Method and system for capturing and controlling access to information in a coupling facility

Abstract

A method and system for capturing and controlling access to information in a data processing system is provided. The data processing system includes one or more operating systems coupled to a coupling facility. When one or more operating systems lose communication with the coupling facility, a surviving operating system captures some or all of the information in the coupling facility, including that information associated with the failed operating system(s). In order to capture the information when a system fails or at any other time, the information in the coupling facility is serialized, thereby preventing all access to the information except for those commands capturing the information. While the information is serialized, requests for the information are queued and then re-driven once serialization is released. If an operating system loses communication with the coupling facility during the creation of a dump, another operating system will continue the dump.

Claims

What is claimed is:

1. A method for capturing data in a data processing system having one or more operating systems coupled to a coupling facility, said method comprising the step of:

requesting creation of a dump of information stored within said coupling facility, said requesting being performed external to said coupling facility; and

creating said dump within said coupling facility, said creating being performed by processing capabilities of said coupling facility.

2. The method of claim 1, further comprising the step of detecting when an operating system loses communication with said coupling facility and wherein said requesting step includes having a program located within one of said one or more operating systems request said dump, said dump including information located in the coupling facility associated with said operating system which lost communication with said coupling facility.

3. The method of claim 2, wherein said program is located in one of said one or more operating systems which did not lose communication with said coupling facility.

4. The method of claim 1, wherein all of said operating systems coupled to said coupling facility lose communication with said coupling facility and wherein said step of requesting is performed by the first operating system which re-establishes communication with said coupling facility.

5. The method of claim 1, wherein said requesting step comprises the steps of:

building a parameter list to identify said information to be included in said dump, said identified information including a portion or all of the information stored in said coupling facility; and

using a dumping macro to initiate said dump, said dumping macro using said parameter list.

6. The method of claim 5, wherein said building step further comprises the step of building the parameter list based on one or more predefined options associated with said dump.

7. The method of claim 1, wherein said requesting step further comprises the step of initiating a dump request by an operator of said data processing system.

8. The method of claim 7, wherein said initiating step comprises the steps of:

building a parameter list to identify said information to be included in said dump, said identified information including a portion or all of the information stored in said coupling facility; and

using a dumping command issued by said operator to initiate said dump, said dumping command using said parameter list.

9. The method of claim 8, wherein said dumping command comprises at least one of a DUMP command and a SLIP command.

10. The method of claim 1, further comprising the step of serializing said information to be included in said dump such that said serialized information is limited to being accessed by a predefined set of commands.

11. The method of claim 10, further comprising the steps of:

determining an amount of time said information is to be serialized; and

releasing serialization when said determined amount of time has been exceeded.

12. The method of claim 11, further comprising the step of overriding said determined amount of time when the determined time is unacceptable.

13. The method of claim 10, further comprising the step of storing a request to access said serialized information.

14. The method of claim 13, further comprising the step of redriving said request when serialization of said information is released.

15. The method of claim 1, wherein said information is located within one or more structures stored within said coupling facility, each said one or more structures comprised of identifiable data of one or more types.

16. A system for capturing data in a data processing system having one or more operating systems coupled to a coupling facility, said system for capturing data comprising:

means for requesting, external to said coupling facility, creation of a dump of information stored within said coupling facility; and

means for creating said dump within said coupling facility, said means for creating being included within said coupling facility.

17. The system of claim 16, further comprising means for detecting when an operating system loses communication with said coupling facility and wherein said requesting means includes means for having a program located within one of said one or more operating systems that has not lost communication with said coupling facility request said dump, said dump including information located in the coupling facility associated with said operating system which lost communication with said coupling facility.

18. The system of claim 17, wherein said program is located in one of said one or more operating systems which did not lose communication with said coupling facility.

19. The system of claim 16, wherein all of said operating systems coupled to said coupling facility lose communication with said coupling facility and wherein said means for requesting is performed by the first operating system which re-establishes communication with said coupling facility.

20. The system of claim 16, wherein said requesting means comprises:

means for building a parameter list to identify said information to be included in said dump, said identified information including a portion or all of the information stored in said coupling facility; and

means for using a dumping macro to initiate said dump, said dumping macro using said parameter list.

21. The system of claim 20, wherein said building means further comprises means for building said parameter list based on one or more predefined options associated with said dump.

22. The system of claim 16, wherein said requesting means further comprises means for initiating a dump request by an operator of said data processing system.

23. The system of claim 22, wherein said initiating means comprises:

means for building a parameter list to identify said information to be included in said dump, said identified information including a portion or all of the information stored in said coupling facility; and

means for using a dumping command issued by said operator to initiate said dump, said dumping command using said parameter list.

24. The system of claim 23, wherein said dumping command comprises at least one of a DUMP command and a SLIP command.

25. The system of claim 16, further comprising means for serializing said information to be included in said dump such that said serialized information is limited to being accessed by a predefined set of commands.

26. The system of claim 25, further comprising:

means for determining an amount of time said information is to be serialized; and

means for releasing serialization when said determined amount of time has been exceeded.

27. The system of claim 26, further comprising means for overriding said determined amount of time when said determined amount of time is unacceptable.

28. The system of claim 25, further comprising means for storing a request to access said serialized information.

29. The system of claim 28, further comprising means for redriving said request when serialization of said information is released.

30. The system of claim 16, wherein said information is located within one or more structures stored within said coupling facility, each said one or more structures comprised of identifiable data of one or more types.

31. The system of claim 16, wherein said information is at least one of control information, entry data and adjunct data.

32. A method for capturing data in a data processing system having a plurality of operating systems coupled to a coupling facility, said method comprising the steps of:

initiating creation of a dump of information stored in said coupling facility by a first of said plurality of operating systems; and

continuing to request creation of said dump by a second of said plurality of operating systems when said first of said plurality of operating systems is unable to proceed with said dump.

33. The method of claim 32, wherein said continuing step comprises the steps of:

updating a status control at said coupling facility representing which operating system is responsible for completing said dump; and

specifying to said operating system responsible for said dump that said dump is to be continued.

34. The method of claim 32, wherein said information comprises one or more of control information, data and adjunct data.

35. The method of claim 32, wherein said information is located within one or more structures stored within said coupling facility, each said one or more structures comprised of identifiable data of one or more types.

36. A system for capturing data in a data processing system having a plurality of operating systems coupled to a coupling facility, said system for capturing data comprising:

means for initiating creation of a dump of information stored in said coupling facility by a first of said plurality of operating systems; and

means for continuing to request creation of said dump by a second of said plurality of operating systems when said first of said plurality of operating systems is unable to proceed with said dump.

37. The system of claim 36, wherein said continuing means comprises:

a status control at said coupling facility representing which operating system is responsible for completing said dump; and

means for specifying to said operating system responsible for said dump that said dump is to be continued.

38. The system of claim 36, wherein said information comprises one or more of control information, data and adjunct data.

39. The system of claim 36, wherein said information is located within one or more structures stored within said coupling facility, each said one or more structures comprised of identifiable data of one or more types.

Description

TECHNICAL FIELD

This invention relates in general to the field of data processing and, in particular, to a facility for capturing and/or accessing a portion or all of the information stored within a shared or coupling facility.

CROSS REFERENCE TO RELATED APPLICATIONS

This application contains subject matter which is related to the subject matter of the following applications which are assigned to the same assignee as this application. Each of the below listed applications is hereby incorporated by reference in its entirety:

"Configurable, Recoverable Parallel Bus," by N. G. Bartow et al., Ser. No. 07/839,657, (Docket No. PO9-91-066), Filed: Feb. 20, 1992;

"High Performance Intersystem Communications For Data Processing Systems," by N. G. Bartow et al., Ser. No. 07/839,652, (Docket No. PO9-91-067), Filed: Feb. 20, 1992;

"Frame-Group Transmission And Reception For Parallel/Serial Buses," by N. G. Bartow et al., Ser. No. 07/839,986, (Docket No. PO9-92-001), Filed: Feb. 20, 1992;

"Communicating Messages Between Processors And A Coupling Facility," by D. A. Elko et al., Ser. No. 07/860,380, (Docket No. PO9-91-006), Filed: Mar. 30, 1992;

"Sysplex Shared Data Coherency Method And Means," by D. A. Elko et al., Ser. No. 07/860,805, (Docket No. PO9-91-052), Filed: Mar. 30, 1992;

"Method And Apparatus For Distributed Locking Of Shared Data, Employing A Central Coupling Facility," by D. A. Elko et al., Ser. No. 07/860,808, (Docket No. PO9-91-059), Filed: Mar. 30, 1992;

"Command Quiesce Function," by D. A. Elko et al., Ser. No. 07/860,330, (Docket No. PO9-91-062), Filed: Mar. 30, 1992;

"Storage Element For A Shared Electronic Storage Cache," by D. A. Elko et al., Ser. No. 07/860,807, (Docket No. PO9-91-078), Filed: Mar. 30, 1992;

"Management Of Data Movement From A SES Cache To DASD," by D. A. Elko et al., Ser. No. 07/860,806, (Docket No. PO9-91-079), Filed: Mar. 30, 1992;

"Command Retry System," by D. A. Elko et al., Ser. No. 07/860,378, (Docket No. PO9-92-002), Filed: Mar. 30, 1992;

"Integrity Of Data Objects Used To Maintain State Information For Shared Data At A Local Complex," by D. A. Elko et al., Ser. No. 07/860,800, (Docket No. PO9-92-003), Filed: Mar. 30, 1992;

"Management Of Data Objects Used To Maintain State Information For Shared Data At A Local Complex," by J. A. Frey et al., Ser. No. 07/860,797, (Docket No. PO9-92-004), Filed: Mar. 30, 1992;

"Recovery Of Data Objects Used To Maintain State Information For Shared Data At A Local Complex," by J. A. Frey et al., Ser. No. 07/860,647, (Docket No. PO9-92-005), Filed: Mar. 30, 1992;

"Message Path Mechanism For Managing Connections Between Processors And A Coupling Facility," by D. A. Elko et al., Ser. No. 07/860,646, (Docket No. PO9-92-006), Filed: Mar. 30, 1992;

"Method And Apparatus For Notification Of State Transitions For Shared Lists Of Data Entries," by J. A. Frey et al., Ser. No. 07/860,809, (Docket No. PO9-92-007), Filed: Mar. 30, 1992;

"Method And Apparatus For Performing Conditional Operations On Externally Shared Data," by J. A. Frey et al., Ser. No. 07/860,655, (Docket No. PO9-92-008), Filed: Mar. 30, 1992;

"Apparatus And Method For List Management In A Coupled DP System," by J. A. Frey et al., Ser. No. 07/860,633, (Docket No. PO9-92-009), Filed: Mar. 30, 1992;

"Interdicting I/O And Messaging Operations In A Multi-System Complex," by D. A. Elko et al., Ser. No. 07/860,489, (Docket No. PO9-92-010), Filed: Mar. 30, 1992;

"Method And Apparatus For Coupling Data Processing Systems," by Elko et al., Ser. No. 07/860,803, (Docket No. PO9-92-012), Filed: Mar. 30, 1992;

"Authorization Method For Conditional Command Execution," by Elko et al., Ser. No. 08/021,285, (Docket No. PO9-92-018), Filed: Feb. 22, 1993; and

"A Dumping Service Facility For Multisystem Environments," by Elko et al., Ser. No. 08/073,909, (Docket No. PO9-92-068), Filed: Jun. 8, 1993.

BACKGROUND ART

When a system failure occurs, information necessary to determine the cause must be recorded for service. This information includes data and control information in storage. In a single system, this storage may be in private address spaces or in common area. Units of work which may alter this storage are stopped while storage content is recorded. In particular, all address spaces, except those which are not needed, are set non-dispatchable. When the storage has been captured, the address spaces are reset and made dispatchable by the operating system.

By stopping the units of work that use the resources, system performance is degraded, since there is a great deal of idle time. In a multisystem environment, work units which alter shared resources execute across operating system images. Control information exists in each of the sharing systems and data exists on a commonly accessible data store. Gathering information to service a failure is a problem since work units which alter the data exists across operating systems, control information about data access exists across operating systems, and the data exists on a commonly accessible data store and is not captured on a failure.

Therefore, a need exists for a technique for serializing coupling facility data by preventing access to the data, not by stopping the work that may be using the data. In particular, a need exists for a technique for queuing requests to use the data until the serialization is released and the data is available. A further need exists for a method and system for accessing information in a data processing system such that requests to use data are queued until serialization is released and then the requests are re-driven. A further need exists for a technique for determining the amount of time that all users of a particular structure can tolerate not having access to that structure. A further need exists for a method and system for overriding the predefined amount of time, if it is determined such step is desirable. A further need exists for a technique for continuing a dump by another system in the sysplex when communication is lost between one or more operating systems and the coupling facility. Further, a need exists for a technique for capturing data when one or more operating systems coupled to a coupling facility lose communication with the coupling facility.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a method for capturing data in a data processing system having one or more operating systems coupled to a coupling facility. A dump of information stored within the coupling facility is requested and the dump is created within the coupling facility.

In one embodiment, when an operating system loses communication with the coupling facility, it is detected. A program within one of the operating systems requests the dump and the dump includes information located in the coupling facility associated with the operating system which lost communication with the coupling facility.

In a further embodiment, the program requesting the dump is located in an operating system, which did not lose communication with the coupling facility. In yet a further embodiment, all of the operating systems lose communication with the coupling facility, and therefore, the dump is requested by the first operating system which re-establishes communication with the coupling facility.

In a further embodiment, an operator requests the dump using, for instance, a dump command. Examples of commands which may cause a dump are DUMP and SLIP.

In one embodiment, in requesting the dump, a parameter list is built, which identifies the information to be included in the dump. The identified information may include a portion or all of the information stored in the coupling facility. A dumping macro uses the parameter list and initiates the dump.

When a dump is requested of the information stored in the coupling facility, the information to be captured is serialized such that the information can only be accessed by a predefined set of commands. Therefore, a request for the information is stored. Subsequent to releasing serialization of the information, the request is redriven.

In yet a further embodiment of the invention, a method for controlling access to information stored in a data processing system is provided. A request for information located in a coupling facility of the data processing system is initiated. A determination is made as to whether the information can be accessed. If the information cannot be accessed, the request is stored. Once the information is available, the request is re-initiated.

In another embodiment of the invention, a method for capturing data in a data processing system having a plurality of operating systems coupled to a coupling facility is provided. A dump of information stored in the coupling facility is initiated by a first of the plurality of operating systems. This dump is continued by a second of the plurality of operating systems when the first of the plurality of operating systems is unable to proceed with the dump. In one embodiment, the dump is continued by updating a status control at the coupling facility representing which operating system is responsible for completing the dump and specifying to the operating system responsible for the dump that the dump is to be continued.

In another aspect of the invention, a system for capturing data in a data processing system having one or more operating systems coupled to a coupling facility is provided. The system includes means for requesting a dump of information stored within the coupling facility and means for creating the dump within the coupling facility.

In another embodiment of the invention, a system for capturing data in a data processing system having a plurality of operating systems coupled to a coupling facility is provided. Included in the system are means for initiating a dump of information stored in the coupling facility by a first of the plurality of operating systems and means for continuing the dump by another operating system, when the first operating system is unable to proceed with the dump.

In yet a further embodiment of the invention, a system for controlling access to information stored in a data processing system is provided. The system includes means for initiating a request for information located in a coupling facility of the data processing system, means for determining whether the information can be accessed, means for storing the request when the information cannot be accessed, and means for re-initiating the request when the information is available.

In another aspect of the invention, a system for capturing data in a data processing system having one or more operating systems coupled to a coupling system is provided. The system includes means for detecting when an operating system loses communication with the coupling facility and means for requesting a dump of information stored within the coupling facility. The dump includes information from the operating system which lost communication with the coupling facility.

In accordance with the principles of the present invention, a control facility is provided for capturing and accessing data in a data processing system. The mechanisms of the present invention advantageously enable users of shared data the ability to specify a maximum time over which serialization of the shared data may be held. Further, the ability to override the time limit is provided.

The shared data may be accessed by a number of operating systems, but the mechanisms of the present invention do not require all the operating systems to coordinate stopping of work units referencing shared data. Further, the mechanisms advantageously allow the capture of service data and control information to occur at the shared data facility and, it allows the capture to be initiated by systems following the failure of one or more of the sharing systems. In addition, following the failure of one or more sharing systems, service data and control information capture can be continued by surviving systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts one example of a block diagram of a data processing system incorporating the control facility of the present invention;

FIG. 2 depicts one example of a coupling facility including multiple storage structures, in accordance with the principles of the present invention;

FIG. 3 depicts one embodiment of a three-level storage hierarchy in a network of attached processors, in accordance with the principles of the present invention;

FIG. 4 depicts one example of the controls associated with a cache structure, in accordance with the principles of the present invention;

FIG. 5 depicts one example of a local cache control block associated with each local cache of the data processing system depicted in FIG. 1, in accordance with the principles of the present invention;

FIG. 6 depicts one embodiment of a directory information block in connection with the directory depicted in FIG. 3, in accordance with the principles of the present invention;

FIG. 7 depicts one example of a list structure, in accordance with the principles of the present invention;

FIG. 8 depicts one example of the controls associated with the list structure of FIG. 7, in accordance with the principles of the present invention;

FIG. 9 depicts one embodiment of a list-user control block, in accordance with the principles of the present invention;

FIG. 10 depicts one example of the controls associated with a list within the list structure of FIG. 7, in accordance with the principles of the present invention;

FIG. 11 illustrates one example of a list entry control block, in accordance with the principles of the present invention;

FIG. 12 depicts one example of a message command/response block, in accordance with the principles of the present invention;

FIG. 13 depicts one embodiment of request/response operands, in accordance with the principles of the present invention;

FIG. 14 depicts one example of a coupling facility in which dump tables are present in a dump space, in accordance with the principles of the present invention;

FIG. 15 depicts one example of a dump table, in accordance with the principles of the present invention;

FIG. 16 depicts one example of a dump header of the dump table of FIG. 15, in accordance with the principles of the present invention;

FIG. 17 depicts one example of an associated request block, in accordance with the principles of the present invention;

FIG. 18 depicts one example of the operands associated with an object header of the dump table of FIG. 15, in accordance with the principles of the present invention;

FIG. 19 illustrates one embodiment of an overview diagram representing the capture portion of the present invention;

FIGS. 20a-20b illustrate one embodiment of the logic associated with the capture portion of the present invention;

FIG. 21 illustrates one embodiment of the logic associated with an operator dump command, in accordance with the principles of the present invention;

FIG. 21a illustrates one embodiment of the logic associated with an operator CHNGDUMP command, in accordance with the principles of the present invention;

FIG. 21b illustrates one embodiment of the logic associated with an operator SLIP command, in accordance with the principles of the present invention;

FIG. 22 is one example of an overview diagram relating to the timing of a dump request, in accordance with the principles of the present invention;

FIG. 23 illustrates one example of the logic associated with a dump timer routine, of the present invention;

FIGS. 24a-24b illustrate one embodiment of the logic associated with a replace dumping controls command, in accordance with the principles of the present invention;

FIG. 25 depicts one embodiment of a dump authority block, in accordance with the principles of the present invention;

FIGS. 26a-26e illustrate one embodiment of the logic associated with an associate dump table command, in accordance with the principles of the present invention;

FIGS. 27a-27e illustrate one embodiment of the logic associated with a capture dump data command, in accordance with the principles of the present invention;

FIG. 28 depicts one example of a coupling facility structure in which dumping serialization is held, in accordance with the principles of the present invention;

FIG. 29 depicts one example of a coupling facility structure in which dumping serialization is released, in accordance with the principles of the present invention;

FIG. 30 depicts one embodiment of the logic associated with the read captured block command, in accordance with the principles of the present invention;

FIGS. 31a-31b depict one embodiment of the logic associated with a read dumping-object data command, in accordance with the principles of the present invention;

FIG. 32 depicts one embodiment of the logic associated with a release dump table command, in accordance with the principles of the present invention;

FIG. 33 illustrates one embodiment of a diagram associated with queuing of requests during dumping serialization, in accordance with the principles of the present invention;

FIG. 34 illustrates one embodiment of the logic associated with queuing requests for dumping serialization, in accordance with the principle of the present invention;

FIG. 35 illustrates one embodiment of the logic associated with re-driving of delayed coupling facility requests, in accordance with the principles of the present invention;

FIG. 36 illustrates one example of a diagram associated with completing a dump for an operating system that has lost communication with a coupling facility, in accordance with the principles of the present invention;

FIGS. 37a-37b illustrate one embodiment of the logic associated with a dump clean-up routine, in accordance with the principle of the present;

FIG. 38 illustrates one example of the logic associated with a read dumping controls command, in accordance with the principles of the present invention;

FIG. 39 illustrates one embodiment of the logic associated with a dump request for a continuation of a dump, in accordance with the principles of the present invention; and

FIG. 40 illustrates one embodiment of the logic associated with a dump initiation routine, in accordance with the principles of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In accordance with the principles of the present invention, a control facility is provided for capturing and accessing data in a data processing system. As described in further detail below, in one example, the data processing system has a plurality of operating systems coupled to a coupling facility. Programs executing under the control of one of the operating systems may request a dump of coupling facility structures at any time. When one or more of the operating systems loses communication with the coupling facility by, for example, failing or losing connectivity to the coupling facility, one of the surviving systems requests a dump of some or all of the information stored in the coupling facility. This dump includes information from the operating systems that lost communication with the coupling facility. Further, if all of the operating systems lose communication with the coupling facility, the first operating system to re-communicate with the coupling facility will request a dump of some or all of the information located in the coupling facility. The information to be included may be selected by the user in a manner described in detail below. Likewise, if a system loses communication with a coupling facility while it is creating a dump, another operating system will continue the dump for the system that lost communication.

Before a dump may be taken of the information located in the coupling facility, the information or, more particularly, the individual structures containing the information, is serialized so that no other requests, beside the dumping requests, may access the information to be dumped.

In accordance with the principles of the present invention, while a structure is serialized, no further requests may be made against the structure. Thus, a queue is created for holding the requests. After the structure is no longer serialized, the requests on the queue are re-driven.

FIG. 1 is a block diagram of a data processing system 10 incorporating the control facility of the present invention. Data processing system 10 includes multiple central processing complexes (CPCs) 12a through 12n which are coupled to an input/output (I/O) system 14 and a coupling facility 16. (As used herein, central processing complexes 12a-12n are collectively referred to as central processing complex (CPC) 12.) The main components associated with each central processing complex 12, input/output system 14 and coupling facility 16 are described in detail below.

Each of the CPCs 12a-12n may be an International Business Machines' (IBM) system following the Enterprise Systems Architecture/390 Principles of Operation as described in IBM publication SA22-7201-00, which is hereby incorporated by reference in its entirety. Each of CPCs 12a-12n includes one or more central processing units (CPUs) (not shown) which executes an operating system 13a-13n, respectively. As used herein, operating systems 13a-13n are collectively referred to as operating system 13. In one instance, operating system 13 is International Business Machines' Multiple Virtual Storage (MVS) operating system for controlling execution of programs and the processing of data, as is well known. In addition, in accordance with the principles of the present invention, each operating system 13a-13n includes a control facility 15a-15n, respectively, for capturing and accessing information in a coupling facility under program initiated control at any time or operating system initiated control when one or more operating systems lose communication with the coupling facility, as described further below.

In addition, each CPC 12a-12n contains a plurality of intersystem (I/S) channels 18a-18n, a plurality of local caches 20a-20n, and a plurality of input/output (I/O) channels 22a-22n, respectively. (Local caches 20a-20n are referred to herein collectively as local cache 20. Similarly, intersystem channels 18a-18n and input/output channels 22a-22n are collectively referred to as intersystem channels 18 and input/output channels 22, respectively.) It will be understood that input/output channels 22 are part of the well known channel subsystem (CSS), which also includes intersystem channels 18 disclosed herein, even though channels 18 and 22 are shown separately in FIG. 1 for convenience.

Coupled to each CPC 12a-12n is an external time reference (ETR) 24, which provides time stamps of control information used for sequencing events, such as writing into a log to document recovery from failures, backing out of undesired operations and for audit trails. External time reference 24, which uses fiber optic interconnect cables, synchronizes the time clocks (not shown) of CPCs 12a-12n to a precision equal to or less than the duration of the shortest externally visible operation. External time reference 24 provides for cable length propagation time differences, where those differences are important, in order to be able to maintain synchronization to within the length of the mentioned external operation.

As depicted in FIG. 1, each central processing complex 12a-12n is coupled via a link 26a-26n, respectively, to input/output system 14. Input/output system 14 includes, for example, a dynamic switch 28, which controls access to multiple input/output (I/O) control units (CU) 30a through 30n and one or more direct access storage devices (DASD) D1 through DN (collectively referred to as DASD 32), which are controlled by the control units. Dynamic switch 28 may be an ESCON Director Dynamic Switch available from IBM Corporation, Armonk, N.Y. Such a dynamic switch is disclosed in U.S. patent application Ser. No. 07/429,267 for "Switch and its Protocol," filed Oct. 30, 1989 and assigned to the owner of the present invention, which application is incorporated herein by reference in its entirety. As is known, input/output commands and data are sent from a central processing complex 12a-12n to an I/O control unit 30a-30n through dynamic switch 28 by means of I/O channels 22a through 22n of the respective CPCs 12a through 12n. Channel programs for a particular I/O channel are established by channel command words (CCWs), as is well known in the art.

Each central processing complex 12a-12n is also coupled via a bus 34a-34n, respectively, to coupling facility 16. Coupling facility 16 contains storage accessible by the CPCs and performs operations requested by programs in the CPCs. The coupling facility enables sharing of data which is directly accessible by multiple operating systems. As described below, the coupling facility contains control information regarding shared data and may contain shared data. In one embodiment, coupling facility 16 is a structured-external storage (SES) processor and includes, for example, a plurality of intersystem (I/S) channels 36 for communicating with intersystem channels 18a-18n, one or more buffers 38 located within intersystem channels 36 for storing data received from inter-system channels 18a-18n, message processors 40a-40n for handling messages, a selector 44 for directing message requests received over an intersystem channel to a message processor 40a-40n, a dumping facility 45, including the microcode and storage required for creating a dump, as described in detail in co-pending, commonly assigned patent application entitled "A Dumping Service Facility for Multisystem Environments," by Elko et al., Ser. No. 08/073,909, filed Jun. 8, 1993, which is incorporated herein by reference in its entirety, a coupling facility cache 46 and a coupling facility list 52, which are described in further detail below. Even though only one coupling facility 16 is shown in the embodiment of FIG. 1, it will be understood that multiple coupling facilities may be provided for, each with its own I/S channels and message paths connected to all or some subset of the CPCs 12a-12n.

Coupling facility cache 46 of coupling facility 16 is one example of a coupling facility storage structure. As shown in FIG. 2, coupling facility 16 includes multiple storage structures, such as storage structures 46, 52, 54 and 56. The storage structures include, for instance, list structures (for example, 52 and 54) and cache structures (for example, 46 and 56). Each coupling facility storage structure contains data objects and control objects. The data objects may reside in any storage location, whereas the control objects are generally restricted to control area 58.

A set of commands is provided for each coupling facility storage structure type, as well as additional commands for referencing global objects. The creation, deletion and attributes of a particular structure are controlled by the operating system program through allocation and de-allocation commands. Allocation commands for list structures are described in "Apparatus and Method For List Management In A Coupled DP System" (Docket No. PO9-92-009), by J. A. Frey et al., Ser. No. 07/860,633, Filed: Mar. 30, 1992, which is hereby incorporated by reference in its entirety. In addition, allocation commands for cache structures are described in "Sysplex Shared Data Coherency Method and Means" (Docket No. PO9-91-052), by D. A. Elko et al., Ser. No. 07/860,805, Filed: Mar. 30, 1992, which is also hereby incorporated by reference in its entirety.

Allocated structures (such as cache structures 46 and 56 and list structures 52 and 54) reside in separate coupling facility storage locations and are located by a structure identifier (SID). The SID value provides an identification of a target structure by a command. A command of a particular structure type, such as a cache-structure or list-structure command, may only address or alter the contents of a single structure of the given type.

The partitioning of the coupling facility storage and control area 58 into structures, as shown in FIGS. 2, 3 and 7, is managed by the operating system program. The data objects are organized in tables or lists with an optional adjunct data area. The remaining objects are controls. The relative amount of storage assigned to data and control objects is determined by program-specified parameters in the allocation commands.

Referring to FIG. 3, a three-level storage hierarchy in a network of attached processors 12a-12n is described. The lowest level of the hierarchy is DASD 32, the intermediate level is coupling facility cache structure 46, and the highest level is local cache 20 (e.g., local caches 20a and 20b). Each of these levels is described below.

Direct access storage devices 32 include data blocks which represent data stored in the devices. Local caches 20a and 20b include, for instance, a 16-byte name field 60A, 60B for referencing data; a data field 64A, 64B for storing the data; an optional adjunct data field 66A, 66B for additional data; and a state field 68A, 68B, respectively for indicating whether the data is valid or invalid. When the data is located in local cache 20, the state of the data is either valid or invalid. The data is validated by CPU instructions and invalidated by, for example, SES-write and SES-invalidate operations. The valid state of the data is tested by a CPU instruction. A valid named data object must be registered in a coupling facility cache directory, described below, in order to maintain local cache coherency. Local cache coherency is maintained by the invalidation process. A registered local-cache entry may test as invalid.

Cache structure 46 includes, for instance, a number of cache structure controls 69, one or more local-cache control blocks (LCCB) 70, a directory 72, a data area 74, and an adjunct area 75, each of which is explained in further detail below.

As shown in FIG. 4, cache structure controls 69 include, for instance, the following controls:

(a) Total-Directory-Entry Count (TDEC): A value that specifies the number of directory entries allocated for the cache.

(b) Total-Data-Area-Element Count (TDAEC): A value that specifies the number of data-area elements allocated for the cache.

(c) Adjunct-Assignment Indicator (AAI): A value that indicates the presence or absence of adjunct areas. Two possible values are: adjunct areas not assigned; adjunct areas assigned. When adjunct areas are assigned, an adjunct area is associated with each directory entry.

(d) Maximum Storage Class (MSC): A value that specifies the number of storage classes. Valid storage-class values range from one to the maximum-storage-class value.

(e) Maximum Cast-Out Class (MCC): A value that specifies the number of cast-out classes. Valid cast-out class values range from one to the maximum cast-out class value.

(f) Data-Area-Element Characteristic (DAEX): A value that specifies the number of bytes in each data-area element. The size of the data-area element in bytes is the product of 256 and 2 raised to the power of the value specified in the data-area-element characteristic.

(g) Maximum Data-Area Size (MDAS): A value that specifies the maximum allowable size of a data area as an integral multiple of the data-area-element size. The maximum data-area size is set by the program when the cache is allocated.

(h) Structure Size (SS): A value that specifies the number of units of, for example, SES storage allocated for the cache.

(i) Maximum Structure Size (MXSS): A value that specifies the maximum number of units of SES storage that can be allocated for the cache.

(j) Minimum Structure Size (MNSS): A value that specifies the minimum number of units of SES storage that can be allocated for the cache.

(k) Structure Authority (SAU): A value associated with each bit in the SID vector.

(l) User Structure Control (USC): A value defined by the user.

(m) LCID Vector (LCIDV): A bit string with an initial value of zero. The bit positions start at zero and increase sequentially to the local-cache-identifier limit. The bit at position (i) in the string is set to one when a local cache is attached with an LCID value of (i). When the bit is one, the local-cache-identifier is assigned. The bit at position (i) is reset to zero when the local cache is detached and LCID unassignment is requested, when the cache structure is de-allocated, or when a SES power-on reset occurs.

When the bit is zero, the local-cache-identifier is not assigned.

(n) Target Structure Size (TSS): A value that specifies the target number of units of SES storage to be allocated.

(o) Target Data Area Element Count (TGDAEC): A value that specifies the target for the maximum number of data-area elements that are available for assignment to directory entries in a cache structure.

(p) Target Directory-Entry Count (TGDEC): A value that specifies the target for the maximum number of possible directory entries in a cache structure.

As mentioned above, in addition to structure controls 69, cache structure 46 includes local-cache control block 70. In one embodiment, local-cache control block 70 includes the following fields (FIG. 5):

(a) Local Cache Identifier (LCID): A value that identifies a local cache.

(b) Attachment Status (AS): A control that describes the state of the attachment of a local cache. When the value of the attachment status is one, the local cache is attached. When the value of the attachment status is zero, the local cache is detached.

The attachment status controls the execution of commands that specify the local cache. When the local cache is attached, all commands that specify the local cache are processed normally. When the local cache is detached, all commands that specify the local cache, except attach local cache, detach local cache and read local cache information are suppressed with a request-exception condition.

(c) Local-Cache Token (LCT): A value used to identify the local cache on the CPC.

(d) Local-Cache Authority (LCAU): A value set by the program when the local cache is attached.

(e) System Identifier (SYID): A value specified by the program when a message path, used to communicate commands and messages (as described in detail in co-pending U.S. patent application entitled "Communicating Messages Between Processors And A Coupling Facility," by D. A. Elko et al., Ser. No. 07/860,380, (Docket No. PO9-91-006), Filed: Mar. 30, 1992 and co-pending U.S. patent application entitled "Message Path Mechanism For Managing Connections Between Processors And A Coupling Facility," by D. A. Elko et al., Ser. No. 07/860,646 (Docket No. PO9-92-006), filed Mar. 30, 1992, each of which is incorporated herein by reference in its entirety), is activated. The system identifier is maintained in a message-path status vector and copies into the local cache controls when an attach-local-cache command is communicated over the message path.

(f) Attachment Information (AINF): A value set by the program when the local cache is attached.

Referring back to FIG. 3, cache structure 46 also includes directory 72. Directory 72 is a collection of directory entries positioned into storage classes and arranged as a fully associative array. The subset of changed directory entries is additionally positioned into cast-out classes. As described with reference to FIGS. 3 and 6, directory 72 includes a name field 78, a state field 80 for indicating the state of each directory entry and a register field 82, described below. Whenever a named data object is placed in the higher two levels of the storage hierarchy (i.e., coupling facility cache structure 46 and local cache 20), its name is registered in name column 78 and its state is registered in state column 80 by coupling facility cache directory 72. In general, state information indicates whether the data is changed, unchanged, locked for cast-out, or resident in coupling facility 16. In particular, state field 80 includes:

(a) User-Data Field (UDF): The user-data field contains a value that is associated with the data when it is initially changed in the SES cache and is maintained until the data-table entry is re-used. The user-data field is valid when the data is cached as changed.

(b) Storage Class (SC): A value which identifies the storage class assigned for the name.

(c) Change Indicator (C): A value which, in conjunction with the cast-out lock, indicates the changed state of the data. When the change bit is one, the data is cached as changed. When the change bit is zero and the data is not locked for cast-out, the data is either not cached, or is cached but not changed. When the change bit is zero and the data is locked for cast-out, the data is cached as changed. Whenever the data is in the changed state, the most recent version of the data resides in the cache. When the change bit is one, the data bit must also be one.

(d) Data-Cached Indicator (D): A value which indicates whether the data is located in the SES cache. When the data bit is one, the data is cached. When the data bit is zero, the data is not cached.

(e) Cast-Out-Parity-Bits Indicator (CP): A field which indicates the current assignment of the cast-out parity. Three possible values are: cast-out parity is zero; cast-out parity is one; the cast-out parity is unknown.

(f) Cast-Out Class (CC): A value which identifies the cast-out class assigned for the name.

(g) Cast-Out Lock Value (CLV): A value which indicates the cast-out state of the data. When the cast-out lock is zero, the data is not being cast-out. When the cast-out lock is not zero, the value of the first byte of the cast-out lock identifies the local cache that is casting out the data block from the SES cache to DASD. The value of the second byte identifies the cast-out process on the local system. When the cast-out lock is not zero, the data bit must be one.

(h) Data-Area Size (DAS): A value that specifies the size of the data area as an integral multiple of the data-area-element size. The initial value is zero when the directory entry is assigned and is zero until the data bit is set to one.

In addition to the above, register 82 is a table containing information on the location of the locally cached copies of the data block. Each row in the table corresponds to an attached local cache. The columns contain the local-cache entry number (LCEN) and a valid bit (LVI) for the local-cache entry number. When the local-cache entry number-validity indicator (LVI) is zero, the LCEN field is invalid. Location information includes which of the local caches 20a-20n contains a copy. Certain SES-read and SES-write commands register the local cache copy in coupling facility cache directory 72. SES-write and SES-invalidate commands remove the registration and invalidate local copies.

Cache structure 46 further includes data areas 74 and optional adjunct data areas 75. The data sizes are variable with the range of variability being, in one embodiment, between 1 and n times the data-area element size. The data-area element size is fixed for each coupling facility cache structure 46 and is a power of 2 with a minimum size of 256 bytes.

Coupling facility cache 46 is normally smaller than DASD storage 32. Thus, periodically, the changed data is transferred from cache 46 to the backing DASD 32 (FIG. 3). This process, called cast-out, is controlled by the operating system program. In one embodiment, a control associated with a cast-out class includes a cast-out-class-count, which indicates the number of elements associated with the cast-out class. Cast-out involves for a coupling facility, such as a SES facility, the following operations:

A SES-read for cast-out operation is issued that sets the cast-out serialization and copies the data block to main storage which may or may not be put in local cache 20.

An I/O operation is executed that copies the data block to DASD 32.

A SES-unlock cast-out locks operation is issued that releases the cast-out serialization.

Multiple cast-out processes may co-exist for a single one of local caches 20a-20n. Whenever data is locked for cast-out, an identifier for local cache 20a-20n and an identifier for the cast-out process are placed in directory 72. This is disclosed in U.S. patent application Ser. No. 07/860,806 for "Management of Data Movement from a SES Cache to DASD" by D. A. Elko, et al. (Attorney Docket No. PO9-91-079), incorporated herein by reference in its entirety as noted.

The least recently used (LRU) unchanged data and directory resources are reclaimed by coupling facility cache 46 when needed to meet new requests. The data objects are mapped into one of several storage classes by the operating system program. Each storage class includes a number of controls, as well as a reclaiming vector including, for instance, reclaiming-vector entry 1 (RVE1) through reclaiming-vector entry 64 (RVE64), that controls the reclaiming process. This allows the allotment of coupling facility storage among the storage classes to be dynamically adjusted to account for changes in workload characteristics. The reclaiming vector is maintained by the operating system program. The above is disclosed in U.S. patent application Ser. No. 07/860,807 for "Storage Element for a Shared Electronic Storage Cache" by D. A. Elko, et al. (Attorney Docket No. PO9-91-078), incorporated herein by reference in its entirety, as noted above.

Referring back to FIG. 3, cache structure 46 is located within coupling facility 16. Also contained within facility 16 is a set of global controls 67. In one embodiment, global controls 67 include a coupling facility authority control (e.g., a SES authority control) as well as facility dependent information, such as total free space for the coupling facility and the largest data block to be stored in the coupling facility, etc.

Described in detail above is one example of a cache storage structure. In addition to cache structures, there are list structures, such as list structure 52, depicted in FIGS. 2 and 7. Referring to FIG. 7, the contents of a list structure, such as list structure 52, is described in detail.

List structure 52 resides within coupling facility 16. As shown in FIG. 7, in one embodiment, coupling facility 16 is coupled to processor storage 90a-90n located within each CPC 12a-12n, respectively. List structure 52 includes list-structure controls 92, user controls 94 and, optionally, a lock table 96, and/or a list set 98. List set 98 includes list controls 100 and list-entry controls 102. Each of the components of list structure 52 is described in detail below.

List structure controls 92 contain attributes of the structure and are initialized when list structure 52 is created. One example of the controls associated with list structure controls 92 is depicted in FIG. 8. Referring to FIG. 8, list structure controls 92 include:

(a) Maximum Data-List-Entry Size (MDLES): An object or field that specifies the maximum size of the data list entry.

(b) List-Structure Type (LST): An object or field that indicates the list objects created on allocation. A field contains a counter indicator (CI), a lock indicator (LI), a data indicator (DI), an adjunct indicator (AI), a name indicator (NI) and a key indicator (KI).

The counter indicator specifies that either: a list-entry count and list-entry-count limit are defined or a list-element count and list-element-count limit are defined.

The lock indicator specifies whether or not a lock table is created.

The data and adjunct indicators specify whether: no list-set is created; list entries have adjunct only; list entries have data only; or list entries have data and adjunct in the list entries.

The name indicator specifies whether or not list entries are names.

The key indicator specifies whether or not the list entries are keyed.

(c) Lock-Table-Entry Characteristic (LTEX): An object or field that specifies the number of bytes in each lock-table entry. The number of bytes is the product of 2 raised to the power of the LTEX value.

(d) List-Element Characteristic (LELX): An object or field that specifies the number of bytes in each list element. The number of bytes is the product of 256 and 2 raised to the power of the LELX value.

(e) Minimum Structure Size (MNSS): A value that specifies the minimum number of units of SES storage that can be allocated for the list.

(f) Lock-Table-Entry Count (LTEC): An object or field that specifies the number of lock-table entries allocated.

(g) List Count (LC): An object or field that specifies the number of lists created.

(h) Structure Size (SS): An object or field that specifies the amount of storage allocated.

(i) Maximum Structure Size (MXSS): A value that specifies the maximum number of units of SES storage that can be allocated for the list.

(j) Target Structure Size (TSS): A value that specifies the target number of units of SES storage to be allocated.

(k) Target Maximum-Element Count (TMELC): A value that specifies the target for the maximum number of list elements that are available for assignment to list entries or retry-data blocks, or both, in the list set.

(l) Target Maximum-Entry Count (TMEC): A value that specifies the target for the maximum number of possible list entries in a list set.

(m) Maximum List-Set-Element Count (MLSELC): An object or field that specifies the maximum number of list elements that are available for assignment to list entries or retry-data blocks, or both, in the list set.

(n) List-Set-Element Count (LSELC): An object or field that specifies the number of list elements that have been assigned to list entries or retry-data blocks, or both, in the list set.

(o) Non-Zero-Lock-Table-Entry-Count (NLTEC): An object or field that specifies the number of non-zero lock-table entries that exist in the structure.

(p) Maximum List-Set-Entry Count (MLSELC): An object or field that specifies the maximum number of possible list entries in a list set.

(q) List-Set-Entry Count (LSEC): An object or field that specifies the number of existing list entries in the list set.

(r) Structure Authority (SAU): A value associated with each bit in the SID vector.

(s) User Structure Control (USC): A field per structure defined by the user.

(t) User-Identifier Vector (UIDV): An object or field that specifies the assigned UIDs, described below.

Referring back to FIG. 7, user controls 94 are created and initialized when the list-structure user is attached. In one embodiment, user controls 94 include the following fields (FIG. 9):

(a) A User Identifier (UID): A value that identifies an attached list user.

(b) A User State (US): A field that specifies the state of the user. The value has the following encoding: the user is detached; the user is attached.

(c) A List-Notification Token (LNT): A value that specifies a list-notification vector to the system.

(d) A User Authority (UAU): A value that is compared and conditionally updated.

(e) A System Identifier (SYID): A value specified by the program when the message path is activated. The system identifier is maintained in a message-path status vector and copied into the user controls when an attach-list-structure-user command is communicated over the message path.

(f) A User-Attachment Control (UAC): A field per attached user defined by the user.

Referring once again to FIG. 7, lock table 96 consists of a sequence of one or more lock table entries 97 identified by a lock-table-entry number (LTEN). In one embodiment, lock table entry 97 includes a lock-table-entry number (LTEN), which starts at zero and runs consecutively and a lock-table-entry value (LTEV), including a global-lock manager (GLM) object and optionally, a local-lock-manager (LLM) object or both. The lock-table entry format is determined by the list-structure type located within list structure controls 92.

Commands associated with list structure 52 provide a means for updating lock-table entry 97. That is, a command may compare global-lock managers (GLM) and conditionally replace a global-lock manager (GLM), a local-lock manager (LLM), or both the global-lock and local-lock managers (GLM) and (LLM). The list commands also provide a means for reading an entry in lock-table 96 or the next non-zero lock-table entry, or for clearing lock table 96.

As previously mentioned, also contained within list structure 52 is list set 98. In one example, list set 98 includes one or more lists 99 represented by list controls 100, which are numbered consecutively, starting at zero. In one embodiment, list controls 100 include the following controls, as depicted in FIG. 10:

(a) List-Entry-Count Limit (LECL): An object or field that specifies the maximum number of possible list entries in a list. This object is initialized to the maximum list-set-entry count when a list structure is created.

(b) List-Entry Count (LEC): An object or field that specifies the number of list entries currently in the list.

(c) List-State-Transition Count (LSTC): An object or field that specifies the number of empty to not-empty list state transitions that have occurred.

(d) List Authority (LAU): A value that is compared and conditionally updated. The LAU is initialized to zeros.

(e) User List Control (ULC): A field per list defined by the user.

(f) List-Monitor-Table: The list-monitor table contains information used to process the list-notification vector of each user who has registered interest in the state transitions of the list.

The list-monitor table is a sequence of objects, called list-monitor-table entries. The number of list-monitor-table entries is determined when the table is created and is equal to the maximum number of list-structure users. The list-monitor-table entries are numbered from zero to the user-identifier limit.

Each list-monitor-table entry has a list-monitoring-active-bit object, a list-notification-request-type object and a list-notification-entry-number object, each of which is described below:

(1) List-Monitoring-Active Bit (LMAB): An object or field that specifies whether the user associated with the list-monitor-table entry is monitoring the list-state transitions of the list.

When a user is not monitoring a list, all previously issued list-notification commands on behalf of the associated user for this list are complete.

(2) List-Notification-Request Type (LNRT): An object or field that indicates whether the list-notification-vector summaries are to be updated when an empty to not-empty state transition occurs on a monitored list.

(3) List-Notification-Entry Number (LNEN): An object or field that specifies a list-notification-vector entry.

Each list 99 consists of a sequence of zero or more entries. The list-structure type (described above) determines whether all the list entries in list set 98 have a data list entry 104, an adjunct list entry 106, or both. Associated with each entry of a list 99 is one of list-entry controls 102. Controls 102 contain list-entry-location information and other information for controlling operations against data list entry 104.

In particular, list entry controls 102 include the following controls, as depicted in FIG. 11:

(a) Data-List-Entry Size (DLES) indicating the size of the associated data entry.

(b) A List Number (LN) representing the list that a particular entry is associated with.

(c) A List-Entry Identifier (LEID) identifying a particular list entry. The list-entry identifier is unique to a list set 98 and is assigned by coupling facility 16.

(d) A Version Number (VN) object that is conditionally compared and conditionally updated, reflecting a program specified state for the list entry.

(e) An optional List-Entry Key (LEK) indicating a key, if one exists. When list-entry keys exist, the keyed list entries are ordered by the key with the lowest numerical key at the leftmost position. Elements with the same key value may be located by first or last within the same key value.

When an unkeyed list entry is created or moved, the target list-entry position is always located by an unkeyed position. When a keyed list entry is created or moved, the target list-entry position is always located by a keyed position and first or last within the same key value.

(f) An optional List-Entry Name (LEN). A list-entry name is unique to a list set 98 (FIG.7) at any particular instant and is provided by the operating system program.

List commands provide a means for conditionally creating, reading, replacing, moving, or deleting one entry in list 99. A number of comparisons may be requested during these processes. They include a list-number comparison, a version-number comparison, a global-lock-manager (GLM) comparison, or any combination of the preceding. Additionally, when global locks are compared, local locks (LLM) may be compared. A list entry may be moved from one list 99 to another within the same structure 52 or from one position to another within the same list 99. This is disclosed in U.S. patent application Ser. No. 07/860,655 for "Method and Apparatus for Performing Conditional Operations on Externally Shared Data" by J. A. Frey, et al. (Attorney Docket No. PO9-92-008), incorporated herein by reference in its entirety as noted.

The position of a list entry in list 99 is determined when it is created, and may be changed when any entry in the list is created, deleted or moved. A list entry or list-entry position is located within a list set 98 by means of the list-entry identifier or the optional list-entry name (as described above), or by position. Position is specified by means of a list number, a direction, and an optional list-entry key.

The list commands also provide a means for synchronously writing and moving, moving and reading, or reading and deleting one entry of list 99. More than one list entry may be deleted synchronously, and more than one data list entry 104 or adjunct list entry 106 may also be read synchronously. Data list entry 104 is always returned in the data area designated in main storage by a message command/response block, described below. The adjunct list entry is returned in either a message command/response block or the data area, depending on the command. This is disclosed in U.S. patent application Ser. No. 07/860,633 for "Apparatus and Method for List Management in a Coupled DP System" by J. A. Frey, et al., (Attorney Docket No. PO9-92-009), incorporated herein by reference in its entirety, as noted.

In addition to cache and list structures, there also exists, for instance, lock structures. A lock structure is comprised of a coupling facility list structure with an associated lock table and a set of operating system services to assist in lock contention resolution.

In one embodiment, messages are communicated between CPC 12 and coupling facility 16 via a message command/response block 110 (FIG. 12). In one example, message command/response block 110 includes a message command block 112, a message response block 114 and an optional data block 116. Message command block 112 includes a command block 118 and a plurality of request operands 120 and message response block 114 includes a response descriptor 122 and a plurality of response operands 124. In one embodiment of the present invention, request operands 120 and response operands 124 include the operands listed below, which are depicted in FIG. 13. (An operand may be a request operand, a response operand or both, depending upon the command. It is also possible that other request and/or response operands exist, which are not shown in FIG. 13.). In one embodiment, the response/request operands include the following:

(a) Authority (AU): A value that contains the contents of the global-authority control.

(b) Capture Completion Code (CAPCC): A value that indicates whether the capture is completed.

(c) Comparative Authority (CAU): A value that is compared with the value of the global-authority control.

(d) Comparative Dumping Authority (CDAU): A value that is compared with the value of a dumping-authority control, described below.

(e) Comparative Dumping Serialization (CDS): A value that is compared with the value of a dumping-serialization control, described below.

(f) Comparative Structure Authority (CSAU): A comparison authority value operand used to compare to the structure authority control value in structure controls.

(g) Data-Block Size (DBS): A value that specifies the size of the data block as an integral multiple of 4096-byte units. The value must be non-zero.

(h) Dump-Local-Cache Identifier (DLCID): The identifier of an attached local cache associated with a dump table, described below. The dump-local-cache-identifier operand is only meaningful when the structure type is a cache structure. When the dump-local-cache identifier is zero, no local cache is associated with the dump table.

(i) Dump-Table-Entry Number (DTEN): An object or field that identifies a dump-table entry.

(j) Dumping Authority (DAU): A value that contains the contents of the dumping-authority control.

(k) Dumping Information (DINF): A value that contains program-specified information associated with the dump.

(l) Dumping-List Length (DLL): An object or field that specifies the number of ranges in the range list of an associate-dump-table command, which is described in detail below.

(m) Dumping Serialization (DS): A value that contains the value of the dumping-serialization control.

(n) Dump Table Size (DTS): A value that contains the value of the dump table size operand, described below.

(o) Element Name (EN): A value that identifies an element in an object list. The element name depends on the structure type as follows:

    ______________________________________
    SES List       List Entry Identifier (LEID)
    SES Cache      Name (N)
    ______________________________________

    ______________________________________
    [xlabel] IXLCONN
                 STRNAME=xstrname
                 ,CONNAME=xconname
              [,ACCESSTIME=MAXIMUM
                [,MAXTIME={xmaxtime.vertline.0}]]
              [,ACCESSTIME=NOLIMIT]
               ,TYPE=CACHE
                ,VECTORLEN=xvectorlen
                ,NUMCOCLASS=xnumcoclass
                NUMSTGCLASS=xnumstgclass
               ,TYPE=LIST
                ,LISTHEADERS=xlistheaders
               ,TYPE=LOCK
                ,LOCKENTRIES=xlockentries
                NUMUSERS=xnumusers
               ,ANSAREA=xansarea
               ,ANSLEN=xanslen
    ______________________________________

    __________________________________________________________________________
    [xlabel]
        BLDDUMP
                 PARMAREA=xparmarea
                ,TYPE=INITIAL
                ,PARMLENGTH=xparmlength
                ,TYPE=STRUCTURE
                 ,STRNAME=xstrname
                [,CONTOKEN={XCONTOKEN.vertline.NONE}
                 ,CONNAME={xconname}]
                ,TYPE=STRRNG
                ,OBJECT={COCLASS.vertline.STGCLASS.vertline.
                 LISTNUM}
                ,DUMP=ALL
                ,DUMP=RANGE
                 ,STARTVAL=xstartval
                 ,ENDVAL={xendval.vertline.NONE}
                [,ADJUNCT={NO.vertline.CAPTURE.vertline.
                 DIRECTIO}]
                [,ENTRYDATA={NO.vertline.UNSERIALIZE.vertline.
                 SERIALIZE}]
                [,SUMMARY={NO.vertline.YES}]
                ,TYPE=STROPT
                ,OPTION={LOCKENTRIES.vertline.
                 USERCNTLS}
                ,TYPE=ENDLIST
               [,RETCODE=xretcode]
               [,RSNCODE=xrsncode]
    __________________________________________________________________________

    __________________________________________________________________________
    STRLIST=(STRNAME=strname
                     ,CONNAME=conname
                     ,ACCESSTIME=ENFORCE .vertline.
                       OVERRIDE
                     ,LOCKENTRIES
                     ,USERCNTLS
                     ,(COCLASS=ALL .vertline. (list)
                     ,(STGCLASS=ALL .vertline. (list)
                     ,(LISTNUM=ALL .vertline. (list)
                     ,ADJUNCT=CAPTURE .vertline. DIRECTIO
                     ,ENTRYDATA=SERIALIZE .vertline.
                       UNSERIALIZE
                     SUMMARY
    ,STRNAME=strname . . .)
    __________________________________________________________________________