[media] Documentation: media: description of DMABUF exporting in V4L2
This patch adds description and usage examples for exporting DMABUF file descriptor in V4L2. Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> Acked-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Tomasz Stanislawski
Mauro Carvalho Chehab
parent
b799d09a15
commit
19b6ef5164
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@ -2590,6 +2590,9 @@ ioctls.</para>
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<para>Importing DMABUF file descriptors as a new IO method described
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<para>Importing DMABUF file descriptors as a new IO method described
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in <xref linkend="dmabuf" />.</para>
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in <xref linkend="dmabuf" />.</para>
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</listitem>
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</listitem>
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<listitem>
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<para>Exporting DMABUF files using &VIDIOC-EXPBUF; ioctl.</para>
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</listitem>
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</itemizedlist>
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</itemizedlist>
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</section>
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</section>
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@ -488,6 +488,9 @@ DMA buffer from userspace using a file descriptor previously exported for a
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different or the same device (known as the importer role), or both. This
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different or the same device (known as the importer role), or both. This
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section describes the DMABUF importer role API in V4L2.</para>
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section describes the DMABUF importer role API in V4L2.</para>
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<para>Refer to <link linked="vidioc-expbuf"> DMABUF exporting </link> for
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details about exporting V4L2 buffers as DMABUF file descriptors.</para>
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<para>Input and output devices support the streaming I/O method when the
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<para>Input and output devices support the streaming I/O method when the
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<constant>V4L2_CAP_STREAMING</constant> flag in the
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<constant>V4L2_CAP_STREAMING</constant> flag in the
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<structfield>capabilities</structfield> field of &v4l2-capability; returned by
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<structfield>capabilities</structfield> field of &v4l2-capability; returned by
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@ -543,6 +543,7 @@ and discussions on the V4L mailing list.</revremark>
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&sub-enuminput;
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&sub-enuminput;
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&sub-enumoutput;
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&sub-enumoutput;
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&sub-enumstd;
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&sub-enumstd;
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&sub-expbuf;
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&sub-g-audio;
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&sub-g-audio;
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&sub-g-audioout;
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&sub-g-audioout;
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&sub-g-crop;
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&sub-g-crop;
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212
Documentation/DocBook/media/v4l/vidioc-expbuf.xml
Normal file
212
Documentation/DocBook/media/v4l/vidioc-expbuf.xml
Normal file
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@ -0,0 +1,212 @@
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<refentry id="vidioc-expbuf">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_EXPBUF</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_EXPBUF</refname>
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<refpurpose>Export a buffer as a DMABUF file descriptor.</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_exportbuffer *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_EXPBUF</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<note>
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<title>Experimental</title>
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<para>This is an <link linkend="experimental"> experimental </link>
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interface and may change in the future.</para>
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</note>
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<para>This ioctl is an extension to the <link linkend="mmap">memory
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mapping</link> I/O method, therefore it is available only for
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<constant>V4L2_MEMORY_MMAP</constant> buffers. It can be used to export a
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buffer as a DMABUF file at any time after buffers have been allocated with the
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&VIDIOC-REQBUFS; ioctl.</para>
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<para> To export a buffer, applications fill &v4l2-exportbuffer;. The
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<structfield> type </structfield> field is set to the same buffer type as was
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previously used with &v4l2-requestbuffers;<structfield> type </structfield>.
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Applications must also set the <structfield> index </structfield> field. Valid
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index numbers range from zero to the number of buffers allocated with
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&VIDIOC-REQBUFS; (&v4l2-requestbuffers;<structfield> count </structfield>)
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minus one. For the multi-planar API, applications set the <structfield> plane
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</structfield> field to the index of the plane to be exported. Valid planes
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range from zero to the maximal number of valid planes for the currently active
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format. For the single-planar API, applications must set <structfield> plane
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</structfield> to zero. Additional flags may be posted in the <structfield>
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flags </structfield> field. Refer to a manual for open() for details.
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Currently only O_CLOEXEC is supported. All other fields must be set to zero.
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In the case of multi-planar API, every plane is exported separately using
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multiple <constant> VIDIOC_EXPBUF </constant> calls. </para>
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<para> After calling <constant>VIDIOC_EXPBUF</constant> the <structfield> fd
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</structfield> field will be set by a driver. This is a DMABUF file
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descriptor. The application may pass it to other DMABUF-aware devices. Refer to
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<link linkend="dmabuf">DMABUF importing</link> for details about importing
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DMABUF files into V4L2 nodes. It is recommended to close a DMABUF file when it
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is no longer used to allow the associated memory to be reclaimed. </para>
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</refsect1>
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<refsect1>
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<section>
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<title>Examples</title>
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<example>
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<title>Exporting a buffer.</title>
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<programlisting>
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int buffer_export(int v4lfd, &v4l2-buf-type; bt, int index, int *dmafd)
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{
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&v4l2-exportbuffer; expbuf;
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memset(&expbuf, 0, sizeof(expbuf));
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expbuf.type = bt;
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expbuf.index = index;
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if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &expbuf) == -1) {
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perror("VIDIOC_EXPBUF");
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return -1;
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}
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*dmafd = expbuf.fd;
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return 0;
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}
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</programlisting>
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</example>
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<example>
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<title>Exporting a buffer using the multi-planar API.</title>
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<programlisting>
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int buffer_export_mp(int v4lfd, &v4l2-buf-type; bt, int index,
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int dmafd[], int n_planes)
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{
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int i;
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for (i = 0; i < n_planes; ++i) {
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&v4l2-exportbuffer; expbuf;
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memset(&expbuf, 0, sizeof(expbuf));
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expbuf.type = bt;
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expbuf.index = index;
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expbuf.plane = i;
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if (ioctl(v4lfd, &VIDIOC-EXPBUF;, &expbuf) == -1) {
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perror("VIDIOC_EXPBUF");
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while (i)
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close(dmafd[--i]);
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return -1;
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}
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dmafd[i] = expbuf.fd;
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}
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return 0;
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}
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</programlisting>
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</example>
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</section>
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</refsect1>
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<refsect1>
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<table pgwide="1" frame="none" id="v4l2-exportbuffer">
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<title>struct <structname>v4l2_exportbuffer</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry>Type of the buffer, same as &v4l2-format;
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<structfield>type</structfield> or &v4l2-requestbuffers;
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<structfield>type</structfield>, set by the application. See <xref
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linkend="v4l2-buf-type" /></entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>index</structfield></entry>
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<entry>Number of the buffer, set by the application. This field is
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only used for <link linkend="mmap">memory mapping</link> I/O and can range from
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zero to the number of buffers allocated with the &VIDIOC-REQBUFS; and/or
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&VIDIOC-CREATE-BUFS; ioctls. </entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>plane</structfield></entry>
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<entry>Index of the plane to be exported when using the
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multi-planar API. Otherwise this value must be set to zero. </entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Flags for the newly created file, currently only <constant>
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O_CLOEXEC </constant> is supported, refer to the manual of open() for more
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details.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>fd</structfield></entry>
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<entry>The DMABUF file descriptor associated with a buffer. Set by
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the driver.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved[11]</structfield></entry>
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<entry>Reserved field for future use. Must be set to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>A queue is not in MMAP mode or DMABUF exporting is not
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supported or <structfield> flags </structfield> or <structfield> type
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</structfield> or <structfield> index </structfield> or <structfield> plane
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</structfield> fields are invalid.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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