I don't know about 'b5' but OpenBSD has chosen 'a6' as its
partition id.
And I also am unable to mount OpenBSD partitions from
within Linux.
Currently, it appears that genhd.c looks for a primary
partition of type 'a5' .. I've modified it to look for
'a6' as well, and it finds the disklabel fine (because
the disklabel is treated as an extended partition)..
However, what about the case where BSD is able to
'disklabel' a disk 'ignoring' the mbr record, taking
over the disk with a disklabel? I don't think this
would be too hard to support, I'll look into it.
Anyway, I'm needing to mount OpenBSD partitions from
linux .. and thus will be doing one of two things:
a) updating 'ufs' to be able to handle ffs filesystems
b) creating 'ffs' as a filesystem in the event that
modifying the existing 'ufs' is not desirable
-- Todd T. Fries .. friest@acm.org