Documentation/media/uapi/v4l/func-open.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _func-open:
   4
   5 ***********
   6 V4L2 open()
   7 ***********
   8
   9 Name
  10 ====
  11
  12 v4l2-open - Open a V4L2 device
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. code-block:: c
  19
  20     #include <fcntl.h>
  21
  22
  23 .. cpp:function:: int open( const char *device_name, int flags )
  24
  25
  26 Arguments
  27 =========
  28
  29 ``device_name``
  30     Device to be opened.
  31
  32 ``flags``
  33     Open flags. Access mode must be ``O_RDWR``. This is just a
  34     technicality, input devices still support only reading and output
  35     devices only writing.
  36
  37     When the ``O_NONBLOCK`` flag is given, the :ref:`read() <func-read>`
  38     function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will
  39     return the ``EAGAIN`` error code when no data is available or no
  40     buffer is in the driver outgoing queue, otherwise these functions
  41     block until data becomes available. All V4L2 drivers exchanging data
  42     with applications must support the ``O_NONBLOCK`` flag.
  43
  44     Other flags have no effect.
  45
  46
  47 Description
  48 ===========
  49
  50 To open a V4L2 device applications call :ref:`open() <func-open>` with the
  51 desired device name. This function has no side effects; all data format
  52 parameters, current input or output, control values or other properties
  53 remain unchanged. At the first :ref:`open() <func-open>` call after loading the
  54 driver they will be reset to default values, drivers are never in an
  55 undefined state.
  56
  57
  58 Return Value
  59 ============
  60
  61 On success :ref:`open() <func-open>` returns the new file descriptor. On error
  62 -1 is returned, and the ``errno`` variable is set appropriately.
  63 Possible error codes are:
  64
  65 EACCES
  66     The caller has no permission to access the device.
  67
  68 EBUSY
  69     The driver does not support multiple opens and the device is already
  70     in use.
  71
  72 ENXIO
  73     No device corresponding to this device special file exists.
  74
  75 ENOMEM
  76     Not enough kernel memory was available to complete the request.
  77
  78 EMFILE
  79     The process already has the maximum number of files open.
  80
  81 ENFILE
  82     The limit on the total number of files open on the system has been
  83     reached.