Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758188Ab1FIN6L (ORCPT ); Thu, 9 Jun 2011 09:58:11 -0400 Received: from mail-px0-f179.google.com ([209.85.212.179]:56079 "EHLO mail-px0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758164Ab1FIN6I convert rfc822-to-8bit (ORCPT ); Thu, 9 Jun 2011 09:58:08 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; b=hk8tJO4TJ0mOBv94s6UjXbm38Zokat7T3vQVe7N2OTIQEmZx65L4qm3P2XneGKwxPb 86GAsAhPwXCiUkS5Wah9D/tZ1mibLv0y6Fmq4rbPZMo83E2yE1W3IC6vEwwDPcr9Ajlx DX3jF7fooGNQz5kLTK6HmMwbaYcQ3ZugrZLjk= MIME-Version: 1.0 In-Reply-To: <20110608205233.ebfedc4d.akpm@linux-foundation.org> References: <1306932380-10280-1-git-send-email-miklos@szeredi.hu> <20110608153208.dc705cda.akpm@linux-foundation.org> <20110609115934.3c53f78f@notabene.brown> <20110608205233.ebfedc4d.akpm@linux-foundation.org> From: Michal Suchanek Date: Thu, 9 Jun 2011 15:57:48 +0200 X-Google-Sender-Auth: qda9rQuPw6B1mBu7LHzBMxherWg Message-ID: Subject: Re: [PATCH 0/7] overlay filesystem: request for inclusion To: Andrew Morton Cc: NeilBrown , Miklos Szeredi , viro@zeniv.linux.org.uk, torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, apw@canonical.com, nbd@openwrt.org, jordipujolp@gmail.com, ezk@fsl.cs.sunysb.edu, mszeredi@suse.cz Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2825 Lines: 76 On 9 June 2011 05:52, Andrew Morton wrote: > On Thu, 9 Jun 2011 11:59:34 +1000 NeilBrown wrote: > >> On Wed, 8 Jun 2011 15:32:08 -0700 Andrew Morton >> wrote: >> >> > On Wed,  1 Jun 2011 14:46:13 +0200 >> > Miklos Szeredi wrote: >> > >> > > I'd like to ask for overlayfs to be merged into 3.1. >> > >> > Dumb questions: >> > >> > I've never really understood the need for fs overlaying.  Who wants it? >> > What are the use-cases? >> >> https://lwn.net/Articles/324291/ >> >> I think the strongest use case is that LIVE-DVD's want it to have a write-able >> root filesystem which is stored on the DVD. > > Well, these things have been around for over 20 years.  What motivated > the developers of other OS's to develop these things and how are their > users using them? FWIW there is an union solution in NetBSD. I am not sure it is used in the LiveCD but you can definitely use it to build a piece of software without actually touching the source directory. > >> > >> > This sort of thing could be implemented in userspace and wired up via >> > fuse, I assume.  Has that been attempted and why is it inadequate? >> >> I think that would be a valid question if the proposal was large and >> complex.  But overlayfs is really quite small and self-contained. > > Not merging it would be even smaller and simpler.  If there is a > userspace alternative then that option should be evaluated and compared > in a rational manner. The problem with the userspace alternative is that it does not work. I tried to run my live CD on top of unionfs-fuse and the filesystem would fail intermittently leading to random errors during boot. > > > > Another issue: there have been numerous attempts at Linux overlay > filesystems from numerous parties.  Does (or will) this implementation > satisfy all their requirements? No implementation will satisfy all needs. There is always some compromise between availability (userspace/in-tree/easy to patch in) feature completeness (eg. AuFS is not so easy to forward-port to new kernels but has numerous features) performance, reliability. > > Because if not, we're in a situation where the in-kernel code is > unfixably inadequate so we end up merging another similar-looking > thing, or the presence of this driver makes it harder for them to get > other drivers merged and the other parties' requirements remain > unsatisfied. One of the major use cases is building live CDs. That and other things can be done with overlayfs. Thanks Michal -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/