[deliverable/linux.git] / Documentation / linux_tv / media / v4l / querycap.rst

.. -*- coding: utf-8; mode: rst -*-

.. _querycap:

*********************
Querying Capabilities
*********************

Because V4L2 covers a wide variety of devices not all aspects of the API
are equally applicable to all types of devices. Furthermore devices of
the same type have different capabilities and this specification permits
the omission of a few complicated and less important parts of the API.

The :ref:`VIDIOC_QUERYCAP <vidioc-querycap>` ioctl is available to
check if the kernel device is compatible with this specification, and to
query the :ref:`functions <devices>` and :ref:`I/O methods <io>`
supported by the device.

Starting with kernel version 3.1, VIDIOC-QUERYCAP will return the V4L2
API version used by the driver, with generally matches the Kernel
version. There's no need of using
:ref:`VIDIOC_QUERYCAP <vidioc-querycap>` to check if a specific ioctl
is supported, the V4L2 core now returns ENOTTY if a driver doesn't
provide support for an ioctl.

Other features can be queried by calling the respective ioctl, for
example :ref:`VIDIOC_ENUMINPUT <vidioc-enuminput>` to learn about the
number, types and names of video connectors on the device. Although
abstraction is a major objective of this API, the
:ref:`VIDIOC_QUERYCAP <vidioc-querycap>` ioctl also allows driver
specific applications to reliably identify the driver.

All V4L2 drivers must support ``VIDIOC_QUERYCAP``. Applications should
always call this ioctl after opening the device.


.. ------------------------------------------------------------------------------
.. This file was automatically converted from DocBook-XML with the dbxml
.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
.. from the linux kernel, refer to:
..
.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
.. ------------------------------------------------------------------------------
Commit	Line	Data
5377d91f MH	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, VIDIOC-QUERYCAP will return the V4L2
	20	API version used by the driver, with generally matches the Kernel
	21	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 ``VIDIOC_QUERYCAP``. Applications should
	34	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	.. ------------------------------------------------------------------------------