Documentation/linux_tv/media/v4l/querycap.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   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 <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 <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 <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 <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 <VIDIOC_QUERYCAP>` ioctl also allows driver
  31 specific applications to reliably identify the driver.
  32
  33 All V4L2 drivers must support :ref:`VIDIOC_QUERYCAP <VIDIOC_QUERYCAP>`.
  34 Applications should always call this ioctl after opening the device.
  35
  36
  37 .. ------------------------------------------------------------------------------
  38 .. This file was automatically converted from DocBook-XML with the dbxml
  39 .. library (https://github.com/return42/sphkerneldoc). The origin XML comes
  40 .. from the linux kernel, refer to:
  41 ..
  42 .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
  43 .. ------------------------------------------------------------------------------