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networkd: distinguish between static and dynamic addresses/routes
[elogind.git] / man / sd-id128.xml
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
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8   Copyright 2012 Lennart Poettering
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23
24 <refentry id="sd-id128">
25
26         <refentryinfo>
27                 <title>sd-id128</title>
28                 <productname>systemd</productname>
29
30                 <authorgroup>
31                         <author>
32                                 <contrib>Developer</contrib>
33                                 <firstname>Lennart</firstname>
34                                 <surname>Poettering</surname>
35                                 <email>lennart@poettering.net</email>
36                         </author>
37                 </authorgroup>
38         </refentryinfo>
39
40         <refmeta>
41                 <refentrytitle>sd-id128</refentrytitle>
42                 <manvolnum>3</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>sd-id128</refname>
47                 <refname>sd_id128_t</refname>
48                 <refname>SD_ID128_MAKE</refname>
49                 <refname>SD_ID128_CONST_STR</refname>
50                 <refname>SD_ID128_FORMAT_STR</refname>
51                 <refname>SD_ID128_FORMAT_VAL</refname>
52                 <refname>sd_id128_equal</refname>
53                 <refpurpose>APIs for processing 128-bit IDs</refpurpose>
54         </refnamediv>
55
56         <refsynopsisdiv>
57                 <funcsynopsis>
58                         <funcsynopsisinfo>#include &lt;systemd/sd-id128.h&gt;</funcsynopsisinfo>
59                 </funcsynopsis>
60
61                 <cmdsynopsis>
62                         <command>pkg-config --cflags --libs libsystemd-id128</command>
63                 </cmdsynopsis>
64
65         </refsynopsisdiv>
66
67         <refsect1>
68                 <title>Description</title>
69
70                 <para><filename>sd-id128.h</filename> provides APIs to
71                 process and generate 128-bit ID values. The 128-bit ID
72                 values processed and generated by these APIs are a
73                 generalization of OSF UUIDs as defined by <ulink
74                 url="https://tools.ietf.org/html/rfc4122">RFC
75                 4122</ulink> but use a simpler string
76                 format. These functions impose no structure on the
77                 used IDs, much unlike OSF UUIDs or Microsoft GUIDs,
78                 but are fully compatible with those types of IDs.
79                 </para>
80
81                 <para>See
82                 <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
83                 <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
84                 <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>
85                 for more information about the implemented
86                 functions.</para>
87
88                 <para>A 128-bit ID is implemented as the following
89                 union type:</para>
90
91                 <programlisting>typedef union sd_id128 {
92         uint8_t bytes[16];
93         uint64_t qwords[2];
94 } sd_id128_t;</programlisting>
95
96                 <para>This union type allows accessing the 128-bit ID
97                 as 16 separate bytes or two 64-bit words. It is generally
98                 safer to access the ID components by their 8-bit array
99                 to avoid endianness issues. This union is intended to
100                 be passed call-by-value (as opposed to
101                 call-by-reference) and may be directly manipulated by
102                 clients.</para>
103
104                 <para>A couple of macros are defined to denote and
105                 decode 128-bit IDs:</para>
106
107                 <para><function>SD_ID128_MAKE()</function> may be used
108                 to denote a constant 128-bit ID in source code. A
109                 commonly used idiom is to assign a name to a 128-bit
110                 ID using this macro:</para>
111
112                 <programlisting>#define SD_MESSAGE_COREDUMP SD_ID128_MAKE(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)</programlisting>
113
114                 <para><function>SD_ID128_CONST_STR()</function> may be
115                 used to convert constant 128-bit IDs into constant
116                 strings for output. The following example code will
117                 output the string
118                 "fc2e22bc6ee647b6b90729ab34a250b1":</para>
119                 <programlisting>int main(int argc, char *argv[]) {
120         puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
121 }</programlisting>
122
123                 <para><function>SD_ID128_FORMAT_STR</function> and
124                 <function>SD_ID128_FORMAT_VAL()</function> may be used
125                 to format a 128-bit ID in a
126                 <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
127                 format string, as shown in the following
128                 example:</para>
129
130                 <programlisting>int main(int argc, char *argv[]) {
131         sd_id128_t id;
132         id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
133         printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
134         return 0;
135 }</programlisting>
136
137                 <para>Use <function>sd_id128_equal()</function> to compare two 128-bit IDs:</para>
138
139                 <programlisting>int main(int argc, char *argv[]) {
140         sd_id128_t a, b, c;
141         a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
142         b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
143         c = a;
144         assert(sd_id128_equal(a, c));
145         assert(!sd_id128_equal(a, b));
146         return 0;
147 }</programlisting>
148
149                 <para>Note that new, randomized IDs may be generated
150                 with
151                 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
152                 <option>--new-id</option> option.</para>
153         </refsect1>
154
155         <refsect1>
156                 <title>Notes</title>
157
158                 <para>These APIs are implemented as a shared library,
159                 which can be compiled and linked to with the
160                 <literal>libsystemd-id128</literal> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
161                 file.</para>
162
163         </refsect1>
164
165         <refsect1>
166                 <title>See Also</title>
167                 <para>
168                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
169                         <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
170                         <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
171                         <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
172                         <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
173                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
174                         <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
175                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
176                         <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
177                 </para>
178         </refsect1>
179
180 </refentry>