libcamera: buffer: Add an accessor to the BufferMemory

Buffer instances reference memory, which is modelled internally by a
BufferMemory instance. Store a pointer to the BufferMemory in the Buffer
class, and populate it when the buffer is queued to the camera through a
request. This is useful for applications to access the buffer memory in
the buffer or request completion handler.

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

include/libcamera/buffer.h

@@ -77,6 +77,7 @@ public:
 
 	unsigned int index() const { return index_; }
 	const std::array<int, 3> &dmabufs() const { return dmabuf_; }
+	BufferMemory *mem() { return mem_; }
 
 	unsigned int bytesused() const { return bytesused_; }
 	uint64_t timestamp() const { return timestamp_; }
@@ -87,6 +88,7 @@ public:
 	Stream *stream() const { return stream_; }
 
 private:
+	friend class Camera;
 	friend class PipelineHandler;
 	friend class Request;
 	friend class Stream;
@@ -98,6 +100,7 @@ private:
 
 	unsigned int index_;
 	std::array<int, 3> dmabuf_;
+	BufferMemory *mem_;
 
 	unsigned int bytesused_;
 	uint64_t timestamp_;

src/cam/buffer_writer.cpp

@@ -19,8 +19,7 @@ BufferWriter::BufferWriter(const std::string &pattern)
 {
 }
 
-int BufferWriter::write(libcamera::Buffer *buffer, libcamera::BufferMemory *mem,
-			const std::string &streamName)
+int BufferWriter::write(libcamera::Buffer *buffer, const std::string &streamName)
 {
 	std::string filename;
 	size_t pos;
@@ -41,6 +40,7 @@ int BufferWriter::write(libcamera::Buffer *buffer, libcamera::BufferMemory *mem,
 	if (fd == -1)
 		return -errno;
 
+	libcamera::BufferMemory *mem = buffer->mem();
 	for (libcamera::Plane &plane : mem->planes()) {
 		void *data = plane.mem();
 		unsigned int length = plane.length();

src/cam/buffer_writer.h

@@ -16,8 +16,7 @@ class BufferWriter
 public:
 	BufferWriter(const std::string &pattern = "frame-#.bin");
 
-	int write(libcamera::Buffer *buffer, libcamera::BufferMemory *mem,
-		  const std::string &streamName);
+	int write(libcamera::Buffer *buffer, const std::string &streamName);
 
 private:
 	std::string pattern_;

src/cam/capture.cpp

@@ -154,7 +154,6 @@ void Capture::requestComplete(Request *request, const std::map<Stream *, Buffer
 	for (auto it = buffers.begin(); it != buffers.end(); ++it) {
 		Stream *stream = it->first;
 		Buffer *buffer = it->second;
-		BufferMemory *mem = &stream->buffers()[buffer->index()];
 		const std::string &name = streamName_[stream];
 
 		info << " " << name
@@ -163,7 +162,7 @@ void Capture::requestComplete(Request *request, const std::map<Stream *, Buffer
 		     << " bytesused: " << buffer->bytesused();
 
 		if (writer_)
-			writer_->write(buffer, mem, name);
+			writer_->write(buffer, name);
 	}
 
 	std::cout << info.str() << std::endl;

src/libcamera/buffer.cpp

@@ -300,6 +300,17 @@ Buffer::Buffer(unsigned int index, const Buffer *metadata)
  * \return The dmabuf file descriptors
  */
 
+/**
+ * \fn Buffer::mem()
+ * \brief Retrieve the BufferMemory this buffer is associated with
+ *
+ * The association between the buffer and a BufferMemory instance is valid from
+ * the time the request containing this buffer is queued to a camera to the end
+ * of that request's completion handler.
+ *
+ * \return The BufferMemory this buffer is associated with
+ */
+
 /**
  * \fn Buffer::bytesused()
  * \brief Retrieve the number of bytes occupied by the data in the buffer

src/libcamera/camera.cpp

@@ -811,10 +811,14 @@ int Camera::queueRequest(Request *request)
 
 	for (auto const &it : request->buffers()) {
 		Stream *stream = it.first;
+		Buffer *buffer = it.second;
+
 		if (activeStreams_.find(stream) == activeStreams_.end()) {
 			LOG(Camera, Error) << "Invalid request";
 			return -EINVAL;
 		}
+
+		buffer->mem_ = &stream->buffers()[buffer->index_];
 	}
 
 	int ret = request->prepare();

src/qcam/main_window.cpp

@@ -221,7 +221,6 @@ void MainWindow::requestComplete(Request *request,
 
 	framesCaptured_++;
 
-	Stream *stream = buffers.begin()->first;
 	Buffer *buffer = buffers.begin()->second;
 
 	double fps = buffer->timestamp() - lastBufferTime_;
@@ -235,8 +234,7 @@ void MainWindow::requestComplete(Request *request,
 		  << " fps: " << std::fixed << std::setprecision(2) << fps
 		  << std::endl;
 
-	BufferMemory *mem = &stream->buffers()[buffer->index()];
-	display(buffer, mem);
+	display(buffer);
 
 	request = camera_->createRequest();
 	if (!request) {
@@ -261,8 +259,9 @@ void MainWindow::requestComplete(Request *request,
 	camera_->queueRequest(request);
 }
 
-int MainWindow::display(Buffer *buffer, BufferMemory *mem)
+int MainWindow::display(Buffer *buffer)
 {
+	BufferMemory *mem = buffer->mem();
 	if (mem->planes().size() != 1)
 		return -EINVAL;
 

src/qcam/main_window.h

@@ -48,7 +48,7 @@ private:
 
 	void requestComplete(Request *request,
 			     const std::map<Stream *, Buffer *> &buffers);
-	int display(Buffer *buffer, BufferMemory *mem);
+	int display(Buffer *buffer);
 
 	QString title_;
 	QTimer titleTimer_;