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243 lines
14 KiB
HTML
243 lines
14 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<!--
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This file is autogenerated from api.html.in
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Do not edit this file. Changes will be lost.
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-->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
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<link rel="stylesheet" type="text/css" href="main.css" />
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<link rel="SHORTCUT ICON" href="32favicon.png" />
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<title>libvirt: The libvirt API concepts</title>
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<meta name="description" content="libvirt, virtualization, virtualization API" />
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</head>
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<body>
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<div id="header">
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<div id="headerLogo"></div>
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<div id="headerSearch">
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<form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><div>
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<input id="query" name="query" type="text" size="12" value="" />
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<input id="submit" name="submit" type="submit" value="Search" />
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</div></form>
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<div id="body">
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<div id="menu">
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<ul class="l0"><li>
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<div>
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<a title="Front page of the libvirt website" class="inactive" href="index.html">Home</a>
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</div>
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</li><li>
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<div>
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<a title="Details of new features and bugs fixed in each release" class="inactive" href="news.html">News</a>
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</div>
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</li><li>
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<div>
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<a title="Get the latest source releases, binary builds and get access to the source repository" class="inactive" href="downloads.html">Downloads</a>
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</div>
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</li><li>
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<div>
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<a title="Information for users, administrators and developers" class="active" href="docs.html">Documentation</a>
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<ul class="l1"><li>
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<div>
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<a title="Information about deploying and using libvirt" class="inactive" href="deployment.html">Deployment</a>
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</div>
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</li><li>
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<div>
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<a title="Overview of the logical subsystems in the libvirt API" class="active" href="intro.html">Architecture</a>
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<ul class="l2"><li>
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<div>
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<a title="Terminology and goals of libvirt API" class="inactive" href="goals.html">Goals</a>
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</div>
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</li><li>
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<div>
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<span class="active">API concepts</span>
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</div>
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</li><li>
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<div>
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<a title="Managing virtual machines" class="inactive" href="archdomain.html">Domains</a>
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</div>
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</li><li>
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<div>
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<a title="Providing isolated networks and NAT based network connectivity" class="inactive" href="archnetwork.html">Network</a>
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</div>
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</li><li>
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<div>
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<a title="Managing storage pools and volumes" class="inactive" href="archstorage.html">Storage</a>
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</div>
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</li><li>
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<div>
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<a title="Enumerating host node devices" class="inactive" href="archnode.html">Node Devices</a>
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</div>
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</li></ul>
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</div>
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</li><li>
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<div>
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<a title="Description of the XML formats used in libvirt" class="inactive" href="format.html">XML format</a>
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</div>
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</li><li>
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<div>
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<a title="Hypervisor specific driver information" class="inactive" href="drivers.html">Drivers</a>
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</div>
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</li><li>
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<div>
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<a title="Reference manual for the C public API" class="inactive" href="html/index.html">API reference</a>
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</div>
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</li><li>
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<div>
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<a title="Bindings of the libvirt API for other languages" class="inactive" href="bindings.html">Language bindings</a>
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</div>
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</li></ul>
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</div>
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</li><li>
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<div>
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<a title="User contributed content" class="inactive" href="http://wiki.libvirt.org">Wiki</a>
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</div>
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</li><li>
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<div>
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<a title="Frequently asked questions" class="inactive" href="FAQ.html">FAQ</a>
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</div>
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</li><li>
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<div>
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<a title="How and where to report bugs and request features" class="inactive" href="bugs.html">Bug reports</a>
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</div>
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</li><li>
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<div>
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<a title="How to contact the developers via email and IRC" class="inactive" href="contact.html">Contact</a>
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</div>
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</li><li>
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<div>
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<a title="Miscellaneous links of interest related to libvirt" class="inactive" href="relatedlinks.html">Related Links</a>
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</div>
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</li><li>
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<div>
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<a title="Overview of all content on the website" class="inactive" href="sitemap.html">Sitemap</a>
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</div>
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</li></ul>
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</div>
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<div id="content">
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<h1>The libvirt API concepts</h1>
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<p> This page describes the main principles and architecture choices
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behind the definition of the libvirt API:
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</p>
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<ul><li>
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<a href="#Objects">Objects exposed</a>
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</li><li>
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<a href="#Functions">Functions and naming conventions</a>
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</li><li>
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<a href="#Driver">The drivers</a>
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</li><li>
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<a href="#Remote">Daemon and remote access</a>
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</li></ul>
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<h2>
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<a name="Objects" id="Objects">Objects exposed</a>
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</h2>
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<p> As defined in the <a href="goals.html">goals section</a>, libvirt
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API need to expose all the resources needed to manage the virtualization
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support of recent operating systems. The first object manipulated though
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the API is <code>virConnectPtr</code> which represent a connection to
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an hypervisor. Any application using libvirt is likely to start using the
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API by calling one of <a href="html/libvirt-libvirt.html#virConnectOpen">the virConnectOpen functions</a>. You will note that those functions take
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a name argument which is actually an URI to select the right hypervisor to
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open, this is needed to allow remote connections and also select between
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different possible hypervisors (for example on a Linux system it may be
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possible to use both KVM and LinuxContainers on the same node). A NULL
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name will default to a preselected hypervisor but it's probably not a
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wise thing to do in most cases. See the <a href="uri.html">connection
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URI</a> page for a full descriptions of the values allowed.</p>
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<p>
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</p>
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<p> Once the application obtained a <a href="html/libvirt-libvirt.html#virConnectPtr"><code>virConnectPtr</code></a>
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connection to the
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hypervisor it can then use it to manage domains and related resources
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available for virtualization like storage and networking. All those are
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exposed as first class objects, and connected to the hypervisor connection
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(and the node or cluster where it is available).</p>
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<p class="image">
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<img alt="first class objects exposed by the API" src="libvirt-object-model.png" /></p>
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<p> The figure above shows the five main objects exported by the API:</p>
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<ul><li>virConnectPtr: represent a connection to an hypervisor.</li><li>virDomainPtr: represent one domain either active or defined (i.e.
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existing as permanent config file and storage but not currently running
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on that node). The function <a href="html/libvirt-libvirt.html#virConnectListDomains"><code>virConnectListDomains</code></a>
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allows to list all the IDs for the domains active on this hypervisor.</li><li>virNetworkPtr: represent one network either active or defined (i.e.
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existing as permanent config file and storage but not currently activated.
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The function <a href="html/libvirt-libvirt.html#virConnectListNetworks"><code>virConnectListNetworks</code></a>
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allows to list all the virtualization networks actived on this node.</li><li>virStorageVolPtr: represent one storage volume, usually this is used
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as a block device available to one of the domains. The function
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<a href="html/libvirt-libvirt.html#virStorageVolLookupByPath"><code>virStorageVolLookupByPath</code></a> allows to find
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the object based on its path on the node.</li><li>virStoragePoolPtr: represent a storage pool, i.e. a logical area
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which can be used to allocate and store storage volumes. The function
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<a href="html/libvirt-libvirt.html#virStoragePoolLookupByVolume"><code>virStoragePoolLookupByVolume</code></a> allows to find
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the storage pool containing a given storage volume.</li></ul>
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<p> Most object manipulated by the library can also be represented using
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XML descriptions. This is used primarily to create those object, but is
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also helpful to modify or save their description back.</p>
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<p> Domains, network and storage pools can be either <code>active</code>
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i.e. either running or available for immediate use, or
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<code>defined</code> in which case they are inactive but there is
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a permanent definition available in the system for them. Based on this
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thay can be activated dynamically in order to be used.</p>
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<p> Most kind of object can also be named in various ways:</p>
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<p>
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</p>
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<ul><li>by their <code>name</code>, an user friendly identifier but
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whose unicity cannot be garanteed between two nodes.</li><li>by their <code>ID</code>, which is a runtime unique identifier
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provided by the hypervisor for one given activation of the object,
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but it becomes invalid once the resource is deactivated.</li><li>by their <code>UUID</code>, a 16 bytes unique identifier
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as defined in <a href="http://www.ietf.org/rfc/rfc4122.txt">RFC 4122</a>,
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which is garanteed to be unique for long term usage and across a
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set of nodes.</li></ul>
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<h2>
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<a name="Functions" id="Functions">Functions and naming
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conventions</a>
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</h2>
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<p> The naming of the functions present in the library is usually
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made of a prefix describing the object associated to the function
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and a verb describing the action on that object.</p>
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<p> For each first class object you will find apis
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for the following actions:</p>
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<ul><li><b>Lookup</b>:...LookupByName,
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</li><li><b>Enumeration</b>:virConnectList... and virConnectNumOf...:
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those are used to enumerate a set of object available to an given
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hypervisor connection like:
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<a href="html/libvirt-libvirt.html#virConnectListDomains"><code>virConnectListDomains</code></a>,
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<a href="html/libvirt-libvirt.html#virConnectNumOfDomains"><code>virConnectNumOfDomains</code></a>,
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<a href="html/libvirt-libvirt.html#virConnectListNetworks"><code>virConnectListNetworks</code></a>,
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<a href="html/libvirt-libvirt.html#virConnectListStoragePools"><code>virConnectListStoragePools</code></a>, etc.</li><li><b>Description</b>: ...GetInfo: those are generic accessor providing
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a set of informations about an object, they are
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<a href="html/libvirt-libvirt.html#virNodeGetInfo"><code>virNodeGetInfo</code></a>,
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<a href="html/libvirt-libvirt.html#virDomainGetInfo"><code>virDomainGetInfo</code></a>,
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<a href="html/libvirt-libvirt.html#virStoragePoolGetInfo"><code>virStoragePoolGetInfo</code></a>,
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<a href="html/libvirt-libvirt.html#virStorageVolGetInfo"><code>virStorageVolGetInfo</code></a>.</li><li><b>Accessors</b>: ...Get... and ...Set...: those are more specific
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accessors to query or modify the given object, like
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<a href="html/libvirt-libvirt.html#virConnectGetType"><code>virConnectGetType</code></a>,
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<a href="html/libvirt-libvirt.html#virDomainGetMaxMemory"><code>virDomainGetMaxMemory</code></a>,
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<a href="html/libvirt-libvirt.html#virDomainSetMemory"><code>virDomainSetMemory</code></a>,
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<a href="html/libvirt-libvirt.html#virDomainGetVcpus"><code>virDomainGetVcpus</code></a>,
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<a href="html/libvirt-libvirt.html#virStoragePoolSetAutostart"><code>virStoragePoolSetAutostart</code></a>,
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<a href="html/libvirt-libvirt.html#virNetworkGetBridgeName"><code>virNetworkGetBridgeName</code></a>, etc.</li><li><b>Creation</b>: </li><li><b>Destruction</b>: ... </li></ul>
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<p> For more in-depth details of the storage related APIs see
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<a href="storage.html">the storage management page</a>,
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</p>
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<h2>
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<a name="Driver" id="Driver">The libvirt drivers</a>
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</h2>
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<p></p>
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<p class="image">
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<img alt="The libvirt driver architecture" src="libvirt-driver-arch.png" /></p>
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<h2>
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<a name="Remote" id="Remote">Daemon and remote access</a>
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</h2>
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<p></p>
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<p class="image">
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<img alt="The libvirt daemon and remote architecture" src="libvirt-daemon-arch.png" /></p>
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</div>
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</div>
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<div id="footer">
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<p id="sponsor">
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Sponsored by:<br /><a href="http://et.redhat.com/"><img src="et.png" alt="Project sponsored by Red Hat Emerging Technology" /></a></p>
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</div>
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</body>
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</html>
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