settings: implement KeyValueStore (#1659)

* settings: implement KeyValueStore and dependencies

* settings: update KeyValueStore for recent refactoring

* settings: address feedback

libraries/libstratosphere/source/settings/impl/settings_system_save_data.hpp

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+namespace ams::settings::impl {
+
+    class SystemSaveData {
+        NON_COPYABLE(SystemSaveData);
+        private:
+            fs::SystemSaveDataId m_system_save_data_id;
+            fs::SaveDataSpaceId m_save_data_space_id;
+            s64 m_total_size;
+            s64 m_journal_size;
+            u32 m_flags;
+            char m_mount_name[fs::MountNameLengthMax + 1];
+        public:
+            SystemSaveData() : m_system_save_data_id(0), m_save_data_space_id(fs::SaveDataSpaceId::System), m_total_size(0), m_journal_size(0), m_flags(0) { /* ... */ }
+
+            void SetSystemSaveDataId(u64 id);
+            void SetTotalSize(s64 size);
+            void SetJournalSize(s64 size);
+            void SetFlags(u32 flags);
+            void SetMountName(const char *name);
+
+            Result Mount(bool create_save);
+            Result Commit(bool synchronous);
+            Result Create(s64 size);
+            Result OpenToRead();
+            Result OpenToWrite();
+            void Close();
+            Result Read(s64 offset, void *buf, size_t size);
+            Result Write(s64 offset, const void *buf, size_t size);
+            Result Flush();
+            Result SetFileSize(s64 size);
+    };
+
+}