efivar(8) status/usability/functionality in 15

Hi folks,

After 15.1-R branched, I performed major upgrade and took the idea of
setting up Secure Boot from my personal backlog. As a preparation
step, wanted to see which EFI variables I have, but that failed:
$ sudo efivar -l
efivar: error listing variables: Function not implemented

Tried to get variable that exists for sure but it also failed:
$ sudo efivar -n e11207ca-d4ad-11ee-928b-589cfc102103-Boot0000 -p
efivar: show variable: Function not implemented

Of course, module is loaded:
$ kldstat -v | grep efi
20    1 0xffffffff839a6000     46e9 efirt.ko (/boot/kernel/efirt.ko)
                177 efidev
                178 nexus/efirtc
                176 efirt

And basically every command (except '-w' which I haven't verified
because I can't read variables, and '-L' which lists some GUIDs) fails
and efivar feels like a stub (at first glance it all was the same on
14). If I'm doing something wrong--I'd love to see some success
stories.

//CC: imp@ who's the only effective committer for the path of utility.
Please let me know if this is unwelcome.

--
wbr,
Anton