linux/kernel/user mode VM

Overview

This section is intended to help users interested in developing Linux kernel modules to setup an UML VM to debug it during development phase.

Please note that this page will focus in configuring a VM running on a Debian distribution based host.

Installation

First of all you need to install the package user-mode-linux <bash>apt-get install user-mode-linux</bash> Then you need the package uml-utilities <bash>apt-get install uml-utilities</bash>

Configuration

File System Image

The easiest way to do that is to download an already built image <bash>wget ftp://ftp.freepascal.org/some path/umlrootfs.img.bz2</bash> Then you need to decompress it <bash>bunzip2 umlrootfs.img.bz2</bash> Please note that this is really a minimal installation, including the fp-compiler and aptitude packages. The latter will allow you to install any package you want providing you set up your network correctly.

The provided root file system image has networking configured already for the VM, so you need just to configure the host part as described in the next section.

Networking

Creating TAP interface

In order to setup networking you need to configure a tap interface: <bash>cat - > /etc/network/interfaces</bash>

# /etc/network/interfaces -- configuration file for ifup(8), ifdown(8)
# In this configuration example we will setup two physical networking
# cards eth0 and eth1. The first card, eth0, will be automatically
# configured at host starting up, while the second one will be configured
# on manual demand using "ifup eth1".
# We will also configure a virtual networking card tap0 which will be
# configured at system startup too.

auto lo eth0 tap0

# The loopback interface 
iface lo inet loopback

iface eth0 inet static
  address 192.168.1.2
  netmask 255.255.255.0
  network 192.168.1.0
  gateway 192.168.1.1

iface eth1 inet static
  address 192.168.2.1
  netmask 255.255.255.0
  network 192.168.2.0

iface tap0 inet static
  address 192.168.3.1
  netmask 255.255.255.0
  network 192.168.3.0
  tunctl_user uml-net
  uml_proxy_arp 192.168.3.2
  uml_proxy_ether eth0

Enabling IP forwarding

In addition to this networking configuration, you need to instruct your kernel to forward IP packets, so the VM can communicate with the rest of your network and the internet. <bash>cat - > /etc/sysctl.conf</bash>

#
# /etc/sysctl.conf - Configuration file for setting system variables
# See sysctl.conf (5) for information.
#

##############################################################3
# Functions previously found in netbase
#

# Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1

Configuring UML switch

<bash>cat - > /etc/default/uml-utilities</bash>

 # Options to pass to uml_switch.

# set to "false" if you want to prevent uml_switch from
# starting with SysV scripts in /etc/init.d
UML_SWITCH_START="true"

# For preconfigured tap setup, see
# /usr/share/doc/uml-utilities/examples/interfaces.example
UML_SWITCH_OPTIONS="-tap tap0"

# User as which to run uml_switch
UML_SWITCH_USER="uml-net"

# Socket file to use
# Debian's default is:
UML_SWITCH_CTL="/var/run/uml-utilities/uml_switch.ctl"
#
# if you instead use your rolled up kernel from upstream
# sources you may want to uncomment the following:
#UML_SWITCH_CTL="/tmp/uml.ctl"

Starting the UML VM

Starting script

Starting UML VM requires too many arguments, but a small script can ease this task: <bash>cat - > ${HOME}/bin/startUML.sh</bash>

#! /bin/sh
UML_BIN=linux
UML_ROOT_FS=${HOME}/umlrootfs.img
UML_SWITCH_SOCKET=/var/run/uml-utilities/uml_switch.ctl
exec ${UML_BIN} \
	umid=uml1 \
	mem=512M \
	ubd0=${UML_ROOT_FS} \
	eth0=daemon,fe:fd:fe:ed:b0:0f,,${UML_SWITCH_SOCKET} \
	con0=xterm xterm=/usr/bin/xterm,-T,-e \

--Mazen 23:52, 16 October 2007 (CEST)