From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Subject: Re: [PATCHSET 3/4] sysfs: divorce sysfs from kobject and driver model Date: Tue, 9 Oct 2007 15:51:39 -0700 Message-ID: <20071009225139.GF21228@kroah.com> References: <11902755392688-git-send-email-htejun@gmail.com> <20070925221736.GA3566@kroah.com> <46FB956B.8000205@gmail.com> <20071005062302.GB16914@kroah.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org 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 List-Id: containers.vger.kernel.org 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. > 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? And that is not valid as sda for that namespace must always map to the device with a 8:0 major:minor as per the LSB spec. So, no, that's not going to be allowed, sorry. thanks, greg k-h