Completely disable the zfs binary from attempting to directly update
/etc/mtab. The Linux port relies entirely on the mount.zfs helper
to safely update /etc/mtab. If we left the /etc/mtab updates to
the zfs binary then they could race with concurrent non-zfs mounts.
Routing everything through the system mount command ensures the
/etc/mtab updates are locked properly.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #329
b740d602bd