Use python-native api to get disk size

In before, we shellout a command to retrieve the total disk size
of the host. A better approach is to leverage the python-native
library psutil to do that. Using python api would have less
overhead than spawning a shell command.

Change-Id: I02e2babac9bc36f5d738cff0b17ebd9416bd1757

lower-constraints.txt

@@ -98,6 +98,7 @@ pep8==1.5.7
 pika==0.10.0
 pika-pool==0.1.3
 prettytable==0.7.2
+psutil==3.2.2
 pyasn1==0.4.2
 pycadf==2.7.0
 pycparser==2.18

requirements.txt

@@ -6,6 +6,7 @@ PyYAML>=3.12 # MIT
 eventlet!=0.18.3,!=0.20.1,>=0.18.2 # MIT
 keystonemiddleware>=4.17.0 # Apache-2.0
 pecan!=1.0.2,!=1.0.3,!=1.0.4,!=1.2,>=1.0.0 # BSD
+psutil>=3.2.2 # BSD
 python-etcd>=0.4.3 # MIT License
 python-glanceclient>=2.8.0 # Apache-2.0
 python-neutronclient>=6.7.0 # Apache-2.0

zun/container/docker/driver.py

@@ -21,6 +21,7 @@ from neutronclient.common import exceptions as n_exc
 from oslo_log import log as logging
 from oslo_utils import timeutils
 from oslo_utils import uuidutils
+import psutil
 import six
 
 from zun.common import consts
@@ -1117,17 +1118,8 @@ class DockerDriver(driver.ContainerDriver):
                     runtimes)
 
     def get_total_disk_for_container(self):
-        try:
-            (output, err) = utils.execute('df', '-B', '1G',
-                                          CONF.docker.docker_data_root,
-                                          run_as_root=True)
-        except exception.CommandError as e:
-            LOG.info('There was a problem while executing df -B 1G %s',
-                     CONF.docker.docker_data_root)
-            raise exception.CommandError(cmd='df',
-                                         error=six.text_type(e))
-
-        total_disk = int(output.split('\n')[1].split()[1])
+        disk_usage = psutil.disk_usage(CONF.docker.docker_data_root)
+        total_disk = disk_usage.total / 1024 ** 3
         return int(total_disk * (1 - CONF.compute.reserve_disk_for_image))
 
     def get_cpu_used(self):