"zfs upgrade" of a mounted filesystem?

[Neil Hoggarth]

I have a 7-STABLE system with root-on-ZFS using the recipe from the wiki 
(http://wiki.freebsd.org/ZFSOnRoot), with a small UFS /boot partition on a 
flash disk.

I updated the system a few days ago and have upgraded the zpool to version 
13 and most of the filesystems to version 3, but I can't upgrade the 
filesystem version for the root filesystem as this is always mounted and 
it seems that "zfs upgrade" needs to unmount a filesystem to work on it?

neilhoggarth-2# zfs upgrade
This system is currently running ZFS filesystem version 3.

The following filesystems are out of date, and can be upgraded.  After 
being upgraded, these filesystems (and any 'zfs send' streams generated 
from subsequent snapshots) will no longer be accessible by older software 
versions.


VER  FILESYSTEM
---  ------------
  1   newtank
neilhoggarth-2# zfs upgrade newtank
cannot unmount '/': Invalid argument

Is there any way to work around this?

Or will I need alternate boot/livefs media that incorporates ZFS v13 
userland utilities to make the change?

Regards,

Neil.