In article [ref] (at Thu, 24 Jul 2003 18:02:35 +0400 (MSD)), kuznet@ms2.inr.ac.ru says:

Maybe, struct is better, but I am inclined to think in this case it is wrong.
It is going to be extended, so newly compiled applications will see
truncated structs from older kernels and will have to do ugly job
verifying validity of fields using some offsetof. In the case of array
it is natural at least.

I'm not so sure about the "array," but anyway,
I don't think it is so ugly to use struct / offsetof.

--yoshfuji