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+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _func-ioctl:
+
+************
+V4L2 ioctl()
+************
+
+Name
+====
+
+v4l2-ioctl - Program a V4L2 device
+
+Synopsis
+========
+
+.. code-block:: c
+
+    #include <sys/ioctl.h>
+
+``int ioctl(int fd, int request, void *argp)``
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :c:func:`open()`.
+
+``request``
+    V4L2 ioctl request code as defined in the ``videodev2.h`` header
+    file, for example VIDIOC_QUERYCAP.
+
+``argp``
+    Pointer to a function parameter, usually a structure.
+
+Description
+===========
+
+The :ref:`ioctl() <func-ioctl>` function is used to program V4L2 devices. The
+argument ``fd`` must be an open file descriptor. An ioctl ``request``
+has encoded in it whether the argument is an input, output or read/write
+parameter, and the size of the argument ``argp`` in bytes. Macros and
+defines specifying V4L2 ioctl requests are located in the
+``videodev2.h`` header file. Applications should use their own copy, not
+include the version in the kernel sources on the system they compile on.
+All V4L2 ioctl requests, their respective function and parameters are
+specified in :ref:`user-func`.
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.
+
+When an ioctl that takes an output or read/write parameter fails, the
+parameter remains unmodified.