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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 | |
11 | ||
12 | systemd is free software; you can redistribute it and/or modify it | |
13 | under the terms of the GNU Lesser General Public License as published by | |
14 | the Free Software Foundation; either version 2.1 of the License, or | |
15 | (at your option) any later version. | |
16 | ||
17 | systemd is distributed in the hope that it will be useful, but | |
18 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
20 | Lesser General Public License for more details. | |
21 | ||
22 | You should have received a copy of the GNU Lesser General Public License | |
23 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
24 | --> | |
25 | ||
26 | <refentry id="sd_journal_enumerate_fields"> | |
27 | ||
28 | <refentryinfo> | |
29 | <title>sd_journal_enumerate_fields</title> | |
30 | <productname>systemd</productname> | |
31 | ||
32 | <authorgroup> | |
33 | <author> | |
34 | <contrib>Developer</contrib> | |
35 | <firstname>Lennart</firstname> | |
36 | <surname>Poettering</surname> | |
37 | <email>lennart@poettering.net</email> | |
38 | </author> | |
39 | </authorgroup> | |
40 | </refentryinfo> | |
41 | ||
42 | <refmeta> | |
43 | <refentrytitle>sd_journal_enumerate_fields</refentrytitle> | |
44 | <manvolnum>3</manvolnum> | |
45 | </refmeta> | |
46 | ||
47 | <refnamediv> | |
48 | <refname>sd_journal_enumerate_fields</refname> | |
49 | <refname>sd_journal_restart_fields</refname> | |
50 | <refname>SD_JOURNAL_FOREACH_FIELD</refname> | |
51 | <refpurpose>Read used field names from the journal</refpurpose> | |
52 | </refnamediv> | |
53 | ||
54 | <refsynopsisdiv> | |
55 | <funcsynopsis> | |
56 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
57 | ||
58 | <funcprototype> | |
59 | <funcdef>int <function>sd_journal_enumerate_fields</function></funcdef> | |
60 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
61 | <paramdef>const char **<parameter>field</parameter></paramdef> | |
62 | </funcprototype> | |
63 | ||
64 | <funcprototype> | |
65 | <funcdef>void <function>sd_journal_restart_fields</function></funcdef> | |
66 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
67 | </funcprototype> | |
68 | ||
69 | <funcprototype> | |
70 | <funcdef><function>SD_JOURNAL_FOREACH_FIELD</function></funcdef> | |
71 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
72 | <paramdef>const char *<parameter>field</parameter></paramdef> | |
73 | </funcprototype> | |
74 | ||
75 | </funcsynopsis> | |
76 | </refsynopsisdiv> | |
77 | ||
78 | <refsect1> | |
79 | <title>Description</title> | |
80 | ||
81 | <para><function>sd_journal_enumerate_fields()</function> may be used to iterate through all field names used in the | |
82 | opened journal files. On each invocation the next field name is returned. The order of the returned field names is | |
83 | not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where | |
84 | the field name is stored in. The returned data is in a read-only memory map and is only valid until the next | |
85 | invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field | |
86 | size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para> | |
87 | ||
88 | <para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of | |
89 | the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field | |
90 | name again.</para> | |
91 | ||
92 | <para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around | |
93 | <function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para> | |
94 | ||
95 | <para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function> | |
96 | but this might change in a later version of this software.</para> | |
97 | ||
98 | <para>To retrieve the possible values a specific field can take use | |
99 | <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
100 | </refsect1> | |
101 | ||
102 | <refsect1> | |
103 | <title>Return Value</title> | |
104 | ||
105 | <para><function>sd_journal_enumerate_fields()</function> returns a | |
106 | positive integer if the next field name has been read, 0 when no | |
107 | more field names are known, or a negative errno-style error code. | |
108 | <function>sd_journal_restart_fields()</function> returns | |
109 | nothing.</para> | |
110 | </refsect1> | |
111 | ||
112 | <refsect1> | |
113 | <title>Notes</title> | |
114 | ||
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115 | <para>All functions listed here are thread-agnostic and only a single thread may operate |
116 | on a given <structname>sd_journal</structname> object.</para> | |
117 | ||
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118 | <para>The <function>sd_journal_enumerate_fields()</function> and <function>sd_journal_restart_fields()</function> |
119 | interfaces are available as a shared library, which can be compiled and linked to with the | |
120 | <constant>libsystemd</constant> <citerefentry | |
121 | project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para> | |
122 | </refsect1> | |
123 | ||
124 | <refsect1> | |
125 | <title>Examples</title> | |
126 | ||
127 | <para>Use the <function>SD_JOURNAL_FOREACH_FIELD</function> macro to iterate through all field names in use in the | |
128 | current journal.</para> | |
129 | ||
130 | <programlisting>#include <stdio.h> | |
131 | #include <string.h> | |
132 | #include <systemd/sd-journal.h> | |
133 | ||
134 | int main(int argc, char *argv[]) { | |
135 | sd_journal *j; | |
136 | const char *field; | |
137 | int r; | |
138 | ||
139 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
140 | if (r < 0) { | |
141 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
142 | return 1; | |
143 | } | |
144 | SD_JOURNAL_FOREACH_FIELD(j, field) | |
145 | printf("%s\n", field); | |
146 | sd_journal_close(j); | |
147 | return 0; | |
148 | }</programlisting> | |
149 | ||
150 | </refsect1> | |
151 | ||
152 | <refsect1> | |
153 | <title>See Also</title> | |
154 | ||
155 | <para> | |
156 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
157 | <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
158 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
159 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
160 | <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
161 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
162 | <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
163 | </para> | |
164 | </refsect1> | |
165 | ||
166 | </refentry> |