FreeBSD: Update usage of py-sysctl

py-sysctl now includes the CTLTYPE_NODE type nodes in the list returned
by sysctl.filter() on FreeBSD head.  It also provides descriptions now.

Eliminate the subprocess call to get descriptions, and filter out the
nodes so we only deal with values.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #11318

cmd/arc_summary/arc_summary2

@@ -59,14 +59,20 @@ if sys.platform.startswith('freebsd'):
     # Requires py27-sysctl on FreeBSD
     import sysctl
 
+    def is_value(ctl):
+        return ctl.type != sysctl.CTLTYPE_NODE
+
     def load_kstats(namespace):
         """Collect information on a specific subsystem of the ARC"""
 
         base = 'kstat.zfs.misc.%s.' % namespace
-        return [(kstat.name, D(kstat.value)) for kstat in sysctl.filter(base)]
+        fmt = lambda kstat: (kstat.name, D(kstat.value))
+        kstats = sysctl.filter(base)
+        return [fmt(kstat) for kstat in kstats if is_value(kstat)]
 
     def load_tunables():
-        return dict((ctl.name, ctl.value) for ctl in sysctl.filter('vfs.zfs'))
+        ctls = sysctl.filter('vfs.zfs')
+        return dict((ctl.name, ctl.value) for ctl in ctls if is_value(ctl))
 
 elif sys.platform.startswith('linux'):