With the update to onnv_141 how minor devices were created and
removed for ZVOL was substantially changed. The updated system
is much more tightly integrated with Solaris's /dev/ filesystem.
This is great for Solaris but bad for Linux.
This patch keeps as much of those changes as possible which as
useful for Linux. But it also reverts back to use the old system
of explicit minor node creation via a decicated ioctl(). This
worked well in zfs-0.4.9 and it should continue to work well.
Solaris recently introduced the idea of drive topology because
where a drive is located does matter. I have already handled
this with udev/blkid integration under Linux so I'm hopeful
this case can simply be removed but for now I've just stubbed
out what is needed in libspl and commented out the rest here.
Brian Behlendorf