From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. R. Okajima" Subject: Re: [LSF/MM ATTEND] Stackable Union Filesystem Implementation Date: Thu, 09 Jan 2014 16:32:05 +0900 Message-ID: <523.1389252725@jrobl> References: <20140107122301.GC16640@quack.suse.cz> <6469.1389157809@jrobl> Cc: Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org To: Saket Sinha Return-path: Received: from mail02-md.ns.itscom.net ([175.177.155.112]:37187 "EHLO mail02-md.ns.itscom.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751925AbaAIHcK (ORCPT ); Thu, 9 Jan 2014 02:32:10 -0500 In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Saket Sinha: > > For such purpose, a "block device level union" (instead of filesystem > > level union) may be an option for you, such as "dm snapshot". > > > I imagine that this would make things more complicated as ideally this > should be done in a filesystem driver. Again a "block device level > union" would all the more have lesser chances of getting this > filesystem driver included in the mainline kernel as kernel > maintainers prefer the drivers to be as simple as possible. ?? I am afraid that I cannot fully understand what you wrote. If you think "dm snapshot" does not exist currently, and you or someone else are going to develop a new feature, that is wrong. You already have "dm snapshot" feature and you can "stack" the block devices by using it. (cf. http://aufs.sourceforge.net/aufs2/report/sq/sq.pdf which is a bit old) J. R. Okajima