linux-kernel - Re: [PATCH] init: fix name of root device in /proc/mounts

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Message-Id: <1363763000.15703.47@driftwood>
Date:	Wed, 20 Mar 2013 02:03:20 -0500
From:	Rob Landley <rob@...dley.net>
To:	William Hubbs <w.d.hubbs@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	mpagano@...too.org, ryao@...too.org, gregkh@...too.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] init: fix name of root device in /proc/mounts

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.

Heck, the userspace "stat /" command says "Device: 801h" and /dev/sda1  
is 08:01 on my netbook.

Rob--
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