Fix spelling errors using 'codespell' tool

[thirdparty/systemd.git] / man / sd_login_monitor_new.xml

<?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 and users</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
                        <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</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 and seats. 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, or seat 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) or <literal>uid</literal> (to get only
                notifications when a user changes state in respect to
                logins). If notifications shall be generated in all
                these conditions, NULL 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
                <literal>POLLIN</literal>, <literal>POLLOUT</literal>
                and similar to fill into the
                <literal>.events</literal> field of <literal>struct
                pollfd</literal>.</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 CLOCK_MONOTONIC for
                timing out <function>poll()</function> in
                <literal>timeout_usec</literal>. See
                <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
                for details about
                <literal>CLOCK_MONOTONIC</literal>. If there's no
                timeout to wait for this will fill in
                <literal>(uint64_t) -1</literal> 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, &amp;t);
if (t == (uint64_t) -1)
        msec = -1;
else {
        struct timespec ts;
        uint64_t n;
        clock_getttime(CLOCK_MONOTONIC, &amp;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 <literal>msec</literal>
                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 <literal>POLLIN</literal>,
                <literal>POLLOUT</literal> and suchlike. On failure,
                these calls return a negative errno-style error
                code.</para>

                <para><function>sd_login_monitor_unref()</function>
                always returns NULL.</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 shared library, which can
                be compiled and linked to with the
                <literal>libsystemd-login</literal>
                <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>