Return-Path: Received: from ipmail04.adl6.internode.on.net ([150.101.137.141]:12671 "EHLO ipmail04.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752712AbcCVWuV (ORCPT ); Tue, 22 Mar 2016 18:50:21 -0400 Date: Wed, 23 Mar 2016 09:50:18 +1100 From: Dave Chinner To: "J. Bruce Fields" Cc: Richard Yao , linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, Christoph Hellwig Subject: Re: Making an interface for alternative data streams Message-ID: <20160322225018.GV11812@dastard> References: <56F03945.40208@gentoo.org> <56F05745.50204@gentoo.org> <20160321204041.GA807@fieldses.org> <34E9F5BC-E8D4-405E-926E-DF2058E31B5F@gentoo.org> <20160322212931.GQ11812@dastard> <20160322215232.GK4083@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20160322215232.GK4083@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Mar 22, 2016 at 05:52:32PM -0400, J. Bruce Fields wrote: > On Wed, Mar 23, 2016 at 08:29:31AM +1100, Dave Chinner wrote: > > If you want additional seekable data streams, then come up with a > > filesystem namespace method of addressing these alternate data > > streams as *separate files containing data*. That's all an ADS is - > > a namespace hack to address multiple data files through a single > > file name. That's the problem that needs solving and it has nothing > > to do with xattrs. > > There was some thread about this years ago. Looking... "silent semantic > changes with reiser4" or "possible design issues for hybrids" look like > the relevant threads. > > One good starting point might be: > > http://mid.gmane.org/20040826212853.GA21964@parcelfarce.linux.theplanet.co.uk > > Don't know how out of date that might be now. Not sure it is the same issue - that looks like auto-bind-mount stuff. There are some relevant questions though, like "directory over file" semantics and implications... But we have covered this ground before, and at LSF/MM summits, too. historically it has been made pretty clear that xattrs are not something that can be used for alternate data streams. I think ADS is primarily a namespace and API problem - that needs to be sorted out first, and then what filesytems need to implement will be obvious. Perhaps overlayfs is a good place to start prototyping such functionality as there is an abstraction between the presented namespace and the underlying storage of the data.... Cheers, Dave. -- Dave Chinner david@fromorbit.com