How do you do ZFS legacy mounts on 7.0.0 ?

["Jay F. Shachter" <jay%m5.chicago.il.us@localhost>]

Esteemed Colleagues:

I have just installed, fresh out of the oven, NetBSD 7.0.0 on my
multiboot computer.  NetBSD was the last operating system to be
installed, because I was waiting for 7.0.0 to come out.

I use ZFS to provide continuity among the different operating systems
installed on my computer.  I can be working on something on, e.g.,
Linux, and then reboot into, e.g., Solaris, or FreeBSD, and continue
working exactly where I left off, because directories like /home/jay
and /var/mail and /opt/assp and /var/www/htdocs reside on a ZFS pool
which is common to all the operating systems (well, most of them --
OpenBSD, alas, does not support ZFS, and neither do non-Unix systems
like Haiku or SkyOS, so I cannot use those operating systems for
serious work, even though I would very much like to, because my work
would be visible only on the system on which I started it).

I was astonished to discover that NetBSD 7.0.0, the newest of the
operating systems installed on my computer, required me to downrev my
zpool from Version 28 to Version 23, which was far from trivial, but I
am not writing to complain about that.  I am writing to ask, How do
you do a legacy ZFS mount on NetBSD?  I have two legacy filesystems in
my zpool.  One is my home directory, which I earlier referred to as
/home/jay, but you cannot use that name on a default-configured
Solaris system (/home belongs to the automounter, by default, on
Solaris) and also on FreeBSD, the default name for jay's home
directory is /usr/home/jay and not /home/jay (but that is less of a
problem, there are symbolic links).  An even better example is the
filesystem that contains my atjobs.  I want an atjob to run when it is
due even when I am working on a different operating system than the
one on which I originally scheduled it, but there is no common name
for the directory containing atjobs.  Consequently those filesystems
were created with mountpoint=legacy and they are asssociated with the
appropriate directory in each system's /etc/[v]fstab file.

Except on NetBSD, where I cannot get the bloody thing to work.  On
NetBSD, when I run

  mount -t zfs m5/jay /home/jay

I get an error message complaining about the nonexistence of
mounts_zfs, just as I do when I put

  m5/jay /home/jay zfs rw 0 0

in /etc/fstab, which works in every system that has an /etc/fstab
file, except for NetBSD.  Legacy mounts are not something that
requires a zpool version greater than 23 (parenthetically, I don't
know why NetBSD is still stuck there, since everything up to 28 was
open-sourced, but I am not complaining about that), so there is no
reason why they should be unavailable; I am assuming, in fact, that
they are available, I just need someone to tell me the correct
procedure.  Thank you in advance for any and all replies.

                        Jay F. Shachter
                        6424 N Whipple St
                        Chicago IL  60645-4111
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                                jay%m5.chicago.il.us@localhost
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