From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933479Ab1JYNfQ (ORCPT ); Tue, 25 Oct 2011 09:35:16 -0400 Received: from li9-11.members.linode.com ([67.18.176.11]:37084 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933399Ab1JYNfO (ORCPT ); Tue, 25 Oct 2011 09:35:14 -0400 Date: Tue, 25 Oct 2011 09:35:05 -0400 From: "Ted Ts'o" To: "Darrick J. Wong" Cc: Tao Ma , linux-ext4@vger.kernel.org, linux-kernel Subject: Re: [PATCH 5/5] ext4: Fix endian problem in MMP initialization Message-ID: <20111025133505.GL31921@thunk.org> Mail-Followup-To: Ted Ts'o , "Darrick J. Wong" , Tao Ma , linux-ext4@vger.kernel.org, linux-kernel References: <20111021211759.10784.17257.stgit@elm3c44.beaverton.ibm.com> <20111021211825.10784.97113.stgit@elm3c44.beaverton.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111021211825.10784.97113.stgit@elm3c44.beaverton.ibm.com> User-Agent: Mutt/1.5.20 (2009-06-14) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on test.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 21, 2011 at 02:18:25PM -0700, Darrick J. Wong wrote: > As part of startup, the MMP initialization code does this: > > mmp->mmp_seq = seq = cpu_to_le32(mmp_new_seq()); > > Next, mmp->mmp_seq is written out to disk, a delay happens, and then the MMP > block is read back in and the sequence value is tested: > > if (seq != le32_to_cpu(mmp->mmp_seq)) { > /* fail the mount */ > > On a LE system such as x86, the *le32* functions do nothing and this works. > Unfortunately, on a BE system such as ppc64, this comparison becomes: > > if (cpu_to_le32(new_seq) != le32_to_cpu(cpu_to_le32(new_seq)) { > /* fail the mount */ > > Except for a few palindromic sequence numbers, this test always > causes the mount to fail, which makes MMP filesystems generally > unmountable on ppc64. The attached patch fixes this situation. > > Signed-off-by: Darrick J. Wong Thanks, this is already in the ext4 tree, although not yet in the master branch (just the dev branch). - Ted