Program products for repositioning an input/output device without knowledge of current positioning of the device

• US 6,336,194 B1
• Filed: 10/29/1998
• Issued: 01/01/2002
• Est. Priority Date: 10/29/1998
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Yudenfriend, Harry M., Dahman, Kirby G., Perry, Larry R., Johnson, Gavin S.
• Primary Examiner(s): Iqbal, Nadeem
• Application Number:
  US09/181,966
• Time in Patent Office: 1,160 Days
• Field of Search: 714/17, 714/16, 714/5, 714/7, 714/13, 714/21, 714/20, 714/42, 714/43, 714/44, 710/15, 710/16, 710/17, 710/36, 710/37
• US Class Current: 714/17
• CPC Class Codes: G06F 11/1415 at system level
• CPC Class Codes: G06F 3/0617 in relation to availability
• CPC Class Codes: G06F 3/0686 Libraries, e.g. tape libraries, jukebox
• CPC Class Codes: G11B 15/026 by using processor, e.g. microcomputer
• CPC Class Codes: G11B 15/20 Moving record carrier backwards or forwards by finite amounts, i.e. backspacing, forward spacing

Abstract

Repositioning within an input/output device is accomplished without any knowledge of where the input/output device is currently positioned. The input/output device is repositioned to a predetermined position, in order for a program to be retried. The predetermined position is determined from a previously executed program. The previously executed program is scanned looking for commands. For each command found, a position identifier is adjusted based upon the type of command. When the scan and adjustments are complete, the position identifier represents the predetermined position used for repositioning the input/output device.

Claims

1. At least one program storage device readable by a machine, tangibly embodying at least one program of instructions executable by the machine to perform a method of repositioning within an input/output device, said method comprising:

ascertaining that a program, that was executing on an input/output device sensitive to positioning, is to be retried; and

repositioning said input/output device to a predetermined position in order to retry said program, wherein said repositioning is performed without knowledge of current positioning within said input/output device and without knowledge of which part of the program caused the retry.

2. The at least one program storage device of claim 1, wherein said repositioning further comprises:

determining whether said predetermined position is valid; and

repositioning to said predetermined position when said predetermined position is valid.

3. The at least one program storage device of claim 1, wherein said method further comprises determining said predetermined position.

11. The at least one program storage device of claim 1, wherein said method further comprises retrying said program, after said repositioning.

12. The at least one program storage device of claim 1, wherein said program is a channel program comprising one or more channel command words.

13. The at least one program storage device of claim 12, wherein said repositioning lacks knowledge of which channel command word of said channel program failed.

17. The at least one program storage device of claim 3, wherein said determining comprises:

scanning a previously executed program for a command;

adjusting a position identifier of said input/output device based upon a type of said command; and

repeating said scanning and said adjusting until a prespecified limit is reached, wherein said position identifier then represents said predetermined position.

18. The at least one program storage device of claim 12, further comprising:

determining said predetermined position, said determining comprising;

scanning a previously executed channel program for a channel command word;

adjusting a block-id of said input/output device based upon a type of operand of said channel command word; and

repeating said scanning and said adjusting for each channel command word of said previously executed channel program, wherein said block-id then represents said predetermined position.

19. The at least one program storage device of claim 1, wherein said part of the program comprises a command of the program.

4. At least one program storage device readable by a machine, tangibly embodying at least one program of instructions executable by the machine to perform a method of repositioning within an input/output device, said method comprising:

ascertaining that a program, that was executing on an input/output device sensitive to positioning, is to be retried;

repositioning said input/output device to a predetermined position in order to retry said program, wherein said repositioning is performed without knowledge of current positioning within said input/output device; and

determining said predetermined position, wherein the determining comprises;

scanning a previously executed program for a command;

adjusting a position identifier of said input/output device based upon a type of said command; and

repeating said scanning and said adjusting until a prespecified limit is reached, wherein said position identifier then represents said predetermined position.

5. The at least one program storage device of claim 4, wherein said scanning comprises scanning a previously successfully executed program.

6. The at least one program storage device of claim 4, wherein said adjusting comprises:

incrementing said position identifier when said command is an Add type;

decrementing said position identifier when said command is a Delete type; and

invalidating said position identifier when said command is an Invalidate type.

7. The at least one program storage device of claim 4, wherein said method further comprises ensuring, prior to said determining, said position identifier is valid, wherein said determining begins with a valid position identifier.

8. The at least one program storage device of claim 4, wherein said method further comprises storing said position identifier in a control block associated with said input/output device for use during said repositioning.

9. The at least one program storage device of claim 8, wherein said method further comprises storing a state associated with said position identifier in said control block.

10. The at least one program storage device of claim 4, wherein said prespecified limit is an end of said previously executed program.

14. At least one program storage device readable by a machine, tangibly embodying at least one program of instructions executable by the machine to perform a method of repositioning within an input/output device, said method comprising:

ascertaining that a program, that was executing on an input/output device sensitive to positioning, is to be retried, wherein said program is a channel program comprising one or more channel command words;

repositioning said input/output device to a predetermined position in order to retry said program, wherein said repositioning is performed without knowledge of current positioning within said input/output device; and

determining said predetermined position, said determining comprising;

scanning a previously executed channel program for a channel command word;

adjusting a block-id of said input/output device based upon a type of operand of said channel command word; and

repeating said scanning and said adjusting for each channel command word of said previously executed channel program, wherein said block-id then represents said predetermined position.

15. An article of manufacture, comprising:

at least one computer usable medium having computer readable program code means embodied therein for causing repositioning within an input/output device, the computer readable program code means in said article of manufacture comprising;

computer readable program code means for causing a computer to determine a position, within an input/output device sensitive to positioning, that is to be used to retry a program, wherein said computer readable program code means for causing a computer to determine uses a first address representative of where a channel associated with said input/output device stopped processing said program and a second address representative of where a control unit associated with said input/output device stopped processing said program; and

computer readable program code means for causing a computer to reposition said input/output device to said position in order to retry said program.

16. The article of manufacture of claim 15, wherein said computer readable program code means for causing a computer to determine comprises computer readable program code means for causing a computer to scan said program from said first address to said second address and to calculate, during said scanning, a number of records to be used to reposition said input/output device.