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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 <systemd/sd-id128.h></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>
~ianmdlvl / elogind.git / blobdiff