[libvirt] API calls to get interfaces and block devices

[Daniel P. Berrange]

On Fri, Apr 11, 2014 at 01:56:31PM +0200, Ruben Kerkhof wrote:
> On Fri, Apr 11, 2014 at 1:23 PM, Daniel P. Berrange <berrange at redhat.com> wrote:
> > On Fri, Apr 11, 2014 at 01:14:50PM +0200, Ruben Kerkhof wrote:
> >> Hi all,
> >>
> >> I have a few python scripts which use the libvirt api to get interface and block device statistics.
> >> What has been bugging me for a while now that is that there’s no high level api to get a list of all interfaces or block devices for a vm.
> >> The list can be retrieved from the xml with a bit of Xpath magic, but this seems to me to break the nice abstraction layer libvirt provides.
> >> Ideally, I don’t have to do anything with xml, and add dependencies on xml parsers to my code.
> >>
> >> I’ve seen examples of code doing this, for example the collectd libvirt plugin, but there must be many others.
> >>
> >> Can I kindly ask for such an API? Unfortunately I don’t have the skills to code this up myself.
> >
> > The libvirt-glib project provides a set of libraries including
> > libvirt-gconfig which intend to fill the gap you describe. They
> > are accessible from Python using GObject Introspection support.
> > The goal of libvirt-gconfig is to remove the need for apps to
> > know anything about XML at all.
> 
> So now instead of having to learn XML parsing I'll have to learn
> GObject and glib?
> And instead of a dependency on an xml parser I'll have to add one on glib.
> Not exactly the easy solution I was hoping for ;-)

Since you're using this from python, you don't have to learn / use
any of glib / gobject, beyond the way you right the "import"
statements. As the example I gave showed, the libvirt gconfig API
just appears mapped into the regular Python object model. A dep
on glib is really totally inconsequential compared to the deps that
the main libvirt.so already has.

This effort wouldn't be practical without using GObject, because
this frees us from having to write bindings for every programming
language which has proved a major timesink with main libvirt library.

> Thanks for the example, I'll dig into it.
> I just read https://www.berrange.com/posts/2011/11/22/introducing-the-libvirt-glib-a-mapping-of-the-libvirt-api-and-xml-to-glibgobject/
> Is there any documentation available for  libvirt-gobject online?

The -devel RPMs include the gtk-doc API docs, but I will freely admit they
are pretty horribly incomplete.  The easiest way to see APIs available is
to use python's built-in introspection eg

>>> from gi.repository import LibvirtGConfig;
>>> print dir(LibvirtGConfig.Domain)
['__class__', '__copy__', '__deepcopy__', '__delattr__', '__dict__', '__doc__', '__eq__', '__format__', '__gdoc__', '__ge__', '__getattribute__', '__gpointer__', '__grefcount__', '__gsignals__', '__gt__', '__gtype__', '__hash__', '__info__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_force_floating', '_ref', '_ref_sink', '_unref', '_unsupported_data_method', '_unsupported_method', 'add_device', 'bind_property', 'bind_property_full', 'chain', 'compat_control', 'connect', 'connect_after', 'connect_object', 'connect_object_after', 'disconnect', 'disconnect_by_func', 'emit', 'emit_stop_by_name', 'error_quark', 'force_floating', 'freeze_notify', 'g_type_instance', 'get_cpu', 'get_current_memory', 'get_custom_xml', 'get_data', 'get_description', 'get_devices', 'get_features', 'get_memory', 'get_name', 'get_os', 'get_properties', 'get_property', 'get_qdata', 'get_schema', 'get_title', 'get_vcpus', 'get_virt_type', 'handler_block', 'handler_block_by_func', 'handler_disconnect', 'handler_is_connected', 'handler_unblock', 'handler_unblock_by_func', 'interface_find_property', 'interface_install_property', 'interface_list_properties', 'is_floating', 'new', 'new_from_xml', 'notify', 'notify_by_pspec', 'parent', 'priv', 'props', 'qdata', 'ref', 'ref_count', 'ref_sink', 'replace_data', 'replace_qdata', 'run_dispose', 'set_clock', 'set_cpu', 'set_current_memory', 'set_custom_xml', 'set_data', 'set_description', 'set_devices', 'set_features', 'set_lifecycle', 'set_memory', 'set_name', 'set_os', 'set_power_management', 'set_properties', 'set_property', 'set_seclabel', 'set_title', 'set_vcpus', 'set_virt_type', 'steal_data', 'steal_qdata', 'stop_emission', 'stop_emission_by_name', 'thaw_notify', 'to_xml', 'unref', 'validate', 'watch_closure', 'weak_ref']

> Unfortunately I'm still stuck on Scientific Linux 6.5
> There are no packages for libvirt-glib in the Scientific Linux repo,
> are they available for libvirt 0.10 on RHEL 6.5?

Ah, I'm afraid you're out of luck on RHEL-6. This is only something we cna
support on Fedora or forthcoming RHEL-7.

Regards,
Daniel
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