According to the documentation, "The lower filesystem can be any filesystem supported by Linux", however this appears to not actually be the case, since using a vfat filesystem results in the mount command printing "mount: wrong fs type, bad option, bad superblock on overlay, missing codepage or helper program, or other error", with dmesg saying "overlayfs: filesystem on '/boot' not supported". (that's from ovl_mount_dir_noesc(), when ovl_dentry_weird() returns nonzero) Should vfat be supported, or is the documentation wrong? If the documentation is wrong, what other filesystems are (not) supported?
