From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Dilger Subject: Re: [PATCH 0/20] return f_fsid for statfs(2) Date: Mon, 19 Jan 2009 21:13:49 -0700 Message-ID: <20090120041349.GL3286@webber.adilger.int> 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> Mime-Version: 1.0 Content-Transfer-Encoding: 7BIT Return-path: In-reply-to: <1232419149.19468.3.camel@norville.austin.ibm.com> Content-disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" 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 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.