Copy-on-write mapping file system

• US 20050004925A1
• Filed: 05/07/2004
• Published: 01/06/2005
• Est. Priority Date: 05/07/2003
• Status: Abandoned Application

• Current Assignee: Levnta Incorporated
• Original Assignee: Levnta Incorporated
• Inventors: Stahl, Nathaniel, Khan, Akmal
• Application Number:
  US10/841,808
• Publication Number:
  US 20050004925A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 21/566 Dynamic detection, i.e. detection performed at run-time, e.g. emulation, suspicious activities

Abstract

A system provides sharing of read-only file systems while at the same time providing each client of the read-only file system the ability to write to its own data store. Files can be either on a read-only persistent repository file system, or on a writeable persistent overlay file system. An “optimistic sharing” paradigm means that by default, everything on the file system is assumed to be read-only. If an attempt is made to modify a file—that is, a private copy is needed—the performance hit is typically minimal, because most written-to files are small. Even in the event of a larger file, the performance hit is a one-time cost.

Claims

1. A computer-implemented method for sharing data, the method comprising:

receiving a first request from a requestor, the first request including a data identifier and a first action to be performed on the identified data;

determining whether the identified data is located at a writeable location;

responsive to the identified data not being located at a writeable location;

automatically copying the identified data to a writeable location; and

performing the first requested action on the copy of the identified data.

2. The computer-implemented method of claim 1 wherein the first requested action is a write operation.

3. The computer-implemented method of claim 1 wherein automatically copying the identified data to the writeable location further comprises:

creating a new data store at the writeable location;

reading the identified data;

writing the identified data to the new data store at the writeable location; and

creating a mapping from the data identifier to the writeable location.

4. The computer-implemented method of claim 3 wherein performing the first requested action on the copy of the identified data further comprises:

determining a mapping from the data identifier to the writeable location; and

performing the first requested action on the data at the writeable location.

5. The computer-implemented method of claim 1 wherein determining whether the identified data is located on a writeable location further comprises:

determining a mapping from the data identifier to a data location; and

determining whether the data location is a writeable location.

6. The computer-implemented method of claim 1 further comprising:

receiving a second request from the requestor, the second request including the data identifier and a second action to be performed on the identified data; and

performing the second requested action on the copy of the data.

7. The computer-implemented method of claim 6 wherein performing the second requested action on the copy of the data further comprises:

determining a mapping from the data identifier to the copy of the data; and

performing the second requested action on the copy of the data.

8. A computer-implemented method for sharing a read-only file system, the method comprising:

receiving a first request from a virtual file system (VFS) layer, the first request including a file identifier and a first operation to be performed on the identified file;

determining whether the identified file is located on a read-only file system;

responsive to the identified file being located on a read-only file system;

automatically copying the identified file to a writeable file system; and

performing the first operation on the copy of the identified file.

9. The computer-implemented method of claim 8 wherein the first operation is a write operation.

10. The computer-implemented method of claim 8 wherein automatically copying the identified file to a writeable file system further comprises:

creating a new file on the writeable file system;

reading contents of the identified file from the read-only file system;

writing the contents of the identified file to the new file on the writeable file system; and

creating a mapping from the file identifier to the new file.

11. The computer-implemented method of claim 10 wherein performing the first operation on the copy of the identified file further comprises:

determining a mapping from the file identifer to the new file; and

performing the first operation on the new file.

12. The computer-implemented method of claim 8 wherein determining whether the identified file is located on a read-only file system further comprises:

determining a mapping from the file identifier to a file location; and

determining whether the file location is associated with a read-only file system.

13. The computer-implemented method of claim 8 further comprising:

receiving a second request from the VFS layer, the second request including the file identifier and a second operation to be performed on the identified file; and

performing the second operation on the copy of the identified file.

14. The computer-implemented method of claim 13 wherein performing the second operation on the copy of the file further comprises:

determining a mapping from the file identifier to the copy of the identified file; and

performing the second operation on the copy of the identified file.

15. The computer-implemented method of claim 8 wherein the read-only storage device receives requests for file operations from a plurality of computers.

16. A computer program product for sharing a read-only file system, the computer program product stored on a computer-readable medium and including instructions configured to cause a processor to carry out the steps of:

receiving a first request from a virtual file system (VFS) layer, the first request including a file identifier and a first operation to be performed on the identified file;

determining whether the identified file is located on a read-only file system;

responsive to the identified file being located on a read-only file system;

automatically copying the identified file to a writeable file system; and

performing the first operation on the copy of the identified file.

17. The computer program product of claim 16 wherein the first operation is a write operation.

18. The program product of claim 16 wherein automatically copying the identified file to a writeable file system further comprises:

creating a new file on the writeable file system;

reading contents of the identified file from the read-only file system;

writing the contents of the identified file to the new file on the writeable file system; and

creating a mapping from the file identifier to the new file.

19. The computer program product of claim 18 wherein performing the first operation on the copy of the identified file further comprises:

determining a mapping from the file identifer to the new file; and

performing the first operation on the new file.

20. The computer program product of claim 16 wherein determining whether the identified file is located on a read-only file system further comprises:

determining a mapping from the file identifier to a file location; and

determining whether the file location is associated with a read-only file system.

21. The computer program product of claim 16 further comprising instructions for carrying out the steps of:

receiving a second request from the VFS layer, the second request including the file identifier and a second operation to be performed on the identified file; and

performing the second operation on the copy of the identified file.

22. The computer program product of claim 21 wherein performing the second operation on the copy of the file further comprises:

determining a mapping from the file identifier to the copy of the identified file; and

performing the second operation on the copy of the identified file.

23. The computer program product of claim 16 wherein the read-only storage device receives requests for file operations from a plurality of computers.

24. A system for sharing a read-only file system, the system comprising:

a file handling module for receiving from a file system a file identifier and an operation to be performed on the identified file;

a mapping module, communicatively coupled to the file handling module, for determining a mapping between the file identifier and a location of a file identified by the identifier; and

a file system communication module, communicatively coupled to the mapping module, for performing the operation on the identified file.

25. The system of claim 24 wherein the operation to be performed on the identified file is a write operation and the location of the file identified by the identifier is on a read-only storage device.

26. The system of claim 24 wherein the file system communication module is further configured to perform the operation on a new file and the mapping module is further configured to establish a new mapping from the file identifier to a location of the new file.

27. A system for sharing a data, the system comprising:

a data handling module for receiving a data identifier and an operation to be performed on the identified data;

a mapping module, communicatively coupled to the data handling module, for determining a mapping between the data identifier and a location of data identified by the identifier; and

a data store communication module, communicatively coupled to the mapping module, for performing the operation on the identified data.

28. The system of claim 27 wherein the operation to be performed on the identified data is a write operation and the location of the data identified by the identifier is a read-only location.

29. The system of claim 27 wherein the data store communication module is further configured to perform the operation on new data and the mapping module is further configured to establish a new mapping from the data identifier to a location of the new data.