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<h1 align="center">Libvir the virtualization API</h1>

<h1>Note: this is the flat content of the <a href="index.html">web
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<h1 style="text-align: center">libvir</h1>

<h3>what is <span class="style1">libvir?</span></h3>

<p>Libvir is a C toolkit to interract with the virtualization capabilities of
recent versions of Linux (and other OSes). It is free software available
under the <a href="http://www.opensource.org/licenses/lgpl-license.html">GNU
Lesser General Public License</a>. Virtualization of the Linux Operating
System means the ability to run multiple instances of Operating Systems
concurently on a single hardware system where the basic resources are driven
by a Linux instance. The library aim at providing long term stable C API
primarily for the <a
href="http://www.cl.cam.ac.uk/Research/SRG/netos/xen/index.html">Xen
paravirtualization</a> mechanism but should be able to integrate other
virtualization mechanisms if needed.</p>

<h2><a name="News">Releases</a></h2>

<p>Here is the list of official releases, however since it is early on in the
development of libvir, it is preferable when possible to just use the <a
href="downloads.html">CVS version or snapshot</a>, contact the mailing list
and check the <a href="ChangeLog.html">ChangeLog</a> to gauge progresses.</p>

<h3>0.0.1: Dec 19 2005</h3>
<ul>
  <li>First release</li>
  <li>Basic management of existing Xen domains</li>
  <li>Minimal autogenerated Python bindings</li>
</ul>

<h2><a name="Introducti">Introduction</a></h2>

<p>Libvir is a C toolkit to interract with the virtualization capabilities of
recent versions of Linux (and other OSes), but ibvir won't try to provide all
possible interfaces for interacting with the virtualization features.</p>

<p>To avoid ambiguity about the terms used here here are the definitions for
soem of the specific terms used in libvir documentation:</p>
<ul>
  <li>a <strong>node</strong> is a single physical machine</li>
  <li>an <strong>hypervisor</strong> is a layer of software allowing to
    virtualize a node in a set of virtual machines with possibly different
    configurations than the node itself</li>
  <li>a <strong>domain</strong> is an instance of an operating system running
    on a virtualized machine</li>
</ul>

<p style="text-align: center"><img
alt="Hypervisor and domains running on a node" src="node.gif"></p>

<p>Now we can define the goal of libvir: to provide the lowest possible
generic and stable layer to manage domains on a node.</p>

<p>This implies the following:</p>
<ul>
  <li>the API should not be targetted to a single virtualization environment
    though Xen is the current default, which also means that some very
    specific capabilities which are not generic enough may not be provided as
    libvir APIs</li>
  <li>the API should allow to do efficiently and cleanly all the operations
    needed to manage domains on a node</li>
  <li>the API will not try to provide hight level multi-nodes management
    features like load balancing, though they could be implemented on top of
    libvir</li>
  <li>stability of the API is a big concern, libvir should isolate
    applications from the frequent changes expected at the lower level of the
    virtualization framework</li>
</ul>

<p>So libvir should be a building block for higher level management tools or
for applications focusing on virtualization on a single node (the only
exception being domain migration between node capabilities which may need to
be added at the libvir level). Where possible libvir should be extendable to
be able to provide the same API for remote nodes, however this is not the
case at the moment, the code currently handle only local node access.</p>

<h2><a name="architecture">libvir architecture</a></h2>

<p>When running in a Xen environment, programs using libvir have to execute
in "Domain 0", which is the primary Linux OS loaded on the machine. That OS
kernel provides most if not all of the actual drivers used by the set of
domains. It also runs the Xen Store, a database of informations shared by the
hypervisor, the kernels, the drivers and the xen daemon. Xend. The xen daemon
supervise the control and execution of the sets of domains. The hypervisor,
drivers, kernels and daemons communicate though a shared system bus
implemented in the hypervisor. The figure below tries to provide a view of
this environment:</p>
<img src="architecture.gif" alt="The Xen architecture">

<p>The library can be initialized in 2 ways depending on the level of
priviledge of the embedding program. If it runs with root access,
virConnectOpen() can be used, it will use three different ways to connect to
the Xen infrastructure:</p>
<ul>
  <li>a connection to the Xen Daemon though an HTTP RPC layer</li>
  <li>a read/write connection to the Xen Store</li>
  <li>use Xen Hypervisor calls</li>
</ul>

<p>The library will usually interract with the Xen daemon for any operation
changing the state of the system, but for performance and accuracy reasons
may talk directly to the hypervisor when gathering state informations at
least when possible (i.e. when the running program using libvir has root
priviledge access). </p>

<p> If it runs without root access virConnectOpenReadOnly() should be used to
connect to initialize the library. It will try to open the read-only socket
<code>/var/run/xenstored/socket_ro</code> to connect to the Xen Store and
also try to use the RPC to the Xen daemon. In this case use of hypervisor
calls and write to the Xen Store will not be possible, restraining the amount
of APIs available and slowing down information gathering about domains. </p>

<h2><a name="Downloads">Downloads</a></h2>

<p>The latest versions of libvir can be found on the  <a
href="ftp://libvir.org/libvir/">libvir.org</a> server ( <a
href="http://libvir.org/sources/">HTTP</a>, <a
href="ftp://libvir.org/libvir/">FTP</a>). You will find there the released
versions as well as <a
href="http://libvir.org/sources/libvir-cvs-snapshot.tar.gz">snapshot
tarballs</a> updated from CVS head every hour</p>

<p>Anonymous <a href="http://ximbiot.com/cvs/cvshome/docs/">CVS</a> is also
available, first register onto the server:</p>

<p><code>cvs -d :pserver:anoncvs@libvir.org:2401/data/cvs login</code></p>

<p>it will request a password, enter <strong>anoncvs</strong>. Then you can
checkout the development tree with:</p>

<p><code>cvs -d :pserver:anoncvs@libvir.org:2401/data/cvs co libvir</code></p>

<p>Use ./autogen.sh to configure the local checkout, then <code>make</code>
and <code>make install</code>, as usual. All normal cvs commands are now
available except commiting to the base.</p>

<h2><a name="FAQ">FAQ</a></h2>

<p>Table of Contents:</p>
<ul>
  <li><a href="FAQ.html#License">License(s)</a></li>
  <li><a href="FAQ.html#Installati">Installation</a></li>
  <li><a href="FAQ.html#Compilatio">Compilation</a></li>
  <li><a href="FAQ.html#Developer">Developer corner</a></li>
</ul>

<h3><a name="License">License</a>(s)</h3>
<ol>
  <li><em>Licensing Terms for libvir</em>
    <p>libvir is released under the <a
    href="http://www.opensource.org/licenses/lgpl-license.html">GNU Lesser
    General Public License</a>, see the file COPYING.LIB in the distribution
    for the precise wording. The only library that libvir depends upon is the
    Xen store access library which is also licenced under the LGPL.</p>
  </li>
  <li><em>Can I embed libvir in a proprietary application ?</em>
    <p>Yes. The LGPL allows you to embed libvir into a proprietary
    application. It would be graceful to send-back bug fixes and improvements
    as patches for possible incorporation in the main development tree. It
    will decrease your maintainance costs anyway if you do so.</p>
  </li>
</ol>

<h3><a name="Installati">Installation</a></h3>
<ol>
  <li><em>Where can I get libvir</em> ?
    <p>The original distribution comes from <a
    href="ftp://libvir.org/libvir/">ftp://libvir.org/libvir/</a>.</p>
  </li>
  <li><em>I can't install the libvir/libvir-devel RPM packages due to failed
    dependencies</em>
    <p>The most generic solution is to re-fetch the latest src.rpm , and
    rebuild it locally with</p>
    <p><code>rpm --rebuild libvir-xxx.src.rpm</code>.</p>
    <p>If everything goes well it will generate two binary rpm packages (one
    providing the shared libs and virsh, and the other one, the -devel
    package, providing includes, static libraries and scripts needed to build
    applications with libvir that you can install locally.</p>
    <p>One can also rebuild the RPMs from a tarball:</p>
    <p><code>rpmbuild -ta libdir-xxx.tar.gz</code></p>
    <p>Or from a configured tree with:</p>
    <p><code>make rpm</code></p>
  </li>
  <li><em>Failure to use the API for non-root users</em>
    <p>Large parts of the API may only be accessible with root priviledges,
    however the read only access to the xenstore data doesnot have to be
    forbidden to user, at least for monitoring purposes. If "virsh info"
    fails to run as an user, change the mode of the xenstore read-only socket
    with:</p>
    <p><code>chmod 666 /var/run/xenstored/socket_ro</code></p>
    <p>and also make sure that the Xen Daemon is running correctly</p>
  </li>
</ol>

<h3><a name="Compilatio">Compilation</a></h3>
<ol>
  <li><em>What is the process to compile libvir ?</em>
    <p>As most UNIX libraries libvir follows the "standard":</p>
    <p><code>gunzip -c libvir-xxx.tar.gz | tar xvf -</code></p>
    <p><code>cd libvir-xxxx</code></p>
    <p><code>./configure --help</code></p>
    <p>to see the options, then the compilation/installation proper</p>
    <p><code>./configure [possible options]</code></p>
    <p><code>make</code></p>
    <p><code>make install</code></p>
    <p>At that point you may have to rerun ldconfig or a similar utility to
    update your list of installed shared libs.</p>
  </li>
  <li><em>What other libraries are needed to compile/install libvir ?</em>
    <p>Libvir requires libxenstore, which is usually provided by the xen
    packages as well as the public headers to compile against libxenstore.</p>
  </li>
  <li><em>I use the CVS version and there is no configure script</em>
    <p>The configure script (and other Makefiles) are generated. Use the
    autogen.sh script to regenerate the configure script and Makefiles,
    like:</p>
    <p><code>./autogen.sh --prefix=/usr --disable-shared</code></p>
  </li>
</ol>

<h3><a name="Developer">Developer</a> corner</h3>
<ol>
  <li><em>Troubles compiling or linking programs using libvir</em>
    <p>To simplify the process of reusing the library, libvir comes with
    pkgconfig support, which can be used directly from autoconf support or
    via the pkg-config command line tool, like:</p>
    <p><code>pkg-config libvir --libs</code></p>
  </li>
</ol>

<h2><a name="Reporting">Reporting bugs and getting help</a></h2>

<p>There is a mailing-list <a
href="mailto:libvir-list@redhat.com">libvir-list@redhat.com</a> for libvir,
with an  <a href="https://www.redhat.com/archives/libvir-list/">on-line
archive</a>. Please subscribe to this list before posting by visiting the <a
href="https://www.redhat.com/mailman/listinfo/libvir-list">associated Web</a>
page and follow the instructions. Patches with explanations and provided as
attachments are really appreciated and will be discussed on the mailing list.
If possible generate the patches by using cvs diff -u in a CVS checkout.</p>

<p>We expect to use <a href="https://bugzilla.redhat.com/">Red Hat
Bugzilla</a> to track bugs for libvir, though there isn't a libvir software
module defined yet, in the meantime use the mailing-list, thanks !.</p>
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