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<a href="systemd.directives.html">Directives </a>·
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<a href="../libudev/index.html">libudev </a>·
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 219</span><hr><div class="refentry"><a name="sd-id128"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd-id128, sd_id128_t, SD_ID128_MAKE, SD_ID128_CONST_STR, SD_ID128_FORMAT_STR, SD_ID128_FORMAT_VAL, sd_id128_equal — APIs for processing 128-bit IDs</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include <systemd/sd-id128.h></pre></div><div class="cmdsynopsis"><p><code class="command">pkg-config --cflags --libs libsystemd</code> </p></div></div><div class="refsect1"><a name="idm140147783872816"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="filename">sd-id128.h</code> 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 <a class="ulink" href="https://tools.ietf.org/html/rfc4122" target="_top">RFC
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4122</a> 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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</p><p>See
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<a href="sd_id128_to_string.html"><span class="citerefentry"><span class="refentrytitle">sd_id128_to_string</span>(3)</span></a>,
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<a href="sd_id128_randomize.html"><span class="citerefentry"><span class="refentrytitle">sd_id128_randomize</span>(3)</span></a>
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and
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<a href="sd_id128_get_machine.html"><span class="citerefentry"><span class="refentrytitle">sd_id128_get_machine</span>(3)</span></a>
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for more information about the implemented functions.</p><p>A 128-bit ID is implemented as the following
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union type:</p><pre class="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;</pre><p>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.</p><p>A couple of macros are defined to denote and decode 128-bit
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IDs:</p><p><code class="function">SD_ID128_MAKE()</code> 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:</p><pre class="programlisting">#define SD_MESSAGE_COREDUMP SD_ID128_MAKE(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)</pre><p><code class="function">SD_ID128_CONST_STR()</code> 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":</p><pre class="programlisting">int main(int argc, char *argv[]) {
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puts(SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));
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}</pre><p><code class="function">SD_ID128_FORMAT_STR</code> and
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<code class="function">SD_ID128_FORMAT_VAL()</code> may be used to format a
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128-bit ID in a
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<a href="http://man7.org/linux/man-pages/man3/printf.3.html"><span class="citerefentry"><span class="refentrytitle">printf</span>(3)</span></a>
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format string, as shown in the following example:</p><pre class="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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}</pre><p>Use <code class="function">sd_id128_equal()</code> to compare two 128-bit IDs:</p><pre class="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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}</pre><p>Note that new, randomized IDs may be generated with
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<a href="journalctl.html"><span class="citerefentry"><span class="refentrytitle">journalctl</span>(1)</span></a>'s
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<code class="option">--new-id</code> option.</p></div><div class="refsect1"><a name="idm140147774744128"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p><a name="pkgconfig-text"></a>These APIs are implemented as a shared
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library, which can be compiled and linked to with the
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<code class="constant">libsystemd</code> <a href="http://linux.die.net/man/1/pkg-config"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
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file.</p></div><div class="refsect1"><a name="idm140147783971584"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
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<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
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<a href="sd_id128_to_string.html"><span class="citerefentry"><span class="refentrytitle">sd_id128_to_string</span>(3)</span></a>,
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<a href="sd_id128_randomize.html"><span class="citerefentry"><span class="refentrytitle">sd_id128_randomize</span>(3)</span></a>,
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<a href="sd_id128_get_machine.html"><span class="citerefentry"><span class="refentrytitle">sd_id128_get_machine</span>(3)</span></a>,
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<a href="http://man7.org/linux/man-pages/man3/printf.3.html"><span class="citerefentry"><span class="refentrytitle">printf</span>(3)</span></a>,
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<a href="journalctl.html"><span class="citerefentry"><span class="refentrytitle">journalctl</span>(1)</span></a>,
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<a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(7)</span></a>,
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<a href="http://linux.die.net/man/1/pkg-config"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>,
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<a href="machine-id.html"><span class="citerefentry"><span class="refentrytitle">machine-id</span>(5)</span></a>
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</p></div></div></body></html>
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