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On Mon, Apr 9, 2012 at 6:06 AM, Stroller <stroller@××××××××××××××××××.uk> wrote: |
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> |
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> On 8 April 2012, at 19:21, Canek Peláez Valdés wrote: |
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>> … |
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>> And (optionally) convert all the files and directories to use extends: |
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>> |
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>> find <directory> -xdev -type f -print0 | xargs -0 chattr +e |
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>> find <directory> -xdev -type d -print0 | xargs -0 chattr +e |
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> |
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> Ok, so I was just casually reading the chattr manpage, following this post… |
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> |
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> The letters `acdeijstuADST' select the new attributes for the files: |
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> append only (a), compressed (c), … |
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> |
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> A file with the `c' attribute set is automatically compressed on the |
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> disk by the kernel. A read from this file returns uncompressed data. |
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> A write to this file compresses data before storing them on the disk. |
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> |
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> COMPRESSED?!?! |
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> |
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> 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? |
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> |
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> 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? |
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> |
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> Is there a reason I've been unaware of this? Why isn't this hugely popular? |
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> |
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> Stroller. |
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From the kernel sources, Documentation/filesystems/ext2.txt: |
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" Specification |
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============= |
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|
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ext2 shares many properties with traditional Unix filesystems. It has |
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the concepts of blocks, inodes and directories. It has space in the |
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specification for Access Control Lists (ACLs), fragments, undeletion and |
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compression though these are not yet implemented (some are available as |
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separate patches). There is also a versioning mechanism to allow new |
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features (such as journalling) to be added in a maximally compatible |
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manner. " |
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So, ext2's extended attribute set listed support for compression |
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(among other things), but it wasn't implemented. None of the other |
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ext*.txt files reference compression. |
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Digging into the kenrel source for ext4 in linux-3.2.1.-gentoo-r2, |
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there are symbols defined for managing compression, but they're not |
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used. In short, compression support is specced, but not implemented. |
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-- |
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:wq |
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