (and data,
at times) to another user. VMCF is implemented by means of subfunctions invoked using the DIAGNOSE instruction with a code of X'68' and a special 40-byte parameter list called VMCPARM. A VMCF subfunction is indicated by a
particular subfunction code in the VMCPFUNC field in the parameter list. BQte: Before you can use any other VMCF subfunction, you must use the AUTHORIZE subfunction for communications. Before you can communicate
with another user, that user must also have used the AUTHORIZE su bfu nct ion.
A special external interrupt (code X'4001') is used by module DMKVKC to notify one virtual machine of a pending transfer of data. This
interrupt is also used to synchronize sending and receiving of data. Along with this interrupt, the virtual machine receives a message
header that is logged into a preassigned virtual storage area. This
message header is used to define the type of request and to provide data
transfer information, such as length of data. The message header is
also used to notify the originator of a transaction of the success or
failure of the transaction. In this case, the message header includes
such information as residual counts and data transfer return codes.
Figure 14 lists the VMCF subfunction$ and qives a brief description
of each. The subfunctions are described in detail in the section
"Descriptions of VMCF Subfunctions." Messages and data are directed to other virtual machines logically
via the userid. Data is transferred in up to 2048-byte blocks from the
sending virtual machine's storage to the receiving virtual machine's
storage. The amount of data that can be moved in a single transfer is
limited only by the sizes of virtual machine storage of the respective
virtual machines. Use of real storage is minimal. Only one real storage
paqe need be locked during the data transfer.
The special message facility uses VKCF to send messages from one
virtual machine storage area to another virtual machine storage area.
For a description of the special message facility and how it uses VMCF, see "Special Message Facility" in this section. Part 2. Control Proqram (CP) 143

April 1, 1981 r- I Function I Codel comments I I AUTHORIZE I Control Initializes VMCF for a given virtual machine. I I I UNAUTHORIZE SEND SEND/RECV SENDX RECEIVE CANCEL REPLY QUIESCE RESUME , IDENTIFY I I , REJECT I , .. , Once AUTHORIZE is executed, the virtual I , machine can execute other VMCF subfunctions I , and receive messages or requests from other I I I ,Control I , Data
Data
Data
Data Control Data Control Control Control Control users. I Terminates VMCF activity. I I Directs a message or block of data to another
virtual machine.
Directs a message or block of data to another
virtual machine, and requests notification
of a reply.
Directs data to another virtual machine on a
faster but more restrictive protocol than
the SEND subfunction.
fAllows you to accept selective messages or
data sent via a SEND or SEND/RECV subfunction. Cancels a message or data transfer directed
to another user but not yet accepted by that
user.
Allows you to direct data back to the
originator of a SEND/RECV subfunction,
simUlating full duplex communication.
Temporarily rejects further SEND, SENDX, SEND/RECV, or IDENTIFY requests from other
users.
Resets the status set by the QUIESCE subfunction and allows execution of
subsequent requests from other users.
Notifies another user that your virtual
machine is available for VMCF communication.
Allows you to reject specific SEND or SEND/RECV requests pending for your virtual
machine. flThe word "Data" in this column indicates a data transfer subfunction
, whereas the word "Control" indicates a VMCF control subfunction. L- Figure 14. Virtual Machine Communication Facility (VMCF) Subfunctions 144 IBM VM/370 System Programmer's Guide