-<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
-"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
- This file is part of systemd.
-
- Copyright 2016 Julian Orth
+ Copyright © 2016 Julian Orth
-->
-<refentry id="sd_bus_get_fd">
+<refentry id="sd_bus_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_get_fd</title>
<productname>systemd</productname>
-
- <authorgroup>
- <author>
- <firstname>Julian</firstname>
- <surname>Orth</surname>
- <email>ju.orth@gmail.com</email>
- </author>
- </authorgroup>
</refentryinfo>
<refmeta>
<refnamediv>
<refname>sd_bus_get_fd</refname>
+ <refname>sd_bus_set_fd</refname>
+ <refname>sd_bus_get_events</refname>
+ <refname>sd_bus_get_timeout</refname>
- <refpurpose>Get the file descriptor connected to the message bus</refpurpose>
+ <refpurpose>Get the file descriptor, I/O events and timeout to wait for from a message bus
+ object</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcdef>int <function>sd_bus_get_fd</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
</funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_set_fd</function></funcdef>
+ <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
+ <paramdef>int <parameter>input_fd</parameter></paramdef>
+ <paramdef>int <parameter>output_fd</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_get_events</function></funcdef>
+ <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_bus_get_timeout</function></funcdef>
+ <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
+ <paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef>
+ </funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
- <para>
- <function>sd_bus_get_fd()</function> returns the file descriptor used to
- communicate with the message bus. This descriptor can be used with
- <citerefentry
- project='die-net'><refentrytitle>select</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry
- project='die-net'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- or similar functions to wait for incoming messages.
+ <para><function>sd_bus_get_fd()</function> returns the file descriptor used to communicate from
+ a message bus object. This descriptor can be used with
+ <citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ or a similar function to wait for I/O events on the specified bus connection object. If the bus
+ object was configured with the <function>sd_bus_set_fd()</function> function, then the
+ <parameter>input_fd</parameter> file descriptor used in that call is returned.</para>
+
+ <para><function>sd_bus_set_fd()</function> sets the file descriptors used to communicate from a
+ message bus object. Both <parameter>input_fd</parameter> and <parameter>output_fd</parameter>
+ must be valid file descriptors. The same file descriptor may be used as both the input and the
+ output file descriptor. This function must be called before the bus is started.</para>
+
+ <para><function>sd_bus_get_events()</function> returns the I/O events to wait for, suitable for
+ passing to <function>poll()</function> or a similar call. Returns a combination of
+ <constant>POLLIN</constant>, <constant>POLLOUT</constant>, … events, or negative on error.
</para>
- <para>
- If the bus was created with the
- <citerefentry><refentrytitle>sd_bus_set_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- function, then the <parameter>input_fd</parameter> used in that call is
- returned.
+ <para><function>sd_bus_get_timeout()</function> returns the timeout in µs to pass to
+ <function>poll()</function> or a similar call when waiting for events on the specified bus
+ connection. The returned timeout may be zero, in which case a subsequent I/O polling call
+ should be invoked in non-blocking mode. The returned timeout may be
+ <constant>UINT64_MAX</constant> in which case the I/O polling call may block indefinitely,
+ without any applied timeout. Note that the returned timeout should be considered only a
+ maximum sleeping time. It is permissible (and even expected) that shorter timeouts are used by
+ the calling program, in case other event sources are polled in the same event loop. Note that
+ the returned time-value is relative and specified in microseconds. When converting this value in
+ order to pass it as third argument to <function>poll()</function> (which expects milliseconds),
+ care should be taken to use a division that rounds up to ensure the I/O polling operation
+ doesn't sleep for shorter than necessary, which might result in unintended busy looping
+ (alternatively, use
+ <citerefentry project='man-pages'><refentrytitle>ppoll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ instead of plain <function>poll()</function>, which understands timeouts with nano-second
+ granularity).</para>
+
+ <para>These three functions are useful to hook up a bus connection object with an external or
+ manual event loop involving <function>poll()</function> or a similar I/O polling call. Before
+ each invocation of the I/O polling call, all three functions should be invoked: the file
+ descriptor returned by <function>sd_bus_get_fd()</function> should be polled for the events
+ indicated by <function>sd_bus_get_events()</function>, and the I/O call should block for that up
+ to the timeout returned by <function>sd_bus_get_timeout()</function>. After each I/O polling
+ call the bus connection needs to process incoming or outgoing data, by invoking
+ <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
+
+ <para>Note that these functions are only one of three supported ways to implement I/O event
+ handling for bus connections. Alternatively use
+ <citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ to attach a bus connection to an
+ <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ event loop. Or use
+ <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ as a simple synchronous, blocking I/O waiting call.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
- <para>
- Returns the file descriptor used for incoming messages from the message
- bus.
- </para>
+ <para>On success, <function>sd_bus_get_fd()</function> returns the file descriptor used for
+ communication. On failure, it returns a negative errno-style error code.</para>
+
+ <para>On success, <function>sd_bus_set_fd()</function> returns a non-negative integer. On
+ failure, it returns a negative errno-style error code.</para>
+
+ <para>On success, <function>sd_bus_get_events()</function> returns the I/O event mask to use for
+ I/O event watching. On failure, it returns a negative errno-style error code.</para>
+
+ <para>On success, <function>sd_bus_get_timeout()</function> returns a non-negative integer. On
+ failure, it returns a negative errno-style error code.</para>
+
+ <refsect2>
+ <title>Errors</title>
+
+ <para>Returned errors may indicate the following problems:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><constant>-EINVAL</constant></term>
+
+ <listitem><para>An invalid bus object was passed.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ECHILD</constant></term>
+
+ <listitem><para>The bus connection was allocated in a parent process and is being reused
+ in a child process after <function>fork()</function>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ENOTCONN</constant></term>
+
+ <listitem><para>The bus connection has been terminated.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-EPERM</constant></term>
+
+ <listitem><para>Two distinct file descriptors were passed for input and output using
+ <function>sd_bus_set_fd()</function>, which <function>sd_bus_get_fd()</function> cannot
+ return.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-EBADF</constant></term>
+
+ <listitem><para>An invalid file descriptor was passed to
+ <function>sd_bus_set_fd()</function>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><constant>-ENOPKG</constant></term>
+
+ <listitem><para>The bus cannot be resolved.</para></listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect2>
</refsect1>
+ <xi:include href="libsystemd-pkgconfig.xml" />
+
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_bus_set_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
projects / thirdparty / systemd.git / blobdiff