libcamera: camera_manager, pipeline_handler: allow retrieving cameras by device numbers

The V4L2 compatibility layer will need a way to map device numbers to
libcamera Camera instances. Expose a method in the camera manager to
retrieve Camera instances by devnum. The mapping from device numbers to
Camera instances is optionally declared by pipeline handlers when they
register cameras with the camera manager.

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

3 files changed, 64 insertions, 13 deletions

diff --git a/src/libcamera/camera_manager.cpp b/src/libcamera/camera_manager.cpp
index 7c6f72bb..a71caf85 100644
--- a/src/libcamera/camera_manager.cpp
+++ b/src/libcamera/camera_manager.cpp
@@ -181,14 +181,41 @@ std::shared_ptr<Camera> CameraManager::get(const std::string &name)
 }
 
 /**
+ * \brief Retrieve a camera based on device number
+ * \param[in] devnum Device number of camera to get
+ *
+ * This method is meant solely for the use of the V4L2 compatibility
+ * layer, to map device nodes to Camera instances. Applications shall
+ * not use it and shall instead retrieve cameras by name.
+ *
+ * Before calling this function the caller is responsible for ensuring that
+ * the camera manager is running.
+ *
+ * \return Shared pointer to Camera object, which is empty if the camera is
+ * not found
+ */
+std::shared_ptr<Camera> CameraManager::get(dev_t devnum)
+{
+	auto iter = camerasByDevnum_.find(devnum);
+	if (iter == camerasByDevnum_.end())
+		return nullptr;
+
+	return iter->second.lock();
+}
+
+/**
  * \brief Add a camera to the camera manager
  * \param[in] camera The camera to be added
+ * \param[in] devnum The device number to associate with \a camera
  *
  * This function is called by pipeline handlers to register the cameras they
  * handle with the camera manager. Registered cameras are immediately made
  * available to the system.
+ *
+ * \a devnum is used by the V4L2 compatibility layer to map V4L2 device nodes
+ * to Camera instances.
  */
-void CameraManager::addCamera(std::shared_ptr<Camera> camera)
+void CameraManager::addCamera(std::shared_ptr<Camera> camera, dev_t devnum)
 {
 	for (std::shared_ptr<Camera> c : cameras_) {
 		if (c->name() == camera->name()) {
@@ -200,6 +227,11 @@ void CameraManager::addCamera(std::shared_ptr<Camera> camera)
 	}
 
 	cameras_.push_back(std::move(camera));
+
+	if (devnum) {
+		unsigned int index = cameras_.size() - 1;
+		camerasByDevnum_[devnum] = cameras_[index];
+	}
 }
 
 /**
@@ -212,15 +244,24 @@ void CameraManager::addCamera(std::shared_ptr<Camera> camera)
  */
 void CameraManager::removeCamera(Camera *camera)
 {
-	for (auto iter = cameras_.begin(); iter != cameras_.end(); ++iter) {
-		if (iter->get() == camera) {
-			LOG(Camera, Debug)
-				<< "Unregistering camera '"
-				<< camera->name() << "'";
-			cameras_.erase(iter);
-			return;
-		}
-	}
+	auto iter = std::find_if(cameras_.begin(), cameras_.end(),
+				 [camera](std::shared_ptr<Camera> &c) {
+					 return c.get() == camera;
+				 });
+	if (iter == cameras_.end())
+		return;
+
+	LOG(Camera, Debug)
+		<< "Unregistering camera '" << camera->name() << "'";
+
+	auto iter_d = std::find_if(camerasByDevnum_.begin(), camerasByDevnum_.end(),
+				   [camera](const std::pair<dev_t, std::weak_ptr<Camera>> &p) {
+					   return p.second.lock().get() == camera;
+				   });
+	if (iter_d != camerasByDevnum_.end())
+		camerasByDevnum_.erase(iter_d);
+
+	cameras_.erase(iter);
 }
 
 /**
diff --git a/src/libcamera/include/pipeline_handler.h b/src/libcamera/include/pipeline_handler.h
index f3622631..067baef5 100644
--- a/src/libcamera/include/pipeline_handler.h
+++ b/src/libcamera/include/pipeline_handler.h
@@ -12,6 +12,7 @@
 #include <memory>
 #include <set>
 #include <string>
+#include <sys/sysmacros.h>
 #include <vector>
 
 #include <ipa/ipa_interface.h>
@@ -86,7 +87,7 @@ public:
 
 protected:
 	void registerCamera(std::shared_ptr<Camera> camera,
-			    std::unique_ptr<CameraData> data);
+			    std::unique_ptr<CameraData> data, dev_t devnum = 0);
 	void hotplugMediaDevice(MediaDevice *media);
 
 	virtual int queueRequestDevice(Camera *camera, Request *request) = 0;
diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
index 5badf31c..698dd525 100644
--- a/src/libcamera/pipeline_handler.cpp
+++ b/src/libcamera/pipeline_handler.cpp
@@ -7,6 +7,8 @@
 
 #include "pipeline_handler.h"
 
+#include <sys/sysmacros.h>
+
 #include <libcamera/buffer.h>
 #include <libcamera/camera.h>
 #include <libcamera/camera_manager.h>
@@ -438,19 +440,26 @@ void PipelineHandler::completeRequest(Camera *camera, Request *request)
  * \brief Register a camera to the camera manager and pipeline handler
  * \param[in] camera The camera to be added
  * \param[in] data Pipeline-specific data for the camera
+ * \param[in] devnum Device number of the camera (optional)
  *
  * This method is called by pipeline handlers to register the cameras they
  * handle with the camera manager. It associates the pipeline-specific \a data
  * with the camera, for later retrieval with cameraData(). Ownership of \a data
  * is transferred to the PipelineHandler.
+ *
+ * \a devnum is the device number (as returned by makedev) that the \a camera
+ * is to be associated with. This is for the V4L2 compatibility layer to map
+ * device nodes to Camera instances based on the device number
+ * registered by this method in \a devnum.
  */
 void PipelineHandler::registerCamera(std::shared_ptr<Camera> camera,
-				     std::unique_ptr<CameraData> data)
+				     std::unique_ptr<CameraData> data,
+				     dev_t devnum)
 {
 	data->camera_ = camera.get();
 	cameraData_[camera.get()] = std::move(data);
 	cameras_.push_back(camera);
-	manager_->addCamera(std::move(camera));
+	manager_->addCamera(std::move(camera), devnum);
 }
 
 /**