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https://github.com/systemd/systemd.git
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167 lines
6.5 KiB
XML
167 lines
6.5 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2012 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd-id128"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd-id128</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd-id128</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd-id128</refname>
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<refname>sd_id128_t</refname>
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<refname>SD_ID128_MAKE</refname>
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<refname>SD_ID128_CONST_STR</refname>
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<refname>SD_ID128_FORMAT_STR</refname>
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<refname>SD_ID128_FORMAT_VAL</refname>
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<refname>sd_id128_equal</refname>
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<refpurpose>APIs for processing 128-bit IDs</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo>
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</funcsynopsis>
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<cmdsynopsis>
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<command>pkg-config --cflags --libs libsystemd</command>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>sd-id128.h</filename> provides APIs to process and
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generate 128-bit ID values. The 128-bit ID values processed and
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generated by these APIs are a generalization of OSF UUIDs as
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defined by <ulink url="https://tools.ietf.org/html/rfc4122">RFC
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4122</ulink> but use a simpler string format. These functions
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impose no structure on the used IDs, much unlike OSF UUIDs or
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Microsoft GUIDs, but are fully compatible with those types of IDs.
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</para>
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<para>See
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<citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for more information about the implemented functions.</para>
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<para>A 128-bit ID is implemented as the following
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union type:</para>
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<programlisting>typedef union sd_id128 {
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uint8_t bytes[16];
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uint64_t qwords[2];
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} sd_id128_t;</programlisting>
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<para>This union type allows accessing the 128-bit ID as 16
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separate bytes or two 64-bit words. It is generally safer to
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access the ID components by their 8-bit array to avoid endianness
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issues. This union is intended to be passed call-by-value (as
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opposed to call-by-reference) and may be directly manipulated by
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clients.</para>
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<para>A couple of macros are defined to denote and decode 128-bit
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IDs:</para>
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<para><function>SD_ID128_MAKE()</function> may be used to denote a
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constant 128-bit ID in source code. A commonly used idiom is to
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assign a name to a 128-bit ID using this macro:</para>
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<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>
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<para><function>SD_ID128_CONST_STR()</function> may be used to
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convert constant 128-bit IDs into constant strings for output. The
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following example code will output the string
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"fc2e22bc6ee647b6b90729ab34a250b1":</para>
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<programlisting>int main(int argc, char *argv[]) {
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puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
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}</programlisting>
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<para><function>SD_ID128_FORMAT_STR</function> and
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<function>SD_ID128_FORMAT_VAL()</function> may be used to format a
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128-bit ID in a
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<citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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format string, as shown in the following example:</para>
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<programlisting>int main(int argc, char *argv[]) {
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sd_id128_t id;
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id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
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printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
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return 0;
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}</programlisting>
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<para>Use <function>sd_id128_equal()</function> to compare two 128-bit IDs:</para>
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<programlisting>int main(int argc, char *argv[]) {
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sd_id128_t a, b, c;
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a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
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b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
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c = a;
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assert(sd_id128_equal(a, c));
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assert(!sd_id128_equal(a, b));
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return 0;
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}</programlisting>
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<para>Note that new, randomized IDs may be generated with
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<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
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<option>--new-id</option> option.</para>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_id128_to_string</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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