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1320 lines
60 KiB
HTML
1320 lines
60 KiB
HTML
<html>
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<head>
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<meta http-equiv="content-type" content="">
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<title>Libvirt the virtualization API</title>
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</head>
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<body bgcolor="#ffffff">
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<h1 align="center">Libvirt the virtualization API</h1>
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<h1>Note: this is the flat content of the <a
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href="index.html">website</a></h1>
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<h1 style="text-align: center">libvirt</h1>
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<h3>what is <span class="style1">libvirt?</span></h3>
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<p>Libvirt is a C toolkit to interact with the virtualization capabilitiesof
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recent versions of Linux (and other OSes). It is free software availableunder
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the <a href="http://www.opensource.org/licenses/lgpl-license.html">GNULesser
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General Public License</a>. Virtualization of the Linux OperatingSystem means
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the ability to run multiple instances of Operating Systemsconcurently on a
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single hardware system where the basic resources are drivenby a Linux
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instance. The library aim at providing long term stable C APIinitially for
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the <a
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href="http://www.cl.cam.ac.uk/Research/SRG/netos/xen/index.html">Xenparavirtualization</a>but
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should be able to integrate other virtualizationmechanisms if needed.</p>
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<h2><a name="News">Releases</a></h2>
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<p>Here is the list of official releases, however since it is early on in
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thedevelopment of libvirt, it is preferable when possible to just use the <a
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href="downloads.html">CVS version or snapshot</a>, contact the mailing
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listand check the <a href="ChangeLog.html">ChangeLog</a>to gauge
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progresses.</p>
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<h3>0.2.1: Mar 16 2007</h3>
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<ul>
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<li>Various internal cleanups (Richard Jones,Daniel Berrange,Mark McLoughlin)</li>
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<li>Bug fixes: libvirt_qemud daemon path (Daniel Berrange), libvirt
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config directory (Daniel Berrange and Mark McLoughlin), memory leak in qemud (Mark), various fixes on network support (Mark), avoid Xen domain zombies on device hotplug errors (Daniel Berrange), various fixes on qemud (Mark),
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argsparsing (Richard Jones), virsh -t argument (Saori Fukuta), avoid virsh
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crash on TAB key (Daniel Berrange), detect xend operation failures (Kazuki Mizushima), don't listen on null socket (Rich Jones), read-only socket cleanup (Rich Jones), use of vnc port 5900 (Nobuhiro Itou), assorted networking fixes
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(Daniel Berrange), shutoff and shutdown mismatches (Kazuki Mizushima), unlimited memory handling (Atsushi SAKAI), python binding fixes (Tatsuro Enokura)</li>
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<li>Build and portability fixes: IA64 fixes (Atsushi SAKAI), dependancies and build (Daniel Berrange), fix xend port detection (Daniel Berrange), icompile time warnings (Mark), avoid const related compiler warnings (Daniel Berrange), automated builds (Daniel Berrange), pointer/int mismatch (Richard Jones), configure time selection of drivers, libvirt spec hacking (Daniel Berrange)</li>
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<li>Add support for network autostart and init scripts (Mark McLoughlin)</li>
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<li>New API virConnectGetCapabilities() to detect the virtualization
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capabilities of a host (Richard Jones)</li>
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<li>Minor improvements: qemud signal handling (Mark), don't shutdown or reboot
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domain0 (Kazuki Mizushima), QEmu version autodetection (Daniel Berrange),
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network UUIDs (Mark), speed up UUID domain lookups (Tatsuro Enokura and
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Daniel Berrange), support for paused QEmu CPU (Daniel Berrange), keymap
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VNC attribute support (Takahashi Tomohiro and Daniel Berrange), maximum
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number of virtual CPU (Masayuki Sunou), virtsh --readonly option (Rich
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Jones), python bindings for new functions (Daniel Berrange)</li>
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<li>Documentation updates especially on the XML formats</li>
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</ul>
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<h3>0.2.0: Feb 14 2007</h3>
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<ul>
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<li>Various internal cleanups (Mark McLoughlin, Richard Jones,Daniel
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Berrange, Karel Zak)</li>
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<li>Bug fixes: avoid a crash in connect (Daniel Berrange), virsh
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argsparsing (Richard Jones)</li>
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<li>Add support for QEmu and KVM virtualization (Daniel Berrange)</li>
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<li>Add support for network configuration (Mark McLoughlin)</li>
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<li>Minor improvements: regression testing (Daniel Berrange),localization
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string updates</li>
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</ul>
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<h3>0.1.11: Jan 22 2007</h3>
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<ul>
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<li>Finish XML <-> XM config files support</li>
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<li>Remove memory leak when freeing virConf objects</li>
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<li>Finishing inactive domain support (Daniel Berrange)</li>
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<li>Added a Relax-NG schemas to check XML instances</li>
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</ul>
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<h3>0.1.10: Dec 20 2006</h3>
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<ul>
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<li>more localizations</li>
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<li>bug fixes: VCPU info breakages on xen 3.0.3, xenDaemonListDomains
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buffer overflow (Daniel Berrange), reference count bug when creating Xen
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domains (Daniel Berrange).</li>
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<li>improvements: support graphic framebuffer for Xen paravirt (Daniel
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Berrange), VNC listen IP range support (Daniel Berrange), support for
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default Xen config files and inactive domains of 3.0.4 (Daniel
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Berrange).</li>
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</ul>
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<h3>0.1.9: Nov 29 2006</h3>
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<ul>
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<li>python bindings: release interpeter lock when calling C (Daniel
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Berrange)</li>
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<li>don't raise HTTP error when looking informations for a domain</li>
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<li>some refactoring to use the driver for all entry points</li>
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<li>better error reporting (Daniel Berrange)</li>
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<li>fix OS reporting when running as non-root</li>
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<li>provide XML parsing errors</li>
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<li>extension of the test framework (Daniel Berrange)</li>
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<li>fix the reconnect regression test</li>
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<li>python bindings: Domain instances now link to the Connect to avoid
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garbage collection and disconnect</li>
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<li>separate the notion of maximum memory and current use at the XML
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level</li>
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<li>Fix a memory leak (Daniel Berrange)</li>
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<li>add support for shareable drives</li>
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<li>add support for non-bridge style networking configs for guests(Daniel
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Berrange)</li>
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<li>python bindings: fix unsigned long marshalling (Daniel Berrange)</li>
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<li>new config APIs virConfNew() and virConfSetValue() to build configs
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from scratch</li>
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<li>hot plug device support based on Michel Ponceau patch</li>
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<li>added support for inactive domains, new APIs, various associated
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cleanup (Daniel Berrange)</li>
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<li>special device model for HVM guests (Daniel Berrange)</li>
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<li>add API to dump core of domains (but requires a patched xend)</li>
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<li>pygrub bootloader informations take over <os> informations</li>
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<li>updated the localization strings</li>
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</ul>
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<h3>0.1.8: Oct 16 2006</h3>
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<ul>
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<li>Bug for system with page size != 4k</li>
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<li>vcpu number initialization (Philippe Berthault)</li>
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<li>don't label crashed domains as shut off (Peter Vetere)</li>
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<li>fix virsh man page (Noriko Mizumoto)</li>
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<li>blktapdd support for alternate drivers like blktap (Daniel
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Berrange)</li>
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<li>memory leak fixes (xend interface and XML parsing) (Daniel
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Berrange)</li>
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<li>compile fix</li>
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<li>mlock/munlock size fixes (Daniel Berrange)</li>
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<li>improve error reporting</li>
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</ul>
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<h3>0.1.7: Sep 29 2006</h3>
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<ul>
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<li>fix a memory bug on getting vcpu informations from xend (Daniel
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Berrange)</li>
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<li>fix another problem in the hypercalls change in Xen
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changeset86d26e6ec89b when getting domain informations (Daniel
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Berrange)</li>
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</ul>
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<h3>0.1.6: Sep 22 2006</h3>
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<ul>
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<li>Support for localization of strings using gettext (Daniel Berrange)</li>
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<li>Support for new Xen-3.0.3 cdrom and disk configuration (Daniel
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Berrange)</li>
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<li>Support for setting VNC port when creating domains with newxend config
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files (Daniel Berrange)</li>
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<li>Fix bug when running against xen-3.0.2 hypercalls (Jim Fehlig)</li>
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<li>Fix reconnection problem when talking directly to http xend</li>
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</ul>
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<h3>0.1.5: Sep 5 2006</h3>
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<ul>
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<li>Support for new hypercalls change in Xen changeset 86d26e6ec89b</li>
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<li>bug fixes: virParseUUID() was wrong, netwoking for paravirt
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guestsi(Daniel Berrange), virsh on non-existent domains (Daniel
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Berrange),string cast bug when handling error in python (Pete Vetere),
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HTTP500 xend error code handling (Pete Vetere and Daniel Berrange)</li>
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<li>improvements: test suite for SEXPR <-> XML format conversions
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(DanielBerrange), virsh output regression suite (Daniel Berrange), new
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environvariable VIRSH_DEFAULT_CONNECT_URI for the default URI when
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connecting(Daniel Berrange), graphical console support for paravirt
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guests(Jeremy Katz), parsing of simple Xen config files (with Daniel
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Berrange),early work on defined (not running) domains (Daniel
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Berrange),virsh output improvement (Daniel Berrange</li>
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</ul>
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<h3>0.1.4: Aug 16 2006</h3>
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<ul>
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<li>bug fixes: spec file fix (Mark McLoughlin), error report problem
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(withHugh Brock), long integer in Python bindings (with Daniel Berrange),
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XMLgeneration bug for CDRom (Daniel Berrange), bug whem using number()
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XPathfunction (Mark McLoughlin), fix python detection code, remove
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duplicateinitialization errors (Daniel Berrange)</li>
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<li>improvements: UUID in XML description (Peter Vetere), proxy
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codecleanup, virtual CPU and affinity support + virsh support
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(MichelPonceau, Philippe Berthault, Daniel Berrange), port and tty
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informationsfor console in XML (Daniel Berrange), added XML dump to
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driver and proxysupport (Daniel Berrange), extention of boot options with
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support forfloppy and cdrom (Daniel Berrange), features block in XML to
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report/askPAE, ACPI, APIC for HVM domains (Daniel Berrange), fail
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saide-effectoperations when using read-only connection, large
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improvements to testdriver (Daniel Berrange)</li>
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<li>documentation: spelling (Daniel Berrange), test driver examples.</li>
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</ul>
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<h3>0.1.3: Jul 11 2006</h3>
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<ul>
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<li>bugfixes: build as non-root, fix xend access when root, handling
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ofempty XML elements (Mark McLoughlin), XML serialization and parsing
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fixes(Mark McLoughlin), allow to create domains without disk
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(MarkMcLoughlin),</li>
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<li>improvement: xenDaemonLookupByID from O(n^2) to O(n) (Daniel
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Berrange),support for fully virtualized guest (Jim Fehlig, DV, Mark
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McLoughlin)</li>
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<li>documentation: augmented to cover hvm domains</li>
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</ul>
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<h3>0.1.2: Jul 3 2006</h3>
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<ul>
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<li>headers include paths fixup</li>
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<li>proxy mechanism for unpriviledged read-only access by httpu</li>
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</ul>
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<h3>0.1.1: Jun 21 2006</h3>
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<ul>
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<li>building fixes: ncurses fallback (Jim Fehlig), VPATH builds (Daniel
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P.Berrange)</li>
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<li>driver cleanups: new entry points, cleanup of libvirt.c (with Daniel
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P.Berrange)</li>
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<li>Cope with API change introduced in Xen changeset 10277</li>
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<li>new test driver for regression checks (Daniel P. Berrange)</li>
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<li>improvements: added UUID to XML serialization, buffer usage (KarelZak),
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--connect argument to virsh (Daniel P. Berrange),</li>
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<li>bug fixes: uninitialized memory access in error reporting,
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S-Exprparsing (Jim Fehlig, Jeremy Katz), virConnectOpen bug, remove a
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TODO inxs_internal.c</li>
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<li>documentation: Python examples (David Lutterkort), new Perl bindingURL,
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man page update (Karel Zak)</li>
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</ul>
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<h3>0.1.0: Apr 10 2006</h3>
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<ul>
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<li>building fixes: --with-xen-distdir option (Ronald Aigner), out of
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treebuild and pkginfo cflag fix (Daniel Berrange)</li>
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<li>enhancement and fixes of the XML description format (David
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Lutterkortand Jim Fehlig)</li>
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<li>new APIs: for Node information and Reboot</li>
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<li>internal code cleanup: refactoring internals into a driver model,
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moreerror handling, structure sharing, thread safety and ref counting</li>
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<li>bug fixes: error message (Jim Meyering), error allocation in virsh
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(JimMeyering), virDomainLookupByID (Jim Fehlig),</li>
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<li>documentation: updates on architecture, and format, typo fix
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(JimMeyering)</li>
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<li>bindings: exception handling in examples (Jim Meyering), perl ones
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outof tree (Daniel Berrange)</li>
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<li>virsh: more options, create, nodeinfo (Karel Zak), renaming of
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someoptions (Karel Zak), use stderr only for errors (Karel Zak), man
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page(Andrew Puch)</li>
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</ul>
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<h3>0.0.6: Feb 28 2006</h3>
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<ul>
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<li>add UUID lookup and extract API</li>
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<li>add error handling APIs both synchronous and asynchronous</li>
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<li>added minimal hook for error handling at the python level, improved
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thepython bindings</li>
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<li>augment the documentation and tests to cover error handling</li>
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</ul>
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<h3>0.0.5: Feb 23 2006</h3>
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<ul>
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<li>Added XML description parsing, dependance to libxml2, implemented
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thecreation API virDomainCreateLinux()</li>
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<li>new APIs to lookup and name domain by UUID</li>
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<li>fixed the XML dump when using the Xend access</li>
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<li>Fixed a few more problem related to the name change</li>
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<li>Adding regression tests in python and examples in C</li>
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<li>web site improvement, extended the documentation to cover the XMLformat
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and Python API</li>
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<li>Added devhelp help for Gnome/Gtk programmers</li>
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</ul>
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<h3>0.0.4: Feb 10 2006</h3>
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<ul>
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<li>Fix various bugs introduced in the name change</li>
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</ul>
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<h3>0.0.3: Feb 9 2006</h3>
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<ul>
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<li>Switch name from from 'libvir' to libvirt</li>
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<li>Starting infrastructure to add code examples</li>
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<li>Update of python bindings for completeness</li>
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</ul>
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<h3>0.0.2: Jan 29 2006</h3>
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<ul>
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<li>Update of the documentation, web site redesign (Diana Fong)</li>
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<li>integration of HTTP xend RPC based on libxend by Anthony Liquori
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formost operations</li>
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<li>Adding Save and Restore APIs</li>
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<li>extended the virsh command line tool (Karel Zak)</li>
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<li>remove xenstore transactions (Anthony Liguori)</li>
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<li>fix the Python bindings bug when domain and connections where freed</li>
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</ul>
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<h3>0.0.1: Dec 19 2005</h3>
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<ul>
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<li>First release</li>
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<li>Basic management of existing Xen domains</li>
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<li>Minimal autogenerated Python bindings</li>
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</ul>
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<h2><a name="Introducti">Introduction</a></h2>
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<p>Libvirt is a C toolkit to interact with the virtualization capabilities
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ofrecent versions of Linux (and other OSes), but libvirt won't try to
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provideall possible interfaces for interacting with the virtualization
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features.</p>
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<p>To avoid ambiguity about the terms used here here are the definitions
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forsome of the specific concepts used in libvirt documentation:</p>
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<ul>
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<li>a <strong>node</strong>is a single physical machine</li>
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<li>an <strong>hypervisor</strong>is a layer of software allowing
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tovirtualize a node in a set of virtual machines with possibly
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differentconfigurations than the node itself</li>
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<li>a <strong>domain</strong>is an instance of an operating system
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runningon a virtualized machine provided by the hypervisor</li>
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</ul>
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<p style="text-align: center"><img
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alt="Hypervisor and domains running on a node" src="node.gif"></p>
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<p>Now we can define the goal of libvirt: to provide the lowest
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possiblegeneric and stable layer to manage domains on a node.</p>
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<p>This implies the following:</p>
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<ul>
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<li>the API is not targetted to a single virtualization environment,
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itcurrently supports Xen and QEmu/KVM. This also implies that some
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veryspecific capabilities which are not generic enough may not be
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provided aslibvirt APIs</li>
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<li>the API should allow to do efficiently and cleanly all the
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operationsneeded to manage domains on a node</li>
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<li>the API will not try to provide hight level multi-nodes
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managementfeatures like load balancing, though they could be implemented
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on top oflibvirt</li>
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<li>stability of the API is a big concern, libvirt should
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isolateapplications from the frequent changes expected at the lower level
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of thevirtualization framework</li>
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</ul>
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<p>So libvirt should be a building block for higher level management toolsand
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for applications focusing on virtualization of a single node (the
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onlyexception being domain migration between node capabilities which may need
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tobe added at the libvirt level). Where possible libvirt should be
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extendableto be able to provide the same API for remote nodes, however this
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is not thecase at the moment, the code currently handle only local node
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accesses(extension for remote access support is being worked on, see<a
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href="bugs.html">the mailing list</a>discussions about it).</p>
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<h2><a name="architecture">libvirt architecture</a></h2>
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<p>Currently libvirt supports 2 kind of virtualization, and its
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internalstructure is based on a driver model which simplifies adding new
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engines:</p>
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<ul>
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<li><a href="#Xen">Xen hypervisor</a></li>
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<li><a href="#QEmu">QEmu and KVM based virtualization</a></li>
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<li><a href="#drivers">the driver architecture</a></li>
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</ul>
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<h3><a name="Xen">Libvirt Xen support</a></h3>
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<p>When running in a Xen environment, programs using libvirt have to
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executein "Domain 0", which is the primary Linux OS loaded on the machine.
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That OSkernel provides most if not all of the actual drivers used by the set
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ofdomains. It also runs the Xen Store, a database of informations shared by
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thehypervisor, the kernels, the drivers and the xen daemon. Xend. The xen
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daemonsupervise the control and execution of the sets of domains. The
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hypervisor,drivers, kernels and daemons communicate though a shared system
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busimplemented in the hypervisor. The figure below tries to provide a view
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ofthis environment:</p>
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<img src="architecture.gif" alt="The Xen architecture">
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<p>The library can be initialized in 2 ways depending on the level
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ofpriviledge of the embedding program. If it runs with root
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access,virConnectOpen() can be used, it will use different ways to connect
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tothe Xen infrastructure:</p>
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<ul>
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<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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<li>when used as non-root libvirt connect to a proxy daemon runningas root
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and providing read-only support</li>
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</ul>
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<p>The library will usually interact with the Xen daemon for any
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operationchanging the state of the system, but for performance and accuracy
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reasonsmay talk directly to the hypervisor when gathering state informations
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atleast when possible (i.e. when the running program using libvirt has
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rootpriviledge access).</p>
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<p>If it runs without root access virConnectOpenReadOnly() should be used
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toconnect to initialize the library. It will then fork a libvirt_proxy
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programrunning as root and providing read_only access to the API, this is
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thenonly useful for reporting and monitoring.</p>
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<h3><a name="QEmu">Libvirt QEmu and KVM support</a></h3>
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<p>The model for QEmu and KVM is completely similar, basically KVM isbased on
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QEmu for the process controlling a new domain, only small detailsdiffers
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between the two. In both case the libvirt API is providedby a controlling
|
|
process forked by libvirt in the background andwhich launch and control the
|
|
QEmu or KVM process. That program calledlibvirt_qemud talks though a specific
|
|
protocol to the library, andconnects to the console of the QEmu process in
|
|
order to control andreport on its status. Libvirt tries to expose all the
|
|
emulationsmodels of QEmu, the selection is done when creating the new
|
|
domain,by specifying the architecture and machine type targetted.</p>
|
|
|
|
<p>The code controlling the QEmu process is available in
|
|
the<code>qemud/</code>subdirectory.</p>
|
|
|
|
<h3><a name="drivers">the driver based architecture</a></h3>
|
|
|
|
<p>As the previous section explains, libvirt can communicate using
|
|
differentchannels with the Xen hypervisor, and is also able to use different
|
|
kindof hypervisor. To simplify the internal design, code, easemaintainance
|
|
and simplify the support of other virtualization engine theinternals have
|
|
been structured as one core component, the libvirt.c moduleacting as a
|
|
front-end for the library API and a set of hypvisor driversdefining a common
|
|
set of routines. That way the Xen Daemon accces, the XenStore one, the
|
|
Hypervisor hypercall are all isolated in separate C modulesimplementing at
|
|
least a subset of the common operations defined by thedrivers present in
|
|
driver.h. The driver architecture is used to add supportfor other
|
|
virtualization engines and</p>
|
|
<ul>
|
|
<li>xend_internal: implements the driver functions though the
|
|
XenDaemon.</li>
|
|
<li>xs_internal: implements the subset of the driver availble though theXen
|
|
Store.</li>
|
|
<li>xen_internal: provide the implementation of the functions possible
|
|
viadirect Xen hypervisor access.</li>
|
|
<li>proxy_internal: provide read-only Xen access via a proxy, the proxycode
|
|
is in the <code>proxy/</code>sub directory.</li>
|
|
<li>xm_internal: provide support for Xen defined but not running
|
|
domains.</li>
|
|
<li>qemu_internal: implement the driver functions for QEmu and
|
|
KVMvirtualization engines. It also uses a qemud/ specific daemon
|
|
whichinterracts with the QEmu process to implement libvirt API.</li>
|
|
<li>test: this is a test driver useful for regression tests of thefront-end
|
|
part of libvirt.</li>
|
|
</ul>
|
|
|
|
<p>Note that a given driver may only implement a subset of those
|
|
functions,for example saving a Xen domain state to disk and restoring it is
|
|
only possiblethough the Xen Daemon, in that case the driver entry points are
|
|
initialized toNULL.</p>
|
|
|
|
<p></p>
|
|
|
|
<h2><a name="Downloads">Downloads</a></h2>
|
|
|
|
<p>The latest versions of libvirt can be found on the <a
|
|
href="ftp://libvirt.org/libvirt/">libvirt.org</a>server ( <a
|
|
href="http://libvirt.org/sources/">HTTP</a>, <a
|
|
href="ftp://libvirt.org/libvirt/">FTP</a>). You will find there the
|
|
releasedversions as well as <a
|
|
href="http://libvirt.org/sources/libvirt-cvs-snapshot.tar.gz">snapshottarballs</a>updated
|
|
from CVS head every hour</p>
|
|
|
|
<p>Anonymous <a href="http://ximbiot.com/cvs/cvshome/docs/">CVS</a>is
|
|
alsoavailable, first register onto the server:</p>
|
|
|
|
<p><code>cvs -d :pserver:anoncvs@libvirt.org:2401/data/cvs login</code></p>
|
|
|
|
<p>it will request a password, enter <strong>anoncvs</strong>. Then you
|
|
cancheckout the development tree with:</p>
|
|
|
|
<p><code>cvs -d :pserver:anoncvs@libvirt.org:2401/data/cvs
|
|
colibvirt</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 nowavailable except commiting to the base.</p>
|
|
|
|
<h2><a name="Format">XML Formats</a></h2>
|
|
|
|
<p>This section describes the XML formats used mostly to represent domains,
|
|
there are variations on the format based on the kind of domains run and the
|
|
options used to launch them:</p>
|
|
<ul>
|
|
<li><a href="#Normal1">Normal paravirtualized Xen domains</a></li>
|
|
<li><a href="#Fully1">Fully virtualized Xen domains</a></li>
|
|
<li><a href="#KVM1">KVM domains</a></li>
|
|
<li><a href="#Net1">Networking options for QEmu and KVM</a></li>
|
|
<li><a href="#QEmu1">QEmu domains</a></li>
|
|
<li><a href="#Capa1">Discovering virtualization capabilities</a></li>
|
|
</ul>
|
|
|
|
<p>The formats try as much as possible to follow the same structure and reuse
|
|
elements and attributes where it makes sense.</p>
|
|
|
|
<h3 id="Normal"><a name="Normal1" id="Normal1">Normal paravirtualized
|
|
Xendomains</a>:</h3>
|
|
|
|
<p>The library use an XML format to describe domains, as input to <a
|
|
href="html/libvirt-libvirt.html#virDomainCreateLinux">virDomainCreateLinux()</a>and
|
|
as the output of <a
|
|
href="html/libvirt-libvirt.html#virDomainGetXMLDesc">virDomainGetXMLDesc()</a>,the
|
|
following is an example of the format as returned by the shell
|
|
command<code>virsh xmldump fc4</code>, where fc4 was one of the running
|
|
domains:</p>
|
|
<pre><domain type='xen' <span style="color: #0071FF; background-color: #FFFFFF">id='18'</span>>
|
|
<name>fc4</name>
|
|
<span style="color: #00B200; background-color: #FFFFFF"><os>
|
|
<type>linux</type>
|
|
<kernel>/boot/vmlinuz-2.6.15-1.43_FC5guest</kernel>
|
|
<initrd>/boot/initrd-2.6.15-1.43_FC5guest.img</initrd>
|
|
<root>/dev/sda1</root>
|
|
<cmdline> ro selinux=0 3</cmdline>
|
|
</os></span>
|
|
<memory>131072</memory>
|
|
<vcpu>1</vcpu>
|
|
<devices>
|
|
<span style="color: #FF0080; background-color: #FFFFFF"><disk type='file'>
|
|
<source file='/u/fc4.img'/>
|
|
<target dev='sda1'/>
|
|
</disk></span>
|
|
<span style="color: #0000FF; background-color: #FFFFFF"><interface type='bridge'>
|
|
<source bridge='xenbr0'/>
|
|
<mac address='</span><span style="color: #0000FF; background-color: #FFFFFF"></span><span style="color: #0000FF; background-color: #FFFFFF">aa:00:00:00:00:11'/>
|
|
<script path='/etc/xen/scripts/vif-bridge'/>
|
|
</interface></span>
|
|
<span style="color: #FF8000; background-color: #FFFFFF"><console tty='/dev/pts/5'/></span>
|
|
</devices>
|
|
</domain></pre>
|
|
|
|
<p>The root element must be called <code>domain</code>with no namespace,
|
|
the<code>type</code>attribute indicates the kind of hypervisor used, 'xen'
|
|
isthe default value. The <code>id</code>attribute gives the domain id
|
|
atruntime (not however that this may change, for example if the domain is
|
|
savedto disk and restored). The domain has a few children whose order is
|
|
notsignificant:</p>
|
|
<ul>
|
|
<li>name: the domain name, preferably ASCII based</li>
|
|
<li>memory: the maximum memory allocated to the domain in kilobytes</li>
|
|
<li>vcpu: the number of virtual cpu configured for the domain</li>
|
|
<li>os: a block describing the Operating System, its content will
|
|
bedependant on the OS type
|
|
<ul>
|
|
<li>type: indicate the OS type, always linux at this point</li>
|
|
<li>kernel: path to the kernel on the Domain 0 filesystem</li>
|
|
<li>initrd: an optional path for the init ramdisk on the Domain
|
|
0filesystem</li>
|
|
<li>cmdline: optional command line to the kernel</li>
|
|
<li>root: the root filesystem from the guest viewpoint, it may bepassed
|
|
as part of the cmdline content too</li>
|
|
</ul>
|
|
</li>
|
|
<li>devices: a list of <code>disk</code>,
|
|
<code>interface</code>and<code>console</code>descriptions in no special
|
|
order</li>
|
|
</ul>
|
|
|
|
<p>The format of the devices and their type may grow over time, but
|
|
thefollowing should be sufficient for basic use:</p>
|
|
|
|
<p>A <code>disk</code>device indicates a block device, it can have twovalues
|
|
for the type attribute either 'file' or 'block' corresponding to the 2options
|
|
availble at the Xen layer. It has two mandatory children, and oneoptional one
|
|
in no specific order:</p>
|
|
<ul>
|
|
<li>source with a file attribute containing the path in Domain 0 to thefile
|
|
or a dev attribute if using a block device, containing the devicename
|
|
('hda5' or '/dev/hda5')</li>
|
|
<li>target indicates in a dev attribute the device where it is mapped inthe
|
|
guest</li>
|
|
<li>readonly an optional empty element indicating the device
|
|
isread-only</li>
|
|
</ul>
|
|
|
|
<p>An <code>interface</code>element describes a network device mapped on
|
|
theguest, it also has a type whose value is currently 'bridge', it also have
|
|
anumber of children in no specific order:</p>
|
|
<ul>
|
|
<li>source: indicating the bridge name</li>
|
|
<li>mac: the optional mac address provided in the address attribute</li>
|
|
<li>ip: the optional IP address provided in the address attribute</li>
|
|
<li>script: the script used to bridge the interfcae in the Domain 0</li>
|
|
<li>target: and optional target indicating the device name.</li>
|
|
</ul>
|
|
|
|
<p>A <code>console</code>element describes a serial console connection tothe
|
|
guest. It has no children, and a single attribute
|
|
<code>tty</code>whichprovides the path to the Pseudo TTY on which the guest
|
|
console can beaccessed</p>
|
|
|
|
<p>Life cycle actions for the domain can also be expressed in the XML
|
|
format,they drive what should be happening if the domain crashes, is rebooted
|
|
or ispoweroff. There is various actions possible when this happen:</p>
|
|
<ul>
|
|
<li>destroy: The domain is cleaned up (that's the default normal
|
|
processingin Xen)</li>
|
|
<li>restart: A new domain is started in place of the old one with the
|
|
sameconfiguration parameters</li>
|
|
<li>preserve: The domain will remain in memory until it is
|
|
destroyedmanually, it won't be running but allows for post-mortem
|
|
debugging</li>
|
|
<li>rename-restart: a variant of the previous one but where the old
|
|
domainis renamed before being saved to allow a restart</li>
|
|
</ul>
|
|
|
|
<p>The following could be used for a Xen production system:</p>
|
|
<pre><domain>
|
|
...
|
|
<on_reboot>restart</on_reboot>
|
|
<on_poweroff>destroy</on_poweroff>
|
|
<on_crash>rename-restart</on_crash>
|
|
...
|
|
</domain></pre>
|
|
|
|
<p>While the format may be extended in various ways as support for
|
|
morehypervisor types and features are added, it is expected that this core
|
|
subsetwill remain functional in spite of the evolution of the library.</p>
|
|
|
|
<h3 id="Fully"><a name="Fully1" id="Fully1">Fully virtualized
|
|
guests</a>(added in 0.1.3):</h3>
|
|
|
|
<p>Here is an example of a domain description used to start a
|
|
fullyvirtualized (a.k.a. HVM) Xen domain. This requires hardware
|
|
virtualizationsupport at the processor level but allows to run unmodified
|
|
operatingsystems:</p>
|
|
<pre><domain type='xen' id='3'>
|
|
<name>fv0</name>
|
|
<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
|
|
<os>
|
|
<span style="color: #0000E5; background-color: #FFFFFF"><type>hvm</type></span>
|
|
<span style="color: #0000E5; background-color: #FFFFFF"><loader>/usr/lib/xen/boot/hvmloader</loader></span>
|
|
<span style="color: #0000E5; background-color: #FFFFFF"><boot dev='hd'/></span>
|
|
</os>
|
|
<memory>524288</memory>
|
|
<vcpu>1</vcpu>
|
|
<on_poweroff>destroy</on_poweroff>
|
|
<on_reboot>restart</on_reboot>
|
|
<on_crash>restart</on_crash>
|
|
<features>
|
|
<span style="color: #E50000; background-color: #FFFFFF"><pae/>
|
|
<acpi/>
|
|
<apic/></span>
|
|
</features>
|
|
<devices>
|
|
<span style="color: #0000E5; background-color: #FFFFFF"><emulator>/usr/lib/xen/bin/qemu-dm</emulator></span>
|
|
<interface type='bridge'>
|
|
<source bridge='xenbr0'/>
|
|
<mac address='00:16:3e:5d:c7:9e'/>
|
|
<script path='vif-bridge'/>
|
|
</interface>
|
|
<disk type='file'>
|
|
<source file='/root/fv0'/>
|
|
<target <span style="color: #0000E5; background-color: #FFFFFF">dev='hda'</span>/>
|
|
</disk>
|
|
<disk type='file' <span style="color: #0000E5; background-color: #FFFFFF">device='cdrom'</span>>
|
|
<source file='/root/fc5-x86_64-boot.iso'/>
|
|
<target <span style="color: #0000E5; background-color: #FFFFFF">dev='hdc'</span>/>
|
|
<readonly/>
|
|
</disk>
|
|
<disk type='file' <span style="color: #0000E5; background-color: #FFFFFF">device='floppy'</span>>
|
|
<source file='/root/fd.img'/>
|
|
<target <span style="color: #0000E5; background-color: #FFFFFF">dev='fda'</span>/>
|
|
</disk>
|
|
<span style="color: #0000E5; background-color: #FFFFFF"><graphics type='vnc' port='5904'/></span>
|
|
</devices>
|
|
</domain></pre>
|
|
|
|
<p>There is a few things to notice specifically for HVM domains:</p>
|
|
<ul>
|
|
<li>the optional <code><features></code>block is used to
|
|
enablecertain guest CPU / system features. For HVM guests the
|
|
followingfeatures are defined:
|
|
<ul>
|
|
<li><code>pae</code>- enable PAE memory addressing</li>
|
|
<li><code>apic</code>- enable IO APIC</li>
|
|
<li><code>acpi</code>- enable ACPI bios</li>
|
|
</ul>
|
|
</li>
|
|
<li>the <code><os></code>block description is very different, firstit
|
|
indicates that the type is 'hvm' for hardware virtualization, theninstead
|
|
of a kernel, boot and command line arguments, it points to an osboot
|
|
loader which will extract the boot informations from the boot
|
|
devicespecified in a separate boot element. The <code>dev</code>attribute
|
|
onthe <code>boot</code>tag can be one of:
|
|
<ul>
|
|
<li><code>fd</code>- boot from first floppy device</li>
|
|
<li><code>hd</code>- boot from first harddisk device</li>
|
|
<li><code>cdrom</code>- boot from first cdrom device</li>
|
|
</ul>
|
|
</li>
|
|
<li>the <code><devices></code>section includes an emulator
|
|
entrypointing to an additional program in charge of emulating the
|
|
devices</li>
|
|
<li>the disk entry indicates in the dev target section that the
|
|
emulationfor the drive is the first IDE disk device hda. The list of
|
|
device namessupported is dependant on the Hypervisor, but for Xen it can
|
|
be any IDEdevice <code>hda</code>-<code>hdd</code>, or a floppy
|
|
device<code>fda</code>, <code>fdb</code>. The
|
|
<code><disk></code>elementalso supports a 'device' attribute to
|
|
indicate what kinda of hardware toemulate. The following values are
|
|
supported:
|
|
<ul>
|
|
<li><code>floppy</code>- a floppy disk controller</li>
|
|
<li><code>disk</code>- a generic hard drive (the default itomitted)</li>
|
|
<li><code>cdrom</code>- a CDROM device</li>
|
|
</ul>
|
|
For Xen 3.0.2 and earlier a CDROM device can only be emulated on
|
|
the<code>hdc</code>channel, while for 3.0.3 and later, it can be
|
|
emulatedon any IDE channel.</li>
|
|
<li>the <code><devices></code>section also include at least oneentry
|
|
for the graphic device used to render the os. Currently there isjust 2
|
|
types possible 'vnc' or 'sdl'. If the type is 'vnc', then anadditional
|
|
<code>port</code>attribute will be present indicating the TCPport on
|
|
which the VNC server is accepting client connections.</li>
|
|
</ul>
|
|
|
|
<p>It is likely that the HVM description gets additional optional elementsand
|
|
attributes as the support for fully virtualized domain expands,especially for
|
|
the variety of devices emulated and the graphic supportoptions offered.</p>
|
|
|
|
<h3><a name="KVM1">KVM domain (added in 0.2.0)</a></h3>
|
|
|
|
<p>Support for the <a href="http://kvm.qumranet.com/">KVM virtualization</a>
|
|
is provided in recent Linux kernels (2.6.20 and onward). This requires
|
|
specific hardware with acceleration support and the availability of the
|
|
special version of the <a
|
|
href="http://fabrice.bellard.free.fr/qemu/">QEmu</a> binary. Since this
|
|
relies on QEmu for the machine emulation like fully virtualized guests the
|
|
XML description is quite similar, here is a simple example:</p>
|
|
<pre><domain <span style="color: #FF0000; background-color: #FFFFFF">type='kvm'</span>>
|
|
<name>demo2</name>
|
|
<uuid>4dea24b3-1d52-d8f3-2516-782e98a23fa0</uuid>
|
|
<memory>131072</memory>
|
|
<vcpu>1</vcpu>
|
|
<os>
|
|
<type>hvm</type>
|
|
</os>
|
|
<devices>
|
|
<span style="color: #FF0000; background-color: #FFFFFF"><emulator>/home/user/usr/kvm-devel/bin/qemu-system-x86_64</emulator></span>
|
|
<disk type='file' device='disk'>
|
|
<source file='/home/user/fedora/diskboot.img'/>
|
|
<target dev='hda'/>
|
|
</disk>
|
|
<interface <span style="color: #FF0000; background-color: #FFFFFF">type='user'</span>>
|
|
<mac address='24:42:53:21:52:45'/>
|
|
</interface>
|
|
<graphics type='vnc' port='-1'/>
|
|
</devices>
|
|
</domain></pre>
|
|
|
|
<p>The specific points to note if using KVM are:</p>
|
|
<ul>
|
|
<li>the top level domain element carries a type of 'kvm'</li>
|
|
<li>the <devices> emulator points to the special qemu binary required
|
|
for KVM</li>
|
|
<li>networking interface definitions definitions are somewhat different due
|
|
to a different model from Xen see below</li>
|
|
</ul>
|
|
|
|
<p>except those points the options should be quite similar to Xen HVM
|
|
ones.</p>
|
|
|
|
<h3><a name="Net1">Networking options for QEmu and KVM (added in 0.2.0)</a></h3>
|
|
|
|
<p>The networking support in the QEmu and KVM case is more flexible, and
|
|
support a variety of options:</p>
|
|
<ol>
|
|
<li>Userspace SLIRP stack
|
|
<p>Provides a virtual LAN with NAT to the outside world. The virtual
|
|
network has DHCP & DNS services and will give the guest VM addresses
|
|
starting from <code>10.0.2.15</code>. The default router will be
|
|
<code>10.0.2.2</code> and the DNS server will be <code>10.0.2.3</code>.
|
|
This networking is the only option for unprivileged users who need their
|
|
VMs to have outgoing access. Example configs are:</p>
|
|
<pre><interface type='user'/></pre>
|
|
<pre>
|
|
<interface type='user'>
|
|
<mac address="11:22:33:44:55:66:/>
|
|
</interface>
|
|
</pre>
|
|
</li>
|
|
<li>Virtual network
|
|
<p>Provides a virtual network using a bridge device in the host.
|
|
Depending on the virtual network configuration, the network may be
|
|
totally isolated,NAT'ing to aan explicit network device, or NAT'ing to
|
|
the default route. DHCP and DNS are provided on the virtual network in
|
|
all cases and the IP range can be determined by examining the virtual
|
|
network config with '<code>virsh net-dumpxml <network
|
|
name></code>'. There is one virtual network called'default' setup out
|
|
of the box which does NAT'ing to the default route and has an IP range of
|
|
<code>192.168.22.0/255.255.255.0</code>. Each guest will have an
|
|
associated tun device created with a name of vnetN, which can also be
|
|
overriden with the <target> element. Example configs are:</p>
|
|
<pre><interface type='network'>
|
|
<source network='default'/>
|
|
</interface>
|
|
|
|
<interface type='network'>
|
|
<source network='default'/>
|
|
<target dev='vnet7'/>
|
|
<mac address="11:22:33:44:55:66:/>
|
|
</interface>
|
|
</pre>
|
|
</li>
|
|
<li>Bridge to to LAN
|
|
<p>Provides a bridge from the VM directly onto the LAN. This assumes
|
|
there is a bridge device on the host which has one or more of the hosts
|
|
physical NICs enslaved. The guest VM will have an associated tun device
|
|
created with a name of vnetN, which can also be overriden with the
|
|
<target> element. The tun device will be enslaved to the bridge.
|
|
The IP range / network configuration is whatever is used on the LAN. This
|
|
provides the guest VM full incoming & outgoing net access just like a
|
|
physical machine. Examples include:</p>
|
|
<pre><interface type='bridge'>
|
|
<source dev='br0'/>
|
|
</interface>
|
|
|
|
<interface type='bridge'>
|
|
<source dev='br0'/>
|
|
<target dev='vnet7'/>
|
|
<mac address="11:22:33:44:55:66:/>
|
|
</interface> <interface type='bridge'>
|
|
<source dev='br0'/>
|
|
<target dev='vnet7'/>
|
|
<mac address="11:22:33:44:55:66:/>
|
|
</interface></pre>
|
|
</li>
|
|
<li>Generic connection to LAN
|
|
<p>Provides a means for the administrator to execute an arbitrary script
|
|
to connect the guest's network to the LAN. The guest will have a tun
|
|
device created with a name of vnetN, which can also be overriden with the
|
|
<target> element. After creating the tun device a shell script will
|
|
be run which is expected to do whatever host network integration is
|
|
required. By default this script is called /etc/qemu-ifup but can be
|
|
overriden.</p>
|
|
<pre><interface type='ethernet'/>
|
|
|
|
<interface type='ethernet'>
|
|
<target dev='vnet7'/>
|
|
<script path='/etc/qemu-ifup-mynet'/>
|
|
</interface></pre>
|
|
</li>
|
|
<li>Multicast tunnel
|
|
<p>A multicast group is setup to represent a virtual network. Any VMs
|
|
whose network devices are in the same multicast group can talk to each
|
|
other even across hosts. This mode is also available to unprivileged
|
|
users. There is no default DNS or DHCP support and no outgoing network
|
|
access. To provide outgoing network access, one of the VMs should have a
|
|
2nd NIC which is connected to one of the first 4 network types and do the
|
|
appropriate routing. The multicast protocol is compatible with that used
|
|
by user mode linux guests too. The source address used must be from the
|
|
multicast address block.</p>
|
|
<pre><interface type='mcast'>
|
|
<source address='230.0.0.1' port='5558'/>
|
|
</interface></pre>
|
|
</li>
|
|
<li>TCP tunnel
|
|
<p>A TCP client/server architecture provides a virtual network. One VM
|
|
provides the server end of the netowrk, all other VMS are configured as
|
|
clients. All network traffic is routed between the VMs via the server.
|
|
This mode is also available to unprivileged users. There is no default
|
|
DNS or DHCP support and no outgoing network access. To provide outgoing
|
|
network access, one of the VMs should have a 2nd NIC which is connected
|
|
to one of the first 4 network types and do the appropriate routing.</p>
|
|
<p>Example server config:</p>
|
|
<pre><interface type='server'>
|
|
<source address='192.168.0.1' port='5558'/>
|
|
</interface></pre>
|
|
<p>Example client config:</p>
|
|
<pre><interface type='client'>
|
|
<source address='192.168.0.1' port='5558'/>
|
|
</interface></pre>
|
|
</li>
|
|
</ol>
|
|
|
|
<p>To be noted, options 2, 3, 4 are also supported by Xen VMs, so it is
|
|
possible to use these configs to have networking with both Xen &
|
|
QEMU/KVMs connected to each other.</p>
|
|
|
|
<h3>Q<a name="QEmu1">Emu domain (added in 0.2.0)</a></h3>
|
|
|
|
<p>Libvirt support for KVM and QEmu is the same code base with only minor
|
|
changes. The configuration is as a result nearly identical, the only changes
|
|
are related to QEmu ability to emulate <a
|
|
href="http://www.qemu.org/status.html">various CPU type and hardware
|
|
platforms</a>, and kqemu support (QEmu own kernel accelerator when the
|
|
emulated CPU is i686 as well as the target machine):</p>
|
|
<pre><domain <span style="color: #FF0000; background-color: #FFFFFF">type='qemu'</span>>
|
|
<name>QEmu-fedora-i686</name>
|
|
<uuid>c7a5fdbd-cdaf-9455-926a-d65c16db1809</uuid>
|
|
<memory>219200</memory>
|
|
<currentMemory>219200</currentMemory>
|
|
<vcpu>2</vcpu>
|
|
<os>
|
|
<span style="color: #FF0000; background-color: #FFFFFF"><type arch='i686' machine='pc'>hvm</type></span>
|
|
<boot dev='cdrom'/>
|
|
</os>
|
|
<devices>
|
|
<span style="color: #FF0000; background-color: #FFFFFF"><emulator>/usr/bin/qemu</emulator></span>
|
|
<disk type='file' device='cdrom'>
|
|
<source file='/home/user/boot.iso'/>
|
|
<target dev='hdc'/>
|
|
<readonly/>
|
|
</disk>
|
|
<disk type='file' device='disk'>
|
|
<source file='/home/user/fedora.img'/>
|
|
<target dev='hda'/>
|
|
</disk>
|
|
<interface type='network'>
|
|
<source name='default'/>
|
|
</interface>
|
|
<graphics type='vnc' port='-1'/>
|
|
</devices>
|
|
</domain></pre>
|
|
|
|
<p>The difference here are:</p>
|
|
<ul>
|
|
<li>the value of type on top-level domain, it's 'qemu' or kqemu if asking
|
|
for <a href="http://www.qemu.org/kqemu-tech.html">kernel assisted
|
|
acceleration</a></li>
|
|
<li>the os type block defines the architecture to be emulated, and
|
|
optionally the machine type, see the discovery API below</li>
|
|
<li>the emulator string must point to the right emulator for that
|
|
architecture</li>
|
|
</ul>
|
|
|
|
<h3><a name="Capa1">Discovering virtualization capabilities (Added in 0.2.1)</a></h3>
|
|
|
|
<p>As new virtualization engine support gets added to libvirt, and to handle
|
|
cases like QEmu supporting a variety of emulations, a query interface has
|
|
been added in 0.2.1 allowing to list the set of supported virtualization
|
|
capabilities on the host:</p>
|
|
<pre> char * virConnectGetCapabilities (virConnectPtr conn);</pre>
|
|
|
|
<p>The value returned is an XML document listing the virtualization
|
|
capabilities of the host and virtualization engine to which
|
|
<code>@conn</code> is connected. One can test it using <code>virsh</code>
|
|
command line tool command '<code>capabilities</code>', it dumps the XML
|
|
associated to the current connection. For example in the case of a 64 bits
|
|
machine with hardware virtualization capabilities enabled in the chip and
|
|
BIOS you will see</p>
|
|
<pre><capabilities>
|
|
<span style="color: #E50000; background-color: #FFFFFF"><host>
|
|
<cpu>
|
|
<arch>x86_64</arch>
|
|
<features>
|
|
<vmx/>
|
|
</features>
|
|
</cpu>
|
|
</host></span>
|
|
|
|
<!-- xen-3.0-x86_64 -->
|
|
<span style="color: #0000E5; background-color: #FFFFFF"><guest>
|
|
<os_type>xen</os_type>
|
|
<arch name="x86_64">
|
|
<wordsize>64</wordsize>
|
|
<domain type="xen"></domain>
|
|
<emulator>/usr/lib64/xen/bin/qemu-dm</emulator>
|
|
</arch>
|
|
<features>
|
|
</features>
|
|
</guest></span>
|
|
|
|
<!-- hvm-3.0-x86_32 -->
|
|
<span style="color: #00B200; background-color: #FFFFFF"><guest>
|
|
<os_type>hvm</os_type>
|
|
<arch name="i686">
|
|
<wordsize>32</wordsize>
|
|
<domain type="xen"></domain>
|
|
<emulator>/usr/lib/xen/bin/qemu-dm</emulator>
|
|
<machine>pc</machine>
|
|
<machine>isapc</machine>
|
|
<loader>/usr/lib/xen/boot/hvmloader</loader>
|
|
</arch>
|
|
<features>
|
|
</features>
|
|
</guest></span>
|
|
...
|
|
</capabilities></pre>
|
|
|
|
<p>The fist block (in red) indicates the host hardware capbilities, currently
|
|
it is limited to the CPU properties but other information may be available,
|
|
it shows the CPU architecture, and the features of the chip (the feature
|
|
block is similar to what you will find in a Xen fully virtualized domain
|
|
description).</p>
|
|
|
|
<p>The second block (in blue) indicates the paravirtualization support of the
|
|
Xen support, you will see the os_type of xen to indicate a paravirtual
|
|
kernel, then architecture informations and potential features.</p>
|
|
|
|
<p>The third block (in green) gives similar informations but when running a
|
|
32 bit OS fully virtualized with Xen using the hvm support.</p>
|
|
|
|
<p>This section is likely to be updated and augmented in the future, see <a
|
|
href="https://www.redhat.com/archives/libvir-list/2007-March/msg00215.html">the
|
|
discussion</a> which led to the capabilities format in the mailing-list
|
|
archives.</p>
|
|
|
|
<h2><a name="Python" id="Python">Binding for Python</a></h2>
|
|
|
|
<p>Libvirt comes with direct support for the Python language (just make
|
|
sureyou installed the libvirt-python package if not compiling from sources).
|
|
Alsonote that Daniel Berrange provides <a
|
|
href="http://search.cpan.org/~danberr/Sys-Virt-0.1.0/">bindings for
|
|
Perl</a>too.</p>
|
|
|
|
<p>The Python binding should be complete and are mostly
|
|
automaticallygenerated from the formal description of the API in xml. The
|
|
bindings arearticulated around 2 classes <code>virConnect</code>and virDomain
|
|
mapping tothe C types. Functions in the C API taking either type as argument
|
|
thenbecomes methods for the classes, their name is just stripped from
|
|
thevirConnect or virDomain(Get) prefix and the first letter gets converted
|
|
tolower case, for example the C functions:</p>
|
|
|
|
<p><code>int <a
|
|
href="html/libvirt-libvirt.html#virConnectNumOfDomains">virConnectNumOfDomains</a>(virConnectPtr
|
|
conn);</code></p>
|
|
|
|
<p><code>int <a
|
|
href="html/libvirt-libvirt.html#virDomainSetMaxMemory">virDomainSetMaxMemory</a>(virDomainPtr
|
|
domain, unsigned long memory);</code></p>
|
|
|
|
<p>become</p>
|
|
|
|
<p><code>virConn::numOfDomains(self)</code></p>
|
|
|
|
<p><code>virDomain::setMaxMemory(self, memory)</code></p>
|
|
|
|
<p>This process is fully automated, you can get a summary of the conversionin
|
|
the file libvirtclass.txt present in the python dir or in the docs.Thereis a
|
|
couple of function who don't map directly to their C counterparts due
|
|
tospecificities in their argument conversions:</p>
|
|
<ul>
|
|
<li><code><a
|
|
href="html/libvirt-libvirt.html#virConnectListDomains">virConnectListDomains</a></code>is
|
|
replaced by <code>virDomain::listDomainsID(self)</code>which returnsa
|
|
list of the integer ID for the currently running domains</li>
|
|
<li><code><a
|
|
href="html/libvirt-libvirt.html#virDomainGetInfo">virDomainGetInfo</a></code>is
|
|
replaced by <code>virDomain::info()</code>which returns a list of
|
|
<ol>
|
|
<li>state: one of the state values (virDomainState)</li>
|
|
<li>maxMemory: the maximum memory used by the domain</li>
|
|
<li>memory: the current amount of memory used by the domain</li>
|
|
<li>nbVirtCPU: the number of virtual CPU</li>
|
|
<li>cpuTime: the time used by the domain in nanoseconds</li>
|
|
</ol>
|
|
</li>
|
|
</ul>
|
|
|
|
<p>So let's look at a simple example inspired from the
|
|
<code>basic.py</code>test found in <code>python/tests/</code>in the source
|
|
tree:</p>
|
|
<pre>import <span style="color: #0071FF; background-color: #FFFFFF">libvirt</span>
|
|
import sys
|
|
|
|
conn = <span style="color: #0071FF; background-color: #FFFFFF">libvirt</span>.openReadOnly(None)
|
|
if conn == None:
|
|
print 'Failed to open connection to the hypervisor'
|
|
sys.exit(1)
|
|
|
|
try:
|
|
dom0 = conn.<span style="color: #007F00; background-color: #FFFFFF">lookupByName</span>("Domain-0")
|
|
except:
|
|
print 'Failed to find the main domain'
|
|
sys.exit(1)
|
|
|
|
print "Domain 0: id %d running %s" % (dom0.<span style="color: #FF0080; background-color: #FFFFFF">ID</span>(), dom0.<span style="color: #FF0080; background-color: #FFFFFF">OSType</span>())
|
|
print dom0.<span style="color: #FF0080; background-color: #FFFFFF">info</span>()</pre>
|
|
|
|
<p>There is not much to comment about it, it really is a straight mappingfrom
|
|
the C API, the only points to notice are:</p>
|
|
<ul>
|
|
<li>the import of the module called <code><span
|
|
style="color: #0071FF; background-color: #FFFFFF">libvirt</span></code></li>
|
|
<li>getting a connection to the hypervisor, in that case using
|
|
theopenReadOnly function allows the code to execute as a normal user.</li>
|
|
<li>getting an object representing the Domain 0 using <span
|
|
style="color: #007F00; background-color: #FFFFFF">lookupByName</span></li>
|
|
<li>if the domain is not found a libvirtError exception will be raised</li>
|
|
<li>extracting and printing some informations about the domain usingvarious
|
|
<span
|
|
style="color: #E50073; background-color: #FFFFFF">methods</span>associated
|
|
to the virDomain class.</li>
|
|
</ul>
|
|
|
|
<h2><a name="Errors" id="Errors">Handling of errors</a></h2>
|
|
|
|
<p>The main goals of libvirt when it comes to error handling are:</p>
|
|
<ul>
|
|
<li>provide as much detail as possible</li>
|
|
<li>provide the informations as soon as possible</li>
|
|
<li>dont force the library user into one style of error handling</li>
|
|
</ul>
|
|
|
|
<p>As result the library provide both synchronous, callback based
|
|
andasynchronous error reporting. When an error happens in the library code
|
|
theerror is logged, allowing to retrieve it later and if the user registered
|
|
anerror callback it will be called synchronously. Once the call to libvirt
|
|
endsthe error can be detected by the return value and the full information
|
|
forthe last logged error can be retrieved.</p>
|
|
|
|
<p>To avoid as much as prossible troubles with a global variable in
|
|
amultithreaded environment, libvirt will associate when possible the errors
|
|
tothe current connection they are related to, that way the error is stored in
|
|
adynamic structure which can be made thread specific. Error callback can
|
|
beset specifically to a connection with</p>
|
|
|
|
<p>So error handling in the code is the following:</p>
|
|
<ol>
|
|
<li>if the error can be associated to a connection for example when
|
|
failingto look up a domain
|
|
<ol>
|
|
<li>if there is a callback associated to the connection set with <a
|
|
href="html/libvirt-virterror.html#virConnSetErrorFunc">virConnSetErrorFunc</a>,call
|
|
it with the error informations</li>
|
|
<li>otherwise if there is a global callback set with <a
|
|
href="html/libvirt-virterror.html#virSetErrorFunc">virSetErrorFunc</a>,call
|
|
it with the error information</li>
|
|
<li>otherwise call <a
|
|
href="html/libvirt-virterror.html#virDefaultErrorFunc">virDefaultErrorFunc</a>which
|
|
is the default error function of the library issuing the erroron
|
|
stderr</li>
|
|
<li>save the error in the connection for later retrieval with <a
|
|
href="html/libvirt-virterror.html#virConnGetLastError">virConnGetLastError</a></li>
|
|
</ol>
|
|
</li>
|
|
<li>otherwise like when failing to create an hypervisor connection:
|
|
<ol>
|
|
<li>if there is a global callback set with <a
|
|
href="html/libvirt-virterror.html#virSetErrorFunc">virSetErrorFunc</a>,call
|
|
it with the error information</li>
|
|
<li>otherwise call <a
|
|
href="html/libvirt-virterror.html#virDefaultErrorFunc">virDefaultErrorFunc</a>which
|
|
is the default error function of the library issuing the erroron
|
|
stderr</li>
|
|
<li>save the error in the connection for later retrieval with <a
|
|
href="html/libvirt-virterror.html#virGetLastError">virGetLastError</a></li>
|
|
</ol>
|
|
</li>
|
|
</ol>
|
|
|
|
<p>In all cases the error informations are provided as a <a
|
|
href="html/libvirt-virterror.html#virErrorPtr">virErrorPtr</a>pointer
|
|
toread-only structure <a
|
|
href="html/libvirt-virterror.html#virError">virError</a>containing
|
|
thefollowing fields:</p>
|
|
<ul>
|
|
<li>code: an error number from the <a
|
|
href="html/libvirt-virterror.html#virErrorNumber">virErrorNumber</a>enum</li>
|
|
<li>domain: an enum indicating which part of libvirt raised the error see<a
|
|
href="html/libvirt-virterror.html#virErrorDomain">virErrorDomain</a></li>
|
|
<li>level: the error level, usually VIR_ERR_ERROR, though there is room
|
|
forwarnings like VIR_ERR_WARNING</li>
|
|
<li>message: the full human-readable formatted string of the error</li>
|
|
<li>conn: if available a pointer to the <a
|
|
href="html/libvirt-libvirt.html#virConnectPtr">virConnectPtr</a>connection
|
|
to the hypervisor where this happened</li>
|
|
<li>dom: if available a pointer to the <a
|
|
href="html/libvirt-libvirt.html#virDomainPtr">virDomainPtr</a>domaintargetted
|
|
in the operation</li>
|
|
</ul>
|
|
|
|
<p>and then extra raw informations about the error which may be initializedto
|
|
0 or NULL if unused</p>
|
|
<ul>
|
|
<li>str1, str2, str3: string informations, usually str1 is the errormessage
|
|
format</li>
|
|
<li>int1, int2: integer informations</li>
|
|
</ul>
|
|
|
|
<p>So usually, setting up specific error handling with libvirt consist
|
|
ofregistering an handler with with <a
|
|
href="html/libvirt-virterror.html#virSetErrorFunc">virSetErrorFunc</a>orwith
|
|
<a
|
|
href="html/libvirt-virterror.html#virConnSetErrorFunc">virConnSetErrorFunc</a>,chech
|
|
the value of the code value, take appropriate action, if needed letlibvirt
|
|
print the error on stderr by calling <a
|
|
href="html/libvirt-virterror.html#virDefaultErrorFunc">virDefaultErrorFunc</a>.For
|
|
asynchronous error handing, set such a function doing nothing to avoidthe
|
|
error being reported on stderr, and call virConnGetLastError
|
|
orvirGetLastError when an API call returned an error value. It can be a
|
|
goodidea to use <a
|
|
href="html/libvirt-virterror.html#virResetLastError">virResetError</a>or <a
|
|
href="html/libvirt-virterror.html#virConnResetLastError">virConnResetLastError</a>once
|
|
an error has been processed fully.</p>
|
|
|
|
<p>At the python level, there only a global reporting callback function
|
|
atthis point, see the error.py example about it:</p>
|
|
<pre>def handler(ctxt, err):
|
|
global errno
|
|
|
|
#print "handler(%s, %s)" % (ctxt, err)
|
|
errno = err
|
|
|
|
libvirt.registerErrorHandler(handler, 'context') </pre>
|
|
|
|
<p>the second argument to the registerErrorHandler function is passed as
|
|
thefist argument of the callback like in the C version. The error is a
|
|
tuplecontaining the same field as a virError in C, but cast to Python.</p>
|
|
|
|
<h2><a name="FAQ" id="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 libvirt</em>
|
|
<p>libvirt is released under the <a
|
|
href="http://www.opensource.org/licenses/lgpl-license.html">GNU
|
|
LesserGeneral Public License</a>, see the file COPYING.LIB in the
|
|
distributionfor the precise wording. The only library that libvirt
|
|
depends upon isthe Xen store access library which is also licenced under
|
|
the LGPL.</p>
|
|
</li>
|
|
<li><em>Can I embed libvirt in a proprietary application ?</em>
|
|
<p>Yes. The LGPL allows you to embed libvirt into a
|
|
proprietaryapplication. It would be graceful to send-back bug fixes and
|
|
improvementsas patches for possible incorporation in the main development
|
|
tree. Itwill 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 libvirt</em>?
|
|
<p>The original distribution comes from <a
|
|
href="ftp://libvirt.org/libvirt/">ftp://libvirt.org/libvirt/</a>.</p>
|
|
</li>
|
|
<li><em>I can't install the libvirt/libvirt-devel RPM packages due tofailed
|
|
dependencies</em>
|
|
<p>The most generic solution is to re-fetch the latest src.rpm ,
|
|
andrebuild it locally with</p>
|
|
<p><code>rpm --rebuild libvirt-xxx.src.rpm</code>.</p>
|
|
<p>If everything goes well it will generate two binary rpm packages
|
|
(oneproviding the shared libs and virsh, and the other one, the
|
|
-develpackage, providing includes, static libraries and scripts needed to
|
|
buildapplications with libvirt 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 beforbidden to user, at least for monitoring purposes. If "virsh
|
|
dominfo"fails to run as an user, change the mode of the xenstore
|
|
read-only socketwith:</p>
|
|
<p><code>chmod 666 /var/run/xenstored/socket_ro</code></p>
|
|
<p>and also make sure that the Xen Daemon is running correctly with
|
|
localHTTP server enabled, this is defined
|
|
in<code>/etc/xen/xend-config.sxp</code>which need the following line to
|
|
beenabled:</p>
|
|
<p><code>(xend-http-server yes)</code></p>
|
|
<p>If needed restart the xend daemon after making the change with
|
|
thefollowing command run as root:</p>
|
|
<p><code>service xend restart</code></p>
|
|
</li>
|
|
</ol>
|
|
|
|
<h3><a name="Compilatio">Compilation</a></h3>
|
|
<ol>
|
|
<li><em>What is the process to compile libvirt ?</em>
|
|
<p>As most UNIX libraries libvirt follows the "standard":</p>
|
|
<p><code>gunzip -c libvirt-xxx.tar.gz | tar xvf -</code></p>
|
|
<p><code>cd libvirt-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
|
|
toupdate your list of installed shared libs.</p>
|
|
</li>
|
|
<li><em>What other libraries are needed to compile/install libvirt ?</em>
|
|
<p>Libvirt requires libxenstore, which is usually provided by the
|
|
xenpackages 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
|
|
theautogen.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 libvirt</em>
|
|
<p>To simplify the process of reusing the library, libvirt comes
|
|
withpkgconfig support, which can be used directly from autoconf support
|
|
orvia the pkg-config command line tool, like:</p>
|
|
<p><code>pkg-config libvirt --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
|
|
libvirt,with an <a
|
|
href="https://www.redhat.com/archives/libvir-list/">on-linearchive</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 asattachments 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 use Red Hat Bugzilla to track bugs to libvirt. If you want to report
|
|
abug, please check <a
|
|
href="http://bugzilla.redhat.com/bugzilla/buglist.cgi?component=libvirt&component=libvirt-devel&component=libvirt-python&bug_status=ASSIGNED&bug_status=INVESTIGATE&bug_status=NEW&bug_status=REOPENED&bug_status=VERIFIED&short_desc_type=allwordssubstr&short_desc=&long_desc_type=allwordssubstr&long_desc=&Search=Search">the
|
|
existing open bugs</a>, then if yours isn't a duplicate ofan existing bug, <a
|
|
href="http://bugzilla.redhat.com/bugzilla/enter_bug.cgi?product=Fedora%20Core&component=libvirt">log
|
|
a new bug</a>. It may be goodto post to the <a
|
|
href="mailto:libvir-list@redhat.com">mailing-list</a>too if the issue looks
|
|
serious, thanks !</p>
|
|
</body>
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</html>
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