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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

1	<refentry id="func-write">
2	  <refmeta>
3	    <refentrytitle>V4L2 write()</refentrytitle>
4	    &manvol;
5	  </refmeta>
6	
7	  <refnamediv>
8	    <refname>v4l2-write</refname>
9	    <refpurpose>Write to a V4L2 device</refpurpose>
10	  </refnamediv>
11	
12	  <refsynopsisdiv>
13	    <funcsynopsis>
14	      <funcsynopsisinfo>#include &lt;unistd.h&gt;</funcsynopsisinfo>
15	      <funcprototype>
16		<funcdef>ssize_t <function>write</function></funcdef>
17		<paramdef>int <parameter>fd</parameter></paramdef>
18		<paramdef>void *<parameter>buf</parameter></paramdef>
19		<paramdef>size_t <parameter>count</parameter></paramdef>
20	      </funcprototype>
21	    </funcsynopsis>
22	  </refsynopsisdiv>
23	
24	  <refsect1>
25	    <title>Arguments</title>
26	
27	    <variablelist>
28	      <varlistentry>
29		<term><parameter>fd</parameter></term>
30		<listitem>
31		  <para>&fd;</para>
32		</listitem>
33	      </varlistentry>
34	      <varlistentry>
35		<term><parameter>buf</parameter></term>
36		<listitem>
37		  <para></para>
38		</listitem>
39	      </varlistentry>
40	      <varlistentry>
41		<term><parameter>count</parameter></term>
42		<listitem>
43		  <para></para>
44		</listitem>
45	      </varlistentry>
46	    </variablelist>
47	  </refsect1>
48	
49	  <refsect1>
50	    <title>Description</title>
51	
52	    <para><function>write()</function> writes up to
53	<parameter>count</parameter> bytes to the device referenced by the
54	file descriptor <parameter>fd</parameter> from the buffer starting at
55	<parameter>buf</parameter>. When the hardware outputs are not active
56	yet, this function enables them. When <parameter>count</parameter> is
57	zero, <function>write()</function> returns
58	<returnvalue>0</returnvalue> without any other effect.</para>
59	
60	    <para>When the application does not provide more data in time, the
61	previous video frame, raw VBI image, sliced VPS or WSS data is
62	displayed again. Sliced Teletext or Closed Caption data is not
63	repeated, the driver inserts a blank line instead.</para>
64	  </refsect1>
65	
66	  <refsect1>
67	    <title>Return Value</title>
68	
69	    <para>On success, the number of bytes written are returned. Zero
70	indicates nothing was written. On error, <returnvalue>-1</returnvalue>
71	is returned, and the <varname>errno</varname> variable is set
72	appropriately. In this case the next write will start at the beginning
73	of a new frame. Possible error codes are:</para>
74	
75	    <variablelist>
76	      <varlistentry>
77		<term><errorcode>EAGAIN</errorcode></term>
78		<listitem>
79		  <para>Non-blocking I/O has been selected using the <link
80	linkend="func-open"><constant>O_NONBLOCK</constant></link> flag and no
81	buffer space was available to write the data immediately.</para>
82		</listitem>
83	      </varlistentry>
84	      <varlistentry>
85		<term><errorcode>EBADF</errorcode></term>
86		<listitem>
87		  <para><parameter>fd</parameter> is not a valid file
88	descriptor or is not open for writing.</para>
89		</listitem>
90	      </varlistentry>
91	      <varlistentry>
92		<term><errorcode>EBUSY</errorcode></term>
93		<listitem>
94		  <para>The driver does not support multiple write streams and the
95	device is already in use.</para>
96		</listitem>
97	      </varlistentry>
98	      <varlistentry>
99		<term><errorcode>EFAULT</errorcode></term>
100		<listitem>
101		  <para><parameter>buf</parameter> references an inaccessible
102	memory area.</para>
103		</listitem>
104	      </varlistentry>
105	      <varlistentry>
106		<term><errorcode>EINTR</errorcode></term>
107		<listitem>
108		  <para>The call was interrupted by a signal before any
109	data was written.</para>
110		</listitem>
111	      </varlistentry>
112	      <varlistentry>
113		<term><errorcode>EIO</errorcode></term>
114		<listitem>
115		  <para>I/O error. This indicates some hardware problem.</para>
116		</listitem>
117	      </varlistentry>
118	      <varlistentry>
119		<term><errorcode>EINVAL</errorcode></term>
120		<listitem>
121		  <para>The <function>write()</function> function is not
122	supported by this driver, not on this device, or generally not on this
123	type of device.</para>
124		</listitem>
125	      </varlistentry>
126	    </variablelist>
127	  </refsect1>
128	</refentry>
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