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8e080c2e MCC |
1 | <refentry id="func-open"> |
2 | <refmeta> | |
3 | <refentrytitle>V4L2 open()</refentrytitle> | |
4 | &manvol; | |
5 | </refmeta> | |
6 | ||
7 | <refnamediv> | |
8 | <refname>v4l2-open</refname> | |
9 | <refpurpose>Open a V4L2 device</refpurpose> | |
10 | </refnamediv> | |
11 | ||
12 | <refsynopsisdiv> | |
13 | <funcsynopsis> | |
14 | <funcsynopsisinfo>#include <fcntl.h></funcsynopsisinfo> | |
15 | <funcprototype> | |
16 | <funcdef>int <function>open</function></funcdef> | |
17 | <paramdef>const char *<parameter>device_name</parameter></paramdef> | |
18 | <paramdef>int <parameter>flags</parameter></paramdef> | |
19 | </funcprototype> | |
20 | </funcsynopsis> | |
21 | </refsynopsisdiv> | |
22 | ||
23 | <refsect1> | |
24 | <title>Arguments</title> | |
25 | ||
26 | <variablelist> | |
27 | <varlistentry> | |
28 | <term><parameter>device_name</parameter></term> | |
29 | <listitem> | |
30 | <para>Device to be opened.</para> | |
31 | </listitem> | |
32 | </varlistentry> | |
33 | <varlistentry> | |
34 | <term><parameter>flags</parameter></term> | |
35 | <listitem> | |
36 | <para>Open flags. Access mode must be | |
37 | <constant>O_RDWR</constant>. This is just a technicality, input devices | |
38 | still support only reading and output devices only writing.</para> | |
39 | <para>When the <constant>O_NONBLOCK</constant> flag is | |
40 | given, the read() function and the &VIDIOC-DQBUF; ioctl will return | |
41 | the &EAGAIN; when no data is available or no buffer is in the driver | |
42 | outgoing queue, otherwise these functions block until data becomes | |
43 | available. All V4L2 drivers exchanging data with applications must | |
44 | support the <constant>O_NONBLOCK</constant> flag.</para> | |
45 | <para>Other flags have no effect.</para> | |
46 | </listitem> | |
47 | </varlistentry> | |
48 | </variablelist> | |
49 | </refsect1> | |
50 | <refsect1> | |
51 | <title>Description</title> | |
52 | ||
53 | <para>To open a V4L2 device applications call | |
54 | <function>open()</function> with the desired device name. This | |
55 | function has no side effects; all data format parameters, current | |
56 | input or output, control values or other properties remain unchanged. | |
57 | At the first <function>open()</function> call after loading the driver | |
58 | they will be reset to default values, drivers are never in an | |
59 | undefined state.</para> | |
60 | </refsect1> | |
61 | <refsect1> | |
62 | <title>Return Value</title> | |
63 | ||
64 | <para>On success <function>open</function> returns the new file | |
65 | descriptor. On error -1 is returned, and the <varname>errno</varname> | |
66 | variable is set appropriately. Possible error codes are:</para> | |
67 | ||
68 | <variablelist> | |
69 | <varlistentry> | |
70 | <term><errorcode>EACCES</errorcode></term> | |
71 | <listitem> | |
72 | <para>The caller has no permission to access the | |
73 | device.</para> | |
74 | </listitem> | |
75 | </varlistentry> | |
76 | <varlistentry> | |
77 | <term><errorcode>EBUSY</errorcode></term> | |
78 | <listitem> | |
79 | <para>The driver does not support multiple opens and the | |
80 | device is already in use.</para> | |
81 | </listitem> | |
82 | </varlistentry> | |
83 | <varlistentry> | |
84 | <term><errorcode>ENXIO</errorcode></term> | |
85 | <listitem> | |
86 | <para>No device corresponding to this device special file | |
87 | exists.</para> | |
88 | </listitem> | |
89 | </varlistentry> | |
90 | <varlistentry> | |
91 | <term><errorcode>ENOMEM</errorcode></term> | |
92 | <listitem> | |
93 | <para>Not enough kernel memory was available to complete the | |
94 | request.</para> | |
95 | </listitem> | |
96 | </varlistentry> | |
97 | <varlistentry> | |
98 | <term><errorcode>EMFILE</errorcode></term> | |
99 | <listitem> | |
100 | <para>The process already has the maximum number of | |
101 | files open.</para> | |
102 | </listitem> | |
103 | </varlistentry> | |
104 | <varlistentry> | |
105 | <term><errorcode>ENFILE</errorcode></term> | |
106 | <listitem> | |
107 | <para>The limit on the total number of files open on the | |
108 | system has been reached.</para> | |
109 | </listitem> | |
110 | </varlistentry> | |
111 | </variablelist> | |
112 | </refsect1> | |
113 | </refentry> | |
114 | ||
115 | <!-- | |
116 | Local Variables: | |
117 | mode: sgml | |
118 | sgml-parent-document: "v4l2.sgml" | |
119 | indent-tabs-mode: nil | |
120 | End: | |
121 | --> |