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

1	<refentry id="vidioc-querybuf">
2	  <refmeta>
3	    <refentrytitle>ioctl VIDIOC_QUERYBUF</refentrytitle>
4	    &manvol;
5	  </refmeta>
6	
7	  <refnamediv>
8	    <refname>VIDIOC_QUERYBUF</refname>
9	    <refpurpose>Query the status of a buffer</refpurpose>
10	  </refnamediv>
11	
12	  <refsynopsisdiv>
13	    <funcsynopsis>
14	      <funcprototype>
15		<funcdef>int <function>ioctl</function></funcdef>
16		<paramdef>int <parameter>fd</parameter></paramdef>
17		<paramdef>int <parameter>request</parameter></paramdef>
18		<paramdef>struct v4l2_buffer *<parameter>argp</parameter></paramdef>
19	      </funcprototype>
20	    </funcsynopsis>
21	  </refsynopsisdiv>
22	
23	  <refsect1>
24	    <title>Arguments</title>
25	
26	    <variablelist>
27	      <varlistentry>
28		<term><parameter>fd</parameter></term>
29		<listitem>
30		  <para>&fd;</para>
31		</listitem>
32	      </varlistentry>
33	      <varlistentry>
34		<term><parameter>request</parameter></term>
35		<listitem>
36		  <para>VIDIOC_QUERYBUF</para>
37		</listitem>
38	      </varlistentry>
39	      <varlistentry>
40		<term><parameter>argp</parameter></term>
41		<listitem>
42		  <para></para>
43		</listitem>
44	      </varlistentry>
45	    </variablelist>
46	  </refsect1>
47	
48	  <refsect1>
49	    <title>Description</title>
50	
51	    <para>This ioctl is part of the <link linkend="mmap">streaming
52	</link> I/O method. It can be used to query the status of a
53	buffer at any time after buffers have been allocated with the
54	&VIDIOC-REQBUFS; ioctl.</para>
55	
56	    <para>Applications set the <structfield>type</structfield> field
57	    of a &v4l2-buffer; to the same buffer type as was previously used with
58	&v4l2-format; <structfield>type</structfield> and &v4l2-requestbuffers;
59	<structfield>type</structfield>, and the <structfield>index</structfield>
60	    field. Valid index numbers range from zero
61	to the number of buffers allocated with &VIDIOC-REQBUFS;
62	    (&v4l2-requestbuffers; <structfield>count</structfield>) minus one.
63	The <structfield>reserved</structfield> field should to set to 0.
64	When using the <link linkend="planar-apis">multi-planar API</link>, the
65	<structfield>m.planes</structfield> field must contain a userspace pointer to an
66	array of &v4l2-plane; and the <structfield>length</structfield> field has
67	to be set to the number of elements in that array.
68	After calling <constant>VIDIOC_QUERYBUF</constant> with a pointer to
69	    this structure drivers return an error code or fill the rest of
70	the structure.</para>
71	
72	    <para>In the <structfield>flags</structfield> field the
73	<constant>V4L2_BUF_FLAG_MAPPED</constant>,
74	<constant>V4L2_BUF_FLAG_PREPARED</constant>,
75	<constant>V4L2_BUF_FLAG_QUEUED</constant> and
76	<constant>V4L2_BUF_FLAG_DONE</constant> flags will be valid. The
77	<structfield>memory</structfield> field will be set to the current
78	I/O method. For the single-planar API, the <structfield>m.offset</structfield>
79	contains the offset of the buffer from the start of the device memory,
80	the <structfield>length</structfield> field its size. For the multi-planar API,
81	fields <structfield>m.mem_offset</structfield> and
82	<structfield>length</structfield> in the <structfield>m.planes</structfield>
83	array elements will be used instead and the <structfield>length</structfield>
84	field of &v4l2-buffer; is set to the number of filled-in array elements.
85	The driver may or may not set the remaining fields and flags, they are
86	meaningless in this context.</para>
87	
88	    <para>The <structname>v4l2_buffer</structname> structure is
89	    specified in <xref linkend="buffer" />.</para>
90	  </refsect1>
91	
92	  <refsect1>
93	    &return-value;
94	
95	    <variablelist>
96	      <varlistentry>
97		<term><errorcode>EINVAL</errorcode></term>
98		<listitem>
99		  <para>The buffer <structfield>type</structfield> is not
100	supported, or the <structfield>index</structfield> is out of bounds.</para>
101		</listitem>
102	      </varlistentry>
103	    </variablelist>
104	  </refsect1>
105	</refentry>
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