libcamera: pipeline_handler: Add camera disconnection support

Pipeline handlers are responsible for creating camera instances, but
also for destroying them when devices are unplugged. As camera objects
are reference-counted this isn't a straightforward operation and
involves the camera manager and camera object itself. Add two helper
methods in the PipelineHandler base class to register a camera and to
register a media device with the pipeline handler.

When registering a camera, the registerCamera() helper method will add
it to the camera manager. When registering a media device, the
registerMediaDevice() helper method will listen to device disconnection
events, and disconnect all cameras created by the pipeline handler as a
response.

Under the hood the PipelineHandler class needs to keep track of
registered cameras in order to handle disconnection. They can't be
stored as shared pointers as this would create a circular dependency
(the Camera class owns a shared pointer to the pipeline handler). Store
them as weak pointers instead. This is safe as a reference to the camera
is stored in the camera manager, and doesn't get removed until the
camera is unregistered from the manager by the PipelineHandler.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/include/pipeline_handler.h

@@ -16,6 +16,7 @@ namespace libcamera {
 
 class CameraManager;
 class DeviceEnumerator;
+class MediaDevice;
 
 class PipelineHandler : public std::enable_shared_from_this<PipelineHandler>
 {
@@ -27,6 +28,15 @@ public:
 
 protected:
 	CameraManager *manager_;
+
+	void registerCamera(std::shared_ptr<Camera> camera);
+	void hotplugMediaDevice(MediaDevice *media);
+
+private:
+	virtual void disconnect();
+	void mediaDeviceDisconnected(MediaDevice *media);
+
+	std::vector<std::weak_ptr<Camera>> cameras_;
 };
 
 class PipelineHandlerFactory

src/libcamera/pipeline/ipu3/ipu3.cpp

@@ -9,7 +9,6 @@
 #include <vector>
 
 #include <libcamera/camera.h>
-#include <libcamera/camera_manager.h>
 
 #include "device_enumerator.h"
 #include "log.h"
@@ -169,7 +168,7 @@ void PipelineHandlerIPU3::registerCameras()
 
 		std::string cameraName = sensor->name() + " " + std::to_string(id);
 		std::shared_ptr<Camera> camera = Camera::create(this, cameraName);
-		manager_->addCamera(std::move(camera));
+		registerCamera(std::move(camera));
 
 		LOG(IPU3, Info)
 			<< "Registered Camera[" << numCameras << "] \""

src/libcamera/pipeline/uvcvideo.cpp

@@ -6,7 +6,6 @@
  */
 
 #include <libcamera/camera.h>
-#include <libcamera/camera_manager.h>
 
 #include "device_enumerator.h"
 #include "media_device.h"
@@ -49,7 +48,7 @@ bool PipelineHandlerUVC::match(DeviceEnumerator *enumerator)
 	dev_->acquire();
 
 	std::shared_ptr<Camera> camera = Camera::create(this, dev_->model());
-	manager_->addCamera(std::move(camera));
+	registerCamera(std::move(camera));
 
 	return true;
 }

src/libcamera/pipeline/vimc.cpp

@@ -6,7 +6,6 @@
  */
 
 #include <libcamera/camera.h>
-#include <libcamera/camera_manager.h>
 
 #include "device_enumerator.h"
 #include "media_device.h"
@@ -58,7 +57,7 @@ bool PipeHandlerVimc::match(DeviceEnumerator *enumerator)
 	dev_->acquire();
 
 	std::shared_ptr<Camera> camera = Camera::create(this, "Dummy VIMC Camera");
-	manager_->addCamera(std::move(camera));
+	registerCamera(std::move(camera));
 
 	return true;
 }

src/libcamera/pipeline_handler.cpp

@@ -5,7 +5,11 @@
  * pipeline_handler.cpp - Pipeline handler infrastructure
  */
 
+#include <libcamera/camera.h>
+#include <libcamera/camera_manager.h>
+
 #include "log.h"
+#include "media_device.h"
 #include "pipeline_handler.h"
 
 /**
@@ -97,6 +101,73 @@ PipelineHandler::~PipelineHandler()
  * constant for the whole lifetime of the pipeline handler.
  */
 
+/**
+ * \brief Register a camera to the camera manager and pipeline handler
+ * \param[in] camera The camera to be added
+ *
+ * This function is called by pipeline handlers to register the cameras they
+ * handle with the camera manager.
+ */
+void PipelineHandler::registerCamera(std::shared_ptr<Camera> camera)
+{
+	cameras_.push_back(camera);
+	manager_->addCamera(std::move(camera));
+}
+
+/**
+ * \brief Enable hotplug handling for a media device
+ * \param[in] media The media device
+ *
+ * This function enables hotplug handling, and especially hot-unplug handling,
+ * of the \a media device. It shall be called by pipeline handlers for all the
+ * media devices that can be disconnected.
+ *
+ * When a media device passed to this function is later unplugged, the pipeline
+ * handler gets notified and automatically disconnects all the cameras it has
+ * registered without requiring any manual intervention.
+ */
+void PipelineHandler::hotplugMediaDevice(MediaDevice *media)
+{
+	media->disconnected.connect(this, &PipelineHandler::mediaDeviceDisconnected);
+}
+
+/**
+ * \brief Device disconnection handler
+ *
+ * This virtual function is called to notify the pipeline handler that the
+ * device it handles has been disconnected. It notifies all cameras created by
+ * the pipeline handler that they have been disconnected, and unregisters them
+ * from the camera manager.
+ *
+ * The function can be overloaded by pipeline handlers to perform custom
+ * operations at disconnection time. Any overloaded version shall call the
+ * PipelineHandler::disconnect() base function for proper hot-unplug operation.
+ */
+void PipelineHandler::disconnect()
+{
+	for (std::weak_ptr<Camera> ptr : cameras_) {
+		std::shared_ptr<Camera> camera = ptr.lock();
+		if (!camera)
+			continue;
+
+		camera->disconnect();
+		manager_->removeCamera(camera.get());
+	}
+
+	cameras_.clear();
+}
+
+/**
+ * \brief Slot for the MediaDevice disconnected signal
+ */
+void PipelineHandler::mediaDeviceDisconnected(MediaDevice *media)
+{
+	if (cameras_.empty())
+		return;
+
+	disconnect();
+}
+
 /**
  * \class PipelineHandlerFactory
  * \brief Registration of PipelineHandler classes and creation of instances