1 .. -*- coding: utf-8; mode: rst -*-
3 .. _VIDIOC_PREPARE_BUF:
5 ************************
6 ioctl VIDIOC_PREPARE_BUF
7 ************************
12 VIDIOC_PREPARE_BUF - Prepare a buffer for I/O
18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_buffer *argp )
25 File descriptor returned by :ref:`open() <func-open>`.
36 Applications can optionally call the :ref:`VIDIOC_PREPARE_BUF` ioctl to
37 pass ownership of the buffer to the driver before actually enqueuing it,
38 using the :ref:`VIDIOC_QBUF` ioctl, and to prepare it for future I/O. Such
39 preparations may include cache invalidation or cleaning. Performing them
40 in advance saves time during the actual I/O. In case such cache
41 operations are not required, the application can use one of
42 ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` and
43 ``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` flags to skip the respective step.
45 The :ref:`struct v4l2_buffer <v4l2-buffer>` structure is specified in
52 On success 0 is returned, on error -1 and the ``errno`` variable is set
53 appropriately. The generic error codes are described at the
54 :ref:`Generic Error Codes <gen-errors>` chapter.
57 File I/O is in progress.
60 The buffer ``type`` is not supported, or the ``index`` is out of
61 bounds, or no buffers have been allocated yet, or the ``userptr`` or
62 ``length`` are invalid.