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a8d46a1663
Fixes #4056.
148 lines
5.9 KiB
XML
148 lines
5.9 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2012 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_journal_get_cursor">
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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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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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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>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
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cursor string for the current journal entry. A cursor is a
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serialization of the current journal position formatted as text.
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The string only contains printable characters and can be passed
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around in text form. The cursor identifies a journal entry
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globally and in a stable way and may be used to later seek to it
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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
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clients. Seeking to a cursor position without the specific entry
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being available locally will seek to the next closest (in terms of
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time) available entry. The call takes two arguments: a journal
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context object and a pointer to a string pointer where the cursor
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string will be placed. The string is allocated via libc
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<citerefentry project='man-pages'><refentrytitle>malloc</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and should be freed after use with
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<citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>Note that <function>sd_journal_get_cursor()</function> will
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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
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position the read pointer at a valid entry.</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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</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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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>All functions listed here are thread-agnostic and only a single thread may operate
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on a given <structname>sd_journal</structname> object.</para>
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<para>The <function>sd_journal_get_cursor()</function> and
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<function>sd_journal_test_cursor()</function> interfaces are
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available as a shared library, which can be compiled and linked to
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with the
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<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_seek_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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