Kernel: Introduce the new SysFS

The intention is to add dynamic mechanism for notifying the userspace
about hotplug events. Currently, the DMI (SMBIOS) blobs and ACPI tables
are exposed in the new filesystem.

Kernel/SystemExposed.cpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2021, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/FileSystem/SysFS.h>
+#include <Kernel/SystemExposed.h>
+
+namespace Kernel {
+
+static SpinLock<u8> s_index_lock;
+static InodeIndex s_next_inode_index { 0 };
+
+static size_t allocate_inode_index()
+{
+    ScopedSpinLock lock(s_index_lock);
+    s_next_inode_index = s_next_inode_index.value() + 1;
+    VERIFY(s_next_inode_index > 0);
+    return s_next_inode_index.value();
+}
+
+SystemExposedComponent::SystemExposedComponent(StringView name)
+    : m_name(KString::try_create(name).release_nonnull())
+    , m_component_index(allocate_inode_index())
+{
+}
+
+KResult SystemExposedFolder::traverse_as_directory(unsigned fsid, Function<bool(const FS::DirectoryEntryView&)> callback) const
+{
+    Locker locker(SystemRegistrar::the().m_lock);
+    VERIFY(m_parent_folder);
+    callback({ ".", { fsid, component_index() }, 0 });
+    callback({ "..", { fsid, m_parent_folder->component_index() }, 0 });
+
+    for (auto& component : m_components) {
+        InodeIdentifier identifier = { fsid, component.component_index() };
+        callback({ component.name(), identifier, 0 });
+    }
+    return KSuccess;
+}
+
+RefPtr<SystemExposedComponent> SystemExposedFolder::lookup(StringView name)
+{
+    for (auto& component : m_components) {
+        if (component.name() == name) {
+            return component;
+        }
+    }
+    return {};
+}
+
+SystemExposedFolder::SystemExposedFolder(String name)
+    : SystemExposedComponent(name)
+{
+}
+
+SystemExposedFolder::SystemExposedFolder(String name, const SystemExposedFolder& parent_folder)
+    : SystemExposedComponent(name)
+    , m_parent_folder(parent_folder)
+{
+}
+
+NonnullRefPtr<Inode> SystemExposedFolder::to_inode(const SysFS& sysfs_instance) const
+{
+    return SysFSDirectoryInode::create(sysfs_instance, *this);
+}
+
+NonnullRefPtr<Inode> SystemExposedComponent::to_inode(const SysFS& sysfs_instance) const
+{
+    return SysFSInode::create(sysfs_instance, *this);
+}
+
+}