Virtual Filesystem (#597)

* Add VfsFile and VfsDirectory classes

* Finish abstract Vfs classes

* Implement RealVfsFile (computer fs backend)

* Finish RealVfsFile and RealVfsDirectory

* Finished OffsetVfsFile

* More changes

* Fix import paths

* Major refactor

* Remove double const

* Use experimental/filesystem or filesystem depending on compiler

* Port partition_filesystem

* More changes

* More Overhaul

* FSP_SRV fixes

* Fixes and testing

* Try to get filesystem to compile

* Filesystem on linux

* Remove std::filesystem and document/test

* Compile fixes

* Missing include

* Bug fixes

* Fixes

* Rename v_file and v_dir

* clang-format fix

* Rename NGLOG_* to LOG_*

* Most review changes

* Fix TODO

* Guess 'main' to be Directory by filename

5 files changed, 405 insertions, 71 deletions

diff --git a/src/core/hle/service/am/am.cpp b/src/core/hle/service/am/am.cpp
index a871b3eaa..7bb13c735 100644
--- a/src/core/hle/service/am/am.cpp
+++ b/src/core/hle/service/am/am.cpp
@@ -621,7 +621,7 @@ void IApplicationFunctions::EnsureSaveData(Kernel::HLERequestContext& ctx) {
     IPC::ResponseBuilder rb{ctx, 4};
 
     FileSys::Path unused;
-    auto savedata = FileSystem::OpenFileSystem(FileSystem::Type::SaveData, unused);
+    auto savedata = FileSystem::OpenFileSystem(FileSystem::Type::SaveData);
     if (savedata.Failed()) {
         // Create the save data and return an error indicating that the operation was performed.
         FileSystem::FormatFileSystem(FileSystem::Type::SaveData);
diff --git a/src/core/hle/service/filesystem/filesystem.cpp b/src/core/hle/service/filesystem/filesystem.cpp
index f58b518b6..25810c165 100644
--- a/src/core/hle/service/filesystem/filesystem.cpp
+++ b/src/core/hle/service/filesystem/filesystem.cpp
@@ -2,36 +2,221 @@
 // Licensed under GPLv2 or any later version
 // Refer to the license.txt file included.
 
-#include <boost/container/flat_map.hpp>
+#include "boost/container/flat_map.hpp"
+#include "common/assert.h"
+#include "common/common_paths.h"
 #include "common/file_util.h"
+#include "core/core.h"
+#include "core/file_sys/errors.h"
 #include "core/file_sys/filesystem.h"
-#include "core/file_sys/savedata_factory.h"
-#include "core/file_sys/sdmc_factory.h"
+#include "core/file_sys/vfs.h"
+#include "core/file_sys/vfs_offset.h"
+#include "core/file_sys/vfs_real.h"
+#include "core/hle/kernel/process.h"
 #include "core/hle/service/filesystem/filesystem.h"
 #include "core/hle/service/filesystem/fsp_srv.h"
 
 namespace Service::FileSystem {
 
+// Size of emulated sd card free space, reported in bytes.
+// Just using 32GB because thats reasonable
+// TODO(DarkLordZach): Eventually make this configurable in settings.
+constexpr u64 EMULATED_SD_REPORTED_SIZE = 32000000000;
+
+static FileSys::VirtualDir GetDirectoryRelativeWrapped(FileSys::VirtualDir base,
+                                                       const std::string& dir_name) {
+    if (dir_name == "." || dir_name == "" || dir_name == "/" || dir_name == "\\")
+        return base;
+
+    return base->GetDirectoryRelative(dir_name);
+}
+
+VfsDirectoryServiceWrapper::VfsDirectoryServiceWrapper(FileSys::VirtualDir backing_)
+    : backing(backing_) {}
+
+std::string VfsDirectoryServiceWrapper::GetName() const {
+    return backing->GetName();
+}
+
+ResultCode VfsDirectoryServiceWrapper::CreateFile(const std::string& path, u64 size) const {
+    auto dir = GetDirectoryRelativeWrapped(backing, FileUtil::GetParentPath(path));
+    auto file = dir->CreateFile(FileUtil::GetFilename(path));
+    if (file == nullptr)
+        return ResultCode(-1);
+    if (!file->Resize(size))
+        return ResultCode(-1);
+    return RESULT_SUCCESS;
+}
+
+ResultCode VfsDirectoryServiceWrapper::DeleteFile(const std::string& path) const {
+    auto dir = GetDirectoryRelativeWrapped(backing, FileUtil::GetParentPath(path));
+    if (!backing->DeleteFile(FileUtil::GetFilename(path)))
+        return ResultCode(-1);
+    return RESULT_SUCCESS;
+}
+
+ResultCode VfsDirectoryServiceWrapper::CreateDirectory(const std::string& path) const {
+    auto dir = GetDirectoryRelativeWrapped(backing, FileUtil::GetParentPath(path));
+    if (dir == nullptr && FileUtil::GetFilename(FileUtil::GetParentPath(path)).empty())
+        dir = backing;
+    auto new_dir = dir->CreateSubdirectory(FileUtil::GetFilename(path));
+    if (new_dir == nullptr)
+        return ResultCode(-1);
+    return RESULT_SUCCESS;
+}
+
+ResultCode VfsDirectoryServiceWrapper::DeleteDirectory(const std::string& path) const {
+    auto dir = GetDirectoryRelativeWrapped(backing, FileUtil::GetParentPath(path));
+    if (!dir->DeleteSubdirectory(FileUtil::GetFilename(path)))
+        return ResultCode(-1);
+    return RESULT_SUCCESS;
+}
+
+ResultCode VfsDirectoryServiceWrapper::DeleteDirectoryRecursively(const std::string& path) const {
+    auto dir = GetDirectoryRelativeWrapped(backing, FileUtil::GetParentPath(path));
+    if (!dir->DeleteSubdirectoryRecursive(FileUtil::GetFilename(path)))
+        return ResultCode(-1);
+    return RESULT_SUCCESS;
+}
+
+ResultCode VfsDirectoryServiceWrapper::RenameFile(const std::string& src_path,
+                                                  const std::string& dest_path) const {
+    auto src = backing->GetFileRelative(src_path);
+    if (FileUtil::GetParentPath(src_path) == FileUtil::GetParentPath(dest_path)) {
+        // Use more-optimized vfs implementation rename.
+        if (src == nullptr)
+            return FileSys::ERROR_PATH_NOT_FOUND;
+        if (!src->Rename(FileUtil::GetFilename(dest_path)))
+            return ResultCode(-1);
+        return RESULT_SUCCESS;
+    }
+
+    // Move by hand -- TODO(DarkLordZach): Optimize
+    auto c_res = CreateFile(dest_path, src->GetSize());
+    if (c_res != RESULT_SUCCESS)
+        return c_res;
+
+    auto dest = backing->GetFileRelative(dest_path);
+    ASSERT_MSG(dest != nullptr, "Newly created file with success cannot be found.");
+
+    ASSERT_MSG(dest->WriteBytes(src->ReadAllBytes()) == src->GetSize(),
+               "Could not write all of the bytes but everything else has succeded.");
+
+    if (!src->GetContainingDirectory()->DeleteFile(FileUtil::GetFilename(src_path)))
+        return ResultCode(-1);
+
+    return RESULT_SUCCESS;
+}
+
+ResultCode VfsDirectoryServiceWrapper::RenameDirectory(const std::string& src_path,
+                                                       const std::string& dest_path) const {
+    auto src = GetDirectoryRelativeWrapped(backing, src_path);
+    if (FileUtil::GetParentPath(src_path) == FileUtil::GetParentPath(dest_path)) {
+        // Use more-optimized vfs implementation rename.
+        if (src == nullptr)
+            return FileSys::ERROR_PATH_NOT_FOUND;
+        if (!src->Rename(FileUtil::GetFilename(dest_path)))
+            return ResultCode(-1);
+        return RESULT_SUCCESS;
+    }
+
+    // TODO(DarkLordZach): Implement renaming across the tree (move).
+    ASSERT_MSG(false,
+               "Could not rename directory with path \"{}\" to new path \"{}\" because parent dirs "
+               "don't match -- UNIMPLEMENTED",
+               src_path, dest_path);
+
+    return ResultCode(-1);
+}
+
+ResultVal<FileSys::VirtualFile> VfsDirectoryServiceWrapper::OpenFile(const std::string& path,
+                                                                     FileSys::Mode mode) const {
+    auto file = backing->GetFileRelative(path);
+    if (file == nullptr)
+        return FileSys::ERROR_PATH_NOT_FOUND;
+
+    if ((static_cast<u32>(mode) & static_cast<u32>(FileSys::Mode::Append)) != 0) {
+        return MakeResult<FileSys::VirtualFile>(
+            std::make_shared<FileSys::OffsetVfsFile>(file, 0, file->GetSize()));
+    }
+
+    return MakeResult<FileSys::VirtualFile>(file);
+}
+
+ResultVal<FileSys::VirtualDir> VfsDirectoryServiceWrapper::OpenDirectory(const std::string& path) {
+    auto dir = GetDirectoryRelativeWrapped(backing, path);
+    if (dir == nullptr)
+        return ResultCode(-1);
+    return MakeResult(dir);
+}
+
+u64 VfsDirectoryServiceWrapper::GetFreeSpaceSize() const {
+    if (backing->IsWritable())
+        return EMULATED_SD_REPORTED_SIZE;
+
+    return 0;
+}
+
+ResultVal<FileSys::EntryType> VfsDirectoryServiceWrapper::GetEntryType(
+    const std::string& path) const {
+    auto dir = GetDirectoryRelativeWrapped(backing, FileUtil::GetParentPath(path));
+    if (dir == nullptr)
+        return ResultCode(-1);
+    auto filename = FileUtil::GetFilename(path);
+    if (dir->GetFile(filename) != nullptr)
+        return MakeResult(FileSys::EntryType::File);
+    if (dir->GetSubdirectory(filename) != nullptr)
+        return MakeResult(FileSys::EntryType::Directory);
+    return ResultCode(-1);
+}
+
+// A deferred filesystem for nand save data.
+// This must be deferred because the directory is dependent on title id, which is not set at
+// registration time.
+struct SaveDataDeferredFilesystem : DeferredFilesystem {
+protected:
+    FileSys::VirtualDir CreateFilesystem() override {
+        u64 title_id = Core::CurrentProcess()->program_id;
+        // TODO(DarkLordZach): Users
+        u32 user_id = 0;
+        std::string nand_directory = fmt::format(
+            "{}save/{:016X}/{:08X}/", FileUtil::GetUserPath(D_NAND_IDX), title_id, user_id);
+
+        auto savedata =
+            std::make_shared<FileSys::RealVfsDirectory>(nand_directory, FileSys::Mode::Write);
+        return savedata;
+    }
+};
+
 /**
  * Map of registered file systems, identified by type. Once an file system is registered here, it
  * is never removed until UnregisterFileSystems is called.
  */
-static boost::container::flat_map<Type, std::unique_ptr<FileSys::FileSystemFactory>> filesystem_map;
+static boost::container::flat_map<Type, std::unique_ptr<DeferredFilesystem>> filesystem_map;
+static FileSys::VirtualFile filesystem_romfs = nullptr;
 
-ResultCode RegisterFileSystem(std::unique_ptr<FileSys::FileSystemFactory>&& factory, Type type) {
+ResultCode RegisterFileSystem(std::unique_ptr<DeferredFilesystem>&& factory, Type type) {
     auto result = filesystem_map.emplace(type, std::move(factory));
 
     bool inserted = result.second;
     ASSERT_MSG(inserted, "Tried to register more than one system with same id code");
 
     auto& filesystem = result.first->second;
+    LOG_DEBUG(Service_FS, "Registered file system with id code 0x{:08X}", static_cast<u32>(type));
+    return RESULT_SUCCESS;
+}
+
+ResultCode RegisterRomFS(FileSys::VirtualFile filesystem) {
+    ASSERT_MSG(filesystem_romfs == nullptr,
+               "Tried to register more than one system with same id code");
+
+    filesystem_romfs = filesystem;
     LOG_DEBUG(Service_FS, "Registered file system {} with id code 0x{:08X}", filesystem->GetName(),
-              static_cast<u32>(type));
+              static_cast<u32>(Type::RomFS));
     return RESULT_SUCCESS;
 }
 
-ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenFileSystem(Type type,
-                                                                      FileSys::Path& path) {
+ResultVal<FileSys::VirtualDir> OpenFileSystem(Type type) {
     LOG_TRACE(Service_FS, "Opening FileSystem with type={}", static_cast<u32>(type));
 
     auto itr = filesystem_map.find(type);
@@ -40,7 +225,13 @@ ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenFileSystem(Type type,
         return ResultCode(-1);
     }
 
-    return itr->second->Open(path);
+    return MakeResult(itr->second->Get());
+}
+
+ResultVal<FileSys::VirtualFile> OpenRomFS() {
+    if (filesystem_romfs == nullptr)
+        return ResultCode(-1);
+    return MakeResult(filesystem_romfs);
 }
 
 ResultCode FormatFileSystem(Type type) {
@@ -52,21 +243,21 @@ ResultCode FormatFileSystem(Type type) {
         return ResultCode(-1);
     }
 
-    FileSys::Path unused;
-    return itr->second->Format(unused);
+    return itr->second->Get()->GetParentDirectory()->DeleteSubdirectory(
+               itr->second->Get()->GetName())
+               ? RESULT_SUCCESS
+               : ResultCode(-1);
 }
 
 void RegisterFileSystems() {
     filesystem_map.clear();
+    filesystem_romfs = nullptr;
 
-    std::string nand_directory = FileUtil::GetUserPath(D_NAND_IDX);
     std::string sd_directory = FileUtil::GetUserPath(D_SDMC_IDX);
+    auto sdcard = std::make_shared<FileSys::RealVfsDirectory>(sd_directory, FileSys::Mode::Write);
+    RegisterFileSystem(std::make_unique<DeferredFilesystem>(sdcard), Type::SDMC);
 
-    auto savedata = std::make_unique<FileSys::SaveData_Factory>(std::move(nand_directory));
-    RegisterFileSystem(std::move(savedata), Type::SaveData);
-
-    auto sdcard = std::make_unique<FileSys::SDMC_Factory>(std::move(sd_directory));
-    RegisterFileSystem(std::move(sdcard), Type::SDMC);
+    RegisterFileSystem(std::make_unique<SaveDataDeferredFilesystem>(), Type::SaveData);
 }
 
 void InstallInterfaces(SM::ServiceManager& service_manager) {
diff --git a/src/core/hle/service/filesystem/filesystem.h b/src/core/hle/service/filesystem/filesystem.h
index 56d26146e..d3de797f1 100644
--- a/src/core/hle/service/filesystem/filesystem.h
+++ b/src/core/hle/service/filesystem/filesystem.h
@@ -6,6 +6,8 @@
 
 #include <memory>
 #include "common/common_types.h"
+#include "core/file_sys/filesystem.h"
+#include "core/file_sys/vfs.h"
 #include "core/hle/result.h"
 
 namespace FileSys {
@@ -29,12 +31,136 @@ enum class Type {
     SDMC = 3,
 };
 
+// A class that wraps a VfsDirectory with methods that return ResultVal and ResultCode instead of
+// pointers and booleans. This makes using a VfsDirectory with switch services much easier and
+// avoids repetitive code.
+class VfsDirectoryServiceWrapper {
+public:
+    explicit VfsDirectoryServiceWrapper(FileSys::VirtualDir backing);
+
+    /**
+     * Get a descriptive name for the archive (e.g. "RomFS", "SaveData", etc.)
+     */
+    std::string GetName() const;
+
+    /**
+     * Create a file specified by its path
+     * @param path Path relative to the Archive
+     * @param size The size of the new file, filled with zeroes
+     * @return Result of the operation
+     */
+    ResultCode CreateFile(const std::string& path, u64 size) const;
+
+    /**
+     * Delete a file specified by its path
+     * @param path Path relative to the archive
+     * @return Result of the operation
+     */
+    ResultCode DeleteFile(const std::string& path) const;
+
+    /**
+     * Create a directory specified by its path
+     * @param path Path relative to the archive
+     * @return Result of the operation
+     */
+    ResultCode CreateDirectory(const std::string& path) const;
+
+    /**
+     * Delete a directory specified by its path
+     * @param path Path relative to the archive
+     * @return Result of the operation
+     */
+    ResultCode DeleteDirectory(const std::string& path) const;
+
+    /**
+     * Delete a directory specified by its path and anything under it
+     * @param path Path relative to the archive
+     * @return Result of the operation
+     */
+    ResultCode DeleteDirectoryRecursively(const std::string& path) const;
+
+    /**
+     * Rename a File specified by its path
+     * @param src_path Source path relative to the archive
+     * @param dest_path Destination path relative to the archive
+     * @return Result of the operation
+     */
+    ResultCode RenameFile(const std::string& src_path, const std::string& dest_path) const;
+
+    /**
+     * Rename a Directory specified by its path
+     * @param src_path Source path relative to the archive
+     * @param dest_path Destination path relative to the archive
+     * @return Result of the operation
+     */
+    ResultCode RenameDirectory(const std::string& src_path, const std::string& dest_path) const;
+
+    /**
+     * Open a file specified by its path, using the specified mode
+     * @param path Path relative to the archive
+     * @param mode Mode to open the file with
+     * @return Opened file, or error code
+     */
+    ResultVal<FileSys::VirtualFile> OpenFile(const std::string& path, FileSys::Mode mode) const;
+
+    /**
+     * Open a directory specified by its path
+     * @param path Path relative to the archive
+     * @return Opened directory, or error code
+     */
+    ResultVal<FileSys::VirtualDir> OpenDirectory(const std::string& path);
+
+    /**
+     * Get the free space
+     * @return The number of free bytes in the archive
+     */
+    u64 GetFreeSpaceSize() const;
+
+    /**
+     * Get the type of the specified path
+     * @return The type of the specified path or error code
+     */
+    ResultVal<FileSys::EntryType> GetEntryType(const std::string& path) const;
+
+private:
+    FileSys::VirtualDir backing;
+};
+
+// A class that deferres the creation of a filesystem until a later time.
+// This is useful if construction depends on a variable not known when the filesystem is registered.
+// Construct this with a filesystem (VirtualDir) to avoid the deferrence feature or override the
+//     CreateFilesystem method which will be called on first use.
+struct DeferredFilesystem {
+    DeferredFilesystem() = default;
+
+    explicit DeferredFilesystem(FileSys::VirtualDir vfs_directory) : fs(std::move(vfs_directory)) {}
+
+    FileSys::VirtualDir Get() {
+        if (fs == nullptr)
+            fs = CreateFilesystem();
+
+        return fs;
+    }
+
+    virtual ~DeferredFilesystem() = default;
+
+protected:
+    virtual FileSys::VirtualDir CreateFilesystem() {
+        return fs;
+    }
+
+private:
+    FileSys::VirtualDir fs;
+};
+
 /**
  * Registers a FileSystem, instances of which can later be opened using its IdCode.
  * @param factory FileSystem backend interface to use
  * @param type Type used to access this type of FileSystem
  */
-ResultCode RegisterFileSystem(std::unique_ptr<FileSys::FileSystemFactory>&& factory, Type type);
+ResultCode RegisterFileSystem(std::unique_ptr<DeferredFilesystem>&& fs, Type type);
+
+ResultCode RegisterRomFS(FileSys::VirtualFile fs);
 
 /**
  * Opens a file system
@@ -42,8 +168,9 @@ ResultCode RegisterFileSystem(std::unique_ptr<FileSys::FileSystemFactory>&& fact
  * @param path Path to the file system, used with Binary paths
  * @return FileSys::FileSystemBackend interface to the file system
  */
-ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenFileSystem(Type type,
-                                                                      FileSys::Path& path);
+ResultVal<FileSys::VirtualDir> OpenFileSystem(Type type);
+
+ResultVal<FileSys::VirtualFile> OpenRomFS();
 
 /**
  * Formats a file system
diff --git a/src/core/hle/service/filesystem/fsp_srv.cpp b/src/core/hle/service/filesystem/fsp_srv.cpp
index 216bfea0a..26e8a8c88 100644
--- a/src/core/hle/service/filesystem/fsp_srv.cpp
+++ b/src/core/hle/service/filesystem/fsp_srv.cpp
@@ -19,8 +19,8 @@ namespace Service::FileSystem {
 
 class IStorage final : public ServiceFramework<IStorage> {
 public:
-    IStorage(std::unique_ptr<FileSys::StorageBackend>&& backend)
-        : ServiceFramework("IStorage"), backend(std::move(backend)) {
+    IStorage(FileSys::VirtualFile backend_)
+        : ServiceFramework("IStorage"), backend(std::move(backend_)) {
         static const FunctionInfo functions[] = {
             {0, &IStorage::Read, "Read"}, {1, nullptr, "Write"},   {2, nullptr, "Flush"},
             {3, nullptr, "SetSize"},      {4, nullptr, "GetSize"}, {5, nullptr, "OperateRange"},
@@ -29,7 +29,7 @@ public:
     }
 
 private:
-    std::unique_ptr<FileSys::StorageBackend> backend;
+    FileSys::VirtualFile backend;
 
     void Read(Kernel::HLERequestContext& ctx) {
         IPC::RequestParser rp{ctx};
@@ -51,8 +51,8 @@ private:
         }
 
         // Read the data from the Storage backend
-        std::vector<u8> output(length);
-        ResultVal<size_t> res = backend->Read(offset, length, output.data());
+        std::vector<u8> output = backend->ReadBytes(length, offset);
+        auto res = MakeResult<size_t>(output.size());
         if (res.Failed()) {
             IPC::ResponseBuilder rb{ctx, 2};
             rb.Push(res.Code());
@@ -69,8 +69,8 @@ private:
 
 class IFile final : public ServiceFramework<IFile> {
 public:
-    explicit IFile(std::unique_ptr<FileSys::StorageBackend>&& backend)
-        : ServiceFramework("IFile"), backend(std::move(backend)) {
+    explicit IFile(FileSys::VirtualFile backend_)
+        : ServiceFramework("IFile"), backend(std::move(backend_)) {
         static const FunctionInfo functions[] = {
             {0, &IFile::Read, "Read"},       {1, &IFile::Write, "Write"},
             {2, &IFile::Flush, "Flush"},     {3, &IFile::SetSize, "SetSize"},
@@ -80,7 +80,7 @@ public:
     }
 
 private:
-    std::unique_ptr<FileSys::StorageBackend> backend;
+    FileSys::VirtualFile backend;
 
     void Read(Kernel::HLERequestContext& ctx) {
         IPC::RequestParser rp{ctx};
@@ -103,8 +103,8 @@ private:
         }
 
         // Read the data from the Storage backend
-        std::vector<u8> output(length);
-        ResultVal<size_t> res = backend->Read(offset, length, output.data());
+        std::vector<u8> output = backend->ReadBytes(length, offset);
+        auto res = MakeResult<size_t>(output.size());
         if (res.Failed()) {
             IPC::ResponseBuilder rb{ctx, 2};
             rb.Push(res.Code());
@@ -139,9 +139,10 @@ private:
             return;
         }
 
-        // Write the data to the Storage backend
         std::vector<u8> data = ctx.ReadBuffer();
-        ResultVal<size_t> res = backend->Write(offset, length, true, data.data());
+        data.resize(length);
+        // Write the data to the Storage backend
+        auto res = MakeResult<size_t>(backend->WriteBytes(data, offset));
         if (res.Failed()) {
             IPC::ResponseBuilder rb{ctx, 2};
             rb.Push(res.Code());
@@ -154,7 +155,8 @@ private:
 
     void Flush(Kernel::HLERequestContext& ctx) {
         LOG_DEBUG(Service_FS, "called");
-        backend->Flush();
+
+        // Exists for SDK compatibiltity -- No need to flush file.
 
         IPC::ResponseBuilder rb{ctx, 2};
         rb.Push(RESULT_SUCCESS);
@@ -163,7 +165,7 @@ private:
     void SetSize(Kernel::HLERequestContext& ctx) {
         IPC::RequestParser rp{ctx};
         const u64 size = rp.Pop<u64>();
-        backend->SetSize(size);
+        backend->Resize(size);
         LOG_DEBUG(Service_FS, "called, size={}", size);
 
         IPC::ResponseBuilder rb{ctx, 2};
@@ -180,19 +182,38 @@ private:
     }
 };
 
+template <typename T>
+static void BuildEntryIndex(std::vector<FileSys::Entry>& entries, const std::vector<T>& new_data,
+                            FileSys::EntryType type) {
+    for (const auto& new_entry : new_data) {
+        FileSys::Entry entry;
+        entry.filename[0] = '\0';
+        std::strncat(entry.filename, new_entry->GetName().c_str(), FileSys::FILENAME_LENGTH - 1);
+        entry.type = type;
+        entry.file_size = new_entry->GetSize();
+        entries.emplace_back(std::move(entry));
+    }
+}
+
 class IDirectory final : public ServiceFramework<IDirectory> {
 public:
-    explicit IDirectory(std::unique_ptr<FileSys::DirectoryBackend>&& backend)
-        : ServiceFramework("IDirectory"), backend(std::move(backend)) {
+    explicit IDirectory(FileSys::VirtualDir backend_)
+        : ServiceFramework("IDirectory"), backend(std::move(backend_)) {
         static const FunctionInfo functions[] = {
             {0, &IDirectory::Read, "Read"},
             {1, &IDirectory::GetEntryCount, "GetEntryCount"},
         };
         RegisterHandlers(functions);
+
+        // Build entry index now to save time later.
+        BuildEntryIndex(entries, backend->GetFiles(), FileSys::File);
+        BuildEntryIndex(entries, backend->GetSubdirectories(), FileSys::Directory);
     }
 
 private:
-    std::unique_ptr<FileSys::DirectoryBackend> backend;
+    FileSys::VirtualDir backend;
+    std::vector<FileSys::Entry> entries;
+    u64 next_entry_index = 0;
 
     void Read(Kernel::HLERequestContext& ctx) {
         IPC::RequestParser rp{ctx};
@@ -203,26 +224,31 @@ private:
         // Calculate how many entries we can fit in the output buffer
         u64 count_entries = ctx.GetWriteBufferSize() / sizeof(FileSys::Entry);
 
+        // Cap at total number of entries.
+        u64 actual_entries = std::min(count_entries, entries.size() - next_entry_index);
+
         // Read the data from the Directory backend
-        std::vector<FileSys::Entry> entries(count_entries);
-        u64 read_entries = backend->Read(count_entries, entries.data());
+        std::vector<FileSys::Entry> entry_data(entries.begin() + next_entry_index,
+                                               entries.begin() + next_entry_index + actual_entries);
+
+        next_entry_index += actual_entries;
 
         // Convert the data into a byte array
-        std::vector<u8> output(entries.size() * sizeof(FileSys::Entry));
-        std::memcpy(output.data(), entries.data(), output.size());
+        std::vector<u8> output(entry_data.size() * sizeof(FileSys::Entry));
+        std::memcpy(output.data(), entry_data.data(), output.size());
 
         // Write the data to memory
         ctx.WriteBuffer(output);
 
         IPC::ResponseBuilder rb{ctx, 4};
         rb.Push(RESULT_SUCCESS);
-        rb.Push(read_entries);
+        rb.Push(actual_entries);
     }
 
     void GetEntryCount(Kernel::HLERequestContext& ctx) {
         LOG_DEBUG(Service_FS, "called");
 
-        u64 count = backend->GetEntryCount();
+        u64 count = entries.size() - next_entry_index;
 
         IPC::ResponseBuilder rb{ctx, 4};
         rb.Push(RESULT_SUCCESS);
@@ -232,7 +258,7 @@ private:
 
 class IFileSystem final : public ServiceFramework<IFileSystem> {
 public:
-    explicit IFileSystem(std::unique_ptr<FileSys::FileSystemBackend>&& backend)
+    explicit IFileSystem(FileSys::VirtualDir backend)
         : ServiceFramework("IFileSystem"), backend(std::move(backend)) {
         static const FunctionInfo functions[] = {
             {0, &IFileSystem::CreateFile, "CreateFile"},
@@ -267,7 +293,7 @@ public:
         LOG_DEBUG(Service_FS, "called file {} mode 0x{:X} size 0x{:08X}", name, mode, size);
 
         IPC::ResponseBuilder rb{ctx, 2};
-        rb.Push(backend->CreateFile(name, size));
+        rb.Push(backend.CreateFile(name, size));
     }
 
     void DeleteFile(Kernel::HLERequestContext& ctx) {
@@ -279,7 +305,7 @@ public:
         LOG_DEBUG(Service_FS, "called file {}", name);
 
         IPC::ResponseBuilder rb{ctx, 2};
-        rb.Push(backend->DeleteFile(name));
+        rb.Push(backend.DeleteFile(name));
     }
 
     void CreateDirectory(Kernel::HLERequestContext& ctx) {
@@ -291,7 +317,7 @@ public:
         LOG_DEBUG(Service_FS, "called directory {}", name);
 
         IPC::ResponseBuilder rb{ctx, 2};
-        rb.Push(backend->CreateDirectory(name));
+        rb.Push(backend.CreateDirectory(name));
     }
 
     void RenameFile(Kernel::HLERequestContext& ctx) {
@@ -309,7 +335,7 @@ public:
         LOG_DEBUG(Service_FS, "called file '{}' to file '{}'", src_name, dst_name);
 
         IPC::ResponseBuilder rb{ctx, 2};
-        rb.Push(backend->RenameFile(src_name, dst_name));
+        rb.Push(backend.RenameFile(src_name, dst_name));
     }
 
     void OpenFile(Kernel::HLERequestContext& ctx) {
@@ -322,14 +348,14 @@ public:
 
         LOG_DEBUG(Service_FS, "called file {} mode {}", name, static_cast<u32>(mode));
 
-        auto result = backend->OpenFile(name, mode);
+        auto result = backend.OpenFile(name, mode);
         if (result.Failed()) {
             IPC::ResponseBuilder rb{ctx, 2};
             rb.Push(result.Code());
             return;
         }
 
-        auto file = std::move(result.Unwrap());
+        IFile file(result.Unwrap());
 
         IPC::ResponseBuilder rb{ctx, 2, 0, 1};
         rb.Push(RESULT_SUCCESS);
@@ -347,14 +373,14 @@ public:
 
         LOG_DEBUG(Service_FS, "called directory {} filter {}", name, filter_flags);
 
-        auto result = backend->OpenDirectory(name);
+        auto result = backend.OpenDirectory(name);
         if (result.Failed()) {
             IPC::ResponseBuilder rb{ctx, 2};
             rb.Push(result.Code());
             return;
         }
 
-        auto directory = std::move(result.Unwrap());
+        IDirectory directory(result.Unwrap());
 
         IPC::ResponseBuilder rb{ctx, 2, 0, 1};
         rb.Push(RESULT_SUCCESS);
@@ -369,7 +395,7 @@ public:
 
         LOG_DEBUG(Service_FS, "called file {}", name);
 
-        auto result = backend->GetEntryType(name);
+        auto result = backend.GetEntryType(name);
         if (result.Failed()) {
             IPC::ResponseBuilder rb{ctx, 2};
             rb.Push(result.Code());
@@ -389,7 +415,7 @@ public:
     }
 
 private:
-    std::unique_ptr<FileSys::FileSystemBackend> backend;
+    VfsDirectoryServiceWrapper backend;
 };
 
 FSP_SRV::FSP_SRV() : ServiceFramework("fsp-srv") {
@@ -490,8 +516,7 @@ void FSP_SRV::TryLoadRomFS() {
     if (romfs) {
         return;
     }
-    FileSys::Path unused;
-    auto res = OpenFileSystem(Type::RomFS, unused);
+    auto res = OpenRomFS();
     if (res.Succeeded()) {
         romfs = std::move(res.Unwrap());
     }
@@ -507,8 +532,7 @@ void FSP_SRV::Initialize(Kernel::HLERequestContext& ctx) {
 void FSP_SRV::MountSdCard(Kernel::HLERequestContext& ctx) {
     LOG_DEBUG(Service_FS, "called");
 
-    FileSys::Path unused;
-    auto filesystem = OpenFileSystem(Type::SDMC, unused).Unwrap();
+    IFileSystem filesystem(OpenFileSystem(Type::SDMC).Unwrap());
 
     IPC::ResponseBuilder rb{ctx, 2, 0, 1};
     rb.Push(RESULT_SUCCESS);
@@ -531,8 +555,7 @@ void FSP_SRV::CreateSaveData(Kernel::HLERequestContext& ctx) {
 void FSP_SRV::MountSaveData(Kernel::HLERequestContext& ctx) {
     LOG_WARNING(Service_FS, "(STUBBED) called");
 
-    FileSys::Path unused;
-    auto filesystem = OpenFileSystem(Type::SaveData, unused).Unwrap();
+    IFileSystem filesystem(OpenFileSystem(Type::SaveData).Unwrap());
 
     IPC::ResponseBuilder rb{ctx, 2, 0, 1};
     rb.Push(RESULT_SUCCESS);
@@ -559,18 +582,11 @@ void FSP_SRV::OpenDataStorageByCurrentProcess(Kernel::HLERequestContext& ctx) {
         return;
     }
 
-    // Attempt to open a StorageBackend interface to the RomFS
-    auto storage = romfs->OpenFile({}, {});
-    if (storage.Failed()) {
-        LOG_CRITICAL(Service_FS, "no storage interface available!");
-        IPC::ResponseBuilder rb{ctx, 2};
-        rb.Push(storage.Code());
-        return;
-    }
+    IStorage storage(romfs);
 
     IPC::ResponseBuilder rb{ctx, 2, 0, 1};
     rb.Push(RESULT_SUCCESS);
-    rb.PushIpcInterface<IStorage>(std::move(storage.Unwrap()));
+    rb.PushIpcInterface<IStorage>(std::move(storage));
 }
 
 void FSP_SRV::OpenRomStorage(Kernel::HLERequestContext& ctx) {
diff --git a/src/core/hle/service/filesystem/fsp_srv.h b/src/core/hle/service/filesystem/fsp_srv.h
index acb78fac1..b1ef6397f 100644
--- a/src/core/hle/service/filesystem/fsp_srv.h
+++ b/src/core/hle/service/filesystem/fsp_srv.h
@@ -29,7 +29,7 @@ private:
     void OpenDataStorageByCurrentProcess(Kernel::HLERequestContext& ctx);
     void OpenRomStorage(Kernel::HLERequestContext& ctx);
 
-    std::unique_ptr<FileSys::FileSystemBackend> romfs;
+    FileSys::VirtualFile romfs;
 };
 
 } // namespace Service::FileSystem