summaryrefslogtreecommitdiff
path: root/man/sd_journal_get_data.xml
blob: c01db4eb9364acfc26f22d1815cdbce6ce6dcb3f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
<?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_get_data">

        <refentryinfo>
                <title>sd_journal_get_data</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_get_data</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_journal_get_data</refname>
                <refname>sd_journal_enumerate_data</refname>
                <refname>sd_journal_restart_data</refname>
                <refname>SD_JOURNAL_FOREACH_DATA</refname>
                <refname>sd_journal_set_data_threshold</refname>
                <refname>sd_journal_get_data_threshold</refname>
                <refpurpose>Read data fields from the current journal entry</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
                        <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>

                        <funcprototype>
                                <funcdef>int <function>sd_journal_get_data</function></funcdef>
                                <paramdef>sd_journal* <parameter>j</parameter></paramdef>
                                <paramdef>const char* <parameter>field</parameter></paramdef>
                                <paramdef>const void** <parameter>data</parameter></paramdef>
                                <paramdef>size_t* <parameter>length</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_journal_enumerate_data</function></funcdef>
                                <paramdef>sd_journal* <parameter>j</parameter></paramdef>
                                <paramdef>const void** <parameter>data</parameter></paramdef>
                                <paramdef>size_t* <parameter>length</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>void <function>sd_journal_restart_data</function></funcdef>
                                <paramdef>sd_journal* <parameter>j</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef><function>SD_JOURNAL_FOREACH_DATA</function></funcdef>
                                <paramdef>sd_journal* <parameter>j</parameter></paramdef>
                                <paramdef>const void* <parameter>data</parameter></paramdef>
                                <paramdef>size_t <parameter>length</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_journal_set_data_threshold</function></funcdef>
                                <paramdef>sd_journal* <parameter>j</parameter></paramdef>
                                <paramdef>size_t <parameter>sz</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_journal_get_data_threshold</function></funcdef>
                                <paramdef>sd_journal* <parameter>j</parameter></paramdef>
                                <paramdef>size_t* <parameter>sz</parameter></paramdef>
                        </funcprototype>
                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_journal_get_data()</function> gets
                the data object associated with a specific field from
                the current journal entry. It takes four arguments:
                the journal context object, a string with the field
                name to request, plus a pair of pointers to
                pointer/size variables where the data object and its
                size shall be stored in. The field name should be an
                entry field name. Well-known field names are listed in
                <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The
                returned data is in a read-only memory map and is only
                valid until the next invocation of
                <function>sd_journal_get_data()</function> or
                <function>sd_journal_enumerate_data()</function>, or
                the read pointer is altered. Note that the data
                returned will be prefixed with the field name and
                '='. Also note that by default data fields larger than
                64K might get truncated to 64K. This threshold may be
                changed and turned off with
                <function>sd_journal_set_data_threshold()</function> (see
                below).</para>

                <para><function>sd_journal_enumerate_data()</function>
                may be used to iterate through all fields of the
                current entry. On each invocation the data for the
                next field is returned. The order of these fields is
                not defined. The data returned is in the same format
                as with <function>sd_journal_get_data()</function> and
                also follows the same life-time semantics.</para>

                <para><function>sd_journal_restart_data()</function>
                resets the data enumeration index to the beginning of
                the entry. The next invocation of
                <function>sd_journal_enumerate_data()</function> will return the first
                field of the entry again.</para>

                <para>Note that the
                <function>SD_JOURNAL_FOREACH_DATA()</function> macro
                may be used as a handy wrapper around
                <function>sd_journal_restart_data()</function> and
                <function>sd_journal_enumerate_data()</function>.</para>

                <para>Note that these functions will not work before
                <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                (or related call) has been called at least
                once, in order to position the read pointer at a valid entry.</para>

                <para><function>sd_journal_set_data_threshold()</function>
                may be used to change the data field size threshold
                for data returned by
                <function>sd_journal_get_data()</function>,
                <function>sd_journal_enumerate_data()</function> and
                <function>sd_journal_enumerate_unique()</function>. This
                threshold is a hint only: it indicates that the client
                program is interested only in the initial parts of the
                data fields, up to the threshold in size -- but the
                library might still return larger data objects. That
                means applications should not rely exclusively on this
                setting to limit the size of the data fields returned,
                but need to apply a explicit size limit on the
                returned data as well. This threshold defaults to 64K
                by default. To retrieve the complete data fields this
                threshold should be turned off by setting it to 0, so
                that the library always returns the complete data
                objects. It is recommended to set this threshold as
                low as possible since this relieves the library from
                having to decompress large compressed data objects in
                full.</para>

                <para><function>sd_journal_get_data_threshold()</function>
                returns the currently configured data field size
                threshold.</para>
        </refsect1>

        <refsect1>
                <title>Return Value</title>

                <para><function>sd_journal_get_data()</function>
                returns 0 on success or a negative errno-style error
                code. If the current entry does not include the
                specified field, -ENOENT is returned. If
                <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                has not been called at least once, -EADDRNOTAVAIL is
                returned. <function>sd_journal_enumerate_data()</function>
                returns a positive integer if the next field has been
                read, 0 when no more fields are known, or a negative
                errno-style error
                code. <function>sd_journal_restart_data()</function>
                returns
                nothing. <function>sd_journal_set_data_threshold()</function>
                and <function>sd_journal_get_threshold()</function>
                return 0 on success or a negative errno-style error
                code.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>The <function>sd_journal_get_data()</function>,
                <function>sd_journal_enumerate_data()</function>,
                <function>sd_journal_restart_data()</function>,
                <function>sd_journal_set_data_threshold()</function>
                and
                <function>sd_journal_get_data_threshold()</function>
                interfaces are available as a shared library, which can
                be compiled and linked to with the
                <constant>libsystemd</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file.</para>
        </refsect1>

        <refsect1>
                <title>Examples</title>

                <para>See
                <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                for a complete example how to use
                <function>sd_journal_get_data()</function>.</para>

                <para>Use the
                <function>SD_JOURNAL_FOREACH_DATA</function> macro to
                iterate through all fields of the current journal
                entry:</para>

                <programlisting>...
int print_fields(sd_journal *j) {
        const void *data;
        size_t l;
        SD_JOURNAL_FOREACH_DATA(j, data, length)
                printf("%.*s\n", (int) length, data);
}
...</programlisting>

        </refsect1>

        <refsect1>
                <title>See Also</title>

                <para>
                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</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_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>