systemd/man/sd_device_enumerator_new.xml

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  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<refentry id="sd_device_enumerator_new" xmlns:xi="http://www.w3.org/2001/XInclude">
  <refentryinfo>
    <title>sd_device_enumerator_new</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>sd_device_enumerator_new</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd_device_enumerator_new</refname>
    <refname>sd_device_enumerator_ref</refname>
    <refname>sd_device_enumerator_unref</refname>
    <refname>sd_device_enumerator_unrefp</refname>
    <refpurpose>Create, reference, and release a device enumerator object</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-device.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>sd_device_enumerator_new</function></funcdef>
        <paramdef>sd_device_enumerator **<parameter>ret</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>sd_device_enumerator* <function>sd_device_enumerator_ref</function></funcdef>
        <paramdef>sd_device_enumerator *<parameter>enumerator</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>sd_device_enumerator* <function>sd_device_enumerator_unref</function></funcdef>
        <paramdef>sd_device_enumerator *<parameter>enumerator</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>void <function>sd_device_enumerator_unrefp</function></funcdef>
        <paramdef>sd_device_enumerator **<parameter>enumerator</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>
    <para>The <function>sd_device_enumerator</function> family of functions provides a way to iterate
    over devices recognized by <citerefentry><refentrytitle>systemd-udevd</refentrytitle><manvolnum>8</manvolnum>
    </citerefentry>. The enumerator allows filtering and matching devices by subsystem, properties and
    other attributes.</para>

    <para><function>sd_device_enumerator_new()</function> creates a new device enumerator object and
    stores the result in the pointer referenced by <parameter>ret</parameter>. Returns 0 on success,
    or a negative errno-style error code on failure.</para>

    <para><function>sd_device_enumerator_ref()</function> increases the reference count of the
    specified <parameter>enumerator</parameter> by one.</para>

    <para><function>sd_device_enumerator_unref()</function> decreases the reference count of the
    <parameter>enumerator</parameter> by one. When the reference count reaches zero, the enumerator
    object is destroyed and cannot be used anymore, so further calls to <function>sd_device_enumerator_unref()
    </function> or <function>sd_device_enumerator_unrefp()</function> are illegal.</para>

    <para><function>sd_device_enumerator_unrefp()</function> is similar to
    <function>sd_device_enumerator_unref()</function> but takes a pointer to a
    pointer to an <type>sd_device_enumerator</type> object. This call is useful in
    conjunction with GCC's and LLVM's <ulink
    url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
    Variable Attribute</ulink>. Note that this function is defined as an
    inline function. Use a declaration like the following, in order to
    allocate a <type>sd_device_enumerator</type> object that is freed automatically as the code
    block is left:</para>

    <programlisting>{
  __attribute__((cleanup(sd_device_enumerator_unrefp))) sd_device_enumerator *enumerator = NULL;
  int r;
  …
  r = sd_device_enumerator_new(&amp;enumerator);
  if (r &lt; 0)
    fprintf(stderr, "Failed to allocate sd_device_enumerator: %s\n", strerror(-r));
  …
}</programlisting>

    <para><function>sd_device_enumerator_ref()</function> and <function>sd_device_enumerator_unref()</function>
    execute no operation if the <parameter>enumerator</parameter> is <constant>NULL</constant>.
    <function>sd_device_enumerator_unrefp()</function> will first dereference
    its argument, which must not be <constant>NULL</constant>, and will execute no operation if
    <emphasis>that</emphasis> is <constant>NULL</constant>.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para><function>sd_device_enumerator_new()</function> returns 0 on success or a negative
    errno-style error code on failure.</para>

    <para><function>sd_device_enumerator_ref()</function> always returns the enumerator pointer.</para>
    <para><function>sd_device_enumerator_unref()</function> always returns <constant>NULL</constant>.</para>

    <refsect2>
      <title>Errors</title>

      <para>Returned errors may indicate the following problems:</para>

      <variablelist>
        <varlistentry>
          <term><constant>-ENOMEM</constant></term>

          <listitem><para>Memory allocation failed.</para></listitem>
        </varlistentry>
        <varlistentry>
          <term><constant>-EINVAL</constant></term>

          <listitem><para>The argument is invalid.</para></listitem>
        </varlistentry>
      </variablelist>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Example</title>
    <example>
      <title>Using sd_device_enumerator_new()</title>
      <programlisting><xi:include href="sd_device_enumerator_new-example.c" parse="text"/></programlisting>
    </example>
  </refsect1>

  <refsect1>
    <title>History</title>
    <para><function>sd_device_enumerator_new()</function>, <function>sd_device_enumerator_ref()</function>,
    <function>sd_device_enumerator_unref()</function>, and <function>sd_device_enumerator_unrefp()</function>
    were added in version 240.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>sd_device_ref</refentrytitle><manvolnum>3</manvolnum>
      </citerefentry></member>
      <member><citerefentry><refentrytitle>sd_device_enumerator_add_match_parent</refentrytitle>
      <manvolnum>3</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>