e2bitmap

e2bitmap is a quick hack I (pjm) wrote to satisfy my curiosity about what sort of cluster bitmaps most files have.

I include it in the main distribution because someone (Stefan Monnier) once asked for a program to do this.

The e2bitmap program tells you which clusters of a file are compressed, and which are uncompressed. The bitmap is represented as a list of ones and zeros, where `1' means a compressed cluster and `0' an uncompressed cluster, and the first cluster of the file is represented by the left-most digit.

If there are no compressed clusters then the word `uncompressed' is displayed instead of a list of digits.(2)

One use for this program is shown in section Which files have an indirect cluster bitmap block?.

Another use for it is in cases where you want ext2fs to do only the online decompression while leaving the compression to a cron job (for instance). The cron job might use e2bitmap to see which files deserve recompression in order to avoid recompressing unchanged files over and over again. Use `chattr -m none files' to prevent the kernel from doing the compression right away, and, for example, `chattr -m gzip9 -s none files' in the cron job.

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