systemd/man/sd_journal_seek_head.xml
Lennart Poettering 64a7ef8bc0 man: be more explicit about thread safety of sd_journal
Triggered by https://bugzilla.redhat.com/show_bug.cgi?id=1609349

This adds two generic paragaphs we include via xinclude. One is the
"strict" version, which contains wording saying that we are thread
agnostic and what that means. And the other is the "safe" version, for
the cases we provide fully safety.

Let's then change most man pages to use either of these generic
paragraphs. With one exception: man/sd_journal_get_catalog.xml contains
both kinds of function, we hence use manual wording.
2018-08-03 17:36:11 +02:00

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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">
<!--
SPDX-License-Identifier: LGPL-2.1+
-->
<refentry id="sd_journal_seek_head" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_journal_seek_head</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_journal_seek_head</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_journal_seek_head</refname>
<refname>sd_journal_seek_tail</refname>
<refname>sd_journal_seek_monotonic_usec</refname>
<refname>sd_journal_seek_realtime_usec</refname>
<refname>sd_journal_seek_cursor</refname>
<refpurpose>Seek to a position in the
journal</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_journal_seek_head</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_seek_tail</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_seek_monotonic_usec</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>sd_id128_t <parameter>boot_id</parameter></paramdef>
<paramdef>uint64_t <parameter>usec</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_seek_realtime_usec</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>uint64_t <parameter>usec</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_seek_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_seek_head()</function> seeks to the
beginning of the journal, i.e. the oldest available entry.</para>
<para>Similarly, <function>sd_journal_seek_tail()</function> may
be used to seek to the end of the journal, i.e. the most recent
available entry.</para>
<para><function>sd_journal_seek_monotonic_usec()</function> seeks
to the entry with the specified monotonic timestamp, i.e.
<constant>CLOCK_MONOTONIC</constant>. Since monotonic time
restarts on every reboot a boot ID needs to be specified as
well.</para>
<para><function>sd_journal_seek_realtime_usec()</function> seeks
to the entry with the specified realtime (wallclock) timestamp,
i.e. <constant>CLOCK_REALTIME</constant>. Note that the realtime
clock is not necessarily monotonic. If a realtime timestamp is
ambiguous, it is not defined which position is sought to.</para>
<para><function>sd_journal_seek_cursor()</function> seeks to the
entry located at the specified cursor string. For details on
cursors, see
<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
If no entry matching the specified cursor is found the call will
seek to the next closest entry (in terms of time) instead. To
verify whether the newly selected entry actually matches the
cursor, use
<citerefentry><refentrytitle>sd_journal_test_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>Note that these calls do not actually make any entry the new
current entry, this needs to be done in a separate step with a
subsequent
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
invocation (or a similar call). Only then, entry data may be
retrieved via
<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
If no entry exists that matches exactly the specified seek
address, the next closest is sought to. If
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
is used, the closest following entry will be sought to, if
<citerefentry><refentrytitle>sd_journal_previous</refentrytitle><manvolnum>3</manvolnum></citerefentry>
is used the closest preceding entry is sought to.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>The functions return 0 on success or a negative errno-style
error code.</para>
</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>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_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>