Use d_opendata for device specific data.
For me, when booting (amd64, BIOS boot) off ZFS, this clears the 'BTX halted' showstopper during early bootup.
UFS is not involved, installer media is unplugged.
Some console spam, from ffs_subr.c, is shown. Hyperlink to photo: https://plak.infrapuin.nl/selif/20220815135942copy1.jpg
In my automated testing, I don't see any of the reported spam and it works. I'll commit this shortly and let tsoome followup to deal with the 'when do we free' it issue that's still present, but mostly harmless for the environments that we'll be running in.