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4afd3348c7
GLIB has recently started to officially support the gcc cleanup
attribute in its public API, hence let's do the same for our APIs.
With this patch we'll define an xyz_unrefp() call for each public
xyz_unref() call, to make it easy to use inside a
__attribute__((cleanup())) expression. Then, all code is ported over to
make use of this.
The new calls are also documented in the man pages, with examples how to
use them (well, I only added docs where the _unref() call itself already
had docs, and the examples, only cover sd_bus_unrefp() and
sd_event_unrefp()).
This also renames sd_lldp_free() to sd_lldp_unref(), since that's how we
tend to call our destructors these days.
Note that this defines no public macro that wraps gcc's attribute and
makes it easier to use. While I think it's our duty in the library to
make our stuff easy to use, I figure it's not our duty to make gcc's own
features easy to use on its own. Most likely, client code which wants to
make use of this should define its own:
#define _cleanup_(function) __attribute__((cleanup(function)))
Or similar, to make the gcc feature easier to use.
Making this logic public has the benefit that we can remove three header
files whose only purpose was to define these functions internally.
See #2008.
288 lines
12 KiB
XML
288 lines
12 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_login_monitor_new" conditional='HAVE_PAM'>
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<refentryinfo>
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<title>sd_login_monitor_new</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_login_monitor_new</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_login_monitor_new</refname>
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<refname>sd_login_monitor_unref</refname>
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<refname>sd_login_monitor_unrefp</refname>
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<refname>sd_login_monitor_flush</refname>
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<refname>sd_login_monitor_get_fd</refname>
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<refname>sd_login_monitor_get_events</refname>
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<refname>sd_login_monitor_get_timeout</refname>
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<refname>sd_login_monitor</refname>
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<refpurpose>Monitor login sessions, seats, users and virtual machines/containers</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-login.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_new</function></funcdef>
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<paramdef>const char *<parameter>category</parameter></paramdef>
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<paramdef>sd_login_monitor **<parameter>ret</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_login_monitor *<function>sd_login_monitor_unref</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_login_monitor_unrefp</function></funcdef>
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<paramdef>sd_login_monitor **<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_flush</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_get_fd</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_get_events</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_get_timeout</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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<paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_login_monitor_new()</function> may be used to
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monitor login sessions, users, seats, and virtual
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machines/containers. Via a monitor object a file descriptor can be
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integrated into an application defined event loop which is woken
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up each time a user logs in, logs out or a seat is added or
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removed, or a session, user, seat or virtual machine/container
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changes state otherwise. The first parameter takes a string which
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can be <literal>seat</literal> (to get only notifications about
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seats being added, removed or changed), <literal>session</literal>
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(to get only notifications about sessions being created or removed
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or changed), <literal>uid</literal> (to get only notifications
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when a user changes state in respect to logins) or
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<literal>machine</literal> (to get only notifications when a
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virtual machine or container is started or stopped). If
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notifications shall be generated in all these conditions,
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<constant>NULL</constant> may be passed. Note that in the future
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additional categories may be defined. The second parameter returns
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a monitor object and needs to be freed with the
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<function>sd_login_monitor_unref()</function> call after
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use.</para>
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<para><function>sd_login_monitor_unref()</function> may be used to
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destroy a monitor object. Note that this will invalidate any file
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descriptor returned by
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<function>sd_login_monitor_get_fd()</function>.</para>
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<para><function>sd_login_monitor_unrefp()</function> is similar to
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<function>sd_login_monitor_unref()</function> but takes a pointer
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to a pointer to an <type>sd_login_monitor</type> object. This call
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is useful in conjunction with GCC's and LLVM's <ulink
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url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
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Variable Attribute</ulink>. Note that this function is defined as
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inline function. Use a declaration like the following, in order to
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allocate a login monitor object that is freed automatically as the
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code block is left:</para>
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<programlisting>{
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__attribute__((cleanup(sd_login_monitor_unrefp)) sd_login_monitor *m = NULL;
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int r;
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…
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r = sd_login_monitor_default(&m);
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if (r < 0)
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fprintf(stderr, "Failed to allocate login monitor object: %s\n", strerror(-r));
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…
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}</programlisting>
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<para><function>sd_login_monitor_flush()</function> may be used to
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reset the wakeup state of the monitor object. Whenever an event
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causes the monitor to wake up the event loop via the file
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descriptor this function needs to be called to reset the wake-up
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state. If this call is not invoked, the file descriptor will
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immediately wake up the event loop again.</para>
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<para><function>sd_login_monitor_unref()</function> and
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<function>sd_login_monitor_unrefp()</function> execute no
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operation if the passed in monitor object is
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<constant>NULL</constant>.</para>
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<para><function>sd_login_monitor_get_fd()</function> may be used
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to retrieve the file descriptor of the monitor object that may be
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integrated in an application defined event loop, based around
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<citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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or a similar interface. The application should include the
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returned file descriptor as wake-up source for the events mask
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returned by <function>sd_login_monitor_get_events()</function>. It
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should pass a timeout value as returned by
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<function>sd_login_monitor_get_timeout()</function>. Whenever a
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wake-up is triggered the file descriptor needs to be reset via
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<function>sd_login_monitor_flush()</function>. An application
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needs to reread the login state with a function like
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<citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or similar to determine what changed.</para>
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<para><function>sd_login_monitor_get_events()</function> will
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return the <function>poll()</function> mask to wait for. This
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function will return a combination of <constant>POLLIN</constant>,
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<constant>POLLOUT</constant> and similar to fill into the
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<literal>.events</literal> field of <varname>struct
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pollfd</varname>.</para>
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<para><function>sd_login_monitor_get_timeout()</function> will
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return a timeout value for usage in <function>poll()</function>.
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This returns a value in microseconds since the epoch of
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<constant>CLOCK_MONOTONIC</constant> for timing out
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<function>poll()</function> in <varname>timeout_usec</varname>.
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See
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<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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for details about <constant>CLOCK_MONOTONIC</constant>. If there
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is no timeout to wait for this will fill in <constant>(uint64_t)
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-1</constant> instead. Note that <function>poll()</function> takes
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a relative timeout in milliseconds rather than an absolute timeout
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in microseconds. To convert the absolute 'µs' timeout into
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relative 'ms', use code like the following:</para>
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<programlisting>uint64_t t;
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int msec;
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sd_login_monitor_get_timeout(m, &t);
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if (t == (uint64_t) -1)
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msec = -1;
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else {
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struct timespec ts;
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uint64_t n;
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clock_getttime(CLOCK_MONOTONIC, &ts);
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n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
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msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
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}</programlisting>
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<para>The code above does not do any error checking for brevity's
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sake. The calculated <varname>msec</varname> integer can be passed
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directly as <function>poll()</function>'s timeout
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parameter.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success,
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<function>sd_login_monitor_new()</function>,
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<function>sd_login_monitor_flush()</function> and
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<function>sd_login_monitor_get_timeout()</function>
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return 0 or a positive integer. On success,
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<function>sd_login_monitor_get_fd()</function> returns
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a Unix file descriptor. On success,
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<function>sd_login_monitor_get_events()</function>
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returns a combination of <constant>POLLIN</constant>,
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<constant>POLLOUT</constant> and suchlike. On failure,
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these calls return a negative errno-style error
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code.</para>
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<para><function>sd_login_monitor_unref()</function>
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always returns <constant>NULL</constant>.</para>
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</refsect1>
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<refsect1>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>An input parameter was invalid (out of range,
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or NULL, where that is not accepted). The specified category to
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watch is not known.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>The <function>sd_login_monitor_new()</function>,
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<function>sd_login_monitor_unref()</function>,
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<function>sd_login_monitor_flush()</function>,
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<function>sd_login_monitor_get_fd()</function>,
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<function>sd_login_monitor_get_events()</function> and
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<function>sd_login_monitor_get_timeout()</function>
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interfaces are available as a shared library, which can be
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compiled and linked to with the
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<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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