[deliverable/linux.git] / Documentation / media / uapi / v4l / vidioc-prepare-buf.rst

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

.. _VIDIOC_PREPARE_BUF:

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

Name
====

VIDIOC_PREPARE_BUF - Prepare a buffer for I/O


Synopsis
========

.. cpp: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 :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 :ref:`struct v4l2_buffer <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.
Commit	Line	Data
5377d91f MH	1	.. -- coding: utf-8; mode: rst --
5377d91f MH	2
af4a4d0d	3	.. _VIDIOC_PREPARE_BUF:
5377d91f MH	4
	5	************************
	6	ioctl VIDIOC_PREPARE_BUF
	7	************************
	8
15e7d615	9	Name
586027ce	10	====
5377d91f	11
586027ce	12	VIDIOC_PREPARE_BUF - Prepare a buffer for I/O
5377d91f	13
15e7d615 MCC	14
15e7d615 MCC	15	Synopsis
5377d91f MH	16	========
5377d91f MH	17
b7e67f6c	18	.. cpp:function:: int ioctl( int fd, int request, struct v4l2_buffer *argp )
5377d91f	19
586027ce	20
15e7d615	21	Arguments
5377d91f MH	22	=========
	23
	24	``fd``
	25	File descriptor returned by :ref:`open() <func-open>`.
	26
	27	``request``
	28	VIDIOC_PREPARE_BUF
	29
	30	``argp``
	31
	32
15e7d615	33	Description
5377d91f MH	34	===========
5377d91f MH	35
2212ff25	36	Applications can optionally call the :ref:`VIDIOC_PREPARE_BUF` ioctl to
5377d91f	37	pass ownership of the buffer to the driver before actually enqueuing it,
2212ff25	38	using the :ref:`VIDIOC_QBUF` ioctl, and to prepare it for future I/O. Such
5377d91f MH	39	preparations may include cache invalidation or cleaning. Performing them
	40	in advance saves time during the actual I/O. In case such cache
	41	operations are not required, the application can use one of
	42	``V4L2_BUF_FLAG_NO_CACHE_INVALIDATE`` and
	43	``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` flags to skip the respective step.
	44
acf309a2	45	The :ref:`struct v4l2_buffer <v4l2-buffer>` structure is specified in
5377d91f MH	46	:ref:`buffer`.
	47
	48
15e7d615	49	Return Value
5377d91f MH	50	============
	51
	52	On success 0 is returned, on error -1 and the ``errno`` variable is set
	53	appropriately. The generic error codes are described at the
	54	:ref:`Generic Error Codes <gen-errors>` chapter.
	55
	56	EBUSY
	57	File I/O is in progress.
	58
	59	EINVAL
	60	The buffer ``type`` is not supported, or the ``index`` is out of
	61	bounds, or no buffers have been allocated yet, or the ``userptr`` or
	62	``length`` are invalid.