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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_query_unique"> | |
25 | ||
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26 | <refentryinfo> |
27 | <title>sd_journal_query_unique</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_query_unique</refentrytitle> | |
42 | <manvolnum>3</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>sd_journal_query_unique</refname> | |
47 | <refname>sd_journal_enumerate_unique</refname> | |
48 | <refname>sd_journal_restart_unique</refname> | |
49 | <refname>SD_JOURNAL_FOREACH_UNIQUE</refname> | |
50 | <refpurpose>Read unique data fields from the journal</refpurpose> | |
51 | </refnamediv> | |
52 | ||
53 | <refsynopsisdiv> | |
54 | <funcsynopsis> | |
55 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
56 | ||
57 | <funcprototype> | |
58 | <funcdef>int <function>sd_journal_query_unique</function></funcdef> | |
59 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
60 | <paramdef>const char *<parameter>field</parameter></paramdef> | |
61 | </funcprototype> | |
62 | ||
63 | <funcprototype> | |
64 | <funcdef>int <function>sd_journal_enumerate_unique</function></funcdef> | |
65 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
66 | <paramdef>const void **<parameter>data</parameter></paramdef> | |
67 | <paramdef>size_t *<parameter>length</parameter></paramdef> | |
68 | </funcprototype> | |
69 | ||
70 | <funcprototype> | |
71 | <funcdef>void <function>sd_journal_restart_unique</function></funcdef> | |
72 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
73 | </funcprototype> | |
74 | ||
75 | <funcprototype> | |
76 | <funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef> | |
77 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
78 | <paramdef>const void *<parameter>data</parameter></paramdef> | |
79 | <paramdef>size_t <parameter>length</parameter></paramdef> | |
80 | </funcprototype> | |
81 | ||
82 | </funcsynopsis> | |
83 | </refsynopsisdiv> | |
84 | ||
85 | <refsect1> | |
86 | <title>Description</title> | |
87 | ||
88 | <para><function>sd_journal_query_unique()</function> queries the | |
89 | journal for all unique values the specified field can take. It | |
90 | takes two arguments: the journal to query and the field name to | |
91 | look for. Well-known field names are listed on | |
92 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. | |
93 | Field names must be specified without a trailing '='. After this | |
94 | function has been executed successfully the field values may be | |
95 | queried using <function>sd_journal_enumerate_unique()</function>. | |
96 | Invoking this call a second time will change the field name being | |
97 | queried and reset the enumeration index to the first field value | |
98 | that matches.</para> | |
99 | ||
100 | <para><function>sd_journal_enumerate_unique()</function> may be | |
101 | used to iterate through all data fields which match the previously | |
102 | selected field name as set with | |
103 | <function>sd_journal_query_unique()</function>. On each invocation | |
104 | the next field data matching the field name is returned. The order | |
105 | of the returned data fields is not defined. It takes three | |
106 | arguments: the journal context object, plus a pair of pointers to | |
107 | pointer/size variables where the data object and its size shall be | |
108 | stored in. The returned data is in a read-only memory map and is | |
109 | only valid until the next invocation of | |
110 | <function>sd_journal_enumerate_unique()</function>. Note that the | |
111 | data returned will be prefixed with the field name and '='. Note | |
112 | that this call is subject to the data field size threshold as | |
113 | controlled by | |
114 | <function>sd_journal_set_data_threshold()</function>.</para> | |
115 | ||
116 | <para><function>sd_journal_restart_unique()</function> resets the | |
117 | data enumeration index to the beginning of the list. The next | |
118 | invocation of <function>sd_journal_enumerate_unique()</function> | |
119 | will return the first field data matching the field name | |
120 | again.</para> | |
121 | ||
122 | <para>Note that the | |
123 | <function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro may be used | |
124 | as a handy wrapper around | |
125 | <function>sd_journal_restart_unique()</function> and | |
126 | <function>sd_journal_enumerate_unique()</function>.</para> | |
127 | ||
128 | <para>Note that these functions currently are not influenced by | |
129 | matches set with <function>sd_journal_add_match()</function> but | |
130 | this might change in a later version of this software.</para> | |
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131 | |
132 | <para>To enumerate all field names currently in use (and thus all suitable field parameters for | |
133 | <function>sd_journal_query_unique()</function>), use the | |
134 | <citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
135 | call.</para> | |
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136 | </refsect1> |
137 | ||
138 | <refsect1> | |
139 | <title>Return Value</title> | |
140 | ||
141 | <para><function>sd_journal_query_unique()</function> returns 0 on | |
142 | success or a negative errno-style error code. | |
143 | <function>sd_journal_enumerate_unique()</function> returns a | |
144 | positive integer if the next field data has been read, 0 when no | |
145 | more fields are known, or a negative errno-style error code. | |
146 | <function>sd_journal_restart_unique()</function> returns | |
147 | nothing.</para> | |
148 | </refsect1> | |
149 | ||
150 | <refsect1> | |
151 | <title>Notes</title> | |
152 | ||
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153 | <para>All functions listed here are thread-agnostic and only a single thread may operate |
154 | on a given <structname>sd_journal</structname> object.</para> | |
155 | ||
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156 | <para>The <function>sd_journal_query_unique()</function>, |
157 | <function>sd_journal_enumerate_unique()</function> and | |
158 | <function>sd_journal_restart_unique()</function> interfaces are | |
159 | available as a shared library, which can be compiled and linked to | |
160 | with the | |
161 | <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
162 | file.</para> | |
163 | </refsect1> | |
164 | ||
165 | <refsect1> | |
166 | <title>Examples</title> | |
167 | ||
168 | <para>Use the <function>SD_JOURNAL_FOREACH_UNIQUE</function> macro | |
169 | to iterate through all values a field of the journal can take. The | |
170 | following example lists all unit names referenced in the | |
171 | journal:</para> | |
172 | ||
173 | <programlisting>#include <stdio.h> | |
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174 | #include <string.h> |
175 | #include <systemd/sd-journal.h> | |
176 | ||
177 | int main(int argc, char *argv[]) { | |
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178 | sd_journal *j; |
179 | const void *d; | |
180 | size_t l; | |
181 | int r; | |
182 | ||
183 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
184 | if (r < 0) { | |
185 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
186 | return 1; | |
187 | } | |
188 | r = sd_journal_query_unique(j, "_SYSTEMD_UNIT"); | |
189 | if (r < 0) { | |
190 | fprintf(stderr, "Failed to query journal: %s\n", strerror(-r)); | |
191 | return 1; | |
192 | } | |
193 | SD_JOURNAL_FOREACH_UNIQUE(j, d, l) | |
194 | printf("%.*s\n", (int) l, (const char*) d); | |
195 | sd_journal_close(j); | |
196 | return 0; | |
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197 | }</programlisting> |
198 | ||
798d3a52 | 199 | </refsect1> |
1a2be33a | 200 | |
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201 | <refsect1> |
202 | <title>See Also</title> | |
1a2be33a | 203 | |
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204 | <para> |
205 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
206 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
207 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
208 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
eb86030e | 209 | <citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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210 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
211 | <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
212 | </para> | |
213 | </refsect1> | |
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214 | |
215 | </refentry> |