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We expose various other forms of UUID helpers already, i.e. SD_ID128_UUID_FORMAT_STR and SD_ID128_MAKE_UUID_STR(), and we parse UUIDs, hence add a high-level helper for formatting UUIDs too. This doesn't add any new code, it just moves some helpers id128-util.[ch] → sd-id128.[ch], to make them public.
123 lines
5.8 KiB
XML
123 lines
5.8 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_to_string" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_id128_to_string</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_to_string</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_to_string</refname>
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<refname>SD_ID128_TO_STRING</refname>
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<refname>SD_ID128_STRING_MAX</refname>
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<refname>sd_id128_to_uuid_string</refname>
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<refname>SD_ID128_TO_UUID_STRING</refname>
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<refname>SD_ID128_UUID_STRING_MAX</refname>
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<refname>sd_id128_from_string</refname>
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<refpurpose>Format or parse 128-bit IDs as strings</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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<funcsynopsisinfo>#define SD_ID128_STRING_MAX 33U</funcsynopsisinfo>
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<funcsynopsisinfo>#define SD_ID128_UUID_STRING_MAX 37U</funcsynopsisinfo>
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<funcsynopsisinfo>#define SD_ID128_TO_STRING(id) …</funcsynopsisinfo>
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<funcsynopsisinfo>#define SD_ID128_TO_UUID_STRING(id) …</funcsynopsisinfo>
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<funcprototype>
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<funcdef>char *<function>sd_id128_to_string</function></funcdef>
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<paramdef>sd_id128_t <parameter>id</parameter>, char <parameter>s</parameter>[static SD_ID128_STRING_MAX]</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>char *<function>sd_id128_uuid_string</function></funcdef>
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<paramdef>sd_id128_t <parameter>id</parameter>, char <parameter>s</parameter>[static SD_ID128_UUID_STRING_MAX]</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_id128_from_string</function></funcdef>
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<paramdef>const char *<parameter>s</parameter>, 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_to_string()</function> formats a 128-bit ID as a character string. It expects
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the ID and a string array capable of storing 33 characters
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(<constant>SD_ID128_STRING_MAX</constant>). The ID will be formatted as 32 lowercase hexadecimal digits
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and be terminated by a <constant>NUL</constant> byte.</para>
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<para><function>SD_ID128_TO_STRING()</function> is a macro that wraps
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<function>sd_id128_to_string()</function> and passes an appropriately sized buffer as second argument,
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allocated as C99 compound literal. Each use will thus implicitly acquire a suitable buffer on the stack
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which remains valid until the end of the current code block. This is usually the simplest way to acquire
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a string representation of a 128-bit ID in a buffer that is valid in the current code block.</para>
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<para><function>sd_id128_to_uuid_string()</function> and <function>SD_ID128_TO_UUID_STRING()</function>
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are similar to these two functions/macros, but format the 128bit values as RFC4122 UUIDs, i.e. a series
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of 36 lowercase hexadeciaml digits and dashes, terminated by a <constant>NUL</constant> byte.</para>
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<para><function>sd_id128_from_string()</function> implements the reverse operation: it takes a 33
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character string with 32 hexadecimal digits (either lowercase or uppercase, terminated by
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<constant>NUL</constant>) and parses them back into a 128-bit ID returned in
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<parameter>ret</parameter>. Alternatively, this call can also parse a 37-character string with a 128-bit
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ID formatted as RFC UUID. If <parameter>ret</parameter> is passed as <constant>NULL</constant> the
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function will validate the passed ID string, but not actually return it in parsed form.</para>
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<para>Note that when formatting and parsing 36 character UUIDs this is done strictly in Big Endian byte order,
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i.e. according to <ulink url="https://tools.ietf.org/html/rfc4122">RFC4122</ulink> Variant 1 rules, even
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if the UUID encodes a different variant. This matches behaviour in various other Linux userspace
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tools. It's probably wise to avoid UUIDs of other variant types.</para>
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<para>For more information about the <literal>sd_id128_t</literal> type see
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<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>. Note that
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these calls operate the same way on all architectures, i.e. the results do not depend on
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endianness.</para>
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<para>When formatting a 128-bit ID into a string, it is often easier to use a format string for
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<citerefentry
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project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This
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is easily done using the <constant>SD_ID128_FORMAT_STR</constant> and
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<function>SD_ID128_FORMAT_VAL()</function> macros. For more information see
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<citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para><function>sd_id128_to_string()</function> always succeeds and returns a pointer to the string array
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passed in. <function>sd_id128_from_string()</function> returns 0 on success, in which case
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<parameter>ret</parameter> is filled in, or a negative 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 project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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