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: (defpackage :mezzano.ext4-file-system
    (:use :cl :mezzano.file-system :mezzano.file-system-cache :mezzano.disk :iterate)
    (:local-nicknames (:sys.int :mezzano.internals)
                      (:sup :mezzano.supervisor))
    (:export))
  
  (in-package :mezzano.ext4-file-system)
  
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)
  