Documentation/userspace-api/media/dvb/frontend_f_open.rst

Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/dvb/frontend_f_open.rst

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Linux kernel
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Documentation/userspace-api/media/dvb/frontend_f_open.rst
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.rst
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3011 bytes
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105
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: documentation
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: DTV.fe

.. _frontend_f_open:

***************************
Digital TV frontend open()
***************************

Name
====

fe-open - Open a frontend device

Synopsis
========

.. code-block:: c

    #include <fcntl.h>

.. c:function:: int open( const char *device_name, int flags )

Arguments
=========

``device_name``
    Device to be opened.

``flags``
    Open flags. Access can either be ``O_RDWR`` or ``O_RDONLY``.

    Multiple opens are allowed with ``O_RDONLY``. In this mode, only
    query and read ioctls are allowed.

    Only one open is allowed in ``O_RDWR``. In this mode, all ioctls are
    allowed.

    When the ``O_NONBLOCK`` flag is given, the system calls may return
    ``EAGAIN`` error code when no data is available or when the device
    driver is temporarily busy.

    Other flags have no effect.

Description
===========

This system call opens a named frontend device
(``/dev/dvb/adapter?/frontend?``) for subsequent use. Usually the first
thing to do after a successful open is to find out the frontend type
with :ref:`FE_GET_INFO`.

The device can be opened in read-only mode, which only allows monitoring
of device status and statistics, or read/write mode, which allows any
kind of use (e.g. performing tuning operations.)

In a system with multiple front-ends, it is usually the case that
multiple devices cannot be open in read/write mode simultaneously. As
long as a front-end device is opened in read/write mode, other open()
calls in read/write mode will either fail or block, depending on whether
non-blocking or blocking mode was specified. A front-end device opened
in blocking mode can later be put into non-blocking mode (and vice
versa) using the F_SETFL command of the fcntl system call. This is a
standard system call, documented in the Linux manual page for fcntl.
When an open() call has succeeded, the device will be ready for use in
the specified mode. This implies that the corresponding hardware is
powered up, and that other front-ends may have been powered down to make
that possible.

Return Value

Annotation

Implementation Notes