libvirt: guest: introduce blockStats instead of domain.blockStats

We should use nova.virt.libvirt.Guest instead of call from
a virDomain object.

Change-Id: Ifa8fe1b19980cc9e986d26b284d2fb093466d30c
Signed-off-by: Chen Hanxiao <chenhx@certusnet.com.cn>

nova/tests/unit/virt/libvirt/test_guest.py

@@ -813,6 +813,10 @@ class GuestBlockTestCase(test.NoDBTestCase):
         self.assertRaises(fakelibvirt.libvirtError,
                           self.gblock.is_job_complete)
 
+    def test_blockStats(self):
+        self.gblock.blockStats()
+        self.domain.blockStats.assert_called_once_with('vda')
+
 
 class JobInfoTestCase(test.NoDBTestCase):
 

nova/virt/libvirt/driver.py

@@ -6390,12 +6390,8 @@ class LibvirtDriver(driver.ComputeDriver):
         """Note that this function takes an instance name."""
         try:
             guest = self._host.get_guest(instance)
-
-            # TODO(sahid): We are converting all calls from a
-            # virDomain object to use nova.virt.libvirt.Guest.
-            # We should be able to remove domain at the end.
-            domain = guest._domain
-            return domain.blockStats(disk_id)
+            dev = guest.get_block_device(disk_id)
+            return dev.blockStats()
         except libvirt.libvirtError as e:
             errcode = e.get_error_code()
             LOG.info('Getting block stats failed, device might have '

nova/virt/libvirt/guest.py

@@ -861,6 +861,10 @@ class BlockDevice(object):
 
         return False
 
+    def blockStats(self):
+        """Extracts block device statistics for a domain"""
+        return self._guest._domain.blockStats(self._disk)
+
 
 class VCPUInfo(object):
     def __init__(self, id, cpu, state, time):