file_sys: Cleanup to better match Switch file system constructs.

file_sys: Add factory class for RomFS file system.

src/core/file_sys/directory.h

@@ -0,0 +1,58 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <array>
+#include <cstddef>
+#include "common/common_types.h"
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+// FileSys namespace
+
+namespace FileSys {
+
+// Structure of a directory entry, from http://3dbrew.org/wiki/FSDir:Read#Entry_format
+const size_t FILENAME_LENGTH = 0x20C / 2;
+struct Entry {
+    char16_t filename[FILENAME_LENGTH]; // Entry name (UTF-16, null-terminated)
+    std::array<char, 9> short_name; // 8.3 file name ('longfilename' -> 'LONGFI~1', null-terminated)
+    char unknown1;                  // unknown (observed values: 0x0A, 0x70, 0xFD)
+    std::array<char, 4>
+        extension;     // 8.3 file extension (set to spaces for directories, null-terminated)
+    char unknown2;     // unknown (always 0x01)
+    char unknown3;     // unknown (0x00 or 0x08)
+    char is_directory; // directory flag
+    char is_hidden;    // hidden flag
+    char is_archive;   // archive flag
+    char is_read_only; // read-only flag
+    u64 file_size;     // file size (for files only)
+};
+static_assert(sizeof(Entry) == 0x228, "Directory Entry struct isn't exactly 0x228 bytes long!");
+static_assert(offsetof(Entry, short_name) == 0x20C, "Wrong offset for short_name in Entry.");
+static_assert(offsetof(Entry, extension) == 0x216, "Wrong offset for extension in Entry.");
+static_assert(offsetof(Entry, is_archive) == 0x21E, "Wrong offset for is_archive in Entry.");
+static_assert(offsetof(Entry, file_size) == 0x220, "Wrong offset for file_size in Entry.");
+
+class DirectoryBackend : NonCopyable {
+public:
+    DirectoryBackend() {}
+    virtual ~DirectoryBackend() {}
+
+    /**
+     * List files contained in the directory
+     * @param count Number of entries to return at once in entries
+     * @param entries Buffer to read data into
+     * @return Number of entries listed
+     */
+    virtual u32 Read(const u32 count, Entry* entries) = 0;
+
+    /**
+     * Close the directory
+     * @return true if the directory closed correctly
+     */
+    virtual bool Close() const = 0;
+};
+
+} // namespace FileSys