+++ /dev/null
-<?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">
-
-<!--
- This file is part of systemd.
-
- Copyright 2012 Lennart Poettering
-
- systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 2.1 of the License, or
- (at your option) any later version.
-
- systemd is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with systemd; If not, see <http://www.gnu.org/licenses/>.
--->
-
-<refentry id="sd_journal_next">
-
- <refentryinfo>
- <title>sd_journal_next</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_next</refentrytitle>
- <manvolnum>3</manvolnum>
- </refmeta>
-
- <refnamediv>
- <refname>sd_journal_next</refname>
- <refname>sd_journal_previous</refname>
- <refname>sd_journal_next_skip</refname>
- <refname>sd_journal_previous_skip</refname>
- <refname>SD_JOURNAL_FOREACH</refname>
- <refname>SD_JOURNAL_FOREACH_BACKWARDS</refname>
- <refpurpose>Advance or set back the read pointer in the journal</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <funcsynopsis>
- <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
-
- <funcprototype>
- <funcdef>int <function>sd_journal_next</function></funcdef>
- <paramdef>sd_journal *<parameter>j</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_journal_previous</function></funcdef>
- <paramdef>sd_journal *<parameter>j</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_journal_next_skip</function></funcdef>
- <paramdef>sd_journal *<parameter>j</parameter></paramdef>
- <paramdef>uint64_t <parameter>skip</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef>int <function>sd_journal_previous_skip</function></funcdef>
- <paramdef>sd_journal *<parameter>j</parameter></paramdef>
- <paramdef>uint64_t <parameter>skip</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef><function>SD_JOURNAL_FOREACH</function></funcdef>
- <paramdef>sd_journal *<parameter>j</parameter></paramdef>
- </funcprototype>
-
- <funcprototype>
- <funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef>
- <paramdef>sd_journal *<parameter>j</parameter></paramdef>
- </funcprototype>
- </funcsynopsis>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Description</title>
-
- <para><function>sd_journal_next()</function> advances the read
- pointer into the journal by one entry. The only argument taken is
- a journal context object as allocated via
- <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
- After successful invocation the entry may be read with functions
- such as
- <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
-
- <para>Similarly, <function>sd_journal_previous()</function> sets
- the read pointer back one entry.</para>
-
- <para><function>sd_journal_next_skip()</function> and
- <function>sd_journal_previous_skip()</function> advance/set back
- the read pointer by multiple entries at once, as specified in the
- <varname>skip</varname> parameter.</para>
-
- <para>The journal is strictly ordered by reception time, and hence
- advancing to the next entry guarantees that the entry then
- pointing to is later in time than then previous one, or has the
- same timestamp.</para>
-
- <para>Note that
- <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- and related calls will fail unless
- <function>sd_journal_next()</function> has been invoked at least
- once in order to position the read pointer on a journal
- entry.</para>
-
- <para>Note that the <function>SD_JOURNAL_FOREACH()</function>
- macro may be used as a wrapper around
- <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- and <function>sd_journal_next()</function> in order to make
- iterating through the journal easier. See below for an example.
- Similarly, <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> may
- be used for iterating the journal in reverse order.</para>
- </refsect1>
-
- <refsect1>
- <title>Return Value</title>
-
- <para>The four calls return the number of entries advanced/set
- back on success or a negative errno-style error code. When the end
- or beginning of the journal is reached, a number smaller than
- requested is returned. More specifically, if
- <function>sd_journal_next()</function> or
- <function>sd_journal_previous()</function> reach the end/beginning
- of the journal they will return 0, instead of 1 when they are
- successful. This should be considered an EOF marker.</para>
- </refsect1>
-
- <refsect1>
- <title>Notes</title>
-
- <para>The <function>sd_journal_next()</function>,
- <function>sd_journal_previous()</function>,
- <function>sd_journal_next_skip()</function> and
- <function>sd_journal_previous_skip()</function> interfaces are
- available as a shared library, which can be compiled and linked to
- with the
- <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- file.</para>
- </refsect1>
-
- <refsect1>
- <title>Examples</title>
-
- <para>Iterating through the journal:</para>
-
- <programlisting>#include <stdio.h>
-#include <string.h>
-#include <systemd/sd-journal.h>
-
-int main(int argc, char *argv[]) {
- int r;
- sd_journal *j;
- r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
- if (r < 0) {
- fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
- return 1;
- }
- SD_JOURNAL_FOREACH(j) {
- const char *d;
- size_t l;
-
- r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l);
- if (r < 0) {
- fprintf(stderr, "Failed to read message field: %s\n", strerror(-r));
- continue;
- }
-
- printf("%.*s\n", (int) l, d);
- }
- sd_journal_close(j);
- return 0;
-}</programlisting>
-
- </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_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- </para>
- </refsect1>
-
-</refentry>
~ianmdlvl / elogind.git / blobdiff