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 &lt;fcntl.h&gt;</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
38still support only reading and output devices only writing.</para>
39	  <para>When the <constant>O_NONBLOCK</constant> flag is
40given, the read() function and the &VIDIOC-DQBUF; ioctl will return
41the &EAGAIN; when no data is available or no buffer is in the driver
42outgoing queue, otherwise these functions block until data becomes
43available. All V4L2 drivers exchanging data with applications must
44support 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
55function has no side effects; all data format parameters, current
56input or output, control values or other properties remain unchanged.
57At the first <function>open()</function> call after loading the driver
58they will be reset to default values, drivers are never in an
59undefined state.</para>
60  </refsect1>
61  <refsect1>
62    <title>Return Value</title>
63
64    <para>On success <function>open</function> returns the new file
65descriptor. On error -1 is returned, and the <varname>errno</varname>
66variable 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
73device.</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
80device 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
87exists.</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
94request.</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
101files 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
108system has been reached.</para>
109	</listitem>
110      </varlistentry>
111    </variablelist>
112  </refsect1>
113</refentry>
114