1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L 2 .. c:namespace:: V4L
3 3
4 .. _func-open: 4 .. _func-open:
5 5
6 *********** 6 ***********
7 V4L2 open() 7 V4L2 open()
8 *********** 8 ***********
9 9
10 Name 10 Name
11 ==== 11 ====
12 12
13 v4l2-open - Open a V4L2 device 13 v4l2-open - Open a V4L2 device
14 14
15 Synopsis 15 Synopsis
16 ======== 16 ========
17 17
18 .. code-block:: c 18 .. code-block:: c
19 19
20 #include <fcntl.h> 20 #include <fcntl.h>
21 21
22 .. c:function:: int open( const char *device_n 22 .. c:function:: int open( const char *device_name, int flags )
23 23
24 Arguments 24 Arguments
25 ========= 25 =========
26 26
27 ``device_name`` 27 ``device_name``
28 Device to be opened. 28 Device to be opened.
29 29
30 ``flags`` 30 ``flags``
31 Open flags. Access mode must be ``O_RDWR`` 31 Open flags. Access mode must be ``O_RDWR``. This is just a
32 technicality, input devices still support 32 technicality, input devices still support only reading and output
33 devices only writing. 33 devices only writing.
34 34
35 When the ``O_NONBLOCK`` flag is given, the 35 When the ``O_NONBLOCK`` flag is given, the :c:func:`read()`
36 function and the :ref:`VIDIOC_DQBUF <VIDIO 36 function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will
37 return the ``EAGAIN`` error code when no d 37 return the ``EAGAIN`` error code when no data is available or no
38 buffer is in the driver outgoing queue, ot 38 buffer is in the driver outgoing queue, otherwise these functions
39 block until data becomes available. All V4 39 block until data becomes available. All V4L2 drivers exchanging data
40 with applications must support the ``O_NON 40 with applications must support the ``O_NONBLOCK`` flag.
41 41
42 Other flags have no effect. 42 Other flags have no effect.
43 43
44 Description 44 Description
45 =========== 45 ===========
46 46
47 To open a V4L2 device applications call :c:fun 47 To open a V4L2 device applications call :c:func:`open()` with the
48 desired device name. This function has no side 48 desired device name. This function has no side effects; all data format
49 parameters, current input or output, control v 49 parameters, current input or output, control values or other properties
50 remain unchanged. At the first :c:func:`open() 50 remain unchanged. At the first :c:func:`open()` call after loading the
51 driver they will be reset to default values, d 51 driver they will be reset to default values, drivers are never in an
52 undefined state. 52 undefined state.
53 53
54 Return Value 54 Return Value
55 ============ 55 ============
56 56
57 On success :c:func:`open()` returns the new fi 57 On success :c:func:`open()` returns the new file descriptor. On error
58 -1 is returned, and the ``errno`` variable is 58 -1 is returned, and the ``errno`` variable is set appropriately.
59 Possible error codes are: 59 Possible error codes are:
60 60
61 EACCES 61 EACCES
62 The caller has no permission to access the 62 The caller has no permission to access the device.
63 63
64 EBUSY 64 EBUSY
65 The driver does not support multiple opens 65 The driver does not support multiple opens and the device is already
66 in use. 66 in use.
67 67
68 ENODEV 68 ENODEV
69 Device not found or was removed. 69 Device not found or was removed.
70 70
71 ENOMEM 71 ENOMEM
72 Not enough kernel memory was available to 72 Not enough kernel memory was available to complete the request.
73 73
74 EMFILE 74 EMFILE
75 The process already has the maximum number 75 The process already has the maximum number of files open.
76 76
77 ENFILE 77 ENFILE
78 The limit on the total number of files ope 78 The limit on the total number of files open on the system has been
79 reached. 79 reached.
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