libvirt/docs/architecture.html

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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>libvirt architecture</title></head><body><div id="container"><div id="intro"><div id="adjustments"></div><div id="pageHeader"></div><div id="content2"><h1 class="style1">libvirt architecture</h1><h3>This is in a large part Xen specific since this is the only hypervisor
supported at the moment</h3><p>When running in a Xen environment, programs using libvirt 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 libvirt 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><h3>Internal architecture</h3><p>As the previous section explains, libvirt can communicate using different
channels with the current hypervisor, and should also be able to use
different kind of hypervisor. To simplify the internal design, code, ease
maintainance and simplify the support of other virtualization engine the
internals have been structured as one core component, the libvirt.c module
acting as a front-end for the library API and a set of hypvisor drivers
defining a common set of routines. That way the Xen Daemon accces, the Xen
Store one, the Hypervisor hypercall are all isolated in separate C modules
implementing at least a subset of the common operations defined by the
drivers present in driver.h:</p><ul><li>xend_internal: implements the driver functions though the Xen
  Daemon</li>
  <li>xs_internal: implements the subset of the driver availble though the
    Xen Store</li>
  <li>xen_internal: provide the implementation of the functions possible via
    direct hypervisor access</li>
</ul><p>Note that a given driver may only implement a subset of those functions,
for example saving a domain state to disk and restoring it is only possible
though the Xen Daemon, on the other hand all interfaces allow to query the
runtime state of a given domain.</p><p></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&amp;component=libvirt&amp;bug_status=NEW&amp;bug_status=ASSIGNED&amp;bug_status=REOPENED&amp;bug_status=MODIFIED&amp;short_desc_type=allwordssubstr&amp;short_desc=&amp;long_desc_type=allwordssubstr">Open bugs</a></li><li><a href="http://virt-manager.et.redhat.com/">virt-manager</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>
* docs/*: extended the documentation Daniel 2005-12-09 13:04:05 +00:00			`<?xml version="1.0" encoding="ISO-8859-1"?>`
			`<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">`
* doc/: updated module list and rebuilt include/libvirt.h include/libvirt.h.in: added intialization function * include/virterror.h src/virterror.c: one more error code * src/internal.h: first part of Jim's format checking * src/libvirt.c src/xen_internal.[ch] src/xend_internal.[ch] src/xs_internal.[ch]: initialization and registration of drivers Daniel 2006-03-27 15:24:36 +00:00			<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>libvirt architecture</title></head><body><div id="container"><div id="intro"><div id="adjustments"></div><div id="pageHeader"></div><div id="content2"><h1 class="style1">libvirt architecture</h1><h3>This is in a large part Xen specific since this is the only hypervisor
			`supported at the moment</h3><p>When running in a Xen environment, programs using libvirt have to execute`
* doc/*: augment and try to complete the doc in its current state Daniel 2006-01-23 13:24:07 +00:00			`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`
* docs/architecture.* docs/*: added a section on the architecture and regenerated the docs. Daniel 2005-12-21 16:59:34 +00:00			`priviledge of the embedding program. If it runs with root access,`
* doc/*: started to augment and update the documentation Daniel 2006-01-22 16:27:09 +00:00			`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>`
* doc/*: augment and try to complete the doc in its current state Daniel 2006-01-23 13:24:07 +00:00			`</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`
* NEWS docs/*: regenerated and updated the docs post 0.0.3 release Daniel 2006-02-10 08:43:31 +00:00			`least when possible (i.e. when the running program using libvirt has root`
* NEWS docs/news.xsl: added stylesheet to generate NEWS file * docs/*: updated docs preparing for the release Daniel 2006-01-29 10:56:15 +00:00			`priviledge access).</p><p>If it runs without root access virConnectOpenReadOnly() should be used to`
* doc/*: augment and try to complete the doc in its current state Daniel 2006-01-23 13:24:07 +00:00			`connect to initialize the library. It will try to open the read-only socket`
* doc/*: started to augment and update the documentation Daniel 2006-01-22 16:27:09 +00:00			`<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`
* doc/: updated module list and rebuilt include/libvirt.h include/libvirt.h.in: added intialization function * include/virterror.h src/virterror.c: one more error code * src/internal.h: first part of Jim's format checking * src/libvirt.c src/xen_internal.[ch] src/xend_internal.[ch] src/xs_internal.[ch]: initialization and registration of drivers Daniel 2006-03-27 15:24:36 +00:00			`of APIs available and slowing down information gathering about domains.</p><h3>Internal architecture</h3><p>As the previous section explains, libvirt can communicate using different`
			`channels with the current hypervisor, and should also be able to use`
			`different kind of hypervisor. To simplify the internal design, code, ease`
			`maintainance and simplify the support of other virtualization engine the`
			`internals have been structured as one core component, the libvirt.c module`
			`acting as a front-end for the library API and a set of hypvisor drivers`
			`defining a common set of routines. That way the Xen Daemon accces, the Xen`
			`Store one, the Hypervisor hypercall are all isolated in separate C modules`
			`implementing at least a subset of the common operations defined by the`
			`drivers present in driver.h:</p><ul><li>xend_internal: implements the driver functions though the Xen`
			`Daemon</li>`
			`<li>xs_internal: implements the subset of the driver availble though the`
			`Xen Store</li>`
			`<li>xen_internal: provide the implementation of the functions possible via`
			`direct hypervisor access</li>`
			`</ul><p>Note that a given driver may only implement a subset of those functions,`
			`for example saving a domain state to disk and restoring it is only possible`
			`though the Xen Daemon, on the other hand all interfaces allow to query the`
* docs/site.xsl docs/*.html: add links to virt-manager Daniel 2006-08-25 23:16:21 +00:00			runtime state of a given domain.</p><p></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://virt-manager.et.redhat.com/">virt-manager</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>