Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756763AbXJJVDc (ORCPT ); Wed, 10 Oct 2007 17:03:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756252AbXJJVDX (ORCPT ); Wed, 10 Oct 2007 17:03:23 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:43054 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756034AbXJJVDW (ORCPT ); Wed, 10 Oct 2007 17:03:22 -0400 Date: Wed, 10 Oct 2007 13:44:49 -0700 From: Greg KH To: "Eric W. Biederman" 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 Message-ID: <20071010204449.GA23680@kroah.com> References: <11902755392688-git-send-email-htejun@gmail.com> <20070925221736.GA3566@kroah.com> <46FB956B.8000205@gmail.com> <20071005062302.GB16914@kroah.com> <20071009225139.GF21228@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3612 Lines: 95 On Wed, Oct 10, 2007 at 07:16:48AM -0600, Eric W. Biederman wrote: > 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. Ah, ok, that makes more sense. And seems quite difficult to do, good luck with that :) greg k-h - 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/