man/sd_login_monitor_new.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="sd_login_monitor_new" conditional='HAVE_PAM'
   7           xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>sd_login_monitor_new</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>sd_login_monitor_new</refentrytitle>
  16     <manvolnum>3</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>sd_login_monitor_new</refname>
  21     <refname>sd_login_monitor_unref</refname>
  22     <refname>sd_login_monitor_unrefp</refname>
  23     <refname>sd_login_monitor_flush</refname>
  24     <refname>sd_login_monitor_get_fd</refname>
  25     <refname>sd_login_monitor_get_events</refname>
  26     <refname>sd_login_monitor_get_timeout</refname>
  27     <refname>sd_login_monitor</refname>
  28     <refpurpose>Monitor login sessions, seats, users and virtual machines/containers</refpurpose>
  29   </refnamediv>
  30
  31   <refsynopsisdiv>
  32     <funcsynopsis>
  33       <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>
  34
  35       <funcprototype>
  36         <funcdef>int <function>sd_login_monitor_new</function></funcdef>
  37         <paramdef>const char *<parameter>category</parameter></paramdef>
  38         <paramdef>sd_login_monitor **<parameter>ret</parameter></paramdef>
  39       </funcprototype>
  40
  41       <funcprototype>
  42         <funcdef>sd_login_monitor *<function>sd_login_monitor_unref</function></funcdef>
  43         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  44       </funcprototype>
  45
  46       <funcprototype>
  47         <funcdef>void <function>sd_login_monitor_unrefp</function></funcdef>
  48         <paramdef>sd_login_monitor **<parameter>m</parameter></paramdef>
  49       </funcprototype>
  50
  51       <funcprototype>
  52         <funcdef>int <function>sd_login_monitor_flush</function></funcdef>
  53         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  54       </funcprototype>
  55
  56       <funcprototype>
  57         <funcdef>int <function>sd_login_monitor_get_fd</function></funcdef>
  58         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  59       </funcprototype>
  60
  61       <funcprototype>
  62         <funcdef>int <function>sd_login_monitor_get_events</function></funcdef>
  63         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  64       </funcprototype>
  65
  66       <funcprototype>
  67         <funcdef>int <function>sd_login_monitor_get_timeout</function></funcdef>
  68         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  69         <paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef>
  70       </funcprototype>
  71
  72     </funcsynopsis>
  73   </refsynopsisdiv>
  74
  75   <refsect1>
  76     <title>Description</title>
  77
  78     <para><function>sd_login_monitor_new()</function> may be used to
  79     monitor login sessions, users, seats, and virtual
  80     machines/containers. Via a monitor object a file descriptor can be
  81     integrated into an application defined event loop which is woken
  82     up each time a user logs in, logs out or a seat is added or
  83     removed, or a session, user, seat or virtual machine/container
  84     changes state otherwise. The first parameter takes a string which
  85     can be <literal>seat</literal> (to get only notifications about
  86     seats being added, removed or changed), <literal>session</literal>
  87     (to get only notifications about sessions being created or removed
  88     or changed), <literal>uid</literal> (to get only notifications
  89     when a user changes state in respect to logins) or
  90     <literal>machine</literal> (to get only notifications when a
  91     virtual machine or container is started or stopped). If
  92     notifications shall be generated in all these conditions,
  93     <constant>NULL</constant> may be passed. Note that in the future
  94     additional categories may be defined. The second parameter returns
  95     a monitor object and needs to be freed with the
  96     <function>sd_login_monitor_unref()</function> call after
  97     use.</para>
  98
  99     <para><function>sd_login_monitor_unref()</function> may be used to
 100     destroy a monitor object. Note that this will invalidate any file
 101     descriptor returned by
 102     <function>sd_login_monitor_get_fd()</function>.</para>
 103
 104     <para><function>sd_login_monitor_unrefp()</function> is similar to
 105     <function>sd_login_monitor_unref()</function> but takes a pointer
 106     to a pointer to an <type>sd_login_monitor</type> object. This call
 107     is useful in conjunction with GCC's and LLVM's <ulink
 108     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
 109     Variable Attribute</ulink>. Note that this function is defined as
 110     inline function. Use a declaration like the following, in order to
 111     allocate a login monitor object that is freed automatically as the
 112     code block is left:</para>
 113
 114     <programlisting>{
 115   __attribute__((cleanup(sd_login_monitor_unrefp))) sd_login_monitor *m = NULL;
 116   int r;
 117   …
 118   r = sd_login_monitor_new(NULL, &amp;m);
 119   if (r &lt; 0) {
 120     errno = -r;
 121     fprintf(stderr, "Failed to allocate login monitor object: %m\n");
 122   }
 123   …
 124 }</programlisting>
 125
 126     <para><function>sd_login_monitor_flush()</function> may be used to
 127     reset the wakeup state of the monitor object. Whenever an event
 128     causes the monitor to wake up the event loop via the file
 129     descriptor this function needs to be called to reset the wake-up
 130     state. If this call is not invoked, the file descriptor will
 131     immediately wake up the event loop again.</para>
 132
 133     <para><function>sd_login_monitor_unref()</function> and
 134     <function>sd_login_monitor_unrefp()</function> execute no
 135     operation if the passed in monitor object is
 136     <constant>NULL</constant>.</para>
 137
 138     <para><function>sd_login_monitor_get_fd()</function> may be used
 139     to retrieve the file descriptor of the monitor object that may be
 140     integrated in an application defined event loop, based around
 141     <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 142     or a similar interface. The application should include the
 143     returned file descriptor as wake-up source for the events mask
 144     returned by <function>sd_login_monitor_get_events()</function>. It
 145     should pass a timeout value as returned by
 146     <function>sd_login_monitor_get_timeout()</function>. Whenever a
 147     wake-up is triggered the file descriptor needs to be reset via
 148     <function>sd_login_monitor_flush()</function>. An application
 149     needs to reread the login state with a function like
 150     <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 151     or similar to determine what changed.</para>
 152
 153     <para><function>sd_login_monitor_get_events()</function> will
 154     return the <function>poll()</function> mask to wait for. This
 155     function will return a combination of <constant>POLLIN</constant>,
 156     <constant>POLLOUT</constant> and similar to fill into the
 157     <literal>.events</literal> field of <varname>struct
 158     pollfd</varname>.</para>
 159
 160     <para><function>sd_login_monitor_get_timeout()</function> will
 161     return a timeout value for usage in <function>poll()</function>.
 162     This returns a value in microseconds since the epoch of
 163     <constant>CLOCK_MONOTONIC</constant> for timing out
 164     <function>poll()</function> in <varname>timeout_usec</varname>.
 165     See
 166     <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 167     for details about <constant>CLOCK_MONOTONIC</constant>. If there
 168     is no timeout to wait for this will fill in <constant>(uint64_t)
 169     -1</constant> instead. Note that <function>poll()</function> takes
 170     a relative timeout in milliseconds rather than an absolute timeout
 171     in microseconds. To convert the absolute 'μs' timeout into
 172     relative 'ms', use code like the following:</para>
 173
 174     <programlisting>uint64_t t;
 175 int msec;
 176 sd_login_monitor_get_timeout(m, &amp;t);
 177 if (t == (uint64_t) -1)
 178   msec = -1;
 179 else {
 180   struct timespec ts;
 181   uint64_t n;
 182   clock_gettime(CLOCK_MONOTONIC, &amp;ts);
 183   n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
 184   msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
 185 }</programlisting>
 186
 187     <para>The code above does not do any error checking for brevity's
 188     sake. The calculated <varname>msec</varname> integer can be passed
 189     directly as <function>poll()</function>'s timeout
 190     parameter.</para>
 191   </refsect1>
 192
 193   <refsect1>
 194     <title>Return Value</title>
 195
 196     <para>On success,
 197     <function>sd_login_monitor_new()</function>,
 198     <function>sd_login_monitor_flush()</function> and
 199     <function>sd_login_monitor_get_timeout()</function>
 200     return 0 or a positive integer. On success,
 201     <function>sd_login_monitor_get_fd()</function> returns
 202     a Unix file descriptor. On success,
 203     <function>sd_login_monitor_get_events()</function>
 204     returns a combination of <constant>POLLIN</constant>,
 205     <constant>POLLOUT</constant> and suchlike. On failure,
 206     these calls return a negative errno-style error
 207     code.</para>
 208
 209     <para><function>sd_login_monitor_unref()</function>
 210     always returns <constant>NULL</constant>.</para>
 211
 212     <refsect2>
 213       <title>Errors</title>
 214
 215       <para>Returned errors may indicate the following problems:</para>
 216
 217       <variablelist>
 218
 219         <varlistentry>
 220           <term><constant>-EINVAL</constant></term>
 221
 222           <listitem><para>An input parameter was invalid (out of range, or <constant>NULL</constant>, where
 223           that is not accepted). The specified category to watch is not known.</para></listitem>
 224         </varlistentry>
 225
 226         <varlistentry>
 227           <term><constant>-ENOMEM</constant></term>
 228
 229           <listitem><para>Memory allocation failed.</para></listitem>
 230         </varlistentry>
 231       </variablelist>
 232     </refsect2>
 233   </refsect1>
 234
 235   <xi:include href="libsystemd-pkgconfig.xml" />
 236
 237   <refsect1>
 238     <title>History</title>
 239     <para><function>sd_login_monitor_get_events()</function> and
 240     <function>sd_login_monitor_get_timeout()</function> were added in version 201.</para>
 241     <para><function>sd_login_monitor_unrefp()</function> was added in version 229.</para>
 242   </refsect1>
 243
 244   <refsect1>
 245     <title>See Also</title>
 246
 247     <para><simplelist type="inline">
 248       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 249       <member><citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 250       <member><citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 251       <member><citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
 252       <member><citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
 253     </simplelist></para>
 254   </refsect1>
 255
 256 </refentry>