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

.. _VIDIOC_QUERYCAP:

*********************
ioctl VIDIOC_QUERYCAP
*********************

Name
====

VIDIOC_QUERYCAP - Query device capabilities


Synopsis
========

.. c:function:: int ioctl( int fd, VIDIOC_QUERYCAP, struct v4l2_capability *argp )
    :name: VIDIOC_QUERYCAP


Arguments
=========

``fd``
    File descriptor returned by :ref:`open() <func-open>`.

``argp``
    Pointer to struct :c:type:`v4l2_capability`.


Description
===========

All V4L2 devices support the ``VIDIOC_QUERYCAP`` ioctl. It is used to
identify kernel devices compatible with this specification and to obtain
information about driver and hardware capabilities. The ioctl takes a
pointer to a struct :c:type:`v4l2_capability` which is
filled by the driver. When the driver is not compatible with this
specification the ioctl returns an ``EINVAL`` error code.


.. tabularcolumns:: |p{1.5cm}|p{2.5cm}|p{13cm}|

.. c:type:: v4l2_capability

.. flat-table:: struct v4l2_capability
    :header-rows:  0
    :stub-columns: 0
    :widths:       3 4 20

    * - __u8
      - ``driver``\ [16]
      - Name of the driver, a unique NUL-terminated ASCII string. For
	example: "bttv". Driver specific applications can use this
	information to verify the driver identity. It is also useful to
	work around known bugs, or to identify drivers in error reports.

	Storing strings in fixed sized arrays is bad practice but
	unavoidable here. Drivers and applications should take precautions
	to never read or write beyond the end of the array and to make
	sure the strings are properly NUL-terminated.
    * - __u8
      - ``card``\ [32]
      - Name of the device, a NUL-terminated UTF-8 string. For example:
	"Yoyodyne TV/FM". One driver may support different brands or
	models of video hardware. This information is intended for users,
	for example in a menu of available devices. Since multiple TV
	cards of the same brand may be installed which are supported by
	the same driver, this name should be combined with the character
	device file name (e. g. ``/dev/video2``) or the ``bus_info``
	string to avoid ambiguities.
    * - __u8
      - ``bus_info``\ [32]
      - Location of the device in the system, a NUL-terminated ASCII
	string. For example: "PCI:0000:05:06.0". This information is
	intended for users, to distinguish multiple identical devices. If
	no such information is available the field must simply count the
	devices controlled by the driver ("platform:vivi-000"). The
	bus_info must start with "PCI:" for PCI boards, "PCIe:" for PCI
	Express boards, "usb-" for USB devices, "I2C:" for i2c devices,
	"ISA:" for ISA devices, "parport" for parallel port devices and
	"platform:" for platform devices.
    * - __u32
      - ``version``
      - Version number of the driver.

	Starting with kernel 3.1, the version reported is provided by the
	V4L2 subsystem following the kernel numbering scheme. However, it
	may not always return the same version as the kernel if, for
	example, a stable or distribution-modified kernel uses the V4L2
	stack from a newer kernel.

	The version number is formatted using the ``KERNEL_VERSION()``
	macro. For example if the media stack corresponds to the V4L2
	version shipped with Kernel 4.14, it would be equivalent to:
    * - :cspan:`2`

	``#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))``

	``__u32 version = KERNEL_VERSION(4, 14, 0);``

	``printf ("Version: %u.%u.%u\\n",``

	``(version >> 16) & 0xFF, (version >> 8) & 0xFF, version & 0xFF);``
    * - __u32
      - ``capabilities``
      - Available capabilities of the physical device as a whole, see
	:ref:`device-capabilities`. The same physical device can export
	multiple devices in /dev (e.g. /dev/videoX, /dev/vbiY and
	/dev/radioZ). The ``capabilities`` field should contain a union of
	all capabilities available around the several V4L2 devices
	exported to userspace. For all those devices the ``capabilities``
	field returns the same set of capabilities. This allows
	applications to open just one of the devices (typically the video
	device) and discover whether video, vbi and/or radio are also
	supported.
    * - __u32
      - ``device_caps``
      - Device capabilities of the opened device, see
	:ref:`device-capabilities`. Should contain the available
	capabilities of that specific device node. So, for example,
	``device_caps`` of a radio device will only contain radio related
	capabilities and no video or vbi capabilities. This field is only
	set if the ``capabilities`` field contains the
	``V4L2_CAP_DEVICE_CAPS`` capability. Only the ``capabilities``
	field can have the ``V4L2_CAP_DEVICE_CAPS`` capability,
	``device_caps`` will never set ``V4L2_CAP_DEVICE_CAPS``.
    * - __u32
      - ``reserved``\ [3]
      - Reserved for future extensions. Drivers must set this array to
	zero.


.. tabularcolumns:: |p{6.1cm}|p{2.2cm}|p{8.7cm}|

.. _device-capabilities:

.. cssclass:: longtable

.. flat-table:: Device Capabilities Flags
    :header-rows:  0
    :stub-columns: 0
    :widths:       3 1 4

    * - ``V4L2_CAP_VIDEO_CAPTURE``
      - 0x00000001
      - The device supports the single-planar API through the
	:ref:`Video Capture <capture>` interface.
    * - ``V4L2_CAP_VIDEO_CAPTURE_MPLANE``
      - 0x00001000
      - The device supports the :ref:`multi-planar API <planar-apis>`
	through the :ref:`Video Capture <capture>` interface.
    * - ``V4L2_CAP_VIDEO_OUTPUT``
      - 0x00000002
      - The device supports the single-planar API through the
	:ref:`Video Output <output>` interface.
    * - ``V4L2_CAP_VIDEO_OUTPUT_MPLANE``
      - 0x00002000
      - The device supports the :ref:`multi-planar API <planar-apis>`
	through the :ref:`Video Output <output>` interface.
    * - ``V4L2_CAP_VIDEO_M2M``
      - 0x00004000
      - The device supports the single-planar API through the Video
	Memory-To-Memory interface.
    * - ``V4L2_CAP_VIDEO_M2M_MPLANE``
      - 0x00008000
      - The device supports the :ref:`multi-planar API <planar-apis>`
	through the Video Memory-To-Memory interface.
    * - ``V4L2_CAP_VIDEO_OVERLAY``
      - 0x00000004
      - The device supports the :ref:`Video Overlay <overlay>`
	interface. A video overlay device typically stores captured images
	directly in the video memory of a graphics card, with hardware
	clipping and scaling.
    * - ``V4L2_CAP_VBI_CAPTURE``
      - 0x00000010
      - The device supports the :ref:`Raw VBI Capture <raw-vbi>`
	interface, providing Teletext and Closed Caption data.
    * - ``V4L2_CAP_VBI_OUTPUT``
      - 0x00000020
      - The device supports the :ref:`Raw VBI Output <raw-vbi>`
	interface.
    * - ``V4L2_CAP_SLICED_VBI_CAPTURE``
      - 0x00000040
      - The device supports the :ref:`Sliced VBI Capture <sliced>`
	interface.
    * - ``V4L2_CAP_SLICED_VBI_OUTPUT``
      - 0x00000080
      - The device supports the :ref:`Sliced VBI Output <sliced>`
	interface.
    * - ``V4L2_CAP_RDS_CAPTURE``
      - 0x00000100
      - The device supports the :ref:`RDS <rds>` capture interface.
    * - ``V4L2_CAP_VIDEO_OUTPUT_OVERLAY``
      - 0x00000200
      - The device supports the :ref:`Video Output Overlay <osd>` (OSD)
	interface. Unlike the *Video Overlay* interface, this is a
	secondary function of video output devices and overlays an image
	onto an outgoing video signal. When the driver sets this flag, it
	must clear the ``V4L2_CAP_VIDEO_OVERLAY`` flag and vice
	versa. [#f1]_
    * - ``V4L2_CAP_HW_FREQ_SEEK``
      - 0x00000400
      - The device supports the
	:ref:`VIDIOC_S_HW_FREQ_SEEK` ioctl
	for hardware frequency seeking.
    * - ``V4L2_CAP_RDS_OUTPUT``
      - 0x00000800
      - The device supports the :ref:`RDS <rds>` output interface.
    * - ``V4L2_CAP_TUNER``
      - 0x00010000
      - The device has some sort of tuner to receive RF-modulated video
	signals. For more information about tuner programming see
	:ref:`tuner`.
    * - ``V4L2_CAP_AUDIO``
      - 0x00020000
      - The device has audio inputs or outputs. It may or may not support
	audio recording or playback, in PCM or compressed formats. PCM
	audio support must be implemented as ALSA or OSS interface. For
	more information on audio inputs and outputs see :ref:`audio`.
    * - ``V4L2_CAP_RADIO``
      - 0x00040000
      - This is a radio receiver.
    * - ``V4L2_CAP_MODULATOR``
      - 0x00080000
      - The device has some sort of modulator to emit RF-modulated
	video/audio signals. For more information about modulator
	programming see :ref:`tuner`.
    * - ``V4L2_CAP_SDR_CAPTURE``
      - 0x00100000
      - The device supports the :ref:`SDR Capture <sdr>` interface.
    * - ``V4L2_CAP_EXT_PIX_FORMAT``
      - 0x00200000
      - The device supports the struct
	:c:type:`v4l2_pix_format` extended fields.
    * - ``V4L2_CAP_SDR_OUTPUT``
      - 0x00400000
      - The device supports the :ref:`SDR Output <sdr>` interface.
    * - ``V4L2_CAP_META_CAPTURE``
      - 0x00800000
      - The device supports the :ref:`metadata` capture interface.
    * - ``V4L2_CAP_READWRITE``
      - 0x01000000
      - The device supports the :ref:`read() <rw>` and/or
	:ref:`write() <rw>` I/O methods.
    * - ``V4L2_CAP_ASYNCIO``
      - 0x02000000
      - The device supports the :ref:`asynchronous <async>` I/O methods.
    * - ``V4L2_CAP_STREAMING``
      - 0x04000000
      - The device supports the :ref:`streaming <mmap>` I/O method.
    * - ``V4L2_CAP_TOUCH``
      - 0x10000000
      - This is a touch device.
    * - ``V4L2_CAP_DEVICE_CAPS``
      - 0x80000000
      - The driver fills the ``device_caps`` field. This capability can
	only appear in the ``capabilities`` field and never in the
	``device_caps`` field.


Return Value
============

On success 0 is returned, on error -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.

.. [#f1]
   The struct :c:type:`v4l2_framebuffer` lacks an
   enum :c:type:`v4l2_buf_type` field, therefore the
   type of overlay is implied by the driver capabilities.