April 1, 1981 VIRTUAL MACHINE I/O MANAGEMENT
A real disk devicecan be shared among multiple virtual machines.
virtual device sharing is specified in theVK/370 directory entry or by
a user command. If specified by the user, an appropriate password must
be supplied before gaining access to the virtual device. A particular
virtual machine may be assigned read-only or read/write access to a
shared disk device.CP checks each virtual machine input/output
operation against the parameters in the virtual machine configuration to
ensure device integrity.Virtual Reserve/Release support can be used to further enhance device
integrity for data on shared minidisks. Reserve/Release operation codes
are simulated on a virtual basis for minidisks, including full-extent
minidisks. For details on Reserve/Release su pport, refer to theVM/Jlg gng Determination Quide. The virtual machine operating system is responsible for the operation
of all virtual devices associated with it. These virtual devices may be
defined in theVM/310 directory entry of the virtual machine, or they
may be attached to (or detached from) the virtual machine's dynamically, for the duration of the session.
virtual devices may be dedicat.ed, as when mapped to a fully equivalent
real device; shared, as when to a minidisk or when specified as a
shared virtual device; or spooled byCP to intermediate direct access
storage.
In a real machine runninq under control of as, input/output
operations are normally initiated when a problem program requests as to
issue aSTART I/O instruction to a specific device. Device error
recovery is handled by the operating system. In a virtual machine, os
can perform these same functions, but the device address specified and
the storaqe locations referenced will both be virtual. It is the
responsibility ofCP to translate the virtual specifications to real. Virtual I/O can be initiated by either processor; all real I/O requests must be executed by the main processor, and all I/O interrupts must be received on the main processor (the processor with 1/0 capability). Any I/O requests by the attached processor (the
processor withoutIIO capability) are transferred to the main processor.
In addition,the interrupts caused by the input/output operation are
reflected to the virtual machine for its interpretation and processing.
If input/output errors occur,CP records them but does not initiate
error recovery operations. The virtual machine operating system must
handle error recovery, but does not record the error (ifSVC 76 is
used)• Input/output operations initiated by CP and spooling), are performed directly
tr ans lat ion.
for its own purposes (paging
and are not subject toVirtual machines may access data on MSS mass storage
that virtual machine's standard3330 device support.
faults, and associated asynchronous interruptions, are
the virtual machine in this situation.
volumes usingftSS cylinder
transparent toPart 2. ContrJl Program (CP) 79
A real disk device
virtual device sharing is specified in the
a user command. If specified by the user, an appropriate password must
be supplied before gaining access to the virtual device. A particular
virtual machine may be assigned read-only or read/write access to a
shared disk device.
operation against the parameters in the virtual machine configuration to
ensure device integrity.
integrity for data on shared minidisks. Reserve/Release operation codes
are simulated on a virtual basis for minidisks, including full-extent
minidisks. For details on Reserve/Release su pport, refer to the
of all virtual devices associated with it. These virtual devices may be
defined in the
may be attached to (or detached from) the virtual machine's
virtual devices may be dedicat.ed, as when mapped to a fully equivalent
real device; shared, as when
shared virtual device; or spooled by
storage.
In a real machine runninq under control of as, input/output
operations are normally initiated when a problem program requests as to
issue a
recovery is handled by the operating system. In a virtual machine, os
can perform these same functions, but the device address specified and
the storaqe locations referenced will both be virtual. It is the
responsibility of
processor without
In addition,
reflected to the virtual machine for its interpretation and processing.
If input/output errors occur,
error recovery operations. The virtual machine operating system must
handle error recovery, but does not record the error (if
used)
tr ans lat ion.
for its own purposes (paging
and are not subject to
that virtual machine's standard
faults, and associated asynchronous interruptions, are
the virtual machine in this situation.
volumes using
transparent to