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  1. #1

    On-The-Fly File Compression

    I've been searching for ever for a linux fs that will give me on-the-fly compression like ntfs. The closest thing I have found, that is stable, is squashfs. But recently a thought occured to me. (can you believe it, I actually have thoughts ;)
    Is it possible to compress a folder using gzip and then mount the new file in some way so that it could be used for on-the-fly (de)compression? Stretch your mind, open your thoughts... could it be possible at all?

  2. #2
    Linux Guru
    Join Date
    Oct 2001
    Täby, Sweden
    I'm sure that you could modify the loop device kernel driver to include on-the-fly decompression, and maybe even implement a "tarfs". All that would of course be best to do on the Hurd, but since this is Linux, that won't be possible.
    The greatest problem, however, is that gzip isn't seekable, and even less modifyable. I don't know if you've read about LZW compression, but it makes it completely impossible to change the contents of a gzipped file wihtout rebuilding the entire archive (or really just the parts after the one you changed, but it's just marginally better).
    Therefore, it would be much better if you'd find a modifyable compression algorithm, like a block based one or something (I don't really know that much about compression).

  3. #3

    AVFS You Respond

    Thanks Dolda, there are really no words to express how much your comment has helped me and other linux users.

    Anyway, I think I may have found something like what I've been looking for. It's called AVFS. If anyone has ever used this, please write in.

  4. $spacer_open
  5. #4

    linux transparent filesystem compression

    I hope these links help:
    Zlibc is a read-only compressed file-system emulation. It allows executables to uncompress their data files on the fly. No kernel patch, no re-compilation of the executables and the libraries is needed. Using gzip -9, a compression ratio of 1:3 can easily be achieved! (See examples below). This program has (almost) the same effect as a (read-only) compressed file system.

    How it works:
    This package overrides the "open" function (and other similar system call functions) of the C library. this package uses the LD_PRELOAD variable to redirect the dynamic linker to use the relevant functions of uncompress.o instead of the shared library. The behavior of the tools may be tuned using the /etc/zlibc.conf configurator file.
    Can I also compress executables?
    Zlibc cannot use compressed executables. However there is another program, UPX which can do this. To save most disk space, use the two programs together. (zlibc is able to use compressed data files, but not executables, and UPX is able to use compressed executables, but not data files)
    How can I remove zlibc when I don't want it any more?
    Buy a huge disk
    Uncompress your compressed files with gunzip.
    unset LD_PRELOAD, or remove it from /etc/

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