with multiple entries as follows:
start address, end address, resident pages in range, private pages
in range, RW/RO, COW or not, (vnode/device/swap/default).
process won't possibly block before filling in the fsnode pointer (v_data)
which might be dereferenced during a sync since the vnode is put on the
mnt_vnodelist by getnewvnode.
Pointed out by Matt Day <mday@artisoft.com>
