(define (backend-nullwrap be)
   (make-storage
      (storage-max-block-size be)
      (storage-writable? be)
      (storage-unlinkable? be)
      (lambda (key data type) ; put!
         ((storage-put! be) key data type))
      (lambda () ; flush!
        ((storage-flush! be)))
      (lambda (key) ; exists?
         ((storage-exists? be) key))
      (lambda (key) ; get
         ((storage-get be) key))
      (lambda (key) ; link!
         ((storage-link! be) key))
      (lambda (key) ; unlink!
         ((storage-unlink! be) key))
      (lambda (tag key) ; set-tag!
         ((storage-set-tag! be) tag key))
      (lambda (tag) ; tag
         ((storage-tag be) tag))
      (lambda () ; all-tags
         ((storage-all-tags be)))
      (lambda (tag) ; remove-tag!
         ((storage-remove-tag! be) tag))
      (lambda (tag) ; lock-tag!
         ((storage-lock-tag! be) tag))
      (lambda (tag) ; tag-locked?
         ((storage-tag-locked? be) tag))
      (lambda (tag) ; unlock-tag!
         ((storage-unlock-tag! be) tag))
      (lambda (command) ; admin!
         ((storage-admin! be) command))
      (lambda () ; close!
         ((storage-close! be)))))

(define (backend-limit-block-size be max-block-size)
   (make-storage
      (min max-block-size (storage-max-block-size be))
      (storage-writable? be)
      (storage-unlinkable? be)
      (lambda (key data type) ; put!
         ((storage-put! be) key data type))
      (lambda () ; flush!
        ((storage-flush! be)))
      (lambda (key) ; exists?
         ((storage-exists? be) key))
      (lambda (key) ; get
         ((storage-get be) key))
      (lambda (key) ; link!
         ((storage-link! be) key))
      (lambda (key) ; unlink!
         ((storage-unlink! be) key))
      (lambda (tag key) ; set-tag!
         ((storage-set-tag! be) tag key))
      (lambda (tag) ; tag
         ((storage-tag be) tag))
      (lambda () ; all-tags
         ((storage-all-tags be)))
      (lambda (tag) ; remove-tag!
         ((storage-remove-tag! be) tag))
      (lambda (tag) ; lock-tag!
         ((storage-lock-tag! be) tag))
      (lambda (tag) ; tag-locked?
         ((storage-tag-locked? be) tag))
      (lambda (tag) ; unlock-tag!
         ((storage-unlock-tag! be) tag))
      (lambda (command) ; admin!
         ((storage-admin! be) command))
      (lambda () ; close!
         ((storage-close! be)))))