1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _func-open:
5
6***********
7V4L2 open()
8***********
9
10Name
11====
12
13v4l2-open - Open a V4L2 device
14
15Synopsis
16========
17
18.. code-block:: c
19
20    #include <fcntl.h>
21
22.. c:function:: int open( const char *device_name, int flags )
23
24Arguments
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 :c:func:`read()`
36    function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will
37    return the ``EAGAIN`` error code when no data is available or no
38    buffer is in the driver outgoing queue, otherwise these functions
39    block until data becomes available. All V4L2 drivers exchanging data
40    with applications must support the ``O_NONBLOCK`` flag.
41
42    Other flags have no effect.
43
44Description
45===========
46
47To open a V4L2 device applications call :c:func:`open()` with the
48desired device name. This function has no side effects; all data format
49parameters, current input or output, control values or other properties
50remain unchanged. At the first :c:func:`open()` call after loading the
51driver they will be reset to default values, drivers are never in an
52undefined state.
53
54Return Value
55============
56
57On success :c:func:`open()` returns the new file descriptor. On error
58-1 is returned, and the ``errno`` variable is set appropriately.
59Possible error codes are:
60
61EACCES
62    The caller has no permission to access the device.
63
64EBUSY
65    The driver does not support multiple opens and the device is already
66    in use.
67
68ENXIO
69    No device corresponding to this device special file exists.
70
71ENOMEM
72    Not enough kernel memory was available to complete the request.
73
74EMFILE
75    The process already has the maximum number of files open.
76
77ENFILE
78    The limit on the total number of files open on the system has been
79    reached.
80