This was added in #36047 just as a way to make sure the tree is fully
unmounted on shutdown.
For ZFS this could be a breaking change since there was no unmount before.
Someone could have setup the zfs tree themselves. It would be better, if
we really do want the cleanup to actually the unpacked layers checking
for mounts rather than a blind recursive unmount of the root.
BTRFS does not use mounts and does not need to unmount anyway.
These was only an unmount to begin with because for some reason the
btrfs tree was being moutned with `private` propagation.
For the other graphdrivers that still have a recursive unmount here...
these were already being unmounted and performing the recursive unmount
shouldn't break anything. If anyone had anything mounted at the
graphdriver location it would have been unmounted on shutdown anyway.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Upstream-commit: 2fe4f888bee52b1f256d6fa5e20f9b061d30221c
Component: engine
Brian Goff
33ddc6d172