Adding upstream version 252.22.upstream/252.22upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 177 insertions, 0 deletions

diff --git a/man/sd_bus_get_fd.xml b/man/sd_bus_get_fd.xml
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+<?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-or-later
+
+  Copyright © 2016 Julian Orth
+-->
+
+<refentry id="sd_bus_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>sd_bus_get_fd</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>sd_bus_get_fd</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_bus_get_fd</refname>
+    <refname>sd_bus_get_events</refname>
+    <refname>sd_bus_get_timeout</refname>
+
+    <refpurpose>Get the file descriptor, I/O events and timeout to wait for from a message bus
+    object</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_get_fd</function></funcdef>
+        <paramdef>sd_bus *<parameter>bus</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 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_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><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 absolute, based of <constant>CLOCK_MONOTONIC</constant> and specified 
+    in microseconds. When converting this value in order to pass it as third argument to 
+    <function>poll()</function> (which expects relative milliseconds), care should be taken to convert
+    to a relative time and 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>2</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>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_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>-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_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><refentrytitle>sd_bus_set_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>