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| <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
| "http://www.oasis-open.org/docbook/xml/4.2/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> |
| </refentry> |