libcamera: camera_manager: Introduce signals when a camera is added or removed

Emit 'cameraAdded' and 'cameraRemoved' from CameraManager to enable
hotplug and hot-unplug support in application like QCam.

To avoid use-after-free race between the CameraManager and the
application, emit the 'cameraRemoved' with the shared_ptr version
of <Camera *>. This requires to change the function signature of
CameraManager::removeCamera() API.

Also, until now, CameraManager::Private::addCamera() transfers the
entire ownership of camera shared_ptr to CameraManager using
std::move(). This patch changes the signature of Private::addCamera to
accept pass-by-value camera parameter. It is done to make it clear from
the caller point of view that the pointer within the caller will still
be valid after this function returns. With this change in, we can emit
the camera pointer via 'cameraAdded' signal without hitting a segfault.

Signed-off-by: Umang Jain <email@uajain.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/include/libcamera/camera_manager.h b/include/libcamera/camera_manager.h
index 95dc6360..9eb2b6f5 100644
--- a/include/libcamera/camera_manager.h
+++ b/include/libcamera/camera_manager.h
@@ -13,6 +13,7 @@
 #include <vector>
 
 #include <libcamera/object.h>
+#include <libcamera/signal.h>
 
 namespace libcamera {
 
@@ -36,13 +37,16 @@ public:
 
 	void addCamera(std::shared_ptr<Camera> camera,
 		       const std::vector<dev_t> &devnums);
-	void removeCamera(Camera *camera);
+	void removeCamera(std::shared_ptr<Camera> camera);
 
 	static const std::string &version() { return version_; }
 
 	void setEventDispatcher(std::unique_ptr<EventDispatcher> dispatcher);
 	EventDispatcher *eventDispatcher();
 
+	Signal<std::shared_ptr<Camera>> cameraAdded;
+	Signal<std::shared_ptr<Camera>> cameraRemoved;
+
 private:
 	static const std::string version_;
 	static CameraManager *self_;