Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757407Ab0GGQjh (ORCPT ); Wed, 7 Jul 2010 12:39:37 -0400 Received: from fieldses.org ([174.143.236.118]:46208 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756661Ab0GGQjg (ORCPT ); Wed, 7 Jul 2010 12:39:36 -0400 Date: Wed, 7 Jul 2010 12:39:19 -0400 From: "J. Bruce Fields" To: "Aneesh Kumar K. V" Cc: Miklos Szeredi , neilb@suse.de, david@fromorbit.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: <20100707163919.GA28815@fieldses.org> References: <20100706232351.GD25018@dastard> <20100707093629.10c2feab@notabene.brown> <20100707021150.GF25018@dastard> <20100707125726.3695587a@notabene.brown> <20100707125701.GA19872@fieldses.org> <20100707131721.GB19872@fieldses.org> <20100707144511.GA24360@fieldses.org> <877hl7fdzw.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <877hl7fdzw.fsf@linux.vnet.ibm.com> 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: 1714 Lines: 42 On Wed, Jul 07, 2010 at 10:03:39PM +0530, Aneesh Kumar K. V wrote: > On Wed, 7 Jul 2010 10:45:11 -0400, "J. Bruce Fields" wrote: > > 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. > > > > And for this reason we would need this as a syscall right ? That's the only solution I see. (Or use an xattr?) --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/