anchor.diff:                                                    (superblock-desc-size superblock) 32))
                       (with n-octets := (* block-group-size (n-block-groups superblock)))
                       (with block := (read-block disk superblock 1
  +                                               (ceiling
                                                  (/ n-octets
                                                     (block-device-sector-size disk)
  -                                                  (block-size disk superblock))))
  +                                                  (block-size disk superblock)))))
                       (for offset :from 0 :below n-octets :by block-group-size)
                       (collecting (read-block-group-descriptor superblock block offset)))))
   
  
positive.code: 
  (defmethod mount-host ((host ext4-host) block-device)
    (let ((superblock (read-superblock block-device)))
      (when (and superblock (string= (superblock-uuid superblock)
                                     (file-host-mount-args host)))
        (init-host host block-device superblock)
        T)))
  
  
negative.code:   (feature-compat nil :type (unsigned-byte 32))
    (feature-incompat nil :type (unsigned-byte 32))
    (feature-ro-compat nil :type (unsigned-byte 32))
    (uuid nil :type string)
    (volume-name nil :type string)
    (last-mounted nil :type string)
    (algorithm-bitmap nil :type (unsigned-byte 32))
    (prealloc-blocks nil :type (unsigned-byte 8))
    (prealloc-dir-blocks nil :type (unsigned-byte 8))
    (reserved-gdt-blocks nil :type (unsigned-byte 16))
    (journal-uuid nil :type string)
    (journal-inum nil :type (unsigned-byte 32))
    (journal-dev nil :type (unsigned-byte 32))
    (last-orphan nil :type (unsigned-byte 32))
  