> however, the whatever_disk_and_partition argument must be
> the MSDOS partition described on the NetBSD disklabel on that hard disk.
> What this means is that you need to disklabel that hard drive.  This is
> pretty dangerous because you could potentially write over the MSDOS
> partition information, and make it unusable to MSDOS w/o a reformat.

It seems like there ought to be a way to disklabel a disk without writing
the label (and I think that's what DIOCSDINFO does); assuming that's correct,
perhaps the disklabel program can grow an option to soft-label a disk.

Alternatively, the msdos mount system call could observe that a drive is not
partitioned (can it tell?), and hunt around for the necessary information.
(Unfortunately, the FAT doesn't have a really good signature in it (and isn't
guaranteed to have a signature at all if the MSDOS version is too old).)