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">
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   8   Copyright 2012 Lennart Poettering
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  23
  24 <refentry id="sd_journal_get_cursor">
  25
  26         <refentryinfo>
  27                 <title>sd_journal_get_cursor</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>sd_journal_get_cursor</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd_journal_get_cursor</refname>
  47                 <refname>sd_journal_test_cursor</refname>
  48                 <refpurpose>Get cursor string for or test cursor string against the current journal entry</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <funcsynopsis>
  53                         <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
  54
  55                         <funcprototype>
  56                                 <funcdef>int <function>sd_journal_get_cursor</function></funcdef>
  57                                 <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  58                                 <paramdef>char **<parameter>cursor</parameter></paramdef>
  59                         </funcprototype>
  60
  61                         <funcprototype>
  62                                 <funcdef>int <function>sd_journal_test_cursor</function></funcdef>
  63                                 <paramdef>sd_journal *<parameter>j</parameter></paramdef>
  64                                 <paramdef>const char *<parameter>cursor</parameter></paramdef>
  65                         </funcprototype>
  66
  67                 </funcsynopsis>
  68         </refsynopsisdiv>
  69
  70         <refsect1>
  71                 <title>Description</title>
  72
  73                 <para><function>sd_journal_get_cursor()</function>
  74                 returns a cursor string for the current journal
  75                 entry. A cursor is a serialization of the current
  76                 journal position formatted as text. The string only
  77                 contains printable characters and can be passed around
  78                 in text form. The cursor identifies a journal entry
  79                 globally and in a stable way and may be used to later
  80                 seek to it via
  81                 <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
  82                 cursor string should be considered opaque and not be
  83                 parsed by clients. Seeking to a cursor position
  84                 without the specific entry being available locally
  85                 will seek to the next closest (in terms of time)
  86                 available entry. The call takes two arguments: a
  87                 journal context object and a pointer to a string
  88                 pointer where the cursor string will be placed. The
  89                 string is allocated via libc
  90                 <citerefentry><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  91                 and should be freed after use with
  92                 <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
  93
  94                 <para>Note that
  95                 <function>sd_journal_get_cursor()</function> will not
  96                 work before
  97                 <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  98                 (or related call) has been called at least once, in
  99                 order to position the read pointer at a valid
 100                 entry.</para>
 101
 102                 <para><function>sd_journal_test_cursor()</function>
 103                 may be used to check whether the current position in
 104                 the journal matches the specified cursor. This is
 105                 useful since cursor strings do not uniquely identify
 106                 an entry: the same entry might be referred to by
 107                 multiple different cursor strings, and hence string
 108                 comparing cursors is not possible. Use this call to
 109                 verify after an invocation of
 110                 <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 111                 whether the entry being sought to was actually found
 112                 in the journal or the next closest entry was used
 113                 instead.</para>
 114         </refsect1>
 115
 116         <refsect1>
 117                 <title>Return Value</title>
 118
 119                 <para><function>sd_journal_get_cursor()</function>
 120                 returns 0 on success or a negative errno-style error
 121                 code. <function>sd_journal_test_cursor()</function>
 122                 returns positive if the current entry matches the
 123                 specified cursor, 0 if it does not match the specified
 124                 cursor or a negative errno-style error code on
 125                 failure.</para>
 126         </refsect1>
 127
 128         <refsect1>
 129                 <title>Notes</title>
 130
 131                 <para>The <function>sd_journal_get_cursor()</function>
 132                 and <function>sd_journal_test_cursor()</function>
 133                 interfaces are available as a shared library, which can
 134                 be compiled and linked to with the
 135                 <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 136                 file.</para>
 137         </refsect1>
 138
 139         <refsect1>
 140                 <title>See Also</title>
 141
 142                 <para>
 143                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 144                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 145                         <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 146                         <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 147                 </para>
 148         </refsect1>
 149
 150 </refentry>