So I noticed an interesting problem:

# mknod foo c 4095 1048575
# ls -l foo
crw-r--r--  1 root  wheel    0,   0 Jan 17 05:25 foo
# 

This is due to the special case for VNOVAL in ufs_mknod().
Technically, VNOVAL in any vattr field means `no value', so changing
this is really not correct.

What I wonder is why VOP_MKNOD() uses a vattr at all?!  This seems
pretty bogus.