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 *man v4l2-open(2)*
  10
  11 Open a V4L2 device
  12
  13
  14 Synopsis
  15 ========
  16
  17 .. code-block:: c
  18
  19     #include <fcntl.h>
  20
  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 read() function and the
  36     :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will return the EAGAIN
  37     error code when no data is available or no buffer is in the driver
  38     outgoing queue, otherwise these functions block until data becomes
  39     available. All V4L2 drivers exchanging data with applications must
  40     support the ``O_NONBLOCK`` flag.
  41
  42     Other flags have no effect.
  43
  44
  45 Description
  46 ===========
  47
  48 To open a V4L2 device applications call :c:func:`open()` with the
  49 desired device name. This function has no side effects; all data format
  50 parameters, current input or output, control values or other properties
  51 remain unchanged. At the first :c:func:`open()` call after loading the
  52 driver they will be reset to default values, drivers are never in an
  53 undefined state.
  54
  55
  56 Return Value
  57 ============
  58
  59 On success :c:func:`open()` returns the new file descriptor. On error
  60 -1 is returned, and the ``errno`` variable is set appropriately.
  61 Possible error codes are:
  62
  63 EACCES
  64     The caller has no permission to access the device.
  65
  66 EBUSY
  67     The driver does not support multiple opens and the device is already
  68     in use.
  69
  70 ENXIO
  71     No device corresponding to this device special file exists.
  72
  73 ENOMEM
  74     Not enough kernel memory was available to complete the request.
  75
  76 EMFILE
  77     The process already has the maximum number of files open.
  78
  79 ENFILE
  80     The limit on the total number of files open on the system has been
  81     reached.
  82
  83
  84 .. ------------------------------------------------------------------------------
  85 .. This file was automatically converted from DocBook-XML with the dbxml
  86 .. library (https://github.com/return42/sphkerneldoc). The origin XML comes
  87 .. from the linux kernel, refer to:
  88 ..
  89 .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
  90 .. ------------------------------------------------------------------------------