Defining characteristics between processing systems

Details Defining characteristics between processing systems Defining characteristics between processing systems

1998-10-07

2001-03-13

Rinehart, Mark (Department: 2756)

Electrical computers and digital processing systems: multicomput

Computer-to-computer session/connection establishing

C709S228000, C709S201000

Reexamination Certificate

active

06202095

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and system for indicating system characteristics of one processing system to another processing system.
2. Description of the Related Art
FIG. 1
illustrates a hardware environment of a channel subsystem
2
included in a host system
4
providing communication between CPUs
6
a, b
and I/O devices
10
a, b, c.
A storage controller
8
controls access to the I/O devices
10
a, b, c.
The host system
4
communicates with the storage controller
8
via the channel subsystem
2
and subchannels
14
a, b, c
therein. The host system
4
includes CPUs
6
a, b
that contain the sequencing and processing facilities for instruction execution, interruption action, timing functions, initial program loading, and other machine-related functions. The I/O devices
10
a, b, c
may be comprised of printers, magnetic-tape units, direct-access-storage devices (DASDs), displays, keyboards, communications controllers, teleprocessing devices, and sensor-based equipment. The storage controller
8
regulates and controls data transfers to the I/O devices
10
a, b, c.
The storage controller
8
function may be a separate stand alone machine, such as the IBM 3990 Storage Controller, or housed within the I/O device
10
a, b, c
or within the host system
4
. In certain systems, the host system
4
may view the storage controller
8
as a multitude of separate control unit images or logical subsystems (LSSs), wherein each control unit image provides access to one or more I/O devices
10
a, b, c.
The storage controller
8
may include multiple control unit images, i.e., LSSs, each of which may address up to 256 I/O devices.
The CPUs
6
a, b
and the channel subsystem
2
may access a main storage
12
. Programs and data maintained in the I/O devices
10
a, b, c
such as storage drives, must be loaded into the main storage
12
before the CPUs
6
a, b
can process such programs and data. The main storage
12
may include a fast access buffer or cache. I/O operations involve the transfer of data between the main storage
12
and the I/O devices
10
a, b, c.
The channel subsystem
2
directs the flow of data between the storage controller
8
and the main storage
12
. The channel subsystem
2
relieves the CPUs
6
a, b
of handling I/O operations and permits the CPUs
6
a, b
to devote processing cycles to other operations while the channel subsystem
2
concurrently handles data transfers. In typical implementations, the CPUs
6
a, b,
the main storage
12
, and the channel subsystem
2
are all located within a single host
4
that is attached to a single storage controller
8
, such as the IBM 3990 Storage Controller.
Channel paths
13
provide data communication between the channel subsystem
2
and the storage controller
8
. The channel paths
13
may employ a parallel-transmission protocol or a serial-transmission protocol. The storage controller
8
includes control logic to physically access the I/O devices
10
a, b, c
and control data transfer. In preferred embodiments, multiple channel paths
13
may be dedicated for communication with a particular I/O device
10
a, b, c.
A subchannel
14
a, b, c
is dedicated to each I/O device
10
a, b, c
accessible to the channel subsystem
2
, i.e., there is a one-to-one relationship between subchannels
14
a, b, c
and I/O devices
10
a, b, c.
Each subchannel
14
a, b, c
consists of internal storage and includes information relating the I/O devices
10
a, b, c
to the channel subsystem
2
. The channel subsystem
2
uses the information in the subchannels
14
a, b, c
to access the I/O devices
10
a, b, c.
The subchannels
14
a, b, c
are assigned to the I/O devices
10
a, b, c
at initialization. The subchannels
14
a, b, c
maintain information such as the channel command word (CCW), channel-path identifier, device number, etc., concerning operations initiated with respect to the I/O device
10
a, b, c
represented by the subchannel
14
a, b, c.
I/O devices
10
a, b, c
that are attached to the channel subsystem
2
by multiple channel paths
13
may be accessed using any of the available channel paths
13
. An I/O device
10
a, b, c
is addressed by channel-path identifiers (CHPIDs) identifying the path to a device, subchannel numbers identifying the subchannel
14
a, b, c
associated with the device, and a device number uniquely identifying the I/O device
10
a, b, c
to the host system
4
. The IBM S/390 operating system allows for dynamic-reconnection, wherein the storage controller
8
may select any channel path
13
leading to the host system
4
when logically reconnecting to the channel subsystem
2
. A description of these commands is provided in the IBM publication, “IBM 3990/9390 Storage Control Reference,” IBM Document no. GA32-0274-04 (Copyright IBM, 1994, 1996), which publication is incorporated herein by reference in its entirety.
In the IBM mainframe environment, the channel paths
13
from a host system
4
to the storage controller
8
are identified to the storage controller
8
by a Set Path Group Identifier command. This command assigns a path group ID to one or more channel paths that provide communication between a host system
4
and one of the I/O devices
10
a, b, c.
Thus, a subchannel
14
a, b, c
is related to a path group ID, which relates the paths to an I/O device
10
a, b, c
associated with the subchannel
14
a, b, c.
The path group IDs define the paths associated with a host
4
for the purpose of device reservation.
In prior art systems, it is possible for a host
4
to concurrently run two or more operating systems—a host operating system and a guest operating system which runs on top of the host operating For instance, the IBM VM/ESA® operating system supports running a guest system with a different operating system date/time than the host VM/ESA system. This enables testing of MVS®, VM, and VSE/ESA™ systems with different application programs without affecting the host VM/ESA system. VM/ESA and MVS are registered trademarks of IBM and VM/ESA is a trademark of IBM. However, one problem that may arise in such a system is that the guest operating system may have enhanced function capability beyond the capabilities of the host operating system. In such case, the host operating system would not be able to understand certain commands and operations from the storage controller
8
when the storage controller
8
is interacting with the guest operating system in the enhanced capability modes.
In prior art systems, the host may issue commands to inhibit the enhanced operations. For instance, in the IBM mainframe environment, the host system
4
may issue a Set Special Intercept Condition which causes the host operating system to monitor communications from the storage controller
8
to the guest operating system. Under control of the Set Special Intercept Condition, the host
4
monitors commands on a path group. The host operating system may then intercept certain specified commands from the storage controller
8
to the guest operating system on a path associated with the path group ID being monitored and prevent such commands from reaching the guest operating systems. These commands and intercept methods are described in IBM publication “Storage Subsystem Library: IBM 3990 Storage Control Reference (Models 1, 2, and 3)”, IBM document no. GA32-0099-06, (IBM Copyright 1988, 1994), which publication is incorporated herein by reference in its entirety.
Alternatively, to prevent a storage controller
8
implementing operations incompatible with the host system
4
capabilities, a systems administrator may selectively disable certain functions in the storage controller
8
that the host operating system cannot handle.
There is a need in the art for an improved method and system of determining and enabling system capabilities.
SUMMARY OF THE PREFERRED EMBODIMENTS
To overcome the limitations in the prior art described above, the present invention discloses a method and system for indicating system capabilities. A first pr

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