Cut in half longitudinally, cut in half again longitudinally, so you now have 4 long pieces that each begin in one icing covered end, and stretch to the other icing covered end, then cut across the middle.
4 pieces, each with one quarter of an icing covered end and one eighth of the central cake
Surely that is the only way to do it? I was getting funny looks, and comments that yule log pieces are normally disc shape, but how can we each get a nice balance of cake and icing if you cut it all transverse?