add ntfs_inode_base() helper

include/ntfs-3g/inode.h

@@ -149,6 +149,8 @@ struct _ntfs_inode {
 	time_t last_access_time;
 };
 
+extern ntfs_inode *ntfs_inode_base(ntfs_inode *ni);
+
 extern ntfs_inode *ntfs_inode_allocate(ntfs_volume *vol);
 
 extern ntfs_inode *ntfs_inode_open(ntfs_volume *vol, const MFT_REF mref);

libntfs-3g/inode.c

@@ -51,6 +51,13 @@
 #include "logging.h"
 #include "misc.h"
 
+ntfs_inode *ntfs_inode_base(ntfs_inode *ni)
+{
+	if (ni->nr_extents == -1)
+		return ni->base_ni;
+	return ni;
+}
+
 /**
  * ntfs_inode_mark_dirty - set the inode (and its base inode if it exists) dirty
  * @ni:		ntfs inode to set dirty