get_instance_disk_info behaviour changes breaks live migration

run.py

from lxml import etree
import logging

LOG = logging.getLogger(__name__)
LOG.setLevel(logging.DEBUG)
LOG.addHandler(logging.StreamHandler())
_ = lambda x: x

def juno(xml):
    instance_name = 'instance-00000001'
    volume_devices = []


    disk_info = []
    doc = etree.fromstring(xml)
    disk_nodes = doc.findall('.//devices/disk')
    path_nodes = doc.findall('.//devices/disk/source')
    driver_nodes = doc.findall('.//devices/disk/driver')
    target_nodes = doc.findall('.//devices/disk/target')

    for cnt, path_node in enumerate(path_nodes):
        disk_type = disk_nodes[cnt].get('type')
        path = path_node.get('file') or path_node.get('dev')
        target = target_nodes[cnt].attrib['dev']

        if not path:
            LOG.debug('skipping disk for %s as it does not have a path',
                      instance_name)
            continue

        if disk_type not in ['file', 'block']:
            LOG.debug('skipping disk because it looks like a volume', path)
            continue

        if target in volume_devices:
            LOG.debug('skipping disk %(path)s (%(target)s) as it is a '
                      'volume', {'path': path, 'target': target})
            continue

        # get the real disk size or
        # raise a localized error if image is unavailable
        if disk_type == 'file':
            dk_size = int(os.path.getsize(path))
        elif disk_type == 'block':
            dk_size = 1234 #lvm.get_volume_size(path)

        disk_type = driver_nodes[cnt].get('type')
        if disk_type == "qcow2":
            backing_file = libvirt_utils.get_disk_backing_file(path)
            virt_size = disk.get_disk_size(path)
            over_commit_size = int(virt_size) - dk_size
        else:
            backing_file = ""
            virt_size = dk_size
            over_commit_size = 0

        disk_info.append({'type': disk_type,
                          'path': path,
                          'virt_disk_size': virt_size,
                          'backing_file': backing_file,
                          'disk_size': dk_size,
                          'over_committed_disk_size': over_commit_size})
        return disk_info

def icehouse(xml):
    instance_name = 'instance-00000001'
    volume_devices = []

    disk_info = []
    doc = etree.fromstring(xml)
    disk_nodes = doc.findall('.//devices/disk')
    path_nodes = doc.findall('.//devices/disk/source')
    driver_nodes = doc.findall('.//devices/disk/driver')
    target_nodes = doc.findall('.//devices/disk/target')

    for cnt, path_node in enumerate(path_nodes):
        disk_type = disk_nodes[cnt].get('type')
        path = path_node.get('file')
        target = target_nodes[cnt].attrib['dev']

        if not path:
            LOG.debug(_('skipping disk for %s as it does not have a path'),
                      instance_name)
            continue

        if disk_type != 'file':
            LOG.debug(_('skipping %s since it looks like volume'), path)
            continue

        if target in volume_devices:
            LOG.debug(_('skipping disk %(path)s (%(target)s) as it is a '
                        'volume'), {'path': path, 'target': target})
            continue

        # get the real disk size or
        # raise a localized error if image is unavailable
        dk_size = int(os.path.getsize(path))

        disk_type = driver_nodes[cnt].get('type')
        if disk_type == "qcow2":
            backing_file = libvirt_utils.get_disk_backing_file(path)
            virt_size = disk.get_disk_size(path)
            over_commit_size = int(virt_size) - dk_size
        else:
            backing_file = ""
            virt_size = dk_size
            over_commit_size = 0

        disk_info.append({'type': disk_type,
                          'path': path,
                          'virt_disk_size': virt_size,
                          'backing_file': backing_file,
                          'disk_size': dk_size,
                          'over_committed_disk_size': over_commit_size})

xml = open('xml').read()
print icehouse(xml)
print juno(xml)

# daz$ python run.py
# skipping disk for instance-00000001 as it does not have a path
# None
# [{'disk_size': 1234, 'backing_file': '', 'virt_disk_size': 1234, 'path': '/dev/disk/by-path/ip-10.0.0.1:3260-iscsi-iqn.2010-10.org.openstack:volume-73e70dc4-8c0e-4392-9aae-c348d8b02e02-lun-1', 'type': 'raw', 'over_committed_disk_size': 0}]

xml

<domain type='kvm' id='8'>
  <name>instance-00000001</name>
  <uuid>e04b2617-fea4-470f-9dce-340a13a479ac</uuid>
  <memory unit='KiB'>524288</memory>
  <currentMemory unit='KiB'>524288</currentMemory>
  <vcpu placement='static'>1</vcpu>
  <resource>
    <partition>/machine</partition>
  </resource>
  <sysinfo type='smbios'>
    <system>
      <entry name='manufacturer'>OpenStack Foundation</entry>
      <entry name='product'>OpenStack Nova</entry>
      <entry name='version'>2014.1.4</entry>
      <entry name='serial'>44454c4c-3200-1053-8053-b9c04f39354a</entry>
      <entry name='uuid'>e04b2617-fea4-470f-9dce-340a13a479ac</entry>
    </system>
  </sysinfo>
  <os>
    <type arch='x86_64' machine='pc-i440fx-trusty'>hvm</type>
    <boot dev='hd'/>
    <smbios mode='sysinfo'/>
  </os>
  <features>
    <acpi/>
    <apic/>
  </features>
  <cpu mode='host-model'>
    <model fallback='allow'/>
    <feature policy='require' name='rdtscp'/>
    <feature policy='require' name='pdpe1gb'/>
    <feature policy='require' name='dca'/>
    <feature policy='require' name='pcid'/>
    <feature policy='require' name='pdcm'/>
    <feature policy='require' name='xtpr'/>
    <feature policy='require' name='tm2'/>
    <feature policy='require' name='est'/>
    <feature policy='require' name='smx'/>
    <feature policy='require' name='vmx'/>
    <feature policy='require' name='ds_cpl'/>
    <feature policy='require' name='monitor'/>
    <feature policy='require' name='dtes64'/>
    <feature policy='require' name='pclmuldq'/>
    <feature policy='require' name='pbe'/>
    <feature policy='require' name='tm'/>
    <feature policy='require' name='ht'/>
    <feature policy='require' name='ss'/>
    <feature policy='require' name='acpi'/>
    <feature policy='require' name='ds'/>
    <feature policy='require' name='vme'/>
  </cpu>
  <clock offset='utc'>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='hpet' present='no'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/kvm-spice</emulator>
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none'/>
      <source dev='/dev/disk/by-path/ip-10.0.0.1:3260-iscsi-iqn.2010-10.org.openstack:volume-73e70dc4-8c0e-4392-9aae-c348d8b02e02-lun-1'/>
      <target dev='vda' bus='virtio'/>
      <serial>73e70dc4-8c0e-4392-9aae-c348d8b02e02</serial>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>
    <controller type='usb' index='0'>
      <alias name='usb0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pci-root'>
      <alias name='pci.0'/>
    </controller>
    <interface type='bridge'>
      <mac address='fa:16:3e:b3:49:4d'/>
      <source bridge='qbra9105cca-88'/>
      <target dev='tapa9105cca-88'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='file'>
      <source path='/var/lib/nova/instances/e04b2617-fea4-470f-9dce-340a13a479ac/console.log'/>
      <target port='0'/>
      <alias name='serial0'/>
    </serial>
    <serial type='pty'>
      <source path='/dev/pts/3'/>
      <target port='1'/>
      <alias name='serial1'/>
    </serial>
    <console type='file'>
      <source path='/var/lib/nova/instances/e04b2617-fea4-470f-9dce-340a13a479ac/console.log'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    </console>
    <input type='tablet' bus='usb'>
      <alias name='input0'/>
    </input>
    <input type='mouse' bus='ps2'/>
    <input type='keyboard' bus='ps2'/>
    <graphics type='vnc' port='5900' autoport='yes' listen='0.0.0.0' keymap='en-us'>
      <listen type='address' address='0.0.0.0'/>
    </graphics>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
  <seclabel type='dynamic' model='apparmor' relabel='yes'>
    <label>libvirt-e04b2617-fea4-470f-9dce-340a13a479ac</label>
    <imagelabel>libvirt-e04b2617-fea4-470f-9dce-340a13a479ac</imagelabel>
  </seclabel>
</domain>