Booting with root fs on another partition

[Wim Lewis <wiml%hhhh.org@localhost>]

I've installed NetBSD 4.0.1, and more recently 5.0, on a PPC Mac  
Mini. 4.0.1 works fine. And the 5.0 kernel seems to be fine. However,  
I can't figure out how to boot 5.0 so that its root filesystem is the  
partition containing the 5.0 userland --- it always mounts partition  
'a' as root, which holds 4.0.1. What I want to do is have partition  
'e' be the root when booting into 5.0. Is there  a way to do this?  
I've tried various likely-seeming permutations of open firmware  
commands to no avail.

Looking through the kernel sources, I found these lines in  
ofw_autoconf.c:

  186                 /* booted_partition = *p - '';         XXX  
correct? */

  353                 booted_partition = 0; /* XXX -- should be  
extracted from bootpath */

which kind of make me think that there is no way to specify the  
rootfs partition at boot time.

Any ideas? Am I barking up the wrong tree? I'd rather not wipe 4.0.1  
off of partition 'a' just yet.