From a1477cc9f931147b3065a48be8f7d165cb1e622f Mon Sep 17 00:00:00 2001
From: Alex Barney <thealexbarney@gmail.com>
Date: Tue, 18 May 2021 17:57:41 -0700
Subject: [PATCH] Use a lock file for directory save data

---
 .../FsSrv/SaveDataFileSystemServiceImpl.cs    |  2 +-
 .../FsSystem/DirectorySaveDataFileSystem.cs   | 41 +++++++++++++++----
 2 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/src/LibHac/FsSrv/SaveDataFileSystemServiceImpl.cs b/src/LibHac/FsSrv/SaveDataFileSystemServiceImpl.cs
index 5ef851c4..eb743f38 100644
--- a/src/LibHac/FsSrv/SaveDataFileSystemServiceImpl.cs
+++ b/src/LibHac/FsSrv/SaveDataFileSystemServiceImpl.cs
@@ -135,7 +135,7 @@ namespace LibHac.FsSrv
                 bool allowDirectorySaveData = IsAllowedDirectorySaveData2(spaceId, saveDataRootPath);
 
                 // Note: When directory save data is allowed, Nintendo creates the save directory if it doesn't exist.
-                // This bypasses normal save data// creation, leaving the save with empty extra data.
+                // This bypasses normal save data creation, leaving the save with empty extra data.
                 // Instead, we return that the save doesn't exist if the directory is missing.
 
                 // Note: Nintendo doesn't cache directory save data
diff --git a/src/LibHac/FsSystem/DirectorySaveDataFileSystem.cs b/src/LibHac/FsSystem/DirectorySaveDataFileSystem.cs
index a64448d0..3d9b4159 100644
--- a/src/LibHac/FsSystem/DirectorySaveDataFileSystem.cs
+++ b/src/LibHac/FsSystem/DirectorySaveDataFileSystem.cs
@@ -32,13 +32,15 @@ namespace LibHac.FsSystem
     {
         private const int IdealWorkBufferSize = 0x100000; // 1 MiB
 
-        private ReadOnlySpan<byte> CommittedDirectoryBytes => new[] { (byte)'/', (byte)'0', (byte)'/' };
-        private ReadOnlySpan<byte> WorkingDirectoryBytes => new[] { (byte)'/', (byte)'1', (byte)'/' };
-        private ReadOnlySpan<byte> SynchronizingDirectoryBytes => new[] { (byte)'/', (byte)'_', (byte)'/' };
+        private static ReadOnlySpan<byte> CommittedDirectoryBytes => new[] { (byte)'/', (byte)'0', (byte)'/' };
+        private static ReadOnlySpan<byte> WorkingDirectoryBytes => new[] { (byte)'/', (byte)'1', (byte)'/' };
+        private static ReadOnlySpan<byte> SynchronizingDirectoryBytes => new[] { (byte)'/', (byte)'_', (byte)'/' };
+        private static ReadOnlySpan<byte> LockFileBytes => new[] { (byte)'/', (byte)'.', (byte)'l', (byte)'o', (byte)'c', (byte)'k' };
 
-        private U8Span CommittedDirectoryPath => new U8Span(CommittedDirectoryBytes);
-        private U8Span WorkingDirectoryPath => new U8Span(WorkingDirectoryBytes);
-        private U8Span SynchronizingDirectoryPath => new U8Span(SynchronizingDirectoryBytes);
+        private static U8Span CommittedDirectoryPath => new U8Span(CommittedDirectoryBytes);
+        private static U8Span WorkingDirectoryPath => new U8Span(WorkingDirectoryBytes);
+        private static U8Span SynchronizingDirectoryPath => new U8Span(SynchronizingDirectoryBytes);
+        private static U8Span LockFilePath => new U8Span(LockFileBytes);
 
         private FileSystemClient _fsClient;
         private IFileSystem _baseFs;
@@ -60,6 +62,9 @@ namespace LibHac.FsSystem
         private SaveDataSpaceId _spaceId;
         private ulong _saveDataId;
 
+        // Additions to ensure only one directory save data fs is opened at a time
+        private IFile _lockFile;
+
         private class DirectorySaveDataFile : IFile
         {
             private IFile _baseFile;
@@ -183,6 +188,9 @@ namespace LibHac.FsSystem
 
         protected override void Dispose(bool disposing)
         {
+            _lockFile?.Dispose();
+            _lockFile = null;
+
             _cacheObserver?.Unregister(_spaceId, _saveDataId);
             _baseFs?.Dispose();
             base.Dispose(disposing);
@@ -196,14 +204,33 @@ namespace LibHac.FsSystem
         public Result Initialize(ISaveDataCommitTimeStampGetter timeStampGetter, RandomDataGenerator randomGenerator,
             bool isJournalingSupported, bool isMultiCommitSupported, bool isJournalingEnabled)
         {
+            Result rc;
+
             _isJournalingSupported = isJournalingSupported;
             _isMultiCommitSupported = isMultiCommitSupported;
             _isJournalingEnabled = isJournalingEnabled;
             _timeStampGetter = timeStampGetter ?? _timeStampGetter;
             _randomGenerator = randomGenerator ?? _randomGenerator;
 
+            // Open the lock file
+            if (_lockFile is null)
+            {
+                rc = _baseFs.OpenFile(out _lockFile, LockFilePath, OpenMode.ReadWrite);
+
+                if (rc.IsFailure())
+                {
+                    if (!ResultFs.PathNotFound.Includes(rc)) return rc;
+
+                    rc = _baseFs.CreateFile(LockFilePath, 0);
+                    if (rc.IsFailure()) return rc;
+
+                    rc = _baseFs.OpenFile(out _lockFile, LockFilePath, OpenMode.ReadWrite);
+                    if (rc.IsFailure()) return rc;
+                }
+            }
+
             // Ensure the working directory exists
-            Result rc = _baseFs.GetEntryType(out _, WorkingDirectoryPath);
+            rc = _baseFs.GetEntryType(out _, WorkingDirectoryPath);
 
             if (rc.IsFailure())
             {