vidioc-expbuf.rst

.. -*- coding: utf-8; mode: rst -*-

.. _VIDIOC_EXPBUF:

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

*man VIDIOC_EXPBUF(2)*

Export a buffer as a DMABUF file descriptor.


Synopsis
========

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

Arguments
=========

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

``request``
    VIDIOC_EXPBUF

``argp``


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 <VIDIOC_REQBUFS>` ioctl.

To export a buffer, applications fill struct
:ref:`v4l2_exportbuffer <v4l2-exportbuffer>`. The ``type`` field is
set to the same buffer type as was previously used with struct
:ref:`v4l2_requestbuffers <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 <VIDIOC_REQBUFS>` (struct
:ref:`v4l2_requestbuffers <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 ``VIDIOC_EXPBUF`` calls.

After calling ``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;
    }


.. _v4l2-exportbuffer:

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


    -  .. row 1

       -  __u32

       -  ``type``

       -  Type of the buffer, same as struct
          :ref:`v4l2_format <v4l2-format>` ``type`` or struct
          :ref:`v4l2_requestbuffers <v4l2-requestbuffers>` ``type``, set
          by the application. See :ref:`v4l2-buf-type`

    -  .. row 2

       -  __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 <VIDIOC_REQBUFS>` and/or
          :ref:`VIDIOC_CREATE_BUFS <VIDIOC_CREATE_BUFS>` ioctls.

    -  .. row 3

       -  __u32

       -  ``plane``

       -  Index of the plane to be exported when using the multi-planar API.
          Otherwise this value must be set to zero.

    -  .. row 4

       -  __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.

    -  .. row 5

       -  __s32

       -  ``fd``

       -  The DMABUF file descriptor associated with a buffer. Set by the
          driver.

    -  .. row 6

       -  __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.


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.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
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..
.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
.. ------------------------------------------------------------------------------