[libvirt-users] old vm cannot be migrated, new vm can be migrated

[gustavo panizzo (gfa)]

scenario:

i run a mix of libvirt 1.1.1 and 1.2.2 on the source hosts, 1.2.2 on the 
destination hosts
qemu: 1.5.0+dfsg-3ubuntu5.3~cloud0 on all the hosts
openstack havana and icehouse

description:

i have many compute nodes running libvirt+kvm, when i try to migrate 
guest that were created months ago it fails, if i create a vm and then 
migrate it works

the problem is that libvirt cannot retrieve the mtu of the bridge were 
the interfaces are be attached, but bridge is there (up and running)

$ grep qbr32740ab3-b6 /var/log/libvirt/libvirtd.log


2014-11-05 08:44:53.013+0000: 35311: debug : udevGetDeviceProperty:121 : 
udev reports device 'qbr32740ab3-b6' does not have property 'DRIVER'
2014-11-05 08:44:53.013+0000: 35311: debug : udevGetDeviceType:1217 : 
Could not determine device type for device with sysfs name 'qbr32740ab3-b6'
2014-11-05 08:44:53.013+0000: 35311: debug : udevAddOneDevice:1392 : 
Discarding device -1 0x7f36e80bd5c0 /sys/devices/virtual/net/qbr32740ab3-b6
2014-11-05 08:44:53.013+0000: 35311: debug : 
udevProcessDeviceListEntry:1414 : Failed to create node device for udev 
device '/sys/devices/virtual/net/qbr32740ab3-b6'
2014-11-05 08:45:08.458+0000: 35303: error : 
virNetClientProgramDispatchError:175 : Cannot get interface MTU on 
'qbr32740ab3-b6': No such device


# ip l show dev qbr32740ab3-b6
639: qbr32740ab3-b6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc 
noqueue state UP
     link/ether 72:d5:db:f6:b5:30 brd ff:ff:ff:ff:ff:ff

# brctl show qbr32740ab3-b6
bridge name	bridge id		STP enabled	interfaces
qbr32740ab3-b6		8000.72d5dbf6b530	no		qvb32740ab3-b6
							tap32740ab3-b6

the difference between a new defined domain and an old one
is this

<   <alias name='pci0'/>
---
 >   <alias name='pci.0'/>

 >   <timer name='hpet' present='no'/>   ---> old domain does not have it

i even tried patching src/util/virnetdev.c to remove the check and 
always return 1500 but the same thing happens



i'm lost i don't know where to look at it, any clue were to look is 
appreciated





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