mount root from zfs fails under current with "error 6"

[Garrett Cooper]

On Mon, May 30, 2011 at 9:48 AM, Michael Reifenberger
<mike at reifenberger.com> wrote:
> Hi,
> I get the following error with recent -current (r222417) during boot:
> ...
> Trying to mount root from zfs:boot/ROOT/root []...
> Mounting from zfs:boot/ROOT/root failed with error 6.
> ...
>
> What does "error 6" mean?

See ENXIO under errno(2).

> The strange thing is, that I could boot with r222417 a few times
> but after applying a (here unrelated) one-liner from rmacklem@ to
> nfs_clkdtrace.c, recompile the module and reinstall, I could'n load either
> kernel nor kernel.old.
> I didn't even use the patched module.
>
> Only loading a kernel r221381 let me boot again.
>
> So may it be a race condition of some form?
>
> Anyone else sees this?
>
> Any further infos are available on request.

    dmesg for starters (boot -v if possible) would be extremely
helpful. More details like your disk subsystem that you're booting off
of, whether you're using GPT/MBR when booting via ZFS, etc would be
helpful. Also being able to better trace down the root cause would be
nice (not being able to boot a recent kernel, but being able to boot a
kernel from almost a month ago is unfortunately a bit of a non-starter
for tracking down the actual issue because that's such a long span of
time).
Thanks,
-Garrett