zfs_enable vs zfs_load in loader.conf (but neither works)

[Andriy Gapon]

on 15/09/2013 17:16 J David said the following:
> Thanks very much for the info Andriy.
> 
> On Fri, Sep 13, 2013 at 9:22 AM, Andriy Gapon <avg at freebsd.org> wrote:
>> Another piece of information is that neither mountpoint nor canmount property
>> affects ZFS root mounting.
> 
> It is mountpoint=legacy that boots on this machine and mountpoint=/
> that can't find init, with no other changes.  So clearly under some
> obscure edge case, this is not strictly correct.

I am sure that the same can be said about almost anything documented about any
software...

> Did your test include zpool root != filesystem root?  Because as you
> describe one possible cause of the problem is mounting the wrong
> filesystem as root, one wonders if somehow with the mountpoint=/
> setting the zpool root (which has no files at all) is incorrectly
> being chosen as fsroot with mountpoint=/ on data/root.  I.e. perhaps
> somewhere in the code is looking for "legacy" (or skipping anything
> with a mountpoint set) and defaulting back to the zpool root if it is
> not found?

I tried to reproduce with exactly the same configuration as you described.
To be specific, yes I used data/root as a root filesystem and I set its
mountpoint to "/".

> Unfortunately there is no way I know of to check and see what the root
> filesystem turned out to be after the failure to find init.  That
> would reduce speculation about what is happening quite a bit.  Can the
> kernel debugger extract this info?

Unfortunately, I am not sure if it is possible to obtain anu useful information
from ddb and saving a crash dump is not possible in pre-init environment.
I could write a patch that would print some useful debugging info.
Will you able to use it?

-- 
Andriy Gapon