mirror of
https://github.com/systemd/systemd.git
synced 2024-12-22 17:35:35 +03:00
92 lines
3.6 KiB
XML
92 lines
3.6 KiB
XML
<?xml version='1.0'?>
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
|
|
|
|
<refentry id="sd_device_ref" xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
<refentryinfo>
|
|
<title>sd_device_ref</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>sd_device_ref</refentrytitle>
|
|
<manvolnum>3</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>sd_device_ref</refname>
|
|
<refname>sd_device_unref</refname>
|
|
<refname>sd_device_unrefp</refname>
|
|
|
|
<refpurpose>Create or destroy references to a device object</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<funcsynopsis>
|
|
<funcsynopsisinfo>#include <systemd/sd-device.h></funcsynopsisinfo>
|
|
|
|
<funcprototype>
|
|
<funcdef>sd_device* <function>sd_device_ref</function></funcdef>
|
|
<paramdef>sd_device *<parameter>device</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>sd_device* <function>sd_device_unref</function></funcdef>
|
|
<paramdef>sd_device *<parameter>device</parameter></paramdef>
|
|
</funcprototype>
|
|
|
|
<funcprototype>
|
|
<funcdef>void <function>sd_device_unrefp</function></funcdef>
|
|
<paramdef>sd_device **<parameter>device</parameter></paramdef>
|
|
</funcprototype>
|
|
</funcsynopsis>
|
|
|
|
<para><function>sd_device_ref()</function> increases the internal reference counter of
|
|
<parameter>device</parameter> by one.</para>
|
|
|
|
<para><function>sd_device_unref()</function> decreases the internal reference counter of
|
|
<parameter>device</parameter> by one. Once the reference count has dropped to zero,
|
|
<parameter>device</parameter> is destroyed and cannot be used anymore, so further calls to
|
|
<function>sd_device_ref()</function> or <function>sd_device_unref()</function> are illegal.</para>
|
|
|
|
<para><function>sd_device_unrefp()</function> is similar to <function>sd_device_unref()</function> but
|
|
takes a pointer to a pointer to an <type>sd_device</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 device object that is freed automatically as the code block is
|
|
left:</para>
|
|
|
|
<programlisting>{
|
|
__attribute__((cleanup(sd_device_unrefp))) sd_device *device = NULL;
|
|
int r;
|
|
…
|
|
r = sd_device_new_from_syspath(&device, "…");
|
|
if (r < 0) {
|
|
errno = -r;
|
|
fprintf(stderr, "Failed to allocate device: %m\n");
|
|
}
|
|
…
|
|
}</programlisting>
|
|
|
|
<para><function>sd_device_ref()</function> and <function>sd_device_unref()</function> execute no
|
|
operation if the argument is <constant>NULL</constant>. <function>sd_device_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>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Return Value</title>
|
|
|
|
<para><function>sd_device_ref()</function> always returns the argument, and
|
|
<function>sd_device_unref()</function> always returns <constant>NULL</constant>.
|
|
</para>
|
|
</refsect1>
|
|
<refsect1>
|
|
<title>History</title>
|
|
<para><function>sd_device_ref()</function>,
|
|
<function>sd_device_unref()</function>, and
|
|
<function>sd_device_unrefp()</function> were added in version 251.</para>
|
|
</refsect1>
|
|
</refentry>
|