Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753940Ab3COIPc (ORCPT ); Fri, 15 Mar 2013 04:15:32 -0400 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:48525 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753846Ab3COIP0 (ORCPT ); Fri, 15 Mar 2013 04:15:26 -0400 Message-ID: <1363335318.2459.4.camel@dabdike> Subject: Re: [PATCH 0/9] overlay filesystem: request for inclusion (v17) From: James Bottomley To: Al Viro Cc: "J. R. Okajima" , Miklos Szeredi , Andrew Morton , torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, hch@infradead.org, apw@canonical.com, nbd@openwrt.org, neilb@suse.de, jordipujolp@gmail.com, ezk@fsl.cs.sunysb.edu, dhowells@redhat.com, sedat.dilek@googlemail.com, mszeredi@suse.cz Date: Fri, 15 Mar 2013 08:15:18 +0000 In-Reply-To: <20130315051322.GX21522@ZenIV.linux.org.uk> References: <1363184193-1796-1-git-send-email-miklos@szeredi.hu> <20130313160854.54ac0491044371b4db214698@linux-foundation.org> <20130315012541.GU21522@ZenIV.linux.org.uk> <19058.1363320936@jrobl> <20130315044411.GW21522@ZenIV.linux.org.uk> <20079.1363324154@jrobl> <20130315051322.GX21522@ZenIV.linux.org.uk> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.6.3 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1517 Lines: 34 On Fri, 2013-03-15 at 05:13 +0000, Al Viro wrote: > On Fri, Mar 15, 2013 at 02:09:14PM +0900, J. R. Okajima wrote: > > > If so, it has a big disadvantage for the layer-fs (or branch-fs) to have > > to implement a new method for whiteout. > > > > Overlayfs implements whiteout as symlink+xattr which consumes an > > inode. And you don't like it, right? > > What I showed is another generic approach without xattr where the new > > method to whiteout is unnecessary. > > I'm yet to see the reason that would make implementing that method a big > disadvantage, TBH... It's the fact that a directory entry based whiteout limits the amount of change to the VFS, but has to be supported by underlying filesystems. The generic_dirent_fallthrough() mechanism is a nice way of hiding it, but there are still quite a few fs specific mods in the union mount tree because of this. Having to modify filesystems to me indicates the mechanism is a bit fragile. If we could do whiteouts purely in the VFS, so it would work for any filesystem (without needing filesystem modifications) that would seem to be a more robust approach. I'm not saying we can definitely do this in an elegant way ... I'm just saying that if someone comes up with it, it's obviously preferable. James -- 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/