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<refentry id="udev_device_has_tag"
  xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>udev_device_has_tag</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>udev_device_has_tag</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>udev_device_has_tag</refname>
    <refname>udev_device_has_current_tag</refname>
    <refname>udev_device_get_devlinks_list_entry</refname>
    <refname>udev_device_get_properties_list_entry</refname>
    <refname>udev_device_get_tags_list_entry</refname>
    <refname>udev_device_get_current_tags_list_entry</refname>
    <refname>udev_device_get_sysattr_list_entry</refname>
    <refname>udev_device_get_property_value</refname>
    <refname>udev_device_get_sysattr_value</refname>
    <refname>udev_device_set_sysattr_value</refname>

    <refpurpose>Retrieve or set device attributes</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;libudev.h&gt;</funcsynopsisinfo>

      <funcprototype>
        <funcdef>int <function>udev_device_has_tag</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
        <paramdef>const char *<parameter>tag</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>udev_device_has_current_tag</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
        <paramdef>const char *<parameter>tag</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_list_entry *<function>udev_device_get_devlinks_list_entry</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_list_entry *<function>udev_device_get_properties_list_entry</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_list_entry *<function>udev_device_get_tags_list_entry</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_list_entry *<function>udev_device_get_current_tags_list_entry</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_list_entry *<function>udev_device_get_sysattr_list_entry</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>const char *<function>udev_device_get_property_value</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
        <paramdef>const char *<parameter>key</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>const char *<function>udev_device_get_sysattr_value</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
        <paramdef>const char *<parameter>sysattr</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>udev_device_set_sysattr_value</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
        <paramdef>const char *<parameter>sysattr</parameter></paramdef>
        <paramdef>const char *<parameter>value</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>udev_device_has_tag()</function> returns a valuer larger than zero if the specified
    device object has the indicated tag assigned to it, and zero otherwise. See
    <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details on
    the tags concept. <function>udev_device_has_current_tag()</function> executes a similar check, however
    only determines whether the indicated tag was set as result of the most recent event seen for the
    device. Tags are "sticky", i.e. once set for a device they remain on the device until the device is
    unplugged, even if the rules run for later events of the same device do not set them anymore. Any tag for
    which <function>udev_device_has_current_tag()</function> returns true will hence also return true when
    passed to <function>udev_device_has_tag()</function>, but the opposite might not be true, in case a tag is
    no longer configured by the rules applied to the most recent device even.</para>

    <para><function>udev_device_get_tags_list_entry()</function> returns a
    <structname>udev_list_entry</structname> object, encapsulating a list of tags set for the specified
    device. Similar, <function>udev_device_get_current_tags_list_entry()</function> returns a list of tags
    set for the specified device as effect of the most recent device event seen (see above for details on the
    difference).</para>
  </refsect1>

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

    <para>On success, <function>udev_device_has_tag()</function> and
    <function>udev_device_has_current_tag()</function> return positive or <constant>0</constant>, depending
    on whether the device has the given tag or not.  On failure, a negative error code is returned.</para>

    <para>On success, <function>udev_device_get_devlinks_list_entry()</function>,
    <function>udev_device_get_properties_list_entry()</function>,
    <function>udev_device_get_tags_list_entry()</function>,
    <function>udev_device_get_current_tags_list_entry()</function> and
    <function>udev_device_get_sysattr_list_entry()</function> return a pointer to the first entry of the
    retrieved list. If that list is empty, or if an error occurred, <constant>NULL</constant> is
    returned.</para>

    <para>On success,
    <function>udev_device_get_property_value()</function> and
    <function>udev_device_get_sysattr_value()</function> return a
    pointer to a constant string of the requested value. On error,
    <constant>NULL</constant> is returned. Attributes that may
    contain <constant>NUL</constant> bytes should not be retrieved
    with <function>udev_device_get_sysattr_value()</function>;
    instead, read them directly from the files within the device's
    <property>syspath</property>.</para>

    <para>On success,
    <function>udev_device_set_sysattr_value()</function> returns
    an integer greater than, or equal to, <constant>0</constant>.
    On failure, a negative error code is returned. Values that
    contain <constant>NUL</constant> bytes should not be set with
    this function; instead, write them directly to the files within
    the device's <property>syspath</property>.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>

    <para>
      <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev_device_new_from_syspath</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev_device_get_syspath</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev_enumerate_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev_monitor_new_from_netlink</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev_list_entry</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
    </para>
  </refsect1>

</refentry>
