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_summary3

@@ -86,16 +86,24 @@ if sys.platform.startswith('freebsd'):
 
     VDEV_CACHE_SIZE = 'vdev.cache_size'
 
+    def is_value(ctl):
+        return ctl.type != sysctl.CTLTYPE_NODE
+
+    def namefmt(ctl, base='vfs.zfs.'):
+        # base is removed from the name
+        cut = len(base)
+        return ctl.name[cut:]
+
     def load_kstats(section):
         base = 'kstat.zfs.misc.{section}.'.format(section=section)
-        # base is removed from the name
-        fmt = lambda kstat: '{name} : {value}'.format(name=kstat.name[len(base):],
+        fmt = lambda kstat: '{name} : {value}'.format(name=namefmt(kstat, base),
                                                       value=kstat.value)
-        return [fmt(kstat) for kstat in sysctl.filter(base)]
+        kstats = sysctl.filter(base)
+        return [fmt(kstat) for kstat in kstats if is_value(kstat)]
 
     def get_params(base):
-        cut = 8 # = len('vfs.zfs.')
-        return {ctl.name[cut:]: str(ctl.value) for ctl in sysctl.filter(base)}
+        ctls = sysctl.filter(base)
+        return {namefmt(ctl): str(ctl.value) for ctl in ctls if is_value(ctl)}
 
     def get_tunable_params():
         return get_params('vfs.zfs')
@@ -112,25 +120,8 @@ if sys.platform.startswith('freebsd'):
         return '{} version {}'.format(name, version)
 
     def get_descriptions(_request):
-        # py-sysctl doesn't give descriptions, so we have to shell out.
-        command = ['sysctl', '-d', 'vfs.zfs']
-
-        # The recommended way to do this is with subprocess.run(). However,
-        # some installed versions of Python are < 3.5, so we offer them
-        # the option of doing it the old way (for now)
-        if 'run' in dir(subprocess):
-            info = subprocess.run(command, stdout=subprocess.PIPE,
-                                  universal_newlines=True)
-            lines = info.stdout.split('\n')
-        else:
-            info = subprocess.check_output(command, universal_newlines=True)
-            lines = info.split('\n')
-
-        def fmt(line):
-            name, desc = line.split(':', 1)
-            return (name.strip(), desc.strip())
-
-        return dict([fmt(line) for line in lines if len(line) > 0])
+        ctls = sysctl.filter('vfs.zfs')
+        return {namefmt(ctl): ctl.description for ctl in ctls if is_value(ctl)}
 
 
 elif sys.platform.startswith('linux'):