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