The question specifies smoke in the cockpit and flight crew protective breathing equipment makes use of the crew’s normal oxygen masks with the addition of smoke goggles.

The masks form a seal to the face so the ingress of smoke is not a problem.

The normal oxygen supply is a diluter system which cannot be selected when smoke is present so 100% oxygen is selected.

Smoke hoods for use by cabin crew may require a positive pressure to prevent the ingress of smoke.