mirror of
https://github.com/morgan9e/systemd
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148 lines
6.2 KiB
XML
148 lines
6.2 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_journal_get_cursor" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_journal_get_cursor</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_journal_get_cursor</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_journal_get_cursor</refname>
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<refname>sd_journal_test_cursor</refname>
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<refpurpose>Get cursor string for or test cursor string against the current journal entry</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_journal_get_cursor</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>char **<parameter>ret_cursor</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_test_cursor</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const char *<parameter>cursor</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_journal_get_cursor()</function> returns a cursor string for the current journal
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entry. A cursor is a serialization of the current 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
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entry globally and in a stable way and may be used to later seek to it via
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<citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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The cursor string should be considered opaque and not be parsed by clients. Seeking to a cursor position
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without the specific entry being available locally will seek to the next closest (in terms of time)
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available entry. The call takes two arguments: a journal context object and a pointer to a string pointer
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where the cursor string will be placed. The string is allocated via libc <citerefentry
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project='man-pages'><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
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should be freed after use with <citerefentry
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project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>. The
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<parameter>ret_cursor</parameter> parameter may be passed as <constant>NULL</constant> in which case the
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cursor string is not generated, however the return value will indicate whether the journal context is
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currently positioned on an entry, and thus has a cursor associated.</para>
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<para><function>sd_journal_test_cursor()</function>
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may be used to check whether the current position in
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the journal matches the specified cursor. This is
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useful since cursor strings do not uniquely identify
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an entry: the same entry might be referred to by
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multiple different cursor strings, and hence string
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comparing cursors is not possible. Use this call to
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verify after an invocation of
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<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
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instead.</para>
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<para>Note that <function>sd_journal_get_cursor()</function>
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and <function>sd_journal_test_cursor()</function>
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will not work before
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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(or one of the other functions which move to an entry)
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has been called at least once to position the read pointer at a valid entry.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para><function>sd_journal_get_cursor()</function> returns 0 on
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success or a negative errno-style error code.
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<function>sd_journal_test_cursor()</function> returns positive if
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the current entry matches the specified cursor, 0 if it does not
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match the specified cursor or a negative errno-style error code on
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failure.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EADDRNOTAVAIL</constant></term>
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<listitem><para>The journal context is currently not positioned on any entry, and hence no cursor
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string can be generated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>The journal context parameter is <constant>NULL</constant>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The journal context object has been allocated in a different process than it is
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being used in now.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<xi:include href="threads-aware.xml" xpointer="strict" />
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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</refsect1>
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<refsect1>
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<title>History</title>
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<para><function>sd_journal_get_cursor()</function> was added in version 187.</para>
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<para><function>sd_journal_test_cursor()</function> was added in version 195.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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