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