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