Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754182Ab0GGCL5 (ORCPT ); Tue, 6 Jul 2010 22:11:57 -0400 Received: from bld-mail17.adl2.internode.on.net ([150.101.137.102]:42112 "EHLO mail.internode.on.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751814Ab0GGCL4 (ORCPT ); Tue, 6 Jul 2010 22:11:56 -0400 Date: Wed, 7 Jul 2010 12:11:50 +1000 From: Dave Chinner To: Neil Brown Cc: "Aneesh Kumar K. V" , "J. Bruce Fields" , hch@infradead.org, viro@zeniv.linux.org.uk, adilger@sun.com, corbet@lwn.net, serue@us.ibm.com, hooanon05@yahoo.co.jp, linux-fsdevel@vger.kernel.org, sfrench@us.ibm.com, philippe.deniel@CEA.FR, linux-kernel@vger.kernel.org Subject: Re: [PATCH -V14 0/11] Generic name to handle and open by handle syscalls Message-ID: <20100707021150.GF25018@dastard> References: <1276621981-2774-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <871vbn2mk9.fsf@linux.vnet.ibm.com> <20100702064108.64034561@notabene.brown> <87iq4y29a6.fsf@linux.vnet.ibm.com> <20100706161002.GD7387@fieldses.org> <87eifgfsez.fsf@linux.vnet.ibm.com> <20100706232351.GD25018@dastard> <20100707093629.10c2feab@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100707093629.10c2feab@notabene.brown> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1620 Lines: 50 On Wed, Jul 07, 2010 at 09:36:29AM +1000, Neil Brown wrote: > On Wed, 7 Jul 2010 09:23:51 +1000 > Dave Chinner wrote: > > > > I can add a new syscall that returns > > > > > > struct fs_uuid { > > > u8 fs_uuid[16]; > > > }; > > > > > > long sys_get_fs_uuid(int dfd, char *name, struct fs_uuid *fsid, int flag); > > > > libblkid already provides the UUID to userspace applications, doesn't it? > > Yes and no. > > libblkid provides the uuid of the thing that uses a block device. That > doesn't directly map to "UUID of a filesystem". True. > There are two types of filesystem that I can think of for which libblkid > cannot give a uuid. > - network filesystems (or virtual filesystems, or fuse ) How would you guarantee persistent uniqueness for such filesystems? > - filesystems which share a block device, such as btrfs. > btrfs can have 'subvols' - multiple "filesystems" within > the one (set of) block device(s). libblkid cannot be asked about these > different subvols. > > libblkid is useful, but not a real solution. So libblkid doesn't cover everything, but I think my question is still valid - if we want per-filesystem UUIDs, why a syscall and not just publishing it somewhere where we already publish per-mount information? e.g. in /proc/mounts? Cheers, Dave. -- Dave Chinner david@fromorbit.com -- 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/