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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><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><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.

<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>