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<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>
<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(&expbuf, 0, sizeof(expbuf));
expbuf.type = bt;
expbuf.index = index;
if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &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 < n_planes; ++i) {
&v4l2-exportbuffer; expbuf;
memset(&expbuf, 0, sizeof(expbuf));
expbuf.type = bt;
expbuf.index = index;
expbuf.plane = i;
if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &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>
|
