Transaction-safe fat file system improvements

• US 8,738,845 B2
• Filed: 09/19/2011
• Issued: 05/27/2014
• Est. Priority Date: 10/22/2002
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Patel, Sachin, Gopalan, Yadhu N.
• Primary Examiner(s): Bragdon, Reginald
• Assistant Examiner(s): LOONAN, ERIC T
• Application Number:
  US13/235,901
• Publication Number:
  US 20120011177A1
• Time in Patent Office: 981 Days
• Field of Search: None
• US Class Current: 711/103
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: G06F 16/1865 Transactional file systems
• CPC Class Codes: G06F 3/0619 in relation to data integrity, e.g. data losses, bit errors
• CPC Class Codes: G06F 3/0643 Management of files
• CPC Class Codes: G06F 3/0679 Non-volatile semiconductor memory device, e.g. flash memory, one time programmable memory [OTP]
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

Concepts for enhancing operation of transaction-safe file allocation table systems are described. The concepts include writing a file to non-volatile memory media and rendering an update of file size to the TFAT storage medium; and receiving a request to locate data in a non-volatile memory having a TFAT file management system, selecting a sector of the memory to parse to locate the data, determining when the selected sector is a first sector of a directory or subdirectory of the memory and when determining reveals that the selected sector is a first sector, skipping reading data from the selected sector. The concepts also include flushing a cache and synchronizing FATs.

Claims

1. A method comprising:

maintaining a first file allocation table and a second file allocation table for a file system;

synchronizing the first file allocation table and the second file allocation table resulting in the second file allocation table comprising a copy of the first file allocation table, the first file allocation table and the second file allocation table containing sector information for used sectors of the file system;

setting a last known good indicator to indicate that the first file allocation table is a last known good file allocation table;

initiating a write operation to write data to a file in the file system; and

, thereafter;

writing the data to one or more unused sectors in the file system;

subsequent to writing the data to the one or more unused sectors in the file system, rendering an update to the second file allocation table;

preserving the first file allocation table and the last known good indicator between writing the data to the one or more unused sectors in the file system and rendering the update to the second file allocation table; and

maintaining the first file allocation table as the last known good file allocation table when the write operation is interrupted, wherein the last known good indicator is not reset to indicate that the second file allocation table is maintained as the last known good file allocation table.

2. The method of claim 1 wherein:

the write operation comprises overwriting old data of the file, and used sectors containing the old data of the file are preserved.

3. The method of claim 1 further comprising storing data to be written to the file in cache memory prior to writing the data to the one or more unused sectors in the file system.

4. The method of claim 1 further comprising:

determining that the write operation includes re-writing an entire cluster of used sectors with new data; and

writing the new data to a new cluster without first re-writing old data from the used sectors to the new cluster.

5. The method of claim 1 wherein the file system is configured to make file size data transaction safe.

6. The method of claim 1 wherein the write operation comprises performing an atomic memory write via block drivers.

7. The method of claim 1 wherein the write operation comprises writing multiple discontinuous pages to discontinuous locations of the file.

8. The method of claim 7 further comprising opening the file in a write-through mode.

9. The method of claim 7 further comprising rendering an update to the second file allocation table in response to writing first and second discontinuous pages of data to first and second discontinuous locations in the file system.

10. A computer-readable storage medium storing computer-executable instructions that, when executed, cause a computing device to perform a method comprising:

maintaining a first file allocation table and a second file allocation table for a file system;

synchronizing the first file allocation table and the second file allocation table resulting in the second file allocation table comprising a copy of the first file allocation table, the first file allocation table and the second file allocation table containing sector information for used sectors of the file system;

setting a last known good indicator to indicate that the first file allocation table is a last known good file allocation table;

initiating a write operation to write data to a file in the file system; and

, thereafter;

writing the data to one or more unused sectors in the file system;

subsequent to writing the data to the one or more unused sectors in the file system, rendering an update to the second file allocation table;

preserving the first file allocation table and the last known good indicator between writing the data to the one or more unused sectors in the file system and rendering the update to the second file allocation table; and

maintaining the first file allocation table as the last known good file allocation table when the write operation is interrupted, wherein the last known good indicator is not reset to indicate that the second file allocation table is the last known good file allocation table.

11. The computer-readable storage medium of claim 10 wherein:

the write operation comprises overwriting old data of the file, and used sectors containing the old data of the file are preserved.

12. The computer-readable storage medium of claim 10 further comprising computer-executable instructions for storing data to be written to the file in cache memory prior to writing the data to the one or more unused sectors in the file system.

13. The computer-readable storage medium of claim 10 further comprising computer-executable instructions for:

determining that the write operation includes re-writing an entire cluster of used sectors with new data; and

writing the new data to a new cluster without first re-writing old data from the used sectors to the new cluster.

14. The computer-readable storage medium of claim 10 wherein the file system is configured to make file size data transaction safe.

15. The computer-readable storage medium of claim 10 wherein the write operation comprises performing an atomic memory write via block drivers.

16. The computer-readable storage medium of claim 10 wherein the write operation comprises writing multiple discontinuous pages to discontinuous locations of the file.

17. The computer-readable storage medium of claim 16 further comprising computer-executable instructions for opening the file in a write-through mode.

18. The computer-readable storage medium of claim 16 further comprising computer-executable instructions for rendering an update to the second file allocation table in response to writing first and second discontinuous pages of data to first and second discontinuous locations in the file system.

19. A computing device comprising:

a data storage device storing a file system;

a first file allocation table and a second file allocation table for the file system; and

one or more computer storage media storing computer-executable instructions for;

synchronizing the first file allocation table and the second file allocation table resulting in the second file allocation table comprising a copy of the first file allocation table, the first file allocation table and the second file allocation table containing sector information for used sectors of the file system,

setting a last known good indicator to indicate that the first file allocation table is a last known good file allocation table,

initiating a write operation to write data to a file in the file system, and, thereafter;

writing the data to one or more unused sectors in the file system;

subsequent to writing the data to the one or more unused sectors in the file system, rendering an update to the second file allocation table;

preserving the first file allocation table and the last known good indicator between writing the data to the one or more unused sectors in the file system and rendering the update to the second file allocation table; and

maintaining the first file allocation table as the last known good file allocation table when the write operation is interrupted, wherein the last known good indicator is not reset to indicate that the second file allocation table is the last known good file allocation table.

20. The computing device of claim 19 wherein:

the write operation comprises overwriting old data of the file, and

used sectors containing the old data of the file are preserved.