File-based compression on a fat volume
Individual files within a FAT volume may be compressed while other files remain uncompressed. A FAT Compression Filter (FCF) intercepts calls to the file system, performs the compression and decompression tasks relating to the files on the FAT volume. The use of individual file compression with the FAT file system helps to ensure that the flash memory has a long life and does not quickly fail while still providing the benefits of individual file compression. The FAT Compression Filter allows individual files within a volume to be excluded from being compressed.
1 . A computer-implemented method for compressing individual files on a FAT volume while other files remain uncompressed, comprising:
receiving a file system request to read or write data to a file on the FAT volume;
determining whether the file is compressed, and when the file is compressed:
compressing the data and writing the data to the file on the FAT volume when the file system request is to write the data; wherein the FAT volume includes files that are uncompressed and files that are compressed; and
accessing the file on the FAT volume; decompressing the data; and returning the decompressed data when the file system request is to read the data.
2 . The method of claim 1 , wherein receiving the file system request, comprises intercepting the file system request before it reaches the file system.
3 . The method of claim 2 , wherein determining whether the file is compressed comprises checking an exclusion list.
4 . The method of claim 3 , wherein the exclusion list includes files and folders that are to remain uncompressed.
5 . The method of claim 3 , further comprising storing boot files in the exclusion list.
6 . The method of claim 1 , wherein determining whether the file is compressed comprises determining whether the file includes an identifier indicating that the file is compressed.
7 . The method of claim 6 , wherein the identifier is a header that comprises a compression type portion and a mapping portion.
8 . The method of claim 7 , wherein compressing the data and decompressing the data is performed using a compression algorithm that is specified within the compression type portion of the header.
9 . The method of claim 7 , wherein accessing the file comprises accessing the mapping portion of the header and determining a mapping to the data within the file.
10 . A system for compressing individual files on a FAT volume while other files remain uncompressed, comprising:
a FAT volume that includes both compressed files and uncompressed files; and
a File Compression Filter (FCF) program that is configured to perform actions, including to:
receive a file system write request to write data to one of the compressed files on the FAT volume;
receive a file system read request to read data from one of the compressed files on the FAT volume;
decompress the data from the one of the compressed files and return the decompressed data in response to the read request; and
compress the data and store the compressed data within the one of the compressed files in response to the write request.
11 . The system of claim 10 , further comprising an exclusion list that identifies files within the FAT volume that are to be compressed.
12 . The system of claim 11 , wherein the exclusion list includes a checksum that is used to indicate when the exclusion list has been changed.
13 . The system of claim 11 , wherein each of the compressed files on the FAT volume include a header that comprises a compression type that specifies a compression algorithm.
14 . The system of claim 13 , wherein the FCF program further comprises a volume list that indicates at least one attached FAT volume.
15 . The system of claim 13 , wherein the FCF program is further configured to determine whether a minimum compression threshold is met.
16 . The system of claim 13 , further comprising a second FAT volume that includes compressed files and uncompressed files and wherein the FCF program is further configured to copy and move the compressed files and the uncompressed files between the FAT volume and the second FAT volume.
17 . A computer-readable medium having computer executable instructions for adjusting settings relating to individual compressed files on a FAT volume while other files remain uncompressed, the instructions comprising:
receiving a request to update one of: an exclusion list that lists files that are to remain uncompressed on the FAT volume; a compression state of a file on the FAT volume; and a compression algorithm; and
updating the one of the exclusion list; the compression state and the compression algorithm in response to the request.
18 . The computer-readable medium of claim 17 , wherein the request to update the exclusion list indicates to either: add to the exclusion list; remove from the exclusion list; display the exclusion list; and change an element within the exclusion list.
19 . The computer-readable medium of claim 17 , wherein the request to update the compression state of the file on the FAT volume includes an indication of whether to compress the file or whether to decompress the file.
20 . The computer-readable medium of claim 17 , wherein the request to update the compression algorithm comprises indicating a type of compression algorithm.