summaryrefslogtreecommitdiffstats
path: root/man/sd_journal_query_unique.xml
blob: 9adafa114460c05fe7ab3ca47ac32f2cca9c7178 (plain)
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
<?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">

<!--
  SPDX-License-Identifier: LGPL-2.1+
-->

<refentry id="sd_journal_query_unique" xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd_journal_query_unique</title>
    <productname>systemd</productname>
  </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 &lt;systemd/sd-journal.h&gt;</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 '='. Note
    that this call is subject to the data field size threshold as
    controlled by
    <function>sd_journal_set_data_threshold()</function>.</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>

    <para>To enumerate all field names currently in use (and thus all suitable field parameters for
    <function>sd_journal_query_unique()</function>), use the
    <citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call.</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>

    <xi:include href="threads-aware.xml" xpointer="strict"/>

    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
  </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><xi:include href="journal-iterate-unique.c" parse="text" /></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_enumerate_fields</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>