Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab...
[linux-2.6.git] / Documentation / DocBook / media / v4l / vidioc-querybuf.xml
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">memory
52 mapping</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_QUEUED</constant> and
75 <constant>V4L2_BUF_FLAG_DONE</constant> flags will be valid. The
76 <structfield>memory</structfield> field will be set to the current
77 I/O method. For the single-planar API, the <structfield>m.offset</structfield>
78 contains the offset of the buffer from the start of the device memory,
79 the <structfield>length</structfield> field its size. For the multi-planar API,
80 fields <structfield>m.mem_offset</structfield> and
81 <structfield>length</structfield> in the <structfield>m.planes</structfield>
82 array elements will be used instead. The driver may or may not set the remaining
83 fields and flags, they are meaningless in this context.</para>
84
85     <para>The <structname>v4l2_buffer</structname> structure is
86     specified in <xref linkend="buffer" />.</para>
87   </refsect1>
88
89   <refsect1>
90     &return-value;
91
92     <variablelist>
93       <varlistentry>
94         <term><errorcode>EINVAL</errorcode></term>
95         <listitem>
96           <para>The buffer <structfield>type</structfield> is not
97 supported, or the <structfield>index</structfield> is out of bounds.</para>
98         </listitem>
99       </varlistentry>
100     </variablelist>
101   </refsect1>
102 </refentry>