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Browse Prior Art Database

Detection of Configuration Errors

IP.com Disclosure Number: IPCOM000104334D
Original Publication Date: 1993-Apr-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Maeurer, TR: AUTHOR [+2]

Abstract

Disclosed is a method to detect when a single I/O device is incorrectly defined (configured) to more than one subchannel. The method exploits the I/O-device self-description commands provided by IBM* I/O devices.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Detection of Configuration Errors

      Disclosed is a method to detect when a single I/O device is
incorrectly defined (configured) to more than one subchannel.  The
method exploits the I/O-device self-description commands provided by
IBM* I/O devices.

      As prerequisites, a mechanism is required for storing and
manipulating the self-identification information and, when multiple
paths exist to an I/O device, a mechanism must exist for verifying
that each path reaches the same I/O device.  Such techniques exist in
the prior art.

      The system control program (in this case, MVS/ESA*) maintains
and manipulates logical representations of I/O devices called Unit
Control Blocks (UCBs).  These UCBs exist in a one-to-one relationship
with sub-channels, each of which has an associated I/O device.  To
prevent misconfiguration, the system control program must ensure that
no two UCBs represent the same I/O device.  When a UCB is in a state
where it is protected from all misconfigurations, it is said to be in
the protected state.  The system control program prevents any two
UCBs that correspond to the same I/O device from being in the
protected state at the same time.

      To maintain the protected state of UCBs, searches are required
every time a UCB is to enter the protected state.  The purpose of
these searches is to ensure that the physical identifier of the I/O
device associated with the UCB is not associated with any other UCB
in the protected state.  This implies up to n times n compares, where
n is the number of UCBs currently in the protected state.

      The number of compares can be greatly reduced by taking
advantage of the physical grouping of I/O devices.  That is, I/O
devices are connected in groups to other entities, called control
units, that control and oversee the operation of the attached I/O
devices.  A path between an I/O device and a particular system image
cannot pass through more than one control un...