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systemd/man/sd_journal_stream_fd.xml
Zbigniew Jędrzejewski-Szmek 29c45dc434 man: use external .c files for three examples
This way it's much easier to test that the code compiles without issues.
It's also easier to edit the code.

Indentation in one of the examples is reduced to two spaces. This is what we
use in man pages to make them fit on screen better.
2022-10-11 16:59:00 +02:00

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<?xml version='1.0'?> <!--*-nxml-*-->
<!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 -->
<refentry id="sd_journal_stream_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_journal_stream_fd</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_journal_stream_fd</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_journal_stream_fd</refname>
<refpurpose>Create log stream file descriptor to the journal</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_journal_stream_fd</function></funcdef>
<paramdef>const char *<parameter>identifier</parameter></paramdef>
<paramdef>int <parameter>priority</parameter></paramdef>
<paramdef>int <parameter>level_prefix</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_journal_stream_fd()</function> may be used to
create a log stream file descriptor. Log messages written to this
file descriptor as simple newline-separated text strings are
written to the journal. This file descriptor can be used
internally by applications or be made standard output or standard
error of other processes executed.</para>
<para><function>sd_journal_stream_fd()</function> takes a short
program identifier string as first argument, which will be written
to the journal as SYSLOG_IDENTIFIER= field for each log entry
(see
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for more information). The second argument shall be the default
priority level for all messages. The priority level is one of
<constant>LOG_EMERG</constant>, <constant>LOG_ALERT</constant>,
<constant>LOG_CRIT</constant>, <constant>LOG_ERR</constant>,
<constant>LOG_WARNING</constant>, <constant>LOG_NOTICE</constant>,
<constant>LOG_INFO</constant>, <constant>LOG_DEBUG</constant>, as
defined in <filename>syslog.h</filename>, see
<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for details. The third argument is a boolean: if true kernel-style
log level prefixes (such as <constant>SD_WARNING</constant>) are
interpreted, see
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for more information.</para>
<para>It is recommended that applications log UTF-8 messages only
with this API, but this is not enforced.</para>
<para>Each invocation of <function>sd_journal_stream_fd()</function> allocates a new log stream file descriptor,
that is not shared with prior or later invocations. The file descriptor is write-only (its reading direction is
shut down), and <constant>O_NONBLOCK</constant> is turned off initially.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>The call returns a valid write-only file descriptor on
success or a negative errno-style error code.</para>
</refsect1>
<refsect1>
<title>Signal safety</title>
<para><function>sd_journal_stream_fd()</function> is "async signal safe" in the meaning of <citerefentry
project='man-pages'><refentrytitle>signal-safety</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<xi:include href="threads-aware.xml" xpointer="safe"/>
<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
</refsect1>
<refsect1>
<title>Examples</title>
<para>Creating a log stream suitable for
<citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>:</para>
<programlisting><xi:include href="journal-stream-fd.c" parse="text" /></programlisting>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>fprintf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>