libcamera: pipeline_handler: Keep track of MediaDevice

Instead of requiring each pipeline handle implementation to keep track
of calling release() on its media devices upon deletion, keep track of
them in the base class. Add a helper that pipeline handlers shall use
to acquire a media device instead of directly interacting with the
DeviceEnumerator.

This also means that pipeline handler implementations do no need to keep
a shared_ptr<> reference to the media devices they store locally as the
PipelineHandler base class will keep a shared_ptr<> reference to all
media devices consumed for the entire lifetime of the pipeline handler
implementation.

Centrally keeping track of media devices will also be beneficial
to implement exclusive access to pipelines across processes.

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

src/libcamera/include/pipeline_handler.h

@@ -22,6 +22,7 @@ class Camera;
 class CameraConfiguration;
 class CameraManager;
 class DeviceEnumerator;
+class DeviceMatch;
 class MediaDevice;
 class PipelineHandler;
 class Request;
@@ -53,6 +54,8 @@ public:
 	virtual ~PipelineHandler();
 
 	virtual bool match(DeviceEnumerator *enumerator) = 0;
+	MediaDevice *acquireMediaDevice(DeviceEnumerator *enumerator,
+					const DeviceMatch &dm);
 
 	virtual CameraConfiguration
 	streamConfiguration(Camera *camera, const std::vector<StreamUsage> &usages) = 0;
@@ -84,6 +87,7 @@ private:
 	void mediaDeviceDisconnected(MediaDevice *media);
 	virtual void disconnect();
 
+	std::vector<std::shared_ptr<MediaDevice>> mediaDevices_;
 	std::vector<std::weak_ptr<Camera>> cameras_;
 	std::map<const Camera *, std::unique_ptr<CameraData>> cameraData_;
 };