Documentation/guides/introduction.rst


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.. SPDX-License-Identifier: CC-BY-SA-4.0

Developers guide to libcamera
=============================

The Linux kernel handles multimedia devices through the 'Linux media' subsystem
and provides a set of APIs (application programming interfaces) known
collectively as V4L2 (`Video for Linux 2`_) and the `Media Controller`_ API
which provide an interface to interact and control media devices.

Included in this subsystem are drivers for camera sensors, CSI2 (Camera
Serial Interface) recievers, and ISPs (Image Signal Processors)

The usage of these drivers to provide a functioning camera stack is a
responsibility that lies in userspace which is commonly implemented separately
by vendors without a common architecture or API for application developers.

libcamera provides a complete camera stack for Linux based systems to abstract
functionality desired by camera application developers and process the
configuration of hardware and image control algorithms requried to obtain
desireable results from the camera.

.. _Video for Linux 2: https://www.linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/v4l2.html
.. _Media Controller: https://www.linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/mediactl/media-controller.html


In this developers guide, we will explore the `Camera Stack`_ and how it is
can be visualised at a high level, and explore the internal `Architecture`_ of
the libcamera library with its components. The current `Platform Support`_ is
detailed, as well as an overview of the `Licensing`_ requirements of the
project.

This introduction is followed by a walkthrough tutorial to newcomers wishing to
support a new platform with the `Pipeline Handler Writers Guide`_ and for those
looking to make use of the libcamera native API an `Application Writers Guide`_
provides a tutorial of the key APIs exposed by libcamera.

.. _Pipeline Handler Writers Guide: pipeline-handler.html
.. _Application Writers Guide: application-developer.html

.. TODO: Correctly link to the other articles of the guide

Camera Stack
------------

The libcamera library is implemented in userspace, and makes use of underlying
kernel drivers that directly interact with hardware.

Applications can make use of libcamera through the native `libcamera API`_'s or
through an adaptation layer integrating libcamera into a larger framework.

.. _libcamera API: https://www.libcamera.org/api-html/index.html

::

    Application Layer
     /    +--------------+  +--------------+  +--------------+  +--------------+
     |    |    Native    |  |   Framework  |  |    Native    |  |   Android    |
     |    |     V4L2     |  |  Application |  |   libcamera  |  |   Camera     |
     |    |  Application |  |  (gstreamer) |  |  Application |  |  Framework   |
     \    +--------------+  +--------------+  +--------------+  +--------------+

                 ^                 ^                 ^                 ^
                 |                 |                 |                 |
                 |                 |                 |                 |
                 v                 v                 |                 v
    Adaptation Layer                                 |
     /    +--------------+  +--------------+         |          +--------------+
     |    |    V4L2      |  |  gstreamer   |         |          |   Android    |
     |    | Compatability|  |   element    |         |          |   Camera     |
     |    |  (preload)   |  |(libcamerasrc)|         |          |     HAL      |
     \    +--------------+  +--------------+         |          +--------------+
                                                     |
                 ^                 ^                 |                 ^
                 |                 |                 |                 |
                 |                 |                 |                 |
                 v                 v                 v                 v
    libcamera Framework
     /    +--------------------------------------------------------------------+
     |    |                                                                    |
     |    |                             libcamera                              |
     |    |                                                                    |
     \    +--------------------------------------------------------------------+

                         ^                  ^                  ^
    Userspace            |                  |                  |
   --------------------- | ---------------- | ---------------- | ---------------
    Kernel               |                  |                  |
                         v                  v                  v

                   +-----------+      +-----------+      +-----------+
                   |   Media   | <--> |   Video   | <--> |   V4L2    |
                   |  Device   |      |  Device   |      |  Subdev   |
                   +-----------+      +-----------+      +-----------+

The camera stack comprises of four software layers. From bottom to top:

* The kernel drivers control the camera hardware and expose a low-level
  interface to userspace through the Linux kernel V4L2 family of APIs
  (Media Controller API, V4L2 Video Device API and V4L2 Subdev API).

* The libcamera framework is the core part of the stack. It handles all control
  of the camera devices in its core component, libcamera, and exposes a native
  C++ API to upper layers.

* The libcamera adaptation layer is an umbrella term designating the components
  that interface to libcamera in other frameworks. Notable examples are the V4L2
  compatibility layer, the gstreamer libcamera element, and the Android camera
  HAL implementation based on libcamera which are provided as a part of the
  libcamera project.

* The applications and upper level frameworks are based on the libcamera
  framework or libcamera adaptation, and are outside of the scope of the
  libcamera project, however example native applications (cam, qcam) are
  provided for testing.


V4L2 Compatibility Layer
  V4L2 compatibility is achieved through a shared library that traps all
  accesses to camera devices and routes them to libcamera to emulate high-level
  V4L2 camera devices. It is injected in a process address space through
  `LD_PRELOAD` and is completely transparent for applications.

  The compatibility layer exposes camera device features on a best-effort basis,
  and aims for the level of features traditionally available from a UVC camera
  designed for video conferencing.

Android Camera HAL
  Camera support for Android is achieved through a generic Android camera HAL
  implementation on top of libcamera. The HAL implements features required by
  Android and out of scope from libcamera, such as JPEG encoding support.

  This component is used to provide support for ChromeOS platforms

GStreamer element (gstlibcamerasrc)
  A `GStreamer element`_ is provided to allow capture from libcamera supported
  devices through GStreamer pipelines, and connect to other elements for further
  processing.

  Development of this element is ongoing and is limited to a single stream.

Native libcamera API
  Applications can make use of the libcamera API directly using the C++
  API. An example application and walkthrough using the libcamera API can be
  followed in the `Application Writers Guide`_

.. _GStreamer element: https://gstreamer.freedesktop.org/documentation/application-development/basics/elements.html

Architecture
------------

While offering a unified API towards upper layers, and presenting itself as a
single library, libcamera isn’t monolithic. It exposes multiple components
through its public API and is built around a set of separate helpers internally.
Hardware abstractractions are handled through the use of device-specific
components where required and dynamically loadable plugins are used to separate
image processing algorithms from the core libcamera codebase.

::

   --------------------------< libcamera Public API >---------------------------
                 ^                                          ^
                 |                                          |
                 v                                          v
          +-------------+  +---------------------------------------------------+
          |   Camera    |  |  Camera Device                                    |
          |   Manager   |  | +-----------------------------------------------+ |
          +-------------+  | | Device-Agnostic                               | |
                 ^         | |                                               | |
                 |         | |                    +--------------------------+ |
                 |         | |                    |   ~~~~~~~~~~~~~~~~~~~~~~~  |
                 |         | |                    |  {  +-----------------+  } |
                 |         | |                    |  }  | //// Image //// |  { |
                 |         | |                    | <-> | / Processing // |  } |
                 |         | |                    |  }  | / Algorithms // |  { |
                 |         | |                    |  {  +-----------------+  } |
                 |         | |                    |   ~~~~~~~~~~~~~~~~~~~~~~~  |
                 |         | |                    | ========================== |
                 |         | |                    |     +-----------------+    |
                 |         | |                    |     | // Pipeline /// |    |
                 |         | |                    | <-> | /// Handler /// |    |
                 |         | |                    |     | /////////////// |    |
                 |         | +--------------------+     +-----------------+    |
                 |         |                                   Device-Specific |
                 |         +---------------------------------------------------+
                 |                          ^                         ^
                 |                          |                         |
                 v                          v                         v
          +--------------------------------------------------------------------+
          | Helpers and Support Classes                                        |
          | +-------------+  +-------------+  +-------------+  +-------------+ |
          | |  MC & V4L2  |  |   Buffers   |  | Sandboxing  |  |   Plugins   | |
          | |   Support   |  |  Allocator  |  |     IPC     |  |   Manager   | |
          | +-------------+  +-------------+  +-------------+  +-------------+ |
          | +-------------+  +-------------+                                   |
          | |  Pipeline   |  |     ...     |                                   |
          | |   Runner    |  |             |                                   |
          | +-------------+  +-------------+                                   |
          +--------------------------------------------------------------------+

            /// Device-Specific Components
            ~~~ Sandboxing


Camera Manager
  The Camera Manager enumerates cameras and instantiates Pipeline Handlers to
  manage each Camera that libcamera supports. The Camera Manager supports
  hotplug detection and notification events when supported by the underlying
  kernel devices.

  There is only ever one instance of the Camera Manager running per application.
  Each application's instance of the Camera Manager ensures that only a single
  application can take control of a camera device at once.

  Read the `Camera Manager API`_ documentation for more details.

.. _Camera Manager API: http://libcamera.org/api-html/classlibcamera_1_1CameraManager.html

Camera Device
  The Camera class represents a single item of camera hardware that is capable
  of producing one or more image streams, and provides the API to interact with
  the underlying device.

  If a system has multiple instances of the same hardware attached, each has it's
  own instance of the camera class.

  The API exposes full control of the device to upper layers of libcamera through
  the public API, making it the highest level object libcamera exposes, and the
  object that all other API operations interact with from configuration to
  capture.

  Read the `Camera API`_ documentation for more details.

..  _Camera API: http://libcamera.org/api-html/classlibcamera_1_1Camera.html

Pipeline Handler
  The Pipeline Handler manages the complex pipelines exposed by the kernel
  drivers through the Media Controller and V4L2 APIs. It abstracts pipeline
  handling to hide device-specific details from the rest of the library, and
  implements both pipeline configuration based on stream configuration, and
  pipeline runtime execution and scheduling when needed by the device.

  The Pipeline Handler lives in the same process as the rest of the library, and
  has access to all helpers and kernel camera-related devices.

  Hardware abstraction is handled by device specific Pipeline Handlers which are
  derived from the Pipeline Handler base class allowing commonality to be shared
  among the implementations.

  Derived pipeline handlers create Camera device instances based on the devices
  they detect and support on the running system, and are responsible for
  managing the interactions with a camera device.

  More details can be found in the `PipelineHandler API`_ documentation, and the
  `Pipeline Handler Writers Guide`_.

.. _PipelineHandler API: http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html

Image Processing Algorithms
  An image processing algorithm (IPA) component is a loadable plugin that
  implements 3A (Auto-Exposure, Auto-White Balance, and Auto-Focus) and other
  algorithms.

  The algorithms run on the CPU and interact with the camera devices through the
  Pipeline Handler to control hardware image processing based on the parameters
  supplied by upper layers, maintaining state and closing the control loop
  of the ISP.

  The component is sandboxed and can only interact with libcamera through the
  API provided by the Pipeline Handler and an IPA has no direct access to kernel
  camera devices.

  Open source IPA modules built with libcamera can be run in the same process
  space as libcamera, however external IPA modules are run in a separate process
  from the main libcamera process. IPA modules have a restricted view of the
  system, including no access to networking APIs and limited access to file
  systems.

  IPA modules are only required for platforms and devices with an ISP controlled
  by the host CPU. Camera sensors which have an integrated ISP are not
  controlled through the IPA module.

Platform Support
----------------

The library currently supports the following hardware platforms specifically
with dedicated pipeline handlers:

   -  Intel IPU3 (ipu3)
   -  Rockchip RK3399 (rkisp1)
   -  RaspberryPi 3 and 4 (raspberrypi)

Furthermore, generic platform support is provided for the following:

   -  USB video device class cameras (uvcvideo)
   -  iMX7, Allwinner Sun6i (simple)
   -  Virtual media controller driver for test use cases (vimc)

Licensing
---------

The libcamera core, is covered by the `LGPL-2.1-or-later`_ license. Pipeline
Handlers are a part of the libcamera code base and need to be contributed
upstream by device vendors. IPA modules included in libcamera are covered by a
free software license, however third-parties may develop IPA modules outside of
libcamera and distribute them under a closed-source license, provided they do
not include source code from the libcamera project.

The libcamera project itself contains multiple libraries, applications and
utilities. Licenses are expressed through SPDX tags in text-based files that
support comments, and through the .reuse/dep5 file otherwise. A copy of all
licenses are stored in the LICENSES directory, and a full summary of the
licensing used throughout the project can be found in the COPYING.rst document.

Applications which link dynamically against libcamera and use only the public
API are an independent work of the authors and have no license restrictions
imposed upon them from libcamera.

.. _LGPL-2.1-or-later: https://spdx.org/licenses/LGPL-2.1-or-later.html
/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2019, Google Inc.
 *
 * v4l2_videodevice.cpp - V4L2 Video Device
 */

#include "libcamera/internal/v4l2_videodevice.h"

#include <algorithm>
#include <array>
#include <fcntl.h>
#include <iomanip>
#include <sstream>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <unistd.h>
#include <vector>

#include <linux/version.h>

#include <libcamera/base/event_notifier.h>
#include <libcamera/base/log.h>
#include <libcamera/base/shared_fd.h>
#include <libcamera/base/unique_fd.h>
#include <libcamera/base/utils.h>

#include "libcamera/internal/formats.h"
#include "libcamera/internal/framebuffer.h"
#include "libcamera/internal/media_device.h"
#include "libcamera/internal/media_object.h"

/**
 * \file v4l2_videodevice.h
 * \brief V4L2 Video Device
 */

namespace libcamera {

LOG_DECLARE_CATEGORY(V4L2)

/**
 * \struct V4L2Capability
 * \brief struct v4l2_capability object wrapper and helpers
 *
 * The V4L2Capability structure manages the information returned by the
 * VIDIOC_QUERYCAP ioctl.
 */

/**
 * \fn V4L2Capability::driver()
 * \brief Retrieve the driver module name
 * \return The string containing the name of the driver module
 */

/**
 * \fn V4L2Capability::card()
 * \brief Retrieve the video device card name
 * \return The string containing the video device name
 */

/**
 * \fn V4L2Capability::bus_info()
 * \brief Retrieve the location of the video device in the system
 * \return The string containing the video device location
 */

/**
 * \fn V4L2Capability::device_caps()
 * \brief Retrieve the capabilities of the video device
 * \return The video device specific capabilities if V4L2_CAP_DEVICE_CAPS is
 * set or driver capabilities otherwise
 */

/**
 * \fn V4L2Capability::isMultiplanar()
 * \brief Identify if the video device implements the V4L2 multiplanar APIs
 * \return True if the video device supports multiplanar APIs
 */

/**
 * \fn V4L2Capability::isCapture()
 * \brief Identify if the video device captures data
 * \return True if the video device can capture data
 */

/**
 * \fn V4L2Capability::isOutput()
 * \brief Identify if the video device outputs data
 * \return True if the video device can output data
 */

/**
 * \fn V4L2Capability::isVideo()
 * \brief Identify if the video device captures or outputs images
 * \return True if the video device can capture or output images
 */

/**
 * \fn V4L2Capability::isM2M()
 * \brief Identify if the device is a Memory-to-Memory device
 * \return True if the device can capture and output images using the M2M API
 */

/**
 * \fn V4L2Capability::isMeta()
 * \brief Identify if the video device captures or outputs image meta-data
 * \return True if the video device can capture or output image meta-data
 */

/**
 * \fn V4L2Capability::isVideoCapture()
 * \brief Identify if the video device captures images
 * \return True if the video device can capture images
 */

/**
 * \fn V4L2Capability::isVideoOutput()
 * \brief Identify if the video device outputs images
 * \return True if the video device can output images
 */

/**
 * \fn V4L2Capability::isMetaCapture()
 * \brief Identify if the video device captures image meta-data
 * \return True if the video device can capture image meta-data
 */

/**
 * \fn V4L2Capability::isMetaOutput()
 * \brief Identify if the video device outputs image meta-data
 * \return True if the video device can output image meta-data
 */

/**
 * \fn V4L2Capability::hasStreaming()
 * \brief Determine if the video device can perform Streaming I/O
 * \return True if the video device provides Streaming I/O IOCTLs
 */

/**
 * \fn V4L2Capability::hasMediaController()
 * \brief Determine if the video device uses Media Controller to configure I/O
 * \return True if the video device is controlled by a Media Controller device
 */

/**
 * \class V4L2BufferCache
 * \brief Hot cache of associations between V4L2 buffer indexes and FrameBuffer
 *
 * When importing buffers, V4L2 performs lazy mapping of dmabuf instances at
 * VIDIOC_QBUF (or VIDIOC_PREPARE_BUF) time and keeps the mapping associated
 * with the V4L2 buffer, as identified by its index. If the same V4L2 buffer is
 * then reused and queued with different dmabufs, the old dmabufs will be
 * unmapped and the new ones mapped. To keep this process efficient, it is
 * crucial to consistently use the same V4L2 buffer for given dmabufs through
 * the whole duration of a capture cycle.
 *
 * The V4L2BufferCache class keeps a map of previous dmabufs to V4L2 buffer
 * index associations to help selecting V4L2 buffers. It tracks, for every
 * entry, if the V4L2 buffer is in use, and offers lookup of the best free V4L2
 * buffer for a set of dmabufs.
 */

/**
 * \brief Create an empty cache with \a numEntries entries
 * \param[in] numEntries Number of entries to reserve in the cache
 *
 * Create a cache with \a numEntries entries all marked as unused. The entries
 * will be populated as the cache is used. This is typically used to implement
 * buffer import, with buffers added to the cache as they are queued.
 */
V4L2BufferCache::V4L2BufferCache(unsigned int numEntries)
	: lastUsedCounter_(1), missCounter_(0)
{
	cache_.resize(numEntries);
}

/**
 * \brief Create a pre-populated cache
 * \param[in] buffers Array of buffers to pre-populated with
 *
 * Create a cache pre-populated with \a buffers. This is typically used to
 * implement buffer export, with all buffers added to the cache when they are
 * allocated.
 */
V4L2BufferCache::V4L2BufferCache(const std::vector<std::unique_ptr<FrameBuffer>> &buffers)
	: lastUsedCounter_(1), missCounter_(0)
{
	for (const std::unique_ptr<FrameBuffer> &buffer : buffers)
		cache_.emplace_back(true,
				    lastUsedCounter_.fetch_add(1, std::memory_order_acq_rel),
				    *buffer.get());
}

V4L2BufferCache::~V4L2BufferCache()
{
	if (missCounter_ > cache_.size())
		LOG(V4L2, Debug) << "Cache misses: " << missCounter_;
}

/**
 * \brief Check if all the entries in the cache are unused
 */
bool V4L2BufferCache::isEmpty() const
{
	for (auto const &entry : cache_) {
		if (!entry.free_)
			return false;
	}

	return true;
}

/**
 * \brief Find the best V4L2 buffer for a FrameBuffer
 * \param[in] buffer The FrameBuffer
 *
 * Find the best V4L2 buffer index to be used for the FrameBuffer \a buffer
 * based on previous mappings of frame buffers to V4L2 buffers. If a free V4L2
 * buffer previously used with the same dmabufs as \a buffer is found in the
 * cache, return its index. Otherwise return the index of the first free V4L2
 * buffer and record its association with the dmabufs of \a buffer.
 *
 * \return The index of the best V4L2 buffer, or -ENOENT if no free V4L2 buffer
 * is available
 */
int V4L2BufferCache::get(const FrameBuffer &buffer)
{
	bool hit = false;
	int use = -1;
	uint64_t oldest = UINT64_MAX;

	for (unsigned int index = 0; index < cache_.size(); index++) {
		const Entry &entry = cache_[index];

		if (!entry.free_)
			continue;

		/* Try to find a cache hit by comparing the planes. */
		if (entry == buffer) {
			hit = true;
			use = index;
			break;
		}

		if (entry.lastUsed_ < oldest) {
			use = index;
			oldest = entry.lastUsed_;
		}
	}

	if (!hit)
		missCounter_++;

	if (use < 0)
		return -ENOENT;

	cache_[use] = Entry(false,
			    lastUsedCounter_.fetch_add(1, std::memory_order_acq_rel),
			    buffer);

	return use;
}

/**
 * \brief Mark buffer \a index as free in the cache
 * \param[in] index The V4L2 buffer index
 */
void V4L2BufferCache::put(unsigned int index)
{
	ASSERT(index < cache_.size());
	cache_[index].free_ = true;
}

V4L2BufferCache::Entry::Entry()
	: free_(true), lastUsed_(0)
{
}

V4L2BufferCache::Entry::Entry(bool free, uint64_t lastUsed, const FrameBuffer &buffer)
	: free_(free), lastUsed_(lastUsed)
{
	for (const FrameBuffer::Plane &plane : buffer.planes())
		planes_.emplace_back(plane);
}

bool V4L2BufferCache::Entry::operator==(const FrameBuffer &buffer) const
{
	const std::vector<FrameBuffer::Plane> &planes = buffer.planes();

	if (planes_.size() != planes.size())
		return false;

	for (unsigned int i = 0; i < planes.size(); i++)
		if (planes_[i].fd != planes[i].fd.get() ||
		    planes_[i].length != planes[i].length)
			return false;
	return true;
}

/**
 * \class V4L2DeviceFormat
 * \brief The V4L2 video device image format and sizes
 *
 * This class describes the image format and resolution to be programmed on a
 * V4L2 video device. The image format is defined by a fourcc code (as specified
 * by the V4L2 API with the V4L2_PIX_FMT_* macros), a resolution (width and
 * height) and one to three planes with configurable line stride and a total
 * per-plane size in bytes.
 *
 * Image formats, as defined by the V4L2 APIs, are categorised as packed,
 * semi-planar and planar, and describe the layout of the image pixel components
 * stored in memory.
 *
 * Packed image formats store pixel components one after the other, in a
 * contiguous memory area. Examples of packed image formats are YUYV
 * permutations, RGB with different pixel sub-sampling ratios such as RGB565 or
 * RGB666 or Raw-Bayer formats such as SRGGB8 or SGRBG12.
 *
 * Semi-planar and planar image formats store the pixel components in separate
 * and possibly non-contiguous memory areas, named planes, whose sizes depend on
 * the pixel components sub-sampling ratios, which are defined by the format.
 * Semi-planar formats use two planes to store pixel components and notable
 * examples of such formats are the NV12 and NV16 formats, while planar formats
 * use three planes to store pixel components and notable examples are YUV422
 * and YUV420.
 *
 * Image formats supported by the V4L2 API are defined and described in Section
 * number 2 of the "Part I - Video for Linux API" chapter of the "Linux Media
 * Infrastructure userspace API", part of the Linux kernel documentation.
 *
 * In the context of this document, packed image formats are referred to as
 * "packed formats" and semi-planar and planar image formats are referred to as
 * "planar formats".
 *
 * V4L2 also defines two different sets of APIs to work with devices that store
 * planes in contiguous or separate memory areas. They are named "Single-plane
 * APIs" and "Multi-plane APIs" respectively and are documented in Section 2.1
 * and Section 2.2 of the above mentioned "Part I - Video for Linux API"
 * documentation.
 *
 * The single-plane API allows, among other parameters, the configuration of the
 * image resolution, the pixel format and the stride length. In that case the
 * stride applies to all planes (possibly sub-sampled). The multi-plane API
 * allows configuring the resolution, the pixel format and a per-plane stride
 * length and total size.
 *
 * Packed image formats, which occupy a single memory area, are easily described
 * through the single-plane API. When used on a video device that implements the
 * multi-plane API, only the size and stride information contained in the first
 * plane are taken into account.
 *
 * Planar image formats, which occupy distinct memory areas, are easily
 * described through the multi-plane APIs. When used on a video device that
 * implements the single-plane API, all planes are stored one after the other
 * in a contiguous memory area, and it is not possible to configure per-plane
 * stride length and size, but only a global stride length which is applied to
 * all planes.
 *
 * The V4L2DeviceFormat class describes both packed and planar image formats,
 * regardless of the API type (single or multi plane) implemented by the video
 * device the format has to be applied to. The total size and bytes per line
 * of images represented with packed formats are configured using the first
 * entry of the V4L2DeviceFormat::planes array, while the per-plane size and
 * per-plane stride length of images represented with planar image formats are
 * configured using the opportune number of entries of the
 * V4L2DeviceFormat::planes array, as prescribed by the image format
 * definition (semi-planar formats use 2 entries, while planar formats use the
 * whole 3 entries). The number of valid entries of the
 * V4L2DeviceFormat::planes array is defined by the
 * V4L2DeviceFormat::planesCount value.
 */

/**
 * \struct V4L2DeviceFormat::Plane
 * \brief Per-plane memory size information
 * \var V4L2DeviceFormat::Plane::size
 * \brief The plane total memory size (in bytes)
 * \var V4L2DeviceFormat::Plane::bpl
 * \brief The plane line stride (in bytes)
 */

/**
 * \var V4L2DeviceFormat::size
 * \brief The image size in pixels
 */

/**
 * \var V4L2DeviceFormat::fourcc
 * \brief The fourcc code describing the pixel encoding scheme
 *
 * The fourcc code, as defined by the V4L2 API with the V4L2_PIX_FMT_* macros,
 * that identifies the image format pixel encoding scheme.
 */

/**
 * \var V4L2DeviceFormat::colorSpace
 * \brief The color space of the pixels
 *
 * The color space of the image. When setting the format this may be
 * unset, in which case the driver gets to use its default color space.
 * After being set, this value should contain the color space that
 * was actually used. If this value is unset, then the color space chosen
 * by the driver could not be represented by the ColorSpace class (and
 * should probably be added).
 *
 * It is up to the pipeline handler or application to check if the
 * resulting color space is acceptable.
 */

/**
 * \var V4L2DeviceFormat::planes
 * \brief The per-plane memory size information
 *
 * Images are stored in memory in one or more data planes. Each data plane has a
 * specific line stride and memory size, which could differ from the image
 * visible sizes to accommodate padding at the end of lines and end of planes.
 * Only the first \ref planesCount entries are considered valid.
 */

/**
 * \var V4L2DeviceFormat::planesCount
 * \brief The number of valid data planes
 */

/**
 * \brief Assemble and return a string describing the format
 * \return A string describing the V4L2DeviceFormat
 */
const std::string V4L2DeviceFormat::toString() const
{
	std::stringstream ss;
	ss << *this;

	return ss.str();
}

/**
 * \brief Insert a text representation of a V4L2DeviceFormat into an output
 * stream
 * \param[in] out The output stream
 * \param[in] f The V4L2DeviceFormat
 * \return The output stream \a out
 */
std::ostream &operator<<(std::ostream &out, const V4L2DeviceFormat &f)
{
	out << f.size << "-" << f.fourcc;
	return out;
}

/**
 * \class V4L2VideoDevice
 * \brief V4L2VideoDevice object and API
 *
 * The V4L2VideoDevice class models an instance of a V4L2 video device.
 * It is constructed with the path to a V4L2 video device node. The device node
 * is only opened upon a call to open() which must be checked for success.
 *
 * The video device capabilities are validated when the device is opened and the
 * device is rejected if it is not a suitable V4L2 capture or output video
 * device, or if the video device does not support streaming I/O.
 *
 * No API call other than open(), isOpen() and close() shall be called on an
 * unopened device instance.
 *
 * The V4L2VideoDevice class supports the V4L2 MMAP and DMABUF memory types:
 *
 * - The allocateBuffers() function wraps buffer allocation with the V4L2 MMAP
 *   memory type. It requests buffers from the driver, allocating the
 *   corresponding memory, and exports them as a set of FrameBuffer objects.
 *   Upon successful return the driver's internal buffer management is
 *   initialized in MMAP mode, and the video device is ready to accept
 *   queueBuffer() calls.
 *
 *   This is the most traditional V4L2 buffer management, and is mostly useful
 *   to support internal buffer pools in pipeline handlers, either for CPU
 *   consumption (such as statistics or parameters pools), or for internal
 *   image buffers shared between devices.
 *
 * - The exportBuffers() function operates similarly to allocateBuffers(), but
 *   leaves the driver's internal buffer management uninitialized. It uses the
 *   V4L2 buffer orphaning support to allocate buffers with the MMAP method,
 *   export them as a set of FrameBuffer objects, and reset the driver's
 *   internal buffer management. The video device shall be initialized with
 *   importBuffers() or allocateBuffers() before it can accept queueBuffer()
 *   calls. The exported buffers are directly usable with any V4L2 video device
 *   in DMABUF mode, or with other dmabuf importers.
 *
 *   This method is mostly useful to implement buffer allocation helpers or to
 *   allocate ancillary buffers, when a V4L2 video device is used in DMABUF
 *   mode but no other source of buffers is available. An example use case
 *   would be allocation of scratch buffers to be used in case of buffer
 *   underruns on a video device that is otherwise supplied with external
 *   buffers.
 *
 * - The importBuffers() function initializes the driver's buffer management to
 *   import buffers in DMABUF mode. It requests buffers from the driver, but
 *   doesn't allocate memory. Upon successful return, the video device is ready
 *   to accept queueBuffer() calls. The buffers to be imported are provided to
 *   queueBuffer(), and may be supplied externally, or come from a previous
 *   exportBuffers() call.
 *
 *   This is the usual buffers initialization method for video devices whose
 *   buffers are exposed outside of libcamera. It is also typically used on one
 *   of the two video device that participate in buffer sharing inside
 *   pipelines, the other video device typically using allocateBuffers().
 *
 * - The releaseBuffers() function resets the driver's internal buffer
 *   management that was initialized by a previous call to allocateBuffers() or
 *   importBuffers(). Any memory allocated by allocateBuffers() is freed.
 *   Buffer exported by exportBuffers() are not affected by this function.
 *
 * The V4L2VideoDevice class tracks queued buffers and handles buffer events. It
 * automatically dequeues completed buffers and emits the \ref bufferReady
 * signal.
 *
 * Upon destruction any device left open will be closed, and any resources
 * released.
 *
 * \context This class is \threadbound.
 */

/**
 * \typedef V4L2VideoDevice::Formats
 * \brief A map of supported V4L2 pixel formats to frame sizes
 */

/**
 * \brief Construct a V4L2VideoDevice
 * \param[in] deviceNode The file-system path to the video device node
 */
V4L2VideoDevice::V4L2VideoDevice(const std::string &deviceNode)
	: V4L2Device(deviceNode), formatInfo_(nullptr), cache_(nullptr),
	  fdBufferNotifier_(nullptr), state_(State::Stopped),
	  watchdogDuration_(0.0)
{
	/*
	 * We default to an MMAP based CAPTURE video device, however this will
	 * be updated based upon the device capabilities.
	 */
	bufferType_ = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
	memoryType_ = V4L2_MEMORY_MMAP;
}

/**
 * \brief Construct a V4L2VideoDevice from a MediaEntity
 * \param[in] entity The MediaEntity to build the video device from
 *
 * Construct a V4L2VideoDevice from a MediaEntity's device node path.
 */
V4L2VideoDevice::V4L2VideoDevice(const MediaEntity *entity)
	: V4L2VideoDevice(entity->deviceNode())
{
	watchdog_.timeout.connect(this, &V4L2VideoDevice::watchdogExpired);
}

V4L2VideoDevice::~V4L2VideoDevice()
{
	close();
}

/**
 * \brief Open the V4L2 video device node and query its capabilities
 *
 * \return 0 on success or a negative error code otherwise
 */
int V4L2VideoDevice::open()
{
	int ret;

	ret = V4L2Device::open(O_RDWR | O_NONBLOCK);
	if (ret < 0)
		return ret;

	ret = ioctl(VIDIOC_QUERYCAP, &caps_);
	if (ret < 0) {
		LOG(V4L2, Error)
			<< "Failed to query device capabilities: "
			<< strerror(-ret);
		return ret;
	}

	if (caps_.version < KERNEL_VERSION(5, 0, 0)) {
		LOG(V4L2, Error)
			<< "V4L2 API v" << (caps_.version >> 16)
			<< "." << ((caps_.version >> 8) & 0xff)
			<< "." << (caps_.version & 0xff)
			<< " too old, v5.0.0 or later is required";
		return -EINVAL;
	}

	if (!caps_.hasStreaming()) {
		LOG(V4L2, Error) << "Device does not support streaming I/O";
		return -EINVAL;
	}

	/*
	 * Set buffer type and wait for read notifications on CAPTURE video
	 * devices (POLLIN), and write notifications for OUTPUT video devices
	 * (POLLOUT).
	 */
	EventNotifier::Type notifierType;

	if (caps_.isVideoCapture()) {
		notifierType = EventNotifier::Read;
		bufferType_ = caps_.isMultiplanar()
			    ? V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
			    : V4L2_BUF_TYPE_VIDEO_CAPTURE;
	} else if (caps_.isVideoOutput()) {
		notifierType = EventNotifier::Write;
		bufferType_ = caps_.isMultiplanar()
			    ? V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE
			    : V4L2_BUF_TYPE_VIDEO_OUTPUT;
	} else if (caps_.isMetaCapture()) {
		notifierType = EventNotifier::Read;
		bufferType_ = V4L2_BUF_TYPE_META_CAPTURE;
	} else if (caps_.isMetaOutput()) {
		notifierType = EventNotifier::Write;
		bufferType_ = V4L2_BUF_TYPE_META_OUTPUT;
	} else {
		LOG(V4L2, Error) << "Device is not a supported type";
		return -EINVAL;
	}

	fdBufferNotifier_ = new EventNotifier(fd(), notifierType);
	fdBufferNotifier_->activated.connect(this, &V4L2VideoDevice::bufferAvailable);
	fdBufferNotifier_->setEnabled(false);

	LOG(V4L2, Debug)
		<< "Opened device " << caps_.bus_info() << ": "
		<< caps_.driver() << ": " << caps_.card();

	ret = initFormats();
	if (ret)
		return ret;

	return 0;
}

/**
 * \brief Open a V4L2 video device from an opened file handle and query its
 * capabilities
 * \param[in] handle The file descriptor to set
 * \param[in] type The device type to operate on
 *
 * This function opens a video device from the existing file descriptor \a
 * handle. Like open(), this function queries the capabilities of the device,
 * but handles it according to the given device \a type instead of determining
 * its type from the capabilities. This can be used to force a given device type
 * for memory-to-memory devices.
 *
 * The file descriptor \a handle is duplicated, no reference to the original
 * handle is kept.
 *
 * \return 0 on success or a negative error code otherwise
 */
int V4L2VideoDevice::open(SharedFD handle, enum v4l2_buf_type type)
{
	int ret;

	UniqueFD newFd = handle.dup();
	if (!newFd.isValid()) {
		ret = -errno;
		LOG(V4L2, Error) << "Failed to duplicate file handle: "
				 << strerror(-ret);
		return ret;
	}

	ret = V4L2Device::setFd(std::move(newFd));
	if (ret < 0) {
		LOG(V4L2, Error) << "Failed to set file handle: "
				 << strerror(-ret);
		return ret;
	}

	ret = ioctl(VIDIOC_QUERYCAP, &caps_);
	if (ret < 0) {
		LOG(V4L2, Error)
			<< "Failed to query device capabilities: "
			<< strerror(-ret);
		return ret;
	}

	if (!caps_.hasStreaming()) {
		LOG(V4L2, Error) << "Device does not support streaming I/O";
		return -EINVAL;
	}

	/*
	 * Set buffer type and wait for read notifications on CAPTURE video
	 * devices (POLLIN), and write notifications for OUTPUT video devices
	 * (POLLOUT).
	 */
	EventNotifier::Type notifierType;

	switch (type) {
	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
		notifierType = EventNotifier::Write;
		bufferType_ = caps_.isMultiplanar()
			    ? V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE
			    : V4L2_BUF_TYPE_VIDEO_OUTPUT;
		break;
	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
		notifierType = EventNotifier::Read;
		bufferType_ = caps_.isMultiplanar()
			    ? V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
			    : V4L2_BUF_TYPE_VIDEO_CAPTURE;
		break;
	default:
		LOG(V4L2, Error) << "Unsupported buffer type";
		return -EINVAL;
	}

	fdBufferNotifier_ = new EventNotifier(fd(), notifierType);
	fdBufferNotifier_->activated.connect(this, &V4L2VideoDevice::bufferAvailable);
	fdBufferNotifier_->setEnabled(false);

	LOG(V4L2, Debug)
		<< "Opened device " << caps_.bus_info() << ": "
		<< caps_.driver() << ": " << caps_.card();

	ret = initFormats();
	if (ret)
		return ret;

	return 0;
}

int V4L2VideoDevice::initFormats()
{
	const std::vector<V4L2PixelFormat> &deviceFormats = enumPixelformats(0);
	if (deviceFormats.empty()) {
		LOG(V4L2, Error) << "Failed to initialize device formats";
		return -EINVAL;
	}

	pixelFormats_ = { deviceFormats.begin(), deviceFormats.end() };

	int ret = getFormat(&format_);
	if (ret) {
		LOG(V4L2, Error) << "Failed to get format";
		return ret;
	}

	formatInfo_ = &PixelFormatInfo::info(format_.fourcc);

	return 0;
}

/**
 * \brief Close the video device, releasing any resources acquired by open()
 */
void V4L2VideoDevice::close()
{
	if (!isOpen())
		return;

	releaseBuffers();
	delete fdBufferNotifier_;

	formatInfo_ = nullptr;

	V4L2Device::close();
}

/**
 * \fn V4L2VideoDevice::driverName()
 * \brief Retrieve the name of the V4L2 device driver
 * \return The string containing the driver name
 */

/**
 * \fn V4L2VideoDevice::deviceName()
 * \brief Retrieve the name of the V4L2 video device
 * \return The string containing the device name
 */

/**
 * \fn V4L2VideoDevice::busName()
 * \brief Retrieve the location of the device in the system
 * \return The string containing the device location
 */

/**
 * \fn V4L2VideoDevice::caps()
 * \brief Retrieve the device V4L2 capabilities
 * \return The device V4L2 capabilities
 */

std::string V4L2VideoDevice::logPrefix() const
{
	return deviceNode() + "[" + std::to_string(fd()) +
		(V4L2_TYPE_IS_OUTPUT(bufferType_) ? ":out]" : ":cap]");
}

/**
 * \brief Retrieve the image format set on the V4L2 video device
 * \param[out] format The image format applied on the video device
 * \return 0 on success or a negative error code otherwise
 */
int V4L2VideoDevice::getFormat(V4L2DeviceFormat *format)
{
	if (caps_.isMeta())
		return getFormatMeta(format);
	else if (caps_.isMultiplanar())
		return getFormatMultiplane(format);
	else
		return getFormatSingleplane(format);
}

/**
 * \brief Try an image format on the V4L2 video device
 * \param[inout] format The image format to test applicability to the video device
 *
 * Try the supplied \a format on the video device without applying it, returning
 * the format that would be applied. This is equivalent to setFormat(), except
 * that the device configuration is not changed.
 *
 * \return 0 on success or a negative error code otherwise
 */
int V4L2VideoDevice::tryFormat(V4L2DeviceFormat *format)
{
	if (caps_.isMeta())
		return trySetFormatMeta(format, false);
	else if (caps_.isMultiplanar())
		return trySetFormatMultiplane(format, false);
	else
		return trySetFormatSingleplane(format, false);
}

/**
 * \brief Configure an image format on the V4L2 video device
 * \param[inout] format The image format to apply to the video device
 *
 * Apply the supplied \a format to the video device, and return the actually
 * applied format parameters, as \ref V4L2VideoDevice::getFormat would do.
 *
 * \return 0 on success or a negative error code otherwise
 */
int V4L2VideoDevice::setFormat(V4L2DeviceFormat *format)
{
	int ret = 0;
	if (caps_.isMeta())
		ret = trySetFormatMeta(format, true);
	else if (caps_.isMultiplanar())
		ret = trySetFormatMultiplane(format, true);
	else
		ret = trySetFormatSingleplane(format, true);

	/* Cache the set format on success. */
	if (ret)
		return ret;

	format_ = *format;
	formatInfo_ = &PixelFormatInfo::info(format_.fourcc);

	return 0;
}

int V4L2VideoDevice::getFormatMeta(V4L2DeviceFormat *format)
{
	struct v4l2_format v4l2Format = {};
	struct v4l2_meta_format *pix = &v4l2Format.fmt.meta;
	int ret;

	v4l2Format.type = bufferType_;
	ret = ioctl(VIDIOC_G_FMT, &v4l2Format);
	if (ret) {
		LOG(V4L2, Error) << "Unable to get format: " << strerror(-ret);
		return ret;
	}

	format->size.width = 0;
	format->size.height = 0;
	format->fourcc = V4L2PixelFormat(pix->dataformat);
	format->planesCount = 1;
	format->planes[0].bpl = pix->buffersize;
	format->planes[0].size = pix->buffersize;

	return 0;
}

int V4L2VideoDevice::trySetFormatMeta(V4L2DeviceFormat *format, bool set)
{
	struct v4l2_format v4l2Format = {};
	struct v4l2_meta_format *pix = &v4l2Format.fmt.meta;
	int ret;

	v4l2Format.type = bufferType_;
	pix->dataformat = format->fourcc;
	pix->buffersize = format->planes[0].size;
	ret = ioctl(set ? VIDIOC_S_FMT : VIDIOC_TRY_FMT, &v4l2Format);
	if (ret) {
		LOG(V4L2, Error)
			<< "Unable to " << (set ? "set" : "try")
			<< " format: " << strerror(-ret);
		return ret;
	}

	/*
	 * Return to caller the format actually applied on the video device,
	 * which might differ from the requested one.
	 */
	format->size.width = 0;
	format->size.height = 0;
	format->fourcc = V4L2PixelFormat(pix->dataformat);
	format->planesCount = 1;
	format->planes[0].bpl = pix->buffersize;
	format->planes[0].size = pix->buffersize;

	return 0;
}

template<typename T>
std::optional<ColorSpace> V4L2VideoDevice::toColorSpace(const T &v4l2Format)
{
	V4L2PixelFormat fourcc{ v4l2Format.pixelformat };
	return V4L2Device::toColorSpace(v4l2Format, PixelFormatInfo::info(fourcc).colourEncoding);
}

int V4L2VideoDevice::getFormatMultiplane(V4L2DeviceFormat *format)
{
	struct v4l2_format v4l2Format = {};
	struct v4l2_pix_format_mplane *pix = &v4l2Format.fmt.pix_mp;
	int ret;

	v4l2Format.type = bufferType_;
	ret = ioctl(VIDIOC_G_FMT, &v4l2Format);
	if (ret) {
		LOG(V4L2, Error) << "Unable to get format: " << strerror(-ret);
		return ret;
	}

	format->size.width = pix->width;
	format->size.height = pix->height;
	format->fourcc = V4L2PixelFormat(pix->pixelformat);
	format->planesCount = pix->num_planes;
	format->colorSpace = toColorSpace(*pix);

	for (unsigned int i = 0; i < format->planesCount; ++i) {
		format->planes[i].bpl = pix->plane_fmt[i].bytesperline;
		format->planes[i].size = pix->plane_fmt[i].sizeimage;
	}

	return 0;
}

int V4L2VideoDevice::trySetFormatMultiplane(V4L2DeviceFormat *format, bool set)
{
	struct v4l2_format v4l2Format = {};
	struct v4l2_pix_format_mplane *pix = &v4l2Format.fmt.pix_mp;
	int ret;

	v4l2Format.type = bufferType_;
	pix->width = format->size.width;
	pix->height = format->size.height;
	pix->pixelformat = format->fourcc;
	pix->num_planes = format->planesCount;
	pix->field = V4L2_FIELD_NONE;
	if (format->colorSpace) {
		fromColorSpace(format->colorSpace, *pix);

		if (caps_.isVideoCapture())
			pix->flags |= V4L2_PIX_FMT_FLAG_SET_CSC;
	}

	ASSERT(pix->num_planes <= std::size(pix->plane_fmt));

	for (unsigned int i = 0; i < pix->num_planes; ++i) {
		pix->plane_fmt[i].bytesperline = format->planes[i].bpl;
		pix->plane_fmt[i].sizeimage = format->planes[i].size;
	}

	ret = ioctl(set ? VIDIOC_S_FMT : VIDIOC_TRY_FMT, &v4l2Format);
	if (ret) {
		LOG(V4L2, Error)
			<< "Unable to " << (set ? "set" : "try")
			<< " format: " << strerror(-ret);
		return ret;
	}

	/*
	 * Return to caller the format actually applied on the video device,
	 * which might differ from the requested one.
	 */
	format->size.width = pix->width;
	format->size.height = pix->height;
	format->fourcc = V4L2PixelFormat(pix->pixelformat);
	format->planesCount = pix->num_planes;
	for (unsigned int i = 0; i < format->planesCount; ++i) {
		format->planes[i].bpl = pix->plane_fmt[i].bytesperline;
		format->planes[i].size = pix->plane_fmt[i].sizeimage;
	}
	format->colorSpace = toColorSpace(*pix);

	return 0;
}

int V4L2VideoDevice::getFormatSingleplane(V4L2DeviceFormat *format)
{
	struct v4l2_format v4l2Format = {};
	struct v4l2_pix_format *pix = &v4l2Format.fmt.pix;
	int ret;

	v4l2Format.type = bufferType_;
	ret = ioctl(VIDIOC_G_FMT, &v4l2Format);
	if (ret) {
		LOG(V4L2, Error) << "Unable to get format: " << strerror(-ret);
		return ret;
	}

	format->size.width = pix->width;
	format->size.height = pix->height;
	format->fourcc = V4L2PixelFormat(pix->pixelformat);
	format->planesCount = 1;
	format->planes[0].bpl = pix->bytesperline;
	format->planes[0].size = pix->sizeimage;
	format->colorSpace = toColorSpace(*pix);

	return 0;
}

int V4L2VideoDevice::trySetFormatSingleplane(V4L2DeviceFormat *format, bool set)
{
	struct v4l2_format v4l2Format = {};
	struct v4l2_pix_format *pix = &v4l2Format.fmt.pix;
	int ret;

	v4l2Format.type = bufferType_;
	pix->width = format->size.width;
	pix->height = format->size.height;
	pix->pixelformat = format->fourcc;
	pix->bytesperline = format->planes[0].bpl;
	pix->field = V4L2_FIELD_NONE;
	if (format->colorSpace) {
		fromColorSpace(format->colorSpace, *pix);

		if (caps_.isVideoCapture())
			pix->flags |= V4L2_PIX_FMT_FLAG_SET_CSC;
	}

	ret = ioctl(set ? VIDIOC_S_FMT : VIDIOC_TRY_FMT, &v4l2Format);
	if (ret) {
		LOG(V4L2, Error)
			<< "Unable to " << (set ? "set" : "try")
			<< " format: " << strerror(-ret);
		return ret;
	}

	/*
	 * Return to caller the format actually applied on the device,
	 * which might differ from the requested one.
	 */
	format->size.width = pix->width;
	format->size.height = pix->height;
	format->fourcc = V4L2PixelFormat(pix->pixelformat);
	format->planesCount = 1;
	format->planes[0].bpl = pix->bytesperline;
	format->planes[0].size = pix->sizeimage;
	format->colorSpace = toColorSpace(*pix);

	return 0;
}

/**
 * \brief Enumerate all pixel formats and frame sizes
 * \param[in] code Restrict formats to this media bus code.
 *
 * Enumerate all pixel formats and frame sizes supported by the video device.
 * If the \a code argument is not zero, only formats compatible with that media
 * bus code will be enumerated.
 *
 * \return A list of the supported video device formats
 */
V4L2VideoDevice::Formats V4L2VideoDevice::formats(uint32_t code)
{
	Formats formats;

	for (V4L2PixelFormat pixelFormat : enumPixelformats(code)) {
		std::vector<SizeRange> sizes = enumSizes(pixelFormat);
		if (sizes.empty())
			return {};

		if (formats.find(pixelFormat) != formats.end()) {
			LOG(V4L2, Error)
				<< "Could not add sizes for pixel format "
				<< pixelFormat;
			return {};
		}

		formats.emplace(pixelFormat, sizes);
	}

	return formats;
}

std::vector<V4L2PixelFormat> V4L2VideoDevice::enumPixelformats(uint32_t code)
{
	std::vector<V4L2PixelFormat> formats;
	int ret;

	if (code && !caps_.hasMediaController()) {
		LOG(V4L2, Error)
			<< "Media bus code filtering not supported by the device";
		return {};
	}

	for (unsigned int index = 0; ; index++) {
		struct v4l2_fmtdesc pixelformatEnum = {};
		pixelformatEnum.index = index;
		pixelformatEnum.type = bufferType_;
		pixelformatEnum.mbus_code = code;

		ret = ioctl(VIDIOC_ENUM_FMT, &pixelformatEnum);
		if (ret)
			break;

		formats.push_back(V4L2PixelFormat(pixelformatEnum.pixelformat));
	}

	if (ret && ret != -EINVAL) {
		LOG(V4L2, Error)
			<< "Unable to enumerate pixel formats: "
			<< strerror(-ret);
		return {};
	}

	return formats;
}

std::vector<SizeRange> V4L2VideoDevice::enumSizes(V4L2PixelFormat pixelFormat)
{
	std::vector<SizeRange> sizes;
	int ret;

	for (unsigned int index = 0;; index++) {
		struct v4l2_frmsizeenum frameSize = {};
		frameSize.index = index;
		frameSize.pixel_format = pixelFormat;

		ret = ioctl(VIDIOC_ENUM_FRAMESIZES, &frameSize);
		if (ret)
			break;

		if (index != 0 &&
		    frameSize.type != V4L2_FRMSIZE_TYPE_DISCRETE) {
			LOG(V4L2, Error)
				<< "Non-zero index for non discrete type";
			return {};
		}

		switch (frameSize.type) {
		case V4L2_FRMSIZE_TYPE_DISCRETE:
			sizes.emplace_back(Size{ frameSize.discrete.width,
						 frameSize.discrete.height });
			break;
		case V4L2_FRMSIZE_TYPE_CONTINUOUS:
			sizes.emplace_back(Size{ frameSize.stepwise.min_width,
						 frameSize.stepwise.min_height },
					   Size{ frameSize.stepwise.max_width,
						 frameSize.stepwise.max_height });
			break;
		case V4L2_FRMSIZE_TYPE_STEPWISE:
			sizes.emplace_back(Size{ frameSize.stepwise.min_width,
						 frameSize.stepwise.min_height },
					   Size{ frameSize.stepwise.max_width,
						 frameSize.stepwise.max_height },
					   frameSize.stepwise.step_width,
					   frameSize.stepwise.step_height);
			break;
		default:
			LOG(V4L2, Error)
				<< "Unknown VIDIOC_ENUM_FRAMESIZES type "
				<< frameSize.type;
			return {};
		}
	}

	if (ret && ret != -EINVAL) {
		LOG(V4L2, Error)
			<< "Unable to enumerate frame sizes: "
			<< strerror(-ret);
		return {};
	}

	return sizes;
}

/**
 * \brief Set a selection rectangle \a rect for \a target
 * \param[in] target The selection target defined by the V4L2_SEL_TGT_* flags
 * \param[inout] rect The selection rectangle to be applied
 *
 * \todo Define a V4L2SelectionTarget enum for the selection target
 *
 * \return 0 on success or a negative error code otherwise
 */
int V4L2VideoDevice::setSelection(unsigned int target, Rectangle *rect)
{