man: document sd_journal_get_cursor()

Makefile.am

@@ -505,7 +505,8 @@ MANPAGES = \
 	man/sd_journal_next.3 \
 	man/sd_journal_get_data.3 \
 	man/sd_journal_get_realtime_usec.3 \
-	man/sd_journal_get_cutoff_realtime_usec.3
+	man/sd_journal_get_cutoff_realtime_usec.3 \
+	man/sd_journal_get_cursor.3
 
 MANPAGES_ALIAS = \
 	man/reboot.8 \

man/sd_journal_get_cursor.xml

@@ -0,0 +1,122 @@
+<?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_cursor">
+
+        <refentryinfo>
+                <title>sd_journal_get_cursor</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_cursor</refentrytitle>
+                <manvolnum>3</manvolnum>
+        </refmeta>
+
+        <refnamediv>
+                <refname>sd_journal_get_cursor</refname>
+                <refpurpose>Get cursor string for the current journal entry</refpurpose>
+        </refnamediv>
+
+        <refsynopsisdiv>
+                <funcsynopsis>
+                        <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
+
+                        <funcprototype>
+                                <funcdef>int <function>sd_journal_get_cursor</function></funcdef>
+                                <paramdef>sd_journal* <parameter>j</parameter></paramdef>
+                                <paramdef>char ** <parameter>cursor</parameter></paramdef>
+                        </funcprototype>
+
+                </funcsynopsis>
+        </refsynopsisdiv>
+
+        <refsect1>
+                <title>Description</title>
+
+                <para><function>sd_journal_get_cursor()</function>
+                returns a cursor string for the current journal
+                entry. A cursor is a serialization of the current
+                journal position in text form. The string only
+                contains printable characters and can be passed around
+                in text form. The cursor identifies a journal entry
+                globally and in a stable way and may be used to later
+                seek to it via
+                <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
+                cursor string should be considered opaque and not be
+                parsed by clients. Seeking to a cursor position
+                without the specific entry being available locally
+                will seek to the next closest (in terms of time)
+                available entry. The call takes two arguments: a
+                journal context object and a pointer to a
+                string pointer where the cursor string will be
+                placed. The string is allocated via libc <citerefentry><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry> and should
+                be freed after use with
+                <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+
+                <para>Note that this function will not work before
+                <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                (or related call) has been called at least
+                once, in order to position the read pointer at a valid entry.</para>
+        </refsect1>
+
+        <refsect1>
+                <title>Return Value</title>
+
+                <para><function>sd_journal_get_cursor()</function>
+                returns 0 on success or a negative errno-style error
+                code.</para>
+        </refsect1>
+
+        <refsect1>
+                <title>Notes</title>
+
+                <para>The <function>sd_journal_get_cursor()</function>
+                interface is 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_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                </para>
+        </refsect1>
+
+</refentry>

man/sd_journal_get_cutoff_realtime_usec.xml

@@ -45,7 +45,7 @@
         <refnamediv>
                 <refname>sd_journal_get_cutoff_realtime_usec</refname>
                 <refname>sd_journal_get_cutoff_monotonic_usec</refname>
-                <refpurpose>Read timestamps from the current journal entry</refpurpose>
+                <refpurpose>Read cut-off timestamps from the current journal entry</refpurpose>
         </refnamediv>
 
         <refsynopsisdiv>

man/sd_journal_get_data.xml

@@ -127,7 +127,7 @@
                 <para>Note that these functions will not work before
                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                 (or related call) has been called at least
-                once.</para>
+                once, in order to position the read pointer at a valid entry.</para>
         </refsect1>
 
         <refsect1>

man/sd_journal_get_realtime_usec.xml

@@ -99,7 +99,7 @@
                 <para>Note that these functions will not work before
                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                 (or related call) has been called at least
-                once.</para>
+                once, in order to position the read pointer at a valid entry.</para>
         </refsect1>
 
         <refsect1>

man/sd_journal_next.xml

@@ -205,7 +205,9 @@ int main(int argc, char *argv[]) {
                         <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_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                        <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                 </para>
         </refsect1>
 

man/sd_journal_open.xml

@@ -118,6 +118,25 @@
                 for an example how to iterate through the journal
                 after opening it it with
                 <function>sd_journal_open()</function>.</para>
+
+                <para>A journal context object returned by
+                <function>sd_journal_open()</function> references a
+                specific journal entry as <emphasis>current</emphasis> entry,
+                similar to a file seek index in a classic file system
+                file, but without absolute positions. It may be
+                altered with
+                <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                and
+                <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                and related calls. The current entry position may be
+                exported in <emphasis>cursor</emphasis> strings, as accessible
+                via
+                <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Cursor
+                strings may be used to globally identify a specific
+                journal entry in a stable way and then later to seek
+                to it (or if the specific entry is not available
+                locally, to its closest entry in time)
+                <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
         </refsect1>
 
         <refsect1>