man/sd_journal_get_cursor.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
   9
  10   Copyright 2012 Lennart Poettering
  11 -->
  12
  13 <refentry id="sd_journal_get_cursor" xmlns:xi="http://www.w3.org/2001/XInclude">
  14
  15   <refentryinfo>
  16     <title>sd_journal_get_cursor</title>
  17     <productname>systemd</productname>
  18
  19     <authorgroup>
  20       <author>
  21         <contrib>Developer</contrib>
  22         <firstname>Lennart</firstname>
  23         <surname>Poettering</surname>
  24         <email>lennart@poettering.net</email>
  25       </author>
  26     </authorgroup>
  27   </refentryinfo>
  28
  29   <refmeta>
  30     <refentrytitle>sd_journal_get_cursor</refentrytitle>
  31     <manvolnum>3</manvolnum>
  32   </refmeta>
  33
  34   <refnamediv>
  35     <refname>sd_journal_get_cursor</refname>
  36     <refname>sd_journal_test_cursor</refname>
  37     <refpurpose>Get cursor string for or test cursor string against the current journal entry</refpurpose>
  38   </refnamediv>
  39
  40   <refsynopsisdiv>
  41     <funcsynopsis>
  42       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  43
  44       <funcprototype>
  45         <funcdef>int <function>sd_journal_get_cursor</function></funcdef>
  46         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  47         <paramdef>char **<parameter>cursor</parameter></paramdef>
  48       </funcprototype>
  49
  50       <funcprototype>
  51         <funcdef>int <function>sd_journal_test_cursor</function></funcdef>
  52         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  53         <paramdef>const char *<parameter>cursor</parameter></paramdef>
  54       </funcprototype>
  55
  56     </funcsynopsis>
  57   </refsynopsisdiv>
  58
  59   <refsect1>
  60     <title>Description</title>
  61
  62     <para><function>sd_journal_get_cursor()</function> returns a
  63     cursor string for the current journal entry. A cursor is a
  64     serialization of the current journal position formatted as text.
  65     The string only contains printable characters and can be passed
  66     around in text form. The cursor identifies a journal entry
  67     globally and in a stable way and may be used to later seek to it
  68     via
  69     <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  70     The cursor string should be considered opaque and not be parsed by
  71     clients. Seeking to a cursor position without the specific entry
  72     being available locally will seek to the next closest (in terms of
  73     time) available entry. The call takes two arguments: a journal
  74     context object and a pointer to a string pointer where the cursor
  75     string will be placed. The string is allocated via libc
  76     <citerefentry project='man-pages'><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  77     and should be freed after use with
  78     <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  79
  80     <para>Note that <function>sd_journal_get_cursor()</function> will
  81     not work before
  82     <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  83     (or related call) has been called at least once, in order to
  84     position the read pointer at a valid entry.</para>
  85
  86     <para><function>sd_journal_test_cursor()</function>
  87     may be used to check whether the current position in
  88     the journal matches the specified cursor. This is
  89     useful since cursor strings do not uniquely identify
  90     an entry: the same entry might be referred to by
  91     multiple different cursor strings, and hence string
  92     comparing cursors is not possible. Use this call to
  93     verify after an invocation of
  94     <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  95     whether the entry being sought to was actually found
  96     in the journal or the next closest entry was used
  97     instead.</para>
  98   </refsect1>
  99
 100   <refsect1>
 101     <title>Return Value</title>
 102
 103     <para><function>sd_journal_get_cursor()</function> returns 0 on
 104     success or a negative errno-style error code.
 105     <function>sd_journal_test_cursor()</function> returns positive if
 106     the current entry matches the specified cursor, 0 if it does not
 107     match the specified cursor or a negative errno-style error code on
 108     failure.</para>
 109   </refsect1>
 110
 111   <refsect1>
 112     <title>Notes</title>
 113
 114     <para>All functions listed here are thread-agnostic and only a single thread may operate
 115     on a given <structname>sd_journal</structname> object.</para>
 116
 117     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 118   </refsect1>
 119
 120   <refsect1>
 121     <title>See Also</title>
 122
 123     <para>
 124       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 125       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 126       <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 127       <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 128     </para>
 129   </refsect1>
 130
 131 </refentry>