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<book id="index" xmlns:xi="http://www.w3.org/2003/XInclude">
<bookinfo>
<title>libnm Reference Manual</title>
<releaseinfo>
for libnm &version;
The latest version of this documentation can be found on-line at
<ulink url="https://developer.gnome.org/libnm/stable/">https://developer.gnome.org/libnm/stable/</ulink>.
</releaseinfo>
<copyright>
<year>2012</year>
<year>2013</year>
<year>2014</year>
<year>2015</year>
<year>2016</year>
<year>2017</year>
<year>2018</year>
<holder>The NetworkManager Authors</holder>
</copyright>
<legalnotice>
<para>
Permission is granted to copy, distribute and/or modify this
document under the terms of the <citetitle>GNU Free
Documentation License</citetitle>, Version 1.1 or any later
version published by the Free Software Foundation with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. You may obtain a copy of the <citetitle>GNU Free
Documentation License</citetitle> from the Free Software
Foundation by visiting <ulink type="http"
url="http://www.fsf.org">their Web site</ulink> or by writing
to:
<address>
The Free Software Foundation, Inc.,
<street>51 Franklin Street</street> - Fifth Floor,
<city>Boston</city>, <state>MA</state> <postcode>02110-1301</postcode>,
<country>USA</country>
</address>
</para>
</legalnotice>
</bookinfo>
<chapter id="ref-overview">
<title>Overview</title>
<section id="intro">
<title>Introduction to libnm</title>
<para>
libnm is a client library for NetworkManager, the standard Linux network
management service. NetworkManager supports a wide variety of network
configuration scenarios, hardware devices and protocol families. Most of
the functionality is exposed on a
<ulink url="https://developer.gnome.org/NetworkManager/stable/spec.html">D-Bus API</ulink>,
allowing other tools to use the functionality provided by NetworkManager.
</para>
<para>
libnm provides C language bindings for functionality provided by
NetworkManager, optionally useful from other language runtimes as well.
</para>
<para>
libnm maps fairly closely to the actual D-Bus API that NetworkManager
provides, wrapping the remote D-Bus objects as native GObjects,
mapping D-Bus signals and properties to GObject signals and properties,
and providing helpful accessor and utility functions. However, unlike
the old libnm-util/libnm-glib API, the mapping to the D-Bus API is not
exact, and various inconveniences and historical anomalies of the D-Bus
API are papered over.
</para>
<para>
The following is a rough overview of the libnm object structure and
how to use the various parts of it:
<mediaobject id="libnm-overview">
<imageobject>
<imagedata fileref="libnm.png" format="PNG"/>
</imageobject>
</mediaobject>
</para>
</section>
<section id="usage">
<title>Using libnm</title>
<simplesect>
<title>When to use libnm</title>
<para>
libnm is fairly simple to use from C. It's based on glib and GObject.
If your project uses these already you'll find integration libnm with your
project rather convenient. In fact, the <command>nmcli</command> tool shipped
with NetworkManager is based on libnm.
</para>
<para>
libnm should be also the way to go if your project does something non-trivial
with NetworkManager, such as manipulating the connection profiles.
That is, if you're writing a specialized networking control tool or a desktop
environment, libnm is probably the right choice. The popular desktop
environments in fact all use libnm directly or with nm-applet and
nm-connection-editor that are all based on libnm.
</para>
<para>
An alternative to use of libnm is the use of the
<ulink url="https://developer.gnome.org/NetworkManager/stable/spec.html">D-Bus API</ulink>
directly. This gives you larger flexibility and reduces the overhead of linking
with the libnm library. This makes sense if your task is simple and you have a good
D-Bus library at your disposal. Activating a particular connection profile
from a Python script is a good example of a task that is perfectly simple
without using libnm.
</para>
</simplesect>
<simplesect>
<title>How to use libnm</title>
<para>
You can use the libnm's C API directly. To do so, all libnm programs need to
include <filename>NetworkManager.h</filename> that provides necessary definitions.
The rest of the API is documented in the reference manual.
</para>
<informalexample><programlisting><![CDATA[#include <glib.h>
#include <NetworkManager.h>
int
main (int argc, char *argv[])
{
NMClient *client;
client = nm_client_new (NULL, NULL);
if (client)
g_print ("NetworkManager version: %s\n", nm_client_get_version (client));
}]]></programlisting></informalexample>
<para>
Use <command>pkg-config</command> for <varname>libnm</varname> to discover the necessary
compiler flags.
</para>
<screen><prompt>$ </prompt><userinput>cc $(pkg-config --libs --cflags libnm) -o hello-nm hello-nm.c</userinput>
<prompt>$ </prompt><userinput>./hello-nm</userinput>
NetworkManager version: &version;
<prompt>$ </prompt></screen>
<para>
Utilize the <varname>PKG_CHECK_MODULES</varname> macro to integrate with an
autoconf-based build system. It's also recommended to use
<varname>NM_VERSION_MIN_REQUIRED</varname> and <varname>NM_VERSION_MAX_ALLOWED</varname>
macros to tell libnm headers which API version does your application need to work with.
If you use them, the compiler will warn you when you use functionality that is not
available in the versions you specified.
</para>
<informalexample><programlisting><![CDATA[PKG_CHECK_MODULES(LIBNM, libnm >= 1.8)
LIBNM_CFLAGS="$LIBNM_CFLAGS -DNM_VERSION_MIN_REQUIRED=NM_VERSION_1_8"
LIBNM_CFLAGS="$LIBNM_CFLAGS -DNM_VERSION_MAX_ALLOWED=NM_VERSION_1_8"]]></programlisting></informalexample>
<para>
You can use libnm from other languages than C with the use of GObject introspection.
This includes Perl, Python, Javascript, Lua, Ruby and more. The example below shows what the
typical libnm use in Python would look like.
</para>
<informalexample><programlisting><![CDATA[import gi
gi.require_version('NM', '1.0')
from gi.repository import NM
client = NM.Client.new(None)
print ("NetworkManager version " + client.get_version())]]></programlisting></informalexample>
<para>
There's <ulink url="https://lazka.github.io/pgi-docs/#NM-1.0">NM-1.0 Python API Reference</ulink>
maintained a third party that is generated from the introspection metadata.
</para>
<para>
In general, the C API documentation applies to the use GObject introspection
from other languages, with the calling convention respecting the language's
customs. Consult the source tree for
<ulink url="https://gitlab.freedesktop.org/NetworkManager/NetworkManager/tree/master/examples">some examples</ulink>.
</para>
</simplesect>
<simplesect id="sync-api">
<title>Synchronous API in libnm</title>
<para>
Libnm contains some synchronous API. This API basically makes a blocking
D-Bus call (g_dbus_connection_call_sync()) and is now deprecated.
</para>
<para>
Note that D-Bus is fundamentally asynchronous. Doing blocking calls
on top of D-Bus is odd, especially for libnm's NMClient. That is because
NMClient essentially is a client-side cache of the objects of the D-Bus
interface. This cache should be filled exclusively by (asynchronous) D-Bus
events. So, making a blocking D-Bus call means to wait for a response and
return it, while queuing everything that happens in between. Basically,
there are three options how a synchronous API on NMClient could behave:
<orderedlist>
<listitem>
<para>
The call basically calls g_dbus_connection_call_sync(). This means
that libnm sends a D-Bus request via GDBusConnection, and blockingly
waits for the response. All D-Bus messages that get received in the
meantime are queued in the GMainContext that belongs to NMClient.
That means, none of these D-Bus events are processed until we
iterate the GMainContext after the call returns. The effect is,
that NMClient (and all cached objects in there) are unaffected by
the D-Bus request.
Most of the synchronous API calls in libnm are of this kind.
The problem is that the strict ordering of D-Bus events gets
violated.
For some API this is not an immediate problem. Take for example
nm_device_wifi_request_scan(). The call merely blockingly tells
NetworkManager to start scanning, but since NetworkManager's D-Bus
API does not directly expose any state that tells whether we are
currently scanning, this out of order processing of the D-Bus
request is a small issue.
The problem is more obvious for nm_client_networking_set_enabled().
After calling it, NM_CLIENT_NETWORKING_ENABLED is still unaffected
and unchanged, because the PropertiesChanged signal from D-Bus
is not yet processed.
This means, while you make such a blocking call, NMClient's state
does not change. But usually you perform the synchronous call
to change some state. In this form, the blocking call is not useful,
because NMClient only changes the state after iterating the GMainContext,
and not after the blocking call returns.
</para>
</listitem>
<listitem>
<para>
Like 1), but after making the blocking g_dbus_connection_call_sync(),
update the NMClient cache artificially. This is what
nm_manager_check_connectivity() does, to "fix" bgo#784629.
This also has the problem of out-of-order events, but it kinda
solves the problem of not changing the state during the blocking
call. But it does so by hacking the state of the cache. I think
this is really wrong because the state should only be updated from
the ordered stream of D-Bus messages. When libnm decides to modify
the state, there are already D-Bus messages queued that affect this
very state.
</para>
</listitem>
<listitem>
<para>
Instead of calling g_dbus_connection_call_sync(), use the
asynchronous g_dbus_connection_call(). If we would use a separate
GMainContext for all D-Bus related calls, we could ensure that
while we block for the response, we iterate the internal main context.
This might be nice, because all events are processed in order and
after the blocking call returns, the NMClient state is up to date.
The are problems however: current blocking API does not do this,
so it's a significant change in behavior. Also, it might be
unexpected to the user that during the blocking call the entire
content of NMClient's cache might change and all pointers to the
cache might be invalidated. Also, of course NMClient would invoke
signals for all the changes that happen.
Another problem is that this would be more effort to implement
and it involves a small performance overhead for all D-Bus related
calls (because we have to serialize all events in an internal
GMainContext first and then invoke them on the caller's context).
Also, if the users wants this, they could implement it themself
using their own extra GMainContext and the asynchronous API.
</para>
</listitem>
</orderedlist>
See also <ulink url="https://smcv.pseudorandom.co.uk/2008/11/nonblocking/">this blog</ulink>
for why blocking calls are wrong.
</para>
<para>
All possible behaviors for synchronous API have severe behavioural
issues and thus such API is deprecated. Note that "deprecated" here does not
mean that the API is going to be removed. Libnm does not break API. The
user may:
<itemizedlist>
<listitem>
<para>
Continue to use this API. It's deprecated, awkward and discouraged,
but if it works for you, that's fine.
</para>
</listitem>
<listitem>
<para>
Use asynchronous API. That's the only sensible way to use D-Bus.
If libnm lacks a certain asynchronous counterpart, it should be
added.
</para>
</listitem>
<listitem>
<para>
Use GDBusConnection directly. There really isn't anything wrong
with D-Bus or GDBusConnection. This deprecated API is just a wrapper
around g_dbus_connection_call_sync(). You may call it directly
without feeling dirty.
</para>
</listitem>
</itemizedlist>
</para>
</simplesect>
</section>
</chapter>
<chapter>
<title>Client Object API Reference</title>
<xi:include href="xml/nm-client.xml"/>
<xi:include href="xml/nm-secret-agent-old.xml"/>
<xi:include href="xml/nm-object.xml"/>
<xi:include href="xml/nm-errors.xml"/>
<xi:include href="xml/nm-dbus-interface.xml"/>
</chapter>
<chapter>
<title>Connection and Setting API Reference</title>
<xi:include href="xml/nm-connection.xml"/>
<xi:include href="xml/nm-simple-connection.xml"/>
<xi:include href="xml/nm-remote-connection.xml"/>
<xi:include href="xml/nm-setting.xml"/>
<xi:include href="xml/nm-setting-connection.xml"/>
<!-- begin alphabetical -->
<xi:include href="xml/nm-setting-6lowpan.xml"/>
<xi:include href="xml/nm-setting-8021x.xml"/>
<xi:include href="xml/nm-setting-adsl.xml"/>
<xi:include href="xml/nm-setting-bluetooth.xml"/>
<xi:include href="xml/nm-setting-bond.xml"/>
<xi:include href="xml/nm-setting-bridge-port.xml"/>
<xi:include href="xml/nm-setting-bridge.xml"/>
<xi:include href="xml/nm-setting-cdma.xml"/>
<xi:include href="xml/nm-setting-dcb.xml"/>
<xi:include href="xml/nm-setting-dummy.xml"/>
<xi:include href="xml/nm-setting-ethtool.xml"/>
<xi:include href="xml/nm-setting-generic.xml"/>
<xi:include href="xml/nm-setting-gsm.xml"/>
<xi:include href="xml/nm-setting-hostname.xml"/>
<xi:include href="xml/nm-setting-infiniband.xml"/>
<xi:include href="xml/nm-setting-ip4-config.xml"/>
<xi:include href="xml/nm-setting-ip6-config.xml"/>
<xi:include href="xml/nm-setting-ip-config.xml"/>
<xi:include href="xml/nm-setting-ip-tunnel.xml"/>
<xi:include href="xml/nm-setting-macsec.xml"/>
<xi:include href="xml/nm-setting-macvlan.xml"/>
<xi:include href="xml/nm-setting-match.xml"/>
<xi:include href="xml/nm-setting-olpc-mesh.xml"/>
<xi:include href="xml/nm-setting-ovs-bridge.xml"/>
<xi:include href="xml/nm-setting-ovs-interface.xml"/>
<xi:include href="xml/nm-setting-ovs-dpdk.xml"/>
<xi:include href="xml/nm-setting-ovs-patch.xml"/>
<xi:include href="xml/nm-setting-ovs-port.xml"/>
<xi:include href="xml/nm-setting-ovs-external-ids.xml"/>
<xi:include href="xml/nm-setting-ppp.xml"/>
<xi:include href="xml/nm-setting-pppoe.xml"/>
<xi:include href="xml/nm-setting-proxy.xml"/>
<xi:include href="xml/nm-setting-serial.xml"/>
<xi:include href="xml/nm-setting-sriov.xml"/>
<xi:include href="xml/nm-setting-tc-config.xml"/>
<xi:include href="xml/nm-setting-team-port.xml"/>
<xi:include href="xml/nm-setting-team.xml"/>
<xi:include href="xml/nm-setting-tun.xml"/>
<xi:include href="xml/nm-setting-user.xml"/>
<xi:include href="xml/nm-setting-veth.xml"/>
<xi:include href="xml/nm-setting-vlan.xml"/>
<xi:include href="xml/nm-setting-vpn.xml"/>
<xi:include href="xml/nm-setting-vrf.xml"/>
<xi:include href="xml/nm-setting-vxlan.xml"/>
<xi:include href="xml/nm-setting-wifi-p2p.xml"/>
<xi:include href="xml/nm-setting-wimax.xml"/>
<xi:include href="xml/nm-setting-wired.xml"/>
<xi:include href="xml/nm-setting-wireguard.xml"/>
<xi:include href="xml/nm-setting-wireless-security.xml"/>
<xi:include href="xml/nm-setting-wireless.xml"/>
<xi:include href="xml/nm-setting-wpan.xml"/>
<!-- end alphabetical -->
</chapter>
<chapter>
<title>Device and Runtime Configuration API Reference</title>
<xi:include href="xml/nm-device.xml"/>
<!-- begin alphabetical -->
<xi:include href="xml/nm-device-6lowpan.xml"/>
<xi:include href="xml/nm-device-adsl.xml"/>
<xi:include href="xml/nm-device-bond.xml"/>
<xi:include href="xml/nm-device-bridge.xml"/>
<xi:include href="xml/nm-device-bt.xml"/>
<xi:include href="xml/nm-device-dummy.xml"/>
<xi:include href="xml/nm-device-ethernet.xml"/>
<xi:include href="xml/nm-device-generic.xml"/>
<xi:include href="xml/nm-device-infiniband.xml"/>
<xi:include href="xml/nm-device-ip-tunnel.xml"/>
<xi:include href="xml/nm-device-macsec.xml"/>
<xi:include href="xml/nm-device-macvlan.xml"/>
<xi:include href="xml/nm-device-modem.xml"/>
<xi:include href="xml/nm-device-olpc-mesh.xml"/>
<xi:include href="xml/nm-device-ovs-bridge.xml"/>
<xi:include href="xml/nm-device-ovs-interface.xml"/>
<xi:include href="xml/nm-device-ovs-port.xml"/>
<xi:include href="xml/nm-device-ppp.xml"/>
<xi:include href="xml/nm-device-team.xml"/>
<xi:include href="xml/nm-device-tun.xml"/>
<xi:include href="xml/nm-device-veth.xml"/>
<xi:include href="xml/nm-device-vlan.xml"/>
<xi:include href="xml/nm-device-vrf.xml"/>
<xi:include href="xml/nm-device-vxlan.xml"/>
<xi:include href="xml/nm-device-wifi-p2p.xml"/>
<xi:include href="xml/nm-device-wifi.xml"/>
<xi:include href="xml/nm-device-wimax.xml"/>
<xi:include href="xml/nm-device-wireguard.xml"/>
<xi:include href="xml/nm-device-wpan.xml"/>
<!-- end alphabetical -->
<xi:include href="xml/nm-active-connection.xml"/>
<xi:include href="xml/nm-vpn-connection.xml"/>
<xi:include href="xml/nm-access-point.xml"/>
<xi:include href="xml/nm-wifi-p2p-peer.xml"/>
<xi:include href="xml/nm-wimax-nsp.xml"/>
<xi:include href="xml/nm-ip-config.xml"/>
<xi:include href="xml/nm-dhcp-config.xml"/>
<xi:include href="xml/nm-checkpoint.xml"/>
</chapter>
<chapter>
<title>Utility API Reference</title>
<xi:include href="xml/nm-utils.xml"/>
<xi:include href="xml/nm-version.xml"/>
</chapter>
<chapter>
<title>VPN Plugin API Reference</title>
<xi:include href="xml/nm-vpn-service-plugin.xml"/>
<xi:include href="xml/nm-vpn-plugin-info.xml"/>
<xi:include href="xml/nm-vpn-editor.xml"/>
<xi:include href="xml/nm-vpn-editor-plugin.xml"/>
<xi:include href="xml/nm-vpn-plugin-old.xml"/>
</chapter>
<chapter id="object-tree">
<title>Object Hierarchy</title>
<xi:include href="xml/tree_index.sgml"/>
</chapter>
<index id="api-index-full">
<title>API Index</title>
<xi:include href="xml/api-index-full.xml"><xi:fallback /></xi:include>
</index>
<xi:include href="xml/annotation-glossary.xml"><xi:fallback /></xi:include>
<appendix id="license">
<title>License</title>
<para>
This library is free software; you can redistribute
it and/or modify it under the terms of the <citetitle>GNU
Lesser General Public License</citetitle> as published by
the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
</para>
<para>
This library is distributed in the hope that it will
be useful, but WITHOUT ANY WARRANTY; without even the
implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
</para>
<para>
You should have received a copy of the <citetitle>GNU
Lesser General Public License</citetitle> along with this
library; if not, write to the
<address>
Free Software Foundation, Inc.,
<street>51 Franklin Street</street> - Fifth Floor,
<city>Boston</city>, <state>MA</state> <postcode>02110-1301</postcode>,
<country>USA</country>
</address>
</para>
<para>
A copy of the <citetitle>GNU Lesser General Public License</citetitle>
can also be obtained from the <ulink url="https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html">
GNU web site</ulink>.
</para>
</appendix>
</book>