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Diffstat (limited to 'Documentation/linux_tv/media/v4l/querycap.rst')
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diff --git a/Documentation/linux_tv/media/v4l/querycap.rst b/Documentation/linux_tv/media/v4l/querycap.rst new file mode 100644 index 0000000..2568820 --- /dev/null +++ b/Documentation/linux_tv/media/v4l/querycap.rst @@ -0,0 +1,43 @@ +.. -*- 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 +.. ------------------------------------------------------------------------------ |
