-extern struct address_space_operations ext2_aops;
-extern struct address_space_operations ext2_aops_xip;
-extern struct address_space_operations ext2_nobh_aops;
+extern const struct address_space_operations ext2_aops;
+extern const struct address_space_operations ext2_aops_xip;
+extern const struct address_space_operations ext2_nobh_aops;