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.. -*- 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() <func-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 <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 <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.
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