turn-off Nlink readdir() optimization for NFS/CIFS (#19420)

fixes #19418
fixes #19416

cmd/metacache-walk.go

@@ -59,10 +59,22 @@ type WalkDirOptions struct {
 	DiskID string
 }
 
+// supported FS for Nlink optimization in readdir.
+const (
+	xfs  = "XFS"
+	ext4 = "EXT4"
+)
+
 // WalkDir will traverse a directory and return all entries found.
 // On success a sorted meta cache stream will be returned.
 // Metadata has data stripped, if any.
 func (s *xlStorage) WalkDir(ctx context.Context, opts WalkDirOptions, wr io.Writer) (err error) {
+	legacyFS := !(s.fsType == xfs || s.fsType == ext4)
+
+	s.RLock()
+	legacy := s.formatLegacy
+	s.RUnlock()
+
 	// Verify if volume is valid and it exists.
 	volumeDir, err := s.getVolDir(opts.Bucket)
 	if err != nil {
@@ -76,10 +88,6 @@ func (s *xlStorage) WalkDir(ctx context.Context, opts WalkDirOptions, wr io.Writ
 		}
 	}
 
-	s.RLock()
-	legacy := s.formatLegacy
-	s.RUnlock()
-
 	// Use a small block size to start sending quickly
 	w := newMetacacheWriter(wr, 16<<10)
 	w.reuseBlocks = true // We are not sharing results, so reuse buffers.
@@ -353,7 +361,7 @@ func (s *xlStorage) WalkDir(ctx context.Context, opts WalkDirOptions, wr io.Writ
 				// NOT an object, append to stack (with slash)
 				// If dirObject, but no metadata (which is unexpected) we skip it.
 				if !isDirObj {
-					if !isDirEmpty(pathJoinBuf(sb, volumeDir, meta.name)) {
+					if !isDirEmpty(pathJoinBuf(sb, volumeDir, meta.name), legacyFS) {
 						dirStack = append(dirStack, meta.name+slashSeparator)
 					}
 				}