frontend_f_open.rst (3015B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: DTV.fe 3 4.. _frontend_f_open: 5 6*************************** 7Digital TV frontend open() 8*************************** 9 10Name 11==== 12 13fe-open - Open a frontend device 14 15Synopsis 16======== 17 18.. code-block:: c 19 20 #include <fcntl.h> 21 22.. c:function:: int open( const char *device_name, int flags ) 23 24Arguments 25========= 26 27``device_name`` 28 Device to be opened. 29 30``flags`` 31 Open flags. Access can either be ``O_RDWR`` or ``O_RDONLY``. 32 33 Multiple opens are allowed with ``O_RDONLY``. In this mode, only 34 query and read ioctls are allowed. 35 36 Only one open is allowed in ``O_RDWR``. In this mode, all ioctls are 37 allowed. 38 39 When the ``O_NONBLOCK`` flag is given, the system calls may return 40 ``EAGAIN`` error code when no data is available or when the device 41 driver is temporarily busy. 42 43 Other flags have no effect. 44 45Description 46=========== 47 48This system call opens a named frontend device 49(``/dev/dvb/adapter?/frontend?``) for subsequent use. Usually the first 50thing to do after a successful open is to find out the frontend type 51with :ref:`FE_GET_INFO`. 52 53The device can be opened in read-only mode, which only allows monitoring 54of device status and statistics, or read/write mode, which allows any 55kind of use (e.g. performing tuning operations.) 56 57In a system with multiple front-ends, it is usually the case that 58multiple devices cannot be open in read/write mode simultaneously. As 59long as a front-end device is opened in read/write mode, other open() 60calls in read/write mode will either fail or block, depending on whether 61non-blocking or blocking mode was specified. A front-end device opened 62in blocking mode can later be put into non-blocking mode (and vice 63versa) using the F_SETFL command of the fcntl system call. This is a 64standard system call, documented in the Linux manual page for fcntl. 65When an open() call has succeeded, the device will be ready for use in 66the specified mode. This implies that the corresponding hardware is 67powered up, and that other front-ends may have been powered down to make 68that possible. 69 70Return Value 71============ 72 73On success :c:func:`open()` returns the new file descriptor. 74On error, -1 is returned, and the ``errno`` variable is set appropriately. 75 76Possible error codes are: 77 78On success 0 is returned, and :c:type:`ca_slot_info` is filled. 79 80On error -1 is returned, and the ``errno`` variable is set 81appropriately. 82 83.. tabularcolumns:: |p{2.5cm}|p{15.0cm}| 84 85.. flat-table:: 86 :header-rows: 0 87 :stub-columns: 0 88 :widths: 1 16 89 90 - - ``EPERM`` 91 - The caller has no permission to access the device. 92 93 - - ``EBUSY`` 94 - The the device driver is already in use. 95 96 - - ``EMFILE`` 97 - The process already has the maximum number of files open. 98 99 - - ``ENFILE`` 100 - The limit on the total number of files open on the system has been 101 reached. 102 103The generic error codes are described at the 104:ref:`Generic Error Codes <gen-errors>` chapter.