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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>
      <li>
        <strong>libxl</strong>: Starting with Xen 4.2, the legacy XenD/xm
        toolstack is deprecated in favor of libxl, also commonly called
        libxenlight.  libvirt supports this new Xen toolstack via the
        libxl driver.  If XenD is enabled, the legacy xen driver consisting
        of the above mentioned channels will be used.  If XenD is disabled,
        the libxl driver will be used.
      </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 connection 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
&lt;domain type='xen'&gt;
  &lt;name&gt;rhel5pv&lt;/name&gt;
  &lt;uuid&gt;8f07fe28-753f-2729-d76d-bdbd892f949a&lt;/uuid&gt;
  &lt;memory&gt;2560000&lt;/memory&gt;
  &lt;currentMemory&gt;307200&lt;/currentMemory&gt;
  &lt;vcpu&gt;4&lt;/vcpu&gt;
  &lt;bootloader&gt;/usr/bin/pygrub&lt;/bootloader&gt;
  &lt;os&gt;
    &lt;type arch='x86_64' machine='xenpv'&gt;linux&lt;/type&gt;
  &lt;/os&gt;
  &lt;clock offset='utc'/&gt;
  &lt;on_poweroff&gt;destroy&lt;/on_poweroff&gt;
  &lt;on_reboot&gt;restart&lt;/on_reboot&gt;
  &lt;on_crash&gt;restart&lt;/on_crash&gt;
  &lt;devices&gt;
    &lt;disk type='file' device='disk'&gt;
      &lt;driver name='tap' type='aio'/&gt;
      &lt;source file='/var/lib/xen/images/rhel5pv.img'/&gt;
      &lt;target dev='xvda' bus='xen'/&gt;
    &lt;/disk&gt;
    &lt;disk type='file' device='disk'&gt;
      &lt;driver name='tap' type='qcow'/&gt;
      &lt;source file='/root/qcow1-xen.img'/&gt;
      &lt;target dev='xvdd' bus='xen'/&gt;
    &lt;/disk&gt;
    &lt;interface type='bridge'&gt;
      &lt;mac address='00:16:3e:60:36:ba'/&gt;
      &lt;source bridge='xenbr0'/&gt;
    &lt;/interface&gt;
    &lt;console type='pty'&gt;
      &lt;target port='0'/&gt;
    &lt;/console&gt;
    &lt;input type='mouse' bus='xen'/&gt;
    &lt;graphics type='vnc' port='-1' autoport='yes' listen='0.0.0.0'/&gt;
  &lt;/devices&gt;
&lt;/domain&gt;</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>&lt;domain type='xen' &gt;
  &lt;name&gt;fc8&lt;/name&gt;
  &lt;bootloader&gt;/usr/bin/pygrub&lt;/bootloader&gt;
  &lt;os&gt;
    &lt;type&gt;linux&lt;/type&gt;
  &lt;/os&gt;
  &lt;memory&gt;131072&lt;/memory&gt;
  &lt;vcpu&gt;1&lt;/vcpu&gt;
  &lt;devices&gt;
    &lt;disk type='file'&gt;
      &lt;source file='/var/lib/xen/images/fc4.img'/&gt;
      &lt;target dev='sda1'/&gt;
    &lt;/disk&gt;
    &lt;interface type='bridge'&gt;
      &lt;source bridge='xenbr0'/&gt;
      &lt;mac address='aa:00:00:00:00:11'/&gt;
      &lt;script path='/etc/xen/scripts/vif-bridge'/&gt;
    &lt;/interface&gt;
    &lt;console tty='/dev/pts/5'/&gt;
  &lt;/devices&gt;
&lt;/domain&gt;</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>&lt;domain type='xen' &gt;
  &lt;name&gt;fc8&lt;/name&gt;
  &lt;os&gt;
    &lt;type&gt;linux&lt;/type&gt;
    &lt;kernel&gt;/var/lib/xen/install/vmlinuz-fedora8-x86_64&lt;/kernel&gt;
    &lt;initrd&gt;/var/lib/xen/install/initrd-vmlinuz-fedora8-x86_64&lt;/initrd&gt;
    &lt;cmdline&gt; kickstart=http://example.com/myguest.ks &lt;/cmdline&gt;
  &lt;/os&gt;
  &lt;memory&gt;131072&lt;/memory&gt;
  &lt;vcpu&gt;1&lt;/vcpu&gt;
  &lt;devices&gt;
    &lt;disk type='file'&gt;
      &lt;source file='/var/lib/xen/images/fc4.img'/&gt;
      &lt;target dev='sda1'/&gt;
    &lt;/disk&gt;
    &lt;interface type='bridge'&gt;
      &lt;source bridge='xenbr0'/&gt;
      &lt;mac address='aa:00:00:00:00:11'/&gt;
      &lt;script path='/etc/xen/scripts/vif-bridge'/&gt;
    &lt;/interface&gt;
    &lt;graphics type='vnc' port='-1'/&gt;
    &lt;console tty='/dev/pts/5'/&gt;
  &lt;/devices&gt;
&lt;/domain&gt;</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>&lt;domain type='xen' id='3'&gt;
  &lt;name&gt;fv0&lt;/name&gt;
  &lt;uuid&gt;4dea22b31d52d8f32516782e98ab3fa0&lt;/uuid&gt;
  &lt;os&gt;
    &lt;type&gt;hvm&lt;/type&gt;
    &lt;loader&gt;/usr/lib/xen/boot/hvmloader&lt;/loader&gt;
    &lt;boot dev='hd'/&gt;
  &lt;/os&gt;
  &lt;memory&gt;524288&lt;/memory&gt;
  &lt;vcpu&gt;1&lt;/vcpu&gt;
  &lt;on_poweroff&gt;destroy&lt;/on_poweroff&gt;
  &lt;on_reboot&gt;restart&lt;/on_reboot&gt;
  &lt;on_crash&gt;restart&lt;/on_crash&gt;
  &lt;features&gt;
    &lt;pae/&gt;
    &lt;acpi/&gt;
    &lt;apic/&gt;
  &lt;/features&gt;
  &lt;clock sync="localtime"/&gt;
  &lt;devices&gt;
    &lt;emulator&gt;/usr/lib/xen/bin/qemu-dm&lt;/emulator&gt;
    &lt;interface type='bridge'&gt;
      &lt;source bridge='xenbr0'/&gt;
      &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
      &lt;script path='vif-bridge'/&gt;
    &lt;/interface&gt;
    &lt;disk type='file'&gt;
      &lt;source file='/var/lib/xen/images/fv0'/&gt;
      &lt;target dev='hda'/&gt;
    &lt;/disk&gt;
    &lt;disk type='file' device='cdrom'&gt;
      &lt;source file='/var/lib/xen/images/fc5-x86_64-boot.iso'/&gt;
      &lt;target dev='hdc'/&gt;
      &lt;readonly/&gt;
    &lt;/disk&gt;
    &lt;disk type='file' device='floppy'&gt;
      &lt;source file='/root/fd.img'/&gt;
      &lt;target dev='fda'/&gt;
    &lt;/disk&gt;
    &lt;graphics type='vnc' port='5904'/&gt;
  &lt;/devices&gt;
&lt;/domain&gt;</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>&lt;domain type='xen' id='3'&gt;
  &lt;name&gt;fv0&lt;/name&gt;
  &lt;uuid&gt;4dea22b31d52d8f32516782e98ab3fa0&lt;/uuid&gt;
  &lt;os&gt;
    &lt;type&gt;hvm&lt;/type&gt;
    &lt;loader&gt;/usr/lib/xen/boot/hvmloader&lt;/loader&gt;
    &lt;kernel&gt;/var/lib/xen/install/vmlinuz-fedora8-x86_64&lt;/kernel&gt;
    &lt;initrd&gt;/var/lib/xen/install/initrd-vmlinuz-fedora8-x86_64&lt;/initrd&gt;
    &lt;cmdline&gt; kickstart=http://example.com/myguest.ks &lt;/cmdline&gt;
  &lt;/os&gt;
  &lt;memory&gt;524288&lt;/memory&gt;
  &lt;vcpu&gt;1&lt;/vcpu&gt;
  &lt;on_poweroff&gt;destroy&lt;/on_poweroff&gt;
  &lt;on_reboot&gt;restart&lt;/on_reboot&gt;
  &lt;on_crash&gt;restart&lt;/on_crash&gt;
  &lt;features&gt;
    &lt;pae/&gt;
    &lt;acpi/&gt;
    &lt;apic/&gt;
  &lt;/features&gt;
  &lt;clock sync="localtime"/&gt;
  &lt;devices&gt;
    &lt;emulator&gt;/usr/lib/xen/bin/qemu-dm&lt;/emulator&gt;
    &lt;interface type='bridge'&gt;
      &lt;source bridge='xenbr0'/&gt;
      &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
      &lt;script path='vif-bridge'/&gt;
    &lt;/interface&gt;
    &lt;disk type='file'&gt;
      &lt;source file='/var/lib/xen/images/fv0'/&gt;
      &lt;target dev='hda'/&gt;
    &lt;/disk&gt;
    &lt;disk type='file' device='cdrom'&gt;
      &lt;source file='/var/lib/xen/images/fc5-x86_64-boot.iso'/&gt;
      &lt;target dev='hdc'/&gt;
      &lt;readonly/&gt;
    &lt;/disk&gt;
    &lt;disk type='file' device='floppy'&gt;
      &lt;source file='/root/fd.img'/&gt;
      &lt;target dev='fda'/&gt;
    &lt;/disk&gt;
    &lt;graphics type='vnc' port='5904'/&gt;
  &lt;/devices&gt;
&lt;/domain&gt;</pre>

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