1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_PREPARE_BUF: 5 6************************ 7ioctl VIDIOC_PREPARE_BUF 8************************ 9 10Name 11==== 12 13VIDIOC_PREPARE_BUF - Prepare a buffer for I/O 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_PREPARE_BUF 19 20``int ioctl(int fd, VIDIOC_PREPARE_BUF, struct v4l2_buffer *argp)`` 21 22Arguments 23========= 24 25``fd`` 26 File descriptor returned by :c:func:`open()`. 27 28``argp`` 29 Pointer to struct :c:type:`v4l2_buffer`. 30 31Description 32=========== 33 34Applications can optionally call the :ref:`VIDIOC_PREPARE_BUF` ioctl to 35pass ownership of the buffer to the driver before actually enqueuing it, 36using the :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` ioctl, and to prepare it for future I/O. Such 37preparations may include cache invalidation or cleaning. Performing them 38in advance saves time during the actual I/O. 39 40The struct :c:type:`v4l2_buffer` structure is specified in 41:ref:`buffer`. 42 43Return Value 44============ 45 46On success 0 is returned, on error -1 and the ``errno`` variable is set 47appropriately. The generic error codes are described at the 48:ref:`Generic Error Codes <gen-errors>` chapter. 49 50EBUSY 51 File I/O is in progress. 52 53EINVAL 54 The buffer ``type`` is not supported, or the ``index`` is out of 55 bounds, or no buffers have been allocated yet, or the ``userptr`` or 56 ``length`` are invalid. 57