Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753161AbYLZDiT (ORCPT ); Thu, 25 Dec 2008 22:38:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752682AbYLZDiJ (ORCPT ); Thu, 25 Dec 2008 22:38:09 -0500 Received: from BISCAYNE-ONE-STATION.MIT.EDU ([18.7.7.80]:51871 "EHLO biscayne-one-station.mit.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752225AbYLZDiI (ORCPT ); Thu, 25 Dec 2008 22:38:08 -0500 Date: Thu, 25 Dec 2008 22:37:36 -0500 From: Theodore Tso To: Alberto Bertogli Cc: linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com Subject: Re: jbd2 inside a device mapper module Message-ID: <20081226033736.GK9871@mit.edu> Mail-Followup-To: Theodore Tso , Alberto Bertogli , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com References: <20081224211038.GT4127@blitiri.com.ar> <20081224234915.GA23723@mit.edu> <20081225143535.GA4127@blitiri.com.ar> <20081225155248.GJ9871@mit.edu> <20081226000005.GB4127@blitiri.com.ar> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081226000005.GB4127@blitiri.com.ar> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) X-Spam-Flag: NO X-Spam-Score: 0.00 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1451 Lines: 32 On Thu, Dec 25, 2008 at 10:00:05PM -0200, Alberto Bertogli wrote: > > I think I'm not explaining myself correctly. My code has _nothing_ to do > with ext2/3/4 (or any other filesystem) whatsoever. I'm not using the > journal as an external one for a filesystem. I want to use it to be able > to do atomic writes in my own, filesystem independant, device-mapper > code. How many block writes are you batching into a single transaction? If you're not careful you may find that performance overhead will be quite expensive. > After what you told me (both this and the deprecation of > jbd2_journal_create()), I took a look at e2fsprogs' source. From what I > could see, "mke2fs -O journal_dev" creates the external journal inside > some ext2/3/4 structures, which caused my journal-loading code to fail > (because it doesn't know about ext stuff). Yes, this is necessary because in a production system you need to be able to identify the external journal by UUID, and the ext2/3/4 superblock makes it easy to add a label, UUID, et. al. It also significantly lowers the chance that an external journal will get misidentified as some other filesystem based on the data stored in the journal. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/