How to retrieve the "bootpath" variable in a running FreeBSD ?

[Olivier Cochard-Labbé]

Hi all,

I've almost finish my nanobsd-sparc64 script but I meet a problem for
the upgrade script.
The last step of the upgrade process is to modify the OPB for booting
on the new-system-partition "d" of my drive in place of the
old-system-partition "a".
I can use a simple command like this:
eeprom boot-device=disk:d
But this method is too stupid because it didn't works if my nanobsd is
installed on another disk than the disk corresponding to the nvram
alias "disk".
This is why I want to use the more precise variable "bootpath" that is
display during the FreeBSD bootstrap loader like on this capture:

FreeBSD/sparc64 bootstrap loader, Revision 1.0
(root at sparc.orange.bsdrp.net, Sat Jan 12 10:12:01 UTC 2013)
bootpath="/pci at 1f,0/ide at d/disk at 1,0:a"

But, I've checked in "sysctl -a" and in "eeprom -a"… I didn't found it.
Do you know where I can found it from my running FreeBSD ?

Thanks,

Olivier