• Ensures that the
error condition),
disconnect mode. user is not logged on at
or reconnects the user
another terminal (an
if he was running in • Obtains pertinent information on the user's virtual machine from the user machine block portion of the directory. • Stores the correct userid (replacing the LOGONxxx userid used
until now), virtual storage size, and other vital information in
the virtual machine's VMBLOK. • Allocates
(necessary
storage).
and
for
initializes segment, page,
handling of the virtual
and swap
machine's
tables
virtual • Schedules MSS volume mounts for any required MSS volumes if the MSS is available and the volume is not already mounted. • Allocates an extended VMBLOK (ECBLOK) if the user's virtual
machine has the ability to run in the extended control mode. • Allocates and initializes virtual device blocks, control unit
blocks, and channel blocks, using information from the user
device blocks portion of the directory. • Establishes links (as feasible) to all DASD devices included in
the directory, the accessibility of any disk being determined by
the user access mode in the directory, and whether any other
users are presently linked to the disk, in read mode and/or
write aode. • Initializes all other virtual device blocks as appropriate, such
as reader, punch, printer, and terminal. • Maps all virtual devices to real devices. • Performs appropriate accounting. • Informs the user of the date and time of the aost recent
revision to the system log aessage (LOGMSG), and of the presence
of any outstanding spooled files in his virtual reader, printer,
or punch. • Sends a ready message to the user with the date and time (and
weekday), and a aessage to the system operator indicating that
the user has logged on.
If the virtual aachine has a device address or a named system in the
directory and the initialization was not suppressed via an option on the LOGON command line, then that device or named system is then loaded (via 1PL) at the conclusion of the logon process. Otherwise, when the logon
functions are complete, the user's terminal is placed in CP read mode ready for the entry of his first desired command. Under the latter condition of no automatic IPL, the user can 1Pt an
alternate nucleus by using the STOP option in the IPL coa.and. This
option causes the normal IPL procedure to halt execution prior to
loading the initial PSi, and issues a DIAGNOSE code 8 that places the
user's terminal in CP read mode. A hexadecimal character entered in
location X'08' changes the nucleus naae. A hexadecimal character
entered in location X'09' changes the apparent storage size. The BEGIN coamand allows the 1PL procedure to continue.
1-124 IBM VM/370 System Logic and Problem Determination--Volume 1

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 the system. 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. These commands access the
same control-block building subroutines in the m04-u1e--- Dft-KV-DS that DKKLOG, the LOGON processor, uses. § Real The system operator can dedicate any real
device to a single virtual machine by issuing the ATTICH comaand. The
device attached is available only to the given virtual machine, 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 drives must be attached to a
virtual machine to be accessed by 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 spooled by 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 use by 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 DEFINE command 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, pseudo timers, and teaporary disks. With
the DEFINE command, the user can change any existing 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 virtual machine channel mode of operation, that is, either selector or block multiplexer. The
default mode, selector channel mode, reflects a channel busy to any SIO operation attempted on the same channel path that has not coapleted the
previous channel SID operation. Block multiplexer mode allows the
successful initiation of different devices on the same channel path.
Channel 0, 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
virtual machine IPL operation.
Note: The channel mode selected has no bearing on the types of channels
that are attached to the real system. 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