From: Dave Chinner <david@fromorbit.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH 1/2] xfs: add CRC infrastructure
Date: Thu, 8 Nov 2012 09:28:31 +1100 [thread overview]
Message-ID: <20121107222831.GI6434@dastard> (raw)
In-Reply-To: <20121107213946.GB16230@one.firstfloor.org>
On Wed, Nov 07, 2012 at 10:39:46PM +0100, Andi Kleen wrote:
> > Why would that be necessary? We never include the checksum field in
> > the calculation when setting it or verifiying it, and the
> > verification uses exactly the same method as the original
> > calculation to check the CRC, so it doesn't matter if the CRC value
> > is zero or not - if it matches (zero or otherwise), the validation
> > passes....
>
> I thought zero meant the checksum is not there? You stated that
> somewhere else.
That's only to avoid spurious warnings when moving from an existing
kernel to a new kernel that issues advisory warnings on mismatches.
For enforcement, though, when the on-disk format changes so that all
metadata is CRC protected, determination of whether zero is a valid
CRC value is determined by a superblock feature bit, not a magic CRC
mapping value...
Hence mapping the zero value just for advisory warnings really
doesn't buy us that much other than complexity for this single case.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2012-11-07 22:26 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-07 13:37 [PATCH 0/2] xfs: CRCs for log buffers Dave Chinner
2012-11-07 13:37 ` [PATCH 1/2] xfs: add CRC infrastructure Dave Chinner
2012-11-07 16:21 ` Andi Kleen
2012-11-07 20:31 ` Dave Chinner
2012-11-07 21:39 ` Andi Kleen
2012-11-07 22:28 ` Dave Chinner [this message]
2012-11-08 14:42 ` Mark Tinguely
2012-11-08 21:22 ` Dave Chinner
2012-11-09 22:09 ` Mark Tinguely
2012-11-11 1:26 ` Dave Chinner
2012-11-11 19:54 ` Mark Tinguely
2012-11-11 22:51 ` Dave Chinner
2012-11-07 13:37 ` [PATCH 2/2] xfs: add CRC checks to the log Dave Chinner
2012-11-11 19:57 ` Mark Tinguely
2012-11-08 0:21 ` [PATCH 0/2] xfs: CRCs for log buffers Dave Chinner
2012-11-09 0:05 ` Ben Myers
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