libcamera: device_enumerator: Convey device ownership through unique_ptr

Replace usage of shared_ptr with unique_ptr to convey media device
ownership internally in the enumerators when creating the media device.
Once a media device has all its dependencies met, it is converted to a
shared_ptr to keep the external API unchanged.

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

src/libcamera/device_enumerator.cpp

@@ -208,9 +208,9 @@ DeviceEnumerator::~DeviceEnumerator()
  *
  * \return Created media device instance on success, or nullptr otherwise
  */
-std::shared_ptr<MediaDevice> DeviceEnumerator::createDevice(const std::string &deviceNode)
+std::unique_ptr<MediaDevice> DeviceEnumerator::createDevice(const std::string &deviceNode)
 {
-	std::shared_ptr<MediaDevice> media = std::make_shared<MediaDevice>(deviceNode);
+	std::unique_ptr<MediaDevice> media = std::make_unique<MediaDevice>(deviceNode);
 
 	int ret = media->populate();
 	if (ret < 0) {
@@ -236,12 +236,12 @@ std::shared_ptr<MediaDevice> DeviceEnumerator::createDevice(const std::string &d
  * This method shall be called after all members of the entities of the
  * media graph have been confirmed to be initialized.
  */
-void DeviceEnumerator::addDevice(const std::shared_ptr<MediaDevice> &media)
+void DeviceEnumerator::addDevice(std::unique_ptr<MediaDevice> &&media)
 {
 	LOG(DeviceEnumerator, Debug)
 		<< "Added device " << media->deviceNode() << ": " << media->driver();
 
-	devices_.push_back(media);
+	devices_.push_back(std::move(media));
 }
 
 /**
@@ -290,7 +290,7 @@ void DeviceEnumerator::removeDevice(const std::string &deviceNode)
  */
 std::shared_ptr<MediaDevice> DeviceEnumerator::search(const DeviceMatch &dm)
 {
-	for (std::shared_ptr<MediaDevice> media : devices_) {
+	for (std::shared_ptr<MediaDevice> &media : devices_) {
 		if (media->busy())
 			continue;
 

src/libcamera/device_enumerator_sysfs.cpp

@@ -72,11 +72,11 @@ int DeviceEnumeratorSysfs::enumerate()
 			continue;
 		}
 
-		std::shared_ptr<MediaDevice> media = createDevice(devnode);
+		std::unique_ptr<MediaDevice> media = createDevice(devnode);
 		if (!media)
 			continue;
 
-		if (populateMediaDevice(media) < 0) {
+		if (populateMediaDevice(media.get()) < 0) {
 			LOG(DeviceEnumerator, Warning)
 				<< "Failed to populate media device "
 				<< media->deviceNode()
@@ -84,7 +84,7 @@ int DeviceEnumeratorSysfs::enumerate()
 			continue;
 		}
 
-		addDevice(media);
+		addDevice(std::move(media));
 	}
 
 	closedir(dir);
@@ -92,7 +92,7 @@ int DeviceEnumeratorSysfs::enumerate()
 	return 0;
 }
 
-int DeviceEnumeratorSysfs::populateMediaDevice(const std::shared_ptr<MediaDevice> &media)
+int DeviceEnumeratorSysfs::populateMediaDevice(MediaDevice *media)
 {
 	/* Associate entities to device node paths. */
 	for (MediaEntity *entity : media->entities()) {

src/libcamera/device_enumerator_udev.cpp

@@ -76,7 +76,7 @@ int DeviceEnumeratorUdev::addUdevDevice(struct udev_device *dev)
 		return -ENODEV;
 
 	if (!strcmp(subsystem, "media")) {
-		std::shared_ptr<MediaDevice> media =
+		std::unique_ptr<MediaDevice> media =
 			createDevice(udev_device_get_devnode(dev));
 		if (!media)
 			return -ENODEV;
@@ -96,7 +96,7 @@ int DeviceEnumeratorUdev::addUdevDevice(struct udev_device *dev)
 				<< "Defer media device " << media->deviceNode()
 				<< " due to " << ret << " missing dependencies";
 
-			pending_.emplace_back(media, deps);
+			pending_.emplace_back(std::move(media), std::move(deps));
 			MediaDeviceDeps *mediaDeps = &pending_.back();
 			for (const auto &dep : mediaDeps->deps_)
 				devMap_[dep.first] = mediaDeps;
@@ -104,7 +104,7 @@ int DeviceEnumeratorUdev::addUdevDevice(struct udev_device *dev)
 			return 0;
 		}
 
-		addDevice(media);
+		addDevice(std::move(media));
 		return 0;
 	}
 
@@ -319,7 +319,7 @@ int DeviceEnumeratorUdev::addV4L2Device(dev_t devnum)
 		LOG(DeviceEnumerator, Debug)
 			<< "All dependencies for media device "
 			<< deps->media_->deviceNode() << " found";
-		addDevice(deps->media_);
+		addDevice(std::move(deps->media_));
 		pending_.remove(*deps);
 	}
 

src/libcamera/include/device_enumerator.h

@@ -44,8 +44,8 @@ public:
 	std::shared_ptr<MediaDevice> search(const DeviceMatch &dm);
 
 protected:
-	std::shared_ptr<MediaDevice> createDevice(const std::string &deviceNode);
+	std::unique_ptr<MediaDevice> createDevice(const std::string &deviceNode);
-	void addDevice(const std::shared_ptr<MediaDevice> &media);
+	void addDevice(std::unique_ptr<MediaDevice> &&media);
 	void removeDevice(const std::string &deviceNode);
 
 private:

src/libcamera/include/device_enumerator_sysfs.h

@@ -23,7 +23,7 @@ public:
 	int enumerate();
 
 private:
-	int populateMediaDevice(const std::shared_ptr<MediaDevice> &media);
+	int populateMediaDevice(MediaDevice *media);
 	std::string lookupDeviceNode(int major, int minor);
 };
 

src/libcamera/include/device_enumerator_udev.h

@@ -43,9 +43,9 @@ private:
 	using DependencyMap = std::map<dev_t, std::list<MediaEntity *>>;
 
 	struct MediaDeviceDeps {
-		MediaDeviceDeps(const std::shared_ptr<MediaDevice> &media,
+		MediaDeviceDeps(std::unique_ptr<MediaDevice> &&media,
-				const DependencyMap &deps)
+				DependencyMap &&deps)
-			: media_(media), deps_(deps)
+			: media_(std::move(media)), deps_(std::move(deps))
 		{
 		}
 
@@ -54,7 +54,7 @@ private:
 			return media_ == other.media_;
 		}
 
-		std::shared_ptr<MediaDevice> media_;
+		std::unique_ptr<MediaDevice> media_;
 		DependencyMap deps_;
 	};