man/sd_event_add_inotify.xml

   1 <?xml version='1.0'?>
   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_event_add_inotify" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_event_add_inotify</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_event_add_inotify</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_event_add_inotify</refname>
  20     <refname>sd_event_source_get_inotify_mask</refname>
  21     <refname>sd_event_inotify_handler_t</refname>
  22
  23     <refpurpose>Add an "inotify" file system inode event source to an event loop</refpurpose>
  24   </refnamediv>
  25
  26   <refsynopsisdiv>
  27     <funcsynopsis>
  28       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  29
  30       <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
  31
  32       <funcprototype>
  33         <funcdef>typedef int (*<function>sd_event_inotify_handler_t</function>)</funcdef>
  34         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  35         <paramdef>const struct inotify_event *<parameter>event</parameter></paramdef>
  36         <paramdef>void *<parameter>userdata</parameter></paramdef>
  37       </funcprototype>
  38
  39       <funcprototype>
  40         <funcdef>int <function>sd_event_add_inotify</function></funcdef>
  41         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  42         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  43         <paramdef>const char *<parameter>path</parameter></paramdef>
  44         <paramdef>uint32_t <parameter>mask</parameter></paramdef>
  45         <paramdef>sd_event_inotify_handler_t <parameter>handler</parameter></paramdef>
  46         <paramdef>void *<parameter>userdata</parameter></paramdef>
  47       </funcprototype>
  48
  49       <funcprototype>
  50         <funcdef>int <function>sd_event_source_get_inotify_mask</function></funcdef>
  51         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  52         <paramdef>uint32_t *<parameter>mask</parameter></paramdef>
  53       </funcprototype>
  54
  55     </funcsynopsis>
  56   </refsynopsisdiv>
  57
  58   <refsect1>
  59     <title>Description</title>
  60
  61     <para><function>sd_event_add_inotify()</function> adds a new <citerefentry
  62     project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry> file system inode
  63     event source to an event loop. The event loop object is specified in the <parameter>event</parameter> parameter,
  64     the event source object is returned in the <parameter>source</parameter> parameter. The <parameter>path</parameter>
  65     parameter specifies the path of the file system inode to watch. The <parameter>handler</parameter> must reference a
  66     function to call when the inode changes. The handler function will be passed the <parameter>userdata</parameter>
  67     pointer, which may be chosen freely by the caller. The handler also receives a pointer to a <structname>struct
  68     inotify_event</structname> structure containing information about the inode event. The <parameter>mask</parameter>
  69     parameter specifies which types of inode events to watch specifically. It must contain an OR-ed combination of
  70     <constant>IN_ACCESS</constant>, <constant>IN_ATTRIB</constant>, <constant>IN_CLOSE_WRITE</constant>, … flags. See
  71     <citerefentry project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
  72     further information.</para>
  73
  74     <para>If multiple event sources are installed for the same inode the backing inotify watch descriptor is
  75     automatically shared. The mask parameter may contain any flag defined by the inotify API, with the exception of
  76     <constant>IN_MASK_ADD</constant>.</para>
  77
  78     <para>The handler is enabled continuously (<constant>SD_EVENT_ON</constant>), but this may be changed with
  79     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Alternatively,
  80     the <constant>IN_ONESHOT</constant> mask flag may be used to request <constant>SD_EVENT_ONESHOT</constant> mode.
  81     If the handler function returns a negative error code, it will be disabled after the invocation, even if the
  82     <constant>SD_EVENT_ON</constant> mode was requested before.
  83     </para>
  84
  85     <para>As a special limitation the priority of inotify event sources may only be altered (see
  86     <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
  87     in the time between creation of the event source object with <function>sd_event_add_inotify()</function> and the
  88     beginning of the next event loop iteration. Attempts of changing the priority any later will be refused. Consider
  89     freeing and allocating a new inotify event source to change the priority at that point.</para>
  90
  91     <para>To destroy an event source object use
  92     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, but note
  93     that the event source is only removed from the event loop when all references to the event source are dropped. To
  94     make sure an event source does not fire anymore, even when there's still a reference to it kept, consider disabling
  95     it with
  96     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  97
  98     <para>If the second parameter of <function>sd_event_add_inotify()</function> is passed as
  99     <constant>NULL</constant> no reference to the event source object is returned. In this case the event
 100     source is considered "floating", and will be destroyed implicitly when the event loop itself is
 101     destroyed.</para>
 102
 103     <para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_inotify()</function> is
 104     <constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
 105     event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
 106     the exit code parameter to
 107     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 108
 109     <para><function>sd_event_source_get_inotify_mask()</function> retrieves the configured inotify watch mask of an
 110     event source created previously with <function>sd_event_add_inotify()</function>. It takes the event source object
 111     as the <parameter>source</parameter> parameter and a pointer to a <type>uint32_t</type> variable to return the mask
 112     in.</para>
 113   </refsect1>
 114
 115   <refsect1>
 116     <title>Return Value</title>
 117
 118     <para>On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style
 119     error code.</para>
 120
 121     <refsect2>
 122       <title>Errors</title>
 123
 124       <para>Returned errors may indicate the following problems:</para>
 125
 126       <variablelist>
 127         <varlistentry>
 128           <term><constant>-ENOMEM</constant></term>
 129
 130           <listitem><para>Not enough memory to allocate an object.</para></listitem>
 131         </varlistentry>
 132
 133         <varlistentry>
 134           <term><constant>-EINVAL</constant></term>
 135
 136           <listitem><para>An invalid argument has been passed. This includes specifying a mask with
 137           <constant>IN_MASK_ADD</constant> set.</para></listitem>
 138         </varlistentry>
 139
 140         <varlistentry>
 141           <term><constant>-ESTALE</constant></term>
 142
 143           <listitem><para>The event loop is already terminated.</para></listitem>
 144
 145         </varlistentry>
 146
 147         <varlistentry>
 148           <term><constant>-ECHILD</constant></term>
 149
 150           <listitem><para>The event loop has been created in a different process.</para></listitem>
 151
 152         </varlistentry>
 153
 154         <varlistentry>
 155           <term><constant>-EDOM</constant></term>
 156
 157           <listitem><para>The passed event source is not an inotify process event source.</para></listitem>
 158         </varlistentry>
 159
 160       </variablelist>
 161     </refsect2>
 162   </refsect1>
 163
 164   <refsect1>
 165     <title>Examples</title>
 166
 167     <example>
 168       <title>A simple program that uses inotify to monitor one or two directories</title>
 169
 170       <programlisting><xi:include href="inotify-watch-tmp.c" parse="text" /></programlisting>
 171     </example>
 172   </refsect1>
 173
 174   <xi:include href="libsystemd-pkgconfig.xml" />
 175
 176   <refsect1>
 177     <title>See Also</title>
 178
 179     <para>
 180       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 181       <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 182       <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 183       <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 184       <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 185       <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 186       <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 187       <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 188       <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 189       <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 190       <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 191       <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 192       <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 193       <citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 194       <citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 195     </para>
 196   </refsect1>
 197
 198 </refentry>