From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757815Ab0FUXRm (ORCPT ); Mon, 21 Jun 2010 19:17:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26983 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751121Ab0FUXRj (ORCPT ); Mon, 21 Jun 2010 19:17:39 -0400 Date: Mon, 21 Jun 2010 19:17:20 -0400 From: Valerie Aurora To: Miklos Szeredi Cc: raa.lkml@gmail.com, viro@zeniv.linux.org.uk, jblunck@suse.de, hch@infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 17/38] union-mount: Union mounts documentation Message-ID: <20100621231720.GC28850@shell> References: <1276627208-17242-1-git-send-email-vaurora@redhat.com> <1276627208-17242-18-git-send-email-vaurora@redhat.com> <20100617183912.GA14389@shell> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 21, 2010 at 03:14:35PM +0200, Miklos Szeredi wrote: > On Thu, 17 Jun 2010, Valerie Aurora wrote: > > On Thu, Jun 17, 2010 at 10:01:30AM +0200, Alex Riesen wrote: > > > On Tue, Jun 15, 2010 at 20:39, Valerie Aurora wrote: > > > > +git://git.kernel.org/pub/scm/fs/ext2/val/e2fsprogs.git > > > > + > > > > +Currently, whiteout directory entries are not returned to userland. > > > > +While the directory type for whiteouts, DT_WHT, has been defined for > > > > +many years, very little userland code handles them. ??Userland will > > > > +never see fallthru directory entries. > > > > > > This may be a dumb question (I must admit I did only very little research), > > > but how does one cleanup the topmost layer of whiteouts and fallthroughs, > > > so that the entries of lower layer(s) can be made visible again? > > > > I'm not sure how best to do this. We don't want to add more system > > calls. One thought of mine has been to do this offline, when the file > > system is unmounted. For example, e2fsck could add a feature to > > delete whiteouts and fallthrus. Another option is to add a flag to an > > existing system call. > > One more advantage of doing whiteouts, etc. with hard links and > extended attributes instead of as special filesystem objects. That > way they are visible (unless part of a union) and can be treated as > normal filesystem objects. This should be reasonably easy to prototype - the whiteout and fallthru patches are pretty well separated from the rest of union mounts. -VAL