Documentation/userspace-api/media/v4l/func-open.rst

Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/v4l/func-open.rst

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System
Linux kernel
Corpus path
Documentation/userspace-api/media/v4l/func-open.rst
Extension
.rst
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1992 bytes
Lines
80
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:: V4L

.. _func-open:

***********
V4L2 open()
***********

Name
====

v4l2-open - Open a V4L2 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 mode must be ``O_RDWR``. This is just a
    technicality, input devices still support only reading and output
    devices only writing.

    When the ``O_NONBLOCK`` flag is given, the :c:func:`read()`
    function and the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will
    return the ``EAGAIN`` error code when no data is available or no
    buffer is in the driver outgoing queue, otherwise these functions
    block until data becomes available. All V4L2 drivers exchanging data
    with applications must support the ``O_NONBLOCK`` flag.

    Other flags have no effect.

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

To open a V4L2 device applications call :c:func:`open()` with the
desired device name. This function has no side effects; all data format
parameters, current input or output, control values or other properties
remain unchanged. At the first :c:func:`open()` call after loading the
driver they will be reset to default values, drivers are never in an
undefined state.

Return Value
============

On success :c:func:`open()` returns the new file descriptor. On error
-1 is returned, and the ``errno`` variable is set appropriately.
Possible error codes are:

EACCES
    The caller has no permission to access the device.

EBUSY
    The driver does not support multiple opens and the device is already
    in use.

ENODEV
    Device not found or was removed.

Annotation

Implementation Notes