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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd-id128"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd-id128</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd-id128</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd-id128</refname>
<refname>SD_ID128_ALLF</refname>
<refname>SD_ID128_CONST_STR</refname>
<refname>SD_ID128_FORMAT_STR</refname>
<refname>SD_ID128_FORMAT_VAL</refname>
<refname>SD_ID128_MAKE</refname>
<refname>SD_ID128_MAKE_STR</refname>
<refname>SD_ID128_MAKE_UUID_STR</refname>
<refname>SD_ID128_NULL</refname>
<refname>SD_ID128_UUID_FORMAT_STR</refname>
<refname>sd_id128_equal</refname>
<refname>sd_id128_string_equal</refname>
<refname>sd_id128_in_set</refname>
<refname>sd_id128_in_set_sentinel</refname>
<refname>sd_id128_in_setv</refname>
<refname>sd_id128_is_allf</refname>
<refname>sd_id128_is_null</refname>
<refname>sd_id128_t</refname>
<refpurpose>APIs for processing 128-bit IDs</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo>
</funcsynopsis>
<para>
<constant>SD_ID128_ALLF</constant>
</para>
<para>
<constant>SD_ID128_NULL</constant>
</para>
<para>
<constant>SD_ID128_CONST_STR(<replaceable>id</replaceable>)</constant>
</para>
<para>
<constant>SD_ID128_FORMAT_STR</constant>
</para>
<para>
<constant>SD_ID128_FORMAT_VAL(<replaceable>id</replaceable>)</constant>
</para>
<para>
<constant>SD_ID128_MAKE(<replaceable>v0</replaceable>, <replaceable>v1</replaceable>, <replaceable>v2</replaceable>, <replaceable>v3</replaceable>, <replaceable>v4</replaceable>, <replaceable>v5</replaceable>, <replaceable>v6</replaceable>, <replaceable>v7</replaceable>, <replaceable>v8</replaceable>, <replaceable>v9</replaceable>, <replaceable>vA</replaceable>, <replaceable>vB</replaceable>, <replaceable>vC</replaceable>, <replaceable>vD</replaceable>, <replaceable>vE</replaceable>, <replaceable>vF</replaceable>)</constant>
</para>
<para>
<constant>SD_ID128_MAKE_STR(<replaceable>v0</replaceable>, <replaceable>v1</replaceable>, <replaceable>v2</replaceable>, <replaceable>v3</replaceable>, <replaceable>v4</replaceable>, <replaceable>v5</replaceable>, <replaceable>v6</replaceable>, <replaceable>v7</replaceable>, <replaceable>v8</replaceable>, <replaceable>v9</replaceable>, <replaceable>vA</replaceable>, <replaceable>vB</replaceable>, <replaceable>vC</replaceable>, <replaceable>vD</replaceable>, <replaceable>vE</replaceable>, <replaceable>vF</replaceable>)</constant>
</para>
<para>
<constant>SD_ID128_MAKE_UUID_STR(<replaceable>v0</replaceable>, <replaceable>v1</replaceable>, <replaceable>v2</replaceable>, <replaceable>v3</replaceable>, <replaceable>v4</replaceable>, <replaceable>v5</replaceable>, <replaceable>v6</replaceable>, <replaceable>v7</replaceable>, <replaceable>v8</replaceable>, <replaceable>v9</replaceable>, <replaceable>vA</replaceable>, <replaceable>vB</replaceable>, <replaceable>vC</replaceable>, <replaceable>vD</replaceable>, <replaceable>vE</replaceable>, <replaceable>vF</replaceable>)</constant>
</para>
<para>
<constant>SD_ID128_UUID_FORMAT_STR</constant>
</para>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>sd_id128_equal</function></funcdef>
<paramdef>sd_id128_t <parameter>a</parameter></paramdef>
<paramdef>sd_id128_t <parameter>b</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_id128_string_equal</function></funcdef>
<paramdef>const char *<parameter>a</parameter></paramdef>
<paramdef>sd_id128_t <parameter>b</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_id128_is_null</function></funcdef>
<paramdef>sd_id128_t <parameter>id</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_id128_is_allf</function></funcdef>
<paramdef>sd_id128_t <parameter>id</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_id128_in_setv</function></funcdef>
<paramdef>sd_id128_t <parameter>id</parameter></paramdef>
<paramdef>va_list <parameter>ap</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_id128_in_set_sentinel</function></funcdef>
<paramdef>sd_id128_t <parameter>id</parameter></paramdef>
<paramdef>…</paramdef>
<paramdef><parameter><constant>SD_ID128_NULL</constant></parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_id128_in_set</function></funcdef>
<paramdef>sd_id128_t <parameter>id</parameter></paramdef>
<paramdef>…</paramdef>
</funcprototype>
</funcsynopsis>
<cmdsynopsis>
<command>pkg-config --cflags --libs libsystemd</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>sd-id128.h</filename> is part of
<citerefentry><refentrytitle>libsystemd</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
provides APIs to generate, convert, and compare 128-bit ID values. The 128-bit ID values processed and
generated by these APIs are a generalization of OSF UUIDs as defined by <ulink
url="https://tools.ietf.org/html/rfc4122">RFC 4122</ulink> but use a simpler string format. These
functions impose no structure on the used IDs, much unlike OSF UUIDs or Microsoft GUIDs, but are mostly
compatible with those types of IDs.
</para>
<para>A 128-bit ID is implemented as the following
union type:</para>
<programlisting>typedef union sd_id128 {
uint8_t bytes[16];
uint64_t qwords[2];
} sd_id128_t;</programlisting>
<para>This union type allows accessing the 128-bit ID as 16 separate bytes or two 64-bit words. It is
generally safer to access the ID components by their 8-bit array to avoid endianness issues. This union
is intended to be passed by value (as opposed to pass-by-reference) and may be directly manipulated by
clients.</para>
<para>A couple of macros are defined to denote and decode 128-bit
IDs:</para>
<para><function>SD_ID128_MAKE()</function> is used to write a constant ID in source code. A commonly used
idiom is to assign a name to an ID using this macro:</para>
<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>
<para><constant>SD_ID128_NULL</constant> defines an ID consisting of only <constant>NUL</constant> bytes
(i.e. all bits off).</para>
<para><constant>SD_ID128_ALLF</constant> defines an ID consisting of only <constant>0xFF</constant> bytes
(i.e. all bits on).</para>
<para><function>SD_ID128_MAKE_STR()</function> is similar to <function>SD_ID128_MAKE()</function>, but
creates a <type>const char*</type> expression that can be conveniently used in message formats and
such:</para>
<programlisting>#include <stdio.h>
#define SD_MESSAGE_COREDUMP_STR SD_ID128_MAKE_STR(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)
int main(int argc, char **argv) {
puts("Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR);
}</programlisting>
<para><function>SD_ID128_CONST_STR()</function> converts constant IDs into constant strings for
output. The following example code will output the string "fc2e22bc6ee647b6b90729ab34a250b1":</para>
<programlisting>int main(int argc, char *argv[]) {
puts("Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
}</programlisting>
<para><constant>SD_ID128_FORMAT_STR</constant> and <function>SD_ID128_FORMAT_VAL()</function> is used to
format an ID in a <citerefentry
project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> format
string, as shown in the following example:</para>
<programlisting>int main(int argc, char *argv[]) {
sd_id128_t id;
id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
return 0;
}</programlisting>
<para><constant>SD_ID128_UUID_FORMAT_STR</constant> and <function>SD_ID128_MAKE_UUID_STR()</function>
are similar to
<constant>SD_ID128_FORMAT_STR</constant> and <function>SD_ID128_MAKE_STR()</function>,
but include separating hyphens to conform to the
"<ulink url="https://en.wikipedia.org/wiki/Universally_unique_identifier#Format">UUID canonical representation</ulink>".
They format the string based on <ulink
url="https://tools.ietf.org/html/rfc4122">RFC4122</ulink> Variant 1 rules, i.e. converting from Big
Endian byte order. This matches behaviour of most other Linux userspace infrastructure. It's probably
best to avoid UUIDs of other variants, in order to avoid unnecessary ambiguities. All 128-bit IDs
generated by the sd-id128 APIs strictly conform to Variant 1 Version 4 UUIDs, as per RFC 4122.</para>
<para><function>sd_id128_equal()</function> compares two 128-bit IDs:</para>
<programlisting>int main(int argc, char *argv[]) {
sd_id128_t a, b, c;
a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
c = a;
assert(sd_id128_equal(a, c));
assert(!sd_id128_equal(a, b));
return 0;
}</programlisting>
<para><function>sd_id128_string_equal()</function> is similar to <function>sd_id128_equal()</function>,
but the first ID is formatted as <type>const char*</type>. The same restrictions apply as to the first
argument of <function>sd_id128_from_string()</function>.</para>
<para><function>sd_id128_is_null()</function> checks if an ID consists of only <constant>NUL</constant>
bytes:</para>
<programlisting>assert(sd_id128_is_null(SD_ID128_NULL));</programlisting>
<para>Similarly, <function>sd_id128_is_allf()</function> checks if an ID consists of only
<constant>0xFF</constant> bytes (all bits on):</para>
<programlisting>assert(sd_id128_is_allf(SD_ID128_ALLF));</programlisting>
<para><function>sd_id128_in_set_sentinel()</function> takes a list of IDs and returns true if the first
argument is equal to any of the subsequent arguments. The argument list is terminated by an
<constant>SD_ID128_NULL</constant> sentinel, which must be present.</para>
<para><function>sd_id128_in_set()</function> is a convenience function that takes a list of IDs and
returns true if the first argument is equal to any of the subsequent arguments:</para>
<programlisting>int main(int argc, char *argv[]) {
sd_id12_t a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
assert(sd_id128_in_set(a, a));
assert(sd_id128_in_set(a, a, a));
assert(!sd_id128_in_set(a));
assert(!sd_id128_in_set(a,
SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e)
SD_ID128_MAKE(2f,88,28,5f,9c,44,09,9d,d7,15,77,04,bc,85,7e,e3)
SD_ID128_ALLF));
return 0;
}
</programlisting>
<para><function>sd_id128_in_set()</function> is defined as a macro over
<function>sd_id128_in_set_sentinel()</function>, adding the <constant>SD_ID128_NULL</constant> sentinel
automatically. Since <function>sd_id128_in_set_sentinel()</function> uses
<constant>SD_ID128_NULL</constant> as the sentinel, <constant>SD_ID128_NULL</constant> cannot be
otherwise placed in the argument list.</para>
<para><function>sd_id128_in_setv()</function> is similar to
<function>sd_id128_in_set_sentinel()</function>, but takes a <structname>struct varargs</structname>
argument.</para>
<para>New randomized IDs may be generated with
<citerefentry><refentrytitle>systemd-id128</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
<command>new</command> command.</para>
<para>See
<citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for information about other implemented functions.</para>
</refsect1>
<xi:include href="libsystemd-pkgconfig.xml" />
<refsect1>
<title>History</title>
<para><function>sd_id128_equal()</function>,
<function>sd_id128_string_equal()</function>,
<function>sd_id128_is_null()</function>,
<function>sd_id128_is_allf()</function>,
<function>sd_id128_in_setv()</function>,
<function>sd_id128_in_set_sentinel()</function>, and
<function>sd_id128_in_set()</function> were added in version 252.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para><simplelist type="inline">
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
<member><citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
<member><citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
<member><citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
</simplelist></para>
</refsect1>
</refentry>
|
