Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756165Ab0GGOpg (ORCPT ); Wed, 7 Jul 2010 10:45:36 -0400 Received: from fieldses.org ([174.143.236.118]:40025 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755169Ab0GGOpf (ORCPT ); Wed, 7 Jul 2010 10:45:35 -0400 Date: Wed, 7 Jul 2010 10:45:11 -0400 From: "J. Bruce Fields" To: Miklos Szeredi Cc: neilb@suse.de, david@fromorbit.com, aneesh.kumar@linux.vnet.ibm.com, 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: <20100707144511.GA24360@fieldses.org> References: <20100706161002.GD7387@fieldses.org> <87eifgfsez.fsf@linux.vnet.ibm.com> <20100706232351.GD25018@dastard> <20100707093629.10c2feab@notabene.brown> <20100707021150.GF25018@dastard> <20100707125726.3695587a@notabene.brown> <20100707125701.GA19872@fieldses.org> <20100707131721.GB19872@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: 1327 Lines: 35 On Wed, Jul 07, 2010 at 03:35:50PM +0200, Miklos Szeredi wrote: > On Wed, 7 Jul 2010, J. Bruce Fields wrote: > > > > If you use sys or proc, is it possible to get the uuid from a file > > > > descriptor or pathname without races? > > > > > > You can do stat/fstat to find out the device number (which is unique, > > > but not persistent) > > > > Is it really unique over time? (Can't a given st_dev value map to one > > filesystem now, and another later?) > > It's unique at a single point in time. But if you have a reference > (e.g. open file descriptor) on the mount then that's not a problem. > > fd = open(path, ...); > fstat(fd, &st); > search st.st_dev in mountinfo > close(fd) > > is effectively the same as an getuuid(path) syscall (lazy unmounted > filesystems will not be found in mountinfo, but the reference is still > there so st_dev will not be reused for other filesystems). OK, cool. That still leaves the problem that there isn't always an underlying block device, and/or when there is it doesn't always uniquely specify the filesystem. --b. -- 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/