[native] Skip F_FULLFSYNC on macOS for network file systems

src/coreclr/vm/wasm/browser/callhelpers-pinvoke.cpp

@@ -79,7 +79,7 @@ extern "C" {
     int32_t SystemNative_FChflags (void *, uint32_t);
     int32_t SystemNative_FLock (void *, int32_t);
     int32_t SystemNative_FStat (void *, void *);
-    int32_t SystemNative_FSync (void *);
+    int32_t SystemNative_FSync (void *, int32_t);
     int32_t SystemNative_FTruncate (void *, int64_t);
     int32_t SystemNative_FUTimens (void *, void *);
     int32_t SystemNative_FcntlGetIsNonBlocking (void *, void *);

src/coreclr/vm/wasm/wasi/callhelpers-pinvoke.cpp

@@ -76,7 +76,7 @@ extern "C" {
     int32_t SystemNative_FChflags (void *, uint32_t);
     int32_t SystemNative_FLock (void *, int32_t);
     int32_t SystemNative_FStat (void *, void *);
-    int32_t SystemNative_FSync (void *);
+    int32_t SystemNative_FSync (void *, int32_t);
     int32_t SystemNative_FTruncate (void *, int64_t);
     int32_t SystemNative_FUTimens (void *, void *);
     int32_t SystemNative_FcntlGetFD (void *);

src/libraries/Common/src/Interop/Unix/System.Native/Interop.FSync.cs

@@ -9,6 +9,6 @@ internal static partial class Interop
     internal static partial class Sys
     {
         [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_FSync", SetLastError = true)]
-        internal static partial int FSync(SafeFileHandle fd);
+        internal static partial int FSync(SafeFileHandle fd, [MarshalAs(UnmanagedType.Bool)] bool useFullFSync);
     }
 }

src/libraries/System.Private.CoreLib/src/Microsoft/Win32/SafeHandles/SafeFileHandle.Unix.cs

@@ -41,9 +41,35 @@ public sealed partial class SafeFileHandle : SafeHandleZeroOrMinusOneIsInvalid
         private NullableBool _canSeek /* = NullableBool.Undefined */;
         private NullableBool _supportsRandomAccess /* = NullableBool.Undefined */;
         private NullableBool _isAsync /* = NullableBool.Undefined */;
+        // Lazily initialized on Apple platforms (macOS, iOS, tvOS, Mac Catalyst).
+        // True = use F_FULLFSYNC.
+        // False = skip F_FULLFSYNC because the probe indicates the file system should avoid it
+        // (e.g., NFS/SMB/CIFS/SMB2, or when the probe fails).
+        // Stays Undefined until first queried; UseFullFSync treats Undefined as True.
+        // See https://github.com/dotnet/runtime/issues/124722.
+        private NullableBool _useFullFsync /* = NullableBool.Undefined */;
         private bool _deleteOnClose;
         private bool _isLocked;
 
+        // Returns true when F_FULLFSYNC should be attempted. Returns false when
+        // FileSystemSupportsLocking(LOCK_SH, accessWrite: true) reports the file system as unsupported
+        // for this probe, which includes known network file systems and probe failures.
+        // The value is only used on Apple platforms; native code ignores it on other platforms.
+        // Lazily computed and cached on first access to avoid a syscall for callers that never flush to disk.
+        internal bool UseFullFSync
+        {
+            get
+            {
+                NullableBool useFullFsync = _useFullFsync;
+                if (useFullFsync == NullableBool.Undefined && !IsClosed && OperatingSystem.IsApplePlatform())
+                {
+                    _useFullFsync = useFullFsync = Interop.Sys.FileSystemSupportsLocking(this, Interop.Sys.LockOperations.LOCK_SH, accessWrite: true)
+                        ? NullableBool.True : NullableBool.False;
+                }
+                return useFullFsync != NullableBool.False;
+            }
+        }
+
         public SafeFileHandle() : this(ownsHandle: true)
         {
         }
@@ -461,6 +487,7 @@ private bool Init(string path, FileMode mode, FileAccess access, FileShare share
                     return false;
                 }
             }
+
             // Enable DeleteOnClose when we've successfully locked the file.
             // On Windows, the locking happens atomically as part of opening the file.
             _deleteOnClose = (options & FileOptions.DeleteOnClose) != 0;

src/libraries/System.Private.CoreLib/src/System/IO/Strategies/FileStreamHelpers.Unix.cs

@@ -39,7 +39,7 @@ internal static void ThrowInvalidArgument(SafeFileHandle handle) =>
         /// <summary>Flushes the file's OS buffer.</summary>
         internal static void FlushToDisk(SafeFileHandle handle)
         {
-            if (Interop.Sys.FSync(handle) < 0)
+            if (Interop.Sys.FSync(handle, handle.UseFullFSync) < 0)
             {
                 Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
                 switch (errorInfo.Error)

src/native/libs/System.Native/pal_io.c

@@ -783,21 +783,26 @@ int32_t SystemNative_FChMod(intptr_t fd, int32_t mode)
 #endif /* HAVE_FCHMOD */
 }
 
-int32_t SystemNative_FSync(intptr_t fd)
+int32_t SystemNative_FSync(intptr_t fd, int32_t useFullFSync)
 {
     int fileDescriptor = ToFileDescriptor(fd);
 
     int32_t result;
 #ifdef TARGET_OSX
-    while ((result = fcntl(fileDescriptor, F_FULLFSYNC)) < 0 && errno == EINTR);
-    if (result >= 0)
+    if (useFullFSync)
     {
-        return result;
-    }
+        while ((result = fcntl(fileDescriptor, F_FULLFSYNC)) < 0 && errno == EINTR);
+        if (result >= 0)
+        {
+            return result;
+        }
 
-    // F_FULLFSYNC is not supported on all file systems and handle types (e.g.,
-    // network file systems, read-only handles). Fall back to fsync.
-    // For genuine I/O errors (e.g., EIO), fsync will also fail and propagate the error.
+        // F_FULLFSYNC is not supported on all file systems and handle types (e.g.,
+        // network file systems, read-only handles). Fall back to fsync.
+        // For genuine I/O errors (e.g., EIO), fsync will also fail and propagate the error.
+    }
+#else
+    (void)useFullFSync;
 #endif
     while ((result = fsync(fileDescriptor)) < 0 && errno == EINTR);
     return result;

src/native/libs/System.Native/pal_io.h

@@ -535,11 +535,12 @@ PALEXPORT int32_t SystemNative_ChMod(const char* path, int32_t mode);
 PALEXPORT int32_t SystemNative_FChMod(intptr_t fd, int32_t mode);
 
 /**
- * Flushes all modified data and attribtues of the specified File Descriptor to the storage medium.
+ * Flushes all modified data and attributes of the specified File Descriptor to the storage medium.
+ * On macOS, attempts F_FULLFSYNC when useFullFSync is non-zero, falling back to fsync on failure.
  *
  * Returns 0 for success; on fail, -1 is returned and errno is set.
  */
-PALEXPORT int32_t SystemNative_FSync(intptr_t fd);
+PALEXPORT int32_t SystemNative_FSync(intptr_t fd, int32_t useFullFSync);
 
 /**
  * Changes the advisory lock status on a given File Descriptor