From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932676AbWF1Bii (ORCPT ); Tue, 27 Jun 2006 21:38:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932685AbWF1Bii (ORCPT ); Tue, 27 Jun 2006 21:38:38 -0400 Received: from smtp.osdl.org ([65.172.181.4]:46232 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S932676AbWF1Bih (ORCPT ); Tue, 27 Jun 2006 21:38:37 -0400 Date: Tue, 27 Jun 2006 18:38:22 -0700 From: Andrew Morton To: Dave Hansen Cc: linux-kernel@vger.kernel.org, herbert@13thfloor.at, viro@ftp.linux.org.uk, serue@us.ibm.com, haveblue@us.ibm.com Subject: Re: [PATCH 00/20] Mount writer count and read-only bind mounts (v3) Message-Id: <20060627183822.667d9d49.akpm@osdl.org> In-Reply-To: <20060627221436.77CCB048@localhost.localdomain> References: <20060627221436.77CCB048@localhost.localdomain> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.17; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 27 Jun 2006 15:14:36 -0700 Dave Hansen wrote: > I think these are ready for -mm. They've gone through a few revisions > and a week or two of normal burn-in testing. > > --- > > The following series implements read-only bind mounts. This feature > allows a read-only view into a read-write filesystem. In the process > of doing that, it also provides infrastructure for keeping track of > the number of writers to any given mount. New in this version is that > if that number is non-zero, remounts from r/w to r/o are not allowed. > > This set does not take the previously tried approach of pushing down > the vfsmount structure deeply into call paths, such that it might be > checked in functions like permission(), may_create() and may_open(). > Instead, it does checks near the entry points in the kernel, bumping > a reference count in the vfsmount structure. I've also eliminated > the use of the MNT_RDONLY flag. It was redundant since we have the > reference count. > > This set also makes no attempt to keep the return codes for these > r/o bind mounts the same as for a real r/o filesystem or device. > It would require significantly more code and be quite a bit more > invasive. Unless there is a very strong reason to do so, I believe > it isn't worth the trouble. > > One note: the previous patches all worked this way: > > mount --bind -o ro /source /dest > > These patches have changed that behavior. It now requires two steps: > > mount --bind /source /dest > mount -o remount,ro /dest That seems a step backwards. > Since the last revision, the locking in faccessat() and > mnt_is_readonly() has been changed to fix a race which might have > caused a false-negative mount-is-readonly return when faccessat() > is called while another two processes are racing to make a mount > readonly. > > Signed-off-by: Dave Hansen umm, what's it all for?