func-open.rst (2018B)
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.