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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2 3.. _querycap:4 5*********************6Querying Capabilities7*********************8 9Because V4L2 covers a wide variety of devices not all aspects of the API10are equally applicable to all types of devices. Furthermore devices of11the same type have different capabilities and this specification permits12the omission of a few complicated and less important parts of the API.13 14The :ref:`VIDIOC_QUERYCAP` ioctl is available to15check if the kernel device is compatible with this specification, and to16query the :ref:`functions <devices>` and :ref:`I/O methods <io>`17supported by the device.18 19Starting with kernel version 3.1, :ref:`VIDIOC_QUERYCAP`20will return the V4L2 API version used by the driver, with generally21matches the Kernel version. There's no need of using22:ref:`VIDIOC_QUERYCAP` to check if a specific ioctl23is supported, the V4L2 core now returns ``ENOTTY`` if a driver doesn't24provide support for an ioctl.25 26Other features can be queried by calling the respective ioctl, for27example :ref:`VIDIOC_ENUMINPUT` to learn about the28number, types and names of video connectors on the device. Although29abstraction is a major objective of this API, the30:ref:`VIDIOC_QUERYCAP` ioctl also allows driver31specific applications to reliably identify the driver.32 33All V4L2 drivers must support :ref:`VIDIOC_QUERYCAP`.34Applications should always call this ioctl after opening the device.35