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Message-ID: <bda6d13a0606091613h3334facbrcb86dbb2de01b412@mail.gmail.com>
Date: Fri, 9 Jun 2006 16:13:13 -0700
From: "Joshua Hudson" <joshudson@gmail.com>
To: linux-kernel@vger.kernel.org
Subject: Re: klibc
In-Reply-To: <e6ctsb$hij$1@terminus.zytor.com>
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	 <bda6d13a0606091050n40fda044v668eef09af3c29a7@mail.gmail.com>
	 <871wty6rl9.fsf@hades.wkstn.nix>
	 <bda6d13a0606091528h4e85265du8651818c73827b7d@mail.gmail.com>
	 <e6ctsb$hij$1@terminus.zytor.com>
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On 6/9/06, H. Peter Anvin <hpa@zytor.com> wrote:
> Followup to:  <bda6d13a0606091528h4e85265du8651818c73827b7d@mail.gmail.com>
> By author:    "Joshua Hudson" <joshudson@gmail.com>
> In newsgroup: linux.dev.kernel
> >
> > Once again. Loopback mount requires a clean unmount of root and
> > host filesystem. After remounting root read-only, host is still read-write
> > and cannot be remounted read-only.
> >
> > It is necessary to provide access to the rootfs tree somewhere else
> > or use pivot_root, like the initrd solution below:
> >
> > initrd: /linuxrc
> > #!/bin/sh
> > mount /dev/hda1 -o rw -t ntfs /host
> > mount /host/linux/root.img -o loop,ro -t ext3 /root
> > pivot_root /root /root/initrd
> > exec /initrd/bin/init
> >
> > root:/etc/rc.d/rc.halt:
> > #!/bin/sh
> > pivot_root /initrd /initrd/root
> > cd /
> > exec /stop $RUNLEVEL
> >
> > initrd:/stop
> > #!/bin/sh
> > kill -SIGUSR1 1
> > umount /root
> > umount /host
> > case $1 in
> > 0) poweroff -f ;;
> > *) reboot -f ;;
> > esac
> >
> > This requires static binaries of init, sh, mount, umount, an extant /etc, and a
> > few nodes in /dev.
>
> Another solution is to leave a process with its cwd parked in the
> rootfs.  Look at run_linuxrc() in usr/kinit/initrd.c of any klibc tree
> to see how this can be used.  (That is there to support old-style
> /linuxrc, but should be applicable here, too.)
>
>         -hpa
Should work if the following is true:
   if pwd is /, mount / followed by ls . retunrs the contents of initramfs.