207 lines
4.8 KiB
HTML
207 lines
4.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of SD_EVENT_GET_FD</TITLE>
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</HEAD><BODY>
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<H1>SD_EVENT_GET_FD</H1>
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Section: sd_event_get_fd (3)<BR>Updated: <BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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sd_event_get_fd - Obtain a file descriptor to poll for event loop events
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<P>
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<B>
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</B><PRE>
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#include <<A HREF="file:///usr/include/systemd/sd-event.h">systemd/sd-event.h</A>>
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</PRE>
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<DL COMPACT>
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<DT id="1">
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<B>int sd_event_get_fd(sd_event *</B><I>event</I><B>);</B>
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<P>
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<B>sd_event_get_fd()</B>
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<DD>returns the file descriptor that an event loop object returned by the
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<B><A HREF="/cgi-bin/man/man2html?3+sd_event_new">sd_event_new</A></B>(3)
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function uses to wait for events. This file descriptor may itself be polled for
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<B>POLLIN</B>/<B>EPOLLIN</B>
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events. This makes it possible to embed an
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<B><A HREF="/cgi-bin/man/man2html?3+sd-event">sd-event</A></B>(3)
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event loop into another, possibly foreign, event loop.
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<P>
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The returned file descriptor refers to an
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<B><A HREF="/cgi-bin/man/man2html?7+epoll">epoll</A></B>(7)
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object. It is recommended not to alter it by invoking
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<B><A HREF="/cgi-bin/man/man2html?2+epoll_ctl">epoll_ctl</A></B>(2)
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on it, in order to avoid interference with the event loop's inner logic and assumptions.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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<P>
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On success,
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<B>sd_event_get_fd()</B>
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returns a non-negative file descriptor. On failure, it returns a negative errno-style error code.
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<A NAME="lbAF"> </A>
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<H3>Errors</H3>
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<P>
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Returned errors may indicate the following problems:
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<P>
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<B>-EINVAL</B>
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<DL COMPACT><DT id="2"><DD>
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<I>event</I>
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is not a valid pointer to an
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sd_event
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structure.
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</DL>
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<P>
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<B>-ECHILD</B>
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<DL COMPACT><DT id="3"><DD>
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The event loop has been created in a different process.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>EXAMPLES</H2>
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<P>
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<B>Example 1. Integration in the GLib event loop</B>
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<P>
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<DL COMPACT><DT id="4"><DD>
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<PRE>
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/* SPDX-License-Identifier: MIT */
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#include <<A HREF="file:///usr/include/stdlib.h">stdlib.h</A>>
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#include <<A HREF="file:///usr/include/glib.h">glib.h</A>>
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#include <<A HREF="file:///usr/include/systemd/sd-event.h">systemd/sd-event.h</A>>
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typedef struct SDEventSource {
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GSource source;
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GPollFD pollfd;
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sd_event *event;
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} SDEventSource;
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static gboolean event_prepare(GSource *source, gint *timeout_) {
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return sd_event_prepare(((SDEventSource *)source)->event) > 0;
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}
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static gboolean event_check(GSource *source) {
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return sd_event_wait(((SDEventSource *)source)->event, 0) > 0;
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}
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static gboolean event_dispatch(GSource *source, GSourceFunc callback, gpointer user_data) {
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return sd_event_dispatch(((SDEventSource *)source)->event) > 0;
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}
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static void event_finalize(GSource *source) {
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sd_event_unref(((SDEventSource *)source)->event);
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}
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static GSourceFuncs event_funcs = {
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.prepare = event_prepare,
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.check = event_check,
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.dispatch = event_dispatch,
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.finalize = event_finalize,
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};
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GSource *g_sd_event_create_source(sd_event *event) {
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SDEventSource *source;
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source = (SDEventSource *)g_source_new(&event_funcs, sizeof(SDEventSource));
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source->event = sd_event_ref(event);
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source->pollfd.fd = sd_event_get_fd(event);
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source->pollfd.events = G_IO_IN | G_IO_HUP | G_IO_ERR;
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g_source_add_poll((GSource *)source, &source->pollfd);
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return (GSource *)source;
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}
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</PRE>
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</DL>
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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<P>
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These APIs are implemented as a shared library, which can be compiled and linked to with the
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<B>libsystemd</B> <B><A HREF="/cgi-bin/man/man2html?1+pkg-config">pkg-config</A></B>(1)
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file.
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<A NAME="lbAI"> </A>
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<H2>SEE ALSO</H2>
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<P>
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<B><A HREF="/cgi-bin/man/man2html?3+sd-event">sd-event</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sd_event_new">sd_event_new</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sd_event_wait">sd_event_wait</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?2+epoll_ctl">epoll_ctl</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+epoll">epoll</A></B>(7)
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="5"><A HREF="#lbAB">NAME</A><DD>
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<DT id="6"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="7"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="8"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DL>
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<DT id="9"><A HREF="#lbAF">Errors</A><DD>
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</DL>
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<DT id="10"><A HREF="#lbAG">EXAMPLES</A><DD>
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<DT id="11"><A HREF="#lbAH">NOTES</A><DD>
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<DT id="12"><A HREF="#lbAI">SEE ALSO</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:55 GMT, March 31, 2021
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</BODY>
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</HTML>
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