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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 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> | |
5 | ||
6 | <refentry id="sd_journal_get_data" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
7 | ||
8 | <refentryinfo> | |
9 | <title>sd_journal_get_data</title> | |
10 | <productname>systemd</productname> | |
11 | </refentryinfo> | |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_journal_get_data</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_journal_get_data</refname> | |
20 | <refname>sd_journal_enumerate_data</refname> | |
21 | <refname>sd_journal_restart_data</refname> | |
22 | <refname>SD_JOURNAL_FOREACH_DATA</refname> | |
23 | <refname>sd_journal_set_data_threshold</refname> | |
24 | <refname>sd_journal_get_data_threshold</refname> | |
25 | <refpurpose>Read data fields from the current journal entry</refpurpose> | |
26 | </refnamediv> | |
27 | ||
28 | <refsynopsisdiv> | |
29 | <funcsynopsis> | |
30 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
31 | ||
32 | <funcprototype> | |
33 | <funcdef>int <function>sd_journal_get_data</function></funcdef> | |
34 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
35 | <paramdef>const char *<parameter>field</parameter></paramdef> | |
36 | <paramdef>const void **<parameter>data</parameter></paramdef> | |
37 | <paramdef>size_t *<parameter>length</parameter></paramdef> | |
38 | </funcprototype> | |
39 | ||
40 | <funcprototype> | |
41 | <funcdef>int <function>sd_journal_enumerate_data</function></funcdef> | |
42 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
43 | <paramdef>const void **<parameter>data</parameter></paramdef> | |
44 | <paramdef>size_t *<parameter>length</parameter></paramdef> | |
45 | </funcprototype> | |
46 | ||
47 | <funcprototype> | |
48 | <funcdef>void <function>sd_journal_restart_data</function></funcdef> | |
49 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
50 | </funcprototype> | |
51 | ||
52 | <funcprototype> | |
53 | <funcdef><function>SD_JOURNAL_FOREACH_DATA</function></funcdef> | |
54 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
55 | <paramdef>const void *<parameter>data</parameter></paramdef> | |
56 | <paramdef>size_t <parameter>length</parameter></paramdef> | |
57 | </funcprototype> | |
58 | ||
59 | <funcprototype> | |
60 | <funcdef>int <function>sd_journal_set_data_threshold</function></funcdef> | |
61 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
62 | <paramdef>size_t <parameter>sz</parameter></paramdef> | |
63 | </funcprototype> | |
64 | ||
65 | <funcprototype> | |
66 | <funcdef>int <function>sd_journal_get_data_threshold</function></funcdef> | |
67 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
68 | <paramdef>size_t *<parameter>sz</parameter></paramdef> | |
69 | </funcprototype> | |
70 | </funcsynopsis> | |
71 | </refsynopsisdiv> | |
72 | ||
73 | <refsect1> | |
74 | <title>Description</title> | |
75 | ||
76 | <para><function>sd_journal_get_data()</function> gets the data | |
77 | object associated with a specific field from the current journal | |
78 | entry. It takes four arguments: the journal context object, a | |
79 | string with the field name to request, plus a pair of pointers to | |
80 | pointer/size variables where the data object and its size shall be | |
81 | stored in. The field name should be an entry field name. | |
82 | Well-known field names are listed in | |
83 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. | |
84 | The returned data is in a read-only memory map and is only valid | |
85 | until the next invocation of | |
86 | <function>sd_journal_get_data()</function> or | |
87 | <function>sd_journal_enumerate_data()</function>, or the read | |
88 | pointer is altered. Note that the data returned will be prefixed | |
89 | with the field name and '='. Also note that, by default, data fields | |
90 | larger than 64K might get truncated to 64K. This threshold may be | |
91 | changed and turned off with | |
92 | <function>sd_journal_set_data_threshold()</function> (see | |
93 | below).</para> | |
94 | ||
95 | <para><function>sd_journal_enumerate_data()</function> may be used | |
96 | to iterate through all fields of the current entry. On each | |
97 | invocation the data for the next field is returned. The order of | |
98 | these fields is not defined. The data returned is in the same | |
99 | format as with <function>sd_journal_get_data()</function> and also | |
100 | follows the same life-time semantics.</para> | |
101 | ||
102 | <para><function>sd_journal_restart_data()</function> resets the | |
103 | data enumeration index to the beginning of the entry. The next | |
104 | invocation of <function>sd_journal_enumerate_data()</function> | |
105 | will return the first field of the entry again.</para> | |
106 | ||
107 | <para>Note that the <function>SD_JOURNAL_FOREACH_DATA()</function> | |
108 | macro may be used as a handy wrapper around | |
109 | <function>sd_journal_restart_data()</function> and | |
110 | <function>sd_journal_enumerate_data()</function>.</para> | |
111 | ||
112 | <para>Note that these functions will not work before | |
113 | <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
114 | (or related call) has been called at least once, in order to | |
115 | position the read pointer at a valid entry.</para> | |
116 | ||
117 | <para><function>sd_journal_set_data_threshold()</function> may be | |
118 | used to change the data field size threshold for data returned by | |
119 | <function>sd_journal_get_data()</function>, | |
120 | <function>sd_journal_enumerate_data()</function> and | |
121 | <function>sd_journal_enumerate_unique()</function>. This threshold | |
122 | is a hint only: it indicates that the client program is interested | |
123 | only in the initial parts of the data fields, up to the threshold | |
124 | in size — but the library might still return larger data objects. | |
125 | That means applications should not rely exclusively on this | |
126 | setting to limit the size of the data fields returned, but need to | |
127 | apply an explicit size limit on the returned data as well. This | |
128 | threshold defaults to 64K by default. To retrieve the complete | |
129 | data fields this threshold should be turned off by setting it to | |
130 | 0, so that the library always returns the complete data objects. | |
131 | It is recommended to set this threshold as low as possible since | |
132 | this relieves the library from having to decompress large | |
133 | compressed data objects in full.</para> | |
134 | ||
135 | <para><function>sd_journal_get_data_threshold()</function> returns | |
136 | the currently configured data field size threshold.</para> | |
137 | </refsect1> | |
138 | ||
139 | <refsect1> | |
140 | <title>Return Value</title> | |
141 | ||
142 | <para><function>sd_journal_get_data()</function> returns 0 on | |
143 | success or a negative errno-style error code. If the current entry | |
144 | does not include the specified field, -ENOENT is returned. If | |
145 | <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
146 | has not been called at least once, -EADDRNOTAVAIL is returned. | |
147 | <function>sd_journal_enumerate_data()</function> returns a | |
148 | positive integer if the next field has been read, 0 when no more | |
149 | fields are known, or a negative errno-style error code. | |
150 | <function>sd_journal_restart_data()</function> returns nothing. | |
151 | <function>sd_journal_set_data_threshold()</function> and | |
152 | <function>sd_journal_get_threshold()</function> return 0 on | |
153 | success or a negative errno-style error code.</para> | |
154 | </refsect1> | |
155 | ||
156 | <refsect1> | |
157 | <title>Notes</title> | |
158 | ||
159 | <xi:include href="threads-aware.xml" xpointer="strict"/> | |
160 | ||
161 | <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/> | |
162 | </refsect1> | |
163 | ||
164 | <refsect1> | |
165 | <title>Examples</title> | |
166 | ||
167 | <para>See | |
168 | <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
169 | for a complete example how to use | |
170 | <function>sd_journal_get_data()</function>.</para> | |
171 | ||
172 | <para>Use the | |
173 | <function>SD_JOURNAL_FOREACH_DATA</function> macro to | |
174 | iterate through all fields of the current journal | |
175 | entry:</para> | |
176 | ||
177 | <programlisting>… | |
178 | int print_fields(sd_journal *j) { | |
179 | const void *data; | |
180 | size_t length; | |
181 | SD_JOURNAL_FOREACH_DATA(j, data, length) | |
182 | printf("%.*s\n", (int) length, data); | |
183 | } | |
184 | …</programlisting> | |
185 | </refsect1> | |
186 | ||
187 | <refsect1> | |
188 | <title>See Also</title> | |
189 | ||
190 | <para> | |
191 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
192 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
193 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
194 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
195 | <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
196 | <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
197 | <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
198 | </para> | |
199 | </refsect1> | |
200 | ||
201 | </refentry> |