samples update for //build

1 files changed, 117 insertions, 0 deletions

diff --git a/serial/VirtualSerial2/ringbuffer.h b/serial/VirtualSerial2/ringbuffer.h
new file mode 100644
index 00000000..8c5e3e39
--- /dev/null
+++ b/serial/VirtualSerial2/ringbuffer.h
@@ -0,0 +1,117 @@
+/*++
+
+Copyright (C) Microsoft Corporation, All Rights Reserved
+
+Module Name:
+
+    Ringbuffer.h
+
+--*/
+
+#pragma once
+
+typedef struct _RING_BUFFER
+{
+    //
+    // The size in bytes of the ring buffer.
+    //
+    size_t          Size;
+
+    //
+    // A pointer to the base of the ring buffer.
+    //
+    BYTE*           Base;
+
+    //
+    // A pointer to the byte beyond the end of the ring buffer.  Used for
+    // quick comparisons when determining if we need to wrap.
+    //
+    BYTE*           End;
+
+    //
+    // A pointer to the current read point in the ring buffer.
+    //
+    // Updates to this are not protected by any lock. This is different from
+    // the write pointer, which is protected by the "pending read pointer"
+    // lock. The reason for this difference is that in this driver, we do not
+    // keep write requests pending. If there is not enough space to write all
+    // the data that was requested, we write as much as we can and drop the
+    // rest (lossy data transfer).
+    //
+    // If we had multiple threads modifying this pointer, then that would
+    // provide yet another reason for protecting updates to the pointer using a
+    // lock. However, in this driver, at any given time we have only one thread
+    // that modifies this pointer (the thread that runs the read callback).
+    // This is true because we use a sequential queue for read requests. If we
+    // were to change our read queue to be a parallel queue, this would no
+    // longer be true.
+    //
+    //
+    BYTE*           Head;
+
+    //
+    // A pointer to the current write point in the ring buffer.
+    //
+    // Updates to this pointer are protected by the "pending read pointer
+    // lock", because we do not want a consumer thread to mark a read request
+    // as pending while we are in the process of writing data to the buffer.
+    // The reason is that the write that we are currently performing might
+    // actually supply enough data to satisfy the read request, in which case
+    // it should not be marked pending at all.
+    // If the read request were to be marked pending in the situation described
+    // above, then we would need some trigger to later retrieve the request and
+    // complete it. In our driver, arrival of data is the only event that can
+    // trigger this. So if no more data arrives, the request will remain
+    // pending forever, even though there is enough data in the buffer to
+    // complete it. Hence we do not keep a read request pending in situations
+    // where the read buffer contains enough data to satisfy it.
+    //
+    // If we had multiple threads modifying this pointer, then that would
+    // provide yet another reason for protecting updates to the pointer using a
+    // lock. However, in this driver, at any given time we have only one thread
+    // that modifies this pointer (the thread that runs the write callback).
+    // This is true because we use a sequential queue for write requests. If we
+    // were to change our write queue to be a parallel queue, this would no
+    // longer be true.
+    //
+    BYTE*           Tail;
+
+} RING_BUFFER, *PRING_BUFFER;
+
+
+VOID
+RingBufferInitialize(
+    _In_  PRING_BUFFER      Self,
+    _In_reads_bytes_(BufferSize)
+          BYTE*             Buffer,
+    _In_  size_t            BufferSize
+    );
+
+NTSTATUS
+RingBufferWrite(
+    _In_  PRING_BUFFER      Self,
+    _In_reads_bytes_(DataSize)
+          BYTE*             Data,
+    _In_  size_t            DataSize
+    );
+
+NTSTATUS
+RingBufferRead(
+    _In_  PRING_BUFFER      Self,
+    _Out_writes_bytes_to_(DataSize, *BytesCopied)
+          BYTE*             Data,
+    _In_  size_t            DataSize,
+    _Out_ size_t            *BytesCopied
+    );
+
+VOID
+RingBufferGetAvailableSpace(
+    _In_  PRING_BUFFER      Self,
+    _Out_ size_t            *AvailableSpace
+    );
+
+VOID
+RingBufferGetAvailableData(
+    _In_  PRING_BUFFER      Self,
+    _Out_ size_t            *AvailableData
+    );