device filtering support

[Segher Boessenkool]

> Yeah. The problem is select is non-portable, so we can't really go  
> adding platform specific items we're going to remove anyway.

select() is portable just fine; you just don't have a fast  
implementation
of it on your platform.

We aren't going to remove select() usage, it is part of the API.  We can
(and should) add some alternative(s) and gently nudge people to use  
those
(if they want their program to be ultimately portable).

> Callbacks have the advantage of being universal,

That isn't quite true in the face of preemptive threading,  
unfortunately.

> We could suffix _dev to any new API call from the dev branch, such  
> as any hotplug callback API to make it clear that one should expect  
> potential breakage or removal.

Let's not, it is just churn.  People should expect the API to be  
unstable
simply when we tell them it is :-)


Segher