From: Eric Sandeen Subject: Re: [PATCH] ext4: add support for multiple mount protection Date: Tue, 12 Apr 2011 15:39:33 -0500 Message-ID: <4DA4B885.6020004@redhat.com> References: <1302631493-9778-1-git-send-email-johann@whamcloud.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org, Andreas Dilger To: Johann Lombardi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:39724 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756813Ab1DLUje (ORCPT ); Tue, 12 Apr 2011 16:39:34 -0400 In-Reply-To: <1302631493-9778-1-git-send-email-johann@whamcloud.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 4/12/11 1:04 PM, Johann Lombardi wrote: > Prevent an ext4 filesystem from being mounted multiple times. > A sequence number is stored on disk and is periodically updated (every 5 > seconds by default) by a mounted filesystem. > At mount time, we now wait for s_mmp_update_interval seconds to make sure > that the MMP sequence does not change. > In case of failure, the nodename, bdevname and the time at which the MMP > block was last updated is displayed. > > Signed-off-by: Andreas Dilger > Signed-off-by: Johann Lombardi > --- > fs/ext4/ext4.h | 56 ++++++++- > fs/ext4/super.c | 363 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- > 2 files changed, 416 insertions(+), 3 deletions(-) > There was a lot of skepticism about this last time, and I imagine there still is... 400 new lines of kernel code for this, and if the other machine is hung up for 5 seconds and doesn't update, it can still be multiply-mounted anyway, right? BUG: soft lockup - CPU#0 stuck for 10s! anyone? :( I don't see the value in it for upstream ext4, but then hey, ext4 rarely meets a feature it doesn't like ;) -Eric