diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 8d0f71e..926ebcb 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1610,6 +1610,17 @@
 }
 
 /*
+ * helper functions to deal with 32 or 64bit block numbers.
+ */
+size_t journal_tag_bytes(journal_t *journal)
+{
+	if (JBD2_HAS_INCOMPAT_FEATURE(journal, JBD2_FEATURE_INCOMPAT_64BIT))
+		return JBD_TAG_SIZE64;
+	else
+		return JBD_TAG_SIZE32;
+}
+
+/*
  * Simple support for retrying memory allocations.  Introduced to help to
  * debug different VM deadlock avoidance strategies.
  */