LZO support

[C. Scott Ananian]

On Mon, Jul 14, 2008 at 1:27 PM, Chris Ball <cjb at laptop.org> wrote:
>   > - Another option is to provide a one-time flag passed at file
>   > creation time (O_CREAT) to enable/disable compression. This would
>   > also require VFS changes but I think would be simpler; however,
>   > this case has the problem that all applications that may at one
>   > time write a file that does not need compression need to be
>   > modified to support this extension.
>
> I think this would get us 90% of the way there with a little work.
> I don't care about arbitrary code being able to set no-compression
> as much as I care about code we control being able to do so.

I prefer an xattr being set in addition, so that the 'no compression'
information is saved across backup/restore etc.  I'd prefer "in place
of" instead of "in addition to", but the POSIX apis for xattrs would
make this really inconvenient on the kernel side: you'd have to open
the file, then set the xattr, *then* write the data.

>   > Do we have some idea of how much of our data in general is
>   > compressed and how much is not?
>
> Yes:
>
> -rw-r--r-- 1 cjb cjb 928M 2008-07-14 01:57 joyride-2158.ext3.img
> -rw-r--r-- 1 cjb cjb 349M 2008-07-14 01:57 joyride-2158.jffs2.img
> -rw-r--r-- 1 cjb cjb 264M 2008-07-14 01:57 joyride-2158.ext3.img.bz2

Look also at the .usb file, which is an uncompressed ISO9660 image of
our filesystem.  Using an uncompressed filesystem is really not an
option.
 --scott

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