Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932291Ab3CVDA7 (ORCPT ); Thu, 21 Mar 2013 23:00:59 -0400 Received: from mail-ie0-f171.google.com ([209.85.223.171]:59144 "EHLO mail-ie0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754471Ab3CVDAv convert rfc822-to-8bit (ORCPT ); Thu, 21 Mar 2013 23:00:51 -0400 Date: Thu, 21 Mar 2013 22:00:46 -0500 From: Rob Landley Subject: Re: [PATCH] init: fix name of root device in /proc/mounts To: William Hubbs Cc: "H. Peter Anvin" , linux-kernel@vger.kernel.org, mpagano@gentoo.org, ryao@gentoo.org, gregkh@gentoo.org, torvalds@linux-foundation.org, w.d.hubbs@gmail.com In-Reply-To: <20130320211125.GA26595@linux1> (from williamh@gentoo.org on Wed Mar 20 16:11:25 2013) X-Mailer: Balsa 2.4.11 Message-Id: <1363921246.15703.54@driftwood> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; DelSp=Yes; Format=Flowed Content-Disposition: inline Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3478 Lines: 94 On 03/20/2013 04:11:25 PM, William Hubbs wrote: > On Wed, Mar 20, 2013 at 02:03:20AM -0500, Rob Landley wrote: > > On 03/19/2013 07:20:17 PM, William Hubbs wrote: > > > On Tue, Mar 19, 2013 at 04:17:11PM -0700, H. Peter Anvin wrote: > > > > On 03/19/2013 03:28 PM, William Hubbs wrote: > > > > > The issue is that /dev/root appears in /proc/mounts if you do > not > > > > > boot with an initramfs, but /dev/root is not a device node. > In the > > > > > past, udev created a symbolic link from /dev/root to the > > > > > appropriate block device, but it does not do this any longer. > > > Also, > > > > > devtmpfs does not create this symbolic link. > > > > > > > > > > This is causing bugs with software that depends on the > existence > > > > > of /dev/root [2] for example. > > > > > > > > Seems okay to me, although even better would be to use the udev > name > > > > of the device in question. > > > > > > I'm not following what you mean. > > > > > > The problem is that "/dev/root" should not be in /proc/mounts, > > > since there is always another entry that points to the root > > > file system. > > > > What gave you that idea? > > > > wget http://landley.net/aboriginal/bin/system-image-i686.tar.bz2 > > extract it and ./run-emulator.sh and in there: > > > > (i686:1) /home # cat /proc/mounts > > rootfs / rootfs rw 0 0 > > /dev/root / squashfs ro,relatime 0 0 > > proc /proc proc rw,relatime 0 0 > > sys /sys sysfs rw,relatime 0 0 > > dev /dev devtmpfs rw,relatime,size=63072k,nr_inodes=15768,mode=755 > 0 0 > > dev/pts /dev/pts devpts rw,relatime,mode=600 0 0 > > /tmp /tmp tmpfs rw,relatime 0 0 > > /home /home tmpfs rw,relatime 0 0 > > > > Userspace can totally determine what /dev/root points to, I made > mdev > > do it in 2006 (udev started doing so shortly thereafter). Busybox > git > > commit a7e3d052.:4 > > There are situations where it doesn't work though -- suppose that root > is btrfs for example. So you're saying there's a bug in btrfs? > Also, the other message that answered you is correct, the udev > maintainers say we should not be relying on /dev/root at all so to > make > it work distro packagers have to add a rule themselves. These udev maintainers? http://lkml.indiana.edu/hypermail/linux/kernel/1210.0/01889.html This is the udev that got Katamari'd into systemd, not one of the forks that ran screaming trying not to get sucked into the latest escapade of King of All Cosmos? Look, if you want to add /dev/root to devtmpfs, that makes a certain amount of sense. But your patch seems to have missed do_mounts.c doing: if (strncmp(root_device_name, "/dev/", 5) == 0) root_device_name += 5; Which means that if the user does "root=sda1" on the kernel command line you're not passing an absolute path to create_dev(): - create_dev("/dev/root", ROOT_DEV); - mount_block_root("/dev/root", root_mountflags); + if (saved_root_name[0]) { + create_dev(saved_root_name, ROOT_DEV); And last I checked that means /proc/mounts will have a relative path in it... I.E. you're modifying kernel code you're not familiar with to fix a non-problem caused by your unfamiliarity with the corresponding userspace code. I'm really not seeing the upside here. Rob-- 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/