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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd 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.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd_login_monitor_new" conditional='HAVE_PAM'>
<refentryinfo>
<title>sd_login_monitor_new</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>sd_login_monitor_new</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_login_monitor_new</refname>
<refname>sd_login_monitor_unref</refname>
<refname>sd_login_monitor_flush</refname>
<refname>sd_login_monitor_get_fd</refname>
<refname>sd_login_monitor_get_events</refname>
<refname>sd_login_monitor_get_timeout</refname>
<refname>sd_login_monitor</refname>
<refpurpose>Monitor login sessions, seats, users and virtual machines/containers</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-login.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_login_monitor_new</function></funcdef>
<paramdef>const char* <parameter>category</parameter></paramdef>
<paramdef>sd_login_monitor** <parameter>ret</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>sd_login_monitor* <function>sd_login_monitor_unref</function></funcdef>
<paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_login_monitor_flush</function></funcdef>
<paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_login_monitor_get_fd</function></funcdef>
<paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_login_monitor_get_events</function></funcdef>
<paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_login_monitor_get_timeout</function></funcdef>
<paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
<paramdef>uint64_t* <parameter>timeout_usec</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_login_monitor_new()</function> may
be used to monitor login sessions, users, seats, and
virtual machines/containers. Via a monitor object a
file descriptor can be integrated into an application
defined event loop which is woken up each time a user
logs in, logs out or a seat is added or removed, or a
session, user, seat or virtual machine/container
changes state otherwise. The first parameter takes a
string which can be <literal>seat</literal> (to get
only notifications about seats being added, removed or
changed), <literal>session</literal> (to get only
notifications about sessions being created or removed
or changed), <literal>uid</literal> (to get only
notifications when a user changes state in respect to
logins) or <literal>machine</literal> (to get only
notifications when a virtual machine or container is
started or stopped). If notifications shall be
generated in all these conditions, <constant>NULL</constant> may be
passed. Note that in the future additional categories
may be defined. The second parameter returns a monitor
object and needs to be freed with the
<function>sd_login_monitor_unref()</function> call
after use.</para>
<para><function>sd_login_monitor_unref()</function>
may be used to destroy a monitor object. Note that
this will invalidate any file descriptor returned by
<function>sd_login_monitor_get_fd()</function>.</para>
<para><function>sd_login_monitor_flush()</function>
may be used to reset the wakeup state of the monitor
object. Whenever an event causes the monitor to wake
up the event loop via the file descriptor this
function needs to be called to reset the wake-up
state. If this call is not invoked, the file descriptor
will immediately wake up the event loop again.</para>
<para><function>sd_login_monitor_get_fd()</function>
may be used to retrieve the file descriptor of the
monitor object that may be integrated in an
application defined event loop, based around
<citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
or a similar interface. The application should include
the returned file descriptor as wake-up source for the
events mask returned by
<function>sd_login_monitor_get_events()</function>. It
should pass a timeout value as returned by
<function>sd_login_monitor_get_timeout()</function>. Whenever
a wake-up is triggered the file descriptor needs to be
reset via
<function>sd_login_monitor_flush()</function>. An
application needs to reread the login state with a
function like
<citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
or similar to determine what changed.</para>
<para><function>sd_login_monitor_get_events()</function>
will return the <function>poll()</function> mask to
wait for. This function will return a combination of
<constant>POLLIN</constant>, <constant>POLLOUT</constant>
and similar to fill into the
<literal>.events</literal> field of <varname>struct
pollfd</varname>.</para>
<para><function>sd_login_monitor_get_timeout()</function>
will return a timeout value for usage in
<function>poll()</function>. This returns a value in
microseconds since the epoch of <constant>CLOCK_MONOTONIC</constant>
for timing out <function>poll()</function> in
<varname>timeout_usec</varname>. See
<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details about
<constant>CLOCK_MONOTONIC</constant>. If there is no
timeout to wait for this will fill in
<constant>(uint64_t) -1</constant> instead. Note that
<function>poll()</function> takes a relative timeout
in milliseconds rather than an absolute timeout in
microseconds. To convert the absolute 'us' timeout into
relative 'ms', use code like the following:</para>
<programlisting>uint64_t t;
int msec;
sd_login_monitor_get_timeout(m, &t);
if (t == (uint64_t) -1)
msec = -1;
else {
struct timespec ts;
uint64_t n;
clock_getttime(CLOCK_MONOTONIC, &ts);
n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
}</programlisting>
<para>The code above does not do any error checking
for brevity's sake. The calculated <varname>msec</varname>
integer can be passed directly as
<function>poll()</function>'s timeout
parameter.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>On success
<function>sd_login_monitor_new()</function>,
<function>sd_login_monitor_flush()</function> and
<function>sd_login_monitor_get_timeout()</function>
return 0 or a positive integer. On success
<function>sd_login_monitor_get_fd()</function> returns
a Unix file descriptor. On success
<function>sd_login_monitor_get_events()</function>
returns a combination of <constant>POLLIN</constant>,
<constant>POLLOUT</constant> and suchlike. On failure,
these calls return a negative errno-style error
code.</para>
<para><function>sd_login_monitor_unref()</function>
always returns <constant>NULL</constant>.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>The <function>sd_login_monitor_new()</function>,
<function>sd_login_monitor_unref()</function>,
<function>sd_login_monitor_flush()</function>,
<function>sd_login_monitor_get_fd()</function>,
<function>sd_login_monitor_get_events()</function> and
<function>sd_login_monitor_get_timeout()</function>
interfaces are available as a shared library, which can
be compiled and linked to with the
<constant>libsystemd-login</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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