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Markus Heiser5377d912016-06-30 15:18:56 +02001.. -*- coding: utf-8; mode: rst -*-
2
3.. _func-open:
4
5***********
6V4L2 open()
7***********
8
Mauro Carvalho Chehab15e7d612016-07-05 15:14:35 -03009Name
Mauro Carvalho Chehab586027c2016-07-05 07:58:48 -030010====
Markus Heiser5377d912016-06-30 15:18:56 +020011
Mauro Carvalho Chehab586027c2016-07-05 07:58:48 -030012v4l2-open - Open a V4L2 device
Markus Heiser5377d912016-06-30 15:18:56 +020013
Mauro Carvalho Chehab15e7d612016-07-05 15:14:35 -030014
15Synopsis
Markus Heiser5377d912016-06-30 15:18:56 +020016========
17
18.. code-block:: c
19
20 #include <fcntl.h>
21
22
Mauro Carvalho Chehabb7e67f62016-07-02 09:49:16 -030023.. cpp:function:: int open( const char *device_name, int flags )
Markus Heiser5377d912016-06-30 15:18:56 +020024
Mauro Carvalho Chehab586027c2016-07-05 07:58:48 -030025
Mauro Carvalho Chehab15e7d612016-07-05 15:14:35 -030026Arguments
Markus Heiser5377d912016-06-30 15:18:56 +020027=========
28
29``device_name``
30 Device to be opened.
31
32``flags``
33 Open flags. Access mode must be ``O_RDWR``. This is just a
34 technicality, input devices still support only reading and output
35 devices only writing.
36
Mauro Carvalho Chehabf84dd902016-07-04 18:16:57 -030037 When the ``O_NONBLOCK`` flag is given, the :ref:`read() <func-read>`
38 function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will
39 return the ``EAGAIN`` error code when no data is available or no
40 buffer is in the driver outgoing queue, otherwise these functions
41 block until data becomes available. All V4L2 drivers exchanging data
42 with applications must support the ``O_NONBLOCK`` flag.
Markus Heiser5377d912016-06-30 15:18:56 +020043
44 Other flags have no effect.
45
46
Mauro Carvalho Chehab15e7d612016-07-05 15:14:35 -030047Description
Markus Heiser5377d912016-06-30 15:18:56 +020048===========
49
Mauro Carvalho Chehab760c7012016-07-04 12:56:17 -030050To open a V4L2 device applications call :ref:`open() <func-open>` with the
Markus Heiser5377d912016-06-30 15:18:56 +020051desired device name. This function has no side effects; all data format
52parameters, current input or output, control values or other properties
Mauro Carvalho Chehab760c7012016-07-04 12:56:17 -030053remain unchanged. At the first :ref:`open() <func-open>` call after loading the
Markus Heiser5377d912016-06-30 15:18:56 +020054driver they will be reset to default values, drivers are never in an
55undefined state.
56
57
Mauro Carvalho Chehab15e7d612016-07-05 15:14:35 -030058Return Value
Markus Heiser5377d912016-06-30 15:18:56 +020059============
60
Mauro Carvalho Chehab760c7012016-07-04 12:56:17 -030061On success :ref:`open() <func-open>` returns the new file descriptor. On error
Markus Heiser5377d912016-06-30 15:18:56 +020062-1 is returned, and the ``errno`` variable is set appropriately.
63Possible error codes are:
64
65EACCES
66 The caller has no permission to access the device.
67
68EBUSY
69 The driver does not support multiple opens and the device is already
70 in use.
71
72ENXIO
73 No device corresponding to this device special file exists.
74
75ENOMEM
76 Not enough kernel memory was available to complete the request.
77
78EMFILE
79 The process already has the maximum number of files open.
80
81ENFILE
82 The limit on the total number of files open on the system has been
83 reached.