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Hi,
attached is a quick howto for NetBSD and xen 2.0. Should be enouth to get you
NetBSD running as domain0 and domainU.
Comments and corrections welcome.

Once reviewed, this should be added to the xen home page on www.netbsd.org.

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--

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                      Short howto for NetBSD/Xen

Xen is a virtual machine motinor for x86 harware (runs only on i686-class CPUs),
which supports running multiple guests operating systems on a single
machine. Guest OSes (also called domains) requires a modified kernel which
supports Xen hypercalls in remplacement to access to the physical hardware.
At boot, the xen kernel is loaded (via grub) along with the guest kernel
for the first domain (called domain0). domain0 has privileges to access
the physical hardware (PCI and ISA devices), administrate other domains and
provide virtual devices (disks and network) to other domains.
For more details, see http://www.cl.cam.ac.uk/Research/SRG/netos/xen/.

NetBSD can be used for both domain0 and others, uprivileged domains.
(in fact there can be multiple privileged domains accessing different parts
of the hardware, all providing virtual devices to uprivileged domains.
We will only talk about the case of only one privileged domain, domain0).
domain0 will see physical devices much like a regular i386 kernel, and will
own the physical console (VGA or serial). Uprivileged domains will only see
a character-only virtual console, virtual disks (xbd) and virtual network
interfaces (xennet) provided by a privileged domain (usually domain0).
xbd devices are connected to a physical block device (i.e. a partition of
a disk, raid, ccd, ... device) in the privileged domain. xennet devices
are connected to virtual devices in the privileged domain, named
xvif<domain number>.<if number for this domain> (e.g. xvif1.0). Both
xennet and xvif devices are seen as regular ethernet devices (they can
be seen as a crossover cable between 2 PCs) and can be assigned addresses
(and be routed or NATed, filtered using IPF, etc ...) or be added as
part of a bridge.



                      Installing NetBSD as domain0
First do a NetBSD/i386 installation as you usually do on i386 hardware.
When partitionning the disk, keep in mind that you'll probably want to provide
virtual disks to other domains, to reserve some partitions for these
virtual domains.
Next step is to install the grub and xentools20 packages. grub is needed to
load the xen and domain0 kernels; xentools20 contains the utilities to
control xen from domain0.
Next you need the Xen 2.0 kernel itself. You can get one from the binaries
provided on http://www.cl.cam.ac.uk/Research/SRG/netos/xen/downloads.html
(get the xen-2.0.x-install.tgz tarball). The file you're looking for
is xen.gz. Copy it to your root filesystem.
You'll then need a NetBSD/Xen kernel for domain0 on your root filesystem.
The XEN0 kernel provided as part of the i386 binaries is suitable for this,
but you may want to customise it. Keep your NetBSD/i386 kernel around, it can
be usefull for recovery.
Next you need to install Grub to load the xen.gz kernel, and the NetBSD domain0
kernel as a module. In the grub config you'll also specify the memory allocted
to domain0, the console to use, etc ...
Here is a self-documented /grub/menu.lst file:

#Grub config file for NetBSD/xen. Copy as /grub/menu.lst and run
# grub-install /dev/rwd0d (assuming your boot device is wd0).
#
# The default entry to load will be the first one
default=0
# boot after 10s the default entry if the user didn't hit keyboard
timeout=10
# Configure serial port to use as console. Ignore if you'll use VGA only
serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1
# Let the user select which console to use (serial or VGA), default
# to serial after 10s
terminal --timeout=10 serial console
# An entry for NetBSD/xen, using /netbsd as the domain0 kernel, and serial
# console. Domain0 will have 64MB RAM allocated.
# Assume NetBSD is installed in the first MBR partition.
title Xen 2.0 / NetBSD (hda0, serial)
  root(hd0,0)
  kernel (hd0,a)/xen.gz dom0_mem=65536 com1=115200,8n1
  module (hd0,a)/netbsd root=/dev/hda1 ro console=ttyS0 
# Same as above, but using VGA console
# We can use console=tty0 (linux syntax) or console=pc (NetBSD syntax)
title Xen 2.0 / NetBSD (hda0, vga)
  root(hd0,0)
  kernel (hd0,a)/xen.gz dom0_mem=65536 
  module (hd0,a)/netbsd root=/dev/hda1 ro console=tty0 
# NetBSD/xen using a backup domain0 kernel (in case you installed a
# nonworking kernel as /netbsd
title Xen 2.0 / NetBSD (hda0, backup, serial)
  root(hd0,0)
  kernel (hd0,a)/xen.gz dom0_mem=65536 com1=115200,8n1
  module (hd0,a)/netbsd.backup root=/dev/hda1 ro console=ttyS0
title Xen 2.0 / NetBSD (hda0, backup, VGA)
  root(hd0,0)
  kernel (hd0,a)/xen.gz dom0_mem=65536
  module (hd0,a)/netbsd.backup root=/dev/hda1 ro console=tty0
#Load a regular NetBSD/i386 kernel. Can be usefull if you end up with a
#nonworking /xen.gz
title NetBSD 2.0
  root (hd0,a)
  kernel --type=netbsd /netbsd-GENERIC
#Load the NetBSD bootloader, letting it load the NetBSD/i386 kernel.
#May be better than the above, as grub can't pass all required infos
#to the NetBSD/i386 kernel (e.g. console, root device, ...)
title NetBSD chain
  root        (hd0,0)
  chainloader +1
## end of grub config file.


                      Creating unprivileged domains
Once you have domain0 running, you need to start the xen tool daemon
(/usr/pkg/sbin/xend start). xend will write logs to /var/log/xend.log and
/var/log/xend-debug.log. You can then control xen with the xm tool.
'xm list' you show something like:
borneo# xm list
Name              Id  Mem(MB)  CPU  State  Time(s)  Console
Domain-0           0       64    0  r----     58.1        
Note that all communications between xend and xm happen via a TCP socket,
and xend listen to *.8000, *.8001 and *.8002. Anyone will be able to control
xen via these ports. I strongly suggest that you filter these ports on your
domain0 (using IPF or PF) allowing access only from 127.0.0.1, and restrict
users able to log in to domain0.

'xm create' allows you to create a new domain. It use a config file for
its parameters in /etc/xen/. On creation, a kernel has to be specified,
which will be executed in the new domain (this kernel is in the
domain0 filesystem, not on the new domain virtual disk). A suitable kernel
is provided as part of the i386 binary sets, XENU.
Here is an /etc/xen/nbsd example config file:

#  -*- mode: python; -*-
#============================================================================
# Python defaults setup for 'xm create'.
# Edit this file to reflect the configuration of your system.
#============================================================================

#----------------------------------------------------------------------------
# Kernel image file. This kernel will be loaded in the new domain.
kernel = "/home/bouyer/netbsd-XENU"
#kernel = "/home/bouyer/netbsd-INSTALL_XENU"

# Memory allocation (in megabytes) for the new domain.
memory = 128

# A handy name for your new domain. This will appear in 'xm list',
# and you can use this as parameters for xm in place of the domain number.
name = "nbsd"

# Which CPU to start domain on (only relevant for SMP hardware)
cpu = -1   # leave to Xen to pick

#----------------------------------------------------------------------------
# Define network interfaces for the new domain.

# Number of network interfaces. Default is 1.
nics=1

# Optionally define mac and/or bridge for the network interfaces.
# Random MACs are assigned if not given.
# The MAC address specified is the one used for the interface in the new
# domain. The interface in domain0 will use this address xor'd with
# 00:00:00:01:00:00 (i.e. aa:00:00:51:02:f0 in our example)
# bridge is a required parameter, which will be passed to the vif script
# called by xend when a new domain is created to configure the new
# xvif interface in domain0. We can pass any information here.
# In our example, the xvif won't be added to a bridge, but configured with a
# private address. Pass the ifconfig line which will be used by the script
# here instead.
vif = [ 'mac=aa:00:00:50:02:f0, bridge=10.0.0.254 netmask 255.255.255.0' ]

#----------------------------------------------------------------------------
# Define the disk devices you want the domain to have access to, and
# what you want them accessible as.
# Each disk entry is of the form phy:DEV,VDEV,MODE
# where DEV is the device, VDEV is the device name the domain will see,
# and MODE is r for read-only, w for read-write.
# VDEV doens't really matter for NetBSD guest OS, but does for linux.
# Worse, the device has to exists in /dev/ of domain0, because xm will
# try to stat() it. This means that in order to load a linux guest OS
# from a NetBSD domain0, you'll have to create /dev/hda1, /dev/hda2, ...
# on domain0, with the major/minor from linux :(

disk = [ 'phy:/dev/wd0e,wd0d,w' ]

#----------------------------------------------------------------------------
# Set the kernel command line for the new domain.

# Set root device. This one does matter for NetBSD
root = "/dev/wd0d"
# extra parameters passed to the kernel
#extra = ""

#----------------------------------------------------------------------------
# Set according to whether you want the domain  restarted when it exits.
# The default is False.
#autorestart = True

# end of nbsd config file ====================================================

When a new domain is created, xen calls a script /etc/xen/scripts/vif-bridge
for each virtual network interface created in domain0.
This can be used to configure automatically the xvif?.? interfaces in domain0.
In our example, these will get an IP (domain0 then provide routing and NAT for
internet access via IPF).
Here is a suitable /etc/xen/scripts/vif-bridge for this:
#!/bin/sh
#============================================================================
# /etc/xen/vif-bridge
#
# Script for configuring a vif.
# Xend calls a vif script when configuring a vif up or down.
# This script is the default - but it can be configured for each vif.
#
# Example invocation:
#
# vif-bridge up domain=VM1 vif=vif1.0 bridge=xen-br0 mac=aa:00:00:50:02:f0
#
#
# Usage:
# vif-bridge (up|down) {VAR=VAL}*
#
# Vars:
#
# domain  name of the domain the interface is on (required).
# vif     vif interface name (required).
# mac     vif MAC address (required).
# bridge  bridge to add the vif to (required).
#
#============================================================================

# Exit if anything goes wrong
set -e 

#this will be logged in xend-debug.log
echo "vif-bridge $*"

# Operation name.
OP=$1
shift

# Pull variables in args into environment
for arg ; do export "${arg}" ; done

# Required parameters. Fail if not set.
domain=${domain:?}
vif=${vif:?}
mac=${mac:?}
bridge=${bridge:?}

# Are we going up or down?
case $OP in
    up)
	# ${bridge} contains ifconfig parameters in our case.
        # It could also be parameters to brctl, or anything else we
        # want.
	# xend gives us vif?.? as interface name, but on NetBSD
	# they're called xvif?.?
	ifconfig x${vif} ${bridge}
	exit 0

	;;
    down)
	exit 0
	;;
    *)
	echo 'Invalid command: ' $OP
	echo 'Valid commands are: up, down'
	exit 1
	;;
esac
#end of /etc/xen/scripts/vif-bridge

Now, running
xm create -c /etc/xen/nbsd
(note: -c cause xm to connect to the domain's console once created)
should create a domain and load a NetBSD kernel in it. But the kernel will
try to find its root filesystem on xbd0 (i.e. wd0e) which doesn't exists yet.
wd0e will be seen as a disk device in the new domain, so it will be
'sub-partitionned'. We could attach a ccd to wd0e and partition it, newfs
and extract the NetBSD/i386 tarballs here, but there's an easier way:
load the INSTALL_XENU kernel provided in the NetBSD/i386 binary sets.
Like others i386 install kernels, it contains a ramdisk with sysinst,
so you can install NetBSD using sysinst on your new domain.
Once done, 'halt -p' the new domain (don't reboot or halt, it would reload the
INSTALL_XENU kernel even if you changed the config file), switch bask to the
XENU kernel in the config file, and start the new domain again.
Now it should be able to use 'root on xbd0a' and have a second, functionnal
NetBSD/i386 system on your xen installation.

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