sd_journal_get_cursor.xml 7.06 KB
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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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  Copyright 2012 Lennart Poettering

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<refentry id="sd_journal_get_cursor">

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

                <authorgroup>
                        <author>
                                <contrib>Developer</contrib>
                                <firstname>Lennart</firstname>
                                <surname>Poettering</surname>
                                <email>lennart@poettering.net</email>
                        </author>
                </authorgroup>
        </refentryinfo>

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

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

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                        <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>

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                </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
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                journal position formatted as text. The string only
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                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
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                journal context object and a pointer to a string
                pointer where the cursor string will be placed. The
                string is allocated via libc
                <citerefentry><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                and should be freed after use with
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                <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>

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                <para>Note that
                <function>sd_journal_get_cursor()</function> will not
                work before
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                <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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                (or related call) has been called at least once, in
                order to position the read pointer at a valid
                entry.</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>
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                whether the entry being sought to was actually found
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                in the journal or the next closest entry was used
                instead.</para>
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        </refsect1>

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

                <para><function>sd_journal_get_cursor()</function>
                returns 0 on success or a negative errno-style error
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                code. <function>sd_journal_test_cursor()</function>
                returns positive if the current entry matches the
                specified cursor, 0 if it doesn't match the specified
                cursor or a negative errno-style error code on
                failure.</para>
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        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>The <function>sd_journal_get_cursor()</function>
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                and <function>sd_journal_test_cursor()</function>
                interfaces are available as shared library, which can
                be compiled and linked to with the
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                <literal>libsystemd-journal</literal>
                <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file.</para>
        </refsect1>

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

                <para>
                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>