What function does the loop serve? It looks [pointless to me].
I looked at the loop and my impression is the same.
Okay, so that substantially reduces the chance I just missed something.
I guess it was meant at some point to find an un-aligned disklabel,
or something like that.
I suspect you are correct. On various other ports, disksubr.c contains
code that _does_ look for a disklabel all through the relevant sector.
I suspect this was copied, changed, and never cleaned up. (I'm doing
an experiment involving disklabels, involving going through all ports
on the version I'm using, looking at most disklabel code, so I am in a
position to be confident that other ports have relatively similar code
that does loop.)
This code comes from pmax port around 1994.