Kernel: Create VM::RingBuffer class

Kernel/CMakeLists.txt

@@ -236,6 +236,7 @@ set(KERNEL_SOURCES
     VM/Range.cpp
     VM/RangeAllocator.cpp
     VM/Region.cpp
+    VM/RingBuffer.cpp
     VM/ScatterGatherList.cpp
     VM/SharedInodeVMObject.cpp
     VM/Space.cpp

Kernel/VM/RingBuffer.cpp

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2021, Sahan Fernando <sahan.h.fernando@gmail.com>.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/UserOrKernelBuffer.h>
+#include <Kernel/VM/MemoryManager.h>
+#include <Kernel/VM/RingBuffer.h>
+
+namespace Kernel {
+
+RingBuffer::RingBuffer(String region_name, size_t capacity)
+    : m_region(MM.allocate_contiguous_kernel_region(page_round_up(capacity), move(region_name), Region::Access::Read | Region::Access::Write))
+    , m_capacity_in_bytes(capacity)
+{
+}
+
+bool RingBuffer::copy_data_in(const UserOrKernelBuffer& buffer, size_t offset, size_t length, PhysicalAddress& start_of_copied_data, size_t& bytes_copied)
+{
+    size_t start_of_free_area = (m_start_of_used + m_num_used_bytes) % m_capacity_in_bytes;
+    bytes_copied = min(m_capacity_in_bytes - m_num_used_bytes, min(m_capacity_in_bytes - start_of_free_area, length));
+    if (bytes_copied == 0)
+        return false;
+    if (buffer.read(m_region->vaddr().offset(start_of_free_area).as_ptr(), offset, bytes_copied)) {
+        m_num_used_bytes += bytes_copied;
+        start_of_copied_data = m_region->physical_page(start_of_free_area / PAGE_SIZE)->paddr().offset(start_of_free_area % PAGE_SIZE);
+        return true;
+    }
+    return false;
+}
+
+void RingBuffer::reclaim_space(PhysicalAddress chunk_start, size_t chunk_size)
+{
+    VERIFY(start_of_used() == chunk_start);
+    VERIFY(m_num_used_bytes >= chunk_size);
+    m_num_used_bytes -= chunk_size;
+    m_start_of_used += chunk_size;
+}
+
+PhysicalAddress RingBuffer::start_of_used() const
+{
+    size_t start = m_start_of_used % m_capacity_in_bytes;
+    return m_region->physical_page(start / PAGE_SIZE)->paddr().offset(start % PAGE_SIZE);
+}
+
+}

Kernel/VM/RingBuffer.h

@@ -0,0 +1,33 @@
+/*
+ * 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>
+
+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);
+    void reclaim_space(PhysicalAddress chunk_start, size_t chunk_size);
+    PhysicalAddress start_of_used() const;
+
+    SpinLock<u8>& lock() { return m_lock; }
+
+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 {};
+};
+
+}