man/sd_login_monitor_new.xml

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  10   Copyright 2010 Lennart Poettering
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  25
  26 <refentry id="sd_login_monitor_new" conditional='HAVE_PAM'>
  27
  28   <refentryinfo>
  29     <title>sd_login_monitor_new</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_login_monitor_new</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_login_monitor_new</refname>
  49     <refname>sd_login_monitor_unref</refname>
  50     <refname>sd_login_monitor_unrefp</refname>
  51     <refname>sd_login_monitor_flush</refname>
  52     <refname>sd_login_monitor_get_fd</refname>
  53     <refname>sd_login_monitor_get_events</refname>
  54     <refname>sd_login_monitor_get_timeout</refname>
  55     <refname>sd_login_monitor</refname>
  56     <refpurpose>Monitor login sessions, seats, users and virtual machines/containers</refpurpose>
  57   </refnamediv>
  58
  59   <refsynopsisdiv>
  60     <funcsynopsis>
  61       <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>
  62
  63       <funcprototype>
  64         <funcdef>int <function>sd_login_monitor_new</function></funcdef>
  65         <paramdef>const char *<parameter>category</parameter></paramdef>
  66         <paramdef>sd_login_monitor **<parameter>ret</parameter></paramdef>
  67       </funcprototype>
  68
  69       <funcprototype>
  70         <funcdef>sd_login_monitor *<function>sd_login_monitor_unref</function></funcdef>
  71         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  72       </funcprototype>
  73
  74       <funcprototype>
  75         <funcdef>void <function>sd_login_monitor_unrefp</function></funcdef>
  76         <paramdef>sd_login_monitor **<parameter>m</parameter></paramdef>
  77       </funcprototype>
  78
  79       <funcprototype>
  80         <funcdef>int <function>sd_login_monitor_flush</function></funcdef>
  81         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  82       </funcprototype>
  83
  84       <funcprototype>
  85         <funcdef>int <function>sd_login_monitor_get_fd</function></funcdef>
  86         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  87       </funcprototype>
  88
  89       <funcprototype>
  90         <funcdef>int <function>sd_login_monitor_get_events</function></funcdef>
  91         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  92       </funcprototype>
  93
  94       <funcprototype>
  95         <funcdef>int <function>sd_login_monitor_get_timeout</function></funcdef>
  96         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  97         <paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef>
  98       </funcprototype>
  99
 100     </funcsynopsis>
 101   </refsynopsisdiv>
 102
 103   <refsect1>
 104     <title>Description</title>
 105
 106     <para><function>sd_login_monitor_new()</function> may be used to
 107     monitor login sessions, users, seats, and virtual
 108     machines/containers. Via a monitor object a file descriptor can be
 109     integrated into an application defined event loop which is woken
 110     up each time a user logs in, logs out or a seat is added or
 111     removed, or a session, user, seat or virtual machine/container
 112     changes state otherwise. The first parameter takes a string which
 113     can be <literal>seat</literal> (to get only notifications about
 114     seats being added, removed or changed), <literal>session</literal>
 115     (to get only notifications about sessions being created or removed
 116     or changed), <literal>uid</literal> (to get only notifications
 117     when a user changes state in respect to logins) or
 118     <literal>machine</literal> (to get only notifications when a
 119     virtual machine or container is started or stopped). If
 120     notifications shall be generated in all these conditions,
 121     <constant>NULL</constant> may be passed. Note that in the future
 122     additional categories may be defined. The second parameter returns
 123     a monitor object and needs to be freed with the
 124     <function>sd_login_monitor_unref()</function> call after
 125     use.</para>
 126
 127     <para><function>sd_login_monitor_unref()</function> may be used to
 128     destroy a monitor object. Note that this will invalidate any file
 129     descriptor returned by
 130     <function>sd_login_monitor_get_fd()</function>.</para>
 131
 132     <para><function>sd_login_monitor_unrefp()</function> is similar to
 133     <function>sd_login_monitor_unref()</function> but takes a pointer
 134     to a pointer to an <type>sd_login_monitor</type> object. This call
 135     is useful in conjunction with GCC's and LLVM's <ulink
 136     url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
 137     Variable Attribute</ulink>. Note that this function is defined as
 138     inline function. Use a declaration like the following, in order to
 139     allocate a login monitor object that is freed automatically as the
 140     code block is left:</para>
 141
 142     <programlisting>{
 143         __attribute__((cleanup(sd_login_monitor_unrefp)) sd_login_monitor *m = NULL;
 144         int r;
 145         …
 146         r = sd_login_monitor_default(&amp;m);
 147         if (r &lt; 0)
 148                 fprintf(stderr, "Failed to allocate login monitor object: %s\n", strerror(-r));
 149         …
 150 }</programlisting>
 151
 152     <para><function>sd_login_monitor_flush()</function> may be used to
 153     reset the wakeup state of the monitor object. Whenever an event
 154     causes the monitor to wake up the event loop via the file
 155     descriptor this function needs to be called to reset the wake-up
 156     state. If this call is not invoked, the file descriptor will
 157     immediately wake up the event loop again.</para>
 158
 159     <para><function>sd_login_monitor_unref()</function> and
 160     <function>sd_login_monitor_unrefp()</function> execute no
 161     operation if the passed in monitor object is
 162     <constant>NULL</constant>.</para>
 163
 164     <para><function>sd_login_monitor_get_fd()</function> may be used
 165     to retrieve the file descriptor of the monitor object that may be
 166     integrated in an application defined event loop, based around
 167     <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 168     or a similar interface. The application should include the
 169     returned file descriptor as wake-up source for the events mask
 170     returned by <function>sd_login_monitor_get_events()</function>. It
 171     should pass a timeout value as returned by
 172     <function>sd_login_monitor_get_timeout()</function>. Whenever a
 173     wake-up is triggered the file descriptor needs to be reset via
 174     <function>sd_login_monitor_flush()</function>. An application
 175     needs to reread the login state with a function like
 176     <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 177     or similar to determine what changed.</para>
 178
 179     <para><function>sd_login_monitor_get_events()</function> will
 180     return the <function>poll()</function> mask to wait for. This
 181     function will return a combination of <constant>POLLIN</constant>,
 182     <constant>POLLOUT</constant> and similar to fill into the
 183     <literal>.events</literal> field of <varname>struct
 184     pollfd</varname>.</para>
 185
 186     <para><function>sd_login_monitor_get_timeout()</function> will
 187     return a timeout value for usage in <function>poll()</function>.
 188     This returns a value in microseconds since the epoch of
 189     <constant>CLOCK_MONOTONIC</constant> for timing out
 190     <function>poll()</function> in <varname>timeout_usec</varname>.
 191     See
 192     <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 193     for details about <constant>CLOCK_MONOTONIC</constant>. If there
 194     is no timeout to wait for this will fill in <constant>(uint64_t)
 195     -1</constant> instead. Note that <function>poll()</function> takes
 196     a relative timeout in milliseconds rather than an absolute timeout
 197     in microseconds. To convert the absolute 'µs' timeout into
 198     relative 'ms', use code like the following:</para>
 199
 200     <programlisting>uint64_t t;
 201 int msec;
 202 sd_login_monitor_get_timeout(m, &amp;t);
 203 if (t == (uint64_t) -1)
 204          msec = -1;
 205 else {
 206          struct timespec ts;
 207          uint64_t n;
 208          clock_gettime(CLOCK_MONOTONIC, &amp;ts);
 209          n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
 210          msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
 211 }</programlisting>
 212
 213     <para>The code above does not do any error checking for brevity's
 214     sake. The calculated <varname>msec</varname> integer can be passed
 215     directly as <function>poll()</function>'s timeout
 216     parameter.</para>
 217   </refsect1>
 218
 219   <refsect1>
 220     <title>Return Value</title>
 221
 222     <para>On success,
 223     <function>sd_login_monitor_new()</function>,
 224     <function>sd_login_monitor_flush()</function> and
 225     <function>sd_login_monitor_get_timeout()</function>
 226     return 0 or a positive integer. On success,
 227     <function>sd_login_monitor_get_fd()</function> returns
 228     a Unix file descriptor. On success,
 229     <function>sd_login_monitor_get_events()</function>
 230     returns a combination of <constant>POLLIN</constant>,
 231     <constant>POLLOUT</constant> and suchlike. On failure,
 232     these calls return a negative errno-style error
 233     code.</para>
 234
 235     <para><function>sd_login_monitor_unref()</function>
 236     always returns <constant>NULL</constant>.</para>
 237   </refsect1>
 238
 239   <refsect1>
 240     <title>Errors</title>
 241
 242     <para>Returned errors may indicate the following problems:</para>
 243
 244     <variablelist>
 245
 246       <varlistentry>
 247         <term><constant>-EINVAL</constant></term>
 248
 249         <listitem><para>An input parameter was invalid (out of range,
 250         or NULL, where that is not accepted). The specified category to
 251         watch is not known.</para></listitem>
 252       </varlistentry>
 253
 254       <varlistentry>
 255         <term><constant>-ENOMEM</constant></term>
 256
 257         <listitem><para>Memory allocation failed.</para></listitem>
 258       </varlistentry>
 259     </variablelist>
 260   </refsect1>
 261
 262   <refsect1>
 263     <title>Notes</title>
 264
 265     <para>The <function>sd_login_monitor_new()</function>,
 266     <function>sd_login_monitor_unref()</function>,
 267     <function>sd_login_monitor_flush()</function>,
 268     <function>sd_login_monitor_get_fd()</function>,
 269     <function>sd_login_monitor_get_events()</function> and
 270     <function>sd_login_monitor_get_timeout()</function>
 271     interfaces are available as a shared library, which can be
 272     compiled and linked to with the
 273     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 274     file.</para>
 275   </refsect1>
 276
 277   <refsect1>
 278     <title>See Also</title>
 279
 280     <para>
 281       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 282       <citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 283       <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 284       <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 285       <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 286     </para>
 287   </refsect1>
 288
 289 </refentry>