1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
|
<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2012 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd_journal_query_unique">
<refentryinfo>
<title>sd_journal_query_unique</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>sd_journal_query_unique</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_journal_query_unique</refname>
<refname>sd_journal_enumerate_unique</refname>
<refname>sd_journal_restart_unique</refname>
<refname>SD_JOURNAL_FOREACH_UNIQUE</refname>
<refpurpose>Read unique data fields from the journal</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_journal_query_unique</function></funcdef>
<paramdef>sd_journal* <parameter>j</parameter></paramdef>
<paramdef>const char* <parameter>field</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_enumerate_unique</function></funcdef>
<paramdef>sd_journal* <parameter>j</parameter></paramdef>
<paramdef>const void** <parameter>data</parameter></paramdef>
<paramdef>size_t* <parameter>length</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>sd_journal_restart_unique</function></funcdef>
<paramdef>sd_journal* <parameter>j</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef>
<paramdef>sd_journal* <parameter>j</parameter></paramdef>
<paramdef>const void* <parameter>data</parameter></paramdef>
<paramdef>size_t <parameter>length</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_journal_query_unique()</function>
queries the journal for all unique values the
specified field can take. It takes two arguments: the
journal to query and the field name to look
for. Well-known field names are listed on
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. Field
names must be specified without a trailing '='. After
this function has been executed successfully the field
values may be queried using
<function>sd_journal_enumerate_unique()</function>. Invoking
this call a second time will change the field name
being queried and reset the enumeration index to the
first field value that matches.</para>
<para><function>sd_journal_enumerate_unique()</function>
may be used to iterate through all data fields which
match the previously selected field name as set with
<function>sd_journal_query_unique()</function>. On
each invocation the next field data matching the field
name is returned. The order of the returned data
fields is not defined. It takes three arguments: the
journal context object, plus a pair of pointers to
pointer/size variables where the data object and its
size shall be stored in. The returned data is in a
read-only memory map and is only valid until the next
invocation of
<function>sd_journal_enumerate_unique()</function>. Note
that the data returned will be prefixed with the field
name and '='.</para>
<para><function>sd_journal_restart_unique()</function>
resets the data enumeration index to the beginning of
the list. The next invocation of
<function>sd_journal_enumerate_unique()</function>
will return the first field data matching the field
name again.</para>
<para>Note that the
<function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro
may be used as a handy wrapper around
<function>sd_journal_restart_unique()</function> and
<function>sd_journal_enumerate_unique()</function>.</para>
<para>Note that these functions currently are not
influenced by matches set with
<function>sd_journal_add_match()</function> but this
might change in a later version of this
software.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para><function>sd_journal_query_unique()</function>
returns 0 on success or a negative errno-style error
code. <function>sd_journal_enumerate_unique()</function>
returns a positive integer if the next field data has
been read, 0 when no more fields are known, or a
negative errno-style error
code. <function>sd_journal_restart_unique()</function>
returns nothing.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>The <function>sd_journal_query_unique()</function>,
<function>sd_journal_enumerate_unique()</function> and
<function>sd_journal_restart_unique()</function>
interfaces are available as shared library, which can
be compiled and linked to with the
<literal>libsystemd-journal</literal>
<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>Use the
<function>SD_JOURNAL_FOREACH_UNIQUE</function> macro
to iterate through all values a field of the journal
can take. The following example lists all unit names
referenced in the journal:</para>
<programlisting>#include <stdio.h>
#include <string.h>
#include <systemd/sd-journal.h>
int main(int argc, char *argv[]) {
sd_journal *j;
const void *d;
size_t l;
int r;
r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
if (r < 0) {
fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
return 1;
}
r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
if (r < 0) {
fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
return 1;
}
SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
printf("%.*s\n", (int) l, d);
sd_journal_close(j);
return 0;
}</programlisting>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
|
