169 lines
4.6 KiB
ReStructuredText
Executable file
169 lines
4.6 KiB
ReStructuredText
Executable file
.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_EXPBUF:
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*******************
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ioctl VIDIOC_EXPBUF
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*******************
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Name
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====
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VIDIOC_EXPBUF - Export a buffer as a DMABUF file descriptor.
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_EXPBUF, struct v4l2_exportbuffer *argp )
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:name: VIDIOC_EXPBUF
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Pointer to struct :c:type:`v4l2_exportbuffer`.
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Description
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===========
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This ioctl is an extension to the :ref:`memory mapping <mmap>` I/O
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method, therefore it is available only for ``V4L2_MEMORY_MMAP`` buffers.
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It can be used to export a buffer as a DMABUF file at any time after
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buffers have been allocated with the
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:ref:`VIDIOC_REQBUFS` ioctl.
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To export a buffer, applications fill struct
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:c:type:`v4l2_exportbuffer`. The ``type`` field is
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set to the same buffer type as was previously used with struct
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:c:type:`v4l2_requestbuffers` ``type``.
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Applications must also set the ``index`` field. Valid index numbers
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range from zero to the number of buffers allocated with
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:ref:`VIDIOC_REQBUFS` (struct
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:c:type:`v4l2_requestbuffers` ``count``) minus
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one. For the multi-planar API, applications set the ``plane`` field to
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the index of the plane to be exported. Valid planes range from zero to
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the maximal number of valid planes for the currently active format. For
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the single-planar API, applications must set ``plane`` to zero.
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Additional flags may be posted in the ``flags`` field. Refer to a manual
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for open() for details. Currently only O_CLOEXEC, O_RDONLY, O_WRONLY,
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and O_RDWR are supported. All other fields must be set to zero. In the
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case of multi-planar API, every plane is exported separately using
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multiple :ref:`VIDIOC_EXPBUF` calls.
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After calling :ref:`VIDIOC_EXPBUF` the ``fd`` field will be set by a
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driver. This is a DMABUF file descriptor. The application may pass it to
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other DMABUF-aware devices. Refer to :ref:`DMABUF importing <dmabuf>`
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for details about importing DMABUF files into V4L2 nodes. It is
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recommended to close a DMABUF file when it is no longer used to allow
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the associated memory to be reclaimed.
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Examples
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========
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.. code-block:: c
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int buffer_export(int v4lfd, enum v4l2_buf_type bt, int index, int *dmafd)
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{
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struct 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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.. code-block:: c
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int buffer_export_mp(int v4lfd, enum 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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struct 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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.. c:type:: v4l2_exportbuffer
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. flat-table:: struct v4l2_exportbuffer
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``type``
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- Type of the buffer, same as struct
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:c:type:`v4l2_format` ``type`` or struct
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:c:type:`v4l2_requestbuffers` ``type``, set
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by the application. See :c:type:`v4l2_buf_type`
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* - __u32
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- ``index``
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- Number of the buffer, set by the application. This field is only
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used for :ref:`memory mapping <mmap>` I/O and can range from
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zero to the number of buffers allocated with the
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:ref:`VIDIOC_REQBUFS` and/or
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:ref:`VIDIOC_CREATE_BUFS` ioctls.
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* - __u32
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- ``plane``
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- Index of the plane to be exported when using the multi-planar API.
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Otherwise this value must be set to zero.
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* - __u32
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- ``flags``
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- Flags for the newly created file, currently only ``O_CLOEXEC``,
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``O_RDONLY``, ``O_WRONLY``, and ``O_RDWR`` are supported, refer to
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the manual of open() for more details.
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* - __s32
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- ``fd``
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- The DMABUF file descriptor associated with a buffer. Set by the
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driver.
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* - __u32
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- ``reserved[11]``
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- Reserved field for future use. Drivers and applications must set
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the array to zero.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EINVAL
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A queue is not in MMAP mode or DMABUF exporting is not supported or
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``flags`` or ``type`` or ``index`` or ``plane`` fields are invalid.
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