> rename it, and keep the old one if COMPAT_15 is defined...

Um, would that present *both* names on a system with COMPAT_15, or
just the old name?

Both names is good backward compatibility but having only one name or
the other depending on a kernel define would not be so good.  At this
point it may be obvious I'm not very familiar with the sysctl code. :-)

Giles