Revert "Kernel/Storage: Remove the ramdisk implementation"

This reverts commit 4e0f85432a as the
ramdisk code is useful for the bring-up of the aarch64 port. Once the
kernel supports better ram-based filesystems, this code will be removed
again.

Kernel/Storage/Ramdisk/Controller.cpp

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/OwnPtr.h>
+#include <AK/Types.h>
+#include <Kernel/Library/LockRefPtr.h>
+#include <Kernel/Storage/Ramdisk/Controller.h>
+
+namespace Kernel {
+
+NonnullLockRefPtr<RamdiskController> RamdiskController::initialize()
+{
+    return adopt_lock_ref(*new RamdiskController());
+}
+
+bool RamdiskController::reset()
+{
+    TODO();
+}
+
+bool RamdiskController::shutdown()
+{
+    TODO();
+}
+
+size_t RamdiskController::devices_count() const
+{
+    return m_devices.size();
+}
+
+void RamdiskController::complete_current_request(AsyncDeviceRequest::RequestResult)
+{
+    VERIFY_NOT_REACHED();
+}
+
+RamdiskController::RamdiskController()
+    : StorageController(0)
+{
+    // Populate ramdisk controllers from Multiboot boot modules, if any.
+    size_t count = 0;
+    MM.for_each_used_memory_range([&](auto& used_memory_range) {
+        if (used_memory_range.type == Memory::UsedMemoryRangeType::BootModule) {
+            size_t length = Memory::page_round_up(used_memory_range.end.get()).release_value_but_fixme_should_propagate_errors() - used_memory_range.start.get();
+            auto region_or_error = MM.allocate_kernel_region(used_memory_range.start, length, "Ramdisk"sv, Memory::Region::Access::ReadWrite);
+            if (region_or_error.is_error()) {
+                dmesgln("RamdiskController: Failed to allocate kernel region of size {}", length);
+            } else {
+                m_devices.append(RamdiskDevice::create(*this, region_or_error.release_value(), 6, count));
+            }
+            count++;
+        }
+    });
+}
+
+RamdiskController::~RamdiskController() = default;
+
+LockRefPtr<StorageDevice> RamdiskController::device(u32 index) const
+{
+    if (index >= m_devices.size())
+        return nullptr;
+    return m_devices[index];
+}
+
+}