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>

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();