0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002 .. c:namespace:: V4L
0003
0004 .. _func-open:
0005
0006 ***********
0007 V4L2 open()
0008 ***********
0009
0010 Name
0011 ====
0012
0013 v4l2-open - Open a V4L2 device
0014
0015 Synopsis
0016 ========
0017
0018 .. code-block:: c
0019
0020 #include <fcntl.h>
0021
0022 .. c:function:: int open( const char *device_name, int flags )
0023
0024 Arguments
0025 =========
0026
0027 ``device_name``
0028 Device to be opened.
0029
0030 ``flags``
0031 Open flags. Access mode must be ``O_RDWR``. This is just a
0032 technicality, input devices still support only reading and output
0033 devices only writing.
0034
0035 When the ``O_NONBLOCK`` flag is given, the :c:func:`read()`
0036 function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will
0037 return the ``EAGAIN`` error code when no data is available or no
0038 buffer is in the driver outgoing queue, otherwise these functions
0039 block until data becomes available. All V4L2 drivers exchanging data
0040 with applications must support the ``O_NONBLOCK`` flag.
0041
0042 Other flags have no effect.
0043
0044 Description
0045 ===========
0046
0047 To open a V4L2 device applications call :c:func:`open()` with the
0048 desired device name. This function has no side effects; all data format
0049 parameters, current input or output, control values or other properties
0050 remain unchanged. At the first :c:func:`open()` call after loading the
0051 driver they will be reset to default values, drivers are never in an
0052 undefined state.
0053
0054 Return Value
0055 ============
0056
0057 On success :c:func:`open()` returns the new file descriptor. On error
0058 -1 is returned, and the ``errno`` variable is set appropriately.
0059 Possible error codes are:
0060
0061 EACCES
0062 The caller has no permission to access the device.
0063
0064 EBUSY
0065 The driver does not support multiple opens and the device is already
0066 in use.
0067
0068 ENXIO
0069 No device corresponding to this device special file exists.
0070
0071 ENOMEM
0072 Not enough kernel memory was available to complete the request.
0073
0074 EMFILE
0075 The process already has the maximum number of files open.
0076
0077 ENFILE
0078 The limit on the total number of files open on the system has been
0079 reached.
