Base class for V4L2VideoDevice and V4L2Subdevice. More...

Inheritance diagram for libcamera::V4L2Device:

Collaboration diagram for libcamera::V4L2Device:

Public Member Functions
void	close ()
	Close the device node. More...

bool	isOpen () const
	Check if the V4L2 device node is open. More...

const ControlInfoMap &	controls () const
	Retrieve the supported V4L2 controls and their information. More...

ControlList	getControls (const std::vector< uint32_t > &ids)
	Read controls from the device. More...

int	setControls (ControlList *ctrls)
	Write controls to the device. More...

const struct v4l2_query_ext_ctrl *	controlInfo (uint32_t id) const
	Retrieve the v4l2_query_ext_ctrl information for the given control. More...

const std::string &	deviceNode () const
	Retrieve the device node path. More...

std::string	devicePath () const
	Retrieve the device path in sysfs. More...

int	setFrameStartEnabled (bool enable)
	Enable or disable frame start event notification. More...

void	updateControlInfo ()
	Update the information for all device controls. More...

Public Attributes
Signal< uint32_t >	frameStart
	A Signal emitted when capture of a frame has started.

Protected Member Functions
	V4L2Device (const std::string &deviceNode)
	Construct a V4L2Device. More...

	~V4L2Device ()
	Destroy a V4L2Device.

int	open (unsigned int flags)
	Open a V4L2 device node. More...

int	setFd (UniqueFD fd)
	Set the file descriptor of a V4L2 device. More...

int	ioctl (unsigned long request, void *argp)
	Perform an IOCTL system call on the device node. More...

int	fd () const
	Retrieve the V4L2 device file descriptor. More...

Protected Member Functions inherited from libcamera::Loggable
virtual std::string	logPrefix () const =0
	Retrieve a string to be prefixed to the log message. More...

LogMessage	_log (const LogCategory category, LogSeverity severity, const char fileName=__builtin_FILE(), unsigned int line=__builtin_LINE()) const
	Create a temporary LogMessage object to log a message. More...

Static Protected Member Functions
template<typename T >
static std::optional< ColorSpace >	toColorSpace (const T &v4l2Format, PixelFormatInfo::ColourEncoding colourEncoding)
	Convert the color space fields in a V4L2 format to a ColorSpace. More...

template<typename T >
static int	fromColorSpace (const std::optional< ColorSpace > &colorSpace, T &v4l2Format)
	Fill in the color space fields of a V4L2 format from a ColorSpace. More...

Detailed Description

Base class for V4L2VideoDevice and V4L2Subdevice.

The V4L2Device class groups together the functions and fields common to both the V4L2VideoDevice and V4L2Subdevice classes, and provides a base class with functions to open and close the device node associated with the device and to perform IOCTL system calls on it.

The V4L2Device class cannot be instantiated directly, as its constructor is protected. Users should instead create instances of one the derived classes to model either a V4L2 video device or a V4L2 subdevice.

Constructor & Destructor Documentation

◆ V4L2Device()

libcamera::V4L2Device::V4L2Device ( const std::string & deviceNode )

protected

Construct a V4L2Device.

Parameters

[in] deviceNode The device node filesystem path

Initialize the file descriptor to -1 and store the deviceNode to be used at open() time, and the logTag to prefix log messages with.

Member Function Documentation

◆ close()

void libcamera::V4L2Device::close ( )

Close the device node.

Reset the file descriptor to -1

◆ controlInfo()

const struct v4l2_query_ext_ctrl * libcamera::V4L2Device::controlInfo ( uint32_t id ) const

Retrieve the v4l2_query_ext_ctrl information for the given control.

Parameters

[in] id The V4L2 control id

Returns: A pointer to the v4l2_query_ext_ctrl structure for the given control, or a null pointer if not found

◆ controls()

libcamera::V4L2Device::controls ( ) const

inline

Retrieve the supported V4L2 controls and their information.

Returns: A map of the V4L2 controls supported by the device

◆ deviceNode()

libcamera::V4L2Device::deviceNode ( ) const

inline

Retrieve the device node path.

Returns: The device node path

◆ devicePath()

std::string libcamera::V4L2Device::devicePath ( ) const

Retrieve the device path in sysfs.

This function returns the sysfs path to the physical device backing the V4L2 device. The path is guaranteed to be an absolute path, without any symbolic link.

It includes the sysfs mount point prefix

Returns: The device path in sysfs

◆ fd()

libcamera::V4L2Device::fd ( ) const

inlineprotected

Retrieve the V4L2 device file descriptor.

Returns: The V4L2 device file descriptor, -1 if the device node is not open

◆ fromColorSpace()

template<typename T >

template int libcamera::V4L2Device::fromColorSpace	(	const std::optional< ColorSpace > &	colorSpace,
		T &	v4l2Format
	)

staticprotected

Fill in the color space fields of a V4L2 format from a ColorSpace.

Parameters

[in]	colorSpace	The ColorSpace to be converted
[out]	v4l2Format	A V4L2 format containing color space information

The colorspace, ycbcr_enc, xfer_func and quantization fields within a V4L2 format structure are filled in from a corresponding ColorSpace.

An error is returned if any of the V4L2 fields do not support the value given in the ColorSpace. Such fields are set to the V4L2 "default" values, but all other fields are still filled in where possible.

If the color space is completely unset, "default" V4L2 values are used everywhere, so a driver would then choose its preferred color space.

Returns: 0 on success or a negative error code otherwise

Return values

-EINVAL The ColorSpace does not have a representation using V4L2 enums

◆ getControls()

ControlList libcamera::V4L2Device::getControls ( const std::vector< uint32_t > & ids )

Read controls from the device.

Parameters

[in] ids The list of controls to read, specified by their ID

This function reads the value of all controls contained in ids, and returns their values as a ControlList.

If any control in ids is not supported by the device, is disabled (i.e. has the V4L2_CTRL_FLAG_DISABLED flag set), or if any other error occurs during validation of the requested controls, no control is read and this function returns an empty control list.

Returns: The control values in a ControlList on success, or an empty list on error

◆ ioctl()

int libcamera::V4L2Device::ioctl	(	unsigned long	request,
		void *	argp
	)

protected

Perform an IOCTL system call on the device node.

Parameters

[in]	request	The IOCTL request code
[in]	argp	A pointer to the IOCTL argument

Returns: 0 on success or a negative error code otherwise

◆ isOpen()

libcamera::V4L2Device::isOpen ( ) const

inline

Check if the V4L2 device node is open.

Returns: True if the V4L2 device node is open, false otherwise

◆ open()

int libcamera::V4L2Device::open ( unsigned int flags )

protected

Open a V4L2 device node.

Parameters

[in] flags Access mode flags

Open the device node path with the provided access mode flags and initialize the file descriptor, which was initially set to -1.

Returns: 0 on success or a negative error code otherwise

◆ setControls()

int libcamera::V4L2Device::setControls ( ControlList * ctrls )

Write controls to the device.

Parameters

[in] ctrls The list of controls to write

This function writes the value of all controls contained in ctrls, and stores the values actually applied to the device in the corresponding ctrls entry.

If any control in ctrls is not supported by the device, is disabled (i.e. has the V4L2_CTRL_FLAG_DISABLED flag set), is read-only, if any other error occurs during validation of the requested controls, no control is written and this function returns -EINVAL.

If an error occurs while writing the controls, the index of the first control that couldn't be written is returned. All controls below that index are written and their values are updated in ctrls, while all other controls are not written and their values are not changed.

Returns: 0 on success or an error code otherwise

Return values

-EINVAL	One of the control is not supported or not accessible
i	The index of the control that failed

◆ setFd()

int libcamera::V4L2Device::setFd ( UniqueFD fd )

protected

Set the file descriptor of a V4L2 device.

Parameters

[in] fd The file descriptor handle

This function allows a device to provide an already opened file descriptor referring to the V4L2 device node, instead of opening it with open(). This can be used for V4L2 M2M devices where a single video device node is used for both the output and capture devices, or when receiving an open file descriptor in a context that doesn't have permission to open the device node itself.

This function and the open() function are mutually exclusive, only one of the two shall be used for a V4L2Device instance.

Returns: 0 on success or a negative error code otherwise

◆ setFrameStartEnabled()

int libcamera::V4L2Device::setFrameStartEnabled ( bool enable )

Enable or disable frame start event notification.

Parameters

[in] enable True to enable frame start events, false to disable them

This function enables or disables generation of frame start events. Once enabled, the events are signalled through the frameStart signal.

Returns: 0 on success, a negative error code otherwise

◆ toColorSpace()

template<typename T >

template std::optional< ColorSpace > libcamera::V4L2Device::toColorSpace	(	const T &	v4l2Format,
		PixelFormatInfo::ColourEncoding	colourEncoding
	)

staticprotected

Convert the color space fields in a V4L2 format to a ColorSpace.

Parameters

[in]	v4l2Format	A V4L2 format containing color space information
[in]	colourEncoding	Type of colour encoding

The colorspace, ycbcr_enc, xfer_func and quantization fields within a V4L2 format structure are converted to a corresponding ColorSpace.

If any V4L2 fields are not recognised then we return an "unset" color space.

Returns: The ColorSpace corresponding to the input V4L2 format

Return values

std::nullopt One or more V4L2 color space fields were not recognised

◆ updateControlInfo()

void libcamera::V4L2Device::updateControlInfo ( )

Update the information for all device controls.

The V4L2Device class caches information about all controls supported by the device and exposes it through the controls() and controlInfo() functions. Control information may change at runtime, for instance when formats on a subdev are modified. When this occurs, this function can be used to refresh control information. The information is refreshed in-place, all pointers to v4l2_query_ext_ctrl instances previously returned by controlInfo() and iterators to the ControlInfoMap returned by controls() remain valid.

Note that control information isn't refreshed automatically is it may be an expensive operation. The V4L2Device users are responsible for calling this function when required, based on their usage pattern of the class.

The documentation for this class was generated from the following files:

include/libcamera/internal/v4l2_device.h
src/libcamera/v4l2_device.cpp

Public Member Functions

Public Attributes

Protected Member Functions

Static Protected Member Functions

Detailed Description

Constructor & Destructor Documentation

◆ V4L2Device()

Member Function Documentation

◆ close()

◆ controlInfo()

◆ controls()

◆ deviceNode()

◆ devicePath()

◆ fd()

◆ fromColorSpace()

◆ getControls()

◆ ioctl()

◆ isOpen()

◆ open()

◆ setControls()

◆ setFd()

◆ setFrameStartEnabled()

◆ toColorSpace()

◆ updateControlInfo()