Fix variable return bugs in kvm plugin

This patch ensures that monitorstack connects to the system URI for
libvirt. Without this, a regular user may connect to libvirt without
full access to the existing virtual machines.

It also adds the gathered variables to the output dictionatry so they
are returned when the plugin runs.

Tests have been adjusted to match the new changes, including a new
constructor that takes the system connection URI into consideration.

Closes-Bug: 1684235
Change-Id: Ieacc69ee495268b3b20974eb2f01ff1d2c9195c1

monitorstack/plugins/kvm.py

@@ -12,8 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 """Get metrics from a KVM hypervisor."""
-
-import platform
 import socket
 
 import click
@@ -43,23 +41,33 @@ def cli(ctx):
     output = {
         'measurement_name': 'kvm',
         'meta': {
-            'platform': platform.platform(),
             'kvm_host_id': abs(hash(socket.getfqdn()))
         }
     }
-    conn = libvirt.openReadOnly()
+
+    # Open a read-only connection to libvirt
+    conn = libvirt.openReadOnly("qemu:///system")
+
     try:
-        variables = output['variables'] = dict()
+        variables = dict()
+
+        # Get all of the KVM instances on this host.
         domains = conn.listDomainsID()
         variables['kvm_vms'] = len(domains)
         variables['kvm_total_vcpus'] = conn.getCPUMap()[0]
         variables['kvm_scheduled_vcpus'] = 0
+
+        # Loop through each instance to gather additional data.
         for domain in domains:
             variables['kvm_scheduled_vcpus'] += conn.lookupByID(
                 domain
             ).maxVcpus()
 
+        # Return the data.
+        output['variables'] = variables
+
     except Exception as exp:
+        # We may have picked up an exception while querying libvirt for data.
         output['exit_code'] = 1
         output['message'] = '{} failed -- {}'.format(
             COMMAND_NAME,

tests/test_plugin_kvm.py

@@ -39,6 +39,9 @@ class LibvirtStub(object):
     class openReadOnly(object):  # noqa
         """Stubbed openReadOnly class."""
 
+        def __init__(self, connection_uri):  # noqa
+            pass
+
         def close(self, *args, **kwargs):  # noqa
             pass
 
@@ -63,6 +66,9 @@ class LibvirtStubFailed(object):
     class openReadOnly(object):  # noqa
         """Stubbed openReadOnly class."""
 
+        def __init__(self, connection_uri):  # noqa
+            pass
+
         def close(self, *args, **kwargs):  # noqa
             pass
 
@@ -94,7 +100,6 @@ class TestKvm(unittest.TestCase):
         assert variables['kvm_total_vcpus'] == 1
         assert 'kvm_scheduled_vcpus' in variables
         assert variables['kvm_scheduled_vcpus'] == 6
-        assert 'platform' in meta
         assert 'kvm_host_id' in meta
         assert result['exit_code'] == 0