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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+ This file is part of systemd.
+
+ Copyright 2012 Lennart Poettering
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd_journal_get_fd">
+
+ <refentryinfo>
+ <title>sd_journal_get_fd</title>
+ <productname>systemd</productname>
+
+ <authorgroup>
+ <author>
+ <contrib>Developer</contrib>
+ <firstname>Lennart</firstname>
+ <surname>Poettering</surname>
+ <email>lennart@poettering.net</email>
+ </author>
+ </authorgroup>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_journal_get_fd</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_journal_get_fd</refname>
+ <refname>sd_journal_get_process</refname>
+ <refname>sd_journal_get_wait</refname>
+ <refpurpose>Journal change notification
+ interface</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_get_fd</function></funcdef>
+ <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_process</function></funcdef>
+ <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_wait</function></funcdef>
+ <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+ <paramdef>uint64_t <parameter>timeout_usec</parameter></paramdef>
+ </funcprototype>
+
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_journal_get_fd()</function> returns
+ a file descriptor that may be asynchronously polled in
+ an external event loop and is signalled readable as
+ soon as the journal changes, for example because new
+ entries were added. The file descriptor is suitable
+ for usage in
+ <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+ where it will yield POLLIN on all changes. The call
+ takes one argument: the journal context object.</para>
+
+ <para>After each POLLIN wake-up
+ <function>sd_journal_process()</function> needs to be
+ called to process events and reset the readable state
+ of the file descriptor. This call will also indicate
+ what kind of change has been detected (see below; note
+ that spurious wake-ups are possible).</para>
+
+ <para>A synchronous alternative for using
+ <function>sd_journal_get_fd()</function> and
+ <function>sd_journal_process()</function> is
+ <function>sd_journal_wait()</function>. It will
+ synchronously wait until the journal gets changed up
+ to a certain time-out as specified in its second
+ argument. Pass <literal>(uint64_t) -1</literal> to
+ wait indefinitely. Internally this call simply
+ combines <function>sd_journal_get_fd()</function>,
+ <function>poll()</function> and
+ <function>sd_journal_process()</function> into
+ one.</para>
+
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para><function>sd_journal_get_fd()</function> returns a valid file descriptor on success or a negative errno-style error
+ code.</para>
+
+ <para><function>sd_journal_process()</function> and
+ <function>sd_journal_wait()</function> return one of
+ <literal>SD_JOURNAL_NOP</literal>,
+ <literal>SD_JOURNAL_APPEND</literal> or
+ <literal>SD_JOURNAL_INVALIDATE</literal> on success or
+ a negative errno-style error code. If
+ <literal>SD_JOURNAL_NOP</literal> is returned the
+ journal didn't change since the last invocation. If
+ <literal>SD_JOURNAL_APPEND</literal> is returned new
+ entries have been appended to the end of the
+ journal. If <literal>SD_JOURNAL_INVALIDATE</literal>
+ journal files were added or removed (possibly due to
+ rotation). In the latter event live-view UIs should
+ probably refresh their entire display while in the
+ case of <literal>SD_JOURNAL_APPEND</literal> it is
+ sufficient to simply continue reading at the previous
+ end of the journal.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <para>The <function>sd_journal_get_fd()</function>,
+ <function>sd_journal_process()</function> and
+ <function>sd_journal_wait()</function> interfaces are
+ available as shared library, which can be compiled and
+ linked to with the
+ <literal>libsystemd-journal</literal>
+ <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ file.</para>
+ </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_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>