file_sys: Cleanup to better match Switch file system constructs.

file_sys: Add factory class for RomFS file system.

src/core/file_sys/romfs_filesystem.h

@@ -0,0 +1,80 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <cstddef>
+#include <memory>
+#include <string>
+#include <vector>
+#include "common/common_types.h"
+#include "common/file_util.h"
+#include "core/file_sys/directory.h"
+#include "core/file_sys/filesystem.h"
+#include "core/file_sys/storage.h"
+#include "core/hle/result.h"
+
+namespace FileSys {
+
+/**
+ * Helper which implements an interface to deal with Switch .istorage ROMFS images used in some
+ * archives This should be subclassed by concrete archive types, which will provide the input data
+ * (load the raw ROMFS archive) and override any required methods
+ */
+class RomFS_FileSystem : public FileSystemBackend {
+public:
+    RomFS_FileSystem(std::shared_ptr<FileUtil::IOFile> file, u64 offset, u64 size)
+        : romfs_file(file), data_offset(offset), data_size(size) {}
+
+    std::string GetName() const override;
+
+    ResultVal<std::unique_ptr<StorageBackend>> OpenFile(const Path& path,
+                                                        const Mode& mode) const override;
+    ResultCode DeleteFile(const Path& path) const override;
+    ResultCode RenameFile(const Path& src_path, const Path& dest_path) const override;
+    ResultCode DeleteDirectory(const Path& path) const override;
+    ResultCode DeleteDirectoryRecursively(const Path& path) const override;
+    ResultCode CreateFile(const Path& path, u64 size) const override;
+    ResultCode CreateDirectory(const Path& path) const override;
+    ResultCode RenameDirectory(const Path& src_path, const Path& dest_path) const override;
+    ResultVal<std::unique_ptr<DirectoryBackend>> OpenDirectory(const Path& path) const override;
+    u64 GetFreeSpaceSize() const override;
+
+protected:
+    std::shared_ptr<FileUtil::IOFile> romfs_file;
+    u64 data_offset;
+    u64 data_size;
+};
+
+class RomFS_Storage : public StorageBackend {
+public:
+    RomFS_Storage(std::shared_ptr<FileUtil::IOFile> file, u64 offset, u64 size)
+        : romfs_file(file), data_offset(offset), data_size(size) {}
+
+    ResultVal<size_t> Read(u64 offset, size_t length, u8* buffer) const override;
+    ResultVal<size_t> Write(u64 offset, size_t length, bool flush, const u8* buffer) const override;
+    u64 GetSize() const override;
+    bool SetSize(u64 size) const override;
+    bool Close() const override {
+        return false;
+    }
+    void Flush() const override {}
+
+private:
+    std::shared_ptr<FileUtil::IOFile> romfs_file;
+    u64 data_offset;
+    u64 data_size;
+};
+
+class ROMFSDirectory : public DirectoryBackend {
+public:
+    u32 Read(const u32 count, Entry* entries) override {
+        return 0;
+    }
+    bool Close() const override {
+        return false;
+    }
+};
+
+} // namespace FileSys