Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758122AbZATEOV (ORCPT ); Mon, 19 Jan 2009 23:14:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754064AbZATEOB (ORCPT ); Mon, 19 Jan 2009 23:14:01 -0500 Received: from sca-es-mail-2.Sun.COM ([192.18.43.133]:65313 "EHLO sca-es-mail-2.sun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752950AbZATEN7 (ORCPT ); Mon, 19 Jan 2009 23:13:59 -0500 Date: Mon, 19 Jan 2009 21:13:49 -0700 From: Andreas Dilger Subject: Re: [PATCH 0/20] return f_fsid for statfs(2) In-reply-to: <1232419149.19468.3.camel@norville.austin.ibm.com> To: Dave Kleikamp Cc: coly.li@suse.de, linux-kernel@vger.kernel.org, Andrew Morton , Roman Zippel , "Sergey S. Kostyliov" , OGAWA Hirofumi , Mikulas Patocka , Bob Copeland , Anders Larsen , reiserfs-devel@vger.kernel.org, Phillip Lougher , Christoph Hellwig , Evgeniy Dushistov , Jan Kara , linux-fsdevel Message-id: <20090120041349.GL3286@webber.adilger.int> MIME-version: 1.0 Content-type: text/plain; charset=us-ascii Content-transfer-encoding: 7BIT Content-disposition: inline X-GPG-Key: 1024D/0D35BED6 X-GPG-Fingerprint: 7A37 5D79 BF1B CECA D44F 8A29 A488 39F5 0D35 BED6 References: <4974B8C4.3070703@suse.de> <1232393334.5893.42.camel@norville.austin.ibm.com> <20090119233651.GK3286@webber.adilger.int> <1232419149.19468.3.camel@norville.austin.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1179 Lines: 26 On Jan 19, 2009 20:39 -0600, Dave Kleikamp wrote: > On Tue, 2009-01-20 at 07:36 +0800, Andreas Dilger wrote: > > The whole point of fsid (for NFS) is that this identifies the filesystem > > over reboot, even if the block device ID changes, or if the filesystem > > doesn't have a block device at all (e.g. cluster filesystem). > > I guess that just demonstrates how little I know about what the fsid is > about. Would it be preferable for file systems that have a uuid to use > that instead? Of course anything is an improvement over zeroes. Yes, that is what the ext* patches do - fold the 128-bit UUID into a 64-bit fsid so that it is constant across reboots. The chance of UUID collision is about 1/2^32 due to birthday paradox, which is fairly low, and in case this happens one of the filesystem UUIDs can be regenerated. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. -- 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/