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<?xml version='1.0'?>
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< !DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX - License - Identifier: LGPL - 2.1+ -->
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<refentry id= "sd_event_get_fd" xmlns:xi= "http://www.w3.org/2001/XInclude" >
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<refentryinfo >
<title > sd_event_get_fd</title>
<productname > systemd</productname>
</refentryinfo>
<refmeta >
<refentrytitle > sd_event_get_fd</refentrytitle>
<manvolnum > 3</manvolnum>
</refmeta>
<refnamediv >
<refname > sd_event_get_fd</refname>
<refpurpose > Obtain a file descriptor to poll for event loop events</refpurpose>
</refnamediv>
<refsynopsisdiv >
<funcsynopsis >
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<funcsynopsisinfo > #include < systemd/sd-event.h> </funcsynopsisinfo>
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<funcprototype >
<funcdef > int <function > sd_event_get_fd</function> </funcdef>
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<paramdef > sd_event *<parameter > event</parameter> </paramdef>
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</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 >
<title > Description</title>
<para > <function > sd_event_get_fd()</function> returns the file
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descriptor that an event loop object returned by the
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<citerefentry > <refentrytitle > sd_event_new</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry>
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function uses to wait for events. This file descriptor may itself
be polled for
<constant > POLLIN</constant> /<constant > EPOLLIN</constant>
events. This makes it possible to embed an
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<citerefentry > <refentrytitle > sd-event</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry>
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event loop into another, possibly foreign, event loop.</para>
<para > The returned file descriptor refers to an <citerefentry
project='man-pages'><refentrytitle > epoll</refentrytitle> <manvolnum > 7</manvolnum> </citerefentry>
object. It is recommended not to alter it by invoking
<citerefentry
project='man-pages'><refentrytitle > epoll_ctl</refentrytitle> <manvolnum > 2</manvolnum> </citerefentry>
on it, in order to avoid interference with the event loop's inner
logic and assumptions.</para>
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</refsect1>
<refsect1 >
<title > Return Value</title>
<para > On success, <function > sd_event_get_fd()</function> returns a
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non-negative file descriptor. On failure, it returns a negative
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errno-style error code.</para>
</refsect1>
<refsect1 >
<title > Errors</title>
<para > Returned errors may indicate the following problems:</para>
<variablelist >
<varlistentry >
<term > <constant > -EINVAL</constant> </term>
<listitem > <para > <parameter > event</parameter> is not a valid
pointer to an <structname > sd_event</structname> structure.
</para> </listitem>
</varlistentry>
<varlistentry >
<term > <constant > -ECHILD</constant> </term>
<listitem > <para > The event loop has been created in a different process.</para> </listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 >
<title > Examples</title>
<example >
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<title > Integration in the GLib event loop</title>
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<programlisting > <xi:include href= "glib-event-glue.c" parse= "text" /> </programlisting>
</example>
</refsect1>
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<xi:include href= "libsystemd-pkgconfig.xml" />
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<refsect1 >
<title > See Also</title>
<para >
<citerefentry > <refentrytitle > sd-event</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry> ,
<citerefentry > <refentrytitle > sd_event_new</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry> ,
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<citerefentry > <refentrytitle > sd_event_wait</refentrytitle> <manvolnum > 3</manvolnum> </citerefentry> ,
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<citerefentry project= 'man-pages' > <refentrytitle > epoll_ctl</refentrytitle> <manvolnum > 2</manvolnum> </citerefentry> ,
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<citerefentry project= 'man-pages' > <refentrytitle > epoll</refentrytitle> <manvolnum > 7</manvolnum> </citerefentry>
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</para>
</refsect1>
</refentry>