Re: GuixSD bootable ISO-9669 image

[Danny Milosavljevic <dannym@scratchpost.org>]

Hi Ludo,

>I’d prefer to add a special ‘iso-9660-uuid’ form similar to ‘uuid’ in (gnu system file-systems).
> That way we could detect that we get a valid UUID at macro-expansion
> time or system-instantiation time, rather than end up with an error at
> boot time.

Hmm, I've never seen that macro before.  Should it be used in config.scm ?

Right now config.scm could have:

  (file-systems (cons* (file-system
                        (device "1234-5678-....")
                        (title 'uuid)
                        (mount-point "/")
                        (type "ext4")
                        (needed-for-boot? #t))

Which kind of UUID is it then?  Should string->uuid try to be clever about it?  Or a new function string->uuid-like ?

find-partition-by-uuid right now uses read-partition-uuid and then uses bytevector=?.

So all these forms should continue to be bytevectors.  Then it would work fine without lots of changes.

So something like this?

- Add "string->uuid-like" and use it in canonical-title (instead of using "string->uuid").
- string->uuid-like would have a case analysis by some weird markers, then parse the uuid using the right parser into a bytevector with length typical-for-this-filesystem-but-not-unique.
- Modify uuid->string to have a case analysis by the bytevector length, then print the uuid using the right printer into a string typical-for-this-filesystem.  This will fail to detect ISO9660 correctly because these are the same length as real uuids (Linux uses 16 bytes of the 17-byte iso9660-uuid)
- Leave the uuid macro as-is since it should already do the right thing then?
- Add a new macro fat32-uuid, and a new macro iso9660-uuid.

String lengths:
- FAT32 UUID-string: 3 Byte to 9 Byte (variable-length numerals.  Is that actually how Linux writes them?  I misplaced my USB stick... where is it? *mumbles*)
- ISO9660 UUID-string: 16 Byte (fixed-length numerals).  That's the same length as the ISO9660 bytevector since it's actually the same content
- Real UUID-string: 36 Byte

Bytevector lengths (right now):
- FAT32 UUID: 4 Byte
- ISO9660 UUID: 16 Byte (oops...)
- Real UUID: 16 Byte