add error message for vkernel started with vm.vkernel_enable=0

[Joe Talbott]

On Thu, Jul 19, 2007 at 10:15:43AM -0700, Matthew Dillon wrote:
> :I'd like to add something like the attached patch to the vkernel to
> :let the user know that vm.vkernel_enable = 0.  I spent quite a while
> :today chasing down why mmap() was failing before remembering that I
> :needed to turn vm.vkernel_enable on.
> :
> :Joe
> 
>     That's fine, but adjust the sysctl to only read the variable, not
>     set it also (pass NULL for the newp argument to sysctlbyname).
> 

That's newlen that's 0.

Joe