fs.mitm: implement ifilesystem wrapper

stratosphere/ams_mitm/source/fs_mitm/fs_ifilesystem.hpp

@@ -20,6 +20,8 @@
 
 #include "fs_results.hpp"
 #include "fs_filesystem_types.hpp"
+#include "fs_path_utils.hpp"
+
 #include "fs_ifile.hpp"
 #include "fs_idirectory.hpp"
 
@@ -38,85 +40,58 @@ enum FsIFileSystemCmd : u32 {
     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;
-            }
+
+        Result CreateFile(FsPath &path, uint64_t size, int flags) {
             return CreateFileImpl(path, size, flags);
         }
-        
-        Result DeleteFile(const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
-            return DeleteFileImpl(path);                
+
+        Result DeleteFile(FsPath &path) {
+            return DeleteFileImpl(path);
         }
-        
-        Result CreateDirectory(const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
-            return CreateDirectoryImpl(path);                
+
+        Result CreateDirectory(FsPath &path) {
+            return CreateDirectoryImpl(path);
         }
-        
-        Result DeleteDirectory(const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
-            return DeleteDirectoryImpl(path);                
+
+        Result DeleteDirectory(FsPath &path) {
+            return DeleteDirectoryImpl(path);
         }
-        
-        Result DeleteDirectoryRecursively(const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
-            return DeleteDirectoryRecursivelyImpl(path);                
+
+        Result DeleteDirectoryRecursively(FsPath &path) {
+            return DeleteDirectoryRecursivelyImpl(path);
         }
-        
-        Result RenameFile(const char *old_path, const char *new_path) {
-            if (old_path == nullptr || new_path == nullptr) {
-                return ResultFsInvalidPath;
-            }
+
+        Result RenameFile(FsPath &old_path, FsPath &new_path) {
             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;
-            }
+
+        Result RenameDirectory(FsPath &old_path, FsPath &new_path) {
             return RenameDirectoryImpl(old_path, new_path);
         }
-        
-        Result GetEntryType(DirectoryEntryType *out, const char *path) {
+
+        Result GetEntryType(DirectoryEntryType *out, FsPath &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;
-            }
+
+        Result OpenFile(std::unique_ptr<IFile> &out_file, FsPath &path, OpenMode mode) {
             if (out_file == nullptr) {
                 return ResultFsNullptrArgument;
             }
@@ -128,11 +103,8 @@ class IFileSystem {
             }
             return OpenFileImpl(out_file, path, mode);
         }
-        
-        Result OpenDirectory(std::unique_ptr<IDirectory> *out_dir, const char *path, DirectoryOpenMode mode) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
+
+        Result OpenDirectory(std::unique_ptr<IDirectory> &out_dir, FsPath &path, DirectoryOpenMode mode) {
             if (out_dir == nullptr) {
                 return ResultFsNullptrArgument;
             }
@@ -144,92 +116,77 @@ class IFileSystem {
             }
             return OpenDirectory(out_dir, path, mode);
         }
-        
+
         Result Commit() {
             return CommitImpl();
         }
-        
-        Result GetFreeSpaceSize(uint64_t *out, const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
+
+        Result GetFreeSpaceSize(uint64_t *out, FsPath &path) {
             if (out == nullptr) {
                 return ResultFsNullptrArgument;
             }
             return GetFreeSpaceSizeImpl(out, path);
         }
-        
-        Result GetTotalSpaceSize(uint64_t *out, const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
+
+        Result GetTotalSpaceSize(uint64_t *out, FsPath &path) {
             if (out == nullptr) {
                 return ResultFsNullptrArgument;
             }
             return GetTotalSpaceSizeImpl(out, path);
         }
-        
-        Result CleanDirectoryRecursively(const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
-            return CleanDirectoryRecursivelyImpl(path);                
+
+        Result CleanDirectoryRecursively(FsPath &path) {
+            return CleanDirectoryRecursivelyImpl(path);
         }
-        
-        Result GetFileTimeStampRaw(FsTimeStampRaw *out, const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
+
+        Result GetFileTimeStampRaw(FsTimeStampRaw *out, 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, const char *path) {
-            if (path == nullptr) {
-                return ResultFsInvalidPath;
-            }
+
+        Result QueryEntry(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, FsPath &path) {
             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 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 CommitImpl() = 0;
-        
-        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, const char *path) {
+
+        virtual Result GetFreeSpaceSizeImpl(uint64_t *out, FsPath &path) {
             (void)(out);
             (void)(path);
             return ResultFsNotImplemented;
         }
-        
-        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, const char *path) {
+
+        virtual Result GetTotalSpaceSizeImpl(uint64_t *out, FsPath &path) {
             (void)(out);
             (void)(path);
             return ResultFsNotImplemented;
         }
-        
-        virtual Result CleanDirectoryRecursivelyImpl(const char *path) = 0;
-        
-        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, const char *path) {
+
+        virtual Result CleanDirectoryRecursivelyImpl(FsPath &path) = 0;
+
+        virtual Result GetFileTimeStampRawImpl(FsTimeStampRaw *out, 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, const char *path) {
+
+        virtual Result QueryEntryImpl(char *out, uint64_t out_size, const char *in, uint64_t in_size, int query, FsPath &path) {
             (void)(out);
             (void)(out_size);
             (void)(in);
@@ -250,36 +207,225 @@ class IFileSystemInterface : public IServiceObject {
         IFileSystemInterface(std::unique_ptr<IFileSystem> fs) : base_fs(std::move(fs)) {
             /* ... */
         };
-        
+
     private:
         /* Actual command API. */
-        /* TODO.... */
+        virtual Result CreateFile(InPointer<char> in_path, uint64_t size, int flags) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->CreateFile(path, size, flags);
+        }
+
+        virtual Result DeleteFile(InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->DeleteFile(path);
+        }
+
+        virtual Result CreateDirectory(InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->CreateDirectory(path);
+        }
+
+        virtual Result DeleteDirectory(InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->DeleteDirectory(path);
+        }
+
+        virtual Result DeleteDirectoryRecursively(InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->DeleteDirectoryRecursively(path);
+        }
+
+        virtual Result RenameFile(InPointer<char> in_old_path, InPointer<char> in_new_path) final {
+            FsPath old_path;
+            FsPath new_path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&old_path, in_old_path.pointer)))) {
+                return rc;
+            }
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&new_path, in_new_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->RenameFile(old_path, new_path);
+        }
+
+        virtual Result RenameDirectory(InPointer<char> in_old_path, InPointer<char> in_new_path) final {
+            FsPath old_path;
+            FsPath new_path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&old_path, in_old_path.pointer)))) {
+                return rc;
+            }
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&new_path, in_new_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->RenameDirectory(old_path, new_path);
+        }
+
+
+        virtual Result GetEntryType(Out<u32> out_type, InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            DirectoryEntryType type;
+            rc = this->base_fs->GetEntryType(&type, path);
+            if (R_SUCCEEDED(rc)) {
+                out_type.SetValue(type);
+            }
+            return rc;
+        }
+
+        virtual Result OpenFile(Out<std::shared_ptr<IFileInterface>> out_intf, InPointer<char> in_path, uint32_t mode) final {
+            FsPath path;
+            std::unique_ptr<IFile> out_file;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            rc = this->base_fs->OpenFile(out_file, path, static_cast<OpenMode>(mode));
+            if (R_SUCCEEDED(rc)) {
+                out_intf.SetValue(std::make_shared<IFileInterface>(std::move(out_file)));
+                /* TODO: Nintendo checks allocation success here, should we?. */
+            }
+            return rc;
+        }
+
+        virtual Result OpenDirectory(Out<std::shared_ptr<IDirectoryInterface>> out_intf, InPointer<char> in_path, uint32_t mode) final {
+            FsPath path;
+            std::unique_ptr<IDirectory> out_dir;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            rc = this->base_fs->OpenDirectory(out_dir, path, static_cast<DirectoryOpenMode>(mode));
+            if (R_SUCCEEDED(rc)) {
+                out_intf.SetValue(std::make_shared<IDirectoryInterface>(std::move(out_dir)));
+                /* TODO: Nintendo checks allocation success here, should we?. */
+            }
+            return rc;
+        }
+
+        virtual Result Commit() final {
+            return this->base_fs->Commit();
+        }
+
+        virtual Result GetFreeSpaceSize(Out<uint64_t> out_size, InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->GetFreeSpaceSize(out_size.GetPointer(), path);
+        }
+
+        virtual Result GetTotalSpaceSize(Out<uint64_t> out_size, InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->GetTotalSpaceSize(out_size.GetPointer(), path);
+        }
+
+        virtual Result CleanDirectoryRecursively(InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->CleanDirectoryRecursively(path);
+        }
+
+        virtual Result GetFileTimeStampRaw(Out<FsTimeStampRaw> out_timestamp, InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->GetFileTimeStampRaw(out_timestamp.GetPointer(), path);
+        }
+
+        virtual Result QueryEntry(OutBuffer<char, BufferType_Type1> out_buffer, InBuffer<char, BufferType_Type1> in_buffer, int query, InPointer<char> in_path) final {
+            FsPath path;
+
+            Result rc;
+            if (R_FAILED((rc = FsPathUtils::ConvertPathForServiceObject(&path, in_path.pointer)))) {
+                return rc;
+            }
+
+            return this->base_fs->QueryEntry(out_buffer.buffer, out_buffer.num_elements, in_buffer.buffer, in_buffer.num_elements, query, path);
+        }
     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>(),
-            */
+            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>(),
-            */
+            MakeServiceCommandMeta<FsIFileSystemCmd_CleanDirectoryRecursively, &IFileSystemInterface::CleanDirectoryRecursively, FirmwareVersion_300>(),
+            MakeServiceCommandMeta<FsIFileSystemCmd_GetFileTimeStampRaw, &IFileSystemInterface::GetFileTimeStampRaw, FirmwareVersion_300>(),
 
             /* 4.0.0- */
-            /* <FsIFileSystemCmd_QueryEntry, &IFileSystemInterface::QueryEntry, FirmwareVersion_400>(), */
+            MakeServiceCommandMeta<FsIFileSystemCmd_QueryEntry, &IFileSystemInterface::QueryEntry, FirmwareVersion_400>(),
         };
 };

stratosphere/ams_mitm/source/fs_mitm/fs_path_utils.cpp

@@ -0,0 +1,73 @@
+/*
+ * 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 "fs_path_utils.hpp"
+#include "fs_results.hpp"
+
+Result FsPathUtils::VerifyPath(const char *path, size_t max_path_len, size_t max_name_len) {
+    const char *cur = path;
+    size_t name_len = 0;
+
+    for (size_t path_len = 0; path_len <= max_path_len && name_len <= max_name_len; path_len++) {
+        const char c = *cur;
+        /* If terminated, we're done. */
+        if (c == 0) {
+            return 0;
+        }
+
+        /* TODO: Nintendo converts the path from utf-8 to utf-32, one character at a time. */
+        /* We should do this. */
+
+        /* Banned characters: :*?<>| */
+        if (c == ':' || c == '*' || c == '?' || c == '<' || c == '>' || c == '|') {
+            return ResultFsInvalidCharacter;
+        }
+
+        name_len++;
+        /* Check for separator. */
+        if (c == '/' || c == '\\') {
+            name_len = 0;
+        }
+    }
+
+    return ResultFsTooLongPath;
+}
+
+Result FsPathUtils::ConvertPathForServiceObject(FsPath *out, const char *path) {
+    /* Check for nullptr. */
+    if (out == nullptr || path == nullptr) {
+        return ResultFsInvalidPath;
+    }
+
+    /* Copy string, NULL terminate. */
+    /* NOTE: Nintendo adds an extra char at 0x301 for NULL terminator */
+    /* But then forces 0x300 to NULL anyway... */
+    std::strncpy(out->str, path, sizeof(out->str) - 1);
+    out->str[sizeof(out->str)-1] = 0;
+
+    /* Replace any instances of \ with / */
+    for (size_t i = 0; i < sizeof(out->str); i++) {
+        if (out->str[i] == '\\') {
+            out->str[i] = '/';
+        }
+    }
+
+    /* Nintendo allows some liberties if the path is a windows path. Who knows why... */
+    const auto prefix_len = FsPathUtils::IsWindowsAbsolutePath(path) ? 2 : 0;
+    const size_t max_len = (FS_MAX_PATH-1) - prefix_len;
+    return FsPathUtils::VerifyPath(out->str + prefix_len, max_len, max_len);
+}

stratosphere/ams_mitm/source/fs_mitm/fs_path_utils.hpp

@@ -0,0 +1,34 @@
+/*
+ * 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>
+
+struct FsPath {
+    char str[FS_MAX_PATH];
+};
+
+class FsPathUtils {
+    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);
+
+        static bool IsWindowsAbsolutePath(const char *path) {
+            /* Nintendo uses this in path comparisons... */
+            return (('a' <= path[0] && path[0] <= 'z') || (('A' <= path[0] && path[0] <= 'Z'))) &&
+                    path[0] != 0 && path[1] == ':';
+        }
+};

stratosphere/ams_mitm/source/fs_mitm/fs_results.hpp

@@ -24,6 +24,8 @@ static constexpr Result ResultFsOutOfRange           = MAKERESULT(Module_Fs, 300
 
 static constexpr Result ResultFsInvalidArgument      = MAKERESULT(Module_Fs, 6001);
 static constexpr Result ResultFsInvalidPath          = MAKERESULT(Module_Fs, 6002);
+static constexpr Result ResultFsTooLongPath          = MAKERESULT(Module_Fs, 6003);
+static constexpr Result ResultFsInvalidCharacter     = MAKERESULT(Module_Fs, 6004);
 
 static constexpr Result ResultFsInvalidOffset        = MAKERESULT(Module_Fs, 6061);
 static constexpr Result ResultFsInvalidSize          = MAKERESULT(Module_Fs, 6062);