IoUringAssmEngn: map StagingBuff w/mmap; reg w/io_uring; add eventFd

StagingBuffer:
We now allocate memory with mmap(MAP_ANONYMOUS) so that we can be
sure it can be pinned with io_uring_register_buffers(). This
ensures that if DMA is possible, it should be usable.

	IoUringAssemblyEngine:
We now register an eventfd with io_uring so that we can listen
for CQEs with boost::asio.

stimBuffApis/livoxGen1/ioUringAssemblyEngine.cpp

@@ -1,6 +1,9 @@
 #include <boostAsioLinkageFix.h>
 #include <cstring>
 #include <sys/socket.h>
+#include <sys/eventfd.h>
+#include <sys/uio.h>
+#include <unistd.h>
 #include <boost/system/error_code.hpp>
 #include <livoxProto1/device.h>
 #include <livoxProto1/livoxProto1.h>
@@ -33,7 +36,7 @@ IoUringAssemblyEngine::IoUringAssemblyEngine(PcloudStimulusBuffer& parent_)
 : parent(parent_),
 frameAssemblyDesc(nullptr), ring{},
 isSetup(false),
-stallTimer(parent_.device->componentThread->getIoService())
+eventfdFd(-1), stallTimer(parent_.device->componentThread->getIoService())
 {}
 
 bool IoUringAssemblyEngine::setup()
@@ -61,17 +64,47 @@ bool IoUringAssemblyEngine::setup()
 	if (udpFd < 0)
 		{ return false; }
 
+	// Declare iovec early to avoid goto crossing initialization
+	struct iovec iov;
+	int ret;
+
 	/**	EXPLANATION:
 	 * Initialize io_uring ring - allocate SQEs and CQEs for one frame assembly
 	 * One SQE per slot (one datagram per slot)
 	 */
-	int ret = io_uring_queue_init(
+	ret = io_uring_queue_init(
 		static_cast<unsigned int>(frameAssemblyDesc->numSlots), &ring, 0);
 	if (ret < 0)
-		{ return false; }
+		{ goto cleanup; }
+
+	// Register staging buffer with io_uring for DMA-apt I/O
+	iov = parent.stagingBuffer.getIoUringRegisterIoVec();
+	ret = io_uring_register_buffers(&ring, &iov, 1);
+	if (ret < 0)
+		{ goto cleanup_ring; }
+
+	// Create eventfd for CQE notifications (used with boost's unified loop)
+	eventfdFd = eventfd(0, EFD_NONBLOCK);
+	if (eventfdFd < 0)
+		{ goto cleanup_buffers; }
+
+	// Register eventfd with io_uring
+	ret = io_uring_register_eventfd(&ring, eventfdFd);
+	if (ret < 0)
+		{ goto cleanup_eventfd; }
 
 	isSetup = true;
 	return true;
+
+cleanup_eventfd:
+	close(eventfdFd);
+	eventfdFd = -1;
+cleanup_buffers:
+	io_uring_unregister_buffers(&ring);
+cleanup_ring:
+	io_uring_queue_exit(&ring);
+cleanup:
+	return false;
 }
 
 void IoUringAssemblyEngine::finalize()
@@ -79,9 +112,16 @@ void IoUringAssemblyEngine::finalize()
 	// Call stop() to cancel in-flight operations (stop() already cancels the timer)
 	stop();
 
-	// Clean up io_uring ring if it was initialized
+	if (eventfdFd >= 0)
+	{
+		io_uring_unregister_eventfd(&ring);
+		close(eventfdFd);
+		eventfdFd = -1;
+	}
+
 	if (isSetup)
 	{
+		io_uring_unregister_buffers(&ring);
 		io_uring_queue_exit(&ring);
 		isSetup = false;
 	}
@@ -109,6 +149,9 @@ void IoUringAssemblyEngine::stop()
 	// 1. Cancel all pending SQEs using io_uring cancellation mechanisms
 	// 2. Cancel in-flight stall timeout timer via stallTimer.cancel()
 	// 3. Set appropriate state flags
+
+	// Cancel in-flight stall timeout timer
+	stallTimer.cancel();
 }
 
 void IoUringAssemblyEngine::cancelIncompleteAndFillDummies()

stimBuffApis/livoxGen1/ioUringAssemblyEngine.h

@@ -46,6 +46,8 @@ private:
 	struct io_uring ring;
 	bool isSetup;
 
+	// Eventfd for CQE notifications (used with boost's unified loop)
+	int eventfdFd;
 	// Point cloud data socket descriptor
 	std::shared_ptr<boost::asio::posix::stream_descriptor> pcloudDataFdDesc;
 

stimBuffApis/livoxGen1/stagingBuffer.h

@@ -9,6 +9,9 @@
 #include <string>
 #include <sstream>
 #include <algorithm>
+#include <sys/mman.h>
+#include <sys/uio.h>
+#include <unistd.h>
 
 #include "frameAssemblyDesc.h"
 
@@ -96,6 +99,18 @@ public:
 	void startAssembly() { assemblingFlag.store(true); }
 	void stopAssembly() { assemblingFlag.store(false); }
 
+	/**	EXPLANATION:
+	 * Returns an iovec for io_uring registration.
+	 * The buffer is mmap()-allocated and suitable for IORING_REGISTER_BUFFERS.
+	 */
+	struct iovec getIoUringRegisterIoVec() const
+	{
+		struct iovec iov;
+		iov.iov_base = buffer.get();
+		iov.iov_len = bufferNBytes;
+		return iov;
+	}
+
 	inline std::string stringify() const
 	{
 		std::ostringstream oss;
@@ -111,8 +126,25 @@ public:
 private:
 	void computeSlotStrideAndBufferSize();
 
-	// Buffer data
-	std::unique_ptr<uint8_t[]> buffer;
+	// Custom deleter for mmap-allocated buffer
+	struct MmapDeleter
+	{
+		size_t size;
+		MmapDeleter(size_t s) : size(s) {}
+		
+		void operator()(uint8_t* ptr) const
+		{
+			if (ptr != nullptr && size > 0)
+			{
+				munmap(ptr, size);
+			}
+		}
+	};
+
+	// Buffer data - mmap-allocated for io_uring registration
+	// Using unique_ptr<uint8_t, MmapDeleter> instead of array syntax
+	// since we have a custom deleter that knows the size
+	std::unique_ptr<uint8_t, MmapDeleter> buffer;
 	size_t bufferNBytes;
 
 	// Layout/invariants
@@ -135,7 +167,7 @@ inline StagingBuffer::StagingBuffer(
 	const InputEngineConstraints& inputEngineConstraints_,
 	const OutputEngineConstraints& /*outputEngineConstraints*/,
 	size_t nDgramsPerFrame)
-: buffer(nullptr), bufferNBytes(0),
+: buffer(nullptr, MmapDeleter(0)), bufferNBytes(0),
 nDgramsPerFrame(nDgramsPerFrame), slotStrideNBytes(0),
 inputConstraints(inputEngineConstraints_),
 assemblingFlag(false)
@@ -148,7 +180,23 @@ assemblingFlag(false)
 
 	computeSlotStrideAndBufferSize();
 
-	buffer = std::make_unique<uint8_t[]>(bufferNBytes);
+	/* Allocate buffer using mmap() for io_uring registration
+	 * MAP_ANONYMOUS | MAP_PRIVATE creates anonymous, non-file-backed memory
+	 */
+	void* mmapped = mmap(
+		nullptr, bufferNBytes,
+		PROT_READ | PROT_WRITE,
+		MAP_ANONYMOUS | MAP_PRIVATE,
+		-1, 0);
+
+	if (mmapped == MAP_FAILED)
+	{
+		throw std::runtime_error(std::string(__func__)
+			+ ": StagingBuffer: mmap() failed");
+	}
+
+	buffer = std::unique_ptr<uint8_t, MmapDeleter>(
+		static_cast<uint8_t*>(mmapped), MmapDeleter(bufferNBytes));
 	currentNBytes.store(0);
 
 	// Build FrameAssemblyDesc once

todo

@@ -39,3 +39,5 @@
   to the io_context of the thread it should post its callbacks to, and
   then post callbacks to those io_contexts when UDP cmd responses
   come in.
+* Consider using MAP_HUGEPAGE with both PcloudStimBuff::StagingBuffer
+  and in the PcloudStimulusBuffer's ringbuff.