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/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   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_default(&amp;m);
 119   if (r &lt; 0)
 120     fprintf(stderr, "Failed to allocate login monitor object: %s\n", strerror(-r));
 121   …
 122 }</programlisting>
 123
 124     <para><function>sd_login_monitor_flush()</function> may be used to
 125     reset the wakeup state of the monitor object. Whenever an event
 126     causes the monitor to wake up the event loop via the file
 127     descriptor this function needs to be called to reset the wake-up
 128     state. If this call is not invoked, the file descriptor will
 129     immediately wake up the event loop again.</para>
 130
 131     <para><function>sd_login_monitor_unref()</function> and
 132     <function>sd_login_monitor_unrefp()</function> execute no
 133     operation if the passed in monitor object is
 134     <constant>NULL</constant>.</para>
 135
 136     <para><function>sd_login_monitor_get_fd()</function> may be used
 137     to retrieve the file descriptor of the monitor object that may be
 138     integrated in an application defined event loop, based around
 139     <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 140     or a similar interface. The application should include the
 141     returned file descriptor as wake-up source for the events mask
 142     returned by <function>sd_login_monitor_get_events()</function>. It
 143     should pass a timeout value as returned by
 144     <function>sd_login_monitor_get_timeout()</function>. Whenever a
 145     wake-up is triggered the file descriptor needs to be reset via
 146     <function>sd_login_monitor_flush()</function>. An application
 147     needs to reread the login state with a function like
 148     <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 149     or similar to determine what changed.</para>
 150
 151     <para><function>sd_login_monitor_get_events()</function> will
 152     return the <function>poll()</function> mask to wait for. This
 153     function will return a combination of <constant>POLLIN</constant>,
 154     <constant>POLLOUT</constant> and similar to fill into the
 155     <literal>.events</literal> field of <varname>struct
 156     pollfd</varname>.</para>
 157
 158     <para><function>sd_login_monitor_get_timeout()</function> will
 159     return a timeout value for usage in <function>poll()</function>.
 160     This returns a value in microseconds since the epoch of
 161     <constant>CLOCK_MONOTONIC</constant> for timing out
 162     <function>poll()</function> in <varname>timeout_usec</varname>.
 163     See
 164     <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 165     for details about <constant>CLOCK_MONOTONIC</constant>. If there
 166     is no timeout to wait for this will fill in <constant>(uint64_t)
 167     -1</constant> instead. Note that <function>poll()</function> takes
 168     a relative timeout in milliseconds rather than an absolute timeout
 169     in microseconds. To convert the absolute 'µs' timeout into
 170     relative 'ms', use code like the following:</para>
 171
 172     <programlisting>uint64_t t;
 173 int msec;
 174 sd_login_monitor_get_timeout(m, &amp;t);
 175 if (t == (uint64_t) -1)
 176   msec = -1;
 177 else {
 178   struct timespec ts;
 179   uint64_t n;
 180   clock_gettime(CLOCK_MONOTONIC, &amp;ts);
 181   n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
 182   msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
 183 }</programlisting>
 184
 185     <para>The code above does not do any error checking for brevity's
 186     sake. The calculated <varname>msec</varname> integer can be passed
 187     directly as <function>poll()</function>'s timeout
 188     parameter.</para>
 189   </refsect1>
 190
 191   <refsect1>
 192     <title>Return Value</title>
 193
 194     <para>On success,
 195     <function>sd_login_monitor_new()</function>,
 196     <function>sd_login_monitor_flush()</function> and
 197     <function>sd_login_monitor_get_timeout()</function>
 198     return 0 or a positive integer. On success,
 199     <function>sd_login_monitor_get_fd()</function> returns
 200     a Unix file descriptor. On success,
 201     <function>sd_login_monitor_get_events()</function>
 202     returns a combination of <constant>POLLIN</constant>,
 203     <constant>POLLOUT</constant> and suchlike. On failure,
 204     these calls return a negative errno-style error
 205     code.</para>
 206
 207     <para><function>sd_login_monitor_unref()</function>
 208     always returns <constant>NULL</constant>.</para>
 209
 210     <refsect2>
 211       <title>Errors</title>
 212
 213       <para>Returned errors may indicate the following problems:</para>
 214
 215       <variablelist>
 216
 217         <varlistentry>
 218           <term><constant>-EINVAL</constant></term>
 219
 220           <listitem><para>An input parameter was invalid (out of range, or <constant>NULL</constant>, where
 221           that is not accepted). The specified category to watch is not known.</para></listitem>
 222         </varlistentry>
 223
 224         <varlistentry>
 225           <term><constant>-ENOMEM</constant></term>
 226
 227           <listitem><para>Memory allocation failed.</para></listitem>
 228         </varlistentry>
 229       </variablelist>
 230     </refsect2>
 231   </refsect1>
 232
 233   <xi:include href="libsystemd-pkgconfig.xml" />
 234
 235   <refsect1>
 236     <title>See Also</title>
 237
 238     <para>
 239       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 240       <citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 241       <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 242       <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 243       <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 244     </para>
 245   </refsect1>
 246
 247 </refentry>