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28 lines
3.8 KiB
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28 lines
3.8 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>libvir architecture</title></head><body><div id="container"><div id="intro"><div id="adjustments"></div><div id="pageHeader"></div><div id="content2"><h1 class="style1">libvir architecture</h1><h3>This is Xen specific since this is the only hypervisor supported at the
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moment</h3><p>When running in a Xen environment, programs using libvir have to execute
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in "Domain 0", which is the primary Linux OS loaded on the machine. That OS
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kernel provides most if not all of the actual drivers used by the set of
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domains. It also runs the Xen Store, a database of informations shared by the
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hypervisor, the kernels, the drivers and the xen daemon. Xend. The xen daemon
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supervise the control and execution of the sets of domains. The hypervisor,
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drivers, kernels and daemons communicate though a shared system bus
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implemented in the hypervisor. The figure below tries to provide a view of
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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
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priviledge of the embedding program. If it runs with root access,
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virConnectOpen() can be used, it will use three different ways to connect to
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the Xen infrastructure:</p><ul><li>a connection to the Xen Daemon though an HTTP RPC layer</li>
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<li>a read/write connection to the Xen Store</li>
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<li>use Xen Hypervisor calls</li>
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</ul><p>The library will usually interract with the Xen daemon for any operation
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changing the state of the system, but for performance and accuracy reasons
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may talk directly to the hypervisor when gathering state informations at
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least when possible (i.e. when the running program using libvir has root
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priviledge access).</p><p>If it runs without root access virConnectOpenReadOnly() should be used to
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connect to initialize the library. It will try to open the read-only socket
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<code>/var/run/xenstored/socket_ro</code> to connect to the Xen Store and
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also try to use the RPC to the Xen daemon. In this case use of hypervisor
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calls and write to the Xen Store will not be possible, restraining the amount
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of APIs available and slowing down information gathering about domains.</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">libvir architecture</a></li><li><a href="downloads.html">Downloads</a></li><li><a href="FAQ.html">FAQ</a></li><li><a href="bugs.html">Reporting bugs and getting help</a></li><li><a style="font-weight:bold" href="html/index.html">API Menu</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="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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