[deliverable/linux.git] / Documentation / linux_tv / media / v4l / func-open.rst

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

.. _func-open:

***********
V4L2 open()
***********

*man v4l2-open(2)*

Open a V4L2 device


Synopsis
========

.. code-block:: c

    #include <fcntl.h>


.. c:function:: int open( const char *device_name, int flags )

Arguments
=========

``device_name``
    Device to be opened.

``flags``
    Open flags. Access mode must be ``O_RDWR``. This is just a
    technicality, input devices still support only reading and output
    devices only writing.

    When the ``O_NONBLOCK`` flag is given, the read() function and the
    :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will return the EAGAIN
    error code when no data is available or no buffer is in the driver
    outgoing queue, otherwise these functions block until data becomes
    available. All V4L2 drivers exchanging data with applications must
    support the ``O_NONBLOCK`` flag.

    Other flags have no effect.


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

To open a V4L2 device applications call :c:func:`open()` with the
desired device name. This function has no side effects; all data format
parameters, current input or output, control values or other properties
remain unchanged. At the first :c:func:`open()` call after loading the
driver they will be reset to default values, drivers are never in an
undefined state.


Return Value
============

On success :c:func:`open()` returns the new file descriptor. On error
-1 is returned, and the ``errno`` variable is set appropriately.
Possible error codes are:

EACCES
    The caller has no permission to access the device.

EBUSY
    The driver does not support multiple opens and the device is already
    in use.

ENXIO
    No device corresponding to this device special file exists.

ENOMEM
    Not enough kernel memory was available to complete the request.

EMFILE
    The process already has the maximum number of files open.

ENFILE
    The limit on the total number of files open on the system has been
    reached.


.. ------------------------------------------------------------------------------
.. 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
.. ------------------------------------------------------------------------------
Commit	Line	Data
5377d91f MH	1	.. -- coding: utf-8; mode: rst --
	2
	3	.. _func-open:
	4
	5	***********
	6	V4L2 open()
	7	***********
	8
	9	man v4l2-open(2)
	10
	11	Open a V4L2 device
	12
	13
	14	Synopsis
	15	========
	16
	17	.. code-block:: c
	18
	19	#include <fcntl.h>
	20
	21
	22	.. c:function:: int open( const char *device_name, int flags )
	23
	24	Arguments
	25	=========
	26
	27	``device_name``
	28	Device to be opened.
	29
	30	``flags``
	31	Open flags. Access mode must be ``O_RDWR``. This is just a
	32	technicality, input devices still support only reading and output
	33	devices only writing.
	34
	35	When the ``O_NONBLOCK`` flag is given, the read() function and the
af4a4d0d	36	:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will return the EAGAIN
5377d91f MH	37	error code when no data is available or no buffer is in the driver
	38	outgoing queue, otherwise these functions block until data becomes
	39	available. All V4L2 drivers exchanging data with applications must
	40	support the ``O_NONBLOCK`` flag.
	41
	42	Other flags have no effect.
	43
	44
	45	Description
	46	===========
	47
	48	To open a V4L2 device applications call :c:func:`open()` with the
	49	desired device name. This function has no side effects; all data format
	50	parameters, current input or output, control values or other properties
	51	remain unchanged. At the first :c:func:`open()` call after loading the
	52	driver they will be reset to default values, drivers are never in an
	53	undefined state.
	54
	55
	56	Return Value
	57	============
	58
	59	On success :c:func:`open()` returns the new file descriptor. On error
	60	-1 is returned, and the ``errno`` variable is set appropriately.
	61	Possible error codes are:
	62
	63	EACCES
	64	The caller has no permission to access the device.
	65
	66	EBUSY
	67	The driver does not support multiple opens and the device is already
	68	in use.
	69
	70	ENXIO
	71	No device corresponding to this device special file exists.
	72
	73	ENOMEM
	74	Not enough kernel memory was available to complete the request.
	75
	76	EMFILE
	77	The process already has the maximum number of files open.
	78
	79	ENFILE
	80	The limit on the total number of files open on the system has been
	81	reached.
	82
	83
	84	.. ------------------------------------------------------------------------------
	85	.. This file was automatically converted from DocBook-XML with the dbxml
	86	.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
	87	.. from the linux kernel, refer to:
	88	..
	89	.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
	90	.. ------------------------------------------------------------------------------