From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id qA7MQbvH187846 for ; Wed, 7 Nov 2012 16:26:37 -0600 Received: from ipmail04.adl6.internode.on.net (ipmail04.adl6.internode.on.net [150.101.137.141]) by cuda.sgi.com with ESMTP id 9jK9WjYcFRDStxtq for ; Wed, 07 Nov 2012 14:28:34 -0800 (PST) Date: Thu, 8 Nov 2012 09:28:31 +1100 From: Dave Chinner Subject: Re: [PATCH 1/2] xfs: add CRC infrastructure Message-ID: <20121107222831.GI6434@dastard> References: <1352295452-4726-1-git-send-email-david@fromorbit.com> <1352295452-4726-2-git-send-email-david@fromorbit.com> <20121107203105.GE6434@dastard> <20121107213946.GB16230@one.firstfloor.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20121107213946.GB16230@one.firstfloor.org> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Andi Kleen Cc: xfs@oss.sgi.com 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 _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs