Contiguous file allocation in an extensible file system

• US 9,575,972 B2
• Filed: 12/06/2013
• Issued: 02/21/2017
• Est. Priority Date: 12/17/2004
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Inventors: Pudipeddi, Ravisankar V., Ghotge, Vishal V., Thind, Ravinder S., Goebel, David A.
• Primary Examiner(s): PYO, MONICA M
• Application Number:
  US14/099,307
• Publication Number:
  US 20140149344A1
• Time in Patent Office: 1,173 Days
• Field of Search: 707/821, 707/770, 707/620, 709/217
• US Class Current: 1/1
• CPC Class Codes: G06F 16/11 File system administration, e.g. details of archiving or snapshots file system backup G06F11/14
• CPC Class Codes: G06F 16/13 File access structures, e.g. distributed indices arrangements of input from, or output to, record carriers G06F3/06
• CPC Class Codes: G06F 16/1727 Details of free space management performed by the file system saving storage space on storage systems G06F3/0608; management of blocks in storage devices G06F3/064

Abstract

Disclosed is a method for creating and reading a contiguous file in an extensible file system. During the creation of a file on the storage media, the file system format check the bitmap to determine if there are areas of free space on the media that would permit the storage of the file in a contiguous manner. By storing the file in a contiguous manner the file may later be read without resorting to the file allocation table, because the file itself would not be fragmented on the storage media. Once an area of free space has been identified, the file is written to the media in a contiguous manner. Further, an associated entry for the file in the directory entry is updated or created to indicate that the file is a contiguous file and also provides basic parameters necessary to read the file without resorting to accessing the file allocation table.

Claims

1. A computer-implemented method of writing, by a file system of a computer system, a file to a storage media comprising:

receiving data associated with the file to be written;

determining an amount of space associated with the file;

reading a bitmap associated with the storage media to identify areas of free space on the media;

identifying from the areas of free space on the storage media contiguous free space equal to or greater than the space associated with the file;

writing the file to the storage media as a contiguous file when an area of contiguous free space on the media greater than or equal to the space associated with the file is identified; and

setting a contiguous file flag in a directory entry associated with the file in a file directory of the storage medium, when the file is written as a contiguous file, without storing information about the contiguously written file in a file allocation table of the storage medium.

2. The method of claim 1 wherein writing the file to the storage media, further comprises:

setting a file size entry of the directory entry associated with the file in the file directory of the storage media, the file directory being separate from the file allocation table; and

setting a starting cluster indication entry of the directory entry associated with the file in the file directory.

3. The method of claim 1 wherein when the file is written to the storage media as a contiguous file, the file allocation table for the storage media is not updated.

4. The method of claim 1 wherein receiving data associated with the file receives data indicative of an update to a file that is stored previously on the storage media, the method further comprising:

determining if there is enough free space in the area of contiguous free space for the updated file;

writing the updated file in the area of contiguous free space when there is enough free space.

5. The method of claim 1 wherein receiving data associated with the file receives data indicative of an update to a file that is stored previously on the storage media in a non-contiguous manner, the method further comprising:

determining that the amount of space associated with the updated file is smaller than an amount of space currently occupied by the file on the storage media;

searching the bitmap to identify contiguous free space that is greater than the amount of space associated with the updated file;

deleting the file from the storage media and writing the updated file to the identified contiguous free space when the updated file can be written in a contiguous manner; and

updating the contiguous file flag in the directory entry associated with the file to indicate that the file is now contiguously written, without storing information about the contiguously written file in the file allocation table of the storage medium.

6. The method of claim 1 wherein the received data associated with the file to be written is received from a consumer electronics device.

7. The method of claim 1 wherein receiving data associated with the file receives data indicative of an update to a file that is stored previously on the storage media, the method further comprising:

determining if there is enough free space in the area of contiguous free space for the updated file;

when there is not enough free space in the area of contiguous free space for the updated file, reading the bitmap to identify if there is another area of free space on the storage media that has contiguous free space that is greater than or equal to the space associated with the updated file;

writing the updated file to the another area of contiguous free space when the another area of contiguous free space is identified as having contiguous free space greater than or equal to the space associated with the updated file; and

when there is not another area of contiguous free space on the storage media for the updated file, writing the updated file to the storage media in a non-contiguous manner;

clearing the contiguous file flag in the directory entry for the file; and

updating the file allocation table with information about the non-contiguously written file.

8. A computing device having storage that stores computer-executable instructions and a processor for executing the instructions, the instructions, when executed by the processor, causing the device to perform operations comprising:

receiving data associated with a file to be written to a storage media;

determining an amount of space associated with the file;

reading a bitmap associated with the storage media to identify areas of free space on the media;

identifying from the areas of free space on the storage media contiguous free space equal to or greater than the space associated with the file;

writing the file to the storage media as a contiguous file when an area of contiguous free space on the media greater than or equal to the space associated with the file is identified; and

setting a contiguous file flag in a directory entry associated with the file in a file directory of the storage medium, when the file is written as a contiguous file, without storing information about the contiguously written file in a file allocation table of the storage medium.

9. The computing device of claim 8 wherein the operation of writing the file to the storage media, further comprises:

setting a file size entry of the directory entry associated with the file in the file directory of the storage media, the file directory being separate from the file allocation table; and

setting a starting cluster indication entry of the directory entry associated with the file in the file directory.

10. The computing device of claim 8 wherein when the file is written to the storage media as a contiguous file, the file allocation table for the storage media is not updated.

11. The computing device of claim 8 wherein receiving data associated with the file receives data indicative of an update to a file that is stored previously on the storage media, and wherein the operations further comprise:

determining if there is enough free space in the area of contiguous free space for the updated file;

writing the updated file in the area of contiguous free space when there is enough free space;

when there is not enough free space in the area of contiguous free space for the updated file, reading the bitmap to identify if there is another area of free space on the storage media that has contiguous free space that is greater than or equal to the space associated with the updated file;

writing the updated file to the another area of contiguous free space when the another area of contiguous free space is identified as having contiguous free space greater than or equal to the space associated with the updated file; and

when there is not another area of contiguous free space on the storage media for the updated file, writing the updated file to the storage media in a non-contiguous manner;

clearing the contiguous file flag in the directory entry for the file; and

updating the file allocation table with information about the non-contiguously written file.

12. The computing device of claim 8 wherein receiving data associated with the file receives data indicative of an update to a file that is stored previously on the storage media in a non-contiguous manner, and wherein the operations further comprise:

determining that the amount of space associated with the updated file is smaller than an amount of space currently occupied by the file on the storage media;

searching the bitmap to identify contiguous free space that is greater than the amount of space associated with the updated file;

deleting the file from the storage media and writing the updated file to the identified contiguous free space when the updated file can be written in a contiguous manner; and

updating the contiguous file flag in the directory entry associated with the file to indicate that the file is now contiguously written, without storing information about the contiguously written file in the file allocation table of the storage medium.

13. The computing device of claim 8 wherein the received data associated with the file to be written is received from a consumer electronics device.