From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754223AbZESMWQ (ORCPT ); Tue, 19 May 2009 08:22:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751790AbZESMWI (ORCPT ); Tue, 19 May 2009 08:22:08 -0400 Received: from moutng.kundenserver.de ([212.227.126.177]:54681 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751190AbZESMWH (ORCPT ); Tue, 19 May 2009 08:22:07 -0400 From: Arnd Bergmann To: Jan Blunck Subject: Re: [PATCH 00/32] VFS based Union Mount (V3) Date: Tue, 19 May 2009 14:21:20 +0200 User-Agent: KMail/1.9.9 Cc: Miklos Szeredi , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, bharata@in.ibm.com, dwmw2@infradead.org, mszeredi@suse.cz, vaurora@redhat.com References: <1242662968-11684-1-git-send-email-jblunck@suse.de> <200905191354.08701.arnd@arndb.de> <20090519121504.GO16526@bolzano.suse.de> In-Reply-To: <20090519121504.GO16526@bolzano.suse.de> X-Face: I@=L^?./?$U,EK.)V[4*>`zSqm0>65YtkOe>TFD'!aw?7OVv#~5xd\s,[~w]-J!)|%=]>=?utf-8?q?+=0A=09=7EohchhkRGW=3F=7C6=5FqTmkd=5Ft=3FLZC=23Q-=60=2E=60Y=2Ea=5E?= =?utf-8?q?3zb?=) =?utf-8?q?+U-JVN=5DWT=25cw=23=5BYo0=267C=26bL12wWGlZi=0A=09=7EJ=3B=5Cwg?= =?utf-8?q?=3B3zRnz?=,J"CT_)=\H'1/{?SR7GDu?WIopm.HaBG=QYj"NZD_[zrM\Gip^U MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200905191421.21026.arnd@arndb.de> X-Provags-ID: V01U2FsdGVkX19LUlAw4b3riuFD0VfTfQOjeM90AshTOe0MW0r L79F1+7IavQ4yLCcGFyNC1y6h3JALg5WItuCxyCyWxPZhM0NVt +g31V8En7cqXc1ftXcSMg== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 19 May 2009, Jan Blunck wrote: > On Tue, May 19, Arnd Bergmann wrote: > > This would work, but you'd have to do this for each file system if you want > > to be able to use it as the top of the union while backed by a read-only > > block device or when you don't want it to be written. > > I know that the requirement for the topmost filesystem to be able to create > directories and fill them with fallthrus is an unattractive one. On the other > hand this is the cost that you have to pay at the moment to get this kind of > functionality. This implementation will not help with all use-cases. Its focus > is to get certain use-cases right. So what would go wrong if you only made them persistent for writable file systems, but allowed fallthrough dentries to be discarded for read-only file systems? As long as the lower layers don't change, you should still be able to reconstruct the same dentries every time you do a readdir, right? Arnd <><