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Based on kernel version 3.16. Page generated on 2014-08-06 21:38 EST.

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
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>
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