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From: Lowell Gilbert <freebsd-questions-local@be-well.ilk.org>
To: paul beard <paulbeard@gmail.com>
Subject: Re: what should uname -v be telling me here?
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 (paul beard's message of "Fri, 27 Jun 2014 13:57:06 -0700")
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paul beard <paulbeard@gmail.com> writes:

> On Fri, Jun 27, 2014 at 1:36 PM, Polytropon <freebsd@edvax.de> wrote:
>> You need to find out where /boot resides (in my case,
>> it's on ad4s1a, which is mounted at /) to identify the boot
>> device (or to be precise, the device the kernel has been read
>> from).
>
>
> I keep thinking this should be something you ought to be able to
> discover without being on console. I realize the BIOS can't be
> interrogated but if I knew that the active kernel was ad3:/boot/kernel
> or ad2:/boot/kernel, it would be useful. Kind of surprised that
> doesn't appear anywhere in dmesg or that it can't be read out of
> somewhere.

The boot procedure has to load and boot the kernel without having the
kernel available to create the device nomenclature. [Kind of obvious,
if you think about it.] So interrogating the firmware is the only way
the kernel *could* know where it was booted from. That's impossible 
in the BIOS world, and even if there were a table indicating it in an
ACPI table, that would only tell you which disk the bootloader came
from, which isn't necessarily where the kernel came from.