LZO support

[Chris Ball]

Hi,

   > - One option, as suggested in the trac, is to have the kernel trap
   > file extensions and disable compression based on that. Doable, but
   > I expect a rather large hack to VFS to do this. An extension to
   > this idea is to look for specific signatures in files that disable
   > compression.

Not sure we need to go this far.

   > - 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.

   > 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

- Chris.
-- 
Chris Ball   <cjb at laptop.org>