anchor.diff:    (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 (unsigned-byte 128))
  +  (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 (unsigned-byte 128))
  +  (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))
  
positive.code:                                                   (superblock-desc-size superblock) 32))
                      (with n-octets := (* block-group-size (n-block-groups superblock)))
                      (with block := (read-block disk superblock 1
                                                 (/ n-octets
                                                    (block-device-sector-size disk)
                                                    (block-size disk superblock))))
                      (for offset :from 0 :below n-octets :by block-group-size)
                      (collecting (read-block-group-descriptor superblock block offset)))))
  
  
negative.code:                          :feature-compat (sys.int::ub32ref/le superblock 92)
                           :feature-incompat feature-incompat
                           :feature-ro-compat (sys.int::ub32ref/le superblock 100)
                           :uuid  (uuid:uuid-buffer->string superblock :offset 104)
                           :volume-name (map 'string #'code-char (subseq superblock 120 136))
                           :last-mounted (map 'string #'code-char (subseq superblock 136 200))
                           :algorithm-bitmap (sys.int::ub32ref/le superblock 200)
                           :prealloc-blocks (aref superblock 204)
                           :prealloc-dir-blocks (aref superblock 205)
                           :reserved-gdt-blocks (sys.int::ub16ref/le superblock 206)
                           :journal-uuid (uuid:uuid-buffer->string superblock :offset 208)
                           :journal-inum (sys.int::ub32ref/le superblock 224)
                           :journal-dev (sys.int::ub32ref/le superblock 228)
                           :last-orphan (sys.int::ub32ref/le superblock 232)
  