Anyone who's looking to use overlayfs on versions of openSUSE prior to linux kernel 3.18 (such as openSUSE 13.2):

The documentation is sparse. After much searching and experimentation, I found that openSUSE's implementation of overlayfs must be used exactly this way:

mount -t overlayfs -o lowerdir=/path/to/lowerdir,upperdir=/path/to/upperdir overlayfs /mount/point

That is to say: the filesystem type must be overlayfs, the lowerdir and upperdir option parameters are required, and the openSUSE implementation does not recognize the workdir option parameter.