libcamera, android, cam, gstreamer, qcam, v4l2: Reuse Request

Allow reuse of the Request object by implementing reuse(). This means
the applications now have the responsibility of freeing the Request
objects, so make all libcamera users (cam, qcam, v4l2-compat, gstreamer,
android) do so.

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

include/libcamera/camera.h

@@ -96,7 +96,7 @@ public:
 	std::unique_ptr<CameraConfiguration> generateConfiguration(const StreamRoles &roles = {});
 	int configure(CameraConfiguration *config);
 
-	Request *createRequest(uint64_t cookie = 0);
+	std::unique_ptr<Request> createRequest(uint64_t cookie = 0);
 	int queueRequest(Request *request);
 
 	int start();

include/libcamera/request.h

@@ -31,6 +31,11 @@ public:
 		RequestCancelled,
 	};
 
+	enum ReuseFlag {
+		Default = 0,
+		ReuseBuffers = (1 << 0),
+	};
+
 	using BufferMap = std::map<const Stream *, FrameBuffer *>;
 
 	Request(Camera *camera, uint64_t cookie = 0);
@@ -38,6 +43,8 @@ public:
 	Request &operator=(const Request &) = delete;
 	~Request();
 
+	void reuse(ReuseFlag flags = Default);
+
 	ControlList &controls() { return *controls_; }
 	ControlList &metadata() { return *metadata_; }
 	const BufferMap &buffers() const { return bufferMap_; }