THE IDENTIFY PROTOCOL The IDENTIFY protocol defines a means for virtual machines to identify
themselves to other virtual machines by passing user-defined control
information via a standard VMCF message header. Figure 18 shows the IDENTIFY protocol graphically. When the IDENTIFY subfunction is issued, CP directs an external
interrupt to the sink virtual machine. Along with the external
interrupt, the sink virtual machine receives a standard VMCF message header that contains user-defined information. The IDENTIFY protocol
does not cause a response external interrupt to be directed the source
virtual machine. Source Virtual Machine DMKVMC VMCF Interface Module I I I I I I I I I I I I I I Sink Virtual Machine IDENTIFY--->---------->I I I I I I I I I--External Interrupt-------> I (IDENTIFY Sequence Complete) I I Figure 18. The IDENTIFY Protocol
152 IBM VM/370 System programmer's Guide
April 1, 1981
Descriptions of VMCF Subfunctions
There are two types of VMCF subfunctions: data transfer and control.
THE CONTROL SUBFUNCTIONS The VMCF control subfunctions allow efficient management
transfer operations from your virtual machine console. The
subfunctions are: AUTHORIZE, UNAUTHORIZE, CANCEL, QUIESCE, IDENTIFY, and REJECT.
of data
control RESUME, AUTHORIZE enables VMCF for a virtual machine; once AUTHORIZE has been
executed, the virtual machine can execute other VMCF subfunctions and
receive messaqes and data from other authorized VMCF virtual machines.
It is possible to specify three options with the AUTHORIZE subfunction: SPECIFIC, PRIORITY, and VMCPSMSG. The SPECIFIC option authorizes communication with a specific virtual Any messaqes sent to the virtual machine from other than the
specified virtual machine will be rejected. The SPECIFIC option can be
used in an application where virtual machines desire to communicate with
a master controller but not among themselves. Under the message
facility, CP is authorized with every virtual machine that is to receive
messages sent via the SMSG command. Virtual machines that are to
receive messages must authorize themselves.
The PRIORITY option allows a virtual machine to authorize the receipt
of priority messaqes. A virtual machine is allowed to send priority
messages to another virtual machine only if the other virtual machine is
authorized to receive priority messages. A priority message is one that
will be queued ahead of nonpriority messages and therefore accepted
first. When you execute the AUTHORIZE subfunction, you must specify the
address and length of the external interrupt buffer for your virtual
machine. The buffer must be large enough to contain a £ixed message
header (40 bytes). The message header identifies messages sent by other
virtual machines or responses to messages you might send to your own
virtual machine.
If you are going to accept SENDX-type communications, you must
specify the size of the external interrupt buffer as 40 plus the maximum
size of SENDX data that you plan to accept. This has the effect of
authorizing SENDX protocol. That is, a virtual machine may receive data
along with the external interrupt in its external interrupt buffer. When a virtual machine sends data to another virtual machine via the SENDX the data must fit in that virtual machine's externaJ
interrupt buffer or the subfunction will be rejected. Messages sent via
the special message facility require a buffer length of 169 bytes.
Any AUTHORIZE options in effect can
reexecuting the AUTHORIZE subfunction. If
execution of the AUTHORIZE subfunction,
authorization status is not changed.
be reset or changed by
there are errors during
a virtual machine's Part 2. Control Program (CP) 153
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