problem upgrading to 2.1 - kernel moved to boot

[Thomas Nikolajsen <thomas.nikolajsen@xxxxxxx>]

I upgraded a host from DragonFly 2.0 to 2.1, it caused trouble:
 - world was build on other host; /usr/{src,obj} NFS mounted by this host
 - using normal procedure, as described in build(7) failed at installkernel:
root file system filled up; didn't stop with message that I
'.. need to make buildworld, installworld, and upgrade ..'
before installing kernel. sys/conf/kern.post.mk not used?
 - doing `make upgrade' before installkernel works

What is reason to demand `make upgrade' before installkernel?

Couldn't we just move old kernel/modules to boot in installkernel?
(then we wouldn't need special instructions for vkernel upgrade either)

 -thomas