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<h1>Xen hypervisor driver</h1>
<ul id="toc"></ul>
<p>
The libvirt Xen driver provides the ability to manage virtual machines
on any Xen release from 3.0.1 onwards.
</p>
<h2><a name="project">Project Links</a></h2>
<ul>
<li>
The <a href="http://www.cl.cam.ac.uk/Research/SRG/netos/xen/index.html">Xen</a>
hypervisor on Linux and Solaris hosts
</li>
</ul>
<h2><a name="prereq">Deployment pre-requisites</a></h2>
<p>
The libvirt Xen driver uses a combination of channels to manage Xen
virtual machines.
</p>
<ul>
<li>
<strong>XenD</strong>: Access to the Xen daemon is a mandatory
requirement for the libvirt Xen driver. It requires that the UNIX
socket interface be enabled in the <code>/etc/xen/xend-config.sxp</code>
configuration file. Specifically the config settings
<code>(xend-unix-server yes)</code>. This path is usually restricted
to only allow the <code>root</code> user access. As an alternative,
the HTTP interface can be used, however, this has significant security
implications.
</li>
<li>
<strong>XenStoreD</strong>: Access to the Xenstore daemon enables
more efficient codepaths for looking up domain information which
lowers the CPU overhead of management.
</li>
<li>
<strong>Hypercalls</strong>: The ability to make direct hypercalls
allows the most efficient codepaths in the driver to be used for
monitoring domain status.
</li>
<li>
<strong>XM config</strong>: When using Xen releases prior to 3.0.4,
there is no inactive domain management in XenD. For such releases,
libvirt will automatically process XM configuration files kept in
the <code>/etc/xen</code> directory. It is important not to place
any other non-config files in this directory.
</li>
</ul>
<h2><a name="uri">Connections to Xen driver</a></h2>
<p>
The libvirt Xen driver is a single-instance privileged driver,
with a driver name of 'xen'. Some example conection URIs for
the libvirt driver are:
</p>
<pre>
xen:/// (local access, direct)
xen+unix:/// (local access, via daemon)
xen://example.com/ (remote access, TLS/x509)
xen+tcp://example.com/ (remote access, SASl/Kerberos)
xen+ssh://root@example.com/ (remote access, SSH tunnelled)
</pre>
<h2><a name="imex">Import and export of libvirt domain XML configs</a></h2>
<p>The Xen driver currently supports two native
config formats. The first known as <code>xen-xm</code> is the format
used by the XM tool for files in <code>/etc/xen</code>. The second
known as <code>xen-sxpr</code>, is the format used for interacting
with the XenD's legacy HTTP RPC service.</p>
<h3><a name="xmlimport">Converting from XM config files to domain XML</a></h3>
<p>
The <code>virsh domxml-from-native</code> provides a way to convert an
existing set of XM config files into a guest description using libvirt Domain XML
that can then be used by libvirt.
</p>
<pre>$ virsh -c xen:/// domxml-from-native xen-xm rhel5.cfg
<domain type='xen'>
<name>rhel5pv</name>
<uuid>8f07fe28-753f-2729-d76d-bdbd892f949a</uuid>
<memory>2560000</memory>
<currentMemory>307200</currentMemory>
<vcpu>4</vcpu>
<bootloader>/usr/bin/pygrub</bootloader>
<os>
<type arch='x86_64' machine='xenpv'>linux</type>
</os>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<disk type='file' device='disk'>
<driver name='tap' type='aio'/>
<source file='/var/lib/xen/images/rhel5pv.img'/>
<target dev='xvda' bus='xen'/>
</disk>
<disk type='file' device='disk'>
<driver name='tap' type='qcow'/>
<source file='/root/qcow1-xen.img'/>
<target dev='xvdd' bus='xen'/>
</disk>
<interface type='bridge'>
<mac address='00:16:3e:60:36:ba'/>
<source bridge='xenbr0'/>
</interface>
<console type='pty'>
<target port='0'/>
</console>
<input type='mouse' bus='xen'/>
<graphics type='vnc' port='-1' autoport='yes' listen='0.0.0.0'/>
</devices>
</domain></pre>
<h3><a name="xmlexport">Converting from domain XML to XM config files</a></h3>
<p>
The <code>virsh domxml-to-native</code> provides a way to convert a
guest description using libvirt Domain XML, into the XM config file
format.
</p>
<pre>$ virsh -c xen:/// domxml-to-native xen-xm rhel5pv.xml
name = "rhel5pv"
uuid = "8f07fe28-753f-2729-d76d-bdbd892f949a"
maxmem = 2500
memory = 300
vcpus = 4
bootloader = "/usr/bin/pygrub"
kernel = "/var/lib/xen/boot_kernel.0YK-cS"
ramdisk = "/var/lib/xen/boot_ramdisk.vWgrxK"
extra = "ro root=/dev/VolGroup00/LogVol00 rhgb quiet"
on_poweroff = "destroy"
on_reboot = "restart"
on_crash = "restart"
sdl = 0
vnc = 1
vncunused = 1
vnclisten = "0.0.0.0"
disk = [ "tap:aio:/var/lib/xen/images/rhel5pv.img,xvda,w", "tap:qcow:/root/qcow1-xen.img,xvdd,w" ]
vif = [ "mac=00:16:3e:60:36:ba,bridge=virbr0,script=vif-bridge,vifname=vif5.0" ]</pre>
<h2><a name="xmlconfig">Example domain XML config</a></h2>
<p>
Below are some example XML configurations for Xen guest domains.
For full details of the available options, consult the <a href="formatdomain.html">domain XML format</a>
guide.
</p>
<h3>Paravirtualized guest bootloader</h3>
<p>
Using a bootloader allows a paravirtualized guest to be booted using
a kernel stored inside its virtual disk image
</p>
<pre><domain type='xen' >
<name>fc8</name>
<bootloader>/usr/bin/pygrub</bootloader>
<os>
<type>linux</type>
</os>
<memory>131072</memory>
<vcpu>1</vcpu>
<devices>
<disk type='file'>
<source file='/var/lib/xen/images/fc4.img'/>
<target dev='sda1'/>
</disk>
<interface type='bridge'>
<source bridge='xenbr0'/>
<mac address='aa:00:00:00:00:11'/>
<script path='/etc/xen/scripts/vif-bridge'/>
</interface>
<console tty='/dev/pts/5'/>
</devices>
</domain></pre>
<h3>Paravirtualized guest direct kernel boot</h3>
<p>
For installation of paravirtualized guests it is typical to boot the
domain using a kernel and initrd stored in the host OS
</p>
<pre><domain type='xen' >
<name>fc8</name>
<os>
<type>linux</type>
<kernel>/var/lib/xen/install/vmlinuz-fedora8-x86_64</kernel>
<initrd>/var/lib/xen/install/initrd-vmlinuz-fedora8-x86_64</initrd>
<cmdline> kickstart=http://example.com/myguest.ks </cmdline>
</os>
<memory>131072</memory>
<vcpu>1</vcpu>
<devices>
<disk type='file'>
<source file='/var/lib/xen/images/fc4.img'/>
<target dev='sda1'/>
</disk>
<interface type='bridge'>
<source bridge='xenbr0'/>
<mac address='aa:00:00:00:00:11'/>
<script path='/etc/xen/scripts/vif-bridge'/>
</interface>
<graphics type='vnc' port='-1'/>
<console tty='/dev/pts/5'/>
</devices>
</domain></pre>
<h3>Fullyvirtualized guest BIOS boot</h3>
<p>
Fullyvirtualized guests use the emulated BIOS to boot off the primary
harddisk, CDROM or Network PXE ROM.
</p>
<pre><domain type='xen' id='3'>
<name>fv0</name>
<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
<os>
<type>hvm</type>
<loader>/usr/lib/xen/boot/hvmloader</loader>
<boot dev='hd'/>
</os>
<memory>524288</memory>
<vcpu>1</vcpu>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<features>
<pae/>
<acpi/>
<apic/>
</features>
<clock sync="localtime"/>
<devices>
<emulator>/usr/lib/xen/bin/qemu-dm</emulator>
<interface type='bridge'>
<source bridge='xenbr0'/>
<mac address='00:16:3e:5d:c7:9e'/>
<script path='vif-bridge'/>
</interface>
<disk type='file'>
<source file='/var/lib/xen/images/fv0'/>
<target dev='hda'/>
</disk>
<disk type='file' device='cdrom'>
<source file='/var/lib/xen/images/fc5-x86_64-boot.iso'/>
<target dev='hdc'/>
<readonly/>
</disk>
<disk type='file' device='floppy'>
<source file='/root/fd.img'/>
<target dev='fda'/>
</disk>
<graphics type='vnc' port='5904'/>
</devices>
</domain></pre>
<h3>Fullyvirtualized guest direct kernel boot</h3>
<p>
With Xen 3.2.0 or later it is possible to bypass the BIOS and directly
boot a Linux kernel and initrd as a fullyvirtualized domain. This allows
for complete automation of OS installation, for example using the Anaconda
kickstart support.
</p>
<pre><domain type='xen' id='3'>
<name>fv0</name>
<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
<os>
<type>hvm</type>
<loader>/usr/lib/xen/boot/hvmloader</loader>
<kernel>/var/lib/xen/install/vmlinuz-fedora8-x86_64</kernel>
<initrd>/var/lib/xen/install/initrd-vmlinuz-fedora8-x86_64</initrd>
<cmdline> kickstart=http://example.com/myguest.ks </cmdline>
</os>
<memory>524288</memory>
<vcpu>1</vcpu>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<features>
<pae/>
<acpi/>
<apic/>
</features>
<clock sync="localtime"/>
<devices>
<emulator>/usr/lib/xen/bin/qemu-dm</emulator>
<interface type='bridge'>
<source bridge='xenbr0'/>
<mac address='00:16:3e:5d:c7:9e'/>
<script path='vif-bridge'/>
</interface>
<disk type='file'>
<source file='/var/lib/xen/images/fv0'/>
<target dev='hda'/>
</disk>
<disk type='file' device='cdrom'>
<source file='/var/lib/xen/images/fc5-x86_64-boot.iso'/>
<target dev='hdc'/>
<readonly/>
</disk>
<disk type='file' device='floppy'>
<source file='/root/fd.img'/>
<target dev='fda'/>
</disk>
<graphics type='vnc' port='5904'/>
</devices>
</domain></pre>
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