>>>>> On Sat, 08 Jul 2006 11:37:33 +1000,
      Simon Burge <simonb@NetBSD.org> said:

> For some sysctls (eg KERN_PROC2), a length arg for the output struct is
> passed by userland.  If that grows in the future, the userland program
> only sees how much of the struct it asked for.  New fields are added to
> the end only of the struct, and old programs continue to work.

Isn't a length arg passed for ioctls too?
(i.e. 4th argument of _IOC() macro).
-- 
soda