v4l2: v4l2_compat: Add V4L2 compatibility layer

Add libcamera V4L2 compatibility layer.

This initial implementation supports the minimal set of V4L2 operations,
which allows getting, setting, and enumerating formats, and streaming
frames from a video device. Some data about the wrapped V4L2 video
device are hardcoded.

Add a build option named 'v4l2' and adjust the build system to
selectively compile the V4L2 compatibility layer.

For now we match the V4L2 device node to a libcamera camera based on a
devnum that a pipeline handler may optionally map to a libcamera
camera.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

10 files changed, 1486 insertions, 0 deletions

diff --git a/meson_options.txt b/meson_options.txt
index 1a328045..79ee4de6 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -10,3 +10,8 @@ option('documentation',
 option('test',
         type : 'boolean',
         description: 'Compile and include the tests')
+
+option('v4l2',
+        type : 'boolean',
+        value : false,
+        description : 'Compile the V4L2 compatibility layer')
diff --git a/src/meson.build b/src/meson.build
index 67ad20aa..5adcd61f 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -6,3 +6,7 @@ subdir('libcamera')
 subdir('ipa')
 subdir('cam')
 subdir('qcam')
+
+if get_option('v4l2')
+    subdir('v4l2')
+endif
diff --git a/src/v4l2/meson.build b/src/v4l2/meson.build
new file mode 100644
index 00000000..14ee3594
--- /dev/null
+++ b/src/v4l2/meson.build
@@ -0,0 +1,31 @@
+v4l2_compat_sources = files([
+    'v4l2_camera.cpp',
+    'v4l2_camera_proxy.cpp',
+    'v4l2_compat.cpp',
+    'v4l2_compat_manager.cpp',
+])
+
+v4l2_compat_includes = [
+    libcamera_includes,
+    libcamera_internal_includes,
+]
+
+v4l2_compat_cpp_args = [
+    # Meson enables large file support unconditionally, which redirect file
+    # operations to 64-bit versions. This results in some symbols being
+    # renamed, for instance open() being renamed to open64(). As the V4L2
+    # adaptation wrapper needs to provide both 32-bit and 64-bit versions of
+    # file operations, disable transparent large file support.
+    '-U_FILE_OFFSET_BITS',
+    '-D_FILE_OFFSET_BITS=32',
+    '-fvisibility=hidden',
+]
+
+v4l2_compat = shared_library('v4l2-compat',
+                             v4l2_compat_sources,
+                             name_prefix : '',
+                             install : true,
+                             link_with : libcamera,
+                             include_directories : v4l2_compat_includes,
+                             dependencies : libcamera_deps,
+                             cpp_args : v4l2_compat_cpp_args)
diff --git a/src/v4l2/v4l2_camera.cpp b/src/v4l2/v4l2_camera.cpp
new file mode 100644
index 00000000..3590730f
--- /dev/null
+++ b/src/v4l2/v4l2_camera.cpp
@@ -0,0 +1,224 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_camera.cpp - V4L2 compatibility camera
+ */
+
+#include "v4l2_camera.h"
+
+#include <errno.h>
+
+#include "log.h"
+#include "utils.h"
+
+using namespace libcamera;
+
+LOG_DECLARE_CATEGORY(V4L2Compat);
+
+FrameMetadata::FrameMetadata(Buffer *buffer)
+	: index_(buffer->index()), bytesused_(buffer->bytesused()),
+	  timestamp_(buffer->timestamp()), sequence_(buffer->sequence()),
+	  status_(buffer->status())
+{
+}
+
+V4L2Camera::V4L2Camera(std::shared_ptr<Camera> camera)
+	: camera_(camera), isRunning_(false)
+{
+	camera_->requestCompleted.connect(this, &V4L2Camera::requestComplete);
+}
+
+V4L2Camera::~V4L2Camera()
+{
+	camera_->release();
+}
+
+void V4L2Camera::open(int *ret)
+{
+	/* \todo Support multiple open. */
+	if (camera_->acquire() < 0) {
+		LOG(V4L2Compat, Error) << "Failed to acquire camera";
+		*ret = -EINVAL;
+		return;
+	}
+
+	config_ = camera_->generateConfiguration({ StreamRole::Viewfinder });
+	if (!config_) {
+		camera_->release();
+		*ret = -EINVAL;
+		return;
+	}
+
+	*ret = 0;
+}
+
+void V4L2Camera::close()
+{
+	camera_->release();
+}
+
+void V4L2Camera::getStreamConfig(StreamConfiguration *streamConfig)
+{
+	*streamConfig = config_->at(0);
+}
+
+std::vector<FrameMetadata> V4L2Camera::completedBuffers()
+{
+	std::vector<FrameMetadata> v;
+
+	bufferLock_.lock();
+	for (std::unique_ptr<FrameMetadata> &metadata : completedBuffers_)
+		v.push_back(*metadata.get());
+	completedBuffers_.clear();
+	bufferLock_.unlock();
+
+	return v;
+}
+
+void V4L2Camera::requestComplete(Request *request)
+{
+	if (request->status() == Request::RequestCancelled)
+		return;
+
+	/* We only have one stream at the moment. */
+	bufferLock_.lock();
+	Buffer *buffer = request->buffers().begin()->second;
+	std::unique_ptr<FrameMetadata> metadata =
+		utils::make_unique<FrameMetadata>(buffer);
+	completedBuffers_.push_back(std::move(metadata));
+	bufferLock_.unlock();
+
+	bufferSema_.release();
+}
+
+void V4L2Camera::configure(int *ret, StreamConfiguration *streamConfigOut,
+			   const Size &size, PixelFormat pixelformat,
+			   unsigned int bufferCount)
+{
+	StreamConfiguration &streamConfig = config_->at(0);
+	streamConfig.size.width = size.width;
+	streamConfig.size.height = size.height;
+	streamConfig.pixelFormat = pixelformat;
+	streamConfig.bufferCount = bufferCount;
+	/* \todo memoryType (interval vs external) */
+
+	CameraConfiguration::Status validation = config_->validate();
+	if (validation == CameraConfiguration::Invalid) {
+		LOG(V4L2Compat, Debug) << "Configuration invalid";
+		*ret = -EINVAL;
+		return;
+	}
+	if (validation == CameraConfiguration::Adjusted)
+		LOG(V4L2Compat, Debug) << "Configuration adjusted";
+
+	LOG(V4L2Compat, Debug) << "Validated configuration is: "
+			      << streamConfig.toString();
+
+	*ret = camera_->configure(config_.get());
+	if (*ret < 0)
+		return;
+
+	*streamConfigOut = config_->at(0);
+}
+
+void V4L2Camera::mmap(void **ret, unsigned int index)
+{
+	Stream *stream = *camera_->streams().begin();
+	*ret = stream->buffers()[index].planes()[0].mem();
+}
+
+void V4L2Camera::allocBuffers(int *ret, unsigned int count)
+{
+	*ret = camera_->allocateBuffers();
+	if (*ret == -EACCES)
+		*ret = -EBUSY;
+}
+
+void V4L2Camera::freeBuffers()
+{
+	camera_->freeBuffers();
+}
+
+void V4L2Camera::streamOn(int *ret)
+{
+	*ret = 0;
+
+	if (isRunning_)
+		return;
+
+	*ret = camera_->start();
+	if (*ret < 0) {
+		if (*ret == -EACCES)
+			*ret = -EBUSY;
+		return;
+	}
+	isRunning_ = true;
+
+	for (std::unique_ptr<Request> &req : pendingRequests_) {
+		/* \todo What should we do if this returns -EINVAL? */
+		*ret = camera_->queueRequest(req.release());
+		if (*ret < 0) {
+			if (*ret == -EACCES)
+				*ret = -EBUSY;
+			return;
+		}
+	}
+
+	pendingRequests_.clear();
+}
+
+void V4L2Camera::streamOff(int *ret)
+{
+	*ret = 0;
+
+	/* \todo Restore buffers to reqbufs state? */
+	if (!isRunning_)
+		return;
+
+	*ret = camera_->stop();
+	if (*ret < 0) {
+		if (*ret == -EACCES)
+			*ret = -EBUSY;
+		return;
+	}
+	isRunning_ = false;
+}
+
+void V4L2Camera::qbuf(int *ret, unsigned int index)
+{
+	Stream *stream = config_->at(0).stream();
+	std::unique_ptr<Buffer> buffer = stream->createBuffer(index);
+	if (!buffer) {
+		LOG(V4L2Compat, Error) << "Can't create buffer";
+		*ret = -ENOMEM;
+		return;
+	}
+
+	std::unique_ptr<Request> request =
+		std::unique_ptr<Request>(camera_->createRequest());
+	if (!request) {
+		LOG(V4L2Compat, Error) << "Can't create request";
+		*ret = -ENOMEM;
+		return;
+	}
+
+	*ret = request->addBuffer(std::move(buffer));
+	if (*ret < 0) {
+		LOG(V4L2Compat, Error) << "Can't set buffer for request";
+		*ret = -ENOMEM;
+		return;
+	}
+
+	if (!isRunning_) {
+		pendingRequests_.push_back(std::move(request));
+		return;
+	}
+
+	*ret = camera_->queueRequest(request.release());
+	if (*ret < 0) {
+		LOG(V4L2Compat, Error) << "Can't queue request";
+		if (*ret == -EACCES)
+			*ret = -EBUSY;
+	}
+}
diff --git a/src/v4l2/v4l2_camera.h b/src/v4l2/v4l2_camera.h
new file mode 100644
index 00000000..d24dbca6
--- /dev/null
+++ b/src/v4l2/v4l2_camera.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_camera.h - V4L2 compatibility camera
+ */
+
+#ifndef __V4L2_CAMERA_H__
+#define __V4L2_CAMERA_H__
+
+#include <deque>
+#include <linux/videodev2.h>
+#include <mutex>
+
+#include <libcamera/buffer.h>
+#include <libcamera/camera.h>
+
+#include "semaphore.h"
+
+using namespace libcamera;
+
+class FrameMetadata
+{
+public:
+	FrameMetadata(Buffer *buffer);
+
+	int index() const { return index_; }
+
+	unsigned int bytesused() const { return bytesused_; }
+	uint64_t timestamp() const { return timestamp_; }
+	unsigned int sequence() const { return sequence_; }
+
+	Buffer::Status status() const { return status_; }
+
+private:
+	int index_;
+
+	unsigned int bytesused_;
+	uint64_t timestamp_;
+	unsigned int sequence_;
+
+	Buffer::Status status_;
+};
+
+class V4L2Camera : public Object
+{
+public:
+	V4L2Camera(std::shared_ptr<Camera> camera);
+	~V4L2Camera();
+
+	void open(int *ret);
+	void close();
+	void getStreamConfig(StreamConfiguration *streamConfig);
+	std::vector<FrameMetadata> completedBuffers();
+
+	void mmap(void **ret, unsigned int index);
+
+	void configure(int *ret, StreamConfiguration *streamConfigOut,
+		       const Size &size, PixelFormat pixelformat,
+		       unsigned int bufferCount);
+
+	void allocBuffers(int *ret, unsigned int count);
+	void freeBuffers();
+	void streamOn(int *ret);
+	void streamOff(int *ret);
+
+	void qbuf(int *ret, unsigned int index);
+
+	Semaphore bufferSema_;
+
+private:
+	void requestComplete(Request *request);
+
+	std::shared_ptr<Camera> camera_;
+	std::unique_ptr<CameraConfiguration> config_;
+
+	bool isRunning_;
+
+	std::mutex bufferLock_;
+
+	std::deque<std::unique_ptr<Request>> pendingRequests_;
+	std::deque<std::unique_ptr<FrameMetadata>> completedBuffers_;
+};
+
+#endif /* __V4L2_CAMERA_H__ */
diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
new file mode 100644
index 00000000..559caba6
--- /dev/null
+++ b/src/v4l2/v4l2_camera_proxy.cpp
@@ -0,0 +1,644 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_camera_proxy.cpp - Proxy to V4L2 compatibility camera
+ */
+
+#include "v4l2_camera_proxy.h"
+
+#include <algorithm>
+#include <errno.h>
+#include <linux/drm_fourcc.h>
+#include <linux/videodev2.h>
+#include <string.h>
+#include <sys/mman.h>
+
+#include <libcamera/camera.h>
+#include <libcamera/object.h>
+
+#include "log.h"
+#include "utils.h"
+#include "v4l2_camera.h"
+#include "v4l2_compat_manager.h"
+
+#define KERNEL_VERSION(a, b, c) (((a) << 16) + ((b) << 8) + (c))
+
+using namespace libcamera;
+
+LOG_DECLARE_CATEGORY(V4L2Compat);
+
+V4L2CameraProxy::V4L2CameraProxy(unsigned int index,
+				 std::shared_ptr<Camera> camera)
+	: refcount_(0), index_(index), bufferCount_(0), currentBuf_(0),
+	  vcam_(utils::make_unique<V4L2Camera>(camera))
+{
+	querycap(camera);
+}
+
+int V4L2CameraProxy::open(bool nonBlocking)
+{
+	LOG(V4L2Compat, Debug) << "Servicing open";
+
+	int ret;
+	vcam_->invokeMethod(&V4L2Camera::open, ConnectionTypeBlocking,
+			    &ret);
+	if (ret < 0) {
+		errno = -ret;
+		return -1;
+	}
+
+	nonBlocking_ = nonBlocking;
+
+	vcam_->invokeMethod(&V4L2Camera::getStreamConfig,
+			    ConnectionTypeBlocking, &streamConfig_);
+	setFmtFromConfig(streamConfig_);
+	sizeimage_ = calculateSizeImage(streamConfig_);
+
+	refcount_++;
+
+	return 0;
+}
+
+void V4L2CameraProxy::dup()
+{
+	refcount_++;
+}
+
+void V4L2CameraProxy::close()
+{
+	LOG(V4L2Compat, Debug) << "Servicing close";
+
+	if (--refcount_ > 0)
+		return;
+
+	vcam_->invokeMethod(&V4L2Camera::close, ConnectionTypeBlocking);
+}
+
+void *V4L2CameraProxy::mmap(size_t length, int prot, int flags, off_t offset)
+{
+	LOG(V4L2Compat, Debug) << "Servicing mmap";
+
+	/* \todo Validate prot and flags properly. */
+	if (prot != (PROT_READ | PROT_WRITE)) {
+		errno = EINVAL;
+		return MAP_FAILED;
+	}
+
+	unsigned int index = offset / sizeimage_;
+	if (index * sizeimage_ != offset || length != sizeimage_) {
+		errno = EINVAL;
+		return MAP_FAILED;
+	}
+
+	void *val;
+	vcam_->invokeMethod(&V4L2Camera::mmap, ConnectionTypeBlocking,
+			    &val, index);
+
+	buffers_[index].flags |= V4L2_BUF_FLAG_MAPPED;
+	mmaps_[val] = index;
+
+	return val;
+}
+
+int V4L2CameraProxy::munmap(void *addr, size_t length)
+{
+	LOG(V4L2Compat, Debug) << "Servicing munmap";
+
+	auto iter = mmaps_.find(addr);
+	if (iter == mmaps_.end() || length != sizeimage_) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	buffers_[iter->second].flags &= ~V4L2_BUF_FLAG_MAPPED;
+	mmaps_.erase(iter);
+
+	return 0;
+}
+
+bool V4L2CameraProxy::validateBufferType(uint32_t type)
+{
+	return type == V4L2_BUF_TYPE_VIDEO_CAPTURE;
+}
+
+bool V4L2CameraProxy::validateMemoryType(uint32_t memory)
+{
+	return memory == V4L2_MEMORY_MMAP;
+}
+
+void V4L2CameraProxy::setFmtFromConfig(StreamConfiguration &streamConfig)
+{
+	curV4L2Format_.fmt.pix.width = streamConfig.size.width;
+	curV4L2Format_.fmt.pix.height = streamConfig.size.height;
+	curV4L2Format_.fmt.pix.pixelformat = drmToV4L2(streamConfig.pixelFormat);
+	curV4L2Format_.fmt.pix.field = V4L2_FIELD_NONE;
+	curV4L2Format_.fmt.pix.bytesperline =
+		bplMultiplier(curV4L2Format_.fmt.pix.pixelformat) *
+		curV4L2Format_.fmt.pix.width;
+	curV4L2Format_.fmt.pix.sizeimage =
+		imageSize(curV4L2Format_.fmt.pix.pixelformat,
+			  curV4L2Format_.fmt.pix.width,
+			  curV4L2Format_.fmt.pix.height);
+	curV4L2Format_.fmt.pix.colorspace = V4L2_COLORSPACE_SRGB;
+}
+
+unsigned int V4L2CameraProxy::calculateSizeImage(StreamConfiguration &streamConfig)
+{
+	/*
+	 * \todo Merge this method with setFmtFromConfig (need imageSize to
+	 * support all libcamera formats first, or filter out MJPEG for now).
+	 */
+	return imageSize(drmToV4L2(streamConfig.pixelFormat),
+			 streamConfig.size.width,
+			 streamConfig.size.height);
+}
+
+void V4L2CameraProxy::querycap(std::shared_ptr<Camera> camera)
+{
+	std::string driver = "libcamera";
+	std::string bus_info = driver + ":" + std::to_string(index_);
+
+	utils::strlcpy(reinterpret_cast<char *>(capabilities_.driver), driver.c_str(),
+		       sizeof(capabilities_.driver));
+	utils::strlcpy(reinterpret_cast<char *>(capabilities_.card), camera->name().c_str(),
+		       sizeof(capabilities_.card));
+	utils::strlcpy(reinterpret_cast<char *>(capabilities_.bus_info), bus_info.c_str(),
+		       sizeof(capabilities_.bus_info));
+	/* \todo Put this in a header/config somewhere. */
+	capabilities_.version = KERNEL_VERSION(5, 2, 0);
+	capabilities_.device_caps = V4L2_CAP_VIDEO_CAPTURE;
+	capabilities_.capabilities = capabilities_.device_caps
+				   | V4L2_CAP_DEVICE_CAPS;
+	memset(capabilities_.reserved, 0, sizeof(capabilities_.reserved));
+}
+
+void V4L2CameraProxy::updateBuffers()
+{
+	std::vector<FrameMetadata> completedBuffers = vcam_->completedBuffers();
+	for (FrameMetadata &fmd : completedBuffers) {
+		struct v4l2_buffer &buf = buffers_[fmd.index()];
+
+		switch (fmd.status()) {
+		case Buffer::Status::BufferSuccess:
+			buf.bytesused = fmd.bytesused();
+			buf.field = V4L2_FIELD_NONE;
+			buf.timestamp.tv_sec = fmd.timestamp() / 1000000000;
+			buf.timestamp.tv_usec = fmd.timestamp() % 1000000;
+			buf.sequence = fmd.sequence();
+
+			buf.flags |= V4L2_BUF_FLAG_DONE;
+			break;
+		case Buffer::Status::BufferError:
+			buf.flags |= V4L2_BUF_FLAG_ERROR;
+			break;
+		default:
+			break;
+		}
+	}
+}
+
+int V4L2CameraProxy::vidioc_querycap(struct v4l2_capability *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_querycap";
+
+	*arg = capabilities_;
+
+	return 0;
+}
+
+int V4L2CameraProxy::vidioc_enum_fmt(struct v4l2_fmtdesc *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_enum_fmt";
+
+	if (!validateBufferType(arg->type) ||
+	    arg->index > streamConfig_.formats().pixelformats().size())
+		return -EINVAL;
+
+	/* \todo Add map from format to description. */
+	utils::strlcpy(reinterpret_cast<char *>(arg->description), "Video Format Description",
+		       sizeof(arg->description));
+	arg->pixelformat = drmToV4L2(streamConfig_.formats().pixelformats()[arg->index]);
+
+	return 0;
+}
+
+int V4L2CameraProxy::vidioc_g_fmt(struct v4l2_format *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_g_fmt";
+
+	if (!validateBufferType(arg->type))
+		return -EINVAL;
+
+	memset(&arg->fmt, 0, sizeof(arg->fmt));
+	arg->fmt.pix = curV4L2Format_.fmt.pix;
+
+	return 0;
+}
+
+int V4L2CameraProxy::vidioc_s_fmt(struct v4l2_format *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_s_fmt";
+
+	int ret = vidioc_try_fmt(arg);
+	if (ret < 0)
+		return ret;
+
+	Size size(arg->fmt.pix.width, arg->fmt.pix.height);
+	vcam_->invokeMethod(&V4L2Camera::configure, ConnectionTypeBlocking,
+			    &ret, &streamConfig_, size,
+			    v4l2ToDrm(arg->fmt.pix.pixelformat), bufferCount_);
+	if (ret < 0)
+		return -EINVAL;
+
+	unsigned int sizeimage = calculateSizeImage(streamConfig_);
+	if (sizeimage == 0)
+		return -EINVAL;
+
+	sizeimage_ = sizeimage;
+
+	setFmtFromConfig(streamConfig_);
+
+	return 0;
+}
+
+int V4L2CameraProxy::vidioc_try_fmt(struct v4l2_format *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_try_fmt";
+	if (!validateBufferType(arg->type))
+		return -EINVAL;
+
+	PixelFormat format = v4l2ToDrm(arg->fmt.pix.pixelformat);
+	const std::vector<PixelFormat> &formats =
+		streamConfig_.formats().pixelformats();
+	if (std::find(formats.begin(), formats.end(), format) == formats.end())
+		format = streamConfig_.formats().pixelformats()[0];
+
+	Size size(arg->fmt.pix.width, arg->fmt.pix.height);
+	const std::vector<Size> &sizes = streamConfig_.formats().sizes(format);
+	if (std::find(sizes.begin(), sizes.end(), size) == sizes.end())
+		size = streamConfig_.formats().sizes(format)[0];
+
+	arg->fmt.pix.width        = size.width;
+	arg->fmt.pix.height       = size.height;
+	arg->fmt.pix.pixelformat  = v4l2ToDrm(format);
+	arg->fmt.pix.field        = V4L2_FIELD_NONE;
+	arg->fmt.pix.bytesperline = bplMultiplier(drmToV4L2(format)) *
+				    arg->fmt.pix.width;
+	arg->fmt.pix.sizeimage    = imageSize(drmToV4L2(format),
+					      arg->fmt.pix.width,
+					      arg->fmt.pix.height);
+	arg->fmt.pix.colorspace   = V4L2_COLORSPACE_SRGB;
+
+	return 0;
+}
+
+int V4L2CameraProxy::freeBuffers()
+{
+	LOG(V4L2Compat, Debug) << "Freeing libcamera bufs";
+
+	int ret;
+	vcam_->invokeMethod(&V4L2Camera::streamOff,
+			    ConnectionTypeBlocking, &ret);
+	if (ret < 0) {
+		LOG(V4L2Compat, Error) << "Failed to stop stream";
+		return ret;
+	}
+	vcam_->invokeMethod(&V4L2Camera::freeBuffers, ConnectionTypeBlocking);
+	bufferCount_ = 0;
+
+	return 0;
+}
+
+int V4L2CameraProxy::vidioc_reqbufs(struct v4l2_requestbuffers *arg)
+{
+	int ret;
+
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_reqbufs";
+	if (!validateBufferType(arg->type) ||
+	    !validateMemoryType(arg->memory))
+		return -EINVAL;
+
+	LOG(V4L2Compat, Debug) << arg->count << " buffers requested ";
+
+	arg->capabilities = V4L2_BUF_CAP_SUPPORTS_MMAP;
+
+	if (arg->count == 0)
+		return freeBuffers();
+
+	Size size(curV4L2Format_.fmt.pix.width, curV4L2Format_.fmt.pix.height);
+	vcam_->invokeMethod(&V4L2Camera::configure, ConnectionTypeBlocking,
+			    &ret, &streamConfig_, size,
+			    v4l2ToDrm(curV4L2Format_.fmt.pix.pixelformat),
+			    arg->count);
+	if (ret < 0)
+		return -EINVAL;
+
+	sizeimage_ = calculateSizeImage(streamConfig_);
+	if (sizeimage_ == 0)
+		return -EINVAL;
+
+	setFmtFromConfig(streamConfig_);
+
+	arg->count = streamConfig_.bufferCount;
+	bufferCount_ = arg->count;
+
+	vcam_->invokeMethod(&V4L2Camera::allocBuffers,
+			    ConnectionTypeBlocking, &ret, arg->count);
+	if (ret < 0) {
+		arg->count = 0;
+		return ret;
+	}
+
+	buffers_.resize(arg->count);
+	for (unsigned int i = 0; i < arg->count; i++) {
+		struct v4l2_buffer buf = {};
+		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+		buf.length = curV4L2Format_.fmt.pix.sizeimage;
+		buf.memory = V4L2_MEMORY_MMAP;
+		buf.m.offset = i * curV4L2Format_.fmt.pix.sizeimage;
+		buf.index = i;
+
+		buffers_[i] = buf;
+	}
+
+	LOG(V4L2Compat, Debug) << "Allocated " << arg->count << " buffers";
+
+	return 0;
+}
+
+int V4L2CameraProxy::vidioc_querybuf(struct v4l2_buffer *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_querybuf";
+
+	if (!validateBufferType(arg->type) ||
+	    arg->index >= bufferCount_)
+		return -EINVAL;
+
+	updateBuffers();
+
+	*arg = buffers_[arg->index];
+
+	return 0;
+}
+
+int V4L2CameraProxy::vidioc_qbuf(struct v4l2_buffer *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_qbuf, index = "
+			       << arg->index;
+
+	if (!validateBufferType(arg->type) ||
+	    !validateMemoryType(arg->memory) ||
+	    arg->index >= bufferCount_)
+		return -EINVAL;
+
+	int ret;
+	vcam_->invokeMethod(&V4L2Camera::qbuf, ConnectionTypeBlocking,
+			    &ret, arg->index);
+	if (ret < 0)
+		return ret;
+
+	arg->flags |= V4L2_BUF_FLAG_QUEUED;
+	arg->flags &= ~V4L2_BUF_FLAG_DONE;
+
+	return ret;
+}
+
+int V4L2CameraProxy::vidioc_dqbuf(struct v4l2_buffer *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_dqbuf";
+
+	if (!validateBufferType(arg->type) ||
+	    !validateMemoryType(arg->memory))
+		return -EINVAL;
+
+	if (nonBlocking_ && !vcam_->bufferSema_.tryAcquire())
+		return -EAGAIN;
+	else
+		vcam_->bufferSema_.acquire();
+
+	updateBuffers();
+
+	struct v4l2_buffer &buf = buffers_[currentBuf_];
+
+	buf.flags &= ~V4L2_BUF_FLAG_QUEUED;
+	buf.length = sizeimage_;
+	*arg = buf;
+
+	currentBuf_ = (currentBuf_ + 1) % bufferCount_;
+
+	return 0;
+}
+
+int V4L2CameraProxy::vidioc_streamon(int *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_streamon";
+
+	if (!validateBufferType(*arg))
+		return -EINVAL;
+
+	int ret;
+	vcam_->invokeMethod(&V4L2Camera::streamOn,
+			    ConnectionTypeBlocking, &ret);
+
+	return ret;
+}
+
+int V4L2CameraProxy::vidioc_streamoff(int *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_streamoff";
+
+	if (!validateBufferType(*arg))
+		return -EINVAL;
+
+	int ret;
+	vcam_->invokeMethod(&V4L2Camera::streamOff,
+			    ConnectionTypeBlocking, &ret);
+
+	for (struct v4l2_buffer &buf : buffers_)
+		buf.flags &= ~(V4L2_BUF_FLAG_QUEUED | V4L2_BUF_FLAG_DONE);
+
+	return ret;
+}
+
+int V4L2CameraProxy::ioctl(unsigned long request, void *arg)
+{
+	int ret;
+	switch (request) {
+	case VIDIOC_QUERYCAP:
+		ret = vidioc_querycap(static_cast<struct v4l2_capability *>(arg));
+		break;
+	case VIDIOC_ENUM_FMT:
+		ret = vidioc_enum_fmt(static_cast<struct v4l2_fmtdesc *>(arg));
+		break;
+	case VIDIOC_G_FMT:
+		ret = vidioc_g_fmt(static_cast<struct v4l2_format *>(arg));
+		break;
+	case VIDIOC_S_FMT:
+		ret = vidioc_s_fmt(static_cast<struct v4l2_format *>(arg));
+		break;
+	case VIDIOC_TRY_FMT:
+		ret = vidioc_try_fmt(static_cast<struct v4l2_format *>(arg));
+		break;
+	case VIDIOC_REQBUFS:
+		ret = vidioc_reqbufs(static_cast<struct v4l2_requestbuffers *>(arg));
+		break;
+	case VIDIOC_QUERYBUF:
+		ret = vidioc_querybuf(static_cast<struct v4l2_buffer *>(arg));
+		break;
+	case VIDIOC_QBUF:
+		ret = vidioc_qbuf(static_cast<struct v4l2_buffer *>(arg));
+		break;
+	case VIDIOC_DQBUF:
+		ret = vidioc_dqbuf(static_cast<struct v4l2_buffer *>(arg));
+		break;
+	case VIDIOC_STREAMON:
+		ret = vidioc_streamon(static_cast<int *>(arg));
+		break;
+	case VIDIOC_STREAMOFF:
+		ret = vidioc_streamoff(static_cast<int *>(arg));
+		break;
+	default:
+		ret = -ENOTTY;
+		break;
+	}
+
+	if (ret < 0) {
+		errno = -ret;
+		return -1;
+	}
+
+	return ret;
+}
+
+/* \todo make libcamera export these */
+int V4L2CameraProxy::bplMultiplier(unsigned int format)
+{
+	switch (format) {
+	case V4L2_PIX_FMT_NV12:
+	case V4L2_PIX_FMT_NV21:
+	case V4L2_PIX_FMT_NV16:
+	case V4L2_PIX_FMT_NV61:
+	case V4L2_PIX_FMT_NV24:
+	case V4L2_PIX_FMT_NV42:
+		return 1;
+	case V4L2_PIX_FMT_BGR24:
+	case V4L2_PIX_FMT_RGB24:
+		return 3;
+	case V4L2_PIX_FMT_ARGB32:
+		return 4;
+	case V4L2_PIX_FMT_VYUY:
+	case V4L2_PIX_FMT_YVYU:
+	case V4L2_PIX_FMT_UYVY:
+	case V4L2_PIX_FMT_YUYV:
+		return 2;
+	default:
+		return 0;
+	};
+}
+
+int V4L2CameraProxy::imageSize(unsigned int format,
+			       unsigned int width, unsigned int height)
+{
+	switch (format) {
+	case V4L2_PIX_FMT_NV12:
+	case V4L2_PIX_FMT_NV21:
+		return width * height * 3 / 2;
+	case V4L2_PIX_FMT_NV16:
+	case V4L2_PIX_FMT_NV61:
+		return width * height * 2;
+	case V4L2_PIX_FMT_NV24:
+	case V4L2_PIX_FMT_NV42:
+		return width * height * 3;
+	case V4L2_PIX_FMT_BGR24:
+	case V4L2_PIX_FMT_RGB24:
+		return width * height * 3;
+	case V4L2_PIX_FMT_ARGB32:
+		return width * height * 4;
+	case V4L2_PIX_FMT_VYUY:
+	case V4L2_PIX_FMT_YVYU:
+	case V4L2_PIX_FMT_UYVY:
+	case V4L2_PIX_FMT_YUYV:
+		return width * height * 2;
+	default:
+		return 0;
+	};
+}
+
+unsigned int V4L2CameraProxy::v4l2ToDrm(unsigned int pixelformat)
+{
+	switch (pixelformat) {
+	/* RGB formats. */
+	case V4L2_PIX_FMT_RGB24:
+		return DRM_FORMAT_BGR888;
+	case V4L2_PIX_FMT_BGR24:
+		return DRM_FORMAT_RGB888;
+	case V4L2_PIX_FMT_ARGB32:
+		return DRM_FORMAT_BGRA8888;
+
+	/* YUV packed formats. */
+	case V4L2_PIX_FMT_YUYV:
+		return DRM_FORMAT_YUYV;
+	case V4L2_PIX_FMT_YVYU:
+		return DRM_FORMAT_YVYU;
+	case V4L2_PIX_FMT_UYVY:
+		return DRM_FORMAT_UYVY;
+	case V4L2_PIX_FMT_VYUY:
+		return DRM_FORMAT_VYUY;
+
+	/* YUY planar formats. */
+	case V4L2_PIX_FMT_NV16:
+		return DRM_FORMAT_NV16;
+	case V4L2_PIX_FMT_NV61:
+		return DRM_FORMAT_NV61;
+	case V4L2_PIX_FMT_NV12:
+		return DRM_FORMAT_NV12;
+	case V4L2_PIX_FMT_NV21:
+		return DRM_FORMAT_NV21;
+	case V4L2_PIX_FMT_NV24:
+		return DRM_FORMAT_NV24;
+	case V4L2_PIX_FMT_NV42:
+		return DRM_FORMAT_NV42;
+	default:
+		return pixelformat;
+	};
+}
+
+unsigned int V4L2CameraProxy::drmToV4L2(unsigned int pixelformat)
+{
+	switch (pixelformat) {
+	/* RGB formats. */
+	case DRM_FORMAT_BGR888:
+		return V4L2_PIX_FMT_RGB24;
+	case DRM_FORMAT_RGB888:
+		return V4L2_PIX_FMT_BGR24;
+	case DRM_FORMAT_BGRA8888:
+		return V4L2_PIX_FMT_ARGB32;
+
+	/* YUV packed formats. */
+	case DRM_FORMAT_YUYV:
+		return V4L2_PIX_FMT_YUYV;
+	case DRM_FORMAT_YVYU:
+		return V4L2_PIX_FMT_YVYU;
+	case DRM_FORMAT_UYVY:
+		return V4L2_PIX_FMT_UYVY;
+	case DRM_FORMAT_VYUY:
+		return V4L2_PIX_FMT_VYUY;
+
+	/* YUY planar formats. */
+	case DRM_FORMAT_NV16:
+		return V4L2_PIX_FMT_NV16;
+	case DRM_FORMAT_NV61:
+		return V4L2_PIX_FMT_NV61;
+	case DRM_FORMAT_NV12:
+		return V4L2_PIX_FMT_NV12;
+	case DRM_FORMAT_NV21:
+		return V4L2_PIX_FMT_NV21;
+	case DRM_FORMAT_NV24:
+		return V4L2_PIX_FMT_NV24;
+	case DRM_FORMAT_NV42:
+		return V4L2_PIX_FMT_NV42;
+	default:
+		return pixelformat;
+	}
+}
diff --git a/src/v4l2/v4l2_camera_proxy.h b/src/v4l2/v4l2_camera_proxy.h
new file mode 100644
index 00000000..bef0f0af
--- /dev/null
+++ b/src/v4l2/v4l2_camera_proxy.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_camera_proxy.h - Proxy to V4L2 compatibility camera
+ */
+
+#ifndef __V4L2_CAMERA_PROXY_H__
+#define __V4L2_CAMERA_PROXY_H__
+
+#include <linux/videodev2.h>
+#include <map>
+#include <memory>
+#include <sys/types.h>
+#include <vector>
+
+#include <libcamera/camera.h>
+
+#include "v4l2_camera.h"
+
+using namespace libcamera;
+
+class V4L2CameraProxy
+{
+public:
+	V4L2CameraProxy(unsigned int index, std::shared_ptr<Camera> camera);
+
+	int open(bool nonBlocking);
+	void dup();
+	void close();
+	void *mmap(size_t length, int prot, int flags, off_t offset);
+	int munmap(void *addr, size_t length);
+
+	int ioctl(unsigned long request, void *arg);
+
+private:
+	bool validateBufferType(uint32_t type);
+	bool validateMemoryType(uint32_t memory);
+	void setFmtFromConfig(StreamConfiguration &streamConfig);
+	unsigned int calculateSizeImage(StreamConfiguration &streamConfig);
+	void querycap(std::shared_ptr<Camera> camera);
+	void updateBuffers();
+	int freeBuffers();
+
+	int vidioc_querycap(struct v4l2_capability *arg);
+	int vidioc_enum_fmt(struct v4l2_fmtdesc *arg);
+	int vidioc_g_fmt(struct v4l2_format *arg);
+	int vidioc_s_fmt(struct v4l2_format *arg);
+	int vidioc_try_fmt(struct v4l2_format *arg);
+	int vidioc_reqbufs(struct v4l2_requestbuffers *arg);
+	int vidioc_querybuf(struct v4l2_buffer *arg);
+	int vidioc_qbuf(struct v4l2_buffer *arg);
+	int vidioc_dqbuf(struct v4l2_buffer *arg);
+	int vidioc_streamon(int *arg);
+	int vidioc_streamoff(int *arg);
+
+	static int bplMultiplier(unsigned int format);
+	static int imageSize(unsigned int format, unsigned int width,
+			     unsigned int height);
+
+	static unsigned int v4l2ToDrm(unsigned int pixelformat);
+	static unsigned int drmToV4L2(unsigned int pixelformat);
+
+	unsigned int refcount_;
+	unsigned int index_;
+	bool nonBlocking_;
+
+	struct v4l2_format curV4L2Format_;
+	StreamConfiguration streamConfig_;
+	struct v4l2_capability capabilities_;
+	unsigned int bufferCount_;
+	unsigned int currentBuf_;
+	unsigned int sizeimage_;
+
+	std::vector<struct v4l2_buffer> buffers_;
+	std::map<void *, unsigned int> mmaps_;
+
+	std::unique_ptr<V4L2Camera> vcam_;
+};
+
+#endif /* __V4L2_CAMERA_PROXY_H__ */
diff --git a/src/v4l2/v4l2_compat.cpp b/src/v4l2/v4l2_compat.cpp
new file mode 100644
index 00000000..171ebed6
--- /dev/null
+++ b/src/v4l2/v4l2_compat.cpp
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_compat.cpp - V4L2 compatibility layer
+ */
+
+#include "v4l2_compat_manager.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdarg.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#define LIBCAMERA_PUBLIC __attribute__((visibility("default")))
+
+using namespace libcamera;
+
+#define extract_va_arg(type, arg, last)	\
+{					\
+	va_list ap;			\
+	va_start(ap, last);		\
+	arg = va_arg(ap, type);		\
+	va_end(ap);			\
+}
+
+extern "C" {
+
+LIBCAMERA_PUBLIC int open(const char *path, int oflag, ...)
+{
+	mode_t mode = 0;
+	if (oflag & O_CREAT || oflag & O_TMPFILE)
+		extract_va_arg(mode_t, mode, oflag);
+
+	return V4L2CompatManager::instance()->openat(AT_FDCWD, path,
+						     oflag, mode);
+}
+
+/* _FORTIFY_SOURCE redirects open to __open_2 */
+LIBCAMERA_PUBLIC extern __typeof(open) __open_2 __attribute__ ((alias("open")));
+
+LIBCAMERA_PUBLIC int openat(int dirfd, const char *path, int oflag, ...)
+{
+	mode_t mode = 0;
+	if (oflag & O_CREAT || oflag & O_TMPFILE)
+		extract_va_arg(mode_t, mode, oflag);
+
+	return V4L2CompatManager::instance()->openat(dirfd, path, oflag, mode);
+}
+
+LIBCAMERA_PUBLIC extern __typeof(openat) __openat_2 __attribute__ ((alias("openat")));
+
+LIBCAMERA_PUBLIC int dup(int oldfd)
+{
+	return V4L2CompatManager::instance()->dup(oldfd);
+}
+
+LIBCAMERA_PUBLIC int close(int fd)
+{
+	return V4L2CompatManager::instance()->close(fd);
+}
+
+LIBCAMERA_PUBLIC void *mmap(void *addr, size_t length, int prot, int flags,
+			    int fd, off_t offset)
+{
+	return V4L2CompatManager::instance()->mmap(addr, length, prot, flags,
+						   fd, offset);
+}
+
+LIBCAMERA_PUBLIC int munmap(void *addr, size_t length)
+{
+	return V4L2CompatManager::instance()->munmap(addr, length);
+}
+
+LIBCAMERA_PUBLIC int ioctl(int fd, unsigned long request, ...)
+{
+	void *arg;
+	extract_va_arg(void *, arg, request);
+
+	return V4L2CompatManager::instance()->ioctl(fd, request, arg);
+}
+
+}
diff --git a/src/v4l2/v4l2_compat_manager.cpp b/src/v4l2/v4l2_compat_manager.cpp
new file mode 100644
index 00000000..a3d69374
--- /dev/null
+++ b/src/v4l2/v4l2_compat_manager.cpp
@@ -0,0 +1,250 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_compat_manager.cpp - V4L2 compatibility manager
+ */
+
+#include "v4l2_compat_manager.h"
+
+#include <dlfcn.h>
+#include <fcntl.h>
+#include <map>
+#include <stdarg.h>
+#include <string.h>
+#include <sys/eventfd.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <libcamera/camera.h>
+#include <libcamera/camera_manager.h>
+
+#include "log.h"
+
+using namespace libcamera;
+
+LOG_DEFINE_CATEGORY(V4L2Compat)
+
+V4L2CompatManager::V4L2CompatManager()
+	: cm_(nullptr), initialized_(false)
+{
+	openat_func_ = (openat_func_t)dlsym(RTLD_NEXT, "openat");
+	dup_func_    = (dup_func_t   )dlsym(RTLD_NEXT, "dup");
+	close_func_  = (close_func_t )dlsym(RTLD_NEXT, "close");
+	ioctl_func_  = (ioctl_func_t )dlsym(RTLD_NEXT, "ioctl");
+	mmap_func_   = (mmap_func_t  )dlsym(RTLD_NEXT, "mmap");
+	munmap_func_ = (munmap_func_t)dlsym(RTLD_NEXT, "munmap");
+}
+
+V4L2CompatManager::~V4L2CompatManager()
+{
+	devices_.clear();
+	mmaps_.clear();
+
+	if (isRunning()) {
+		exit(0);
+		/* \todo Wait with a timeout, just in case. */
+		wait();
+	}
+}
+
+int V4L2CompatManager::init()
+{
+	start();
+
+	MutexLocker locker(mutex_);
+	cv_.wait(locker, [&] { return initialized_; });
+
+	return 0;
+}
+
+void V4L2CompatManager::run()
+{
+	cm_ = new CameraManager();
+
+	int ret = cm_->start();
+	if (ret) {
+		LOG(V4L2Compat, Error) << "Failed to start camera manager: "
+				       << strerror(-ret);
+		return;
+	}
+
+	LOG(V4L2Compat, Debug) << "Started camera manager";
+
+	/*
+	 * For each Camera registered in the system, a V4L2CameraProxy gets
+	 * created here to wrap a camera device.
+	 */
+	unsigned int index = 0;
+	for (auto &camera : cm_->cameras()) {
+		V4L2CameraProxy *proxy = new V4L2CameraProxy(index, camera);
+		proxies_.emplace_back(proxy);
+		++index;
+	}
+
+	/*
+	 * libcamera has been initialized. Unlock the init() caller as we're
+	 * now ready to handle calls from the framework.
+	 */
+	mutex_.lock();
+	initialized_ = true;
+	mutex_.unlock();
+	cv_.notify_one();
+
+	/* Now start processing events and messages. */
+	exec();
+
+	proxies_.clear();
+	cm_->stop();
+	delete cm_;
+	cm_ = nullptr;
+}
+
+V4L2CompatManager *V4L2CompatManager::instance()
+{
+	static V4L2CompatManager instance;
+	return &instance;
+}
+
+V4L2CameraProxy *V4L2CompatManager::getProxy(int fd)
+{
+	auto device = devices_.find(fd);
+	if (device == devices_.end())
+		return nullptr;
+
+	return device->second;
+}
+
+int V4L2CompatManager::getCameraIndex(int fd)
+{
+	struct stat statbuf;
+	int ret = fstat(fd, &statbuf);
+	if (ret < 0)
+		return -1;
+
+	std::shared_ptr<Camera> target = cm_->get(statbuf.st_rdev);
+	if (!target)
+		return -1;
+
+	unsigned int index = 0;
+	for (auto &camera : cm_->cameras()) {
+		if (camera == target)
+			return index;
+		++index;
+	}
+
+	return -1;
+}
+
+int V4L2CompatManager::openat(int dirfd, const char *path, int oflag, mode_t mode)
+{
+	int fd = openat_func_(dirfd, path, oflag, mode);
+	if (fd < 0)
+		return fd;
+
+	struct stat statbuf;
+	int ret = fstat(fd, &statbuf);
+	if (ret < 0 || (statbuf.st_mode & S_IFMT) != S_IFCHR ||
+	    major(statbuf.st_rdev) != 81)
+		return fd;
+
+	if (!isRunning())
+		init();
+
+	ret = getCameraIndex(fd);
+	if (ret < 0) {
+		LOG(V4L2Compat, Info) << "No camera found for " << path;
+		return fd;
+	}
+
+	close_func_(fd);
+
+	unsigned int camera_index = static_cast<unsigned int>(ret);
+
+	V4L2CameraProxy *proxy = proxies_[camera_index].get();
+	ret = proxy->open(oflag & O_NONBLOCK);
+	if (ret < 0)
+		return ret;
+
+	int efd = eventfd(0, oflag & (O_CLOEXEC | O_NONBLOCK));
+	if (efd < 0) {
+		proxy->close();
+		return efd;
+	}
+
+	devices_.emplace(efd, proxy);
+
+	return efd;
+}
+
+int V4L2CompatManager::dup(int oldfd)
+{
+	int newfd = dup_func_(oldfd);
+	if (newfd < 0)
+		return newfd;
+
+	auto device = devices_.find(oldfd);
+	if (device != devices_.end()) {
+		V4L2CameraProxy *proxy = device->second;
+		devices_[newfd] = proxy;
+		proxy->dup();
+	}
+
+	return newfd;
+}
+
+int V4L2CompatManager::close(int fd)
+{
+	V4L2CameraProxy *proxy = getProxy(fd);
+	if (proxy) {
+		proxy->close();
+		devices_.erase(fd);
+		return 0;
+	}
+
+	return close_func_(fd);
+}
+
+void *V4L2CompatManager::mmap(void *addr, size_t length, int prot, int flags,
+			      int fd, off_t offset)
+{
+	V4L2CameraProxy *proxy = getProxy(fd);
+	if (!proxy)
+		return mmap_func_(addr, length, prot, flags, fd, offset);
+
+	void *map = proxy->mmap(length, prot, flags, offset);
+	if (map == MAP_FAILED)
+		return map;
+
+	mmaps_[map] = proxy;
+	return map;
+}
+
+int V4L2CompatManager::munmap(void *addr, size_t length)
+{
+	auto device = mmaps_.find(addr);
+	if (device == mmaps_.end())
+		return munmap_func_(addr, length);
+
+	V4L2CameraProxy *proxy = device->second;
+
+	int ret = proxy->munmap(addr, length);
+	if (ret < 0)
+		return ret;
+
+	mmaps_.erase(device);
+
+	return 0;
+}
+
+int V4L2CompatManager::ioctl(int fd, unsigned long request, void *arg)
+{
+	V4L2CameraProxy *proxy = getProxy(fd);
+	if (!proxy)
+		return ioctl_func_(fd, request, arg);
+
+	return proxy->ioctl(request, arg);
+}
diff --git a/src/v4l2/v4l2_compat_manager.h b/src/v4l2/v4l2_compat_manager.h
new file mode 100644
index 00000000..dd9d3210
--- /dev/null
+++ b/src/v4l2/v4l2_compat_manager.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * v4l2_compat_manager.h - V4L2 compatibility manager
+ */
+
+#ifndef __V4L2_COMPAT_MANAGER_H__
+#define __V4L2_COMPAT_MANAGER_H__
+
+#include <condition_variable>
+#include <fcntl.h>
+#include <map>
+#include <memory>
+#include <mutex>
+#include <sys/types.h>
+#include <vector>
+
+#include <libcamera/camera_manager.h>
+
+#include "thread.h"
+#include "v4l2_camera_proxy.h"
+
+using namespace libcamera;
+
+class V4L2CompatManager : public Thread
+{
+public:
+	static V4L2CompatManager *instance();
+
+	int init();
+
+	V4L2CameraProxy *getProxy(int fd);
+
+	int openat(int dirfd, const char *path, int oflag, mode_t mode);
+
+	int dup(int oldfd);
+	int close(int fd);
+	void *mmap(void *addr, size_t length, int prot, int flags,
+		   int fd, off_t offset);
+	int munmap(void *addr, size_t length);
+	int ioctl(int fd, unsigned long request, void *arg);
+
+private:
+	V4L2CompatManager();
+	~V4L2CompatManager();
+
+	void run() override;
+	int getCameraIndex(int fd);
+
+	typedef int (*openat_func_t)(int dirfd, const char *path, int oflag, ...);
+	typedef int (*dup_func_t)(int oldfd);
+	typedef int (*close_func_t)(int fd);
+	typedef int (*ioctl_func_t)(int fd, unsigned long request, ...);
+	typedef void *(*mmap_func_t)(void *addr, size_t length, int prot,
+				     int flags, int fd, off_t offset);
+	typedef int (*munmap_func_t)(void *addr, size_t length);
+
+	openat_func_t openat_func_;
+	dup_func_t    dup_func_;
+	close_func_t  close_func_;
+	ioctl_func_t  ioctl_func_;
+	mmap_func_t   mmap_func_;
+	munmap_func_t munmap_func_;
+
+	CameraManager *cm_;
+
+	std::mutex mutex_;
+	std::condition_variable cv_;
+	bool initialized_;
+
+	std::vector<std::unique_ptr<V4L2CameraProxy>> proxies_;
+	std::map<int, V4L2CameraProxy *> devices_;
+	std::map<void *, V4L2CameraProxy *> mmaps_;
+};
+
+#endif /* __V4L2_COMPAT_MANAGER_H__ */