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6f75309295
This is the case because the ID128 we generate are all marked as v4 UUID which requires that some bits are zero and others are one. Let's document this so that people can rely on SD_ID128_NULL being a special value for "uninitialized" that is always distinguishable from generated UUIDs.
81 lines
2.9 KiB
XML
81 lines
2.9 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_id128_randomize" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_id128_randomize</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_id128_randomize</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_randomize</refname>
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<refpurpose>Generate 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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<funcprototype>
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<funcdef>int <function>sd_id128_randomize</function></funcdef>
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<paramdef>sd_id128_t *<parameter>ret</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_id128_randomize()</function> generates a new
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randomized 128-bit ID and returns it in
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<parameter>ret</parameter>. Every invocation returns a new
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randomly generated ID. This uses the
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<filename>/dev/urandom</filename> kernel random number
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generator.</para>
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<para>Note that <function>sd_id128_randomize()</function> always returns a UUID v4-compatible ID. It is
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hence guaranteed that this function will never return the ID consisting of all zero or all one bits
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(<constant>SD_ID128_NULL</constant>, <constant>SD_ID128_ALLF</constant>).</para>
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<para>For more information about the <literal>sd_id128_t</literal>
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type, see
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<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para><citerefentry><refentrytitle>systemd-id128</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
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<command>new</command> command may be used as a command line front-end for
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<function>sd_id128_randomize()</function>.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>The call returns 0 on success (in which case
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<parameter>ret</parameter> is filled in), or a negative
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errno-style error code.</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</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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