diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_dir_utils.cpp b/stratosphere/ams_mitm/source/fs_mitm/fs_dir_utils.cpp
new file mode 100644
index 000000000..5401329d9
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_dir_utils.cpp
@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 2018 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/>.
+ */
+#include <cstring>
+#include <cstdlib>
+#include <switch.h>
+#include "fs_results.hpp"
+#include "fs_dir_utils.hpp"
+#include "fs_ifile.hpp"
+
+Result FsDirUtils::CopyFile(IFileSystem *dst_fs, IFileSystem *src_fs, const FsPath &dst_parent_path, const FsPath &src_path, const FsDirectoryEntry *dir_ent, void *work_buf, size_t work_buf_size) {
+    Result rc;
+    std::unique_ptr<IFile> src_file;
+    std::unique_ptr<IFile> dst_file;
+    const u64 file_size = dir_ent->fileSize;
+
+    /* Open source file for reading. */
+    if (R_FAILED((rc = src_fs->OpenFile(src_file, src_path, OpenMode_Read)))) {
+        return rc;
+    }
+
+    /* Create and open destination file. */
+    {
+        FsPath dst_path;
+        if (static_cast<size_t>(snprintf(dst_path.str, sizeof(dst_path.str), "%s%s", dst_parent_path.str, src_path.str)) >= sizeof(dst_path)) {
+            /* TODO: Error code? N aborts here. */
+            std::abort();
+        }
+
+        if (R_FAILED((rc = dst_fs->CreateFile(dst_path, file_size)))) {
+            return rc;
+        }
+        if (R_FAILED((rc = dst_fs->OpenFile(dst_file, dst_path, OpenMode_Write)))) {
+            return rc;
+        }
+    }
+
+    /* Read/Write work_buf_size chunks. */
+    u64 offset = 0;
+    while (offset < file_size) {
+        u64 read_size;
+        if (R_FAILED((rc = src_file->Read(&read_size, offset, work_buf, work_buf_size)))) {
+            return rc;
+        }
+        if (R_FAILED((rc = dst_file->Write(offset, work_buf, read_size)))) {
+            return rc;
+        }
+
+        offset += read_size;
+    }
+    
+    return 0;
+}
+
+Result FsDirUtils::CopyDirectoryRecursively(IFileSystem *dst_fs, IFileSystem *src_fs, const FsPath &dst_path, const FsPath &src_path, void *work_buf, size_t work_buf_size) {
+    FsPath work_path = dst_path;
+
+    return IterateDirectoryRecursively(src_fs, src_path, 
+        [&](const FsPath &path, const FsDirectoryEntry *dir_ent) -> Result { /* On Enter Directory */
+            /* Update path, create new dir. */
+            strncat(work_path.str, dir_ent->name, sizeof(work_path) - strnlen(work_path.str, sizeof(work_path) - 1) - 1);
+            strncat(work_path.str, "/", sizeof(work_path) - strnlen(work_path.str, sizeof(work_path) - 1) - 1);
+            return dst_fs->CreateDirectory(work_path);
+        }, 
+        [&](const FsPath &path, const FsDirectoryEntry *dir_ent) -> Result { /* On Exit Directory */
+            /* Check we have a parent directory. */
+            const size_t work_path_len = strnlen(work_path.str, sizeof(work_path));
+            if (work_path_len < 2) {
+                return ResultFsInvalidPathFormat;
+            }
+
+            /* Find previous separator, add NULL terminator */
+            char *p = &work_path.str[work_path_len - 2];
+            while (*p != '/' && p > work_path.str) {
+                p--;
+            }
+            p[1] = 0;
+
+            return 0;
+        }, 
+        [&](const FsPath &path, const FsDirectoryEntry *dir_ent) -> Result { /* On File */
+            /* Just copy the file to the new fs. */
+            return CopyFile(dst_fs, src_fs, work_path, path, dir_ent, work_buf, work_buf_size);
+        });
+}
\ No newline at end of file
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_dir_utils.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_dir_utils.hpp
new file mode 100644
index 000000000..76ce21be7
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_dir_utils.hpp
@@ -0,0 +1,155 @@
+/*
+ * Copyright (c) 2018 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 <switch.h>
+
+#include "fs_path_utils.hpp"
+#include "fs_ifilesystem.hpp"
+
+class FsDirUtils {
+    private:
+        template<typename OnEnterDir, typename OnExitDir, typename OnFile>
+        static Result IterateDirectoryRecursivelyInternal(IFileSystem *fs, FsPath &work_path, FsDirectoryEntry *ent_buf, OnEnterDir on_enter_dir, OnExitDir on_exit_dir, OnFile on_file) {
+            Result rc;
+            std::unique_ptr<IDirectory> dir;
+
+            /* Open the directory. */
+            if (R_FAILED((rc = fs->OpenDirectory(dir, work_path, DirectoryOpenMode_All)))) {
+                return rc;
+            }
+
+            const size_t parent_len = strnlen(work_path.str, sizeof(work_path.str - 1));
+
+            /* Read and handle entries. */
+            while (true) {
+                /* Read a single entry. */
+                u64 read_count;
+                if (R_FAILED((rc = dir->Read(&read_count, ent_buf, 1)))) {
+                    return rc;
+                }
+
+                /* If we're out of entries, we're done. */
+                if (read_count == 0) {
+                    break;
+                }
+
+                const size_t child_name_len = strnlen(ent_buf->name, sizeof(ent_buf->name) - 1);
+                const bool is_dir = ent_buf->type == ENTRYTYPE_DIR;
+                const size_t child_path_len = parent_len + child_name_len + (is_dir ? 1 : 0);
+
+                /* Validate child path size. */
+                if (child_path_len >= sizeof(work_path.str)) {
+                    return ResultFsTooLongPath;
+                }
+
+                strncat(work_path.str, ent_buf->name, sizeof(work_path.str) - 1 - parent_len);
+                if (is_dir) {
+                    /* Enter directory. */
+                    if (R_FAILED((rc = on_enter_dir(work_path, ent_buf)))) {
+                        return rc;
+                    }
+
+                    /* Append separator, recurse. */
+                    strncat(work_path.str, "/", sizeof(work_path.str) - 1 - parent_len - child_name_len);
+                    if (R_FAILED((rc = IterateDirectoryRecursivelyInternal(fs, work_path, ent_buf, on_enter_dir, on_exit_dir, on_file)))) {
+                        return rc;
+                    }
+
+                    /* Exit directory. */
+                    if (R_FAILED((rc = on_exit_dir(work_path, ent_buf)))) {
+                        return rc;
+                    }
+                } else {
+                    /* Call file handler. */
+                    if (R_FAILED((rc = on_file(work_path, ent_buf)))) {
+                        return rc;
+                    }
+                }
+
+                /* Restore parent path. */
+                work_path.str[parent_len] = 0;
+            }
+
+            return 0;
+        }
+
+    public:
+        template<typename OnEnterDir, typename OnExitDir, typename OnFile>
+        static Result IterateDirectoryRecursively(IFileSystem *fs, const FsPath &root_path, FsPath &work_path, FsDirectoryEntry *ent_buf, OnEnterDir on_enter_dir, OnExitDir on_exit_dir, OnFile on_file) {
+            /* Ensure valid root path. */
+            size_t root_path_len = strnlen(root_path.str, sizeof(root_path.str));
+            if (root_path_len > FS_MAX_PATH - 1 || ((root_path_len == FS_MAX_PATH - 1) && root_path.str[root_path_len-1] != '/')) {
+                return ResultFsTooLongPath;
+            }
+
+            /* Copy path, ensure terminating separator. */
+            memcpy(work_path.str, root_path.str, root_path_len);
+            if (work_path.str[root_path_len-1] != '/') {
+                root_path_len++;
+                work_path.str[root_path_len-1] = '/';
+            }
+            work_path.str[root_path_len] = 0;
+
+            /* Actually iterate. */
+            return IterateDirectoryRecursivelyInternal(fs, work_path, ent_buf, on_enter_dir, on_exit_dir, on_file);
+        }
+
+        /* Helper for not specifying work path/entry buffer. */
+        template<typename OnEnterDir, typename OnExitDir, typename OnFile>
+        static Result IterateDirectoryRecursively(IFileSystem *fs, const FsPath &root_path, OnEnterDir on_enter_dir, OnExitDir on_exit_dir, OnFile on_file) {
+            FsDirectoryEntry dir_ent = {0};
+            FsPath work_path = {0};
+            return IterateDirectoryRecursively(fs, root_path, work_path, &dir_ent, on_enter_dir, on_exit_dir, on_file);
+        }
+
+        /* Helper for iterating over the filesystem root. */
+        template<typename OnEnterDir, typename OnExitDir, typename OnFile>
+        static Result IterateDirectoryRecursively(IFileSystem *fs, OnEnterDir on_enter_dir, OnExitDir on_exit_dir, OnFile on_file) {
+            return IterateDirectoryRecursively(fs, FsPathUtils::RootPath, on_enter_dir, on_exit_dir, on_file);
+        }
+
+        /* Copy API. */
+        static Result CopyFile(IFileSystem *dst_fs, IFileSystem *src_fs, const FsPath &dst_parent_path, const FsPath &src_path, const FsDirectoryEntry *dir_ent, void *work_buf, size_t work_buf_size);
+        static Result CopyFile(IFileSystem *fs, const FsPath &dst_parent_path, const FsPath &src_path, const FsDirectoryEntry *dir_ent, void *work_buf, size_t work_buf_size) {
+            return CopyFile(fs, fs, dst_parent_path, src_path, dir_ent, work_buf, work_buf_size);
+        }
+
+        static Result CopyDirectoryRecursively(IFileSystem *dst_fs, IFileSystem *src_fs, const FsPath &dst_path, const FsPath &src_path, void *work_buf, size_t work_buf_size);
+        static Result CopyDirectoryRecursively(IFileSystem *fs, const FsPath &dst_path, const FsPath &src_path, void *work_buf, size_t work_buf_size) {
+            return CopyDirectoryRecursively(fs, fs, dst_path, src_path, work_buf, work_buf_size);
+        }
+
+        /* Other Utility. */
+        template<typename F>
+        static Result RetryUntilTargetNotLocked(F f) {
+            const size_t MaxRetries = 10;
+            Result rc = 0;
+
+            for (size_t i = 0; i < MaxRetries; i++) {
+                rc = f();
+
+                if (rc != ResultFsTargetLocked) {
+                    break;
+                }
+
+                /* If target is locked, wait 100ms and try again. */
+                svcSleepThread(100'000'000ul);
+            }
+
+            return rc;
+        }
+};
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.cpp b/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.cpp
new file mode 100644
index 000000000..62e46f700
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.cpp
@@ -0,0 +1,394 @@
+/*
+ * Copyright (c) 2018 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/>.
+ */
+
+#include <cstring>
+#include <switch.h>
+#include <stratosphere.hpp>
+
+#include "../utils.hpp"
+#include "fs_directory_savedata_filesystem.hpp"
+#include "fs_dir_utils.hpp"
+
+class DirectorySaveDataFile : public IFile {
+    private:
+        std::unique_ptr<IFile> base_file;
+        DirectorySaveDataFileSystem *parent_fs; /* TODO: shared_ptr + enabled_shared_from_this? */
+        int open_mode;
+    public:
+        DirectorySaveDataFile(std::unique_ptr<IFile> f, DirectorySaveDataFileSystem *p, int m) : base_file(std::move(f)), parent_fs(p), open_mode(m) {
+            /* ... */
+        }
+
+        virtual ~DirectorySaveDataFile() {
+            /* Observe closing of writable file. */
+            if (this->open_mode & OpenMode_Write) {
+                this->parent_fs->OnWritableFileClose();
+            }
+        }
+    public:
+        virtual Result ReadImpl(u64 *out, u64 offset, void *buffer, u64 size) override {
+            return this->base_file->Read(out, offset, buffer, size);
+        }
+        virtual Result GetSizeImpl(u64 *out) override {
+            return this->base_file->GetSize(out);
+        }
+        virtual Result FlushImpl() override {
+            return this->base_file->Flush();
+        }
+        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, bool flush) override {
+            return this->base_file->Write(offset, buffer, size, flush);
+        }
+        virtual Result SetSizeImpl(u64 size) override {
+            return this->base_file->SetSize(size);
+        }
+        virtual Result OperateRangeImpl(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
+            return this->base_file->OperateRange(operation_type, offset, size, out_range_info);
+        }
+};
+
+/* ================================================================================================ */
+
+Result DirectorySaveDataFileSystem::Initialize() {
+    Result rc;
+    DirectoryEntryType ent_type;
+
+    /* Check that the working directory exists. */
+    if (R_FAILED((rc = this->fs->GetEntryType(&ent_type, WorkingDirectoryPath)))) {
+        /* If path isn't found, create working directory and committed directory. */
+        if (rc == ResultFsPathNotFound) {
+            if (R_FAILED((rc = this->fs->CreateDirectory(WorkingDirectoryPath)))) {
+                return rc;
+            }
+            if (R_FAILED((rc = this->fs->CreateDirectory(CommittedDirectoryPath)))) {
+                return rc;
+            }
+        } else {
+            return rc;
+        }
+    }
+
+    /* Now check for the committed directory. */
+    rc = this->fs->GetEntryType(&ent_type, CommittedDirectoryPath);
+    if (R_SUCCEEDED(rc)) {
+        /* If committed exists, synchronize it to the working directory. */
+        return this->SynchronizeDirectory(WorkingDirectoryPath, CommittedDirectoryPath);
+    } else if (rc == ResultFsPathNotFound) {
+        if (R_FAILED((rc = this->SynchronizeDirectory(SynchronizingDirectoryPath, WorkingDirectoryPath)))) {
+            return rc;
+        }
+        return this->fs->RenameDirectory(SynchronizingDirectoryPath, CommittedDirectoryPath);
+    } else {
+        return rc;
+    }
+}
+
+Result DirectorySaveDataFileSystem::SynchronizeDirectory(const FsPath &dst_dir, const FsPath &src_dir) {
+    Result rc;
+
+    /* Delete destination dir and recreate it. */
+    if (R_FAILED((rc = this->fs->DeleteDirectoryRecursively(dst_dir)))) {
+        /* Nintendo returns error unconditionally, but I think that's a bug in their code. */
+        if (rc != ResultFsPathNotFound) {
+            return rc;
+        }
+    }
+    if (R_FAILED((rc = this->fs->CreateDirectory(dst_dir)))) {
+        return rc;
+    }
+
+    /* Get a buffer to work with. */
+    void *work_buf = nullptr;
+    size_t work_buf_size = 0;
+    if (R_FAILED((rc = this->AllocateWorkBuffer(&work_buf, &work_buf_size, IdealWorkBuffersize)))) {
+        return rc;
+    }
+    ON_SCOPE_EXIT { free(work_buf); };
+
+    return FsDirUtils::CopyDirectoryRecursively(this->fs, dst_dir, src_dir, work_buf, work_buf_size);
+}
+
+Result DirectorySaveDataFileSystem::AllocateWorkBuffer(void **out_buf, size_t *out_size, const size_t ideal_size) {
+    size_t try_size = ideal_size;
+
+    /* Repeatedly try to allocate until success. */
+    while (try_size > 0x200) {
+        void *buf = malloc(try_size);
+        if (buf != nullptr) {
+            *out_buf = buf;
+            *out_size = try_size;
+            return 0;
+        }
+
+        /* Divide size by two. */
+        try_size >>= 1;
+    }
+
+    /* TODO: Return a result here? Nintendo does not, but they have other allocation failed results. */
+    /* Consider returning ResultFsAllocationFailureInDirectorySaveDataFileSystem? */
+    std::abort();
+}
+
+Result DirectorySaveDataFileSystem::GetFullPath(char *out, size_t out_size, const char *relative_path) {
+    /* Validate path. */
+    if (1 + strnlen(relative_path, FS_MAX_PATH) >= out_size) {
+        return ResultFsTooLongPath;
+    }
+    if (relative_path[0] != '/') {
+        return ResultFsInvalidPath;
+    }
+    
+    /* Copy working directory path. */
+    std::strncpy(out, WorkingDirectoryPath.str, out_size);
+    out[out_size-1] = 0;
+    
+    /* Normalize it. */
+    constexpr size_t working_len = WorkingDirectoryPathLen - 1;
+    return FsPathUtils::Normalize(out + working_len, out_size - working_len, relative_path, nullptr);
+}
+
+void DirectorySaveDataFileSystem::OnWritableFileClose() {
+    std::scoped_lock<HosMutex> lk(this->lock);
+    this->open_writable_files--;
+
+    /* TODO: Abort if < 0? N does not. */
+}
+
+/* ================================================================================================ */
+
+Result DirectorySaveDataFileSystem::CreateFileImpl(const FsPath &path, uint64_t size, int flags) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->CreateFile(full_path, size, flags);
+}
+
+Result DirectorySaveDataFileSystem::DeleteFileImpl(const FsPath &path) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->DeleteFile(full_path);
+}
+
+Result DirectorySaveDataFileSystem::CreateDirectoryImpl(const FsPath &path) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->CreateDirectory(full_path);
+}
+
+Result DirectorySaveDataFileSystem::DeleteDirectoryImpl(const FsPath &path) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->DeleteDirectory(full_path);
+}
+
+Result DirectorySaveDataFileSystem::DeleteDirectoryRecursivelyImpl(const FsPath &path) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->DeleteDirectoryRecursively(full_path);
+}
+
+Result DirectorySaveDataFileSystem::RenameFileImpl(const FsPath &old_path, const FsPath &new_path) {
+    Result rc;
+    FsPath full_old_path, full_new_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_old_path, old_path)))) {
+        return rc;
+    }
+    
+    if (R_FAILED((rc = GetFullPath(full_new_path, new_path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->RenameFile(full_old_path, full_new_path);
+}
+
+Result DirectorySaveDataFileSystem::RenameDirectoryImpl(const FsPath &old_path, const FsPath &new_path) {
+    Result rc;
+    FsPath full_old_path, full_new_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_old_path, old_path)))) {
+        return rc;
+    }
+    
+    if (R_FAILED((rc = GetFullPath(full_new_path, new_path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->RenameDirectory(full_old_path, full_new_path);
+}
+
+Result DirectorySaveDataFileSystem::GetEntryTypeImpl(DirectoryEntryType *out, const FsPath &path) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->GetEntryType(out, full_path);
+}
+
+Result DirectorySaveDataFileSystem::OpenFileImpl(std::unique_ptr<IFile> &out_file, const FsPath &path, OpenMode mode) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+
+    std::scoped_lock<HosMutex> lk(this->lock);
+
+    {
+        /* Open the raw file. */
+        std::unique_ptr<IFile> file;
+        if (R_FAILED((rc = this->fs->OpenFile(file, full_path, mode)))) {
+            return rc;
+        }
+
+        /* Create DirectorySaveDataFile wrapper. */
+        out_file = std::make_unique<DirectorySaveDataFile>(std::move(file), this, mode);
+    }
+
+    /* Check for allocation failure. */
+    if (out_file == nullptr) {
+        return ResultFsAllocationFailureInDirectorySaveDataFileSystem;
+    }
+
+    /* Increment open writable files, if needed. */
+    if (mode & OpenMode_Write) {
+        this->open_writable_files++;
+    }
+
+    return 0;
+}
+
+Result DirectorySaveDataFileSystem::OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, const FsPath &path, DirectoryOpenMode mode) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->OpenDirectory(out_dir, full_path, mode);
+}
+
+Result DirectorySaveDataFileSystem::CommitImpl() {
+    /* Here, Nintendo does the following (with retries): */
+    /* - Rename Committed -> Synchronizing. */
+    /* - Synchronize Working -> Synchronizing (deleting Synchronizing). */
+    /* - Rename Synchronizing -> Committed. */
+    /* I think this is not the optimal order to do things, as the previous committed directory */
+    /* will be deleted if there is an error during synchronization. */
+    /* Instead, we will synchronize first, then delete committed, then rename. */
+
+    std::scoped_lock<HosMutex> lk(this->lock);
+    Result rc;
+
+    /* Ensure we don't have any open writable files. */
+    if (this->open_writable_files != 0) {
+        return ResultFsPreconditionViolation;
+    }
+
+    const auto SynchronizeWorkingDir = [&]() { return this->SynchronizeDirectory(SynchronizingDirectoryPath, WorkingDirectoryPath); };
+    const auto DeleteCommittedDir = [&]() { return this->fs->DeleteDirectoryRecursively(CommittedDirectoryPath); };
+    const auto RenameSynchDir = [&]() { return this->fs->RenameDirectory(SynchronizingDirectoryPath, CommittedDirectoryPath); };
+
+    /* Synchronize working directory. */
+    if (R_FAILED((rc = FsDirUtils::RetryUntilTargetNotLocked(std::move(SynchronizeWorkingDir))))) {
+        return rc;
+    }
+
+    /* Delete committed directory. */
+    if (R_FAILED((rc = FsDirUtils::RetryUntilTargetNotLocked(std::move(DeleteCommittedDir))))) {
+        /* It is okay for us to not have a committed directory here. */
+        if (rc != ResultFsPathNotFound) {
+            return rc;
+        }
+    }
+
+    /* Rename synchronizing directory to committed directory. */
+    if (R_FAILED((rc = FsDirUtils::RetryUntilTargetNotLocked(std::move(RenameSynchDir))))) {
+        return rc;
+    }
+
+    /* TODO: Should I call this->fs->Commit()? Nintendo does not. */
+    return rc;
+}
+
+Result DirectorySaveDataFileSystem::GetFreeSpaceSizeImpl(uint64_t *out, const FsPath &path) {
+    /* TODO: How should this work? N returns ResultFsNotImplemented. */
+    return ResultFsNotImplemented;
+}
+
+Result DirectorySaveDataFileSystem::GetTotalSpaceSizeImpl(uint64_t *out, const FsPath &path) {
+    /* TODO: How should this work? N returns ResultFsNotImplemented. */
+    return ResultFsNotImplemented;
+}
+
+Result DirectorySaveDataFileSystem::CleanDirectoryRecursivelyImpl(const FsPath &path) {
+    Result rc;
+    FsPath full_path;
+    
+    if (R_FAILED((rc = GetFullPath(full_path, path)))) {
+        return rc;
+    }
+    
+    std::scoped_lock<HosMutex> lk(this->lock);
+    return this->fs->CleanDirectoryRecursively(full_path);
+}
+
+Result DirectorySaveDataFileSystem::GetFileTimeStampRawImpl(FsTimeStampRaw *out, const FsPath &path) {
+    /* TODO: How should this work? N returns ResultFsNotImplemented. */
+    return ResultFsNotImplemented;
+}
+
+Result DirectorySaveDataFileSystem::QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, const FsPath &path) {
+    /* TODO: How should this work? N returns ResultFsNotImplemented. */
+    return ResultFsNotImplemented;
+}
\ No newline at end of file
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.hpp
new file mode 100644
index 000000000..e40521faa
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_directory_savedata_filesystem.hpp
@@ -0,0 +1,99 @@
+/*
+ * Copyright (c) 2018 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 <switch.h>
+#include <stratosphere.hpp>
+
+#include "fs_ifilesystem.hpp"
+#include "fs_path_utils.hpp"
+
+class DirectorySaveDataFileSystem : public IFileSystem {
+    private:
+        static constexpr FsPath CommittedDirectoryPath     = EncodeConstantFsPath("/0/");
+        static constexpr FsPath WorkingDirectoryPath       = EncodeConstantFsPath("/1/");
+        static constexpr FsPath SynchronizingDirectoryPath = EncodeConstantFsPath("/_/");
+
+        static constexpr size_t CommittedDirectoryPathLen     = GetConstantFsPathLen(CommittedDirectoryPath);
+        static constexpr size_t WorkingDirectoryPathLen       = GetConstantFsPathLen(WorkingDirectoryPath);
+        static constexpr size_t SynchronizingDirectoryPathLen = GetConstantFsPathLen(SynchronizingDirectoryPath);
+
+        static constexpr size_t IdealWorkBuffersize = 0x100000; /* 1 MB */
+    private:
+        std::shared_ptr<IFileSystem> shared_fs;
+        std::unique_ptr<IFileSystem> unique_fs;
+        IFileSystem *fs;
+        HosMutex lock;
+        size_t open_writable_files = 0;
+
+    public:
+        DirectorySaveDataFileSystem(IFileSystem *fs) : unique_fs(fs) {
+            this->fs = this->unique_fs.get();
+            Result rc = this->Initialize();
+            if (R_FAILED(rc)) {
+                fatalSimple(rc);
+            }
+        }
+
+        DirectorySaveDataFileSystem(std::unique_ptr<IFileSystem> fs) : unique_fs(std::move(fs)) {
+            this->fs = this->unique_fs.get();
+            Result rc = this->Initialize();
+            if (R_FAILED(rc)) {
+                fatalSimple(rc);
+            }
+        }
+
+        DirectorySaveDataFileSystem(std::shared_ptr<IFileSystem> fs) : shared_fs(fs) {
+            this->fs = this->shared_fs.get();
+            Result rc = this->Initialize();
+            if (R_FAILED(rc)) {
+                fatalSimple(rc);
+            }
+        }
+
+
+        virtual ~DirectorySaveDataFileSystem() { }
+
+    private:
+        Result Initialize();
+    protected:
+        Result SynchronizeDirectory(const FsPath &dst_dir, const FsPath &src_dir);
+        Result AllocateWorkBuffer(void **out_buf, size_t *out_size, const size_t ideal_size);
+
+        Result GetFullPath(char *out, size_t out_size, const char *relative_path);
+        Result GetFullPath(FsPath &full_path, const FsPath &relative_path) {
+            return GetFullPath(full_path.str, sizeof(full_path.str), relative_path.str);
+        }
+    public:
+        void OnWritableFileClose();
+    public:
+        virtual Result CreateFileImpl(const FsPath &path, uint64_t size, int flags) override;
+        virtual Result DeleteFileImpl(const FsPath &path) override;
+        virtual Result CreateDirectoryImpl(const FsPath &path) override;
+        virtual Result DeleteDirectoryImpl(const FsPath &path) override;
+        virtual Result DeleteDirectoryRecursivelyImpl(const FsPath &path) override;
+        virtual Result RenameFileImpl(const FsPath &old_path, const FsPath &new_path) override;
+        virtual Result RenameDirectoryImpl(const FsPath &old_path, const FsPath &new_path) override;
+        virtual Result GetEntryTypeImpl(DirectoryEntryType *out, const FsPath &path) override;
+        virtual Result OpenFileImpl(std::unique_ptr<IFile> &out_file, const FsPath &path, OpenMode mode) override;
+        virtual Result OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, const FsPath &path, DirectoryOpenMode mode) override;
+        virtual Result CommitImpl() override;
+        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, const FsPath &path) override;
+        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, const FsPath &path) override;
+        virtual Result CleanDirectoryRecursivelyImpl(const FsPath &path) override;
+        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, const FsPath &path) override;
+        virtual Result QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, const FsPath &path) override;
+};
\ No newline at end of file
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp
index 8da0e5838..9f7cb17d2 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp
@@ -49,6 +49,10 @@ class IFile {
             return ReadImpl(out, offset, buffer, size);
         }
 
+        Result Read(uint64_t *out, uint64_t offset, void *buffer, uint64_t size) {
+            return Read(out, offset, buffer, size, 0);
+        }
+
         Result GetSize(uint64_t *out) {
             if (out == nullptr) {
                 return ResultFsNullptrArgument;
@@ -71,8 +75,14 @@ class IFile {
             return WriteImpl(offset, buffer, size, flush);
         }
 
-        Result Write(uint64_t offset, void *buffer, uint64_t size) {
-            return WriteImpl(offset, buffer, size, false);
+        Result Write(uint64_t offset, void *buffer, uint64_t size, bool flush = false) {
+            if (size == 0) {
+                return 0;
+            }
+            if (buffer == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            return WriteImpl(offset, buffer, size, flush);
         }
 
         Result SetSize(uint64_t size) {
@@ -162,7 +172,7 @@ class ProxyFile : public IFile {
             fsFileClose(this->base_file.get());
         }
     public:
-        virtual Result ReadImpl(u64 *out, u64 offset, void *buffer, u64 size) {
+        virtual Result ReadImpl(u64 *out, u64 offset, void *buffer, u64 size) override {
             size_t out_sz;
 
             Result rc = fsFileRead(this->base_file.get(), offset, buffer, size, &out_sz);
@@ -172,13 +182,13 @@ class ProxyFile : public IFile {
 
             return rc;
         }
-        virtual Result GetSizeImpl(u64 *out) {
+        virtual Result GetSizeImpl(u64 *out) override {
             return fsFileGetSize(this->base_file.get(), out);
         }
-        virtual Result FlushImpl() {
+        virtual Result FlushImpl() override {
             return fsFileFlush(this->base_file.get());
         }
-        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, bool flush) {
+        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, bool flush) override {
             Result rc = fsFileWrite(this->base_file.get(), offset, buffer, size);
             if (R_SUCCEEDED(rc)) {
                 /* libnx doesn't allow passing the flush flag. */
@@ -186,10 +196,10 @@ class ProxyFile : public IFile {
             }
             return rc;
         }
-        virtual Result SetSizeImpl(u64 size) {
+        virtual Result SetSizeImpl(u64 size) override {
             return fsFileSetSize(this->base_file.get(), size);
         }
-        virtual Result OperateRangeImpl(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) {
+        virtual Result OperateRangeImpl(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) override {
             return fsFileOperateRange(this->base_file.get(), operation_type, offset, size, out_range_info);
         }
 };
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_ifilesystem.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_ifilesystem.hpp
index 2b3fda4c0..4e176302a 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_ifilesystem.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_ifilesystem.hpp
@@ -58,42 +58,46 @@ class IFileSystem {
     public:
         virtual ~IFileSystem() {}
 
-        Result CreateFile(FsPath &path, uint64_t size, int flags) {
+        Result CreateFile(const FsPath &path, uint64_t size, int flags) {
             return CreateFileImpl(path, size, flags);
         }
 
-        Result DeleteFile(FsPath &path) {
+        Result CreateFile(const FsPath &path, uint64_t size) {
+            return CreateFileImpl(path, size, 0);
+        }
+
+        Result DeleteFile(const FsPath &path) {
             return DeleteFileImpl(path);
         }
 
-        Result CreateDirectory(FsPath &path) {
+        Result CreateDirectory(const FsPath &path) {
             return CreateDirectoryImpl(path);
         }
 
-        Result DeleteDirectory(FsPath &path) {
+        Result DeleteDirectory(const FsPath &path) {
             return DeleteDirectoryImpl(path);
         }
 
-        Result DeleteDirectoryRecursively(FsPath &path) {
+        Result DeleteDirectoryRecursively(const FsPath &path) {
             return DeleteDirectoryRecursivelyImpl(path);
         }
 
-        Result RenameFile(FsPath &old_path, FsPath &new_path) {
+        Result RenameFile(const FsPath &old_path, const FsPath &new_path) {
             return RenameFileImpl(old_path, new_path);
         }
 
-        Result RenameDirectory(FsPath &old_path, FsPath &new_path) {
+        Result RenameDirectory(const FsPath &old_path, const FsPath &new_path) {
             return RenameDirectoryImpl(old_path, new_path);
         }
 
-        Result GetEntryType(DirectoryEntryType *out, FsPath &path) {
+        Result GetEntryType(DirectoryEntryType *out, const FsPath &path) {
             if (out == nullptr) {
                 return ResultFsNullptrArgument;
             }
             return GetEntryTypeImpl(out, path);
         }
 
-        Result OpenFile(std::unique_ptr<IFile> &out_file, FsPath &path, OpenMode mode) {
+        Result OpenFile(std::unique_ptr<IFile> &out_file, const FsPath &path, OpenMode mode) {
             if (!(mode & OpenMode_ReadWrite)) {
                 return ResultFsInvalidArgument;
             }
@@ -103,7 +107,7 @@ class IFileSystem {
             return OpenFileImpl(out_file, path, mode);
         }
 
-        Result OpenDirectory(std::unique_ptr<IDirectory> &out_dir, FsPath &path, DirectoryOpenMode mode) {
+        Result OpenDirectory(std::unique_ptr<IDirectory> &out_dir, const FsPath &path, DirectoryOpenMode mode) {
             if (!(mode & DirectoryOpenMode_All)) {
                 return ResultFsInvalidArgument;
             }
@@ -117,32 +121,32 @@ class IFileSystem {
             return CommitImpl();
         }
 
-        Result GetFreeSpaceSize(uint64_t *out, FsPath &path) {
+        Result GetFreeSpaceSize(uint64_t *out, const FsPath &path) {
             if (out == nullptr) {
                 return ResultFsNullptrArgument;
             }
             return GetFreeSpaceSizeImpl(out, path);
         }
 
-        Result GetTotalSpaceSize(uint64_t *out, FsPath &path) {
+        Result GetTotalSpaceSize(uint64_t *out, const FsPath &path) {
             if (out == nullptr) {
                 return ResultFsNullptrArgument;
             }
             return GetTotalSpaceSizeImpl(out, path);
         }
 
-        Result CleanDirectoryRecursively(FsPath &path) {
+        Result CleanDirectoryRecursively(const FsPath &path) {
             return CleanDirectoryRecursivelyImpl(path);
         }
 
-        Result GetFileTimeStampRaw(FsTimeStampRaw *out, FsPath &path) {
+        Result GetFileTimeStampRaw(FsTimeStampRaw *out, const FsPath &path) {
             if (out == nullptr) {
                 return ResultFsNullptrArgument;
             }
             return GetFileTimeStampRawImpl(out, path);
         }
 
-        Result QueryEntry(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, FsPath &path) {
+        Result QueryEntry(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, const FsPath &path) {
             return QueryEntryImpl(out, out_size, in, in_size, query, path);
         }
 
@@ -150,39 +154,39 @@ class IFileSystem {
     protected:
         /* ...? */
     private:
-        virtual Result CreateFileImpl(FsPath &path, uint64_t size, int flags) = 0;
-        virtual Result DeleteFileImpl(FsPath &path) = 0;
-        virtual Result CreateDirectoryImpl(FsPath &path) = 0;
-        virtual Result DeleteDirectoryImpl(FsPath &path) = 0;
-        virtual Result DeleteDirectoryRecursivelyImpl(FsPath &path) = 0;
-        virtual Result RenameFileImpl(FsPath &old_path, FsPath &new_path) = 0;
-        virtual Result RenameDirectoryImpl(FsPath &old_path, FsPath &new_path) = 0;
-        virtual Result GetEntryTypeImpl(DirectoryEntryType *out, FsPath &path) = 0;
-        virtual Result OpenFileImpl(std::unique_ptr<IFile> &out_file, FsPath &path, OpenMode mode) = 0;
-        virtual Result OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, FsPath &path, DirectoryOpenMode mode) = 0;
+        virtual Result CreateFileImpl(const FsPath &path, uint64_t size, int flags) = 0;
+        virtual Result DeleteFileImpl(const FsPath &path) = 0;
+        virtual Result CreateDirectoryImpl(const FsPath &path) = 0;
+        virtual Result DeleteDirectoryImpl(const FsPath &path) = 0;
+        virtual Result DeleteDirectoryRecursivelyImpl(const FsPath &path) = 0;
+        virtual Result RenameFileImpl(const FsPath &old_path, const FsPath &new_path) = 0;
+        virtual Result RenameDirectoryImpl(const FsPath &old_path, const FsPath &new_path) = 0;
+        virtual Result GetEntryTypeImpl(DirectoryEntryType *out, const FsPath &path) = 0;
+        virtual Result OpenFileImpl(std::unique_ptr<IFile> &out_file, const FsPath &path, OpenMode mode) = 0;
+        virtual Result OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, const FsPath &path, DirectoryOpenMode mode) = 0;
         virtual Result CommitImpl() = 0;
 
-        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, FsPath &path) {
+        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, const FsPath &path) {
             (void)(out);
             (void)(path);
             return ResultFsNotImplemented;
         }
 
-        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, FsPath &path) {
+        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, const FsPath &path) {
             (void)(out);
             (void)(path);
             return ResultFsNotImplemented;
         }
 
-        virtual Result CleanDirectoryRecursivelyImpl(FsPath &path) = 0;
+        virtual Result CleanDirectoryRecursivelyImpl(const FsPath &path) = 0;
 
-        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, FsPath &path) {
+        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, const FsPath &path) {
             (void)(out);
             (void)(path);
             return ResultFsNotImplemented;
         }
 
-        virtual Result QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, FsPath &path) {
+        virtual Result QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, const FsPath &path) {
             (void)(out);
             (void)(out_size);
             (void)(in);
@@ -449,35 +453,35 @@ class ProxyFileSystem : public IFileSystem {
         }
 
     public:
-        virtual Result CreateFileImpl(FsPath &path, uint64_t size, int flags) {
+        virtual Result CreateFileImpl(const FsPath &path, uint64_t size, int flags) {
             return fsFsCreateFile(this->base_fs.get(), path.str, size, flags);
         }
 
-        virtual Result DeleteFileImpl(FsPath &path) {
+        virtual Result DeleteFileImpl(const FsPath &path) {
             return fsFsDeleteFile(this->base_fs.get(), path.str);
         }
 
-        virtual Result CreateDirectoryImpl(FsPath &path) {
+        virtual Result CreateDirectoryImpl(const FsPath &path) {
             return fsFsCreateDirectory(this->base_fs.get(), path.str);
         }
 
-        virtual Result DeleteDirectoryImpl(FsPath &path) {
+        virtual Result DeleteDirectoryImpl(const FsPath &path) {
             return fsFsDeleteDirectory(this->base_fs.get(), path.str);
         }
 
-        virtual Result DeleteDirectoryRecursivelyImpl(FsPath &path) {
+        virtual Result DeleteDirectoryRecursivelyImpl(const FsPath &path) {
             return fsFsDeleteDirectoryRecursively(this->base_fs.get(), path.str);
         }
 
-        virtual Result RenameFileImpl(FsPath &old_path, FsPath &new_path) {
+        virtual Result RenameFileImpl(const FsPath &old_path, const FsPath &new_path) {
             return fsFsRenameFile(this->base_fs.get(), old_path.str, new_path.str);
         }
 
-        virtual Result RenameDirectoryImpl(FsPath &old_path, FsPath &new_path) {
+        virtual Result RenameDirectoryImpl(const FsPath &old_path, const FsPath &new_path) {
             return fsFsRenameDirectory(this->base_fs.get(), old_path.str, new_path.str);
         }
 
-        virtual Result GetEntryTypeImpl(DirectoryEntryType *out, FsPath &path) {
+        virtual Result GetEntryTypeImpl(DirectoryEntryType *out, const FsPath &path) {
             FsEntryType type;
 
             Result rc = fsFsGetEntryType(this->base_fs.get(), path.str, &type);
@@ -487,7 +491,7 @@ class ProxyFileSystem : public IFileSystem {
 
             return rc;
         }
-        virtual Result OpenFileImpl(std::unique_ptr<IFile> &out_file, FsPath &path, OpenMode mode) {
+        virtual Result OpenFileImpl(std::unique_ptr<IFile> &out_file, const FsPath &path, OpenMode mode) {
             FsFile f;
 
             Result rc = fsFsOpenFile(this->base_fs.get(), path.str, static_cast<int>(mode), &f);
@@ -498,7 +502,7 @@ class ProxyFileSystem : public IFileSystem {
             return rc;
         }
 
-        virtual Result OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, FsPath &path, DirectoryOpenMode mode) {
+        virtual Result OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, const FsPath &path, DirectoryOpenMode mode) {
             FsDir d;
 
             Result rc = fsFsOpenDirectory(this->base_fs.get(), path.str, static_cast<int>(mode), &d);
@@ -513,23 +517,23 @@ class ProxyFileSystem : public IFileSystem {
             return fsFsCommit(this->base_fs.get());
         }
 
-        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, FsPath &path) {
+        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, const FsPath &path) {
             return fsFsGetFreeSpace(this->base_fs.get(), path.str, out);
         }
 
-        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, FsPath &path) {
+        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, const FsPath &path) {
             return fsFsGetTotalSpace(this->base_fs.get(), path.str, out);
         }
 
-        virtual Result CleanDirectoryRecursivelyImpl(FsPath &path) {
+        virtual Result CleanDirectoryRecursivelyImpl(const FsPath &path) {
             return fsFsCleanDirectoryRecursively(this->base_fs.get(), path.str);
         }
 
-        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, FsPath &path) {
+        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, const FsPath &path) {
             return fsFsGetFileTimeStampRaw(this->base_fs.get(), path.str, out);
         }
 
-        virtual Result QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, FsPath &path) {
+        virtual Result QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, const FsPath &path) {
             return fsFsQueryEntry(this->base_fs.get(), out, out_size, in, in_size, path.str,static_cast<FsFileSystemQueryType>(query));
         }
 };
\ No newline at end of file
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_path_utils.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_path_utils.hpp
index 142fd25b7..b4ad49863 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_path_utils.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_path_utils.hpp
@@ -21,7 +21,31 @@ struct FsPath {
     char str[FS_MAX_PATH];
 };
 
+constexpr FsPath EncodeConstantFsPath(const char *p) {
+    FsPath path = {0};
+    for (size_t i = 0; i < sizeof(path) - 1; i++) {
+        path.str[i] = p[i];
+        if (p[i] == 0) {
+            break;
+        }
+    }
+    return path;
+}
+
+constexpr size_t GetConstantFsPathLen(FsPath path) {
+    size_t len = 0;
+    for (size_t i = 0; i < sizeof(path) - 1; i++) {
+        if (path.str[i] == 0) {
+            break;
+        }
+        len++;
+    }
+    return len;
+}
+
 class FsPathUtils {
+    public:
+        static constexpr FsPath RootPath = EncodeConstantFsPath("/");
     public:
         static Result VerifyPath(const char *path, size_t max_path_len, size_t max_name_len);
         static Result ConvertPathForServiceObject(FsPath *out, const char *path);
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_results.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_results.hpp
index 9dd12dd60..3bcf5d50a 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_results.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_results.hpp
@@ -19,11 +19,19 @@
 
 static constexpr u32 Module_Fs = 2;
 
+static constexpr Result ResultFsPathNotFound       = MAKERESULT(Module_Fs, 1);
+static constexpr Result ResultFsPathAlreadyExists  = MAKERESULT(Module_Fs, 2);
+
+static constexpr Result ResultFsTargetLocked       = MAKERESULT(Module_Fs, 7);
+static constexpr Result ResultFsDirectoryNotEmpty  = MAKERESULT(Module_Fs, 8);
+
 static constexpr Result ResultFsNotImplemented       = MAKERESULT(Module_Fs, 3001);
 static constexpr Result ResultFsOutOfRange           = MAKERESULT(Module_Fs, 3005);
 
-static constexpr Result ResultFsAllocationFailureInSubDirectoryFileSystem = MAKERESULT(Module_Fs, 3355);
+static constexpr Result ResultFsAllocationFailureInDirectorySaveDataFileSystem = MAKERESULT(Module_Fs, 3321);
+static constexpr Result ResultFsAllocationFailureInSubDirectoryFileSystem      = MAKERESULT(Module_Fs, 3355);
 
+static constexpr Result ResultFsPreconditionViolation = MAKERESULT(Module_Fs, 6000);
 static constexpr Result ResultFsInvalidArgument       = MAKERESULT(Module_Fs, 6001);
 static constexpr Result ResultFsInvalidPath           = MAKERESULT(Module_Fs, 6002);
 static constexpr Result ResultFsTooLongPath           = MAKERESULT(Module_Fs, 6003);
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_subdirectory_filesystem.cpp b/stratosphere/ams_mitm/source/fs_mitm/fs_subdirectory_filesystem.cpp
index 6d14c418a..88622e814 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_subdirectory_filesystem.cpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_subdirectory_filesystem.cpp
@@ -71,7 +71,7 @@ Result SubDirectoryFileSystem::GetFullPath(char *out, size_t out_size, const cha
     return FsPathUtils::Normalize(out + this->base_path_len - 2, out_size - (this->base_path_len - 2), relative_path, nullptr);
 }
 
-Result SubDirectoryFileSystem::CreateFileImpl(FsPath &path, uint64_t size, int flags) {
+Result SubDirectoryFileSystem::CreateFileImpl(const FsPath &path, uint64_t size, int flags) {
     Result rc;
     FsPath full_path;
     
@@ -82,7 +82,7 @@ Result SubDirectoryFileSystem::CreateFileImpl(FsPath &path, uint64_t size, int f
     return this->base_fs->CreateFile(full_path, size, flags);
 }
 
-Result SubDirectoryFileSystem::DeleteFileImpl(FsPath &path) {
+Result SubDirectoryFileSystem::DeleteFileImpl(const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -93,7 +93,7 @@ Result SubDirectoryFileSystem::DeleteFileImpl(FsPath &path) {
     return this->base_fs->DeleteFile(full_path);
 }
 
-Result SubDirectoryFileSystem::CreateDirectoryImpl(FsPath &path) {
+Result SubDirectoryFileSystem::CreateDirectoryImpl(const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -104,7 +104,7 @@ Result SubDirectoryFileSystem::CreateDirectoryImpl(FsPath &path) {
     return this->base_fs->CreateDirectory(full_path);
 }
 
-Result SubDirectoryFileSystem::DeleteDirectoryImpl(FsPath &path) {
+Result SubDirectoryFileSystem::DeleteDirectoryImpl(const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -115,7 +115,7 @@ Result SubDirectoryFileSystem::DeleteDirectoryImpl(FsPath &path) {
     return this->base_fs->DeleteDirectory(full_path);
 }
 
-Result SubDirectoryFileSystem::DeleteDirectoryRecursivelyImpl(FsPath &path) {
+Result SubDirectoryFileSystem::DeleteDirectoryRecursivelyImpl(const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -126,7 +126,7 @@ Result SubDirectoryFileSystem::DeleteDirectoryRecursivelyImpl(FsPath &path) {
     return this->base_fs->DeleteDirectoryRecursively(full_path);
 }
 
-Result SubDirectoryFileSystem::RenameFileImpl(FsPath &old_path, FsPath &new_path) {
+Result SubDirectoryFileSystem::RenameFileImpl(const FsPath &old_path, const FsPath &new_path) {
     Result rc;
     FsPath full_old_path, full_new_path;
     
@@ -141,7 +141,7 @@ Result SubDirectoryFileSystem::RenameFileImpl(FsPath &old_path, FsPath &new_path
     return this->base_fs->RenameFile(full_old_path, full_new_path);
 }
 
-Result SubDirectoryFileSystem::RenameDirectoryImpl(FsPath &old_path, FsPath &new_path) {
+Result SubDirectoryFileSystem::RenameDirectoryImpl(const FsPath &old_path, const FsPath &new_path) {
     Result rc;
     FsPath full_old_path, full_new_path;
     
@@ -156,7 +156,7 @@ Result SubDirectoryFileSystem::RenameDirectoryImpl(FsPath &old_path, FsPath &new
     return this->base_fs->RenameDirectory(full_old_path, full_new_path);
 }
 
-Result SubDirectoryFileSystem::GetEntryTypeImpl(DirectoryEntryType *out, FsPath &path) {
+Result SubDirectoryFileSystem::GetEntryTypeImpl(DirectoryEntryType *out, const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -167,7 +167,7 @@ Result SubDirectoryFileSystem::GetEntryTypeImpl(DirectoryEntryType *out, FsPath
     return this->base_fs->GetEntryType(out, full_path);
 }
 
-Result SubDirectoryFileSystem::OpenFileImpl(std::unique_ptr<IFile> &out_file, FsPath &path, OpenMode mode) {
+Result SubDirectoryFileSystem::OpenFileImpl(std::unique_ptr<IFile> &out_file, const FsPath &path, OpenMode mode) {
     Result rc;
     FsPath full_path;
     
@@ -178,7 +178,7 @@ Result SubDirectoryFileSystem::OpenFileImpl(std::unique_ptr<IFile> &out_file, Fs
     return this->base_fs->OpenFile(out_file, full_path, mode);
 }
 
-Result SubDirectoryFileSystem::OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, FsPath &path, DirectoryOpenMode mode) {
+Result SubDirectoryFileSystem::OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, const FsPath &path, DirectoryOpenMode mode) {
     Result rc;
     FsPath full_path;
     
@@ -193,7 +193,7 @@ Result SubDirectoryFileSystem::CommitImpl() {
     return this->base_fs->Commit();
 }
 
-Result SubDirectoryFileSystem::GetFreeSpaceSizeImpl(uint64_t *out, FsPath &path) {
+Result SubDirectoryFileSystem::GetFreeSpaceSizeImpl(uint64_t *out, const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -204,7 +204,7 @@ Result SubDirectoryFileSystem::GetFreeSpaceSizeImpl(uint64_t *out, FsPath &path)
     return this->base_fs->GetFreeSpaceSize(out, full_path);
 }
 
-Result SubDirectoryFileSystem::GetTotalSpaceSizeImpl(uint64_t *out, FsPath &path) {
+Result SubDirectoryFileSystem::GetTotalSpaceSizeImpl(uint64_t *out, const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -215,7 +215,7 @@ Result SubDirectoryFileSystem::GetTotalSpaceSizeImpl(uint64_t *out, FsPath &path
     return this->base_fs->GetTotalSpaceSize(out, full_path);
 }   
 
-Result SubDirectoryFileSystem::CleanDirectoryRecursivelyImpl(FsPath &path) {
+Result SubDirectoryFileSystem::CleanDirectoryRecursivelyImpl(const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -226,7 +226,7 @@ Result SubDirectoryFileSystem::CleanDirectoryRecursivelyImpl(FsPath &path) {
     return this->base_fs->CleanDirectoryRecursively(full_path);
 }
 
-Result SubDirectoryFileSystem::GetFileTimeStampRawImpl(FsTimeStampRaw *out, FsPath &path) {
+Result SubDirectoryFileSystem::GetFileTimeStampRawImpl(FsTimeStampRaw *out, const FsPath &path) {
     Result rc;
     FsPath full_path;
     
@@ -237,7 +237,7 @@ Result SubDirectoryFileSystem::GetFileTimeStampRawImpl(FsTimeStampRaw *out, FsPa
     return this->base_fs->GetFileTimeStampRaw(out, full_path);
 }
 
-Result SubDirectoryFileSystem::QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, FsPath &path) {
+Result SubDirectoryFileSystem::QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, const FsPath &path) {
     Result rc;
     FsPath full_path;
     
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_subdirectory_filesystem.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_subdirectory_filesystem.hpp
index e6c406fa1..d1a28cef3 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_subdirectory_filesystem.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_subdirectory_filesystem.hpp
@@ -53,25 +53,25 @@ class SubDirectoryFileSystem : public IFileSystem {
         Result Initialize(const char *bp);
     protected:
         Result GetFullPath(char *out, size_t out_size, const char *relative_path);
-        Result GetFullPath(FsPath &full_path, FsPath &relative_path) {
+        Result GetFullPath(FsPath &full_path, const FsPath &relative_path) {
             return GetFullPath(full_path.str, sizeof(full_path.str), relative_path.str);
         }
         
     public:
-        virtual Result CreateFileImpl(FsPath &path, uint64_t size, int flags) override;
-        virtual Result DeleteFileImpl(FsPath &path) override;
-        virtual Result CreateDirectoryImpl(FsPath &path) override;
-        virtual Result DeleteDirectoryImpl(FsPath &path) override;
-        virtual Result DeleteDirectoryRecursivelyImpl(FsPath &path) override;
-        virtual Result RenameFileImpl(FsPath &old_path, FsPath &new_path) override;
-        virtual Result RenameDirectoryImpl(FsPath &old_path, FsPath &new_path) override;
-        virtual Result GetEntryTypeImpl(DirectoryEntryType *out, FsPath &path) override;
-        virtual Result OpenFileImpl(std::unique_ptr<IFile> &out_file, FsPath &path, OpenMode mode) override;
-        virtual Result OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, FsPath &path, DirectoryOpenMode mode) override;
+        virtual Result CreateFileImpl(const FsPath &path, uint64_t size, int flags) override;
+        virtual Result DeleteFileImpl(const FsPath &path) override;
+        virtual Result CreateDirectoryImpl(const FsPath &path) override;
+        virtual Result DeleteDirectoryImpl(const FsPath &path) override;
+        virtual Result DeleteDirectoryRecursivelyImpl(const FsPath &path) override;
+        virtual Result RenameFileImpl(const FsPath &old_path, const FsPath &new_path) override;
+        virtual Result RenameDirectoryImpl(const FsPath &old_path, const FsPath &new_path) override;
+        virtual Result GetEntryTypeImpl(DirectoryEntryType *out, const FsPath &path) override;
+        virtual Result OpenFileImpl(std::unique_ptr<IFile> &out_file, const FsPath &path, OpenMode mode) override;
+        virtual Result OpenDirectoryImpl(std::unique_ptr<IDirectory> &out_dir, const FsPath &path, DirectoryOpenMode mode) override;
         virtual Result CommitImpl() override;
-        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, FsPath &path) override;
-        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, FsPath &path) override;
-        virtual Result CleanDirectoryRecursivelyImpl(FsPath &path) override;
-        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, FsPath &path) override;
-        virtual Result QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, FsPath &path) override;
+        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, const FsPath &path) override;
+        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, const FsPath &path) override;
+        virtual Result CleanDirectoryRecursivelyImpl(const FsPath &path) override;
+        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, const FsPath &path) override;
+        virtual Result QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, const FsPath &path) override;
 };
\ No newline at end of file
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
index 33f6eda10..9541f2d4e 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
@@ -29,6 +29,7 @@
 #include "fsmitm_layeredrom.hpp"
 
 #include "fs_subdirectory_filesystem.hpp"
+#include "fs_directory_savedata_filesystem.hpp"
 
 #include "../debug.hpp"