Three commands alter the I/O configuration of a user's virtual aachine
after he has logged on.Two are user commands, while the third a systea operator command, because it affects the status of real devices attached
to thesystem. The ATTACH and DETACH co.mands are contained in D!KVDI, DMKYDC, DMKYDD, and DKKYDE and the DEFINE command in D!KDEF. The systea command scanner (DMKCFM) calls both page able modules after their foraat
and privilege classes have been validated. Thesecommands access the
same control-block building subroutines in them04-u1e--- Dft-KV-DS that DKKLOG, the LOGON processor, uses. ยง Real The system operator can dedicate any real
device to a single virtual machineby issuing the ATTICH comaand. The
device attached is available only to the given virtualmachine, and all I/O requests to it are handled by CCW If the device is a DASD, cylinder relocation does not occur when SEEK addresses or home addresses are referenced. The I/O supervisor does not queue operations
on the device, nor does it autoaatically restart it or do ordered seek
queuing. Nonsharable devices such as tape drivesmust be attached to a
virtual machine to be accessedby the virtual machine. I virtual machine can also have a dedicated card reader/punch or printer.
However, this is usually not necessary because of the unit record
spooling facilities of CP.Unit record input or output on a dedicated
(attached) device is not spooledby CP. The unit attached =ay be given a virtual address different from its real address; however, the virtual machine may not already have a virtual device at the attached address.
A real device cannot be attached (1) if it is currently dedicated to
another virtual machine, (2) if it contains minidisks that are in useby other vitual machines, or (3) if it is a systea-owned volume that is in
use for spooling or paging.Yiri!!! Device: A system user can define a new virtual device
with the DEFINEcommand that does not require the dedication of a
corresponding real device. Devices that can be defined are consoles,
spooled readers, punches and printers, dialable TP lines, virtual
channel-to-channel adapters, pseudotimers, and teaporary disks. With
the DEFINE command, the user can change anyexisting virtual "device
address whether it corresponds to a shared or dedicated real device or
no real device unit.
The DEFINE command can also describe the virtualmachine channel mode of operation, that is, either selector or block multiplexer. The
default mode, selector channelmode, reflects a channel busy to any SIO operation attempted on the same channel path that has not coapleted the
previous channelSID operation. Block multiplexer mode allows the
successful initiation of different devices on thesame channel path.
Channel0, a byte-multiplexer channel, is unaffected by the DEFINE command. Also, any channel with a channel-to-channel adapter (CTCI) defaults to selector mode of operation regardless of the channel mode selected. Use of the DEFINE command with the CHANNELS operand generates
a virtual machine reset; therefore, it should be invoked prior to the
virtualmachine IPL operation.
Note: The channelmode selected has no bearing on the types of channels
that are attached to the realsystem. Temporary disks are dynamically obtained cylinders of DISD stoiage
space. They are available to the user for as long as they are part of
his virtual aachine configuration, but the data on thea is destroyed
after the user detaches the area. For all other purposes, however, they
appear to be a standard disk.
CP Introduction 1-125
after he has logged on.
to the
and privilege classes have been validated. These
same control-block building subroutines in the
device to a single virtual machine
device attached is available only to the given virtual
on the device, nor does it autoaatically restart it or do ordered seek
queuing. Nonsharable devices such as tape drives
virtual machine to be accessed
However, this is usually not necessary because of the unit record
spooling facilities of CP.
(attached) device is not spooled
A real device cannot be attached (1) if it is currently dedicated to
another virtual machine, (2) if it contains minidisks that are in use
use for spooling or paging.
with the DEFINE
corresponding real device. Devices that can be defined are consoles,
spooled readers, punches and printers, dialable TP lines, virtual
channel-to-channel adapters, pseudo
the DEFINE command, the user can change any
address whether it corresponds to a shared or dedicated real device or
no real device unit.
The DEFINE command can also describe the virtual
default mode, selector channel
previous channel
successful initiation of different devices on the
Channel
a virtual machine reset; therefore, it should be invoked prior to the
virtual
Note: The channel
that are attached to the real
space. They are available to the user for as long as they are part of
his virtual aachine configuration, but the data on thea is destroyed
after the user detaches the area. For all other purposes, however, they
appear to be a standard disk.
CP Introduction 1-125