forks, patches, bikeshedding.
example usage:
; ramfs -u
; unionfs -m /sys -c /tmp /usr/qwx/p/fork/sys /tmp /sys
; cd /tmp
; mkdir -p `{cd /sys; walk -d src include}
; cd /sys/src
; mk nuke
; mk install
unionfs: http://shithub.us/kvik/unionfs/HEAD/f.html