.. 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.

ENXIO No device corresponding to this device special file exists.

ENOMEM Not enough kernel memory was available to complete the request.

EMFILE The process already has the maximum number of files open.

ENFILE The limit on the total number of files open on the system has been reached.