libvirt/docs/format.html
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<?xml version="1.0" encoding="ISO-8859-1"?>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /><link rel="stylesheet" type="text/css" href="libvirt.css" /><link rel="SHORTCUT ICON" href="/32favicon.png" /><title>XML Format</title></head><body><div id="container"><div id="intro"><div id="adjustments"></div><div id="pageHeader"></div><div id="content2"><h1 class="style1">XML Format</h1><p>The library use an XML format to describe domains, as input to <a href="html/libvirt-libvirt.html#virDomainCreateLinux">virDomainCreateLinux()</a>
and as the output of <a href="html/libvirt-libvirt.html#virDomainGetXMLDesc">virDomainGetXMLDesc()</a>,
the following is an example of the format as returned by the shell command
<code>virsh xmldump fc4</code> , where fc4 was one of the running domains:</p><pre>&lt;domain type='xen' <span style="color: #0071FF; background-color: #FFFFFF">id='18'</span>&gt;
&lt;name&gt;fc4&lt;/name&gt;
<span style="color: #00B200; background-color: #FFFFFF">&lt;os&gt;
&lt;type&gt;linux&lt;/type&gt;
&lt;kernel&gt;/boot/vmlinuz-2.6.15-1.43_FC5guest&lt;/kernel&gt;
&lt;initrd&gt;/boot/initrd-2.6.15-1.43_FC5guest.img&lt;/initrd&gt;
&lt;root&gt;/dev/sda1&lt;/root&gt;
&lt;cmdline&gt; ro selinux=0 3&lt;/cmdline&gt;
&lt;/os&gt;</span>
&lt;memory&gt;131072&lt;/memory&gt;
&lt;vcpu&gt;1&lt;/vcpu&gt;
&lt;devices&gt;
<span style="color: #FF0080; background-color: #FFFFFF">&lt;disk type='file'&gt;
&lt;source file='/u/fc4.img'/&gt;
&lt;target dev='sda1'/&gt;
&lt;/disk&gt;</span>
<span style="color: #0000FF; background-color: #FFFFFF">&lt;interface type='bridge'&gt;
&lt;source bridge='xenbr0'/&gt;
&lt;mac address='</span><span style="color: #0000FF; background-color: #FFFFFF"></span><span style="color: #0000FF; background-color: #FFFFFF">aa:00:00:00:00:11'/&gt;
&lt;script path='/etc/xen/scripts/vif-bridge'/&gt;
&lt;/interface&gt;</span>
&lt;/devices&gt;
&lt;/domain&gt;</pre><p>The root element must be called <code>domain</code> with no namespace, the
<code>type</code> attribute indicates the kind of hypervisor used, 'xen' is
the default value. The <code>id</code> attribute gives the domain id at
runtime (not however that this may change, for example if the domain is saved
to disk and restored). The domain has a few children whose order is not
significant:</p><ul><li>name: the domain name, preferably ASCII based</li>
<li>memory: the maximum memory allocated to the domain in kilobytes</li>
<li>vcpu: the number of virtual cpu configured for the domain</li>
<li>os: a block describing the Operating System, its content will be
dependant on the OS type
<ul><li>type: indicate the OS type, always linux at this point</li>
<li>kernel: path to the kernel on the Domain 0 filesystem</li>
<li>initrd: an optional path for the init ramdisk on the Domain 0
filesystem</li>
<li>cmdline: optional command line to the kernel</li>
<li>root: the root filesystem from the guest viewpoint, it may be
passed as part of the cmdline content too</li>
</ul></li>
<li>devices: a list of <code>disk</code> and <code>interface</code>
descriptions in no special order</li>
</ul><p>The format of the devices and their type may grow over time, but the
following should be sufficient for basic use:</p><p>A disk device indicates a block device, it can have two values for the
type attribute either 'file' or 'block' corresponding to the 2 options
availble at the Xen layer. It has two mandatory children, and one optional
one in no specific order:</p><ul><li>source with a file attribute containing the path in Domain 0 to the
file or a dev attribute if using a block device, containing the device
name ('hda5' or '/dev/hda5')</li>
<li>target indicates in a dev attribute the device where it is mapped in
the guest</li>
<li>readonly an optional empty element indicating the device is
read-only</li>
</ul><p>An interface element describes a network device mapped on the guest, it
also has a type whose value is currently 'bridge', it also have a number of
children in no specific order:</p><ul><li>source: indicating the bridge name</li>
<li>mac: the optional mac address provided in the address attribute</li>
<li>ip: the optional IP address provided in the address attribute</li>
<li>script: the script used to bridge the interfcae in the Domain 0</li>
<li>target: and optional target indicating the device name.</li>
</ul><p>Life cycle actions for the domain can also be expressed in the XML format,
they drive what should be happening if the domain crashes, is rebooted or is
poweroff. There is various actions possible when this happen:</p><ul><li>destroy: The domain is cleaned up (that's the default normal processing
in Xen)</li>
<li>restart: A new domain is started in place of the old one with the same
configuration parameters</li>
<li>preserve: The domain will remain in memory until it is destroyed
manually, it won't be running but allows for post-mortem debugging</li>
<li>rename-restart: a variant of the previous one but where the old domain
is renamed before being saved to allow a restart</li>
</ul><p>The following could be used for a Xen production system:</p><pre>&lt;domain&gt;
...
&lt;on_reboot&gt;restart&lt;/on_reboot&gt;
&lt;on_poweroff&gt;destroy&lt;/on_poweroff&gt;
&lt;on_crash&gt;rename-restart&lt;/on_crash&gt;
...
&lt;/domain&gt;</pre><p>While the format may be extended in various ways as support for more
hypervisor types and features are added, it is expected that this core subset
will remain functional in spite of the evolution of the library.</p></div></div><div class="linkList2"><div class="llinks2"><h3 class="links2"><span>main menu</span></h3><ul><li><a href="index.html">Home</a></li><li><a href="news.html">Releases</a></li><li><a href="intro.html">Introduction</a></li><li><a href="architecture.html">libvirt architecture</a></li><li><a href="downloads.html">Downloads</a></li><li><a href="format.html">XML Format</a></li><li><a href="python.html">Binding for Python</a></li><li><a href="errors.html">Handling of errors</a></li><li><a href="FAQ.html">FAQ</a></li><li><a href="bugs.html">Reporting bugs and getting help</a></li><li><a href="html/index.html">API Menu</a></li><li><a href="examples/index.html">C code examples</a></li><li><a href="ChangeLog.html">Recent Changes</a></li></ul></div><div class="llinks2"><h3 class="links2"><span>related links</span></h3><ul><li><a href="https://www.redhat.com/archives/libvir-list/">Mail archive</a></li><li><a href="https://bugzilla.redhat.com/bugzilla/buglist.cgi?product=Fedora+Core&amp;component=libvirt&amp;bug_status=NEW&amp;bug_status=ASSIGNED&amp;bug_status=REOPENED&amp;bug_status=MODIFIED&amp;short_desc_type=allwordssubstr&amp;short_desc=&amp;long_desc_type=allwordssubstr">Open bugs</a></li><li><a href="http://search.cpan.org/~danberr/Sys-Virt-0.1.0/">Perl bindings</a></li><li><a href="http://www.cl.cam.ac.uk/Research/SRG/netos/xen/index.html">Xen project</a></li><li><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="12" value="Search..." /><input name="submit" type="submit" value="Go" /></form></li><li><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-90x34.gif" alt="Made with Libxml2 Logo" /></a></li></ul><p class="credits">Graphics and design by <a href="mail:dfong@redhat.com">Diana Fong</a></p></div></div><div id="bottom"><p class="p1"></p></div></div></body></html>