linux-kernel - Re: dm: improve block integrity support

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Date:	Thu, 14 Apr 2011 10:42:09 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc:	Jens Axboe <jaxboe@...ionio.com>,
	LKML <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...e.de>,
	device-mapper development <dm-devel@...hat.com>
Subject: Re: dm: improve block integrity support

On Thu, Apr 14 2011 at 10:09am -0400,
Mike Snitzer <snitzer@...hat.com> wrote:

> [trimming CCs so as not to pester as many people directly]
> 
> On Fri, Apr 01 2011 at  1:42pm -0400,
> Mike Snitzer <snitzer@...hat.com> wrote:
> 
> > The current block integrity (DIF/DIX) support in DM is verifying that
> > all devices' integrity profiles match during DM device resume (which
> > is past the point of no return).  To some degree that is unavoidable
> > (stacked DM devices force this late checking).  But for most DM
> > devices (which aren't stacking on other DM devices) the ideal time to
> > verify all integrity profiles match is during table load.
> > 
> > Introduce the notion of an "initialized" integrity profile: a profile
> > that was blk_integrity_register()'d with a non-NULL 'blk_integrity'
> > template.  Add blk_integrity_is_initialized() to allow checking if a
> > profile was initialized.
> > 
> > Update DM integrity support to:
> > - check all devices with _initialized_ integrity profiles match
> >   during table load; uninitialized profiles (e.g. for underlying DM
> >   device(s) of a stacked DM device) are ignored.
> > - disallow a table load that would result in an integrity profile that
> >   conflicts with a DM device's existing (in-use) integrity profile
> > - avoid clearing an existing integrity profile
> > - validate all integrity profiles match during resume; but if they
> >   don't all we can do is report the mismatch (during resume we're past
> >   the point of no return)
> > 
> > Signed-off-by: Mike Snitzer <snitzer@...hat.com>
> > Cc: Martin K. Petersen <martin.petersen@...cle.com>
> 
> Hi Martin,
> 
> Any chance you've had a look at this?  I'm most interested in whether
> the code works with the various integrity profiles you have.
> 
> I'd really like to get this reviewed and queued for upstream so that it
> doesn't die on the vine.

Ah wow, just noticed this got in through the block tree over a week ago:
http://git.kernel.org/linus/a63a5cf84dac7a23a57

Thanks Jens!

Martin,
I've done enough testing that I am confident the DM integrity support is
in a better place with this change.  But I'd still really appreciate it
if you could verify all is well.

Mike
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