From d2e2d9bc3b5291face2498fe2c8c7be21c94f2b5 Mon Sep 17 00:00:00 2001
From: Hayodea Hekol <hayodea@protonmail.com>
Date: Sun, 9 Nov 2025 01:16:17 -0400
Subject: [PATCH] StagingBuffer: Prefer mlock to io_uring_register_buffers

---
 .../livoxGen1/ioUringAssemblyEngine.cpp        | 18 +++++++++++++++++-
 stimBuffApis/livoxGen1/stagingBuffer.cpp       |  7 +++++++
 stimBuffApis/livoxGen1/stagingBuffer.h         |  1 +
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/stimBuffApis/livoxGen1/ioUringAssemblyEngine.cpp b/stimBuffApis/livoxGen1/ioUringAssemblyEngine.cpp
index 2a8381b..4329b35 100644
--- a/stimBuffApis/livoxGen1/ioUringAssemblyEngine.cpp
+++ b/stimBuffApis/livoxGen1/ioUringAssemblyEngine.cpp
@@ -26,6 +26,8 @@
 #include "pcloudStimulusBuffer.h"
 #include "livoxGen1.h"
 
+// #define REGISTER_IOURING_BUFFERS
+
 namespace smo {
 namespace stim_buff {
 
@@ -107,7 +109,9 @@ bool IoUringAssemblyEngine::setup()
 	}
 
 	// Declare iovec early to avoid goto crossing initialization
+#ifdef REGISTER_IOURING_BUFFERS
 	struct iovec iov;
+#endif
 	int ret;
 
 	/**	EXPLANATION:
@@ -122,16 +126,24 @@ bool IoUringAssemblyEngine::setup()
 	if (ret < 0)
 		{ goto cleanup; }
 
+#ifdef REGISTER_IOURING_BUFFERS
 	// Register staging buffer with io_uring for DMA-apt I/O
 	iov = parent.assemblyBuffer.getIoUringRegisterIoVec();
 	ret = io_uring_register_buffers(&ring, &iov, 1);
 	if (ret < 0)
 		{ goto cleanup_ring; }
+#endif
 
 	// Create eventfd for CQE notifications (used with boost's unified loop)
 	eventfdFd = eventfd(0, EFD_NONBLOCK);
 	if (eventfdFd < 0)
-		{ goto cleanup_buffers; }
+	{
+#ifdef REGISTER_IOURING_BUFFERS
+		goto cleanup_buffers;
+#else
+		goto cleanup_ring;
+#endif
+	}
 
 	// Register eventfd with io_uring
 	ret = io_uring_register_eventfd(&ring, eventfdFd);
@@ -144,8 +156,10 @@ bool IoUringAssemblyEngine::setup()
 cleanup_eventfd:
 	close(eventfdFd);
 	eventfdFd = -1;
+#ifdef REGISTER_IOURING_BUFFERS
 cleanup_buffers:
 	io_uring_unregister_buffers(&ring);
+#endif
 cleanup_ring:
 	io_uring_queue_exit(&ring);
 cleanup:
@@ -166,7 +180,9 @@ void IoUringAssemblyEngine::finalize()
 
 	if (isSetup)
 	{
+#ifdef REGISTER_IOURING_BUFFERS
 		io_uring_unregister_buffers(&ring);
+#endif
 		io_uring_queue_exit(&ring);
 		isSetup = false;
 	}
diff --git a/stimBuffApis/livoxGen1/stagingBuffer.cpp b/stimBuffApis/livoxGen1/stagingBuffer.cpp
index c9841e6..c74724e 100644
--- a/stimBuffApis/livoxGen1/stagingBuffer.cpp
+++ b/stimBuffApis/livoxGen1/stagingBuffer.cpp
@@ -197,6 +197,13 @@ assemblingFlag(false)
 		static_cast<uint8_t*>(mmapped), MmapDeleter(bufferNBytes));
 	currentNBytes.store(0);
 
+	// Lock the buffer in memory to prevent swapping
+	if (mlock(buffer.get(), bufferNBytes) != 0)
+	{
+		throw std::runtime_error(std::string(__func__)
+			+ ": StagingBuffer: mlock() failed");
+	}
+
 	// Calculate offset and validate invariants (helper function in .cpp)
 	firstSlotOffsetNBytes = StagingBuffer::calculateFirstSlotOffsetAndValidate(
 		buffer.get(), bufferNBytes, nDgramsPerFrame,
diff --git a/stimBuffApis/livoxGen1/stagingBuffer.h b/stimBuffApis/livoxGen1/stagingBuffer.h
index 4ed963f..543467d 100644
--- a/stimBuffApis/livoxGen1/stagingBuffer.h
+++ b/stimBuffApis/livoxGen1/stagingBuffer.h
@@ -149,6 +149,7 @@ private:
 		{
 			if (ptr != nullptr && size > 0)
 			{
+				munlock(ptr, size);
 				munmap(ptr, size);
 			}
 		}