libcamera: media_device: Move recursive lock handling to pipeline handler

The MediaDevice lock is meant to prevent concurrent usage of multiple
cameras from the same pipeline handlers. As media devices are acquired
by pipeline handlers, we can't have multiple pipeline handlers trying to
lock the same media device. The recursive locking detection can thus be
moved to the pipeline handler. This simplifies the media device
implementation that now implements true lock semantics, and prepares for
support of concurrent camera usage.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

include/libcamera/internal/media_device.h

@@ -86,7 +86,6 @@ private:
 	UniqueFD fd_;
 	bool valid_;
 	bool acquired_;
-	bool lockOwner_;
 
 	std::map<unsigned int, MediaObject *> objects_;
 	std::vector<MediaEntity *> entities_;

include/libcamera/internal/pipeline_handler.h

@@ -88,6 +88,8 @@ private:
 
 	const char *name_;
 
+	bool lockOwner_;
+
 	friend class PipelineHandlerFactory;
 };
 

src/libcamera/media_device.cpp

@@ -63,8 +63,7 @@ LOG_DEFINE_CATEGORY(MediaDevice)
  * populate() before the media graph can be queried.
  */
 MediaDevice::MediaDevice(const std::string &deviceNode)
-	: deviceNode_(deviceNode), valid_(false), acquired_(false),
-	  lockOwner_(false)
+	: deviceNode_(deviceNode), valid_(false), acquired_(false)
 {
 }
 
@@ -145,15 +144,9 @@ bool MediaDevice::lock()
 	if (!fd_.isValid())
 		return false;
 
-	/* Do not allow nested locking in the same libcamera instance. */
-	if (lockOwner_)
-		return false;
-
 	if (lockf(fd_.get(), F_TLOCK, 0))
 		return false;
 
-	lockOwner_ = true;
-
 	return true;
 }
 
@@ -171,11 +164,6 @@ void MediaDevice::unlock()
 	if (!fd_.isValid())
 		return;
 
-	if (!lockOwner_)
-		return;
-
-	lockOwner_ = false;
-
 	lockf(fd_.get(), F_ULOCK, 0);
 }
 

src/libcamera/pipeline_handler.cpp

@@ -67,7 +67,7 @@ LOG_DEFINE_CATEGORY(Pipeline)
  * respective factories.
  */
 PipelineHandler::PipelineHandler(CameraManager *manager)
-	: manager_(manager)
+	: manager_(manager), lockOwner_(false)
 {
 }
 
@@ -155,6 +155,10 @@ MediaDevice *PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,
  */
 bool PipelineHandler::lock()
 {
+	/* Do not allow nested locking in the same libcamera instance. */
+	if (lockOwner_)
+		return false;
+
 	for (std::shared_ptr<MediaDevice> &media : mediaDevices_) {
 		if (!media->lock()) {
 			unlock();
@@ -162,6 +166,8 @@ bool PipelineHandler::lock()
 		}
 	}
 
+	lockOwner_ = true;
+
 	return true;
 }
 
@@ -177,8 +183,13 @@ bool PipelineHandler::lock()
  */
 void PipelineHandler::unlock()
 {
+	if (!lockOwner_)
+		return;
+
 	for (std::shared_ptr<MediaDevice> &media : mediaDevices_)
 		media->unlock();
+
+	lockOwner_ = false;
 }
 
 /**