anchor.diff:      (error "Bad magic : #x~x.
     Valid magic value is #xEF53." magic)))
   
  +(defun check-feature-incompat (feature-incompat)
  +  (unless (= #x2 (logand #b11111011111011111 feature-incompat))
  +    (error "Some feature not implemented from Incompatible feature set~%~b"
  +           (- #b11111011111011111 feature-incompat))))
  +
   (defun read-superblock (disk)
     (let* ((superblock (read-sector disk 2 2))
  -         (magic (sys.int::ub16ref/le superblock 56)))
  +         (magic (sys.int::ub16ref/le superblock 56))
  +         (feature-incompat (sys.int::ub32ref/le superblock 96)))
       (check-magic magic)
  +    (check-feature-incompat feature-incompat)
       (make-superblock :inodes-count (sys.int::ub32ref/le superblock 0)
                        :blocks-count (sys.int::ub32ref/le superblock 4)
                        :r-blocks-count (sys.int::ub32ref/le superblock 8)
  
positive.code: 
  (in-package :mezzano.ext-file-system)
  
  (defconstant +unknown-type+ #x0)
  (defconstant +regular-file-type+ #x1)
  (defconstant +directory-type+ #x2)
  
negative.code:                      :inode-size (sys.int::ub16ref/le superblock 88)
                       :block-group-nr (sys.int::ub16ref/le superblock 90)
                       :feature-compat (sys.int::ub32ref/le superblock 92)
                       :feature-incompat feature-incompat
                       :feature-ro-compat (sys.int::ub32ref/le superblock 100)
                       :uuid (logior (ash (sys.int::ub64ref/le superblock 112) 64)
                                     (sys.int::ub64ref/le superblock 104))
  