systemd/man/sd_journal_get_cursor.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<refentry id="sd_journal_get_cursor" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_journal_get_cursor</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_journal_get_cursor</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_journal_get_cursor</refname>
    <refname>sd_journal_test_cursor</refname>
    <refpurpose>Get cursor string for or test cursor string against the current journal entry</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_journal_get_cursor</function></funcdef>
        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
        <paramdef>char **<parameter>ret_cursor</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_journal_test_cursor</function></funcdef>
        <paramdef>sd_journal *<parameter>j</parameter></paramdef>
        <paramdef>const char *<parameter>cursor</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>sd_journal_get_cursor()</function> returns a cursor string for the current journal
    entry. A cursor is a serialization of the current journal position formatted as text.  The string only
    contains printable characters and can be passed around in text form. The cursor identifies a journal
    entry globally and in a stable way and may be used to later seek to it via
    <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    The cursor string should be considered opaque and not be parsed by clients. Seeking to a cursor position
    without the specific entry being available locally will seek to the next closest (in terms of time)
    available entry. The call takes two arguments: a journal context object and a pointer to a string pointer
    where the cursor string will be placed. The string is allocated via libc <citerefentry
    project='man-pages'><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
    should be freed after use with <citerefentry
    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
    <parameter>ret_cursor</parameter> parameter may be passed as <constant>NULL</constant> in which case the
    cursor string is not generated, however the return value will indicate whether the journal context is
    currently positioned on an entry, and thus has a cursor associated.</para>

    <para><function>sd_journal_test_cursor()</function>
    may be used to check whether the current position in
    the journal matches the specified cursor. This is
    useful since cursor strings do not uniquely identify
    an entry: the same entry might be referred to by
    multiple different cursor strings, and hence string
    comparing cursors is not possible. Use this call to
    verify after an invocation of
    <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    whether the entry being sought to was actually found
    in the journal or the next closest entry was used
    instead.</para>

    <para>Note that <function>sd_journal_get_cursor()</function>
    and <function>sd_journal_test_cursor()</function>
    will not work before
    <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    (or one of the other functions which move to an entry)
    has been called at least once to position the read pointer at a valid entry.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para><function>sd_journal_get_cursor()</function> returns 0 on
    success or a negative errno-style error code.
    <function>sd_journal_test_cursor()</function> returns positive if
    the current entry matches the specified cursor, 0 if it does not
    match the specified cursor or a negative errno-style error code on
    failure.</para>

    <refsect2>
      <title>Errors</title>

      <para>Returned errors may indicate the following problems:</para>

      <variablelist>
        <varlistentry>
          <term><constant>-EADDRNOTAVAIL</constant></term>

          <listitem><para>The journal context is currently not positioned on any entry, and hence no cursor
          string can be generated.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-EINVAL</constant></term>

          <listitem><para>The journal context parameter is <constant>NULL</constant>.</para></listitem>
        </varlistentry>

        <varlistentry>
          <term><constant>-ECHILD</constant></term>

          <listitem><para>The journal context object has been allocated in a different process than it is
          being used in now.</para></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <xi:include href="threads-aware.xml" xpointer="strict" />

    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
  </refsect1>

  <refsect1>
    <title>History</title>
    <para><function>sd_journal_get_cursor()</function> was added in version 187.</para>
    <para><function>sd_journal_test_cursor()</function> was added in version 195.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>