Use sys.platform to choose the correct implementation of functions and
values of variables for the platform being run on.
Reword some comments to avoid describing implementation details in the
wrong places.
Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Signed-off-by: Ryan Moeller <ryan@ixsystems.com>
Closes#9561