Looks like a carbon patch on the floor. White smoke should be water/coolant. Next time it smokes white, stick you nose close and sniff it, smell for coolant. Stick your hand in the smoke and feel it between your fingers, then smell your hand.
Do a cylinder pressure test. Take the valve covers off and look for a broken valve spring, bent push rod, broken/bent rocker.
I'll check for coolant smell next time I have time to diagnose it. I don't have a cylinder pressure tester, but they seem pretty cheap on Amazon. I think a coworker of mine might have one.
