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| -rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-expbuf.rst | 162 |
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diff --git a/Documentation/userspace-api/media/v4l/vidioc-expbuf.rst b/Documentation/userspace-api/media/v4l/vidioc-expbuf.rst new file mode 100644 index 000000000..982e8bcd9 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-expbuf.rst @@ -0,0 +1,162 @@ +.. 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. |