Description of problem:
do live migration with used VMDK format disk, it will hang in destination QEMU.
if the vmdk disk did not be used, it can complete migration successfully and the guest work well.

And i check the code that we should diable migration when VMDK images are used:
/* Disable migration when VMDK images are used */
             |    get_cluster_offset(BlockDriverState
error_set(&s->migration_blocker,

             |    get_whole_cluster(BlockDriverState *

QERR_BLOCK_FORMAT_FEATURE_NOT_SUPPORTED, 
                                                                                                                             
             |    vmdk_L2update(VmdkExtent *extent, Vm
"vmdk", bs->device_name, "live migration");
                                                                                                                                        
             |    vmdk_add_extent(BlockDriverState *bs
migrate_add_blocker(s->migration_blocker);

Version-Release number of selected component (if applicable):
host info:
2.6.32-412.el6.x86_64
qemu-kvm-rhev-0.12.1.2-2.397.el6.x86_64
guest info:
2.6.32-413.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
1.create a vmdk format data disk.
# qemu-img create -f vmdk vmdk-data-disk.vmdk 10G
2.boot guest with vmdk format disk in src and do some read from the vmdk disk.
e.g:...-drive file=/mnt/vmdk-data-disk.vmdk,if=none,id=drive-data-disk,format=vmdk,cache=none,werror=stop,rerror=stop,readonly=on -device virtio-blk-pci,bus=pci.0,addr=0x7,drive=drive-data-disk,id=data-disk
guest ]# while true; do dd if=/dev/vdb of=/dev/null bs=1M count=100; done
3.boot a dest with incoming mode.
<same-to-src-cli>-incoming tcp:0:5888,server,nowait
4.migration from src to dest and check it.
(qemu) migrate -d tcp:0:5888
(qemu) info migrate 
Migration status: active
total time: 4056 milliseconds
transferred ram: 116611 kbytes
remaining ram: 542516 kbytes
total ram: 2113920 kbytes
...
(qemu) info migrate 
Migration status: completed
total time: 17509 milliseconds
downtime: 61 milliseconds
transferred ram: 568835 kbytes
remaining ram: 44 kbytes
total ram: 2113920 kbytes
(qemu)

Actual results:
after step 4, it can complete migration in src, but the dest side qemu will hang, can't press anything in HMP monitor and the guest cann't work.

Expected results:
Disable migration when VMDK images are used, and do live migration with used VMDK format disk should fail with a friendly message prompt.

Additional info:
# /usr/libexec/qemu-kvm -M pc -S -cpu SandyBridge -enable-kvm -m 2048 -smp 2,sockets=2,cores=1,threads=1 -no-kvm-pit-reinjection -usb -device usb-tablet,id=input0 -name sluo -uuid 990ea161-6b67-47b2-b803-19fb01d30d30 -rtc base=localtime,clock=host,driftfix=slew -device virtio-serial-pci,id=virtio-serial0,max_ports=16,vectors=0,bus=pci.0,addr=0x3 -chardev socket,id=channel1,path=/tmp/helloworld1,server,nowait -device virtserialport,chardev=channel1,name=com.redhat.rhevm.vdsm,bus=virtio-serial0.0,id=port1 -chardev socket,id=channel2,path=/tmp/helloworld2,server,nowait -device virtserialport,chardev=channel2,name=com.redhat.rhevm.vdsm,bus=virtio-serial0.0,id=port2 -drive file=/mnt/VMwareWorkStation-RHEL-Server-6.5-64bit.qcow2,if=none,id=drive-virtio-disk,format=qcow2,cache=none,aio=native,werror=stop,rerror=stop -device virtio-blk-pci,vectors=0,bus=pci.0,addr=0x4,scsi=off,drive=drive-virtio-disk,id=virtio-disk,bootindex=1 -netdev tap,id=hostnet0,vhost=on,script=/etc/qemu-ifup -device virtio-net-pci,netdev=hostnet0,id=virtio-net-pci0,mac=2C:41:38:B6:40:21,bus=pci.0,addr=0x5 -device virtio-balloon-pci,id=ballooning,bus=pci.0,addr=0x6 -global PIIX4_PM.disable_s3=0 -global PIIX4_PM.disable_s4=0 -drive file=/mnt/vmdk-data-disk.vmdk,if=none,id=drive-data-disk,format=vmdk,cache=none,werror=stop,rerror=stop,readonly=on -device virtio-blk-pci,bus=pci.0,addr=0x7,drive=drive-data-disk,id=data-disk -k en-us -boot menu=on -spice disable-ticketing,port=5931 -monitor stdio