How to run multiple guest OS in QEMU?

This weekend I’ve been fiddling with

QEMU. I’ve installed OpenBSD on a single image and wanted to have two instances of it communicating via network. Installing the system was easy, but the networking setup was quite a pain. See how I did that… To make QEMU instances communicate with each other I needed to plug them to a “network”. That’s why I’ve created a bridge to which Virtual Instances would connect to.

I’ve used the following script:

#!/bin/bash                                                                                                                                                 
# 1st, release all DHCP address and remove all IP address associated
# with the original eth0
#/sbin/dhcpcd -k
kill pidof dhclient
/sbin/ip addr flush eth0
# then take the interface down so we can rename it
/sbin/ip link set eth0 down
# now rename the original eth0 to reth0 (Real ETH0)
nameif reth0 00:24:81:43:61:5b
# OK, bring the same interface (with new name though) back up
/sbin/ip link set reth0 up
# 2nd let's create a bridge called eth0 so other programs think they are
# talking to the same old interface (actually they will talk to the
# bridge which is a clone of the original eth0 - with name MAC addr)
/usr/sbin/brctl addbr eth0
# then add both origianl eth0 and tap1 device to the bridge
/sbin/brctl addif eth0 tap1
/usr/sbin/brctl addif eth0 reth0
echo "showing bridge mac addresses"
/usr/sbin/brctl showmacs eth0
# 3rd, we need to bring the newly created bridge UP
/sbin/ip link set eth0 up
# 4th, renew the DHCP address if possible
#/sbin/dhcpcd -n
dhclient eth0
/sbin/ip addr show

Then I just needed to start Qemu with this command line:

sudo qemu openbsd-4.7.img  -net tap -net nic,macaddr=52:54:00:12:34:57,model=ne2k_pci

Since I’ve set up bridge for Qemu instances, I’ve plugged TAP interfaces into it. That’s why I’ve needed to specify this in my qemu exec line. I’ve also added macaddress setting since both my instances were getting the same one. And that’s all! It works like a charm. Now on to some harder things!

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Spock, Java and Maven

Few months ago I've came across Groovy - powerful language for JVM platform which combines the power of Java with abilities typical for scripting languages (dynamic typing, metaprogramming).

Together with Groovy I've discovered spock framework (https://code.google.com/p/spock/) - specification framework for Groovy (of course you can test Java classes too!). But spock is not only test/specification framework - it also contains powerful mocking tools.

Even though spock is dedicated for Groovy there is no problem with using it for Java classes tests. In this post I'm going to describe how to configure Maven project to build and run spock specifications together with traditional JUnit tests.


Firstly, we need to prepare pom.xml and add necessary dependencies and plugins.

Two obligatory libraries are:
<dependency>
<groupid>org.spockframework</groupId>
<artifactid>spock-core</artifactId>
<version>0.7-groovy-2.0</version>
<scope>test</scope>
</dependency>
<dependency>
<groupid>org.codehaus.groovy</groupId>
<artifactid>groovy-all</artifactId>
<version>${groovy.version}</version>
<scope>test</scope>
</dependency>
Where groovy.version is property defined in pom.xml for more convenient use and easy version change, just like this:
<properties>
<gmaven-plugin.version>1.4</gmaven-plugin.version>
<groovy.version>2.1.5</groovy.version>
</properties>

I've added property for gmaven-plugin version for the same reason ;)

Besides these two dependencies, we can use few additional ones providing extra functionality:
  • cglib - for class mocking
  • objenesis - enables mocking classes without default constructor
To add them to the project put these lines in <dependencies> section of pom.xml:
<dependency>
<groupid>cglib</groupId>
<artifactid>cglib-nodep</artifactId>
<version>3.0</version>
<scope>test</scope>
</dependency>
<dependency>
<groupid>org.objenesis</groupId>
<artifactid>objenesis</artifactId>
<version>1.3</version>
<scope>test</scope>
</dependency>

And that's all for dependencies section. Now we will focus on plugins necessary to compile Groovy classes. We need to add gmaven-plugin with gmaven-runtime-2.0 dependency in plugins section:
<plugin>
<groupid>org.codehaus.gmaven</groupId>
<artifactid>gmaven-plugin</artifactId>
<version>${gmaven-plugin.version}</version>
<configuration>
<providerselection>2.0</providerSelection>
</configuration>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
<dependencies>
<dependency>
<groupid>org.codehaus.gmaven.runtime</groupId>
<artifactid>gmaven-runtime-2.0</artifactId>
<version>${gmaven-plugin.version}</version>
<exclusions>
<exclusion>
<groupid>org.codehaus.groovy</groupId>
<artifactid>groovy-all</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupid>org.codehaus.groovy</groupId>
<artifactid>groovy-all</artifactId>
<version>${groovy.version}</version>
</dependency>
</dependencies>
</plugin>

With these configuration we can use spock and write our first specifications. But there is one issue: default settings for maven-surefire plugin demand that test classes must end with "..Test" postfix, which is ok when we want to use such naming scheme for our spock tests. But if we want to name them like CommentSpec.groovy or whatever with "..Spec" ending (what in my opinion is much more readable) we need to make little change in surefire plugin configuration:
<plugin>
<groupid>org.apache.maven.plugins</groupId>
<artifactid>maven-surefire-plugin</artifactId>
<version>2.15</version>
<configuration>
<includes>
<include>**/*Test.java</include>
<include>**/*Spec.java</include>
</includes>
</configuration>
</plugin>

As you can see there is a little trick ;) We add include directive for standard Java JUnit test ending with "..Test" postfix, but there is also an entry for spock test ending with "..Spec". And there is a trick: we must write "**/*Spec.java", not "**/*Spec.groovy", otherwise Maven will not run spock tests (which is strange and I've spent some time to figure out why Maven can't run my specs).

Little update: instead of "*.java" postfix for both types of tests we can write "*.class" what is in my opinion more readable and clean:
<include>**/*Test.class</include>
<include>**/*Spec.class</include>
(thanks to Tomek Pęksa for pointing this out!)

With such configuration, we can write either traditional JUnit test and put them in src/test/java directory or groovy spock specifications and place them in src/test/groovy. And both will work together just fine :) In one of my next posts I'll write something about using spock and its mocking abilities in practice, so stay in tune.