.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L
.. _VIDIOC_EXPBUF:
*******************
ioctl VIDIOC_EXPBUF
*******************
Name
====
VIDIOC_EXPBUF - Export a buffer as a DMABUF file descriptor.
Synopsis
========
.. c:macro:: VIDIOC_EXPBUF
``int ioctl(int fd, VIDIOC_EXPBUF, struct v4l2_exportbuffer *argp)``
Arguments
=========
``fd``
File descriptor returned by :c: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{8.5cm}|
.. 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.
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