Return-Path: linux-nfs-owner@vger.kernel.org Received: from ipmail05.adl6.internode.on.net ([150.101.137.143]:36291 "EHLO ipmail05.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934226AbaKNEfn (ORCPT ); Thu, 13 Nov 2014 23:35:43 -0500 Date: Fri, 14 Nov 2014 15:35:05 +1100 From: Dave Chinner To: Trond Myklebust Cc: Christoph Hellwig , "J. Bruce Fields" , Linux NFS Mailing List Subject: Re: [PATCH 2/2] nfsd: implement chage_attr_type attribute Message-ID: <20141114043505.GA29950@dastard> References: <20141111162849.GA12527@lst.de> <20141111162704.GA12103@lst.de> <20141111222710.GY23575@dastard> <20141112102440.GA31344@lst.de> <20141113002846.GC23575@dastard> <20141113235400.GM28565@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, Nov 13, 2014 at 07:43:33PM -0500, Trond Myklebust wrote: > On Thu, Nov 13, 2014 at 6:54 PM, Dave Chinner wrote: > > On Thu, Nov 13, 2014 at 08:02:43AM -0500, Trond Myklebust wrote: > >> On Wed, Nov 12, 2014 at 7:28 PM, Dave Chinner wrote: > >> > On Wed, Nov 12, 2014 at 09:26:16AM -0500, Trond Myklebust wrote: > >> >> On Wed, Nov 12, 2014 at 5:24 AM, Christoph Hellwig wrote: > >> >> > On Wed, Nov 12, 2014 at 09:27:10AM +1100, Dave Chinner wrote: > >> >> >> To clarify what Christoph wrote, XFS updates i_version is updated > >> >> >> once per transaction that modifies the inode. So if a VFS level > >> >> >> operation results in multiple transactions then each transaction > >> >> >> will but the version. > >> >> >> > >> >> >> It was implemented that way because nobody could tell me what the > >> >> >> actual granularity requirement for change detection was. Hence what > >> >> >> I implemented was "be able to detect any persistent change that is > >> >> >> made" to cover all bases. > > > > FWIW, ext4 takes the same approach. See Ted's post today: > > > > http://www.spinics.net/lists/linux-ext4/msg46194.html > > > > "The inode_inc_iversion() in mark4_ext4_iloc_dirty() is probably not > > necessary, since we already should be incrementing i_version whenever > > ctime and mtime gets updated. The inode_inc_iversion() there is more > > of a "belt and suspenders" safety thing, on the theory that the extra > > bump in i_version won't hurt anything." > > > > It will hurt if it causes all the NFS clients to blow their caches > unnecessarily. Not my problem. We've just implemented what we were asked to implement. > Who asked for this? The only discussion where actual specifications were enumerated was during a thread about using i_version in the integrity measurement code (IMA subsystem). The NFSv4 requirements for the change counter were expressed here: https://lkml.org/lkml/2012/1/5/408 Don't blame us for implementing the vague "changes every time" requirements in a way that results in no chance of a persistent change to either data or metadata being missed by the filesystem. Cheers, Dave. -- Dave Chinner david@fromorbit.com