<?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>3</manvolnum> </refmeta> <refnamediv> <refname>sd-id128</refname> <refname>sd_id128_t</refname> <refname>SD_ID128_MAKE</refname> <refname>SD_ID128_CONST_STR</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>, <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry> and <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry> for more information about the implemented functions.</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 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 denote a constant 128 bit ID in source code. A commonly used idiom is to assign a name to a 128 bit 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><function>SD_ID128_CONST_STR()</function> may be used to convert constant 128bit IDs into constant strings for output. The following example code will output the string "fc2e22bc6ee647b6b90729ab34a250b1":</para> <programlisting>int main(int argc, char *argv[]) { puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP)); }</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> option.</para> </refsect1> <refsect1> <title>Notes</title> <para>These APIs are implemented as a 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>sd_id128_get_machine</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>