From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757903Ab0FUNOu (ORCPT ); Mon, 21 Jun 2010 09:14:50 -0400 Received: from fxip-0047f.externet.hu ([88.209.222.127]:53197 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751059Ab0FUNOt (ORCPT ); Mon, 21 Jun 2010 09:14:49 -0400 To: Valerie Aurora CC: raa.lkml@gmail.com, viro@zeniv.linux.org.uk, miklos@szeredi.hu, jblunck@suse.de, hch@infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org In-reply-to: <20100617183912.GA14389@shell> (message from Valerie Aurora on Thu, 17 Jun 2010 14:39:13 -0400) Subject: Re: [PATCH 17/38] union-mount: Union mounts documentation References: <1276627208-17242-1-git-send-email-vaurora@redhat.com> <1276627208-17242-18-git-send-email-vaurora@redhat.com> <20100617183912.GA14389@shell> Message-Id: From: Miklos Szeredi Date: Mon, 21 Jun 2010 15:14:35 +0200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Miklos