111 lines
2.9 KiB
ReStructuredText
111 lines
2.9 KiB
ReStructuredText
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.. -*- coding: utf-8; mode: rst -*-
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.. _frontend_f_open:
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***************************
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Digital TV frontend open()
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***************************
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Name
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====
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fe-open - Open a frontend device
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Synopsis
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========
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.. code-block:: c
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#include <fcntl.h>
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.. c:function:: int open( const char *device_name, int flags )
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:name: dvb-fe-open
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Arguments
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=========
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``device_name``
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Device to be opened.
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``flags``
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Open flags. Access can either be ``O_RDWR`` or ``O_RDONLY``.
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Multiple opens are allowed with ``O_RDONLY``. In this mode, only
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query and read ioctls are allowed.
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Only one open is allowed in ``O_RDWR``. In this mode, all ioctls are
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allowed.
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When the ``O_NONBLOCK`` flag is given, the system calls may return
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``EAGAIN`` error code when no data is available or when the device
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driver is temporarily busy.
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Other flags have no effect.
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Description
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===========
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This system call opens a named frontend device
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(``/dev/dvb/adapter?/frontend?``) for subsequent use. Usually the first
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thing to do after a successful open is to find out the frontend type
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with :ref:`FE_GET_INFO`.
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The device can be opened in read-only mode, which only allows monitoring
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of device status and statistics, or read/write mode, which allows any
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kind of use (e.g. performing tuning operations.)
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In a system with multiple front-ends, it is usually the case that
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multiple devices cannot be open in read/write mode simultaneously. As
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long as a front-end device is opened in read/write mode, other open()
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calls in read/write mode will either fail or block, depending on whether
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non-blocking or blocking mode was specified. A front-end device opened
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in blocking mode can later be put into non-blocking mode (and vice
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versa) using the F_SETFL command of the fcntl system call. This is a
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standard system call, documented in the Linux manual page for fcntl.
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When an open() call has succeeded, the device will be ready for use in
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the specified mode. This implies that the corresponding hardware is
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powered up, and that other front-ends may have been powered down to make
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that possible.
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Return Value
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============
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On success :ref:`open() <frontend_f_open>` returns the new file descriptor.
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On error, -1 is returned, and the ``errno`` variable is set appropriately.
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Possible error codes are:
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On success 0 is returned, and :c:type:`ca_slot_info` is filled.
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On error -1 is returned, and the ``errno`` variable is set
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appropriately.
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.. tabularcolumns:: |p{2.5cm}|p{15.0cm}|
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.. flat-table::
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 16
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- - ``EPERM``
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- The caller has no permission to access the device.
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- - ``EBUSY``
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- The the device driver is already in use.
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- - ``EMFILE``
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- The process already has the maximum number of files open.
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- - ``ENFILE``
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- The limit on the total number of files open on the system has been
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reached.
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The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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