block dangerous passthrough operation

[Chaitanya Kulkarni]

> There's nothing preventing a vendor specific command from being just as
> destructive either, but you can't realistically fence those off either.
> I've always said the driver should not police this user interface as
> that inevitably gets in the way of its flexibility.
> 

The list will grow over time and we'll have to deal with all sorts of
patches/spec modifications and even if we all do that as mentioned
earlier I don't see any way to block Vendor specific commands ...

-ck