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diff --git a/Documentation/media/uapi/v4l/vidioc-expbuf.rst b/Documentation/media/uapi/v4l/vidioc-expbuf.rst new file mode 100644 index 000000000000..ded708e647fa --- /dev/null +++ b/Documentation/media/uapi/v4l/vidioc-expbuf.rst @@ -0,0 +1,197 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _VIDIOC_EXPBUF: + +******************* +ioctl VIDIOC_EXPBUF +******************* + +Name +==== + +VIDIOC_EXPBUF - Export a buffer as a DMABUF file descriptor. + + +Synopsis +======== + +.. cpp: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` 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` (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 :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; + } + + +.. _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` and/or + :ref:`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. |