1.. -*- coding: utf-8; mode: rst -*- 2 3.. _VIDIOC_PREPARE_BUF: 4 5************************ 6ioctl VIDIOC_PREPARE_BUF 7************************ 8 9Name 10==== 11 12VIDIOC_PREPARE_BUF - Prepare a buffer for I/O 13 14 15Synopsis 16======== 17 18.. c:function:: int ioctl( int fd, VIDIOC_PREPARE_BUF, struct v4l2_buffer *argp ) 19 :name: VIDIOC_PREPARE_BUF 20 21 22Arguments 23========= 24 25``fd`` 26 File descriptor returned by :ref:`open() <func-open>`. 27 28``argp`` 29 Pointer to struct :c:type:`v4l2_buffer`. 30 31 32Description 33=========== 34 35Applications can optionally call the :ref:`VIDIOC_PREPARE_BUF` ioctl to 36pass ownership of the buffer to the driver before actually enqueuing it, 37using the :ref:`VIDIOC_QBUF` ioctl, and to prepare it for future I/O. Such 38preparations may include cache invalidation or cleaning. Performing them 39in advance saves time during the actual I/O. In case such cache 40operations are not required, the application can use one of 41``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` and 42``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` flags to skip the respective step. 43 44The struct :c:type:`v4l2_buffer` structure is specified in 45:ref:`buffer`. 46 47 48Return Value 49============ 50 51On success 0 is returned, on error -1 and the ``errno`` variable is set 52appropriately. The generic error codes are described at the 53:ref:`Generic Error Codes <gen-errors>` chapter. 54 55EBUSY 56 File I/O is in progress. 57 58EINVAL 59 The buffer ``type`` is not supported, or the ``index`` is out of 60 bounds, or no buffers have been allocated yet, or the ``userptr`` or 61 ``length`` are invalid. 62