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![Lennart Poettering](/assets/img/avatar_default.png)
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.
179 lines
6.3 KiB
XML
179 lines
6.3 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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SPDX-License-Identifier: LGPL-2.1+
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-->
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<refentry id="sd_journal_next" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_journal_next</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_next</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_next</refname>
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<refname>sd_journal_previous</refname>
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<refname>sd_journal_next_skip</refname>
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<refname>sd_journal_previous_skip</refname>
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<refname>SD_JOURNAL_FOREACH</refname>
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<refname>SD_JOURNAL_FOREACH_BACKWARDS</refname>
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<refpurpose>Advance or set back the read pointer in the journal</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_next</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_previous</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_next_skip</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>uint64_t <parameter>skip</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_previous_skip</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>uint64_t <parameter>skip</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef><function>SD_JOURNAL_FOREACH</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef>
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<paramdef>sd_journal *<parameter>j</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_next()</function> advances the read
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pointer into the journal by one entry. The only argument taken is
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a journal context object as allocated via
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<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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After successful invocation the entry may be read with functions
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such as
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>Similarly, <function>sd_journal_previous()</function> sets
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the read pointer back one entry.</para>
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<para><function>sd_journal_next_skip()</function> and
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<function>sd_journal_previous_skip()</function> advance/set back
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the read pointer by multiple entries at once, as specified in the
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<varname>skip</varname> parameter.</para>
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<para>The journal is strictly ordered by reception time, and hence
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advancing to the next entry guarantees that the entry then
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pointing to is later in time than then previous one, or has the
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same timestamp.</para>
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<para>Note that
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and related calls will fail unless
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<function>sd_journal_next()</function> has been invoked at least
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once in order to position the read pointer on a journal
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entry.</para>
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<para>Note that the <function>SD_JOURNAL_FOREACH()</function>
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macro may be used as a wrapper around
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<citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and <function>sd_journal_next()</function> in order to make
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iterating through the journal easier. See below for an example.
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Similarly, <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> may
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be used for iterating the journal in reverse order.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>The four calls return the number of entries advanced/set
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back on success or a negative errno-style error code. When the end
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or beginning of the journal is reached, a number smaller than
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requested is returned. More specifically, if
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<function>sd_journal_next()</function> or
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<function>sd_journal_previous()</function> reach the end/beginning
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of the journal they will return 0, instead of 1 when they are
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successful. This should be considered an EOF marker.</para>
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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>Examples</title>
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<para>Iterating through the journal:</para>
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<programlisting>#include <stdio.h>
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#include <string.h>
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#include <systemd/sd-journal.h>
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int main(int argc, char *argv[]) {
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int r;
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sd_journal *j;
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r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
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if (r < 0) {
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fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
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return 1;
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}
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SD_JOURNAL_FOREACH(j) {
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const char *d;
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size_t l;
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r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l);
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if (r < 0) {
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fprintf(stderr, "Failed to read message field: %s\n", strerror(-r));
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continue;
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}
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printf("%.*s\n", (int) l, d);
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}
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sd_journal_close(j);
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return 0;
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}</programlisting>
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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_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_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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