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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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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:</p>
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<ul id="toc"></ul>
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<h2><a id="Objects">Objects Exposed</a></h2>
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<p> As defined in the <a href="goals.html">goals section</a>, the libvirt
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API is designed to expose all the resources needed to manage the
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virtualization support of recent operating systems. The first object
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manipulated through the API is the <code>virConnectPtr</code>, which
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represents the connection to a hypervisor. Any application using libvirt
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is likely to start using the
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API by calling one of <a href="html/libvirt-libvirt-host.html#virConnectOpen"
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>the virConnectOpen functions</a>. You will note that those functions take
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a name argument which is actually a <a href="uri.html">connection URI</a>
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to select the right hypervisor to open.
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A URI 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> OnDevice the application obtains a
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<a href="/html/libvirt-libvirt-host.html#virConnectPtr">
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<code>virConnectPtr</code>
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</a>
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connection to the hypervisor it can then use it to manage the hypervisor's
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available domains and related virtualization
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resources, such as 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"
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src="libvirt-object-model.png"/>
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</p>
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<p> The figure above shows the five main objects exported by the API:</p>
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<ul>
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<li>
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<a href="html/libvirt-libvirt-host.html#virConnectPtr">
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<code>virConnectPtr</code>
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</a>
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<p>Represents the connection to a hypervisor. Use one of the
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<a href="html/libvirt-libvirt-host.html#virConnectOpen">virConnectOpen</a>
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functions to obtain connection to the hypervisor which is then used
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as a parameter to other connection API's.</p></li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainPtr">
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<code>virDomainPtr</code>
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</a>
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<p>Represents one domain either active or defined (i.e. existing as
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permanent config file and storage but not currently running on that
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node). The function
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<a href="html/libvirt-libvirt-domain.html#virConnectListAllDomains">
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<code>virConnectListAllDomains</code>
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</a>
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lists all the domains for the hypervisor.</p></li>
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<li>
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<a href="html/libvirt-libvirt-network.html#virNetworkPtr">
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<code>virNetworkPtr</code>
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</a>
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<p>Represents one network either active or defined (i.e. existing
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as permanent config file and storage but not currently activated).
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The function
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<a href="html/libvirt-libvirt-network.html#virConnectListAllNetworks">
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<code>virConnectListAllNetworks</code>
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</a>
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lists all the virtualization networks for the hypervisor.</p></li>
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<li>
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<a href="html/libvirt-libvirt-storage.html#virStorageVolPtr">
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<code>virStorageVolPtr</code>
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</a>
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<p>Represents one storage volume generally 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-storage.html#virStorageVolLookupByPath">
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<code>virStorageVolLookupByPath</code>
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</a>
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finds the storage volume object based on its path on the node.</p></li>
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<li>
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<a href="html/libvirt-libvirt-storage.html#virStoragePoolPtr">
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<code>virStoragePoolPtr</code>
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</a>
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<p>Represents a storage pool, which is a logical area
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used to allocate and store storage volumes. The function
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<a href="html/libvirt-libvirt-storage.html#virConnectListAllStoragePools">
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<code>virConnectListAllStoragePools</code>
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</a>
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lists all of the virtualization storage pools on the hypervisor.
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The function
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<a href="html/libvirt-libvirt-storage.html#virStoragePoolLookupByVolume">
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<code>virStoragePoolLookupByVolume</code>
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</a>
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finds the storage pool containing a given storage volume.</p></li>
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</ul>
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<p> Most objects 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, networks, 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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they can be activated dynamically in order to be used.</p>
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<p> Most objects can also be named in various ways:</p>
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<ul>
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<li><code>name</code>
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<p>A user friendly identifier but whose uniqueness
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cannot be guaranteed between two nodes.</p></li>
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<li><code>ID</code>
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<p>A runtime unique identifier
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provided by the hypervisor for one given activation of the object;
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however, it becomes invalid once the resource is deactivated.</p></li >
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<li><code>UUID</code>
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<p> A 16 byte 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 guaranteed to be unique for long term usage and across a
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set of nodes.</p></li>
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</ul>
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<h2><a id="Functions">Functions and Naming Conventions</a></h2>
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<p> The naming of the functions present in the library is usually
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composed by 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>
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<li><b>Lookup</b> [...LookupBy...]
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<p>Used to perform lookups on objects by some type of identifier,
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such as:</p>
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<ul>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainLookupByID">
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<code>virDomainLookupByID</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainLookupByName">
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<code>virDomainLookupByName</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainLookupByUUID">
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<code>virDomainLookupByUUID</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainLookupByUUIDString">
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<code>virDomainLookupByUUIDString</code>
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</a>
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</li>
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</ul>
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</li>
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<li><b>Enumeration</b> [virConnectList..., virConnectNumOf...]
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<p>Used to enumerate a set of object available to a given
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hypervisor connection such as:</p>
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<ul>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virConnectListDomains">
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<code>virConnectListDomains</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virConnectNumOfDomains">
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<code>virConnectNumOfDomains</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-network.html#virConnectListNetworks">
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<code>virConnectListNetworks</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-storage.html#virConnectListStoragePools">
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<code>virConnectListStoragePools</code>
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</a>
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</li>
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</ul>
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</li>
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<li><b>Description</b> [...GetInfo]
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<p>Generic accessor providing a set of generic information about an
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object, such as: </p>
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<ul>
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<li>
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<a href="html/libvirt-libvirt-host.html#virNodeGetInfo">
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<code>virNodeGetInfo</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainGetInfo">
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<code>virDomainGetInfo</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-storage.html#virStoragePoolGetInfo">
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<code>virStoragePoolGetInfo</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-storage.html#virStorageVolGetInfo">
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<code>virStorageVolGetInfo</code>
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</a>
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</li>
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</ul>
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</li>
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<li><b>Accessors</b> [...Get..., ...Set...]
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<p>Specific accessors used to query or modify data for the given object,
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such as: </p>
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<ul>
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<li>
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<a href="html/libvirt-libvirt-host.html#virConnectGetType">
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<code>virConnectGetType</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainGetMaxMemory">
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<code>virDomainGetMaxMemory</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainSetMemory">
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<code>virDomainSetMemory</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainGetVcpus">
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<code>virDomainGetVcpus</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-storage.html#virStoragePoolSetAutostart">
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<code>virStoragePoolSetAutostart</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-network.html#virNetworkGetBridgeName">
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<code>virNetworkGetBridgeName</code>
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</a>
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</li>
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</ul>
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</li>
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<li><b>Creation</b> [...Create, ...CreateXML]
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<p>Used to create and start objects. The ...CreateXML APIs will create
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the object based on an XML description, while the ...Create APIs will
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create the object based on existing object pointer, such as: </p>
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<ul>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainCreate">
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<code>virDomainCreate</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-domain.html#virDomainCreateXML">
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<code>virDomainCreateXML</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-network.html#virNetworkCreate">
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<code>virNetworkCreate</code>
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</a>
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</li>
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<li>
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<a href="html/libvirt-libvirt-network.html#virNetworkCreateXML">
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<code>virNetworkCreateXML</code>
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</a>
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</li>
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</ul>
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</li>
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<li><b>Destruction</b> [...Destroy]
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<p>Used to shutdown or deactivate and destroy objects, such as: </p>
|
|
|
|
|
<ul>
|
2014-12-01 13:36:13 +00:00
|
|
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<li>
|
|
|
|
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<a href="html/libvirt-libvirt-domain.html#virDomainDestroy">
|
|
|
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<code>virDomainDestroy</code>
|
|
|
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</a>
|
|
|
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</li>
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<li>
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<a href="html/libvirt-libvirt-network.html#virNetworkDestroy">
|
|
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|
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<code>virNetworkDestroy</code>
|
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</a>
|
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</li>
|
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|
<li>
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<a href="html/libvirt-libvirt-storage.html#virStoragePoolDestroy">
|
|
|
|
|
<code>virStoragePoolDestroy</code>
|
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</a>
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|
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</li>
|
2013-02-12 17:58:42 +00:00
|
|
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</ul>
|
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</li>
|
2009-04-15 20:42:50 +00:00
|
|
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</ul>
|
2014-07-08 08:27:51 +00:00
|
|
|
<p>Note: functions returning vir*Ptr (like the virDomainLookup functions)
|
|
|
|
|
allocate memory which needs to be freed by the caller by the corresponding
|
|
|
|
|
vir*Free function (e.g. virDomainFree for a virDomainPtr object).
|
|
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|
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</p>
|
2009-04-15 20:42:50 +00:00
|
|
|
<p> For more in-depth details of the storage related APIs see
|
2011-04-01 22:02:10 +00:00
|
|
|
<a href="storage.html">the storage management page</a>.
|
|
|
|
|
</p>
|
2017-07-26 14:52:42 +00:00
|
|
|
<h2><a id="Drivers">The libvirt Drivers</a></h2>
|
2013-02-12 19:01:49 +00:00
|
|
|
<p>Drivers are the basic building block for libvirt functionality
|
|
|
|
|
to support the capability to handle specific hypervisor driver calls.
|
|
|
|
|
Drivers are discovered and registered during connection processing as
|
2014-12-01 13:36:13 +00:00
|
|
|
part of the
|
|
|
|
|
<a href="html/libvirt-libvirt-host.html#virInitialize">
|
|
|
|
|
<code>virInitialize</code>
|
|
|
|
|
</a>
|
|
|
|
|
API. Each driver
|
2013-02-12 19:01:49 +00:00
|
|
|
has a registration API which loads up the driver specific function
|
|
|
|
|
references for the libvirt APIs to call. The following is a simplistic
|
|
|
|
|
view of the hypervisor driver mechanism. Consider the stacked list of
|
|
|
|
|
drivers as a series of modules that can be plugged into the architecture
|
|
|
|
|
depending on how libvirt is configured to be built.</p>
|
2009-04-15 20:42:50 +00:00
|
|
|
<p class="image">
|
|
|
|
|
<img alt="The libvirt driver architecture"
|
|
|
|
|
src="libvirt-driver-arch.png"/>
|
|
|
|
|
</p>
|
2013-02-12 19:01:49 +00:00
|
|
|
<p>The driver architecture is also used to support other virtualization
|
|
|
|
|
components such as storage, storage pools, host device, networking,
|
|
|
|
|
network interfaces, and network filters.</p>
|
|
|
|
|
<p>See the <a href="drivers.html">libvirt drivers</a> page for more
|
|
|
|
|
information on hypervisor and storage specific drivers.</p>
|
|
|
|
|
<p>Not all drivers support every virtualization function possible.
|
|
|
|
|
The <a href="hvsupport.html">libvirt API support matrix</a> lists
|
|
|
|
|
the various functions and support found in each driver by the version
|
|
|
|
|
support was added into libvirt.
|
|
|
|
|
</p>
|
2017-07-26 14:52:42 +00:00
|
|
|
<h2><a id="Remote">Daemon and Remote Access</a></h2>
|
2013-02-14 15:04:13 +00:00
|
|
|
<p>Access to libvirt drivers is primarily handled by the libvirtd
|
|
|
|
|
daemon through the <a href="remote.html">remote</a> driver via an
|
|
|
|
|
<a href="internals/rpc.html">RPC</a>. Some hypervisors do support
|
|
|
|
|
client-side connections and responses, such as Test, OpenVZ, VMware,
|
2015-08-21 21:43:48 +00:00
|
|
|
Power VM (phyp), VirtualBox (vbox), ESX, Hyper-V, Xen, and Virtuozzo.
|
2013-02-14 15:04:13 +00:00
|
|
|
The libvirtd daemon service is started on the host at system boot
|
|
|
|
|
time and can also be restarted at any time by a properly privileged
|
|
|
|
|
user, such as root. The libvirtd daemon uses the same libvirt API
|
2014-12-01 13:36:13 +00:00
|
|
|
<a href="html/libvirt-libvirt-host.html#virInitialize">
|
|
|
|
|
<code>virInitialize</code>
|
|
|
|
|
</a>
|
|
|
|
|
sequence as applications
|
2013-02-14 15:04:13 +00:00
|
|
|
for client-side driver registrations, but then extends the registered
|
|
|
|
|
driver list to encompass all known drivers supported for all driver
|
|
|
|
|
types supported on the host. </p>
|
|
|
|
|
<p>The libvirt client <a href="apps.html">applications</a> use a
|
|
|
|
|
<a href="uri.html">URI</a> to obtain the <code>virConnectPtr</code>.
|
|
|
|
|
The <code>virConnectPtr</code> keeps track of the driver connection
|
|
|
|
|
plus a variety of other connections (network, interface, storage, etc.).
|
|
|
|
|
The <code>virConnectPtr</code> is then used as a parameter to other
|
|
|
|
|
virtualization <a href="#Functions">functions</a>. Depending upon the
|
|
|
|
|
driver being used, calls will be routed through the remote driver to
|
|
|
|
|
the libvirtd daemon. The daemon will reference the connection specific
|
2013-11-30 18:27:15 +00:00
|
|
|
driver in order to retrieve the requested information and then pass
|
2013-02-14 15:04:13 +00:00
|
|
|
back status and/or data through the connection back to the application.
|
|
|
|
|
The application can then decide what to do with that data, such as
|
|
|
|
|
display, write log data, etc. <a href="migration.html">Migration</a>
|
|
|
|
|
is an example of many facets of the architecture in use.</p>
|
|
|
|
|
|
2009-04-15 20:42:50 +00:00
|
|
|
<p class="image">
|
|
|
|
|
<img alt="The libvirt daemon and remote architecture"
|
|
|
|
|
src="libvirt-daemon-arch.png"/>
|
|
|
|
|
</p>
|
2013-02-14 15:04:13 +00:00
|
|
|
<p>
|
|
|
|
|
The key takeaway from the above diagram is that there is a remote driver
|
|
|
|
|
which handles transactions for a majority of the drivers. The libvirtd
|
|
|
|
|
daemon running on the host will receive transaction requests from the
|
|
|
|
|
remote driver and will then query the hypervisor driver as specified in
|
|
|
|
|
the <code>virConnectPtr</code> in order to fetch the data. The data will
|
|
|
|
|
then be returned through the remote driver to the client application
|
|
|
|
|
for processing.
|
|
|
|
|
</p>
|
|
|
|
|
<p>If you are interested in contributing to libvirt, read the
|
|
|
|
|
<a href="http://wiki.libvirt.org/page/FAQ">FAQ</a> and
|
|
|
|
|
<a href="hacking.html">hacking</a> guidelines to gain an understanding
|
|
|
|
|
of basic rules and guidelines. In order to add new API functionality
|
|
|
|
|
follow the instructions regarding
|
|
|
|
|
<a href="api_extension.html">implementing a new API in libvirt</a>.
|
|
|
|
|
</p>
|
|
|
|
|
|
2009-04-15 20:42:50 +00:00
|
|
|
</body>
|
|
|
|
|
</html>
|
