anchor.diff:    (* (index inode-n superblock) (superblock-inode-size superblock)))
   
   (defun n-block-groups (superblock)
  -  (let ((tmp (ceiling (/ (superblock-inodes-count superblock) (superblock-inodes-per-group superblock)))))
  -    (assert (= tmp (ceiling (/ (superblock-blocks-count superblock) (superblock-blocks-per-group superblock)))))
  -    (ceiling (/ (superblock-blocks-count superblock) (superblock-blocks-per-group superblock)))))
  +  (let ((n-block-groups (ceiling (/ (superblock-blocks-count superblock) (superblock-blocks-per-group superblock)))))
  +    (assert (= (ceiling (/ (superblock-inodes-count superblock) (superblock-inodes-per-group superblock)))
  +               n-block-groups))
  +    n-block-groups))
   
   (defstruct block-group-descriptor
     (block-bitmap)
  
positive.code:   (name nil :type string))
  
  (defun read-linked-directory-entry (block offset)
    (let* ((name-len (aref block (+ 6 offset))))
      (make-linked-directory-entry :inode (sys.int::ub32ref/le block (+ 0 offset))
                                   :rec-len (sys.int::ub16ref/le block (+ 4 offset))
                                   :name-len name-len
  
negative.code:                (error ":create not implemented")))))
        (when (and (not created-file) (member direction '(:output :io)))
          (error ":output :io not implemented"))
        (cond ((or (eql element-type :default)
                   (subtypep element-type 'character))
               (assert (member external-format '(:default :utf-8))
                       (external-format))
               (make-instance 'ext-file-character-stream
                              :pathname pathname
                              :host host
                              :direction direction
                              :file-inode file-inode
                              :buffer buffer
                              :position file-position
                              :length file-length
                              :abort-action abort-action))
              ((and (subtypep element-type '(unsigned-byte 8))
                    (subtypep '(unsigned-byte 8) element-type))
               (assert (eql external-format :default) (external-format))
               (make-instance 'ext-file-stream
                              :pathname pathname
                              :host host
                              :direction direction
                              :file-inode file-inode
                              :buffer buffer
                              :position file-position
                              :length file-length
                              :abort-action abort-action))
              (t (error "Unsupported element-type ~S." element-type))))))
  
  (defmethod probe-using-host ((host ext-host) pathname)
    (multiple-value-bind (inode-n) (find-file host pathname)
      (if inode-n t nil)))
  
  (defmethod directory-using-host ((host ext-host) pathname &key)
    (let ((inode-n (find-file host pathname))
          (disk (partition host))
  