On Mon, Apr 9, 2012 at 6:06 AM, Stroller <strol...@stellar.eclipse.co.uk> wrote: > > On 8 April 2012, at 19:21, Canek Peláez Valdés wrote: >> … >> And (optionally) convert all the files and directories to use extends: >> >> find <directory> -xdev -type f -print0 | xargs -0 chattr +e >> find <directory> -xdev -type d -print0 | xargs -0 chattr +e > > Ok, so I was just casually reading the chattr manpage, following this post… > > The letters `acdeijstuADST' select the new attributes for the files: > append only (a), compressed (c), … > > A file with the `c' attribute set is automatically compressed on the > disk by the kernel. A read from this file returns uncompressed data. > A write to this file compresses data before storing them on the disk. > > COMPRESSED?!?! > > You mean, all I need to do is `touch new.dd.img && chattr +c new.dd.img && dd > if=/dev/sdX of=new.dd.img` and I never again need to worry about piping dd > through bzip and bunzip? > > If I have a massive great big uncompressed dd image, I can compress it as > simply as touching a new file, changing this attribute on the new file and > copying it over? > > Is there a reason I've been unaware of this? Why isn't this hugely popular? > > Stroller.
>From the kernel sources, Documentation/filesystems/ext2.txt: " Specification ============= ext2 shares many properties with traditional Unix filesystems. It has the concepts of blocks, inodes and directories. It has space in the specification for Access Control Lists (ACLs), fragments, undeletion and compression though these are not yet implemented (some are available as separate patches). There is also a versioning mechanism to allow new features (such as journalling) to be added in a maximally compatible manner. " So, ext2's extended attribute set listed support for compression (among other things), but it wasn't implemented. None of the other ext*.txt files reference compression. Digging into the kenrel source for ext4 in linux-3.2.1.-gentoo-r2, there are symbols defined for managing compression, but they're not used. In short, compression support is specced, but not implemented. -- :wq
