From: Ben Crocker on
gitlab.com
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/757#note_45044...
The warning actually comes from the text that is being cat'ed to
the output file, so I think this is legitimate, if somewhat confusing.
And no, rootfs is defined in this script; bootprefix will be set,
ultimately, by whomever invokes bls.conf.