Documentation/media/uapi/dvb/frontend_f_open.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _frontend_f_open:
   4
   5 *******************
   6 DVB frontend open()
   7 *******************
   8
   9 Name
  10 ====
  11
  12 fe-open - Open a frontend 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 can either be ``O_RDWR`` or ``O_RDONLY``.
  34
  35     Multiple opens are allowed with ``O_RDONLY``. In this mode, only
  36     query and read ioctls are allowed.
  37
  38     Only one open is allowed in ``O_RDWR``. In this mode, all ioctls are
  39     allowed.
  40
  41     When the ``O_NONBLOCK`` flag is given, the system calls may return
  42     ``EAGAIN`` error code when no data is available or when the device
  43     driver is temporarily busy.
  44
  45     Other flags have no effect.
  46
  47
  48 Description
  49 ===========
  50
  51 This system call opens a named frontend device
  52 (``/dev/dvb/adapter?/frontend?``) for subsequent use. Usually the first
  53 thing to do after a successful open is to find out the frontend type
  54 with :ref:`FE_GET_INFO`.
  55
  56 The device can be opened in read-only mode, which only allows monitoring
  57 of device status and statistics, or read/write mode, which allows any
  58 kind of use (e.g. performing tuning operations.)
  59
  60 In a system with multiple front-ends, it is usually the case that
  61 multiple devices cannot be open in read/write mode simultaneously. As
  62 long as a front-end device is opened in read/write mode, other open()
  63 calls in read/write mode will either fail or block, depending on whether
  64 non-blocking or blocking mode was specified. A front-end device opened
  65 in blocking mode can later be put into non-blocking mode (and vice
  66 versa) using the F_SETFL command of the fcntl system call. This is a
  67 standard system call, documented in the Linux manual page for fcntl.
  68 When an open() call has succeeded, the device will be ready for use in
  69 the specified mode. This implies that the corresponding hardware is
  70 powered up, and that other front-ends may have been powered down to make
  71 that possible.
  72
  73
  74 Return Value
  75 ============
  76
  77 On success :ref:`open() <frontend_f_open>` returns the new file descriptor.
  78 On error, -1 is returned, and the ``errno`` variable is set appropriately.
  79
  80 Possible error codes are:
  81
  82 EACCES
  83     The caller has no permission to access the device.
  84
  85 EBUSY
  86     The the device driver is already in use.
  87
  88 ENXIO
  89     No device corresponding to this device special file exists.
  90
  91 ENOMEM
  92     Not enough kernel memory was available to complete the request.
  93
  94 EMFILE
  95     The process already has the maximum number of files open.
  96
  97 ENFILE
  98     The limit on the total number of files open on the system has been
  99     reached.
 100
 101 ENODEV
 102     The device got removed.