Abstract: A data processing I/O system including a main storage for storing data and data processing instructions arranged in software programs, and a channel subsystem having hardware for reporting conditions in the channel subsystem to the software. A special Channel Subsystem Call (CHSC) instruction is used to store event information from the channel subsystem into the main memory for use by the software such that new or restored resources such as a channel path, a channel path and partial control unit link address, or a channel path and full control unit link address, may be originally made accessible, or may be restored to the I/O system. A mechanism is also provided to inquire of a device how long it expects to not be accessible to give the device sufficient time to reset itself before it is varied offline, thus preventing a device from being isolated or "boxed" prematurely.

Abstract: An installation creates a source I/O definition file (IODF), defining a current system I/O configuration, and a target IODF, defining a future I/O configuration. An activate function is initiated to change the system's hardware and software definition to correspond to the target IODF. A compare function compares the source and target IODFs, and creates a Configuration Change Block (CCB) to efficiently drive the change process. A validation function validates that the proposed change is valid, and the change process updates the hardware and software configuration definitions. If the change process is successful, a notification is sent; if not, a back-out process restores the I/O configuration to its initial state.

Abstract: An installation creates a source I/O definition file (IODF), defining a current system I/O configuration, and a target IODF, defining a future I/O configuration. When the configuration definition is dynamically changed from the current to the target, a serialization mechanism--comprising a "device pin" technique and a "group serialization" technique to handle changed device group definitions--insures that data integrity is not lost on devices undergoing reconfiguration; and a change detection mechanism insures that changes to control structures affected by the dynamic reconfiguration, are noticed by programs accessing those control structures while the structures are changing.

Abstract: A switching error detection and recovery mechanism recognizes that an I/O configuration has changed. Comparing new configuration data to previous data maintained in a CDT table structure, and detecting unequal path information, an error condition is recognized. After recognizing the error condition, recovery actions are taken to notify the operator and insure data integrity. The CDT is structured so that redundant data is eliminated, and so records may be efficiently and dynamically added and deleted.

Abstract: A switching error detection and recovery mechanism recognizes that an I/O configuration has changed. Comparing new configuration data to previous data maintained in a CDT table structure, and detecting unequal path information, an error condition is recognized. After recognizing the error condition, recovery actions are taken to notify the operator and insure data integrity. The CDT is structured so that redundant data is eliminated, and so records may be efficiently and dynamically added and deleted.