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11 KiB
HTML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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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>This section describes the XML format used to represent domains, there are
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variations on the format based on the kind of domains run and the options
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used to launch them:</p><p><a href="#Normal1">Normal paravirtualized Xen domains</a></p><p><a href="#Fully1">Fully virtualized Xen domains</a></p><p>The formats try as much as possible to follow the same structure and reuse
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elements and attributes where it makes sense.</p><h3 id="Normal"><a name="Normal1" id="Normal1">Normal paravirtualized Xen
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guests</a>:</h3><p>The library use an XML format to describe domains, as input to <a href="html/libvirt-libvirt.html#virDomainCreateLinux">virDomainCreateLinux()</a>
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and as the output of <a href="html/libvirt-libvirt.html#virDomainGetXMLDesc">virDomainGetXMLDesc()</a>,
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the following is an example of the format as returned by the shell command
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<code>virsh xmldump fc4</code> , where fc4 was one of the running domains:</p><pre><domain type='xen' <span style="color: #0071FF; background-color: #FFFFFF">id='18'</span>>
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<name>fc4</name>
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<span style="color: #00B200; background-color: #FFFFFF"><os>
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<type>linux</type>
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<kernel>/boot/vmlinuz-2.6.15-1.43_FC5guest</kernel>
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<initrd>/boot/initrd-2.6.15-1.43_FC5guest.img</initrd>
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<root>/dev/sda1</root>
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<cmdline> ro selinux=0 3</cmdline>
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</os></span>
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<memory>131072</memory>
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<vcpu>1</vcpu>
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<devices>
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<span style="color: #FF0080; background-color: #FFFFFF"><disk type='file'>
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<source file='/u/fc4.img'/>
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<target dev='sda1'/>
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</disk></span>
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<span style="color: #0000FF; background-color: #FFFFFF"><interface type='bridge'>
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<source bridge='xenbr0'/>
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<mac address='</span><span style="color: #0000FF; background-color: #FFFFFF"></span><span style="color: #0000FF; background-color: #FFFFFF">aa:00:00:00:00:11'/>
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<script path='/etc/xen/scripts/vif-bridge'/>
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</interface></span>
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</devices>
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</domain></pre><p>The root element must be called <code>domain</code> with no namespace, the
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<code>type</code> attribute indicates the kind of hypervisor used, 'xen' is
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the default value. The <code>id</code> attribute gives the domain id at
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runtime (not however that this may change, for example if the domain is saved
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to disk and restored). The domain has a few children whose order is not
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significant:</p><ul><li>name: the domain name, preferably ASCII based</li>
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<li>memory: the maximum memory allocated to the domain in kilobytes</li>
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<li>vcpu: the number of virtual cpu configured for the domain</li>
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<li>os: a block describing the Operating System, its content will be
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dependant on the OS type
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<ul><li>type: indicate the OS type, always linux at this point</li>
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<li>kernel: path to the kernel on the Domain 0 filesystem</li>
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<li>initrd: an optional path for the init ramdisk on the Domain 0
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filesystem</li>
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<li>cmdline: optional command line to the kernel</li>
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<li>root: the root filesystem from the guest viewpoint, it may be
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passed as part of the cmdline content too</li>
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</ul></li>
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<li>devices: a list of <code>disk</code> and <code>interface</code>
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descriptions in no special order</li>
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</ul><p>The format of the devices and their type may grow over time, but the
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following should be sufficient for basic use:</p><p>A disk device indicates a block device, it can have two values for the
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type attribute either 'file' or 'block' corresponding to the 2 options
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availble at the Xen layer. It has two mandatory children, and one optional
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one in no specific order:</p><ul><li>source with a file attribute containing the path in Domain 0 to the
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file or a dev attribute if using a block device, containing the device
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name ('hda5' or '/dev/hda5')</li>
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<li>target indicates in a dev attribute the device where it is mapped in
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the guest</li>
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<li>readonly an optional empty element indicating the device is
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read-only</li>
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</ul><p>An interface element describes a network device mapped on the guest, it
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also has a type whose value is currently 'bridge', it also have a number of
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children in no specific order:</p><ul><li>source: indicating the bridge name</li>
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<li>mac: the optional mac address provided in the address attribute</li>
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<li>ip: the optional IP address provided in the address attribute</li>
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<li>script: the script used to bridge the interfcae in the Domain 0</li>
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<li>target: and optional target indicating the device name.</li>
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</ul><p>Life cycle actions for the domain can also be expressed in the XML format,
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they drive what should be happening if the domain crashes, is rebooted or is
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poweroff. There is various actions possible when this happen:</p><ul><li>destroy: The domain is cleaned up (that's the default normal processing
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in Xen)</li>
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<li>restart: A new domain is started in place of the old one with the same
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configuration parameters</li>
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<li>preserve: The domain will remain in memory until it is destroyed
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manually, it won't be running but allows for post-mortem debugging</li>
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<li>rename-restart: a variant of the previous one but where the old domain
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is renamed before being saved to allow a restart</li>
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</ul><p>The following could be used for a Xen production system:</p><pre><domain>
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...
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<on_reboot>restart</on_reboot>
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<on_poweroff>destroy</on_poweroff>
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<on_crash>rename-restart</on_crash>
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...
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</domain></pre><p>While the format may be extended in various ways as support for more
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hypervisor types and features are added, it is expected that this core subset
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will remain functional in spite of the evolution of the library.</p><h3 id="Fully"><a name="Fully1" id="Fully1">Fully virtualized guests</a>
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(added in 0.1.3):</h3><p>Here is an example of a domain description used to start a fully
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virtualized (a.k.a. HVM) Xen domain. This requires hardware virtualization
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support at the processor level but allows to run unmodified operating
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systems:</p><pre><domain type='xen' id='3'>
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<name>fv0</name>
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<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
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<os>
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<span style="color: #0000E5; background-color: #FFFFFF"><type>hvm</type></span>
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<span style="color: #0000E5; background-color: #FFFFFF"><loader>/usr/lib/xen/boot/hvmloader</loader></span>
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<span style="color: #0000E5; background-color: #FFFFFF"><boot dev='hda'/></span>
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</os>
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<memory>524288</memory>
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<vcpu>1</vcpu>
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<on_poweroff>destroy</on_poweroff>
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<on_reboot>restart</on_reboot>
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<on_crash>restart</on_crash>
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<devices>
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<span style="color: #0000E5; background-color: #FFFFFF"><emulator>/usr/lib/xen/bin/qemu-dm</emulator></span>
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<interface type='bridge'>
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<source bridge='xenbr0'/>
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<mac address='00:16:3e:5d:c7:9e'/>
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<script path='vif-bridge'/>
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</interface>
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<disk type='file'>
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<source file='/root/fv0'/>
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<target <span style="color: #0000E5; background-color: #FFFFFF">dev='ioemu:hda'</span>/>
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</disk>
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<span style="color: #0000E5; background-color: #FFFFFF"><graphics type='vnc'/></span>
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</devices>
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</domain></pre><p>There is a few things to notice specifically for HVM domains:</p><ul><li>the <os> block description is very different, first it indicates
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that the type is 'hvm' for hardware virtualization, then instead of a
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kernel, boot and command line arguments, it points to an os boot loader
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which will extract the boot informations from the boot device specified
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in a separate boot element</li>
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<li>the <devices> section includes an emulator entry pointing to an
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additional program in charge of emulating the devices</li>
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<li>the disk entry indicates in the dev target section that the emulation
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for the drive is the first IDE disk device hda</li>
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<li>the <devices> section also include at least one entry for the
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graphic device used to render the os. Currently there is just 2 types
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possible 'vnc' or 'sdl'</li>
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</ul><p>It is likely that the HVM description gets additional optional elements
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and attributes as the support for fully virtualized domain expands,
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especially for the variety of devices emulated and the graphic support
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options offered.</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&component=libvirt&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&bug_status=MODIFIED&short_desc_type=allwordssubstr&short_desc=&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>
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