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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
6 | This file is part of systemd. | |
7 | ||
8 | Copyright 2012 Lennart Poettering | |
9 | ||
10 | systemd is free software; you can redistribute it and/or modify it | |
11 | under the terms of the GNU Lesser General Public License as published by | |
12 | the Free Software Foundation; either version 2.1 of the License, or | |
13 | (at your option) any later version. | |
14 | ||
15 | systemd is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | Lesser General Public License for more details. | |
19 | ||
20 | You should have received a copy of the GNU Lesser General Public License | |
21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
22 | --> | |
23 | ||
24 | <refentry id="sd_journal_next"> | |
25 | ||
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26 | <refentryinfo> |
27 | <title>sd_journal_next</title> | |
28 | <productname>systemd</productname> | |
29 | ||
30 | <authorgroup> | |
31 | <author> | |
32 | <contrib>Developer</contrib> | |
33 | <firstname>Lennart</firstname> | |
34 | <surname>Poettering</surname> | |
35 | <email>lennart@poettering.net</email> | |
36 | </author> | |
37 | </authorgroup> | |
38 | </refentryinfo> | |
39 | ||
40 | <refmeta> | |
41 | <refentrytitle>sd_journal_next</refentrytitle> | |
42 | <manvolnum>3</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>sd_journal_next</refname> | |
47 | <refname>sd_journal_previous</refname> | |
48 | <refname>sd_journal_next_skip</refname> | |
49 | <refname>sd_journal_previous_skip</refname> | |
50 | <refname>SD_JOURNAL_FOREACH</refname> | |
51 | <refname>SD_JOURNAL_FOREACH_BACKWARDS</refname> | |
52 | <refpurpose>Advance or set back the read pointer in the journal</refpurpose> | |
53 | </refnamediv> | |
54 | ||
55 | <refsynopsisdiv> | |
56 | <funcsynopsis> | |
57 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
58 | ||
59 | <funcprototype> | |
60 | <funcdef>int <function>sd_journal_next</function></funcdef> | |
61 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
62 | </funcprototype> | |
63 | ||
64 | <funcprototype> | |
65 | <funcdef>int <function>sd_journal_previous</function></funcdef> | |
66 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
67 | </funcprototype> | |
68 | ||
69 | <funcprototype> | |
70 | <funcdef>int <function>sd_journal_next_skip</function></funcdef> | |
71 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
72 | <paramdef>uint64_t <parameter>skip</parameter></paramdef> | |
73 | </funcprototype> | |
74 | ||
75 | <funcprototype> | |
76 | <funcdef>int <function>sd_journal_previous_skip</function></funcdef> | |
77 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
78 | <paramdef>uint64_t <parameter>skip</parameter></paramdef> | |
79 | </funcprototype> | |
80 | ||
81 | <funcprototype> | |
82 | <funcdef><function>SD_JOURNAL_FOREACH</function></funcdef> | |
83 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
84 | </funcprototype> | |
85 | ||
86 | <funcprototype> | |
87 | <funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef> | |
88 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
89 | </funcprototype> | |
90 | </funcsynopsis> | |
91 | </refsynopsisdiv> | |
92 | ||
93 | <refsect1> | |
94 | <title>Description</title> | |
95 | ||
96 | <para><function>sd_journal_next()</function> advances the read | |
97 | pointer into the journal by one entry. The only argument taken is | |
98 | a journal context object as allocated via | |
99 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
100 | After successful invocation the entry may be read with functions | |
101 | such as | |
102 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
103 | ||
104 | <para>Similarly, <function>sd_journal_previous()</function> sets | |
105 | the read pointer back one entry.</para> | |
106 | ||
107 | <para><function>sd_journal_next_skip()</function> and | |
108 | <function>sd_journal_previous_skip()</function> advance/set back | |
109 | the read pointer by multiple entries at once, as specified in the | |
110 | <varname>skip</varname> parameter.</para> | |
111 | ||
112 | <para>The journal is strictly ordered by reception time, and hence | |
113 | advancing to the next entry guarantees that the entry then | |
114 | pointing to is later in time than then previous one, or has the | |
115 | same timestamp.</para> | |
116 | ||
117 | <para>Note that | |
118 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
119 | and related calls will fail unless | |
120 | <function>sd_journal_next()</function> has been invoked at least | |
121 | once in order to position the read pointer on a journal | |
122 | entry.</para> | |
123 | ||
124 | <para>Note that the <function>SD_JOURNAL_FOREACH()</function> | |
125 | macro may be used as a wrapper around | |
126 | <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
127 | and <function>sd_journal_next()</function> in order to make | |
128 | iterating through the journal easier. See below for an example. | |
129 | Similarly, <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> may | |
130 | be used for iterating the journal in reverse order.</para> | |
131 | </refsect1> | |
132 | ||
133 | <refsect1> | |
134 | <title>Return Value</title> | |
135 | ||
136 | <para>The four calls return the number of entries advanced/set | |
137 | back on success or a negative errno-style error code. When the end | |
138 | or beginning of the journal is reached, a number smaller than | |
139 | requested is returned. More specifically, if | |
140 | <function>sd_journal_next()</function> or | |
141 | <function>sd_journal_previous()</function> reach the end/beginning | |
142 | of the journal they will return 0, instead of 1 when they are | |
143 | successful. This should be considered an EOF marker.</para> | |
144 | </refsect1> | |
145 | ||
146 | <refsect1> | |
147 | <title>Notes</title> | |
148 | ||
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149 | <para>All functions listed here are thread-agnostic and only a single thread may operate |
150 | on a given <structname>sd_journal</structname> object.</para> | |
151 | ||
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152 | <para>The <function>sd_journal_next()</function>, |
153 | <function>sd_journal_previous()</function>, | |
154 | <function>sd_journal_next_skip()</function> and | |
155 | <function>sd_journal_previous_skip()</function> interfaces are | |
156 | available as a shared library, which can be compiled and linked to | |
157 | with the | |
158 | <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
159 | file.</para> | |
160 | </refsect1> | |
161 | ||
162 | <refsect1> | |
163 | <title>Examples</title> | |
164 | ||
165 | <para>Iterating through the journal:</para> | |
166 | ||
167 | <programlisting>#include <stdio.h> | |
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168 | #include <string.h> |
169 | #include <systemd/sd-journal.h> | |
170 | ||
171 | int main(int argc, char *argv[]) { | |
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172 | int r; |
173 | sd_journal *j; | |
174 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
175 | if (r < 0) { | |
176 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
177 | return 1; | |
178 | } | |
179 | SD_JOURNAL_FOREACH(j) { | |
180 | const char *d; | |
181 | size_t l; | |
182 | ||
183 | r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l); | |
184 | if (r < 0) { | |
185 | fprintf(stderr, "Failed to read message field: %s\n", strerror(-r)); | |
186 | continue; | |
187 | } | |
188 | ||
189 | printf("%.*s\n", (int) l, d); | |
190 | } | |
191 | sd_journal_close(j); | |
192 | return 0; | |
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193 | }</programlisting> |
194 | ||
798d3a52 | 195 | </refsect1> |
67c3cf4f | 196 | |
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197 | <refsect1> |
198 | <title>See Also</title> | |
67c3cf4f | 199 | |
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200 | <para> |
201 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
202 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
203 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
204 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
205 | <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
206 | <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
207 | </para> | |
208 | </refsect1> | |
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209 | |
210 | </refentry> |