.. -*- coding: utf-8; mode: rst -*-
.. _VIDIOC_QUERYCAP:
*********************
ioctl VIDIOC_QUERYCAP
*********************
Name
====
VIDIOC_QUERYCAP - Query device capabilities
Synopsis
========
.. cpp:function:: int ioctl( int fd, int request, struct v4l2_capability *argp )
Arguments
=========
``fd``
File descriptor returned by :ref:`open() <func-open>`.
``request``
VIDIOC_QUERYCAP
``argp``
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 :ref:`v4l2_capability <v4l2-capability>` which is
filled by the driver. When the driver is not compatible with this
specification the ioctl returns an ``EINVAL`` error code.
.. _v4l2-capability:
.. flat-table:: struct v4l2_capability
:header-rows: 0
:stub-columns: 0
:widths: 1 1 2
- .. row 1
- __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.
- .. row 2
- __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.
- .. row 3
- __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.
- .. row 4
- __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:
- .. row 5
- :cspan:`2`
.. code-block:: c
#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))
__u32 version = KERNEL_VERSION(0, 8, 1);
printf ("Version: %u.%u.%u\\n",
(version >> 16) & 0xFF,
(version >> 8) & 0xFF,
version & 0xFF);
- .. row 6
- __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.
- .. row 7
- __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``.
- .. row 8
- __u32
- ``reserved``\ [3]
- Reserved for future extensions. Drivers must set this array to
zero.
.. _device-capabilities:
.. flat-table:: Device Capabilities Flags
:header-rows: 0
:stub-columns: 0
:widths: 3 1 4
- .. row 1
- ``V4L2_CAP_VIDEO_CAPTURE``
- 0x00000001
- The device supports the single-planar API through the
:ref:`Video Capture <capture>` interface.
- .. row 2
- ``V4L2_CAP_VIDEO_CAPTURE_MPLANE``
- 0x00001000
- The device supports the :ref:`multi-planar API <planar-apis>`
through the :ref:`Video Capture <capture>` interface.
- .. row 3
- ``V4L2_CAP_VIDEO_OUTPUT``
- 0x00000002
- The device supports the single-planar API through the
:ref:`Video Output <output>` interface.
- .. row 4
- ``V4L2_CAP_VIDEO_OUTPUT_MPLANE``
- 0x00002000
- The device supports the :ref:`multi-planar API <planar-apis>`
through the :ref:`Video Output <output>` interface.
- .. row 5
- ``V4L2_CAP_VIDEO_M2M``
- 0x00004000
- The device supports the single-planar API through the Video
Memory-To-Memory interface.
- .. row 6
- ``V4L2_CAP_VIDEO_M2M_MPLANE``
- 0x00008000
- The device supports the :ref:`multi-planar API <planar-apis>`
through the Video Memory-To-Memory interface.
- .. row 7
- ``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.
- .. row 8
- ``V4L2_CAP_VBI_CAPTURE``
- 0x00000010
- The device supports the :ref:`Raw VBI Capture <raw-vbi>`
interface, providing Teletext and Closed Caption data.
- .. row 9
- ``V4L2_CAP_VBI_OUTPUT``
- 0x00000020
- The device supports the :ref:`Raw VBI Output <raw-vbi>`
interface.
- .. row 10
- ``V4L2_CAP_SLICED_VBI_CAPTURE``
- 0x00000040
- The device supports the :ref:`Sliced VBI Capture <sliced>`
interface.
- .. row 11
- ``V4L2_CAP_SLICED_VBI_OUTPUT``
- 0x00000080
- The device supports the :ref:`Sliced VBI Output <sliced>`
interface.
- .. row 12
- ``V4L2_CAP_RDS_CAPTURE``
- 0x00000100
- The device supports the :ref:`RDS <rds>` capture interface.
- .. row 13
- ``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]_
- .. row 14
- ``V4L2_CAP_HW_FREQ_SEEK``
- 0x00000400
- The device supports the
:ref:`VIDIOC_S_HW_FREQ_SEEK` ioctl
for hardware frequency seeking.
- .. row 15
- ``V4L2_CAP_RDS_OUTPUT``
- 0x00000800
- The device supports the :ref:`RDS <rds>` output interface.
- .. row 16
- ``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`.
- .. row 17
- ``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`.
- .. row 18
- ``V4L2_CAP_RADIO``
- 0x00040000
- This is a radio receiver.
- .. row 19
- ``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`.
- .. row 20
- ``V4L2_CAP_SDR_CAPTURE``
- 0x00100000
- The device supports the :ref:`SDR Capture <sdr>` interface.
- .. row 21
- ``V4L2_CAP_EXT_PIX_FORMAT``
- 0x00200000
- The device supports the struct
:ref:`v4l2_pix_format <v4l2-pix-format>` extended fields.
- .. row 22
- ``V4L2_CAP_SDR_OUTPUT``
- 0x00400000
- The device supports the :ref:`SDR Output <sdr>` interface.
- .. row 23
- ``V4L2_CAP_READWRITE``
- 0x01000000
- The device supports the :ref:`read() <rw>` and/or
:ref:`write() <rw>` I/O methods.
- .. row 24
- ``V4L2_CAP_ASYNCIO``
- 0x02000000
- The device supports the :ref:`asynchronous <async>` I/O methods.
- .. row 25
- ``V4L2_CAP_STREAMING``
- 0x04000000
- The device supports the :ref:`streaming <mmap>` I/O method.
- .. row 26
- ``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 :ref:`v4l2_framebuffer <v4l2-framebuffer>` lacks an
enum :ref:`v4l2_buf_type <v4l2-buf-type>` field, therefore the
type of overlay is implied by the driver capabilities.
