From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bk0-f53.google.com (mail-bk0-f53.google.com [209.85.214.53]) by kanga.kvack.org (Postfix) with ESMTP id BB06A6B0036 for ; Thu, 9 Jan 2014 04:19:01 -0500 (EST) Received: by mail-bk0-f53.google.com with SMTP id na10so1042281bkb.12 for ; Thu, 09 Jan 2014 01:19:01 -0800 (PST) Received: from mail-bk0-x22b.google.com (mail-bk0-x22b.google.com [2a00:1450:4008:c01::22b]) by mx.google.com with ESMTPS id og3si1661608bkb.279.2014.01.09.01.19.00 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 09 Jan 2014 01:19:00 -0800 (PST) Received: by mail-bk0-f43.google.com with SMTP id mz12so1025394bkb.2 for ; Thu, 09 Jan 2014 01:19:00 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <523.1389252725@jrobl> References: <20140107122301.GC16640@quack.suse.cz> <6469.1389157809@jrobl> <523.1389252725@jrobl> Date: Thu, 9 Jan 2014 14:49:00 +0530 Message-ID: Subject: Re: [LSF/MM ATTEND] Stackable Union Filesystem Implementation From: Saket Sinha Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: "J. R. Okajima" Cc: Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org On Thu, Jan 9, 2014 at 1:02 PM, J. R. Okajima wrote: > > 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. I am sorry for not explaining it properly. I was abrupt and hence was misunderstood. My fault!. > 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) NO. I know it very much exists. It forms the foundation of LVM2, software RAIDs, dm-crypt disk encryption, and offers additional features such as file system snapshots and I do not doubt either its functionality or usage. What I am referring here is the topic . See DM operates on block device/sector, but a stackable =EF=AC=81lesystem operates on =EF=AC=81lesys= tem/=EF=AC=81le. My point is this that which is the better approach according to the kernel maintainers, so that this concept of Unioning gets universally accepted and we have a mainline kernel union filesystem. Regards, Saket Sinha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org