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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
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_get_data"> | |
25 | ||
26 | <refentryinfo> | |
27 | <title>sd_journal_get_data</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_get_data</refentrytitle> | |
42 | <manvolnum>3</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>sd_journal_get_data</refname> | |
47 | <refname>sd_journal_enumerate_data</refname> | |
48 | <refname>sd_journal_restart_data</refname> | |
49 | <refname>SD_JOURNAL_FOREACH_DATA</refname> | |
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50 | <refname>sd_journal_set_data_threshold</refname> |
51 | <refname>sd_journal_get_data_threshold</refname> | |
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52 | <refpurpose>Read data fields from the current journal entry</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_get_data</function></funcdef> | |
61 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
62 | <paramdef>const char* <parameter>field</parameter></paramdef> | |
63 | <paramdef>const void** <parameter>data</parameter></paramdef> | |
64 | <paramdef>size_t* <parameter>length</parameter></paramdef> | |
65 | </funcprototype> | |
66 | ||
67 | <funcprototype> | |
68 | <funcdef>int <function>sd_journal_enumerate_data</function></funcdef> | |
69 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
70 | <paramdef>const void** <parameter>data</parameter></paramdef> | |
71 | <paramdef>size_t* <parameter>length</parameter></paramdef> | |
72 | </funcprototype> | |
73 | ||
74 | <funcprototype> | |
3c1668da | 75 | <funcdef>void <function>sd_journal_restart_data</function></funcdef> |
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76 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> |
77 | </funcprototype> | |
78 | ||
79 | <funcprototype> | |
80 | <funcdef><function>SD_JOURNAL_FOREACH_DATA</function></funcdef> | |
81 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
82 | <paramdef>const void* <parameter>data</parameter></paramdef> | |
83 | <paramdef>size_t <parameter>length</parameter></paramdef> | |
84 | </funcprototype> | |
85 | ||
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86 | <funcprototype> |
87 | <funcdef>int <function>sd_journal_set_data_threshold</function></funcdef> | |
88 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
89 | <paramdef>size_t <parameter>sz</parameter></paramdef> | |
90 | </funcprototype> | |
91 | ||
92 | <funcprototype> | |
93 | <funcdef>int <function>sd_journal_get_data_threshold</function></funcdef> | |
94 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
95 | <paramdef>size_t* <parameter>sz</parameter></paramdef> | |
96 | </funcprototype> | |
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97 | </funcsynopsis> |
98 | </refsynopsisdiv> | |
99 | ||
100 | <refsect1> | |
101 | <title>Description</title> | |
102 | ||
103 | <para><function>sd_journal_get_data()</function> gets | |
104 | the data object associated with a specific field from | |
105 | the current journal entry. It takes four arguments: | |
106 | the journal context object, a string with the field | |
107 | name to request, plus a pair of pointers to | |
108 | pointer/size variables where the data object and its | |
109 | size shall be stored in. The field name should be an | |
110 | entry field name. Well-known field names are listed in | |
111 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The | |
112 | returned data is in a read-only memory map and is only | |
113 | valid until the next invocation of | |
114 | <function>sd_journal_get_data()</function> or | |
115 | <function>sd_journal_enumerate_data()</function>, or | |
116 | the read pointer is altered. Note that the data | |
117 | returned will be prefixed with the field name and | |
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118 | '='. Also note that by default data fields larger than |
119 | 64K might get truncated to 64K. This threshold may be | |
120 | changed and turned off with | |
121 | <function>sd_journal_set_data_threshold()</function> (see | |
122 | below).</para> | |
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123 | |
124 | <para><function>sd_journal_enumerate_data()</function> | |
125 | may be used to iterate through all fields of the | |
126 | current entry. On each invocation the data for the | |
127 | next field is returned. The order of these fields is | |
128 | not defined. The data returned is in the same format | |
129 | as with <function>sd_journal_get_data()</function> and | |
130 | also follows the same life-time semantics.</para> | |
131 | ||
132 | <para><function>sd_journal_restart_data()</function> | |
133 | resets the data enumeration index to the beginning of | |
134 | the entry. The next invocation of | |
135 | <function>sd_journal_enumerate_data()</function> will return the first | |
136 | field of the entry again.</para> | |
137 | ||
138 | <para>Note that the | |
139 | <function>SD_JOURNAL_FOREACH_DATA()</function> macro | |
3c1668da | 140 | may be used as a handy wrapper around |
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141 | <function>sd_journal_restart_data()</function> and |
142 | <function>sd_journal_enumerate_data()</function>.</para> | |
143 | ||
144 | <para>Note that these functions will not work before | |
145 | <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
7a8a6e88 | 146 | (or related call) has been called at least |
4a010f4e | 147 | once, in order to position the read pointer at a valid entry.</para> |
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148 | |
149 | <para><function>sd_journal_set_data_threshold()</function> | |
150 | may be used to change the data field size threshold | |
151 | for data returned by | |
152 | <function>sd_journal_get_data()</function>, | |
153 | <function>sd_journal_enumerate_data()</function> and | |
154 | <function>sd_journal_enumerate_unique()</function>. This | |
155 | threshold is a hint only: it indicates that the client | |
156 | program is interested only in the initial parts of the | |
157 | data fields, up to the threshold in size -- but the | |
158 | library might still return larger data objects. That | |
159 | means applications should not rely exclusively on this | |
160 | setting to limit the size of the data fields returned, | |
161 | but need to apply a explicit size limit on the | |
162 | returned data as well. This threshold defaults to 64K | |
163 | by default. To retrieve the complete data fields this | |
164 | threshold should be turned off by setting it to 0, so | |
165 | that the library always returns the complete data | |
166 | objects. It is recommended to set this threshold as | |
167 | low as possible since this relieves the library from | |
168 | having to decompress large compressed data objects in | |
169 | full.</para> | |
170 | ||
171 | <para><function>sd_journal_get_data_threshold()</function> | |
172 | returns the currently configured data field size | |
173 | threshold.</para> | |
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174 | </refsect1> |
175 | ||
176 | <refsect1> | |
177 | <title>Return Value</title> | |
178 | ||
179 | <para><function>sd_journal_get_data()</function> | |
180 | returns 0 on success or a negative errno-style error | |
181 | code. If the current entry does not include the | |
182 | specified field -ENOENT is returned. If | |
183 | <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
184 | has not been called at least once -EADDRNOTAVAIL is | |
185 | returned. <function>sd_journal_enumerate_data()</function> | |
186 | returns a positive integer if the next field has been | |
187 | read, 0 when no more fields are known, or a negative | |
188 | errno-style error | |
189 | code. <function>sd_journal_restart_data()</function> | |
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190 | returns |
191 | nothing. <function>sd_journal_set_data_threshold()</function> | |
192 | and <function>sd_journal_get_threshold()</function> | |
193 | return 0 on success or a negative errno-style error | |
194 | code.</para> | |
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195 | </refsect1> |
196 | ||
197 | <refsect1> | |
198 | <title>Notes</title> | |
199 | ||
200 | <para>The <function>sd_journal_get_data()</function>, | |
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201 | <function>sd_journal_enumerate_data()</function>, |
202 | <function>sd_journal_restart_data()</function>, | |
203 | <function>sd_journal_set_data_threshold()</function> | |
204 | and | |
205 | <function>sd_journal_get_data_threshold()</function> | |
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206 | interfaces are available as shared library, which can |
207 | be compiled and linked to with the | |
208 | <literal>libsystemd-journal</literal> | |
209 | <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
210 | file.</para> | |
211 | </refsect1> | |
212 | ||
213 | <refsect1> | |
214 | <title>Examples</title> | |
215 | ||
216 | <para>See | |
217 | <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
218 | for a complete example how to use | |
219 | <function>sd_journal_get_data()</function>.</para> | |
220 | ||
221 | <para>Use the | |
222 | <function>SD_JOURNAL_FOREACH_DATA</function> macro to | |
223 | iterate through all fields of the current journal | |
224 | entry:</para> | |
225 | ||
226 | <programlisting>... | |
227 | int print_fields(sd_journal *j) { | |
228 | const void *data; | |
229 | size_t l; | |
230 | SD_JOURNAL_FOREACH_DATA(j, data, length) | |
231 | printf("%.*s\n", (int) length, data); | |
232 | } | |
233 | ...</programlisting> | |
234 | ||
235 | </refsect1> | |
236 | ||
237 | <refsect1> | |
238 | <title>See Also</title> | |
239 | ||
240 | <para> | |
241 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
242 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
243 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
244 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
7a8a6e88 | 245 | <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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246 | <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
247 | <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
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248 | </para> |
249 | </refsect1> | |
250 | ||
251 | </refentry> |