Save space by ungzipping gzip files

[Ryan Finnie]

Significant space can be saved by uncompressing gzip files in the root, then relying on the compressed root's xz squashfs to provider a higher compression level.

For this to work, the original data must appear within the files, that is "gzip -1" would not produce a file that xz could compress further. GNU gzip does not have a -0 option, but Perl's IO::Compress::Gzip does.

We'd need to decompress during stage1, update /var/lib/dpkg/info/*.md5sums, possibly others. To avoid unnecessary work, there should be some sort of method of tracking which files have been decompressed.

[Ryan Finnie (fo0bar)]

Damn thing took 150 lines of Perl to do completely and safely, but it works. 1.75MB saved on the x86 CD by recompressing.