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

  <refentryinfo>
    <title>udev_device_new_from_syspath</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>David</firstname>
        <surname>Herrmann</surname>
        <email>dh.herrmann@gmail.com</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>udev_device_new_from_syspath</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>udev_device_new_from_syspath</refname>
    <refname>udev_device_new_from_devnum</refname>
    <refname>udev_device_new_from_subsystem_sysname</refname>
    <refname>udev_device_new_from_device_id</refname>
    <refname>udev_device_new_from_environment</refname>
    <refname>udev_device_ref</refname>
    <refname>udev_device_unref</refname>

    <refpurpose>Create, acquire and release a udev device object</refpurpose>
  </refnamediv>

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

      <funcprototype>
        <funcdef>struct udev_device *<function>udev_device_new_from_syspath</function></funcdef>
        <paramdef>struct udev *<parameter>udev</parameter></paramdef>
        <paramdef>const char *<parameter>syspath</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_device *<function>udev_device_new_from_devnum</function></funcdef>
        <paramdef>struct udev *<parameter>udev</parameter></paramdef>
        <paramdef>char <parameter>type</parameter></paramdef>
        <paramdef>dev_t <parameter>devnum</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_device *<function>udev_device_new_from_subsystem_sysname</function></funcdef>
        <paramdef>struct udev *<parameter>udev</parameter></paramdef>
        <paramdef>const char *<parameter>subsystem</parameter></paramdef>
        <paramdef>const char *<parameter>sysname</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_device *<function>udev_device_new_from_device_id</function></funcdef>
        <paramdef>struct udev *<parameter>udev</parameter></paramdef>
        <paramdef>const char *<parameter>id</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_device *<function>udev_device_new_from_environment</function></funcdef>
        <paramdef>struct udev *<parameter>udev</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_device *<function>udev_device_ref</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>struct udev_device *<function>udev_device_unref</function></funcdef>
        <paramdef>struct udev_device *<parameter>udev_device</parameter></paramdef>
      </funcprototype>

    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><function>udev_device_new_from_syspath</function>,
    <function>udev_device_new_from_devnum</function>,
    <function>udev_device_new_from_subsystem_sysname</function>,
    <function>udev_device_new_from_device_id</function>, and
    <function>udev_device_new_from_environment</function>
    allocate a new udev device object and returns a pointer to it. This
    object is opaque and must not be accessed by the caller via different
    means than functions provided by libudev. Initially, the reference count
    of the device is 1. You can acquire further references, and drop
    gained references via <function>udev_device_ref()</function> and
    <function>udev_device_unref()</function>. Once the reference count hits 0,
    the device object is destroyed and freed.</para>

    <para><function>udev_device_new_from_syspath</function>,
    <function>udev_device_new_from_devnum</function>,
    <function>udev_device_new_from_subsystem_sysname</function>, and
    <function>udev_device_new_from_device_id</function>
    create the device object based on information found in
    <filename>/sys</filename>, annotated with properties from the udev-internal
    device database. A syspath is any subdirectory of <filename>/sys</filename>,
    with the restriction that a subdirectory of <filename>/sys/devices</filename>
    (or a symlink to one) represents a real device and as such must contain
    a <filename>uevent</filename> file. <function>udev_device_new_from_devnum</function>
    takes a device type, which can be <constant>b</constant> for block devices or
    <constant>c</constant> for character devices, as well as a devnum (see
    <citerefentry project='man-pages'><refentrytitle>makedev</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
    <function>udev_device_new_from_subsystem_sysname</function> looks up devices based
    on the provided subsystem and sysname
    (see <citerefentry><refentrytitle>udev_device_get_subsystem</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    and
    <citerefentry><refentrytitle>udev_device_get_sysname</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
    and <function>udev_device_new_from_device_id</function> looks up devices based on the provided
    device ID, which is a special string in one of the following four forms:
    <table>
      <title>Device ID strings</title>

      <tgroup cols='2'>
        <colspec colname='example' />
        <colspec colname='explanation' />
        <thead><row>
          <entry>Example</entry>
          <entry>Explanation</entry>
        </row></thead>
        <tbody>
          <row><entry><varname>b8:2</varname></entry>
          <entry>block device major:minor</entry></row>

          <row><entry><varname>c128:1</varname></entry>
          <entry>char device major:minor</entry></row>

          <row><entry><varname>n3</varname></entry>
          <entry>network device ifindex</entry></row>

          <row><entry><varname>+sound:card29</varname></entry>
          <entry>kernel driver core subsystem:device name</entry></row>
        </tbody>
      </tgroup>
    </table>
    </para>

    <para><function>udev_device_new_from_environment</function>
    creates a device from the current environment (see
    <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
    Each key-value pair is interpreted in the same way as if it was
    received in an uevent (see
    <citerefentry><refentrytitle>udev_monitor_receive_device</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
    The keys <constant>DEVPATH</constant>, <constant>SUBSYSTEM</constant>,
    <constant>ACTION</constant>, and <constant>SEQNUM</constant> are mandatory.</para>

  </refsect1>

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

    <para>On success, <function>udev_device_new_from_syspath()</function>,
    <function>udev_device_new_from_devnum()</function>,
    <function>udev_device_new_from_subsystem_sysname()</function>,
    <function>udev_device_new_from_device_id()</function> and
    <function>udev_device_new_from_environment()</function> return a
    pointer to the allocated udev device. On failure,
    <constant>NULL</constant> is returned,
    and <varname>errno</varname> is set appropriately.
    <function>udev_device_ref()</function> returns the argument
    that it was passed, unmodified.
    <function>udev_device_unref()</function> always returns
    <constant>NULL</constant>.</para>
  </refsect1>

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

    <para>
      <citerefentry><refentrytitle>udev_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev_device_get_syspath</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>udev_device_has_tag</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>
