42 lines
1.8 KiB
ReStructuredText
42 lines
1.8 KiB
ReStructuredText
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.. Permission is granted to copy, distribute and/or modify this
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.. document under the terms of the GNU Free Documentation License,
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.. Version 1.1 or any later version published by the Free Software
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.. Foundation, with no Invariant Sections, no Front-Cover Texts
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.. and no Back-Cover Texts. A copy of the license is included at
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.. Documentation/media/uapi/fdl-appendix.rst.
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..
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.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
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.. _querycap:
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*********************
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Querying Capabilities
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*********************
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Because V4L2 covers a wide variety of devices not all aspects of the API
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are equally applicable to all types of devices. Furthermore devices of
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the same type have different capabilities and this specification permits
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the omission of a few complicated and less important parts of the API.
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The :ref:`VIDIOC_QUERYCAP` ioctl is available to
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check if the kernel device is compatible with this specification, and to
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query the :ref:`functions <devices>` and :ref:`I/O methods <io>`
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supported by the device.
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Starting with kernel version 3.1, :ref:`VIDIOC_QUERYCAP`
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will return the V4L2 API version used by the driver, with generally
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matches the Kernel version. There's no need of using
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:ref:`VIDIOC_QUERYCAP` to check if a specific ioctl
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is supported, the V4L2 core now returns ``ENOTTY`` if a driver doesn't
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provide support for an ioctl.
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Other features can be queried by calling the respective ioctl, for
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example :ref:`VIDIOC_ENUMINPUT` to learn about the
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number, types and names of video connectors on the device. Although
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abstraction is a major objective of this API, the
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:ref:`VIDIOC_QUERYCAP` ioctl also allows driver
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specific applications to reliably identify the driver.
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All V4L2 drivers must support :ref:`VIDIOC_QUERYCAP`.
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Applications should always call this ioctl after opening the device.
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