disk capacity is less than disk usage

If the virtual machine mounts cd-rom, libvirt will align by 4K bytes,
causing the disk capacity is less than the disk usage, which does not
seem reasonable.

Maybe we shoulde use the bigger one as disk capacity.

Change-Id: I25808856bce27483da0cb2583ae94e8dc162d647
Closes-Bug: #1819107

ceilometer/compute/virt/libvirt/inspector.py

@@ -154,8 +154,12 @@ class LibvirtInspector(virt_inspector.Inspector):
         domain = self._get_domain_not_shut_off_or_raise(instance)
         for device in self._get_disk_devices(domain):
             block_info = domain.blockInfo(device)
+            # if vm mount cdrom, libvirt will align by 4K bytes, capacity may
+            # be smaller than physical, avoid with this.
+            # https://libvirt.org/html/libvirt-libvirt-domain.html
+            disk_capacity = max(block_info[0], block_info[2])
             yield virt_inspector.DiskInfo(device=device,
-                                          capacity=block_info[0],
+                                          capacity=disk_capacity,
                                           allocation=block_info[1],
                                           physical=block_info[2])
 

ceilometer/tests/unit/compute/virt/libvirt/test_inspector.py

@@ -351,7 +351,7 @@ class TestLibvirtInspection(base.BaseTestCase):
 
             self.assertEqual(1, len(disks))
             self.assertEqual('vda', disks[0].device)
-            self.assertEqual(1, disks[0].capacity)
+            self.assertEqual(3, disks[0].capacity)
             self.assertEqual(2, disks[0].allocation)
             self.assertEqual(3, disks[0].physical)