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