mtdblock mount issue
vicky.irobot at gmail.com
Fri Feb 8 05:31:55 EST 2008
Sergei Sharonov wrote:
>> I am trying to mount a cramfs partition from flash.
> A word of warning. CRAMFS is broken in kernels < 2.6.18. As far as I can tell,
> under heavy load (e.g. reading multiple files in parallel that are not cached)
> it may fail with decompression errors. I think the issue is not exactly with
> cramfs but with some interaction with page cache. Backporting just cramfs files
> to 2.6.15 did not help. If you have drop_caches interface (kernel > 2.6.16 or
> just backport it) it is easy to reproduce. Otherwise it happens _very_
> infrequently because most of the time files are already cached. However the
> consequences are severe - corrupted executables, etc.
> Here is a script to reproduce the problem:
> # Copy large file from cramfs to tmpfs
> cp /bin/smbd /tmp/
> # First concurrent access to files/directories
> while [ 1 ]; do cat /bin/* > /dev/null; done &
> # Second concurrent access to test file and cache flush
> for((i=0;i<99999;i++)) do echo -n "cycle=$i ";
> cmp /bin/smbd /tmp/smbd ;
> echo 3 > /proc/sys/vm/drop_caches ;
> Note that /bin is in cramfs. smbd can be any large file.
> I've also seen statements that drop_caches interface is not 100% reliable.
> Nevertheless I have experienced decompression errors even without forcing
> cache purge.
> Above script has caused failures on PowerPC/2.6.16 and ARM9/2.6.15.
> 2.6.18 and 2.6.23 seem ok.
> P.S. Yes, cramfs has little to do with MTD but since ppl here use it with flash
> I felt it was a good idea to post this warning.
> Linux MTD discussion mailing list
thanks for the info. I think I will check out squashfs then.
But before that I wanted to fix the issue that I am seeing. There might
be something wrong in my implementation?
BTW I thought this was the right mailing list, since I am trying to
mount cramfs image using MTD. Can you point me to the right mailing list?
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