Date: Wed, 23 Nov 2005 03:38:25 +0100
From: Johannes Stezenbach <js@linuxtv.org>
To: Al Viro <viro@ftp.linux.org.uk>
Cc: Neil Brown <neilb@suse.de>, linux-kernel@vger.kernel.org
Message-ID: <20051123023825.GA11869@linuxtv.org>
Mail-Followup-To: Johannes Stezenbach <js@linuxtv.org>,
	Al Viro <viro@ftp.linux.org.uk>, Neil Brown <neilb@suse.de>,
	linux-kernel@vger.kernel.org
References: <17283.52960.913712.454816@cse.unsw.edu.au> <20051123021545.GP27946@ftp.linux.org.uk>
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Subject: Re: pivot_root broken in 2.6.15-rc1-mm2
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On Wed, Nov 23, 2005 at 02:15:45AM +0000, Al Viro wrote:
> On Wed, Nov 23, 2005 at 01:07:28PM +1100, Neil Brown wrote:
> > After putting in copious tracing printk, the offending test is:
> > 
> > 	if (user_nd.mnt->mnt_parent == user_nd.mnt)
> > 		goto out2; /* not attached */
> > 
> > If I remove this, it works (or seems to).
> > Presumably the initial root file system is 'not attached'.  But that
> > shouldn't be a problem, should it?
> 
> Initial root is root and will remain root, period.
> 
> > Could this be related to the new shared mounts stuff???
> 
> No.  And no, it's not going to change - any memory you win on killing
> initramfs is not going to be worth the extra code needed to special-case
> it.
> 
> pivot_root() does work in chroot jail (including the one we get after
> chrooting to "final" root), but that's all it does.

Just want to add that some nice person wrote
Documentation/filesystems/ramfs-rootfs-initramfs.txt.

http://lwn.net/Articles/156098/
http://kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;h=b3404a0325967de5fdce4a29e879258075ede500;hb=4b4a27dff4e2d4cc2eac1cde31aede834a966a48;f=Documentation/filesystems/ramfs-rootfs-initramfs.txt

HTH,
Johannes
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