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/4.5/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   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_add_inotify_fd</refname>
  21     <refname>sd_event_source_get_inotify_mask</refname>
  22     <refname>sd_event_source_get_inotify_path</refname>
  23     <refname>sd_event_inotify_handler_t</refname>
  24
  25     <refpurpose>Add an "inotify" file system inode event source to an event loop</refpurpose>
  26   </refnamediv>
  27
  28   <refsynopsisdiv>
  29     <funcsynopsis>
  30       <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
  31
  32       <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
  33
  34       <funcprototype>
  35         <funcdef>typedef int (*<function>sd_event_inotify_handler_t</function>)</funcdef>
  36         <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
  37         <paramdef>const struct inotify_event *<parameter>event</parameter></paramdef>
  38         <paramdef>void *<parameter>userdata</parameter></paramdef>
  39       </funcprototype>
  40
  41       <funcprototype>
  42         <funcdef>int <function>sd_event_add_inotify</function></funcdef>
  43         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  44         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  45         <paramdef>const char *<parameter>path</parameter></paramdef>
  46         <paramdef>uint32_t <parameter>mask</parameter></paramdef>
  47         <paramdef>sd_event_inotify_handler_t <parameter>handler</parameter></paramdef>
  48         <paramdef>void *<parameter>userdata</parameter></paramdef>
  49       </funcprototype>
  50
  51       <funcprototype>
  52         <funcdef>int <function>sd_event_add_inotify_fd</function></funcdef>
  53         <paramdef>sd_event *<parameter>event</parameter></paramdef>
  54         <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
  55         <paramdef>int <parameter>fd</parameter></paramdef>
  56         <paramdef>uint32_t <parameter>mask</parameter></paramdef>
  57         <paramdef>sd_event_inotify_handler_t <parameter>handler</parameter></paramdef>
  58         <paramdef>void *<parameter>userdata</parameter></paramdef>
  59       </funcprototype>
  60
  61       <funcprototype>
  62         <funcdef>int <function>sd_event_source_get_inotify_mask</function></funcdef>
  63         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  64         <paramdef>uint32_t *<parameter>ret</parameter></paramdef>
  65       </funcprototype>
  66
  67       <funcprototype>
  68         <funcdef>int <function>sd_event_source_get_inotify_path</function></funcdef>
  69         <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
  70         <paramdef>const char **<parameter>ret</parameter></paramdef>
  71       </funcprototype>
  72
  73     </funcsynopsis>
  74   </refsynopsisdiv>
  75
  76   <refsect1>
  77     <title>Description</title>
  78
  79     <para><function>sd_event_add_inotify()</function> adds a new <citerefentry
  80     project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry> file
  81     system inode event source to an event loop. The event loop object is specified in the
  82     <parameter>event</parameter> parameter, the event source object is returned in the
  83     <parameter>source</parameter> parameter. The <parameter>path</parameter> parameter specifies the path of
  84     the file system inode to watch. The <parameter>mask</parameter> parameter specifies which types of inode
  85     events to watch specifically. It must contain an OR-ed combination of <constant>IN_ACCESS</constant>,
  86     <constant>IN_ATTRIB</constant>, <constant>IN_CLOSE_WRITE</constant>, … flags. See <citerefentry
  87     project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
  88     further information.</para>
  89
  90     <para>The <parameter>handler</parameter> must reference a function to call when the inode changes or
  91     <constant>NULL</constant>. The handler function will be passed the <parameter>userdata</parameter> pointer,
  92     which may be chosen freely by the caller. The handler also receives a pointer to a <structname>struct
  93     inotify_event</structname> structure containing information about the inode event. The handler may return
  94     negative to signal an error (see below), other return values are ignored. If
  95     <parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls
  96     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be
  97     used.</para>
  98
  99     <para><function>sd_event_add_inotify_fd()</function> is identical to
 100     <function>sd_event_add_inotify()</function>, except that it takes a file descriptor to an inode (possibly
 101     an <constant>O_PATH</constant> one, but any other will do too) instead of a path in the file system.
 102     </para>
 103
 104     <para>If multiple event sources are installed for the same inode the backing inotify watch descriptor is
 105     automatically shared. The mask parameter may contain any flag defined by the inotify API, with the exception of
 106     <constant>IN_MASK_ADD</constant>.</para>
 107
 108     <para>The handler is enabled continuously (<constant>SD_EVENT_ON</constant>), but this may be changed with
 109     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 110     Alternatively, the <constant>IN_ONESHOT</constant> mask flag may be used to request
 111     <constant>SD_EVENT_ONESHOT</constant> mode. If the handler function returns a negative error code, it
 112     will be disabled after the invocation, even if the <constant>SD_EVENT_ON</constant> mode was requested
 113     before.</para>
 114
 115     <para>As a special limitation the priority of inotify event sources may only be altered (see
 116     <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
 117     in the time between creation of the event source object with <function>sd_event_add_inotify()</function> and the
 118     beginning of the next event loop iteration. Attempts of changing the priority any later will be refused. Consider
 119     freeing and allocating a new inotify event source to change the priority at that point.</para>
 120
 121     <para>To destroy an event source object use
 122     <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, but note
 123     that the event source is only removed from the event loop when all references to the event source are dropped. To
 124     make sure an event source does not fire anymore, even when there's still a reference to it kept, consider disabling
 125     it with
 126     <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 127
 128     <para>If the second parameter of <function>sd_event_add_inotify()</function> is passed as
 129     <constant>NULL</constant> no reference to the event source object is returned. In this case the event
 130     source is considered "floating", and will be destroyed implicitly when the event loop itself is
 131     destroyed.</para>
 132
 133     <para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_inotify()</function> is
 134     <constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
 135     event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
 136     the exit code parameter to
 137     <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 138
 139     <para><function>sd_event_source_get_inotify_mask()</function> retrieves the configured inotify watch mask of an
 140     event source created previously with <function>sd_event_add_inotify()</function>. It takes the event source object
 141     as the <parameter>source</parameter> parameter and a pointer to a <type>uint32_t</type> variable to return the mask
 142     in.</para>
 143
 144     <para><function>sd_event_source_get_inotify_path()</function> retrieves the target path of the configured
 145     inotify watch of an event source created previously with <function>sd_event_add_inotify()</function>. It
 146     takes the event source object as the <parameter>source</parameter> parameter and a pointer to a
 147     <type>const char **</type> variable to return the path in. The caller must not free the returned path.
 148     </para>
 149   </refsect1>
 150
 151   <refsect1>
 152     <title>Return Value</title>
 153
 154     <para>On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style
 155     error code.</para>
 156
 157     <refsect2>
 158       <title>Errors</title>
 159
 160       <para>Returned errors may indicate the following problems:</para>
 161
 162       <variablelist>
 163         <varlistentry>
 164           <term><constant>-ENOMEM</constant></term>
 165
 166           <listitem><para>Not enough memory to allocate an object.</para></listitem>
 167         </varlistentry>
 168
 169         <varlistentry>
 170           <term><constant>-EINVAL</constant></term>
 171
 172           <listitem><para>An invalid argument has been passed. This includes specifying a mask with
 173           <constant>IN_MASK_ADD</constant> set.</para></listitem>
 174         </varlistentry>
 175
 176         <varlistentry>
 177           <term><constant>-ESTALE</constant></term>
 178
 179           <listitem>
 180             <para>Returned by <function>sd_event_source_add_inotify()</function> or
 181             <function>sd_event_source_add_inotify_fd()</function> when the event loop is already terminated.
 182             Returned by <function>sd_event_source_get_inotify_path()</function> when no active inode data is
 183             assigned to the event source, e.g. when the event source is disabled.</para>
 184           </listitem>
 185
 186         </varlistentry>
 187
 188         <varlistentry>
 189           <term><constant>-ECHILD</constant></term>
 190
 191           <listitem><para>The event loop has been created in a different process, library or module instance.</para></listitem>
 192
 193         </varlistentry>
 194
 195         <varlistentry>
 196           <term><constant>-EDOM</constant></term>
 197
 198           <listitem><para>The passed event source is not an inotify process event source.</para></listitem>
 199         </varlistentry>
 200
 201         <varlistentry>
 202           <term><constant>-EBADF</constant></term>
 203
 204           <listitem><para>The passed file descriptor is not valid.</para></listitem>
 205
 206         </varlistentry>
 207
 208         <varlistentry>
 209           <term><constant>-ENOSYS</constant></term>
 210
 211           <listitem>
 212             <para><function>sd_event_add_inotify_fd()</function> or
 213             <function>sd_event_source_get_inotify_path()</function> was called without
 214             <filename>/proc/</filename> mounted.</para>
 215           </listitem>
 216
 217         </varlistentry>
 218
 219       </variablelist>
 220     </refsect2>
 221   </refsect1>
 222
 223   <refsect1>
 224     <title>Examples</title>
 225
 226     <example>
 227       <title>A simple program that uses inotify to monitor one or two directories</title>
 228
 229       <programlisting><xi:include href="inotify-watch-tmp.c" parse="text" /></programlisting>
 230     </example>
 231   </refsect1>
 232
 233   <xi:include href="libsystemd-pkgconfig.xml" />
 234
 235   <refsect1>
 236     <title>History</title>
 237     <para><function>sd_event_inotify_handler_t()</function>,
 238     <function>sd_event_add_inotify()</function>, and
 239     <function>sd_event_source_get_inotify_mask()</function> were added in version 239.</para>
 240     <para><function>sd_event_add_inotify_fd()</function> was added in version 250.</para>
 241     <para><function>sd_event_source_get_inotify_path()</function> was added in version 256.</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-event</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 250       <member><citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 251       <member><citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 252       <member><citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 253       <member><citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 254       <member><citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 255       <member><citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 256       <member><citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 257       <member><citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 258       <member><citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 259       <member><citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 260       <member><citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 261       <member><citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 262       <member><citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
 263     </simplelist></para>
 264   </refsect1>
 265
 266 </refentry>