Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755304AbXJJNp5 (ORCPT ); Wed, 10 Oct 2007 09:45:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753463AbXJJNpu (ORCPT ); Wed, 10 Oct 2007 09:45:50 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:44351 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753445AbXJJNpt (ORCPT ); Wed, 10 Oct 2007 09:45:49 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Greg KH Cc: Tejun Heo , cornelia.huck@de.ibm.com, stern@rowland.harvard.edu, kay.sievers@vrfy.org, linux-kernel@vger.kernel.org, Linux Containers 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> Date: Wed, 10 Oct 2007 07:16:48 -0600 In-Reply-To: <20071009225139.GF21228@kroah.com> (Greg KH's message of "Tue, 9 Oct 2007 15:51:39 -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: 3286 Lines: 90 Greg KH writes: > On Fri, Oct 05, 2007 at 06:12:41AM -0600, Eric W. Biederman wrote: >> Greg KH writes: >> > >> >> Also fun is that the dev file implementation needs to be able to >> >> report different major:minor numbers based on which mount of >> >> sysfs we are dealing with. >> > >> > Um, no, that's not going to happen. /dev/sda will _always_ have the >> > same major:minor number, as defined by the LSB spec. You can not break >> > that at all. So while you might not want to show all mounts >> > /sys/devices/block/sda/ the ones that you do, will all have the LSB >> > defined major:minor number assigned to it. >> >> Hmm. If that is in the LSB it must come from >> Documentation/devices.txt > > Yes, that is the requirement. > >> I'm not after changing the user visible major/minor assignments. > > Oh, I misunderstood what you wrote above then. My above sentence is slightly misleading. That should have been. I am not after changing the device name to major:minor assignments as specified in Documentation/devices.txt. So within a single device namespace everything is normal and as it always has been. Weirdness only ensues when you look across device namespaces. >> Let me see if a concrete example will help. Suppose I have >> have a SAN with two disks: disk-1 and disk-2. I have >> two machines A and B. On machine A I get the mapping: >> sda -> disk-1, sdb ->disk-2. On machine B I wind up with >> a different probe order so I get the mapping: sda -> disk-2 >> sdb ->disk-1. > > Ok. > >> To be very clear by sda I mean the block device with major 8 and >> minor 0, and by sdb I mean the block device with major 8 and minor >> 16. > > Ok. > >> So I decide I want an environment on machine B that looks just >> like the environment on machine A, so I can bring transfer over >> a running program or whatever. So I run around looking at UUID >> labels and what not and I discover that the machine B knows disk-1 as >> sdb and that machine A knows disk-1 as sda. So I want to say: >> /sys/devices/block/sdb show up in this other device namespace as >> /sys/devices/block/sda. > > Ah, but if you do that then the "other" device namespace would have > /sys/devices/block/sda/dev be 8:16, right? 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. 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/