Virtual Filesystem 2: Electric Boogaloo (#676)

* Virtual Filesystem

* Fix delete bug and documentate

* Review fixes + other stuff

* Fix puyo regression

5 files changed, 383 insertions, 116 deletions

diff --git a/src/core/hle/service/am/am.cpp b/src/core/hle/service/am/am.cpp
index 0f0ab1e6a..97ef07bf9 100644
--- a/src/core/hle/service/am/am.cpp
+++ b/src/core/hle/service/am/am.cpp
@@ -5,7 +5,6 @@
 #include <cinttypes>
 #include <stack>
 #include "core/core.h"
-#include "core/file_sys/filesystem.h"
 #include "core/hle/ipc_helpers.h"
 #include "core/hle/kernel/event.h"
 #include "core/hle/kernel/process.h"
diff --git a/src/core/hle/service/filesystem/filesystem.cpp b/src/core/hle/service/filesystem/filesystem.cpp
index 902256757..ec528ef40 100644
--- a/src/core/hle/service/filesystem/filesystem.cpp
+++ b/src/core/hle/service/filesystem/filesystem.cpp
@@ -2,17 +2,204 @@
 // Licensed under GPLv2 or any later version
 // Refer to the license.txt file included.
 
-#include <boost/container/flat_map.hpp>
+#pragma optimize("", off)
+
+#include "common/assert.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/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) {
+        // TODO(DarkLordZach): Find a better error code for this
+        return ResultCode(-1);
+    }
+    if (!file->Resize(size)) {
+        // TODO(DarkLordZach): Find a better error code for this
+        return ResultCode(-1);
+    }
+    return RESULT_SUCCESS;
+}
+
+ResultCode VfsDirectoryServiceWrapper::DeleteFile(const std::string& path) const {
+    auto dir = GetDirectoryRelativeWrapped(backing, FileUtil::GetParentPath(path));
+    if (path == "/" || path == "\\") {
+        // TODO(DarkLordZach): Why do games call this and what should it do? Works as is but...
+        return RESULT_SUCCESS;
+    }
+    if (dir->GetFile(FileUtil::GetFilename(path)) == nullptr)
+        return FileSys::ERROR_PATH_NOT_FOUND;
+    if (!backing->DeleteFile(FileUtil::GetFilename(path))) {
+        // TODO(DarkLordZach): Find a better error code for this
+        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) {
+        // TODO(DarkLordZach): Find a better error code for this
+        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))) {
+        // TODO(DarkLordZach): Find a better error code for this
+        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))) {
+        // TODO(DarkLordZach): Find a better error code for this
+        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))) {
+            // TODO(DarkLordZach): Find a better error code for this
+            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))) {
+        // TODO(DarkLordZach): Find a better error code for this
+        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))) {
+            // TODO(DarkLordZach): Find a better error code for this
+            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);
+
+    // TODO(DarkLordZach): Find a better error code for this
+    return ResultCode(-1);
+}
+
+ResultVal<FileSys::VirtualFile> VfsDirectoryServiceWrapper::OpenFile(const std::string& path,
+                                                                     FileSys::Mode mode) const {
+    auto npath = path;
+    while (npath.size() > 0 && (npath[0] == '/' || npath[0] == '\\'))
+        npath = npath.substr(1);
+    auto file = backing->GetFileRelative(npath);
+    if (file == nullptr)
+        return FileSys::ERROR_PATH_NOT_FOUND;
+
+    if (mode == FileSys::Mode::Append) {
+        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) {
+        // TODO(DarkLordZach): Find a better error code for this
+        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 FileSys::ERROR_PATH_NOT_FOUND;
+    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 FileSys::ERROR_PATH_NOT_FOUND;
+}
+
 /**
  * Map of registered file systems, identified by type. Once an file system is registered here, it
  * is never removed until UnregisterFileSystems is called.
@@ -42,7 +229,7 @@ ResultCode RegisterSDMC(std::unique_ptr<FileSys::SDMCFactory>&& factory) {
     return RESULT_SUCCESS;
 }
 
-ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenRomFS(u64 title_id) {
+ResultVal<FileSys::VirtualFile> OpenRomFS(u64 title_id) {
     LOG_TRACE(Service_FS, "Opening RomFS for title_id={:016X}", title_id);
 
     if (romfs_factory == nullptr) {
@@ -53,19 +240,19 @@ ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenRomFS(u64 title_id) {
     return romfs_factory->Open(title_id);
 }
 
-ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenSaveData(
-    FileSys::SaveDataSpaceId space, FileSys::SaveDataDescriptor save_struct) {
+ResultVal<FileSys::VirtualDir> OpenSaveData(FileSys::SaveDataSpaceId space,
+                                            FileSys::SaveDataDescriptor save_struct) {
     LOG_TRACE(Service_FS, "Opening Save Data for space_id={:01X}, save_struct={}",
-              static_cast<u8>(space), SaveStructDebugInfo(save_struct));
+              static_cast<u8>(space), save_struct.DebugInfo());
 
     if (save_data_factory == nullptr) {
-        return ResultCode(ErrorModule::FS, FileSys::ErrCodes::SaveDataNotFound);
+        return ResultCode(ErrorModule::FS, FileSys::ErrCodes::TitleNotFound);
     }
 
     return save_data_factory->Open(space, save_struct);
 }
 
-ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenSDMC() {
+ResultVal<FileSys::VirtualDir> OpenSDMC() {
     LOG_TRACE(Service_FS, "Opening SDMC");
 
     if (sdmc_factory == nullptr) {
@@ -80,8 +267,10 @@ void RegisterFileSystems() {
     save_data_factory = nullptr;
     sdmc_factory = nullptr;
 
-    std::string nand_directory = FileUtil::GetUserPath(D_NAND_IDX);
-    std::string sd_directory = FileUtil::GetUserPath(D_SDMC_IDX);
+    auto nand_directory = std::make_shared<FileSys::RealVfsDirectory>(
+        FileUtil::GetUserPath(D_NAND_IDX), FileSys::Mode::Write);
+    auto sd_directory = std::make_shared<FileSys::RealVfsDirectory>(
+        FileUtil::GetUserPath(D_SDMC_IDX), FileSys::Mode::Write);
 
     auto savedata = std::make_unique<FileSys::SaveDataFactory>(std::move(nand_directory));
     save_data_factory = std::move(savedata);
diff --git a/src/core/hle/service/filesystem/filesystem.h b/src/core/hle/service/filesystem/filesystem.h
index 45272d326..d4483daa5 100644
--- a/src/core/hle/service/filesystem/filesystem.h
+++ b/src/core/hle/service/filesystem/filesystem.h
@@ -6,15 +6,13 @@
 
 #include <memory>
 #include "common/common_types.h"
+#include "core/file_sys/directory.h"
+#include "core/file_sys/mode.h"
 #include "core/file_sys/romfs_factory.h"
 #include "core/file_sys/savedata_factory.h"
 #include "core/file_sys/sdmc_factory.h"
 #include "core/hle/result.h"
 
-namespace FileSys {
-class FileSystemBackend;
-} // namespace FileSys
-
 namespace Service {
 
 namespace SM {
@@ -29,11 +27,10 @@ ResultCode RegisterSDMC(std::unique_ptr<FileSys::SDMCFactory>&& factory);
 
 // TODO(DarkLordZach): BIS Filesystem
 // ResultCode RegisterBIS(std::unique_ptr<FileSys::BISFactory>&& factory);
-
-ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenRomFS(u64 title_id);
-ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenSaveData(
-    FileSys::SaveDataSpaceId space, FileSys::SaveDataDescriptor save_struct);
-ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenSDMC();
+ResultVal<FileSys::VirtualFile> OpenRomFS(u64 title_id);
+ResultVal<FileSys::VirtualDir> OpenSaveData(FileSys::SaveDataSpaceId space,
+                                            FileSys::SaveDataDescriptor save_struct);
+ResultVal<FileSys::VirtualDir> OpenSDMC();
 
 // TODO(DarkLordZach): BIS Filesystem
 // ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenBIS();
@@ -41,5 +38,100 @@ ResultVal<std::unique_ptr<FileSys::FileSystemBackend>> OpenSDMC();
 /// Registers all Filesystem services with the specified service manager.
 void InstallInterfaces(SM::ServiceManager& service_manager);
 
+// 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;
+};
+
 } // namespace FileSystem
 } // namespace Service
diff --git a/src/core/hle/service/filesystem/fsp_srv.cpp b/src/core/hle/service/filesystem/fsp_srv.cpp
index 22d3e645d..1b003bd84 100644
--- a/src/core/hle/service/filesystem/fsp_srv.cpp
+++ b/src/core/hle/service/filesystem/fsp_srv.cpp
@@ -8,11 +8,7 @@
 #include "core/core.h"
 #include "core/file_sys/directory.h"
 #include "core/file_sys/errors.h"
-#include "core/file_sys/filesystem.h"
-#include "core/file_sys/storage.h"
 #include "core/hle/ipc_helpers.h"
-#include "core/hle/kernel/client_port.h"
-#include "core/hle/kernel/client_session.h"
 #include "core/hle/kernel/process.h"
 #include "core/hle/service/filesystem/filesystem.h"
 #include "core/hle/service/filesystem/fsp_srv.h"
@@ -25,13 +21,13 @@ enum class StorageId : u8 {
     GameCard = 2,
     NandSystem = 3,
     NandUser = 4,
-    SdCard = 5
+    SdCard = 5,
 };
 
 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"},
@@ -40,7 +36,7 @@ public:
     }
 
 private:
-    std::unique_ptr<FileSys::StorageBackend> backend;
+    FileSys::VirtualFile backend;
 
     void Read(Kernel::HLERequestContext& ctx) {
         IPC::RequestParser rp{ctx};
@@ -62,14 +58,7 @@ private:
         }
 
         // Read the data from the Storage backend
-        std::vector<u8> output(length);
-        ResultVal<size_t> res = backend->Read(offset, length, output.data());
-        if (res.Failed()) {
-            IPC::ResponseBuilder rb{ctx, 2};
-            rb.Push(res.Code());
-            return;
-        }
-
+        std::vector<u8> output = backend->ReadBytes(length, offset);
         // Write the data to memory
         ctx.WriteBuffer(output);
 
@@ -80,8 +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"},
@@ -91,7 +80,7 @@ public:
     }
 
 private:
-    std::unique_ptr<FileSys::StorageBackend> backend;
+    FileSys::VirtualFile backend;
 
     void Read(Kernel::HLERequestContext& ctx) {
         IPC::RequestParser rp{ctx};
@@ -114,20 +103,14 @@ private:
         }
 
         // Read the data from the Storage backend
-        std::vector<u8> output(length);
-        ResultVal<size_t> res = backend->Read(offset, length, output.data());
-        if (res.Failed()) {
-            IPC::ResponseBuilder rb{ctx, 2};
-            rb.Push(res.Code());
-            return;
-        }
+        std::vector<u8> output = backend->ReadBytes(length, offset);
 
         // Write the data to memory
         ctx.WriteBuffer(output);
 
         IPC::ResponseBuilder rb{ctx, 4};
         rb.Push(RESULT_SUCCESS);
-        rb.Push(static_cast<u64>(*res));
+        rb.Push(static_cast<u64>(output.size()));
     }
 
     void Write(Kernel::HLERequestContext& ctx) {
@@ -150,14 +133,21 @@ 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());
-        if (res.Failed()) {
-            IPC::ResponseBuilder rb{ctx, 2};
-            rb.Push(res.Code());
-            return;
-        }
+        std::vector<u8> actual_data(length);
+
+        ASSERT_MSG(
+            data.size() <= length,
+            "Attempting to write more data than requested (requested={:016X}, actual={:016X}).",
+            length, data.size());
+
+        std::copy(data.begin(), data.end(), actual_data.begin());
+        // Write the data to the Storage backend
+        auto written = backend->WriteBytes(data, offset);
+
+        ASSERT_MSG(written == length,
+                   "Could not write all bytes to file (requested={:016X}, actual={:016X}).", length,
+                   written);
 
         IPC::ResponseBuilder rb{ctx, 2};
         rb.Push(RESULT_SUCCESS);
@@ -165,7 +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);
@@ -174,7 +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};
@@ -191,19 +182,39 @@ 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);
+
+        // TODO(DarkLordZach): Verify that this is the correct behavior.
+        // 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};
@@ -214,26 +225,31 @@ 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);
@@ -243,7 +259,7 @@ 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"},
@@ -278,7 +294,7 @@ 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) {
@@ -290,7 +306,7 @@ 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) {
@@ -302,7 +318,7 @@ 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) {
@@ -320,7 +336,7 @@ 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) {
@@ -333,14 +349,14 @@ 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);
@@ -358,14 +374,14 @@ 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);
@@ -380,7 +396,7 @@ 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());
@@ -400,7 +416,7 @@ public:
     }
 
 private:
-    std::unique_ptr<FileSys::FileSystemBackend> backend;
+    VfsDirectoryServiceWrapper backend;
 };
 
 FSP_SRV::FSP_SRV() : ServiceFramework("fsp-srv") {
@@ -536,17 +552,19 @@ void FSP_SRV::MountSaveData(Kernel::HLERequestContext& ctx) {
     LOG_INFO(Service_FS, "called with unknown={:08X}", unk);
     auto save_struct = rp.PopRaw<FileSys::SaveDataDescriptor>();
 
-    auto filesystem = OpenSaveData(space_id, save_struct);
+    auto dir = OpenSaveData(space_id, save_struct);
 
-    if (filesystem.Failed()) {
+    if (dir.Failed()) {
         IPC::ResponseBuilder rb{ctx, 2, 0, 0};
-        rb.Push(ResultCode(ErrorModule::FS, FileSys::ErrCodes::SaveDataNotFound));
+        rb.Push(ResultCode(ErrorModule::FS, FileSys::ErrCodes::TitleNotFound));
         return;
     }
 
+    IFileSystem filesystem(std::move(dir.Unwrap()));
+
     IPC::ResponseBuilder rb{ctx, 2, 0, 1};
     rb.Push(RESULT_SUCCESS);
-    rb.PushIpcInterface<IFileSystem>(std::move(filesystem.Unwrap()));
+    rb.PushIpcInterface<IFileSystem>(std::move(filesystem));
 }
 
 void FSP_SRV::GetGlobalAccessLogMode(Kernel::HLERequestContext& ctx) {
@@ -569,18 +587,11 @@ void FSP_SRV::OpenDataStorageByCurrentProcess(Kernel::HLERequestContext& ctx) {
         return;
     }
 
-    auto storage = romfs.Unwrap()->OpenFile({}, {});
-
-    if (storage.Failed()) {
-        LOG_CRITICAL(Service_FS, "no storage interface available!");
-        IPC::ResponseBuilder rb{ctx, 2};
-        rb.Push(storage.Code());
-        return;
-    }
+    IStorage storage(std::move(romfs.Unwrap()));
 
     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) {
@@ -591,33 +602,9 @@ void FSP_SRV::OpenRomStorage(Kernel::HLERequestContext& ctx) {
 
     LOG_DEBUG(Service_FS, "called with storage_id={:02X}, title_id={:016X}",
               static_cast<u8>(storage_id), title_id);
-    if (title_id != Core::System::GetInstance().CurrentProcess()->program_id) {
-        LOG_CRITICAL(
-            Service_FS,
-            "Attempting to access RomFS of another title id (current={:016X}, requested={:016X}).",
-            Core::System::GetInstance().CurrentProcess()->program_id, title_id);
-    }
 
-    auto romfs = OpenRomFS(title_id);
-    if (romfs.Failed()) {
-        LOG_CRITICAL(Service_FS, "no file system interface available!");
-        IPC::ResponseBuilder rb{ctx, 2};
-        rb.Push(ResultCode(ErrorModule::FS, FileSys::ErrCodes::RomFSNotFound));
-        return;
-    }
-
-    auto storage = romfs.Unwrap()->OpenFile({}, {});
-
-    if (storage.Failed()) {
-        LOG_CRITICAL(Service_FS, "no storage interface available!");
-        IPC::ResponseBuilder rb{ctx, 2};
-        rb.Push(storage.Code());
-        return;
-    }
-
-    IPC::ResponseBuilder rb{ctx, 2, 0, 1};
-    rb.Push(RESULT_SUCCESS);
-    rb.PushIpcInterface<IStorage>(std::move(storage.Unwrap()));
+    IPC::ResponseBuilder rb{ctx, 2};
+    rb.Push(ResultCode(ErrorModule::FS, FileSys::ErrCodes::TitleNotFound));
 }
 
 } // namespace Service::FileSystem
diff --git a/src/core/hle/service/filesystem/fsp_srv.h b/src/core/hle/service/filesystem/fsp_srv.h
index 4653eee4e..07f99c93d 100644
--- a/src/core/hle/service/filesystem/fsp_srv.h
+++ b/src/core/hle/service/filesystem/fsp_srv.h
@@ -27,7 +27,7 @@ private:
     void OpenDataStorageByCurrentProcess(Kernel::HLERequestContext& ctx);
     void OpenRomStorage(Kernel::HLERequestContext& ctx);
 
-    std::unique_ptr<FileSys::FileSystemBackend> romfs;
+    FileSys::VirtualFile romfs;
 };
 
 } // namespace Service::FileSystem