network driver

I’m very beginer in writing drivers, and in first I’m get a example of
driver from DDK documentation.
I only change in io_net_registrant_t.top_type as “null”
When I use :
io-net -d null -p tcpip &
I have any errors, can see process ID, but when use ps -A process
“done”, and of course nothing mounted on /dev/io-net/null0.
Is it ok , or I forgot something?