man/sd_login_monitor_new.xml

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  23
  24 <refentry id="sd_login_monitor_new" conditional='HAVE_PAM'>
  25
  26   <refentryinfo>
  27     <title>sd_login_monitor_new</title>
  28     <productname>systemd</productname>
  29
  30     <authorgroup>
  31       <author>
  32         <contrib>Developer</contrib>
  33         <firstname>Lennart</firstname>
  34         <surname>Poettering</surname>
  35         <email>lennart@poettering.net</email>
  36       </author>
  37     </authorgroup>
  38   </refentryinfo>
  39
  40   <refmeta>
  41     <refentrytitle>sd_login_monitor_new</refentrytitle>
  42     <manvolnum>3</manvolnum>
  43   </refmeta>
  44
  45   <refnamediv>
  46     <refname>sd_login_monitor_new</refname>
  47     <refname>sd_login_monitor_unref</refname>
  48     <refname>sd_login_monitor_flush</refname>
  49     <refname>sd_login_monitor_get_fd</refname>
  50     <refname>sd_login_monitor_get_events</refname>
  51     <refname>sd_login_monitor_get_timeout</refname>
  52     <refname>sd_login_monitor</refname>
  53     <refpurpose>Monitor login sessions, seats, users and virtual machines/containers</refpurpose>
  54   </refnamediv>
  55
  56   <refsynopsisdiv>
  57     <funcsynopsis>
  58       <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>
  59
  60       <funcprototype>
  61         <funcdef>int <function>sd_login_monitor_new</function></funcdef>
  62         <paramdef>const char *<parameter>category</parameter></paramdef>
  63         <paramdef>sd_login_monitor **<parameter>ret</parameter></paramdef>
  64       </funcprototype>
  65
  66       <funcprototype>
  67         <funcdef>sd_login_monitor *<function>sd_login_monitor_unref</function></funcdef>
  68         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  69       </funcprototype>
  70
  71       <funcprototype>
  72         <funcdef>int <function>sd_login_monitor_flush</function></funcdef>
  73         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  74       </funcprototype>
  75
  76       <funcprototype>
  77         <funcdef>int <function>sd_login_monitor_get_fd</function></funcdef>
  78         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  79       </funcprototype>
  80
  81       <funcprototype>
  82         <funcdef>int <function>sd_login_monitor_get_events</function></funcdef>
  83         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  84       </funcprototype>
  85
  86       <funcprototype>
  87         <funcdef>int <function>sd_login_monitor_get_timeout</function></funcdef>
  88         <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
  89         <paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef>
  90       </funcprototype>
  91
  92     </funcsynopsis>
  93   </refsynopsisdiv>
  94
  95   <refsect1>
  96     <title>Description</title>
  97
  98     <para><function>sd_login_monitor_new()</function> may be used to
  99     monitor login sessions, users, seats, and virtual
 100     machines/containers. Via a monitor object a file descriptor can be
 101     integrated into an application defined event loop which is woken
 102     up each time a user logs in, logs out or a seat is added or
 103     removed, or a session, user, seat or virtual machine/container
 104     changes state otherwise. The first parameter takes a string which
 105     can be <literal>seat</literal> (to get only notifications about
 106     seats being added, removed or changed), <literal>session</literal>
 107     (to get only notifications about sessions being created or removed
 108     or changed), <literal>uid</literal> (to get only notifications
 109     when a user changes state in respect to logins) or
 110     <literal>machine</literal> (to get only notifications when a
 111     virtual machine or container is started or stopped). If
 112     notifications shall be generated in all these conditions,
 113     <constant>NULL</constant> may be passed. Note that in the future
 114     additional categories may be defined. The second parameter returns
 115     a monitor object and needs to be freed with the
 116     <function>sd_login_monitor_unref()</function> call after
 117     use.</para>
 118
 119     <para><function>sd_login_monitor_unref()</function> may be used to
 120     destroy a monitor object. Note that this will invalidate any file
 121     descriptor returned by
 122     <function>sd_login_monitor_get_fd()</function>.</para>
 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_get_fd()</function> may be used
 132     to retrieve the file descriptor of the monitor object that may be
 133     integrated in an application defined event loop, based around
 134     <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 135     or a similar interface. The application should include the
 136     returned file descriptor as wake-up source for the events mask
 137     returned by <function>sd_login_monitor_get_events()</function>. It
 138     should pass a timeout value as returned by
 139     <function>sd_login_monitor_get_timeout()</function>. Whenever a
 140     wake-up is triggered the file descriptor needs to be reset via
 141     <function>sd_login_monitor_flush()</function>. An application
 142     needs to reread the login state with a function like
 143     <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 144     or similar to determine what changed.</para>
 145
 146     <para><function>sd_login_monitor_get_events()</function> will
 147     return the <function>poll()</function> mask to wait for. This
 148     function will return a combination of <constant>POLLIN</constant>,
 149     <constant>POLLOUT</constant> and similar to fill into the
 150     <literal>.events</literal> field of <varname>struct
 151     pollfd</varname>.</para>
 152
 153     <para><function>sd_login_monitor_get_timeout()</function> will
 154     return a timeout value for usage in <function>poll()</function>.
 155     This returns a value in microseconds since the epoch of
 156     <constant>CLOCK_MONOTONIC</constant> for timing out
 157     <function>poll()</function> in <varname>timeout_usec</varname>.
 158     See
 159     <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 160     for details about <constant>CLOCK_MONOTONIC</constant>. If there
 161     is no timeout to wait for this will fill in <constant>(uint64_t)
 162     -1</constant> instead. Note that <function>poll()</function> takes
 163     a relative timeout in milliseconds rather than an absolute timeout
 164     in microseconds. To convert the absolute 'us' timeout into
 165     relative 'ms', use code like the following:</para>
 166
 167     <programlisting>uint64_t t;
 168 int msec;
 169 sd_login_monitor_get_timeout(m, &amp;t);
 170 if (t == (uint64_t) -1)
 171   msec = -1;
 172 else {
 173   struct timespec ts;
 174   uint64_t n;
 175   clock_getttime(CLOCK_MONOTONIC, &amp;ts);
 176   n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
 177   msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
 178 }</programlisting>
 179
 180     <para>The code above does not do any error checking for brevity's
 181     sake. The calculated <varname>msec</varname> integer can be passed
 182     directly as <function>poll()</function>'s timeout
 183     parameter.</para>
 184   </refsect1>
 185
 186   <refsect1>
 187     <title>Return Value</title>
 188
 189     <para>On success,
 190     <function>sd_login_monitor_new()</function>,
 191     <function>sd_login_monitor_flush()</function> and
 192     <function>sd_login_monitor_get_timeout()</function>
 193     return 0 or a positive integer. On success,
 194     <function>sd_login_monitor_get_fd()</function> returns
 195     a Unix file descriptor. On success,
 196     <function>sd_login_monitor_get_events()</function>
 197     returns a combination of <constant>POLLIN</constant>,
 198     <constant>POLLOUT</constant> and suchlike. On failure,
 199     these calls return a negative errno-style error
 200     code.</para>
 201
 202     <para><function>sd_login_monitor_unref()</function>
 203     always returns <constant>NULL</constant>.</para>
 204   </refsect1>
 205
 206   <refsect1>
 207     <title>Notes</title>
 208
 209     <para>The <function>sd_login_monitor_new()</function>,
 210     <function>sd_login_monitor_unref()</function>,
 211     <function>sd_login_monitor_flush()</function>,
 212     <function>sd_login_monitor_get_fd()</function>,
 213     <function>sd_login_monitor_get_events()</function> and
 214     <function>sd_login_monitor_get_timeout()</function>
 215     interfaces are available as a shared library, which can be
 216     compiled and linked to with the
 217     <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 218     file.</para>
 219   </refsect1>
 220
 221   <refsect1>
 222     <title>See Also</title>
 223
 224     <para>
 225       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 226       <citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 227       <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 228       <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
 229       <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 230     </para>
 231   </refsect1>
 232
 233 </refentry>