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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>udev_device_new_from_syspath</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><style>
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<span style="float:right">systemd 221</span><hr><div class="refentry"><a name="udev_device_new_from_syspath"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>udev_device_new_from_syspath, udev_device_new_from_devnum, udev_device_new_from_subsystem_sysname, udev_device_new_from_device_id, udev_device_new_from_environment, udev_device_ref, udev_device_unref — Create, acquire and release a udev device object</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include <libudev.h></pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">struct udev_device *<b class="fsfunc">udev_device_new_from_syspath</b>(</code></td><td>struct udev *<var class="pdparam">udev</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">syspath</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">struct udev_device *<b class="fsfunc">udev_device_new_from_devnum</b>(</code></td><td>struct udev *<var class="pdparam">udev</var>, </td></tr><tr><td> </td><td>char <var class="pdparam">type</var>, </td></tr><tr><td> </td><td>dev_t <var class="pdparam">devnum</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">struct udev_device *<b class="fsfunc">udev_device_new_from_subsystem_sysname</b>(</code></td><td>struct udev *<var class="pdparam">udev</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">subsystem</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">sysname</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">struct udev_device *<b class="fsfunc">udev_device_new_from_device_id</b>(</code></td><td>struct udev *<var class="pdparam">udev</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">id</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">struct udev_device *<b class="fsfunc">udev_device_new_from_environment</b>(</code></td><td>struct udev *<var class="pdparam">udev</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">struct udev_device *<b class="fsfunc">udev_device_ref</b>(</code></td><td>struct udev_device *<var class="pdparam">udev_device</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">struct udev_device *<b class="fsfunc">udev_device_unref</b>(</code></td><td>struct udev_device *<var class="pdparam">udev_device</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm47609277648160"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">udev_device_new_from_syspath</code>,
<code class="function">udev_device_new_from_devnum</code>,
<code class="function">udev_device_new_from_subsystem_sysname</code>,
<code class="function">udev_device_new_from_device_id</code>, and
<code class="function">udev_device_new_from_environment</code>
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 <code class="function">udev_device_ref()</code> and
<code class="function">udev_device_unref()</code>. Once the reference count hits 0,
the device object is destroyed and freed.</p><p><code class="function">udev_device_new_from_syspath</code>,
<code class="function">udev_device_new_from_devnum</code>,
<code class="function">udev_device_new_from_subsystem_sysname</code>, and
<code class="function">udev_device_new_from_device_id</code>
create the device object based on information found in
<code class="filename">/sys</code> annotated with properties from the udev-internal
device database. A syspath is any subdirectory of <code class="filename">/sys</code>,
with the restriction that a subdirectory of <code class="filename">/sys/devices</code>
(or a symlink to one) represents a real device and as such must contain
a <code class="filename">uevent</code> file. <code class="function">udev_device_new_from_devnum</code>
takes a device type, which can be <code class="constant">b</code> for block devices or
<code class="constant">c</code> for character devices, as well as a devnum (see
<a href="makedev.html"><span class="citerefentry"><span class="refentrytitle">makedev</span>(3)</span></a>).
<code class="function">udev_device_new_from_subsystem_sysname</code> looks up devices based
on the provided subsystem and sysname
(see <a href="udev_device_get_subsystem.html"><span class="citerefentry"><span class="refentrytitle">udev_device_get_subsystem</span>(3)</span></a>
and
<a href="udev_device_get_sysname.html"><span class="citerefentry"><span class="refentrytitle">udev_device_get_sysname</span>(3)</span></a>)
and <code class="function">udev_device_new_from_device_id</code> looks up devices based on the provided
device id which is a special string in one of the following four forms:
</p><div class="table"><a name="idm47609277632032"></a><p class="title"><b>Table 1. Device ID strings</b></p><div class="table-contents"><table summary="Device ID strings" border="1"><colgroup><col class="example"><col class="explanation"></colgroup><thead><tr><th>Example</th><th>Explanation</th></tr></thead><tbody><tr><td><code class="varname">b8:2</code></td><td>block device major:minor</td></tr><tr><td><code class="varname">c128:1</code></td><td>char device major:minor</td></tr><tr><td><code class="varname">n3</code></td><td>network device ifindex</td></tr><tr><td><code class="varname">+sound:card29</code></td><td>kernel driver core subsystem:device name</td></tr></tbody></table></div></div><p><br class="table-break">
</p><p><code class="function">udev_device_new_from_environment</code>
creates a device from the current environment (see
<a href="environ.html"><span class="citerefentry"><span class="refentrytitle">environ</span>(7)</span></a>).
Each key-value pair is interpreted in the same way as if it was
received in an uevent (see
<a href="udev_monitor_receive_device.html"><span class="citerefentry"><span class="refentrytitle">udev_monitor_receive_device</span>(3)</span></a>).
The keys <code class="constant">DEVPATH</code>, <code class="constant">SUBSYSTEM</code>,
<code class="constant">ACTION</code>, and <code class="constant">SEQNUM</code> are mandatory.</p></div><div class="refsect1"><a name="idm47609277619552"></a><h2 id="Return Value">Return Value<a class="headerlink" title="Permalink to this headline" href="#Return%20Value">¶</a></h2><p>On success, <code class="function">udev_device_new_from_syspath()</code>,
<code class="function">udev_device_new_from_devnum()</code>,
<code class="function">udev_device_new_from_subsystem_sysname()</code>,
<code class="function">udev_device_new_from_device_id()</code> and
<code class="function">udev_device_new_from_environment()</code> return a
pointer to the allocated udev device. On failure,
<code class="constant">NULL</code> is returned.
<code class="function">udev_device_ref()</code> returns the argument
that it was passed, unmodified.
<code class="function">udev_device_unref()</code> always returns
<code class="constant">NULL</code>.</p></div><div class="refsect1"><a name="idm47609277613264"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
<a href="udev_new.html"><span class="citerefentry"><span class="refentrytitle">udev_new</span>(3)</span></a>,
<a href="udev_device_get_syspath.html"><span class="citerefentry"><span class="refentrytitle">udev_device_get_syspath</span>(3)</span></a>,
<a href="udev_device_has_tag.html"><span class="citerefentry"><span class="refentrytitle">udev_device_has_tag</span>(3)</span></a>,
<a href="udev_enumerate_new.html"><span class="citerefentry"><span class="refentrytitle">udev_enumerate_new</span>(3)</span></a>,
<a href="udev_monitor_new_from_netlink.html"><span class="citerefentry"><span class="refentrytitle">udev_monitor_new_from_netlink</span>(3)</span></a>,
<a href="udev_list_entry.html"><span class="citerefentry"><span class="refentrytitle">udev_list_entry</span>(3)</span></a>,
<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
</p></div></div></body></html>
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