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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
4 | ||
5 | <!-- | |
572eb058 ZJS |
6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
eb86030e LP |
8 | This file is part of systemd. |
9 | ||
10 | Copyright 2016 Lennart Poettering | |
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11 | --> |
12 | ||
13 | <refentry id="sd_journal_enumerate_fields"> | |
14 | ||
15 | <refentryinfo> | |
16 | <title>sd_journal_enumerate_fields</title> | |
17 | <productname>systemd</productname> | |
18 | ||
19 | <authorgroup> | |
20 | <author> | |
21 | <contrib>Developer</contrib> | |
22 | <firstname>Lennart</firstname> | |
23 | <surname>Poettering</surname> | |
24 | <email>lennart@poettering.net</email> | |
25 | </author> | |
26 | </authorgroup> | |
27 | </refentryinfo> | |
28 | ||
29 | <refmeta> | |
30 | <refentrytitle>sd_journal_enumerate_fields</refentrytitle> | |
31 | <manvolnum>3</manvolnum> | |
32 | </refmeta> | |
33 | ||
34 | <refnamediv> | |
35 | <refname>sd_journal_enumerate_fields</refname> | |
36 | <refname>sd_journal_restart_fields</refname> | |
37 | <refname>SD_JOURNAL_FOREACH_FIELD</refname> | |
38 | <refpurpose>Read used field names from the journal</refpurpose> | |
39 | </refnamediv> | |
40 | ||
41 | <refsynopsisdiv> | |
42 | <funcsynopsis> | |
43 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
44 | ||
45 | <funcprototype> | |
46 | <funcdef>int <function>sd_journal_enumerate_fields</function></funcdef> | |
47 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
48 | <paramdef>const char **<parameter>field</parameter></paramdef> | |
49 | </funcprototype> | |
50 | ||
51 | <funcprototype> | |
52 | <funcdef>void <function>sd_journal_restart_fields</function></funcdef> | |
53 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
54 | </funcprototype> | |
55 | ||
56 | <funcprototype> | |
57 | <funcdef><function>SD_JOURNAL_FOREACH_FIELD</function></funcdef> | |
58 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
59 | <paramdef>const char *<parameter>field</parameter></paramdef> | |
60 | </funcprototype> | |
61 | ||
62 | </funcsynopsis> | |
63 | </refsynopsisdiv> | |
64 | ||
65 | <refsect1> | |
66 | <title>Description</title> | |
67 | ||
68 | <para><function>sd_journal_enumerate_fields()</function> may be used to iterate through all field names used in the | |
69 | opened journal files. On each invocation the next field name is returned. The order of the returned field names is | |
70 | not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where | |
71 | the field name is stored in. The returned data is in a read-only memory map and is only valid until the next | |
72 | invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field | |
73 | size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para> | |
74 | ||
75 | <para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of | |
76 | the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field | |
77 | name again.</para> | |
78 | ||
79 | <para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around | |
80 | <function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para> | |
81 | ||
82 | <para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function> | |
83 | but this might change in a later version of this software.</para> | |
84 | ||
85 | <para>To retrieve the possible values a specific field can take use | |
86 | <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
87 | </refsect1> | |
88 | ||
89 | <refsect1> | |
90 | <title>Return Value</title> | |
91 | ||
92 | <para><function>sd_journal_enumerate_fields()</function> returns a | |
93 | positive integer if the next field name has been read, 0 when no | |
94 | more field names are known, or a negative errno-style error code. | |
95 | <function>sd_journal_restart_fields()</function> returns | |
96 | nothing.</para> | |
97 | </refsect1> | |
98 | ||
99 | <refsect1> | |
100 | <title>Notes</title> | |
101 | ||
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102 | <para>All functions listed here are thread-agnostic and only a single thread may operate |
103 | on a given <structname>sd_journal</structname> object.</para> | |
104 | ||
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105 | <para>The <function>sd_journal_enumerate_fields()</function> and <function>sd_journal_restart_fields()</function> |
106 | interfaces are available as a shared library, which can be compiled and linked to with the | |
107 | <constant>libsystemd</constant> <citerefentry | |
108 | project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para> | |
109 | </refsect1> | |
110 | ||
111 | <refsect1> | |
112 | <title>Examples</title> | |
113 | ||
114 | <para>Use the <function>SD_JOURNAL_FOREACH_FIELD</function> macro to iterate through all field names in use in the | |
115 | current journal.</para> | |
116 | ||
117 | <programlisting>#include <stdio.h> | |
118 | #include <string.h> | |
119 | #include <systemd/sd-journal.h> | |
120 | ||
121 | int main(int argc, char *argv[]) { | |
122 | sd_journal *j; | |
123 | const char *field; | |
124 | int r; | |
125 | ||
126 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
127 | if (r < 0) { | |
128 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
129 | return 1; | |
130 | } | |
131 | SD_JOURNAL_FOREACH_FIELD(j, field) | |
132 | printf("%s\n", field); | |
133 | sd_journal_close(j); | |
134 | return 0; | |
135 | }</programlisting> | |
136 | ||
137 | </refsect1> | |
138 | ||
139 | <refsect1> | |
140 | <title>See Also</title> | |
141 | ||
142 | <para> | |
143 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
144 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
145 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
146 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
147 | <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
148 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
149 | <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
150 | </para> | |
151 | </refsect1> | |
152 | ||
153 | </refentry> |