enabling and disabling file compression

[Deepak Saxena]

On Oct 13 2008, at 14:59, Tomeu Vizoso was caught saying:
> Hi Chris and Deepak,
> 
> in Ubifs, I have tried unsetting the compression xattr on files, but
> reads were equally slow so I guess the contents weren't actually
> uncompressed. Even tried dd'ing to an empty existing file without the
> c attribute, but the result was the same. Any idea what I'm doing
> wrong?

I _think_ the slowness we are seeing might be a side effect of me having
enabled various debug messages in both the UBI and UBIFS layer. I am
rebuilding the image with a new kernel and will post after I do some
testing here.

> Chris, I think you worked on improving the control of on-the-fly
> compression in jffs2, can we control it using the c attribute as in
> ubifs?

I've talked to David Woodhouse about this in the past and it shouldn't
be too hard to do as the ioctl() handler is already in place, it just
means adding a flag to the inode (and each block?) and a check at 
read()/write() time.

One question I've wondered about is what is the meaning of disabling
compression on a file that has already been written to flash compressed?
Do we decompress the file and re-write it to flash or do we just
wait until an update that touches the data?

~Deepak

-- 
Deepak Saxena - Kernel Developer - dsaxena at laptop.org