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Re: XFS information leak during crash

To: Nathan Scott <nathans@xxxxxxx>
Subject: Re: XFS information leak during crash
From: Jan Kasprzak <kas@xxxxxxxxxx>
Date: Wed, 9 Nov 2005 17:55:39 +0100
Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-xfs@xxxxxxxxxxx
In-reply-to: <20051102233629.GD6759@xxxxxxxxxx>
References: <20051102212722.GC6759@xxxxxxxxxx> <20051103101107.O6239737@xxxxxxxxxxxxxxxxxxxxxxxx> <20051102233629.GD6759@xxxxxxxxxx>
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Jan Kasprzak wrote:
: Nathan Scott wrote:
: : 
: : This issue affects every filesystem, right?  Or are you claiming its
: : only XFS affected here?  Have you run your parallel-buffered-writers
: : test case on any other filesystems?  I'd be interested in the results,
: : in particular, with all of the data=xxx modes of other filesystems.
: : 
:       I will do this tomorrow or the day after and post the results.
:
        Sorry for the delay - I did the test on other filesystems
as well: "random" (i.e. not rewritten) data after the hard reset were
inside the files in the following filesystems:

XFS
ext3 data=writeback
JFS

and my test program did not manage to put those "random" blocks into the
files when running on ext3 with data=ordered mode (as expected).

        I have tried ReiserFS as well, with mixed results:

- when I hit "reset" soon enough (but well after the HDD LED starts
        blinking), I end up with an empty directory after the reboot.
        It seems ReiserFS caches the filesystem operations much longer
        than other filesystems.
- I have not seen truly random data in the files on ReiserFS after the
        hard reset, but I have seen blocks of zeros instead of either
        old or new data. This may be a pure coincidence, so ReiserFS
        may belong to the same group as ext3 with data=writeback mode,
        but I was not able to make the files contain truly random
        blocks by hitting the reset button.

        So, does ReiserFS do some kind of data journaling/ordering as well?

-Yenya

-- 
| Jan "Yenya" Kasprzak  <kas at {fi.muni.cz - work | yenya.net - private}> |
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| http://www.fi.muni.cz/~kas/    Journal: http://www.fi.muni.cz/~kas/blog/ |
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> for implementing software.                              --Linus Torvalds <


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