In order to ask What should be done? or What should we do? using an infinitival clause, you can readily say What's to be done? or What to do?.
(1) What's to do?
But I've heard (1) used in the same sense, which looks similar, at first blush, to either What's to be done? or What to do? but may well be syntactically different from either of those.
(A) Is (1) contemporary and legitimate, albeit less common than the other alternatives?
(B) Here are some of the constructions I think are similar to (1) in that the verb be functions as something other than a linking verb. Please see if they really are similar ones.
(2) What's to eat?
(3) What's to tell?
(4) Who's to blame?
(5) What's not to like?
(6) The guardrail is to prevent vehicles from driving off the road.
Edit: One way to find coherence among all of these is that you can insert the dummy "there" right after "is" and make their meanings more apparent.
Edit: As for (6), however, I'm not quite sure whether the there in The guardrail is there to prevent vehicles from driving off the road. would be a locative adverb (as opposed to here) or the dummy there (as in There's a book on the desk.)