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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
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3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [ |
4 | <!ENTITY % entities SYSTEM "custom-entities.ent" > | |
5 | %entities; | |
6 | ]> | |
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7 | |
8 | <!-- | |
9 | This file is part of systemd. | |
10 | ||
11 | Copyright 2012 Lennart Poettering | |
12 | ||
13 | systemd is free software; you can redistribute it and/or modify it | |
14 | under the terms of the GNU Lesser General Public License as published by | |
15 | the Free Software Foundation; either version 2.1 of the License, or | |
16 | (at your option) any later version. | |
17 | ||
18 | systemd is distributed in the hope that it will be useful, but | |
19 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
20 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
21 | Lesser General Public License for more details. | |
22 | ||
23 | You should have received a copy of the GNU Lesser General Public License | |
24 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
25 | --> | |
26 | ||
27 | <refentry id="sd_journal_query_unique"> | |
28 | ||
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29 | <refentryinfo> |
30 | <title>sd_journal_query_unique</title> | |
31 | <productname>systemd</productname> | |
32 | ||
33 | <authorgroup> | |
34 | <author> | |
35 | <contrib>Developer</contrib> | |
36 | <firstname>Lennart</firstname> | |
37 | <surname>Poettering</surname> | |
38 | <email>lennart@poettering.net</email> | |
39 | </author> | |
40 | </authorgroup> | |
41 | </refentryinfo> | |
42 | ||
43 | <refmeta> | |
44 | <refentrytitle>sd_journal_query_unique</refentrytitle> | |
45 | <manvolnum>3</manvolnum> | |
46 | </refmeta> | |
47 | ||
48 | <refnamediv> | |
49 | <refname>sd_journal_query_unique</refname> | |
50 | <refname>sd_journal_enumerate_unique</refname> | |
51 | <refname>sd_journal_restart_unique</refname> | |
52 | <refname>SD_JOURNAL_FOREACH_UNIQUE</refname> | |
53 | <refpurpose>Read unique data fields from the journal</refpurpose> | |
54 | </refnamediv> | |
55 | ||
56 | <refsynopsisdiv> | |
57 | <funcsynopsis> | |
58 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
59 | ||
60 | <funcprototype> | |
61 | <funcdef>int <function>sd_journal_query_unique</function></funcdef> | |
62 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
63 | <paramdef>const char *<parameter>field</parameter></paramdef> | |
64 | </funcprototype> | |
65 | ||
66 | <funcprototype> | |
67 | <funcdef>int <function>sd_journal_enumerate_unique</function></funcdef> | |
68 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
69 | <paramdef>const void **<parameter>data</parameter></paramdef> | |
70 | <paramdef>size_t *<parameter>length</parameter></paramdef> | |
71 | </funcprototype> | |
72 | ||
73 | <funcprototype> | |
74 | <funcdef>void <function>sd_journal_restart_unique</function></funcdef> | |
75 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
76 | </funcprototype> | |
77 | ||
78 | <funcprototype> | |
79 | <funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef> | |
80 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
81 | <paramdef>const void *<parameter>data</parameter></paramdef> | |
82 | <paramdef>size_t <parameter>length</parameter></paramdef> | |
83 | </funcprototype> | |
84 | ||
85 | </funcsynopsis> | |
86 | </refsynopsisdiv> | |
87 | ||
88 | <refsect1> | |
89 | <title>Description</title> | |
90 | ||
91 | <para><function>sd_journal_query_unique()</function> queries the | |
92 | journal for all unique values the specified field can take. It | |
93 | takes two arguments: the journal to query and the field name to | |
94 | look for. Well-known field names are listed on | |
95 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. | |
96 | Field names must be specified without a trailing '='. After this | |
97 | function has been executed successfully the field values may be | |
98 | queried using <function>sd_journal_enumerate_unique()</function>. | |
99 | Invoking this call a second time will change the field name being | |
100 | queried and reset the enumeration index to the first field value | |
101 | that matches.</para> | |
102 | ||
103 | <para><function>sd_journal_enumerate_unique()</function> may be | |
104 | used to iterate through all data fields which match the previously | |
105 | selected field name as set with | |
106 | <function>sd_journal_query_unique()</function>. On each invocation | |
107 | the next field data matching the field name is returned. The order | |
108 | of the returned data fields is not defined. It takes three | |
109 | arguments: the journal context object, plus a pair of pointers to | |
110 | pointer/size variables where the data object and its size shall be | |
111 | stored in. The returned data is in a read-only memory map and is | |
112 | only valid until the next invocation of | |
113 | <function>sd_journal_enumerate_unique()</function>. Note that the | |
114 | data returned will be prefixed with the field name and '='. Note | |
115 | that this call is subject to the data field size threshold as | |
116 | controlled by | |
117 | <function>sd_journal_set_data_threshold()</function>.</para> | |
118 | ||
119 | <para><function>sd_journal_restart_unique()</function> resets the | |
120 | data enumeration index to the beginning of the list. The next | |
121 | invocation of <function>sd_journal_enumerate_unique()</function> | |
122 | will return the first field data matching the field name | |
123 | again.</para> | |
124 | ||
125 | <para>Note that the | |
126 | <function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro may be used | |
127 | as a handy wrapper around | |
128 | <function>sd_journal_restart_unique()</function> and | |
129 | <function>sd_journal_enumerate_unique()</function>.</para> | |
130 | ||
131 | <para>Note that these functions currently are not influenced by | |
132 | matches set with <function>sd_journal_add_match()</function> but | |
133 | this might change in a later version of this software.</para> | |
134 | </refsect1> | |
135 | ||
136 | <refsect1> | |
137 | <title>Return Value</title> | |
138 | ||
139 | <para><function>sd_journal_query_unique()</function> returns 0 on | |
140 | success or a negative errno-style error code. | |
141 | <function>sd_journal_enumerate_unique()</function> returns a | |
142 | positive integer if the next field data has been read, 0 when no | |
143 | more fields are known, or a negative errno-style error code. | |
144 | <function>sd_journal_restart_unique()</function> returns | |
145 | nothing.</para> | |
146 | </refsect1> | |
147 | ||
148 | <refsect1> | |
149 | <title>Notes</title> | |
150 | ||
151 | <para>The <function>sd_journal_query_unique()</function>, | |
152 | <function>sd_journal_enumerate_unique()</function> and | |
153 | <function>sd_journal_restart_unique()</function> interfaces are | |
154 | available as a shared library, which can be compiled and linked to | |
155 | with the | |
156 | <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
157 | file.</para> | |
158 | </refsect1> | |
159 | ||
160 | <refsect1> | |
161 | <title>Examples</title> | |
162 | ||
163 | <para>Use the <function>SD_JOURNAL_FOREACH_UNIQUE</function> macro | |
164 | to iterate through all values a field of the journal can take. The | |
165 | following example lists all unit names referenced in the | |
166 | journal:</para> | |
167 | ||
168 | <programlisting>#include <stdio.h> | |
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169 | #include <string.h> |
170 | #include <systemd/sd-journal.h> | |
171 | ||
172 | int main(int argc, char *argv[]) { | |
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173 | sd_journal *j; |
174 | const void *d; | |
175 | size_t l; | |
176 | int r; | |
177 | ||
178 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
179 | if (r < 0) { | |
180 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
181 | return 1; | |
182 | } | |
183 | r = sd_journal_query_unique(j, "_SYSTEMD_UNIT"); | |
184 | if (r < 0) { | |
185 | fprintf(stderr, "Failed to query journal: %s\n", strerror(-r)); | |
186 | return 1; | |
187 | } | |
188 | SD_JOURNAL_FOREACH_UNIQUE(j, d, l) | |
189 | printf("%.*s\n", (int) l, (const char*) d); | |
190 | sd_journal_close(j); | |
191 | return 0; | |
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192 | }</programlisting> |
193 | ||
798d3a52 | 194 | </refsect1> |
1a2be33a | 195 | |
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196 | <refsect1> |
197 | <title>See Also</title> | |
1a2be33a | 198 | |
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199 | <para> |
200 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
201 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
202 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
203 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
204 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
205 | <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
206 | </para> | |
207 | </refsect1> | |
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208 | |
209 | </refentry> |