Re: what should uname -v be telling me here?

On 06/27/2014 04:22 PM, Lowell Gilbert wrote:
> 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.

Another bit of information is available if you peek at what loader(8)
told the kernel, via kenv(1).

From a box booting UFS:
----8<----
# kenv
....
currdev="disk0s4a:"
loaddev="disk0s4a:"
kernelname="/boot/10.0p6-GENERIC/kernel"
....
----8<----

And from one booting ZFS:
----8<----
# kenv
....
currdev="zfs:paka/root/10.0:"
loaddev="zfs:paka/root/10.0:"
kernelname="/boot/10.0p6-PAKA/kernel"
....
----8<----

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