path: root/Documentation/DocBook/media/v4l/vidioc-querybuf.xml
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authorFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
committerFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
commit3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a (patch)
treeb9996006addfd7ae70a39672b76843b49aebc189 /Documentation/DocBook/media/v4l/vidioc-querybuf.xml
Imported Upstream version 3.9.0HEADupstream/3.9.0upstreammaster
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+<refentry id="vidioc-querybuf">
+ <refmeta>
+ <refentrytitle>ioctl VIDIOC_QUERYBUF</refentrytitle>
+ &manvol;
+ </refmeta>
+ <refnamediv>
+ <refname>VIDIOC_QUERYBUF</refname>
+ <refpurpose>Query the status of a buffer</refpurpose>
+ </refnamediv>
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>int <function>ioctl</function></funcdef>
+ <paramdef>int <parameter>fd</parameter></paramdef>
+ <paramdef>int <parameter>request</parameter></paramdef>
+ <paramdef>struct v4l2_buffer *<parameter>argp</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+ <refsect1>
+ <title>Arguments</title>
+ <variablelist>
+ <varlistentry>
+ <term><parameter>fd</parameter></term>
+ <listitem>
+ <para>&fd;</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>request</parameter></term>
+ <listitem>
+ <para>VIDIOC_QUERYBUF</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>argp</parameter></term>
+ <listitem>
+ <para></para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+ <refsect1>
+ <title>Description</title>
+ <para>This ioctl is part of the <link linkend="mmap">streaming
+</link> I/O method. It can be used to query the status of a
+buffer at any time after buffers have been allocated with the
+&VIDIOC-REQBUFS; ioctl.</para>
+ <para>Applications set the <structfield>type</structfield> field
+ of a &v4l2-buffer; to the same buffer type as was previously used with
+&v4l2-format; <structfield>type</structfield> and &v4l2-requestbuffers;
+<structfield>type</structfield>, and the <structfield>index</structfield>
+ field. Valid index numbers range from zero
+to the number of buffers allocated with &VIDIOC-REQBUFS;
+ (&v4l2-requestbuffers; <structfield>count</structfield>) minus one.
+The <structfield>reserved</structfield> field should to set to 0.
+When using the <link linkend="planar-apis">multi-planar API</link>, the
+<structfield>m.planes</structfield> field must contain a userspace pointer to an
+array of &v4l2-plane; and the <structfield>length</structfield> field has
+to be set to the number of elements in that array.
+After calling <constant>VIDIOC_QUERYBUF</constant> with a pointer to
+ this structure drivers return an error code or fill the rest of
+the structure.</para>
+ <para>In the <structfield>flags</structfield> field the
+<constant>V4L2_BUF_FLAG_QUEUED</constant> and
+<constant>V4L2_BUF_FLAG_DONE</constant> flags will be valid. The
+<structfield>memory</structfield> field will be set to the current
+I/O method. For the single-planar API, the <structfield>m.offset</structfield>
+contains the offset of the buffer from the start of the device memory,
+the <structfield>length</structfield> field its size. For the multi-planar API,
+fields <structfield>m.mem_offset</structfield> and
+<structfield>length</structfield> in the <structfield>m.planes</structfield>
+array elements will be used instead and the <structfield>length</structfield>
+field of &v4l2-buffer; is set to the number of filled-in array elements.
+The driver may or may not set the remaining fields and flags, they are
+meaningless in this context.</para>
+ <para>The <structname>v4l2_buffer</structname> structure is
+ specified in <xref linkend="buffer" />.</para>
+ </refsect1>
+ <refsect1>
+ &return-value;
+ <variablelist>
+ <varlistentry>
+ <term><errorcode>EINVAL</errorcode></term>
+ <listitem>
+ <para>The buffer <structfield>type</structfield> is not
+supported, or the <structfield>index</structfield> is out of bounds.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>