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Re: [Xen-devel] skimmed version of xen

On Tue, Oct 17, 2006 at 04:14:38AM -0700, Sanjam Garg wrote:
> Hi
>  I just  need to run one virtual machine on top of xen and want to use the 
> dom0  to support the minimum functionality.Anybody has some ideas on  it?

I'll be making a system like that, also with DRBD, OCFS2 and a Xen
cluster control system using group communication for the next couple of
months. This will be on my spare time and I can give no guarantee on
anything, including ETAs.

Nevertheless, I'm going to use as base a initramfs system that I've been
developing for other purposes. It includes bash, busybox, dropbear (ssh
client/server), screen, vim, perl, lvm and other things. See
http://gsd.di.uminho.pt/luciano/rd/ for package listing, initramfs and

It consists on various packages, on separate cpios[1] or on a single one:

* btfs.init contains the base /init, that creates a tmpfs[2] filesystem,
unpacks all cpio archives /*.co, /*.cgz and /*.cbz2 to that tmpfs, moves
any remaining files in / to the tmpfs and then executes the real init.

* base.cgz contains the base utilities, listed in
http://gsd.di.uminho.pt/luciano/rd/base_list.txt, and boot/shutdown
scripts. The boot scripts will:
 1. auto-detect most pci modules
 2. move all /etc/add.d/* to /
 3. execute /etc/rc.d/S*

on shutdown:
 1. execute /etc/rc.d/K*
 2. kill all processes
 3. umount all filesystems

The system is to be built combining the required packages for the target
system. On a single cpio, or by using a boot loader that supports
loading multiple cpios.

Syslinux is a case of the latter, so here's what I use (see also

1. init - the btfs.init,
2. pkgs - an uncompressed cpio of the cpios of the other packages (the
decompression of those is done by btfs)

label linux
  kernel vmlinuz
  append initrd=init,pkgs

Don't forget to include in a pkg the modules for the kernel you'll be

Luciano Rocha

[1] initramfs cpios have to be in the new portable format, so don't
forget to add the option -Hnewc to cpio when creating them.

[2] initramfs is an instance of ramfs, that keeps all data in memory.
Tmpfs adds the ability to swap out unused data, so the move to tmpfs
will allow some memory to be regained after a swapon.


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