linux-kernel - Re: [RFC PATCH] dm-csum: A new device mapper target that checks data integrity

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Date:	Mon, 25 May 2009 14:22:23 +0200
From:	Goswin von Brederlow <goswin-v-b@....de>
To:	Alberto Bertogli <albertito@...tiri.com.ar>
Cc:	linux-kernel@...r.kernel.org, dm-devel@...hat.com,
	linux-raid@...r.kernel.org, agk@...hat.com, neilb@...e.de
Subject: Re: [RFC PATCH] dm-csum: A new device mapper target that checks data integrity

Alberto Bertogli <albertito@...tiri.com.ar> writes:

> Hi!
>
> I'm writing this device mapper target that stores checksums on writes and
> verifies them on reads.
>
> It's not widely tested, but you can run mke2fs on it and do basic file
> operations. The to-do list is still large, and most of it can be found within
> the code.
>
> To test it, you will need to format the device using the (very rough) attached
> tool, and then create the dm device with something like:
>
> 	echo 0 $SIZE csum $REALDEVICE 0 | dmsetup create $NAME
>
>
> I think it can be useful for people who want to detect data corruption and are
> either using the block layer directly or a filesystem that doesn't check data
> integrity (which are most, if not all, of the popular ones today). Maybe it
> could also be used for testing the bio-integrity extensions, although at the
> moment it's completely independent and I haven't looked much, but it's on my
> to-do list.
>
> It does NOT pretend to be useful for consistency checks for security purposes.
> Use something else if you do not want someone evil tampering with your data.
>
>
> Comments are obviously welcome. There are also some questions embedded in the
> code, if anyone cares to answer any of them, I'd really appreciate it.
>
> Thanks a lot,
> 		Alberto

How does that behave on crashes? Will checksums be out of sync with data?
Will pending blocks recalculate their checksum?

MfG
        Goswin
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