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

fixes #19418
fixes #19416

cmd/is-dir-empty_linux.go

@@ -25,22 +25,19 @@ import (
 )
 
 // Returns true if no error and there is no object or prefix inside this directory
-func isDirEmpty(dirname string) bool {
+func isDirEmpty(dirname string, legacy bool) bool {
-	var stat syscall.Stat_t
+	if legacy {
-	if err := syscall.Stat(dirname, &stat); err != nil {
+		// On filesystems such as btrfs, nfs this is not true, so fallback
-		return false
+		// to performing readdir() instead.
-	}
-	if stat.Mode&syscall.S_IFMT == syscall.S_IFDIR && stat.Nlink == 2 {
-		return true
-	}
-	// On filesystems such as btrfs, nfs this is not true, so fallback
-	// to performing readdir() instead.
-	if stat.Mode&syscall.S_IFMT == syscall.S_IFDIR && stat.Nlink < 2 {
 		entries, err := readDirN(dirname, 1)
 		if err != nil {
 			return false
 		}
 		return len(entries) == 0
 	}
-	return false
+	var stat syscall.Stat_t
+	if err := syscall.Stat(dirname, &stat); err != nil {
+		return false
+	}
+	return stat.Mode&syscall.S_IFMT == syscall.S_IFDIR && stat.Nlink == 2
 }

cmd/is-dir-empty_other.go

@@ -21,7 +21,7 @@
 package cmd
 
 // isDirEmpty - returns true if there is no error and no object and prefix inside this directory
-func isDirEmpty(dirname string) bool {
+func isDirEmpty(dirname string, _ bool) bool {
 	entries, err := readDirN(dirname, 1)
 	if err != nil {
 		return false

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)
 					}
 				}

cmd/xl-storage.go

@@ -117,6 +117,7 @@ type xlStorage struct {
 
 	nrRequests   uint64
 	major, minor uint32
+	fsType       string
 
 	immediatePurge chan string
 
@@ -254,6 +255,7 @@ func newXLStorage(ep Endpoint, cleanUp bool) (s *xlStorage, err error) {
 	}
 	s.major = info.Major
 	s.minor = info.Minor
+	s.fsType = info.FSType
 
 	if !globalIsCICD && !globalIsErasureSD {
 		var rootDrive bool

cmd/xl-storage_test.go

@@ -190,7 +190,7 @@ func TestXLStorageIsDirEmpty(t *testing.T) {
 
 	// Should give false on non-existent directory.
 	dir1 := slashpath.Join(tmp, "non-existent-directory")
-	if isDirEmpty(dir1) {
+	if isDirEmpty(dir1, true) {
 		t.Error("expected false for non-existent directory, got true")
 	}
 
@@ -201,7 +201,7 @@ func TestXLStorageIsDirEmpty(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if isDirEmpty(dir2) {
+	if isDirEmpty(dir2, true) {
 		t.Error("expected false for a file, got true")
 	}
 
@@ -212,7 +212,7 @@ func TestXLStorageIsDirEmpty(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if !isDirEmpty(dir3) {
+	if !isDirEmpty(dir3, true) {
 		t.Error("expected true for empty dir, got false")
 	}
 }