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+<?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">
+
+<!--
+  This file is part of systemd.
+
+  Copyright 2012 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd-id128">
+
+        <refentryinfo>
+                <title>sd-id128</title>
+                <productname>systemd</productname>
+
+                <authorgroup>
+                        <author>
+                                <contrib>Developer</contrib>
+                                <firstname>Lennart</firstname>
+                                <surname>Poettering</surname>
+                                <email>lennart@poettering.net</email>
+                        </author>
+                </authorgroup>
+        </refentryinfo>
+
+        <refmeta>
+                <refentrytitle>sd-id128</refentrytitle>
+                <manvolnum>7</manvolnum>
+        </refmeta>
+
+        <refnamediv>
+                <refname>sd-id128</refname>
+                <refname>sd_id128_t</refname>
+                <refname>SD_ID128_MAKE</refname>
+                <refname>SD_ID128_FORMAT_STR</refname>
+                <refname>SD_ID128_FORMAT_VAL</refname>
+                <refname>sd_id128_equal</refname>
+                <refpurpose>APIs for processing 128 bit IDs</refpurpose>
+        </refnamediv>
+
+        <refsynopsisdiv>
+                <funcsynopsis>
+                        <funcsynopsisinfo>#include &lt;systemd/sd-id128.h&gt;</funcsynopsisinfo>
+                </funcsynopsis>
+
+                <cmdsynopsis>
+                        <command>pkg-config --cflags --libs libsystemd-id128</command>
+                </cmdsynopsis>
+
+        </refsynopsisdiv>
+
+        <refsect1>
+                <title>Description</title>
+
+                <para><filename>sd-id128.h</filename> provides APIs to
+                process and generate 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="http://tools.ietf.org/html/rfc4122">RFC
+                4122</ulink>, though use a simpler string
+                formatting. These functions impose no structure on the
+                used IDs, much unlike OSF UUIDs or Microsoft GUIDs,
+                but are fully compatible with those types of IDs.
+                </para>
+
+                <para>See
+                <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
+                <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                for more information about the functions
+                implemented.</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 2 64 bit words. It is generally
+                safer to access the ID components by their 8 bit array
+                to avoid endianess issues. This union is intended to
+                be passed call-by-value (as opposed to
+                call-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> may be used
+                to write a 128 bit ID in source code. A commonly used
+                idiom is to give 128 bit IDs names 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><function>SD_ID128_FORMAT_STR</function> and
+                <function>SD_ID128_FORMAT_VAL()</function> may be used
+                to format a 128 bit ID in a
+                <citerefentry><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>Use <function>sd_id128_equal()</function> to compare 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>Note that new, randomized IDs may be generated
+                with
+                <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
+                <literal>--new-id</literal> command.</para>
+        </refsect1>
+
+        <refsect1>
+                <title>Notes</title>
+
+                <para>These APIs are implemented as shared library,
+                which can be compiled and linked to with the
+                <literal>libsystemd-id128</literal>
+                <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+                file.</para>
+
+        </refsect1>
+
+        <refsect1>
+                <title>See Also</title>
+                <para>
+                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+                </para>
+        </refsect1>
+
+</refentry>