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+.. 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.