Hi!

I just tested your patch, Danny (last version attached): I took the
image at
<http://cdimage.debian.org/debian-cd/current/amd64/iso-cd/debian-8.7.1-amd64-netinst.iso>
and then did:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,m (gnu build file-systems)
scheme@(gnu build file-systems)> (define sb (read-iso9660-superblock "/tmp/debian-8.7.1-amd64-netinst.iso.part"))
scheme@(gnu build file-systems)> (iso9660-superblock-volume-name sb)
$2 = "Debian 8.7.1 amd64 1"
scheme@(gnu build file-systems)> (iso9660-superblock-uuid sb)
$3 = #vu8(50 48 49 55 48 49 49 54 49 49 48 49 48 49 48 48 0)
scheme@(gnu build file-systems)> (bytevector-length $3)
$4 = 17
scheme@(gnu build file-systems)> (uuid->string $3)
$5 = "32303137-3031-3136-3131-303130313030"
--8<---------------cut here---------------end--------------->8---

Seems to work!

Could you clarify the two “See grub” in here:

--8<---------------cut here---------------start------------->8---
(define (iso9660-superblock-uuid sblock)
  "Return the Volume ID of a iso9660 superblock SBLOCK as a 4-byte bytevector."
  ;; Note: The field is the volume creation time.
  ;; FIXME Use only certain parts (See grub).
  ;; FIXME treat "all 0" as invalid.
  (sub-bytevector sblock 813 17))

;; FIXME make result human-readable (See grub).
;(define (iso9660-uuid->string uuid)
--8<---------------cut here---------------end--------------->8---

Should ‘iso9660-uuid->string’ be different from ‘uuid->string’?

Anyway, I think we should polish and commit real soon.  :-)  Perhaps we
can add a note about endianness and assume little endian for now.

Thank you Danny!

Ludo’.