From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755466AbZHJPpQ (ORCPT ); Mon, 10 Aug 2009 11:45:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755428AbZHJPpO (ORCPT ); Mon, 10 Aug 2009 11:45:14 -0400 Received: from kroah.org ([198.145.64.141]:55437 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752327AbZHJPpN (ORCPT ); Mon, 10 Aug 2009 11:45:13 -0400 Date: Mon, 10 Aug 2009 08:39:43 -0700 From: Greg KH To: David Dillow Cc: Greg KH , Andi Kleen , Alan Cox , linux-kernel@vger.kernel.org, Kay Sievers , Jan Blunck , Harald Hoyer , Scott James Remnant Subject: Re: [PATCH] Driver Core: devtmpfs - kernel-maintained tmpfs-based /dev Message-ID: <20090810153943.GB7652@kroah.com> References: <20090805171513.GA10443@kroah.com> <20090805192037.19c54c4d@lxorguk.ukuu.org.uk> <20090805182805.GA7534@kroah.com> <20090805185136.GA21442@kroah.com> <87ljlxhrnr.fsf@basil.nowhere.org> <1249575658.19886.8.camel@lap75545.ornl.gov> <20090806183147.GA28409@suse.de> <1249772876.22248.34.camel@obelisk.thedillows.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1249772876.22248.34.camel@obelisk.thedillows.org> 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 On Sat, Aug 08, 2009 at 07:07:56PM -0400, David Dillow wrote: > On Thu, 2009-08-06 at 11:31 -0700, Greg KH wrote: > > On Thu, Aug 06, 2009 at 12:20:58PM -0400, David Dillow wrote: > > > If you use mount by label or UUID, you still need udev (or other tools) > > > in the initrd to find the right disk, correct? > > > > Yes, you would. > > > > > And for distros that want to support that, does this really reduce the > > > amount of code in the initrd? > > > > Yes it does, see the code in the Novell Moblin images for an example of > > how to use devtmpfs with udev for how to do this. > > I followed up with Greg offline to make sure I was looking at the right > thing, but the upshot is that Moblin does not use an initrd and devtmpfs > does not in any way reduce the amount of code for those distros that > want to support more than the root=/dev/blah syntax. Like Scott points out, this option now allows distros to use blkid directly instead of udev if they want to implement things like this without udev. > Given Eric and Arjan's numbers about the time it takes to populate /dev > from /sys -- pointing the speed problem squarely at udev or the ruleset > -- I don't see much of a win for devtmpfs other than avoiding a > static /dev to make init=/bin/sh work. That's a very big win right there, don't you think? Also, embedded and rescue disks also would like it for this very reason. > You cannot rely on it for a hotplug disk such as USB, as it doesn't do > the root=LABEL=usbroot that you'd want to do since the location is not > stable. Again, not all the world requires such labels. thanks, greg k-h