[hacktree] Some discussion about my experimentation with actually doing multiple roots

[Colin Walters <walters src gnome org>]

commit ec2b249c7695e6f113f89750830b7735a1717ddd
Author: Colin Walters <walters verbum org>
Date:   Sun Oct 16 15:51:36 2011 -0400

    Some discussion about my experimentation with actually doing multiple roots

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+Experimenting with multiple roots
+---------------------------------
+
+$ qemu-img create debian.img 600M
+$ mkfs.ext2 debian.img
+$ mkdir debian-mnt
+$ mount -o loop debian.img debian-mnt
+$ debootstrap wheezy debian-mnt
+$ chroot debian-mnt
+$ apt-get install linux-image-3.0.0
+Control-d
+$ cp debian-mnt/boot/vmlinuz* .
+$ cp debian-mnt/boot/initrd* .
+$ umount debian-mnt
+
+You now have a Debian disk image in debian.img and a kernel+initrd that are bootable with qemu.
+
+Modifying the image
+-------------------
+
+The first thing I did was re-mount the image, and move almost everythig
+(/boot, /var, /etc), except lost+found to a new directory "r0".
+
+Then I started hacking on the initrd, making understand how to chroot
+to "r0".
+
+This means that after booting, every process would be in /r0 -
+including any hacktree process.  Assuming objects live in say
+/objects, we need some way for hacktree to switch things.  I think
+just chroot breakout would work.  This has the advantage the daemon
+can continue to use libraries from the active host.
+
+Note there is a self-reference here (as is present in Debian/Fedora
+etc.) - the update system would at present be shipped with the system
+itself.  Should they be independent?  That has advantages and
+disadvantages.  I think we should just try really really hard to avoid
+breaking hacktree in updates.
+