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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 | <!-- | |
572eb058 ZJS |
6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
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8 | This file is part of systemd. |
9 | ||
10 | Copyright 2012 Lennart Poettering | |
11 | ||
12 | systemd is free software; you can redistribute it and/or modify it | |
13 | under the terms of the GNU Lesser General Public License as published by | |
14 | the Free Software Foundation; either version 2.1 of the License, or | |
15 | (at your option) any later version. | |
16 | ||
17 | systemd is distributed in the hope that it will be useful, but | |
18 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
20 | Lesser General Public License for more details. | |
21 | ||
22 | You should have received a copy of the GNU Lesser General Public License | |
23 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
24 | --> | |
25 | ||
26 | <refentry id="sd_journal_query_unique"> | |
27 | ||
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28 | <refentryinfo> |
29 | <title>sd_journal_query_unique</title> | |
30 | <productname>systemd</productname> | |
31 | ||
32 | <authorgroup> | |
33 | <author> | |
34 | <contrib>Developer</contrib> | |
35 | <firstname>Lennart</firstname> | |
36 | <surname>Poettering</surname> | |
37 | <email>lennart@poettering.net</email> | |
38 | </author> | |
39 | </authorgroup> | |
40 | </refentryinfo> | |
41 | ||
42 | <refmeta> | |
43 | <refentrytitle>sd_journal_query_unique</refentrytitle> | |
44 | <manvolnum>3</manvolnum> | |
45 | </refmeta> | |
46 | ||
47 | <refnamediv> | |
48 | <refname>sd_journal_query_unique</refname> | |
49 | <refname>sd_journal_enumerate_unique</refname> | |
50 | <refname>sd_journal_restart_unique</refname> | |
51 | <refname>SD_JOURNAL_FOREACH_UNIQUE</refname> | |
52 | <refpurpose>Read unique data fields from 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_query_unique</function></funcdef> | |
61 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
62 | <paramdef>const char *<parameter>field</parameter></paramdef> | |
63 | </funcprototype> | |
64 | ||
65 | <funcprototype> | |
66 | <funcdef>int <function>sd_journal_enumerate_unique</function></funcdef> | |
67 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
68 | <paramdef>const void **<parameter>data</parameter></paramdef> | |
69 | <paramdef>size_t *<parameter>length</parameter></paramdef> | |
70 | </funcprototype> | |
71 | ||
72 | <funcprototype> | |
73 | <funcdef>void <function>sd_journal_restart_unique</function></funcdef> | |
74 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
75 | </funcprototype> | |
76 | ||
77 | <funcprototype> | |
78 | <funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef> | |
79 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
80 | <paramdef>const void *<parameter>data</parameter></paramdef> | |
81 | <paramdef>size_t <parameter>length</parameter></paramdef> | |
82 | </funcprototype> | |
83 | ||
84 | </funcsynopsis> | |
85 | </refsynopsisdiv> | |
86 | ||
87 | <refsect1> | |
88 | <title>Description</title> | |
89 | ||
90 | <para><function>sd_journal_query_unique()</function> queries the | |
91 | journal for all unique values the specified field can take. It | |
92 | takes two arguments: the journal to query and the field name to | |
93 | look for. Well-known field names are listed on | |
94 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. | |
95 | Field names must be specified without a trailing '='. After this | |
96 | function has been executed successfully the field values may be | |
97 | queried using <function>sd_journal_enumerate_unique()</function>. | |
98 | Invoking this call a second time will change the field name being | |
99 | queried and reset the enumeration index to the first field value | |
100 | that matches.</para> | |
101 | ||
102 | <para><function>sd_journal_enumerate_unique()</function> may be | |
103 | used to iterate through all data fields which match the previously | |
104 | selected field name as set with | |
105 | <function>sd_journal_query_unique()</function>. On each invocation | |
106 | the next field data matching the field name is returned. The order | |
107 | of the returned data fields is not defined. It takes three | |
108 | arguments: the journal context object, plus a pair of pointers to | |
109 | pointer/size variables where the data object and its size shall be | |
110 | stored in. The returned data is in a read-only memory map and is | |
111 | only valid until the next invocation of | |
112 | <function>sd_journal_enumerate_unique()</function>. Note that the | |
113 | data returned will be prefixed with the field name and '='. Note | |
114 | that this call is subject to the data field size threshold as | |
115 | controlled by | |
116 | <function>sd_journal_set_data_threshold()</function>.</para> | |
117 | ||
118 | <para><function>sd_journal_restart_unique()</function> resets the | |
119 | data enumeration index to the beginning of the list. The next | |
120 | invocation of <function>sd_journal_enumerate_unique()</function> | |
121 | will return the first field data matching the field name | |
122 | again.</para> | |
123 | ||
124 | <para>Note that the | |
125 | <function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro may be used | |
126 | as a handy wrapper around | |
127 | <function>sd_journal_restart_unique()</function> and | |
128 | <function>sd_journal_enumerate_unique()</function>.</para> | |
129 | ||
130 | <para>Note that these functions currently are not influenced by | |
131 | matches set with <function>sd_journal_add_match()</function> but | |
132 | this might change in a later version of this software.</para> | |
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133 | |
134 | <para>To enumerate all field names currently in use (and thus all suitable field parameters for | |
135 | <function>sd_journal_query_unique()</function>), use the | |
136 | <citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
137 | call.</para> | |
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138 | </refsect1> |
139 | ||
140 | <refsect1> | |
141 | <title>Return Value</title> | |
142 | ||
143 | <para><function>sd_journal_query_unique()</function> returns 0 on | |
144 | success or a negative errno-style error code. | |
145 | <function>sd_journal_enumerate_unique()</function> returns a | |
146 | positive integer if the next field data has been read, 0 when no | |
147 | more fields are known, or a negative errno-style error code. | |
148 | <function>sd_journal_restart_unique()</function> returns | |
149 | nothing.</para> | |
150 | </refsect1> | |
151 | ||
152 | <refsect1> | |
153 | <title>Notes</title> | |
154 | ||
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155 | <para>All functions listed here are thread-agnostic and only a single thread may operate |
156 | on a given <structname>sd_journal</structname> object.</para> | |
157 | ||
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158 | <para>The <function>sd_journal_query_unique()</function>, |
159 | <function>sd_journal_enumerate_unique()</function> and | |
160 | <function>sd_journal_restart_unique()</function> interfaces are | |
161 | available as a shared library, which can be compiled and linked to | |
162 | with the | |
163 | <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
164 | file.</para> | |
165 | </refsect1> | |
166 | ||
167 | <refsect1> | |
168 | <title>Examples</title> | |
169 | ||
170 | <para>Use the <function>SD_JOURNAL_FOREACH_UNIQUE</function> macro | |
171 | to iterate through all values a field of the journal can take. The | |
172 | following example lists all unit names referenced in the | |
173 | journal:</para> | |
174 | ||
175 | <programlisting>#include <stdio.h> | |
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176 | #include <string.h> |
177 | #include <systemd/sd-journal.h> | |
178 | ||
179 | int main(int argc, char *argv[]) { | |
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180 | sd_journal *j; |
181 | const void *d; | |
182 | size_t l; | |
183 | int r; | |
184 | ||
185 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
186 | if (r < 0) { | |
187 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
188 | return 1; | |
189 | } | |
190 | r = sd_journal_query_unique(j, "_SYSTEMD_UNIT"); | |
191 | if (r < 0) { | |
192 | fprintf(stderr, "Failed to query journal: %s\n", strerror(-r)); | |
193 | return 1; | |
194 | } | |
195 | SD_JOURNAL_FOREACH_UNIQUE(j, d, l) | |
196 | printf("%.*s\n", (int) l, (const char*) d); | |
197 | sd_journal_close(j); | |
198 | return 0; | |
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199 | }</programlisting> |
200 | ||
798d3a52 | 201 | </refsect1> |
1a2be33a | 202 | |
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203 | <refsect1> |
204 | <title>See Also</title> | |
1a2be33a | 205 | |
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206 | <para> |
207 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
208 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
209 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
210 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
eb86030e | 211 | <citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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212 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
213 | <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
214 | </para> | |
215 | </refsect1> | |
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216 | |
217 | </refentry> |