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/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   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>Note that <function>sd_journal_get_cursor()</function> will
  65     not work before
  66     <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  67     (or related call) has been called at least once, in order to
  68     position the read pointer at a valid entry.</para>
  69
  70     <para><function>sd_journal_test_cursor()</function>
  71     may be used to check whether the current position in
  72     the journal matches the specified cursor. This is
  73     useful since cursor strings do not uniquely identify
  74     an entry: the same entry might be referred to by
  75     multiple different cursor strings, and hence string
  76     comparing cursors is not possible. Use this call to
  77     verify after an invocation of
  78     <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  79     whether the entry being sought to was actually found
  80     in the journal or the next closest entry was used
  81     instead.</para>
  82   </refsect1>
  83
  84   <refsect1>
  85     <title>Return Value</title>
  86
  87     <para><function>sd_journal_get_cursor()</function> returns 0 on
  88     success or a negative errno-style error code.
  89     <function>sd_journal_test_cursor()</function> returns positive if
  90     the current entry matches the specified cursor, 0 if it does not
  91     match the specified cursor or a negative errno-style error code on
  92     failure.</para>
  93   </refsect1>
  94
  95   <refsect1>
  96     <title>Notes</title>
  97
  98     <xi:include href="threads-aware.xml" xpointer="strict" />
  99
 100     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 101   </refsect1>
 102
 103   <refsect1>
 104     <title>See Also</title>
 105
 106     <para>
 107       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 108       <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 109       <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 110       <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 111     </para>
 112   </refsect1>
 113
 114 </refentry>