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