media/v4l/mmap.rst

1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
22 memory on a graphics card with a video capture add-on. However, being
24 drivers support streaming as well, allocating buffers in DMA-able main
39 address space with the :c:func:`mmap()` function. The
41 :ref:`VIDIOC_QUERYBUF` ioctl. In the single-planar
44 parameter to the :c:func:`mmap()` function. When using the
45 multi-planar API, struct :c:type:`v4l2_buffer` contains an
48 multi-planar API, every plane of every buffer has to be mapped
54 possible with the :c:func:`munmap()` function.
56 Example: Mapping buffers in the single-planar API
59 .. code-block:: c
73     if (-1 == ioctl (fd, VIDIOC_REQBUFS, &reqbuf)) {
75 	    printf("Video capturing or mmap-streaming is not supported\\n");
101 	if (-1 == ioctl (fd, VIDIOC_QUERYBUF, &buffer)) {
126 Example: Mapping buffers in the multi-planar API
129 .. code-block:: c
148 	    printf("Video capturing or mmap-streaming is not supported\\n");
174 	/* length in struct v4l2_buffer in multi-planar API stores the size
217 to function, apart of this no limit exists on the number of buffers
228 re-enqueues the buffer when the data is no longer needed. Output
241 flag was given to the :c:func:`open()` function,
262 <func-mmap>`, :c:func:`munmap()`, :ref:`select()
263 <func-select>` and :c:func:`poll()` function. [#f3]_
270    but it makes the :c:func:`select()` function ambiguous. We also
279    buffers on a LIFO-basis, taking advantage of caches holding
280    scatter-gather lists and the like.