.. -*- coding: utf-8; mode: rst -*-

.. _vidioc-prepare-buf:

************************
ioctl VIDIOC_PREPARE_BUF
************************

*man VIDIOC_PREPARE_BUF(2)*

Prepare a buffer for I/O


Synopsis
========

.. c:function:: int ioctl( int fd, int request, struct v4l2_buffer *argp )

Arguments
=========

``fd``
    File descriptor returned by :ref:`open() <func-open>`.

``request``
    VIDIOC_PREPARE_BUF

``argp``


Description
===========

Applications can optionally call the ``VIDIOC_PREPARE_BUF`` ioctl to
pass ownership of the buffer to the driver before actually enqueuing it,
using the ``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 :c:type:`struct 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 <gen-errors>` 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.


.. ------------------------------------------------------------------------------
.. This file was automatically converted from DocBook-XML with the dbxml
.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
.. from the linux kernel, refer to:
..
.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
.. ------------------------------------------------------------------------------