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
53buffer 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
61to the number of buffers allocated with &VIDIOC-REQBUFS;
62    (&v4l2-requestbuffers; <structfield>count</structfield>) minus one.
63The <structfield>reserved</structfield> field should to set to 0.
64When using the <link linkend="planar-apis">multi-planar API</link>, the
65<structfield>m.planes</structfield> field must contain a userspace pointer to an
66array of &v4l2-plane; and the <structfield>length</structfield> field has
67to be set to the number of elements in that array.
68After calling <constant>VIDIOC_QUERYBUF</constant> with a pointer to
69    this structure drivers return an error code or fill the rest of
70the 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
78I/O method. For the single-planar API, the <structfield>m.offset</structfield>
79contains the offset of the buffer from the start of the device memory,
80the <structfield>length</structfield> field its size. For the multi-planar API,
81fields <structfield>m.mem_offset</structfield> and
82<structfield>length</structfield> in the <structfield>m.planes</structfield>
83array elements will be used instead and the <structfield>length</structfield>
84field of &v4l2-buffer; is set to the number of filled-in array elements.
85The driver may or may not set the remaining fields and flags, they are
86meaningless 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
100supported, or the <structfield>index</structfield> is out of bounds.</para>
101	</listitem>
102      </varlistentry>
103    </variablelist>
104  </refsect1>
105</refentry>
106