diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_filesystem_types.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_filesystem_types.hpp
new file mode 100644
index 000000000..08d056c29
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_filesystem_types.hpp
@@ -0,0 +1,38 @@
+/*
+ * 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
+    
+enum OpenMode {
+    OpenMode_Read = (1 << 0),
+    OpenMode_Write = (1 << 1),
+    OpenMode_Append = (1 << 2),
+    
+    OpenMode_ReadWrite = OpenMode_Read | OpenMode_Write,
+    OpenMode_All = OpenMode_ReadWrite | OpenMode_Append,
+};
+
+enum DirectoryOpenMode {
+    DirectoryOpenMode_Directories = (1 << 0),
+    DirectoryOpenMode_Files = (1 << 1),
+    
+    DirectoryOpenMode_All = (DirectoryOpenMode_Directories | DirectoryOpenMode_Files),
+};
+
+enum DirectoryEntryType {
+    DirectoryEntryType_Directory,
+    DirectoryEntryType_File,
+};
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_idirectory.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_idirectory.hpp
new file mode 100644
index 000000000..020b67dde
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_idirectory.hpp
@@ -0,0 +1,85 @@
+/*
+ * 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_results.hpp"
+
+enum FsIDirectoryCmd : u32 {
+    FsIDirectoryCmd_Read = 0,
+    FsIDirectoryCmd_GetEntryCount = 1,
+};
+
+class IDirectory {
+    public:
+        virtual ~IDirectory() {}
+        
+        Result Read(uint64_t *out_count, FsDirectoryEntry *out_entries, uint64_t max_entries) {
+            if (out_count == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            if (max_entries == 0) {
+                *out_count = 0;
+                return 0;
+            }
+            if (out_entries == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            return ReadImpl(out_count, out_entries, max_entries);
+        }
+        
+        Result GetEntryCount(uint64_t *count) {
+            if (count == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            return GetEntryCountImpl(count);
+        }
+        
+    protected:
+        /* ...? */
+    private:
+        virtual Result ReadImpl(uint64_t *out_count, FsDirectoryEntry *out_entries, uint64_t max_entries) = 0;
+        virtual Result GetEntryCountImpl(uint64_t *count) = 0;
+};
+
+class IDirectoryInterface : public IServiceObject {
+    private:
+        std::unique_ptr<IDirectory> base_dir;
+    public:
+        IDirectoryInterface(IDirectory *d) : base_dir(d) {
+            /* ... */
+        };
+        IDirectoryInterface(std::unique_ptr<IDirectory> d) : base_dir(std::move(d)) {
+            /* ... */
+        };
+
+    private:
+        /* Actual command API. */
+        virtual Result Read(OutBuffer<FsDirectoryEntry> buffer, Out<u64> out_count) final {
+            return this->base_dir->Read(out_count.GetPointer(), buffer.buffer, buffer.num_elements);
+        };
+        virtual Result GetEntryCount(Out<u64> out_count) final {
+           return this->base_dir->GetEntryCount(out_count.GetPointer());
+        };
+    public:
+        DEFINE_SERVICE_DISPATCH_TABLE {
+            /* 1.0.0- */
+            MakeServiceCommandMeta<FsIDirectoryCmd_Read, &IDirectoryInterface::Read>(),
+            MakeServiceCommandMeta<FsIDirectoryCmd_GetEntryCount, &IDirectoryInterface::GetEntryCount>(),
+        };
+};
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp
new file mode 100644
index 000000000..2a6057179
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_ifile.hpp
@@ -0,0 +1,142 @@
+/*
+ * 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_results.hpp"
+
+enum FsIFileCmd : u32 {
+    FsIFileCmd_Read = 0,
+    FsIFileCmd_Write = 1,
+    FsIFileCmd_Flush = 2,
+    FsIFileCmd_SetSize = 3,
+    FsIFileCmd_GetSize = 4,
+    FsIFileCmd_OperateRange = 5,
+};
+    
+class IFile {
+    public:
+        virtual ~IFile() {}
+        
+        Result Read(uint64_t *out, uint64_t offset, void *buffer, uint64_t size, uint32_t flags) {
+            (void)(flags);
+            if (out == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            if (size == 0) {
+                *out = 0;
+                return 0;
+            }
+            if (buffer == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            return ReadImpl(out, offset, buffer, size);
+        }
+        
+        Result GetSize(uint64_t *out) {
+            if (out == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            return GetSizeImpl(out);
+        }
+        
+        Result Flush() {
+            return FlushImpl();
+        }
+        
+        Result Write(uint64_t offset, void *buffer, uint64_t size, uint32_t flags) {
+            if (size == 0) {
+                return 0;
+            }
+            if (buffer == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            const bool flush = (flags & 1) != 0;
+            return WriteImpl(offset, buffer, size, flush);
+        }
+        
+        Result Write(uint64_t offset, void *buffer, uint64_t size) {
+            return Write(offset, buffer, size, false);
+        }
+        
+        Result SetSize(uint64_t size) {
+            return SetSizeImpl(size);
+        }
+        
+        Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) {
+            if (operation_type != 3) {
+                return OperateRangeImpl(operation_type, offset, size, out_range_info);
+            }
+            return ResultFsUnsupportedOperation;
+        }
+        
+    protected:
+        /* ...? */
+    private:
+        virtual Result ReadImpl(u64 *out, u64 offset, void *buffer, u64 size) = 0;
+        virtual Result GetSizeImpl(u64 *out) = 0;
+        virtual Result FlushImpl() = 0;
+        virtual Result WriteImpl(u64 offset, void *buffer, u64 size, bool flush) = 0;
+        virtual Result SetSizeImpl(u64 size) = 0;
+        virtual Result OperateRangeImpl(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
+};
+
+class IFileInterface : public IServiceObject {
+    private:
+        std::unique_ptr<IFile> base_file;
+    public:
+        IFileInterface(IFile *f) : base_file(f) {
+            /* ... */
+        };
+        IFileInterface(std::unique_ptr<IFile> f) : base_file(std::move(f)) {
+            /* ... */
+        };
+
+    private:
+        /* Actual command API. */
+        virtual Result Read(OutBuffer<u8, BufferType_Type1> buffer, Out<u64> out_read, u64 offset, u64 size, u32 read_flags) final {
+            return this->base_file->Read(out_read.GetPointer(), offset, buffer.buffer, std::min(buffer.num_elements, size), read_flags);
+        };
+        virtual Result Write(InBuffer<u8, BufferType_Type1> buffer, u64 offset, u64 size, u32 write_flags) final {
+           return this->base_file->Write(offset, buffer.buffer, std::min(buffer.num_elements, size), write_flags);
+        };
+        virtual Result Flush() final {
+            return this->base_file->Flush();
+        };
+        virtual Result SetSize(u64 size) final {
+            return this->base_file->SetSize(size);
+        };
+        virtual Result GetSize(Out<u64> size) final {
+            return this->base_file->GetSize(size.GetPointer());
+        };
+        virtual Result OperateRange(Out<FsRangeInfo> range_info, u32 operation_type, u64 offset, u64 size) final {
+            return this->base_file->OperateRange(operation_type, offset, size, range_info.GetPointer());
+        };
+    public:
+        DEFINE_SERVICE_DISPATCH_TABLE {
+            /* 1.0.0- */
+            MakeServiceCommandMeta<FsIFileCmd_Read, &IFileInterface::Read>(),
+            MakeServiceCommandMeta<FsIFileCmd_Write, &IFileInterface::Write>(),
+            MakeServiceCommandMeta<FsIFileCmd_Flush, &IFileInterface::Flush>(),
+            MakeServiceCommandMeta<FsIFileCmd_SetSize, &IFileInterface::SetSize>(),
+            MakeServiceCommandMeta<FsIFileCmd_GetSize, &IFileInterface::GetSize>(),
+            
+            /* 4.0.0- */
+            MakeServiceCommandMeta<FsIFileCmd_OperateRange, &IFileInterface::OperateRange, FirmwareVersion_400>(),
+        };
+};
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_ifilesystem.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_ifilesystem.hpp
new file mode 100644
index 000000000..bc855a4c1
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_ifilesystem.hpp
@@ -0,0 +1,285 @@
+/*
+ * 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_results.hpp"
+#include "fs_filesystem_types.hpp"
+#include "fs_ifile.hpp"
+#include "fs_idirectory.hpp"
+
+enum FsIFileSystemCmd : u32 {
+    /* 1.0.0+ */
+    FsIFileSystemCmd_CreateFile = 0,
+    FsIFileSystemCmd_DeleteFile = 1,
+    FsIFileSystemCmd_CreateDirectory = 2,
+    FsIFileSystemCmd_DeleteDirectory = 3,
+    FsIFileSystemCmd_DeleteDirectoryRecursively = 4,
+    FsIFileSystemCmd_RenameFile = 5,
+    FsIFileSystemCmd_RenameDirectory = 6,
+    FsIFileSystemCmd_GetEntryType = 7,
+    FsIFileSystemCmd_OpenFile = 8,
+    FsIFileSystemCmd_OpenDirectory = 9,
+    FsIFileSystemCmd_Commit = 10,
+    FsIFileSystemCmd_GetFreeSpaceSize = 11,
+    FsIFileSystemCmd_GetTotalSpaceSize = 12,
+    
+    /* 3.0.0+ */
+    FsIFileSystemCmd_CleanDirectoryRecursively = 13,
+    FsIFileSystemCmd_GetFileTimeStampRaw = 14,
+    
+    /* 4.0.0+ */
+    FsIFileSystemCmd_QueryEntry = 15,
+};
+    
+class IFile;
+class IDirectory;
+
+class IFileSystem {
+    public:
+        virtual ~IFileSystem() {}
+        
+        Result CreateFile(const char *path, uint64_t size, int flags) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return CreateFileImpl(path, size, flags);
+        }
+        
+        Result DeleteFile(const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return DeleteFileImpl(path);                
+        }
+        
+        Result CreateDirectory(const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return CreateDirectoryImpl(path);                
+        }
+        
+        Result DeleteDirectory(const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return DeleteDirectoryImpl(path);                
+        }
+        
+        Result DeleteDirectoryRecursively(const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return DeleteDirectoryRecursivelyImpl(path);                
+        }
+        
+        Result RenameFile(const char *old_path, const char *new_path) {
+            if (old_path == nullptr || new_path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return RenameFileImpl(old_path, new_path);
+        }
+        
+        Result RenameDirectory(const char *old_path, const char *new_path) {
+            if (old_path == nullptr || new_path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return RenameDirectoryImpl(old_path, new_path);
+        }
+        
+        Result GetEntryType(DirectoryEntryType *out, const char *path) {
+            if (out == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return GetEntryTypeImpl(out, path);
+        }
+        
+        Result OpenFile(std::unique_ptr<IFile> *out_file, const char *path, OpenMode mode) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            if (out_file == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            if (!(mode & OpenMode_ReadWrite)) {
+                return ResultFsInvalidArgument;
+            }
+            if (mode & ~OpenMode_All) {
+                return ResultFsInvalidArgument;
+            }
+            return OpenFileImpl(out_file, path, mode);
+        }
+        
+        Result OpenDirectory(std::unique_ptr<IDirectory> *out_dir, const char *path, DirectoryOpenMode mode) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            if (out_dir == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            if (!(mode & DirectoryOpenMode_All)) {
+                return ResultFsInvalidArgument;
+            }
+            if (mode & ~DirectoryOpenMode_All) {
+                return ResultFsInvalidArgument;
+            }
+            return OpenDirectory(out_dir, path, mode);
+        }
+        
+        Result Commit() {
+            return CommitImpl();
+        }
+        
+        Result GetFreeSpaceSize(uint64_t *out, const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            if (out == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            return GetFreeSpaceSizeImpl(out, path);
+        }
+        
+        Result GetTotalSpaceSize(uint64_t *out, const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            if (out == nullptr) {
+                return ResultFsNullptrArgument;
+            }
+            return GetTotalSpaceSizeImpl(out, path);
+        }
+        
+        Result CleanDirectoryRecursively(const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return CleanDirectoryRecursivelyImpl(path);                
+        }
+        
+        Result GetFileTimeStampRaw(FsTimeStampRaw *out, const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            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, const char *path) {
+            if (path == nullptr) {
+                return ResultFsInvalidPath;
+            }
+            return QueryEntryImpl(out, out_size, in, in_size, query, path);
+        }
+        
+        
+    protected:
+        /* ...? */
+    private:
+        virtual Result CreateFileImpl(const char *path, uint64_t size, int flags) = 0;
+        virtual Result DeleteFileImpl(const char *path) = 0;
+        virtual Result CreateDirectoryImpl(const char *path) = 0;
+        virtual Result DeleteDirectoryImpl(const char *path) = 0;
+        virtual Result DeleteDirectoryRecursivelyImpl(const char *path) = 0;
+        virtual Result RenameFileImpl(const char *old_path, const char *new_path) = 0;
+        virtual Result RenameDirectoryImpl(const char *old_path, const char *new_path) = 0;
+        virtual Result GetEntryTypeImpl(DirectoryEntryType *out, const char *path) = 0;
+        virtual Result OpenFileImpl(std::unique_ptr<IFile> *out_file, const char *path, OpenMode mode) = 0;
+        virtual Result OpenDirectoryImpl(std::unique_ptr<IDirectory> *out_dir, const char *path, DirectoryOpenMode mode) = 0;
+        virtual Result CommitImpl() = 0;
+        
+        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, const char *path) {
+            (void)(out);
+            (void)(path);
+            return ResultFsNotImplemented;
+        }
+        
+        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, const char *path) {
+            (void)(out);
+            (void)(path);
+            return ResultFsNotImplemented;
+        }
+        
+        virtual Result CleanDirectoryRecursivelyImpl(const char *path) = 0;
+        
+        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, const char *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, const char *path) {
+            (void)(out);
+            (void)(out_size);
+            (void)(in);
+            (void)(in_size);
+            (void)(query);
+            (void)(path);
+            return ResultFsNotImplemented;
+        }
+};
+
+class IFileSystemInterface : public IServiceObject {
+    private:
+        std::unique_ptr<IFileSystem> base_fs;
+    public:
+        IFileSystemInterface(IFileSystem *fs) : base_fs(fs) {
+            /* ... */
+        };
+        IFileSystemInterface(std::unique_ptr<IFileSystem> fs) : base_fs(std::move(fs)) {
+            /* ... */
+        };
+        
+    private:
+        /* Actual command API. */
+        /* TODO.... */
+    public:
+        DEFINE_SERVICE_DISPATCH_TABLE {
+            /* 1.0.0- */
+            /*
+                MakeServiceCommandMeta<FsIFileSystemCmd_CreateFile, &IFileSystemInterface::CreateFile>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_DeleteFile, &IFileSystemInterface::DeleteFile>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_CreateDirectory, &IFileSystemInterface::CreateDirectory>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_DeleteDirectory, &IFileSystemInterface::DeleteDirectory>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_DeleteDirectoryRecursively, &IFileSystemInterface::DeleteDirectoryRecursively>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_RenameFile, &IFileSystemInterface::RenameFile>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_RenameDirectory, &IFileSystemInterface::RenameDirectory>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_GetEntryType, &IFileSystemInterface::GetEntryType>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_OpenFile, &IFileSystemInterface::OpenFile>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_OpenDirectory, &IFileSystemInterface::OpenDirectory>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_Commit, &IFileSystemInterface::Commit>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_GetFreeSpaceSize, &IFileSystemInterface::GetFreeSpaceSize>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_GetTotalSpaceSize, &IFileSystemInterface::GetTotalSpaceSize>(),
+            */
+
+            /* 3.0.0- */
+            /*
+                MakeServiceCommandMeta<FsIFileSystemCmd_CleanDirectoryRecursively, &IFileSystemInterface::CleanDirectoryRecursively, FirmwareVersion_300>(),
+                MakeServiceCommandMeta<FsIFileSystemCmd_GetFileTimeStampRaw, &IFileSystemInterface::GetFileTimeStampRaw, FirmwareVersion_300>(),
+            */
+
+            /* 4.0.0- */
+            /* <FsIFileSystemCmd_QueryEntry, &IFileSystemInterface::QueryEntry, FirmwareVersion_400>(), */
+        };
+};
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_istorage.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_istorage.hpp
index 77e58302d..be019ae12 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fs_istorage.hpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_istorage.hpp
@@ -19,6 +19,8 @@
 #include <stratosphere.hpp>
 #include "fs_shim.h"
 
+#include "fs_results.hpp"
+
 #include "../debug.hpp"
 
 enum FsIStorageCmd : u32 {
@@ -33,13 +35,17 @@ enum FsIStorageCmd : u32 {
 class IStorage {
     public:
         virtual ~IStorage();
-                
+
         virtual Result Read(void *buffer, size_t size, u64 offset) = 0;
         virtual Result Write(void *buffer, size_t size, u64 offset) = 0;
         virtual Result Flush() = 0;
         virtual Result SetSize(u64 size) = 0;
         virtual Result GetSize(u64 *out_size) = 0;
         virtual Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
+
+        static inline bool IsRangeValid(uint64_t offset, uint64_t size, uint64_t total_size) {
+            return size <= total_size && offset <= total_size - size;
+        }
 };
 
 class IStorageInterface : public IServiceObject {
@@ -49,7 +55,7 @@ class IStorageInterface : public IServiceObject {
         IStorageInterface(IStorage *s) : base_storage(s) {
             /* ... */
         };
-                
+
         ~IStorageInterface() {
             delete base_storage;
         };
@@ -95,14 +101,14 @@ class IROStorage : public IStorage {
             (void)(buffer);
             (void)(offset);
             (void)(size);
-            return 0x313802;
+            return ResultFsUnsupportedOperation;
         };
         virtual Result Flush() final {
             return 0x0;
         };
         virtual Result SetSize(u64 size) final {
             (void)(size);
-            return 0x313802;
+            return ResultFsUnsupportedOperation;
         };
         virtual Result GetSize(u64 *out_size) = 0;
         virtual Result OperateRange(u32 operation_type, u64 offset, u64 size, FsRangeInfo *out_range_info) = 0;
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fs_results.hpp b/stratosphere/ams_mitm/source/fs_mitm/fs_results.hpp
new file mode 100644
index 000000000..de45e90f9
--- /dev/null
+++ b/stratosphere/ams_mitm/source/fs_mitm/fs_results.hpp
@@ -0,0 +1,32 @@
+/*
+ * 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>
+
+static constexpr u32 Module_Fs = 2;
+
+static constexpr Result ResultFsNotImplemented       = MAKERESULT(Module_Fs, 3001);
+static constexpr Result ResultFsOutOfRange           = MAKERESULT(Module_Fs, 3005);
+
+static constexpr Result ResultFsInvalidArgument      = MAKERESULT(Module_Fs, 6001);
+static constexpr Result ResultFsInvalidPath          = MAKERESULT(Module_Fs, 6002);
+
+static constexpr Result ResultFsInvalidOffset        = MAKERESULT(Module_Fs, 6061);
+static constexpr Result ResultFsInvalidSize          = MAKERESULT(Module_Fs, 6062);
+static constexpr Result ResultFsNullptrArgument      = MAKERESULT(Module_Fs, 6063);
+
+static constexpr Result ResultFsUnsupportedOperation = MAKERESULT(Module_Fs, 6300);
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.cpp b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.cpp
index fe81b7eeb..a82c733de 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.cpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_layeredrom.cpp
@@ -17,6 +17,8 @@
 #include <switch.h>
 #include <stratosphere.hpp>
 
+#include "fs_results.hpp"
+
 #include "fsmitm_layeredrom.hpp"
 #include "../utils.hpp"
 #include "../debug.hpp"
@@ -54,7 +56,7 @@ Result LayeredRomFS::Read(void *buffer, size_t size, u64 offset)  {
     /* Validate size. */
     u64 virt_size = (*this->p_source_infos)[this->p_source_infos->size() - 1].virtual_offset + (*this->p_source_infos)[this->p_source_infos->size() - 1].size;
     if (offset >= virt_size) {
-        return 0x2F5A02;
+        return ResultFsInvalidOffset;
     }
     if (virt_size - offset < size) {
         size = virt_size - offset;
diff --git a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
index 40b4b70f6..79d490981 100644
--- a/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
+++ b/stratosphere/ams_mitm/source/fs_mitm/fsmitm_service.cpp
@@ -28,6 +28,8 @@
 #include "fsmitm_romstorage.hpp"
 #include "fsmitm_layeredrom.hpp"
 
+#include "fs_ifilesystem.hpp"
+
 #include "../debug.hpp"
 
 static HosMutex g_StorageCacheLock;