Kernel: Rename Kernel/VM/ to Kernel/Memory/

This directory isn't just about virtual memory, it's about all kinds
of memory management.

Kernel/Memory/RingBuffer.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2021, Sahan Fernando <sahan.h.fernando@gmail.com>.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <Kernel/PhysicalAddress.h>
+#include <Kernel/UserOrKernelBuffer.h>
+
+namespace Kernel {
+
+class RingBuffer {
+public:
+    RingBuffer(String region_name, size_t capacity);
+
+    bool has_space() const { return m_num_used_bytes < m_capacity_in_bytes; }
+    bool copy_data_in(const UserOrKernelBuffer& buffer, size_t offset, size_t length, PhysicalAddress& start_of_copied_data, size_t& bytes_copied);
+    KResultOr<size_t> copy_data_out(size_t size, UserOrKernelBuffer& buffer) const;
+    KResultOr<PhysicalAddress> reserve_space(size_t size);
+    void reclaim_space(PhysicalAddress chunk_start, size_t chunk_size);
+    PhysicalAddress start_of_used() const;
+
+    SpinLock<u8>& lock() { return m_lock; }
+    size_t used_bytes() const { return m_num_used_bytes; }
+    PhysicalAddress start_of_region() const { return m_region->physical_page(0)->paddr(); }
+    VirtualAddress vaddr() const { return m_region->vaddr(); }
+    size_t bytes_till_end() const { return (m_capacity_in_bytes - ((m_start_of_used + m_num_used_bytes) % m_capacity_in_bytes)) % m_capacity_in_bytes; };
+
+private:
+    OwnPtr<Region> m_region;
+    SpinLock<u8> m_lock;
+    size_t m_start_of_used {};
+    size_t m_num_used_bytes {};
+    size_t m_capacity_in_bytes {};
+};
+
+}