man/sd_journal_get_cursor.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="sd_journal_get_cursor" xmlns:xi="http://www.w3.org/2001/XInclude">
   7
   8   <refentryinfo>
   9     <title>sd_journal_get_cursor</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>sd_journal_get_cursor</refentrytitle>
  15     <manvolnum>3</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>sd_journal_get_cursor</refname>
  20     <refname>sd_journal_test_cursor</refname>
  21     <refpurpose>Get cursor string for or test cursor string against the current journal entry</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <funcsynopsis>
  26       <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  27
  28       <funcprototype>
  29         <funcdef>int <function>sd_journal_get_cursor</function></funcdef>
  30         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  31         <paramdef>char **<parameter>cursor</parameter></paramdef>
  32       </funcprototype>
  33
  34       <funcprototype>
  35         <funcdef>int <function>sd_journal_test_cursor</function></funcdef>
  36         <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  37         <paramdef>const char *<parameter>cursor</parameter></paramdef>
  38       </funcprototype>
  39
  40     </funcsynopsis>
  41   </refsynopsisdiv>
  42
  43   <refsect1>
  44     <title>Description</title>
  45
  46     <para><function>sd_journal_get_cursor()</function> returns a
  47     cursor string for the current journal entry. A cursor is a
  48     serialization of the current journal position formatted as text.
  49     The string only contains printable characters and can be passed
  50     around in text form. The cursor identifies a journal entry
  51     globally and in a stable way and may be used to later seek to it
  52     via
  53     <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
  54     The cursor string should be considered opaque and not be parsed by
  55     clients. Seeking to a cursor position without the specific entry
  56     being available locally will seek to the next closest (in terms of
  57     time) available entry. The call takes two arguments: a journal
  58     context object and a pointer to a string pointer where the cursor
  59     string will be placed. The string is allocated via libc
  60     <citerefentry project='man-pages'><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  61     and should be freed after use with
  62     <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  63
  64     <para><function>sd_journal_test_cursor()</function>
  65     may be used to check whether the current position in
  66     the journal matches the specified cursor. This is
  67     useful since cursor strings do not uniquely identify
  68     an entry: the same entry might be referred to by
  69     multiple different cursor strings, and hence string
  70     comparing cursors is not possible. Use this call to
  71     verify after an invocation of
  72     <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
  73     whether the entry being sought to was actually found
  74     in the journal or the next closest entry was used
  75     instead.</para>
  76
  77     <para>Note that <function>sd_journal_get_cursor()</function>
  78     and <function>sd_journal_test_cursor()</function>
  79     will not work before
  80     <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  81     (or one of the other functions which move to an entry)
  82     has been called at least once to position the read pointer at a valid entry.</para>
  83   </refsect1>
  84
  85   <refsect1>
  86     <title>Return Value</title>
  87
  88     <para><function>sd_journal_get_cursor()</function> returns 0 on
  89     success or a negative errno-style error code.
  90     <function>sd_journal_test_cursor()</function> returns positive if
  91     the current entry matches the specified cursor, 0 if it does not
  92     match the specified cursor or a negative errno-style error code on
  93     failure.</para>
  94   </refsect1>
  95
  96   <refsect1>
  97     <title>Notes</title>
  98
  99     <xi:include href="threads-aware.xml" xpointer="strict" />
 100
 101     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 102   </refsect1>
 103
 104   <refsect1>
 105     <title>History</title>
 106     <para><function>sd_journal_get_cursor()</function> was added in version 187.</para>
 107     <para><function>sd_journal_test_cursor()</function> was added in version 195.</para>
 108   </refsect1>
 109
 110   <refsect1>
 111     <title>See Also</title>
 112
 113     <para><simplelist type="inline">
 114       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 115       <member><citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 116       <member><citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 117       <member><citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
 118     </simplelist></para>
 119   </refsect1>
 120
 121 </refentry>