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+.. Permission is granted to copy, distribute and/or modify this
+.. document under the terms of the GNU Free Documentation License,
+.. Version 1.1 or any later version published by the Free Software
+.. Foundation, with no Invariant Sections, no Front-Cover Texts
+.. and no Back-Cover Texts. A copy of the license is included at
+.. Documentation/userspace-api/media/fdl-appendix.rst.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _querycap:
+
+*********************
+Querying Capabilities
+*********************
+
+Because V4L2 covers a wide variety of devices not all aspects of the API
+are equally applicable to all types of devices. Furthermore devices of
+the same type have different capabilities and this specification permits
+the omission of a few complicated and less important parts of the API.
+
+The :ref:`VIDIOC_QUERYCAP` ioctl is available to
+check if the kernel device is compatible with this specification, and to
+query the :ref:`functions <devices>` and :ref:`I/O methods <io>`
+supported by the device.
+
+Starting with kernel version 3.1, :ref:`VIDIOC_QUERYCAP`
+will return the V4L2 API version used by the driver, with generally
+matches the Kernel version. There's no need of using
+:ref:`VIDIOC_QUERYCAP` to check if a specific ioctl
+is supported, the V4L2 core now returns ``ENOTTY`` if a driver doesn't
+provide support for an ioctl.
+
+Other features can be queried by calling the respective ioctl, for
+example :ref:`VIDIOC_ENUMINPUT` to learn about the
+number, types and names of video connectors on the device. Although
+abstraction is a major objective of this API, the
+:ref:`VIDIOC_QUERYCAP` ioctl also allows driver
+specific applications to reliably identify the driver.
+
+All V4L2 drivers must support :ref:`VIDIOC_QUERYCAP`.
+Applications should always call this ioctl after opening the device.