.. Permission is granted to copy, distribute and/or modify this
.. document under the terms of the GNU Free Documentation License,
.. Version 1.1 or any later version published by the Free Software
.. Foundation, with no Invariant Sections, no Front-Cover Texts
.. and no Back-Cover Texts. A copy of the license is included at
.. Documentation/media/uapi/fdl-appendix.rst.
..
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

.. _VIDIOC_EXPBUF:

*******************
ioctl VIDIOC_EXPBUF
*******************

Name
====

VIDIOC_EXPBUF - Export a buffer as a DMABUF file descriptor.


Synopsis
========

.. c:function:: int ioctl( int fd, VIDIOC_EXPBUF, struct v4l2_exportbuffer *argp )
    :name: VIDIOC_EXPBUF


Arguments
=========

``fd``
    File descriptor returned by :ref:`open() <func-open>`.

``argp``
    Pointer to struct :c:type:`v4l2_exportbuffer`.


Description
===========

This ioctl is an extension to the :ref:`memory mapping <mmap>` I/O
method, therefore it is available only for ``V4L2_MEMORY_MMAP`` buffers.
It can be used to export a buffer as a DMABUF file at any time after
buffers have been allocated with the
:ref:`VIDIOC_REQBUFS` ioctl.

To export a buffer, applications fill struct
:c:type:`v4l2_exportbuffer`. The ``type`` field is
set to the same buffer type as was previously used with struct
:c:type:`v4l2_requestbuffers` ``type``.
Applications must also set the ``index`` field. Valid index numbers
range from zero to the number of buffers allocated with
:ref:`VIDIOC_REQBUFS` (struct
:c:type:`v4l2_requestbuffers` ``count``) minus
one. For the multi-planar API, applications set the ``plane`` 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 ``plane`` to zero.
Additional flags may be posted in the ``flags`` 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 :ref:`VIDIOC_EXPBUF` calls.

After calling :ref:`VIDIOC_EXPBUF` the ``fd`` 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 :ref:`DMABUF importing <dmabuf>`
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.


Examples
========


.. code-block:: c

    int buffer_export(int v4lfd, enum v4l2_buf_type bt, int index, int *dmafd)
    {
	struct 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;
    }


.. code-block:: c

    int buffer_export_mp(int v4lfd, enum v4l2_buf_type bt, int index,
	int dmafd[], int n_planes)
    {
	int i;

	for (i = 0; i < n_planes; ++i) {
	    struct 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;
    }


.. c:type:: v4l2_exportbuffer

.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|

.. flat-table:: struct v4l2_exportbuffer
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2

    * - __u32
      - ``type``
      - Type of the buffer, same as struct
	:c:type:`v4l2_format` ``type`` or struct
	:c:type:`v4l2_requestbuffers` ``type``, set
	by the application. See :c:type:`v4l2_buf_type`
    * - __u32
      - ``index``
      - Number of the buffer, set by the application. This field is only
	used for :ref:`memory mapping <mmap>` I/O and can range from
	zero to the number of buffers allocated with the
	:ref:`VIDIOC_REQBUFS` and/or
	:ref:`VIDIOC_CREATE_BUFS` ioctls.
    * - __u32
      - ``plane``
      - Index of the plane to be exported when using the multi-planar API.
	Otherwise this value must be set to zero.
    * - __u32
      - ``flags``
      - Flags for the newly created file, currently only ``O_CLOEXEC``,
	``O_RDONLY``, ``O_WRONLY``, and ``O_RDWR`` are supported, refer to
	the manual of open() for more details.
    * - __s32
      - ``fd``
      - The DMABUF file descriptor associated with a buffer. Set by the
	driver.
    * - __u32
      - ``reserved[11]``
      - Reserved field for future use. Drivers and applications must set
	the array to zero.


Return Value
============

On success 0 is returned, on error -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.

EINVAL
    A queue is not in MMAP mode or DMABUF exporting is not supported or
    ``flags`` or ``type`` or ``index`` or ``plane`` fields are invalid.