file_sys: Cleanup to better match Switch file system constructs.

file_sys: Add factory class for RomFS file system.

src/core/file_sys/storage.h

@@ -0,0 +1,63 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <cstddef>
+#include "common/common_types.h"
+#include "core/hle/result.h"
+
+namespace FileSys {
+
+class StorageBackend : NonCopyable {
+public:
+    StorageBackend() {}
+    virtual ~StorageBackend() {}
+
+    /**
+     * Read data from the file
+     * @param offset Offset in bytes to start reading data from
+     * @param length Length in bytes of data to read from file
+     * @param buffer Buffer to read data into
+     * @return Number of bytes read, or error code
+     */
+    virtual ResultVal<size_t> Read(u64 offset, size_t length, u8* buffer) const = 0;
+
+    /**
+     * Write data to the file
+     * @param offset Offset in bytes to start writing data to
+     * @param length Length in bytes of data to write to file
+     * @param flush The flush parameters (0 == do not flush)
+     * @param buffer Buffer to read data from
+     * @return Number of bytes written, or error code
+     */
+    virtual ResultVal<size_t> Write(u64 offset, size_t length, bool flush,
+                                    const u8* buffer) const = 0;
+
+    /**
+     * Flushes the file
+     */
+    virtual void Flush() const = 0;
+
+    /**
+     * Set the size of the file in bytes
+     * @param size New size of the file
+     * @return true if successful
+     */
+    virtual bool SetSize(u64 size) const = 0;
+
+    /**
+     * Get the size of the file in bytes
+     * @return Size of the file in bytes
+     */
+    virtual u64 GetSize() const = 0;
+
+    /**
+     * Close the file
+     * @return true if the file closed correctly
+     */
+    virtual bool Close() const = 0;
+};
+
+} // namespace FileSys