1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3 .. _querycap: 4 5 ********************* 6 Querying Capabilities 7 ********************* 8 9 Because V4L2 covers a wide variety of devices not all aspects of the API 10 are equally applicable to all types of devices. Furthermore devices of 11 the same type have different capabilities and this specification permits 12 the omission of a few complicated and less important parts of the API. 13 14 The :ref:`VIDIOC_QUERYCAP` ioctl is available to 15 check if the kernel device is compatible with this specification, and to 16 query the :ref:`functions <devices>` and :ref:`I/O methods <io>` 17 supported by the device. 18 19 Starting with kernel version 3.1, :ref:`VIDIOC_QUERYCAP` 20 will return the V4L2 API version used by the driver, with generally 21 matches the Kernel version. There's no need of using 22 :ref:`VIDIOC_QUERYCAP` to check if a specific ioctl 23 is supported, the V4L2 core now returns ``ENOTTY`` if a driver doesn't 24 provide support for an ioctl. 25 26 Other features can be queried by calling the respective ioctl, for 27 example :ref:`VIDIOC_ENUMINPUT` to learn about the 28 number, types and names of video connectors on the device. Although 29 abstraction is a major objective of this API, the 30 :ref:`VIDIOC_QUERYCAP` ioctl also allows driver 31 specific applications to reliably identify the driver. 32 33 All V4L2 drivers must support :ref:`VIDIOC_QUERYCAP`. 34 Applications should always call this ioctl after opening the device.
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