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1 | <?xml version='1.0'?> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
4 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> | |
5 | ||
6 | <refentry id="sd_device_ref" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
7 | <refentryinfo> | |
8 | <title>sd_device_ref</title> | |
9 | <productname>systemd</productname> | |
10 | </refentryinfo> | |
11 | ||
12 | <refmeta> | |
13 | <refentrytitle>sd_device_ref</refentrytitle> | |
14 | <manvolnum>3</manvolnum> | |
15 | </refmeta> | |
16 | ||
17 | <refnamediv> | |
18 | <refname>sd_device_ref</refname> | |
19 | <refname>sd_device_unref</refname> | |
20 | <refname>sd_device_unrefp</refname> | |
21 | ||
22 | <refpurpose>Create or destroy references to a device object</refpurpose> | |
23 | </refnamediv> | |
24 | ||
25 | <refsynopsisdiv> | |
26 | <funcsynopsis> | |
27 | <funcsynopsisinfo>#include <systemd/sd-device.h></funcsynopsisinfo> | |
28 | ||
29 | <funcprototype> | |
30 | <funcdef>sd_device* <function>sd_device_ref</function></funcdef> | |
31 | <paramdef>sd_device *<parameter>device</parameter></paramdef> | |
32 | </funcprototype> | |
33 | ||
34 | <funcprototype> | |
35 | <funcdef>sd_device* <function>sd_device_unref</function></funcdef> | |
36 | <paramdef>sd_device *<parameter>device</parameter></paramdef> | |
37 | </funcprototype> | |
38 | ||
39 | <funcprototype> | |
40 | <funcdef>void <function>sd_device_unrefp</function></funcdef> | |
41 | <paramdef>sd_device **<parameter>device</parameter></paramdef> | |
42 | </funcprototype> | |
43 | </funcsynopsis> | |
44 | ||
52e30c6f | 45 | <para><function>sd_device_ref()</function> increases the internal reference counter of |
2a1a7910 ZJS |
46 | <parameter>device</parameter> by one.</para> |
47 | ||
52e30c6f | 48 | <para><function>sd_device_unref()</function> decreases the internal reference counter of |
2a1a7910 ZJS |
49 | <parameter>device</parameter> by one. Once the reference count has dropped to zero, |
50 | <parameter>device</parameter> is destroyed and cannot be used anymore, so further calls to | |
51 | <function>sd_device_ref()</function> or <function>sd_device_unref()</function> are illegal.</para> | |
52 | ||
53 | <para><function>sd_device_unrefp()</function> is similar to <function>sd_device_unref()</function> but | |
54 | takes a pointer to a pointer to an <type>sd_device</type> object. This call is useful in conjunction with | |
55 | GCC's and LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up | |
56 | Variable Attribute</ulink>. Note that this function is defined as an inline function. Use a declaration | |
57 | like the following, in order to allocate a device object that is freed automatically as the code block is | |
58 | left:</para> | |
59 | ||
60 | <programlisting>{ | |
61 | __attribute__((cleanup(sd_device_unrefp))) sd_device *device = NULL; | |
62 | int r; | |
63 | … | |
64 | r = sd_device_new_from_syspath(&device, "…"); | |
b4096cec ZJS |
65 | if (r < 0) { |
66 | errno = -r; | |
67 | fprintf(stderr, "Failed to allocate device: %m\n"); | |
68 | } | |
2a1a7910 ZJS |
69 | … |
70 | }</programlisting> | |
71 | ||
72 | <para><function>sd_device_ref()</function> and <function>sd_device_unref()</function> execute no | |
73 | operation if the argument is <constant>NULL</constant>. <function>sd_device_unrefp()</function> will | |
74 | first dereference its argument, which must not be <constant>NULL</constant>, and will execute no | |
75 | operation if <emphasis>that</emphasis> is <constant>NULL</constant>.</para> | |
76 | </refsynopsisdiv> | |
77 | ||
78 | <refsect1> | |
79 | <title>Return Value</title> | |
80 | ||
81 | <para><function>sd_device_ref()</function> always returns the argument, and | |
82 | <function>sd_device_unref()</function> always returns <constant>NULL</constant>. | |
83 | </para> | |
84 | </refsect1> | |
69106f47 AK |
85 | <refsect1> |
86 | <title>History</title> | |
00f95506 AK |
87 | <para><function>sd_device_ref()</function>, |
88 | <function>sd_device_unref()</function>, and | |
89 | <function>sd_device_unrefp()</function> were added in version 251.</para> | |
69106f47 | 90 | </refsect1> |
2a1a7910 | 91 | </refentry> |