An idea for the EFI (LUA) loader....

Here's the scenario: /You have an embedded system that boots EFI.  You 
can't control other than the media that's in the box that it boots from 
(which someone sticks in there.)  There might be other media in there, 
and there might not./

Right now the FreeBSD EFI loader will boot from the first bootable 
"thing" it finds unless told otherwise (e.g. "rootdev=")

The problem is that it wants something like "rootdev=disk0s1a" -- a full 
specification.

But what happens if someone sticks another device in there /and the EFI 
BIOS enumerates it first?/  Its not bootable (doesn't have an EFI 
partition) so the BIOS doesn't try to boot it, but it /does /enumerate 
it so now the disk is "disk1s1a" -- and if you set disk0 you are now 
stuck at the loader prompt.

Which is ok if there's a console you can key in where to boot from and 
then fix loader.conf.  If the machine is headless.....

If loader.efi could take a syntax /without /the disk (e.g. "s1a") and, 
if that was what was specified /it would look on the device loader.efi 
was loaded from /then it wouldn't matter if someone did this.  Once the 
kernel is loaded it should be ok.

You'd think you could detect this with either efibootmgr (what order 
will it enumerate in?) or from sysctl to figure out where it booted 
from, but nope -- what's in there may not match how the BIOS enumerated 
it, never mind that someone could unplug a USB device (or pull an nVME 
stick) and change it.  I've got a machine here that demonstrates this; 
it SAYS it loaded off disk0 but the BIOS says the boot device is disk1 
and if I put disk0.... in loader.conf it tries to boot the nVME device 
instead of the USB stick.

A minimal way would be to be able to discern what the BIOS saw as the 
enumerated device it loaded from, but even better, I think, would be to 
be able to specify just the partition and slice/filesystem and have the 
drive default to "where loader.efi came from" which, I suspect, would 
resolve both possibilities. Obviously if the BIOS enumerates something 
that has a valid EFI partition it can still get it wrong but if not that 
should work -- yes?

Am I nuts? :-)

PS: I've got zero experience with lua as a language so if I start 
digging into this the learning curve might be pretty steep where for 
someone who's coded in lua it might be five minutes..... unless I'm 
wildly off-base here.

-- 
Karl Denninger
karl@denninger.net
/The Market Ticker/
/[S/MIME encrypted email preferred]/