CooCenter-System-kernel/Documentation/DocBook/media/v4l/vidioc-expbuf.xml

<refentry id="vidioc-expbuf">

  <refmeta>
    <refentrytitle>ioctl VIDIOC_EXPBUF</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_EXPBUF</refname>
    <refpurpose>Export a buffer as a DMABUF file descriptor.</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_exportbuffer *<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_EXPBUF</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <note>
      <title>Experimental</title>
      <para>This is an <link linkend="experimental"> experimental </link>
      interface and may change in the future.</para>
    </note>

<para>This ioctl is an extension to the <link linkend="mmap">memory
mapping</link> I/O method, therefore it is available only for
<constant>V4L2_MEMORY_MMAP</constant> buffers.  It can be used to export a
buffer as a DMABUF file at any time after buffers have been allocated with the
&VIDIOC-REQBUFS; ioctl.</para>

<para> To export a buffer, applications fill &v4l2-exportbuffer;.  The
<structfield>type</structfield> field is set to the same buffer type as was
previously used with &v4l2-requestbuffers; <structfield>type</structfield>.
Applications must also set 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.  For the multi-planar API, applications set the <structfield>plane</structfield>
field to the index of the plane to be exported. Valid planes
range from zero to the maximal number of valid planes for the currently active
format. For the single-planar API, applications must set <structfield>plane</structfield>
to zero.  Additional flags may be posted in the <structfield>flags</structfield>
field.  Refer to a manual for open() for details.
Currently only O_CLOEXEC, O_RDONLY, O_WRONLY, and O_RDWR are supported.  All
other fields must be set to zero.
In the case of multi-planar API, every plane is exported separately using
multiple <constant>VIDIOC_EXPBUF</constant> calls.</para>

<para>After calling <constant>VIDIOC_EXPBUF</constant> the <structfield>fd</structfield>
field will be set by a driver.  This is a DMABUF file
descriptor. The application may pass it to other DMABUF-aware devices. Refer to
<link linkend="dmabuf">DMABUF importing</link> for details about importing
DMABUF files into V4L2 nodes. It is recommended to close a DMABUF file when it
is no longer used to allow the associated memory to be reclaimed.</para>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Exporting a buffer.</title>
      <programlisting>
int buffer_export(int v4lfd, &v4l2-buf-type; bt, int index, int *dmafd)
{
	&v4l2-exportbuffer; expbuf;

	memset(&amp;expbuf, 0, sizeof(expbuf));
	expbuf.type = bt;
	expbuf.index = index;
	if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &amp;expbuf) == -1) {
		perror("VIDIOC_EXPBUF");
		return -1;
	}

	*dmafd = expbuf.fd;

	return 0;
}
      </programlisting>
    </example>

    <example>
      <title>Exporting a buffer using the multi-planar API.</title>
      <programlisting>
int buffer_export_mp(int v4lfd, &v4l2-buf-type; bt, int index,
	int dmafd[], int n_planes)
{
	int i;

	for (i = 0; i &lt; n_planes; ++i) {
		&v4l2-exportbuffer; expbuf;

		memset(&amp;expbuf, 0, sizeof(expbuf));
		expbuf.type = bt;
		expbuf.index = index;
		expbuf.plane = i;
		if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &amp;expbuf) == -1) {
			perror("VIDIOC_EXPBUF");
			while (i)
				close(dmafd[--i]);
			return -1;
		}
		dmafd[i] = expbuf.fd;
	}

	return 0;
}
      </programlisting>
    </example>

    <table pgwide="1" frame="none" id="v4l2-exportbuffer">
      <title>struct <structname>v4l2_exportbuffer</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>type</structfield></entry>
	    <entry>Type of the buffer, same as &v4l2-format;
<structfield>type</structfield> or &v4l2-requestbuffers;
<structfield>type</structfield>, set by the application. See <xref
linkend="v4l2-buf-type" /></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>index</structfield></entry>
	    <entry>Number of the buffer, set by the application. This field is
only used for <link linkend="mmap">memory mapping</link> I/O and can range from
zero to the number of buffers allocated with the &VIDIOC-REQBUFS; and/or
&VIDIOC-CREATE-BUFS; ioctls. </entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>plane</structfield></entry>
	    <entry>Index of the plane to be exported when using the
multi-planar API. Otherwise this value must be set to zero. </entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>flags</structfield></entry>
	    <entry>Flags for the newly created file, currently only
<constant>O_CLOEXEC</constant>, <constant>O_RDONLY</constant>, <constant>O_WRONLY</constant>,
and <constant>O_RDWR</constant> are supported, refer to the manual
of open() for more details.</entry>
	  </row>
	  <row>
	    <entry>__s32</entry>
	    <entry><structfield>fd</structfield></entry>
	    <entry>The DMABUF file descriptor associated with a buffer. Set by
		the driver.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved[11]</structfield></entry>
	    <entry>Reserved field for future use. Drivers and applications must
set the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

  </refsect1>

  <refsect1>
    &return-value;
    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>A queue is not in MMAP mode or DMABUF exporting is not
supported or <structfield>flags</structfield> or <structfield>type</structfield>
or <structfield>index</structfield> or <structfield>plane</structfield> fields
are invalid.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

</refentry>