SODA Noriyuki wrote:

> >>>>> On Fri, 7 Jul 2006 18:05:34 -0700,
>       Jason Thorpe <thorpej@shagadelic.org> said:
> 
> >> this is false.  we have added more info to several sysctl's that
> >> could have been ioctl's and it did not require versioning the
> >> interface.  see KERN_PROC2.
> 
> > I was pretty much speaking about ioctls.
> 
> How ioctls differ from sysctl?
> It's just same with sysctl from this point of view.
> i.e. You can just assign different ioctl number.

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.

Simon.