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4a7cd0caad
Follow-ups for 74c4231ce5.
Previously, the path is obtained from the fd, but it is closed in
sd_event_loop() to unpin the filesystem.
So, let's save the path when the event source is created, and make
sd_event_source_get_inotify_path() simply read it.
267 lines
14 KiB
XML
267 lines
14 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_event_add_inotify" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_event_add_inotify</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_event_add_inotify</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_event_add_inotify</refname>
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<refname>sd_event_add_inotify_fd</refname>
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<refname>sd_event_source_get_inotify_mask</refname>
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<refname>sd_event_source_get_inotify_path</refname>
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<refname>sd_event_inotify_handler_t</refname>
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<refpurpose>Add an "inotify" file system inode event source to an event loop</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo>
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<funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
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<funcprototype>
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<funcdef>typedef int (*<function>sd_event_inotify_handler_t</function>)</funcdef>
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<paramdef>sd_event_source *<parameter>s</parameter></paramdef>
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<paramdef>const struct inotify_event *<parameter>event</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_inotify</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>const char *<parameter>path</parameter></paramdef>
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<paramdef>uint32_t <parameter>mask</parameter></paramdef>
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<paramdef>sd_event_inotify_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_add_inotify_fd</function></funcdef>
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<paramdef>sd_event *<parameter>event</parameter></paramdef>
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<paramdef>sd_event_source **<parameter>source</parameter></paramdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>uint32_t <parameter>mask</parameter></paramdef>
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<paramdef>sd_event_inotify_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void *<parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_inotify_mask</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>uint32_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_event_source_get_inotify_path</function></funcdef>
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<paramdef>sd_event_source *<parameter>source</parameter></paramdef>
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<paramdef>const char **<parameter>ret</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_event_add_inotify()</function> adds a new <citerefentry
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project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry> file
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system inode event source to an event loop. The event loop object is specified in the
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<parameter>event</parameter> parameter, the event source object is returned in the
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<parameter>source</parameter> parameter. The <parameter>path</parameter> parameter specifies the path of
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the file system inode to watch. The <parameter>mask</parameter> parameter specifies which types of inode
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events to watch specifically. It must contain an OR-ed combination of <constant>IN_ACCESS</constant>,
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<constant>IN_ATTRIB</constant>, <constant>IN_CLOSE_WRITE</constant>, … flags. See <citerefentry
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project='man-pages'><refentrytitle>inotify</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
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further information.</para>
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<para>The <parameter>handler</parameter> must reference a function to call when the inode changes or
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<constant>NULL</constant>. The handler function will be passed the <parameter>userdata</parameter> pointer,
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which may be chosen freely by the caller. The handler also receives a pointer to a <structname>struct
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inotify_event</structname> structure containing information about the inode event. The handler may return
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negative to signal an error (see below), other return values are ignored. If
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<parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be
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used.</para>
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<para><function>sd_event_add_inotify_fd()</function> is identical to
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<function>sd_event_add_inotify()</function>, except that it takes a file descriptor to an inode (possibly
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an <constant>O_PATH</constant> one, but any other will do too) instead of a path in the file system.
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</para>
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<para>If multiple event sources are installed for the same inode the backing inotify watch descriptor is
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automatically shared. The mask parameter may contain any flag defined by the inotify API, with the exception of
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<constant>IN_MASK_ADD</constant>.</para>
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<para>The handler is enabled continuously (<constant>SD_EVENT_ON</constant>), but this may be changed with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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Alternatively, the <constant>IN_ONESHOT</constant> mask flag may be used to request
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<constant>SD_EVENT_ONESHOT</constant> mode. If the handler function returns a negative error code, it
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will be disabled after the invocation, even if the <constant>SD_EVENT_ON</constant> mode was requested
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before.</para>
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<para>As a special limitation the priority of inotify event sources may only be altered (see
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<citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
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in the time between creation of the event source object with <function>sd_event_add_inotify()</function> and the
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beginning of the next event loop iteration. Attempts of changing the priority any later will be refused. Consider
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freeing and allocating a new inotify event source to change the priority at that point.</para>
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<para>To destroy an event source object use
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<citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, but note
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that the event source is only removed from the event loop when all references to the event source are dropped. To
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make sure an event source does not fire anymore, even when there's still a reference to it kept, consider disabling
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it with
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<citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>If the second parameter of <function>sd_event_add_inotify()</function> is passed as
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<constant>NULL</constant> no reference to the event source object is returned. In this case the event
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source is considered "floating", and will be destroyed implicitly when the event loop itself is
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destroyed.</para>
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<para>If the <parameter>handler</parameter> parameter to <function>sd_event_add_inotify()</function> is
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<constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
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event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
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the exit code parameter to
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<citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para><function>sd_event_source_get_inotify_mask()</function> retrieves the configured inotify watch mask of an
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event source created previously with <function>sd_event_add_inotify()</function>. It takes the event source object
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as the <parameter>source</parameter> parameter and a pointer to a <type>uint32_t</type> variable to return the mask
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in.</para>
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<para><function>sd_event_source_get_inotify_path()</function> retrieves the target path of the configured
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inotify watch of an event source created previously with <function>sd_event_add_inotify()</function>. It
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takes the event source object as the <parameter>source</parameter> parameter and a pointer to a
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<type>const char **</type> variable to return the path in. The caller must not free the returned path.
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</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style
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error code.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Not enough memory to allocate an object.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>An invalid argument has been passed. This includes specifying a mask with
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<constant>IN_MASK_ADD</constant> set.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem>
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<para>Returned by <function>sd_event_source_add_inotify()</function> or
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<function>sd_event_source_add_inotify_fd()</function> when the event loop is already terminated.
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Returned by <function>sd_event_source_get_inotify_path()</function> when no active inode data is
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assigned to the event source, e.g. when the event source is disabled.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The event loop has been created in a different process, library or module instance.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EDOM</constant></term>
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<listitem><para>The passed event source is not an inotify process event source.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EBADF</constant></term>
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<listitem><para>The passed file descriptor is not valid.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOSYS</constant></term>
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<listitem>
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<para><function>sd_event_add_inotify_fd()</function> or
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<function>sd_event_source_get_inotify_path()</function> was called without
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<filename>/proc/</filename> mounted.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<example>
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<title>A simple program that uses inotify to monitor one or two directories</title>
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<programlisting><xi:include href="inotify-watch-tmp.c" parse="text" /></programlisting>
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</example>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>History</title>
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<para><function>sd_event_inotify_handler_t()</function>,
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<function>sd_event_add_inotify()</function>, and
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<function>sd_event_source_get_inotify_mask()</function> were added in version 239.</para>
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<para><function>sd_event_add_inotify_fd()</function> was added in version 250.</para>
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<para><function>sd_event_source_get_inotify_path()</function> was added in version 256.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry project='man-pages'><refentrytitle>waitid</refentrytitle><manvolnum>2</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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