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