Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935657AbXJPXzz (ORCPT ); Tue, 16 Oct 2007 19:55:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S934029AbXJPXzp (ORCPT ); Tue, 16 Oct 2007 19:55:45 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:53509 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933779AbXJPXzn (ORCPT ); Tue, 16 Oct 2007 19:55:43 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: sukadev@us.ibm.com Cc: Greg KH , Tejun Heo , kay.sievers@vrfy.org, linux-kernel@vger.kernel.org, Linux Containers , stern@rowland.harvard.edu, cornelia.huck@de.ibm.com Subject: Re: [PATCHSET 3/4] sysfs: divorce sysfs from kobject and driver model References: <11902755392688-git-send-email-htejun@gmail.com> <20070925221736.GA3566@kroah.com> <46FB956B.8000205@gmail.com> <20071005062302.GB16914@kroah.com> <20071009225139.GF21228@kroah.com> <20071016221816.GA14787@us.ibm.com> Date: Tue, 16 Oct 2007 17:54:06 -0600 In-Reply-To: <20071016221816.GA14787@us.ibm.com> (sukadev@us.ibm.com's message of "Tue, 16 Oct 2007 15:18:16 -0700") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1914 Lines: 50 sukadev@us.ibm.com writes: > | No. The "other" device namespace I would construct on machine B to > | look just like the device namespace that existed on machine A. > | Making /sys/devices/block/sda would still be 8:0. > | > | So to be very clear on machine B when talking about disk-1 I would have. > | initial device namespace: > | /sys/devices/block/sdb > | /sys/devices/block/sdb/dev 8:16 > | > | "other" device namespace: > | /sys/devices/block/sda > | /sys/devices/block/sda/dev 8:0 > | > | Similarly on machine B when talking about disk-2 I would have. > | initial device namespace: > | /sys/devices/block/sda > | /sys/devices/block/sda/dev 8:0 > | > | "other" device namespace: > | /sys/devices/block/sdb > | /sys/devices/block/sdb/dev 8:16 > | > | So between the two devices namespaces on machine B the two disks > | would exchange their user visible identities. > > So an application that would migrate from machine A to B has to > use virtual names (like "disk-1" and "disk-2") to access the disk > right ? No. It is worse you need to access a filesystem and probably a block device that is available on both machine A and machine B. With care we can introduce appropriate namespaces and namespace semantics so we can make the names be what we need. For a classic tricky case think what it would require to migrate a git archive with checked out files and not need to say "git-update-index --refresh" before you work with the files. I used names like disk-1 and disk-2 instead of UUIDs because it was easier for me to type and think about. You do need some kind of absolute disk or filesystem identity you can refer back to. Eric - 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/