From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Engelhardt Subject: Re: [RFC][PATCH 00/20] Mount writer count and read-only bind mounts (v2) Date: Sat, 17 Jun 2006 11:36:35 +0200 (MEST) Message-ID: References: <20060616231213.D4C5D6AF@localhost.localdomain> <1150501318.7926.22.camel@localhost.localdomain> <20060617033531.GA25823@MAIL.13thfloor.at> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: Grzegorz Kulewski , Dave Hansen , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@ftp.linux.org.uk Return-path: Received: from linux01.gwdg.de ([134.76.13.21]:9391 "EHLO linux01.gwdg.de") by vger.kernel.org with ESMTP id S1751205AbWFQJgv (ORCPT ); Sat, 17 Jun 2006 05:36:51 -0400 To: Herbert Poetzl In-Reply-To: <20060617033531.GA25823@MAIL.13thfloor.at> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org >> >I assume you're talking about this kind of situation: >> > >> >mount --bind /local/writable/dir /chroot/untrusted/area/ >> >mount --o remount,ro /chroot/untrusted/area/ >> >> Well, actually about some kind of VPS: openvz or something like that. >> But yes, this is the same kind of scenario. > >yes, Linux-VServer provides this kind of ro --bind mounts >without the race, as the the flags are passed on the actual >mount > >> >This has no r/w window in the chroot area: >> > >> >mount --bind /local/writable/dir /tmp/area/ >> >mount --o remount,ro /tmp/area/ >> >mount --bind /tmp/area/ /chroot/untrusted/area/ >> >umount /tmp/area/ >> >> Well, it looks a little scarry and complicated at first. And probably >> requires you to know that semantic of --bind lets you do the last >> unmount. But if you are saying that this makes kernel smaller, faster >> and less buggy then you are probably very right. > >well, it makes the kernel more consistant in it's behaviour, >because especially for --rbind mounts, the logic what is >changed where and when is not as well defined as one would >wish ... > >btw, you could get the same result by simply doing: > >mount --bind /local/writable/dir /tmp/area/ >mount --o remount,ro /tmp/area/ >mount --move /tmp/area/ /chroot/untrusted/area/ > Just a nitpick, you all use "--o" ... :) mount: option `--o' is ambiguous Jan Engelhardt --