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