Impolite

Hello,

Some guy was looking for my boss, but my boss wasn't around. And i asked the guy "and who are you sir?" (The guy i was talking with is the big boss of another company.) Then after a couple of minutes i realized that what i said was IMPOLITE.

Which one is more polite? How do native speakers render this?

(I would have said...) Can I have your name sir? May I know your name sir? May I know who wants to speak with my boss? What's your name again sir? May I get your name sir?

Thank you!