NetBSD/xen Howto

Xen is a virtual machine monitor for x86 hardware (requires i686-class CPUs), which supports running multiple guest operating systems on a single machine. Guest OSes (also called “domains”) require a modified kernel which supports Xen hypercalls in replacement to access to the physical hardware. At boot, the Xen kernel (also known as the Xen hypervisor) is loaded (via grub) along with the guest kernel for the first domain (called domain0). The Xen kernel has to be loaded using the multiboot protocol. You can use grub or the NetBSD boot loader for this (grub has some limitations, detailed below). domain0 has special privileges to access the physical hardware (PCI and ISA devices), administrate other domains and provide virtual devices (disks and network) to other domains that lack those privileges. For more details, see http://www.xen.org/.

NetBSD can be used for both domain0 (Dom0) and other, unprivileged (DomU) domains. (Actually there can be multiple privileged domains accessing different parts of the hardware, all providing virtual devices to unprivileged domains. We will only talk about the case of a single privileged domain, domain0). domain0 will see physical devices much like a regular i386 or amd64 kernel, and will own the physical console (VGA or serial). Unprivileged 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 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.

First do a NetBSD/i386 or NetBSD/amd64 installation of the 5.0 release as you usually do on x86 hardware. The binary releases are available from ftp://ftp.NetBSD.org/pub/NetBSD/NetBSD-5.0.2/. Binary snapshots for current and the netbsd-4 branches are available on daily autobuilds. If you plan to use the grub boot loader, when partitioning the disk you have to make the root partition smaller than 512Mb, and formatted as FFSv1 with 8k block/1k fragments. If the partition is larger than this, uses FFSv2 or has different block/fragment sizes, grub may fail to load some files. Also keep in mind that you'll probably want to provide virtual disks to other domains, so reserve some partitions for these virtual disks. Alternatively, you can create large files in the file system, map them to vnd(4) devices and export theses vnd devices to other domains.

Next step is to install the Xen packages via pkgsrc or from binary packages. See the pkgsrc documentation if you are unfamiliar with pkgsrc and/or handling of binary packages. Xen 3.1, 3.3 and 4.1 are available. 3.1 supports PCI pass-through while other versions do not. You'll need either sysutils/xentools3 and sysutils/xenkernel3 for Xen 3.1, sysutils/xentools33 and sysutils/xenkernel33 for Xen 3.3 or sysutils/xentools41 and sysutils/xenkernel41 for Xen 4.1. You'll also need sysutils/grub if you plan do use the grub boot loader. If using Xen 3.1, you may also want to install sysutils/xentools3-hvm which contains the utilities to run unmodified guests OSes using the HVM support (for later versions this is included in sysutils/xentools). Note that your CPU needs to support this. Intel CPUs must have the 'VT' instruction, AMD CPUs the 'SVM' instruction. You can easily find out if your CPU support HVM by using NetBSD's cpuctl command:

# cpuctl identify 0
cpu0: Intel Core 2 (Merom) (686-class), id 0x6f6
cpu0: features 0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR>
cpu0: features 0xbfebfbff<PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX>
cpu0: features 0xbfebfbff<FXSR,SSE,SSE2,SS,HTT,TM,SBF>
cpu0: features2 0x4e33d<SSE3,DTES64,MONITOR,DS-CPL,VMX,TM2,SSSE3,CX16,xTPR,PDCM,DCA>
cpu0: features3 0x20100800<SYSCALL/SYSRET,XD,EM64T>
cpu0: "Intel(R) Xeon(R) CPU            5130  @ 2.00GHz"
cpu0: I-cache 32KB 64B/line 8-way, D-cache 32KB 64B/line 8-way
cpu0: L2 cache 4MB 64B/line 16-way
cpu0: ITLB 128 4KB entries 4-way
cpu0: DTLB 256 4KB entries 4-way, 32 4MB entries 4-way
cpu0: Initial APIC ID 0
cpu0: Cluster/Package ID 0
cpu0: Core ID 0
cpu0: family 06 model 0f extfamily 00 extmodel 00

Depending on your CPU, the feature you are looking for is called HVM, SVM or VMX.

Next you need to copy the selected Xen kernel itself. pkgsrc installed them under /usr/pkg/xen*-kernel/. The file you're looking for is xen.gz. Copy it to your root file system. xen-debug.gz is a kernel with more consistency checks and more details printed on the serial console. It is useful for debugging crashing guests if you use a serial console. It is not useful with a VGA console.

You'll then need a NetBSD/Xen kernel for domain0 on your root file system. The XEN3PAE_DOM0 kernel or XEN3_DOM0 provided as part of the i386 or amd64 binaries is suitable for this, but you may want to customize it. Keep your native kernel around, as it can be useful for recovery. Note: the domain0 kernel must support KERNFS and /kern must be mounted because xend needs access to /kern/xen/privcmd.

Next you need to get a bootloader to load the xen.gz kernel, and the NetBSD domain0 kernel as a module. This can be grub or NetBSD's boot loader. Below is a detailled example for grub, see the boot.cfg(5) manual page for an example using the later.

This is also where you'll specify the memory allocated to domain0, the console to use, etc ...

Here is a commented /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 the default entry after 10s 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 3 / NetBSD (hda0, serial)
  root(hd0,0)
  kernel (hd0,a)/xen.gz dom0_mem=65536 com1=115200,8n1
  module (hd0,a)/netbsd bootdev=wd0a ro console=ttyS0

# Same as above, but using VGA console
# We can use console=tty0 (Linux syntax) or console=pc (NetBSD syntax)
title Xen 3 / NetBSD (hda0, vga)
  root(hd0,0)
  kernel (hd0,a)/xen.gz dom0_mem=65536
  module (hd0,a)/netbsd bootdev=wd0a ro console=tty0

# NetBSD/xen using a backup domain0 kernel (in case you installed a
# nonworking kernel as /netbsd
title Xen 3 / NetBSD (hda0, backup, serial)
  root(hd0,0)
  kernel (hd0,a)/xen.gz dom0_mem=65536 com1=115200,8n1
  module (hd0,a)/netbsd.backup bootdev=wd0a ro console=ttyS0
title Xen 3 / NetBSD (hda0, backup, VGA)
  root(hd0,0)
  kernel (hd0,a)/xen.gz dom0_mem=65536
  module (hd0,a)/netbsd.backup bootdev=wd0a ro console=tty0

#Load a regular NetBSD/i386 kernel. Can be useful if you end up with a
#nonworking /xen.gz
title NetBSD 5.1
  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.
      

Install grub with the following command:

# grub --no-floppy

grub> root (hd0,a)
 Filesystem type is ffs, partition type 0xa9

grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... no
 Checking if "/grub/stage1" exists... yes
 Checking if "/grub/stage2" exists... yes
 Checking if "/grub/ffs_stage1_5" exists... yes
 Running "embed /grub/ffs_stage1_5 (hd0)"...  14 sectors are embedded.
succeeded
 Running "install /grub/stage1 (hd0) (hd0)1+14 p (hd0,0,a)/grub/stage2 /grub/menu.lst"...
 succeeded
Done.
      

Once you have domain0 running, you need to start the xen tool daemon (/usr/pkg/share/examples/rc.d/xend start) and the xen backend daemon (/usr/pkg/share/examples/rc.d/xenbackendd start). Make sure that /dev/xencons and /dev/xenevt exist before starting xend. You can create them with this command:

# cd /dev && sh MAKEDEV xen

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' will show something like:

# xm list
Name              Id  Mem(MB)  CPU  State  Time(s)  Console
Domain-0           0       64    0  r----     58.1

'xm create' allows you to create a new domain. It uses a config file in PKG_SYSCONFDIR for its parameters. By default, this file will be in /usr/pkg/etc/xen/. On creation, a kernel has to be specified, which will be executed in the new domain (this kernel is in the domain0 file system, not on the new domain virtual disk; but please note, you should install the same kernel into domainU as /netbsd in order to make your system tools, like savecore(8), work). A suitable kernel is provided as part of the i386 and amd64 binary sets: XEN3_DOMU.

Here is an /usr/pkg/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-XEN3_DOMU"
#kernel = "/home/bouyer/netbsd-INSTALL_XEN3_DOMU"

# 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. All domains must have different names.
#
name = "nbsd"

# The number of virtual CPUs this domain has.
#
vcpus = 1

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

# Number of network interfaces (must be at least 1). Default is 1.
nics = 1

# Define MAC and/or bridge for the network interfaces.
#
# The MAC address specified in ``mac'' 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). Random
# MACs are assigned if not given.
#
# ``bridge'' is a required parameter, which will be passed to the
# vif-script called by xend(8) when a new domain is created to configure
# the new xvif interface in domain0.
#
# In this example, the xvif is added to bridge0, which should have been
# set up prior to the new domain being created -- either in the
# ``network'' script or using a /etc/ifconfig.bridge0 file.
#
vif = [ 'mac=aa:00:00:50:02:f0, bridge=bridge0' ]

#----------------------------------------------------------------------------
# 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.  You can also create
# file-backed domains using disk entries of the form:
#
#	file:PATH,VDEV,MODE
#
# where PATH is the path to the file used as the virtual disk, and VDEV
# and MODE have the same meaning as for ``phy'' devices.
#
# VDEV doesn't really matter for a NetBSD guest OS (it's just used as an index),
# but it does for Linux.
# Worse, the device has to exist 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 :(
# Alternatively it's possible to specify the device number in hex,
# e.g. 0x301 for /dev/hda1, 0x302 for /dev/hda2, etc ...

disk = [ 'phy:/dev/wd0e,0x1,w' ]
#disk = [ 'file:/var/xen/nbsd-disk,0x01,w' ]
#disk = [ 'file:/var/xen/nbsd-disk,0x301,w' ]

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

# Set root device. This one does matter for NetBSD
root = "xbd0"
# extra parameters passed to the kernel
# this is where you can set boot flags like -s, -a, etc ...
#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 the /usr/pkg/etc/xen/vif-bridge script for each virtual network interface created in domain0. This can be used to automatically configure the xvif?.? interfaces in domain0. In our example, these will be bridged with the bridge0 device in domain0, but the bridge has to exist first. To do this, create the file /etc/ifconfig.bridge0 and make it look like this:

create
!brconfig $int add ex0 up

(replace ex0 with the name of your physical interface). Then bridge0 will be created on boot. See the bridge(4) man page for details.

So, here is a suitable /usr/pkg/etc/xen/vif-bridge for xvif?.? (a working vif-bridge is also provided with xentools20) configuring:

#!/bin/sh
#============================================================================
# $NetBSD: vif-bridge-nbsd,v 1.3 2005/11/08 00:47:35 jlam Exp $
#
# /usr/pkg/etc/xen/vif-bridge
#
# Script for configuring a vif in bridged mode with a dom0 interface.
# The xend(8) daemon calls a vif script when bringing a vif up or down.
# The script name to use is defined in /usr/pkg/etc/xen/xend-config.sxp
# in the ``vif-script'' field.
#
# Usage: vif-bridge up|down [var=value ...]
#
# Actions:
#    up		Adds the vif interface to the bridge.
#    down	Removes the vif interface from the bridge.
#
# Variables:
#    domain	name of the domain the interface is on (required).
#    vifq	vif interface name (required).
#    mac	vif MAC address (required).
#    bridge	bridge to add the vif to (required).
#
# Example invocation:
#
# vif-bridge up domain=VM1 vif=xvif1.0 mac="ee:14:01:d0:ec:af" bridge=bridge0
#
#============================================================================

# Exit if anything goes wrong
set -e

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:?}

# Optional parameters. Set defaults.
ip=${ip:-''}   # default to null (do nothing)

# Are we going up or down?
case $OP in
up)	brcmd='add' ;;
down)	brcmd='delete' ;;
*)
	echo 'Invalid command: ' $OP
	echo 'Valid commands are: up, down'
	exit 1
	;;
esac

# Don't do anything if the bridge is "null".
if [ "${bridge}" = "null" ] ; then
	exit
fi

# Don't do anything if the bridge doesn't exist.
if ! ifconfig -l | grep "${bridge}" >/dev/null; then
	exit
fi

# Add/remove vif to/from bridge.
ifconfig x${vif} $OP
brconfig ${bridge} ${brcmd} x${vif}

Now, running

xm create -c /usr/pkg/etc/xen/nbsd

should create a domain and load a NetBSD kernel in it. (Note: -c causes xm to connect to the domain's console once created.) The kernel will try to find its root file system on xbd0 (i.e., wd0e) which hasn't been created yet. wd0e will be seen as a disk device in the new domain, so it will be 'sub-partitioned'. We could attach a ccd to wd0e in domain0 and partition it, newfs and extract the NetBSD/i386 or amd64 tarballs there, but there's an easier way: load the netbsd-INSTALL_XEN3_DOMU kernel provided in the NetBSD binary sets. Like other install kernels, it contains a ramdisk with sysinst, so you can install NetBSD using sysinst on your new domain.

If you want to install NetBSD/Xen with a CDROM image, the following line should be used in the /usr/pkg/etc/xen/nbsd file:

disk = [ 'phy:/dev/wd0e,0x1,w', 'phy:/dev/cd0a,0x2,r' ]

After booting the domain, the option to install via CDROM may be selected. The CDROM device should be changed to xbd1d.

Once done installing, halt -p the new domain (don't reboot or halt, it would reload the INSTALL_XEN3_DOMU kernel even if you changed the config file), switch the config file back to the XEN3_DOMU kernel, and start the new domain again. Now it should be able to use root on xbd0a and you should have a second, functional NetBSD system on your xen installation.

When the new domain is booting you'll see some warnings about wscons and the pseudo-terminals. These can be fixed by editing the files /etc/ttys and /etc/wscons.conf. You must disable all terminals in /etc/ttys, except console, like this:

console "/usr/libexec/getty Pc"         vt100   on secure
ttyE0   "/usr/libexec/getty Pc"         vt220   off secure
ttyE1   "/usr/libexec/getty Pc"         vt220   off secure
ttyE2   "/usr/libexec/getty Pc"         vt220   off secure
ttyE3   "/usr/libexec/getty Pc"         vt220   off secure

Finally, all screens must be commented out from /etc/wscons.conf.

It is also desirable to add

powerd=YES

in rc.conf. This way, the domain will be properly shut down if xm shutdown -R or xm shutdown -H is used on the domain0.

Your domain should be now ready to work, enjoy.

Creating unprivileged Linux domains isn't much different from unprivileged NetBSD domains, but there are some details to know.

First, the second parameter passed to the disk declaration (the '0x1' in the example below)

disk = [ 'phy:/dev/wd0e,0x1,w' ]

does matter to Linux. It wants a Linux device number here (e.g. 0x300 for hda). Linux builds device numbers as: (major << 8 + minor). So, hda1 which has major 3 and minor 1 on a Linux system will have device number 0x301. Alternatively, devices names can be used (hda, hdb, ...) as xentools has a table to map these names to devices numbers. To export a partition to a Linux guest we can use:

disk = [ 'phy:/dev/wd0e,0x300,w' ]
root = "/dev/hda1 ro"

and it will appear as /dev/hda on the Linux system, and be used as root partition.

To install the Linux system on the partition to be exported to the guest domain, the following method can be used: install sysutils/e2fsprogs from pkgsrc. Use mke2fs to format the partition that will be the root partition of your Linux domain, and mount it. Then copy the files from a working Linux system, make adjustments in /etc (fstab, network config). It should also be possible to extract binary packages such as .rpm or .deb directly to the mounted partition using the appropriate tool, possibly running under NetBSD's Linux emulation. Once the filesystem has been populated, umount it. If desirable, the filesystem can be converted to ext3 using tune2fs -j. It should now be possible to boot the Linux guest domain, using one of the vmlinuz-*-xenU kernels available in the Xen binary distribution.

To get the linux console right, you need to add:

extra = "xencons=tty1"

to your configuration since not all linux distributions auto-attach a tty to the xen console.

Download an Opensolaris release or development snapshot DVD image. Attach the DVD image to a vnd(4) device. Copy the kernel and ramdisk filesystem image to your dom0 filesystem.

dom0# mkdir /root/solaris
dom0# vnconfig vnd0 osol-1002-124-x86.iso
dom0# mount /dev/vnd0a /mnt

## for a 64-bit guest
dom0# cp /mnt/boot/amd64/x86.microroot /root/solaris
dom0# cp /mnt/platform/i86xpv/kernel/amd64/unix /root/solaris

## for a 32-bit guest
dom0# cp /mnt/boot/x86.microroot /root/solaris
dom0# cp /mnt/platform/i86xpv/kernel/unix /root/solaris

dom0# umount /mnt
      

Keep the vnd(4) configured. For some reason the boot process stalls unless the DVD image is attached to the guest as a "phy" device. Create an initial configuration file with the following contents. Substitute /dev/wd0k with an empty partition at least 8 GB large.

memory = 640
name = 'solaris'
disk = [ 'phy:/dev/wd0k,0,w' ]
disk += [ 'phy:/dev/vnd0d,6:cdrom,r' ]
vif = [ 'bridge=bridge0' ]
kernel = '/root/solaris/unix'
ramdisk = '/root/solaris/x86.microroot'
# for a 64-bit guest
extra = '/platform/i86xpv/kernel/amd64/unix - nowin -B install_media=cdrom'
# for a 32-bit guest
#extra = '/platform/i86xpv/kernel/unix - nowin -B install_media=cdrom'
      

Start the guest.

dom0# xm create -c solaris.cfg
Started domain solaris
                      v3.3.2 chgset 'unavailable'
SunOS Release 5.11 Version snv_124 64-bit
Copyright 1983-2009 Sun Microsystems, Inc.  All rights reserved.
Use is subject to license terms.
Hostname: opensolaris
Remounting root read/write
Probing for device nodes ...
WARNING: emlxs: ddi_modopen drv/fct failed: err 2
Preparing live image for use
Done mounting Live image
      

Make sure the network is configured. Note that it can take a minute for the xnf0 interface to appear.

opensolaris console login: jack
Password: jack
Sun Microsystems Inc.   SunOS 5.11      snv_124 November 2008
jack@opensolaris:~$ pfexec sh
sh-3.2# ifconfig -a
sh-3.2# exit
      

Set a password for VNC and start the VNC server which provides the X11 display where the installation program runs.

jack@opensolaris:~$ vncpasswd
Password: solaris
Verify: solaris
jack@opensolaris:~$ cp .Xclients .vnc/xstartup
jack@opensolaris:~$ vncserver :1
      

From a remote machine connect to the VNC server. Use ifconfig xnf0 on the guest to find the correct IP address to use.

remote$ vncviewer 172.18.2.99:1
      

It is also possible to launch the installation on a remote X11 display.

jack@opensolaris:~$ export DISPLAY=172.18.1.1:0
jack@opensolaris:~$ pfexec gui-install
       

After the GUI installation is complete you will be asked to reboot. Before that you need to determine the ZFS ID for the new boot filesystem and update the configuration file accordingly. Return to the guest console.

jack@opensolaris:~$ pfexec zdb -vvv rpool | grep bootfs
                bootfs = 43
^C
jack@opensolaris:~$
       

The final configuration file should look like this. Note in particular the last line.

memory = 640
name = 'solaris'
disk = [ 'phy:/dev/wd0k,0,w' ]
vif = [ 'bridge=bridge0' ]
kernel = '/root/solaris/unix'
ramdisk = '/root/solaris/x86.microroot'
extra = '/platform/i86xpv/kernel/amd64/unix -B zfs-bootfs=rpool/43,bootpath="/xpvd/xdf@0:a"'
       

Restart the guest to verify it works correctly.

dom0# xm destroy solaris
dom0# xm create -c solaris.cfg
Using config file "./solaris.cfg".
v3.3.2 chgset 'unavailable'
Started domain solaris
SunOS Release 5.11 Version snv_124 64-bit
Copyright 1983-2009 Sun Microsystems, Inc.  All rights reserved.
Use is subject to license terms.
WARNING: emlxs: ddi_modopen drv/fct failed: err 2
Hostname: osol
Configuring devices.
Loading smf(5) service descriptions: 160/160
svccfg import warnings. See /var/svc/log/system-manifest-import:default.log .
Reading ZFS config: done.
Mounting ZFS filesystems: (6/6)
Creating new rsa public/private host key pair
Creating new dsa public/private host key pair

osol console login: