.. -*- coding: utf-8; mode: rst -*- .. _VIDIOC_PREPARE_BUF: ************************ ioctl VIDIOC_PREPARE_BUF ************************ Name ==== VIDIOC_PREPARE_BUF - Prepare a buffer for I/O Synopsis ======== .. c:function:: int ioctl( int fd, VIDIOC_PREPARE_BUF, struct v4l2_buffer *argp ) :name: VIDIOC_PREPARE_BUF Arguments ========= ``fd`` File descriptor returned by :ref:`open() `. ``argp`` Pointer to struct :c:type:`v4l2_buffer`. Description =========== Applications can optionally call the :ref:`VIDIOC_PREPARE_BUF` ioctl to pass ownership of the buffer to the driver before actually enqueuing it, using the :ref:`VIDIOC_QBUF ` ioctl, and to prepare it for future I/O. Such preparations may include cache invalidation or cleaning. Performing them in advance saves time during the actual I/O. In case such cache operations are not required, the application can use one of ``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` and ``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` flags to skip the respective step. The struct :c:type:`v4l2_buffer` structure is specified in :ref:`buffer`. 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 ` chapter. EBUSY File I/O is in progress. EINVAL The buffer ``type`` is not supported, or the ``index`` is out of bounds, or no buffers have been allocated yet, or the ``userptr`` or ``length`` are invalid.