[libvirt] Allow to change the maximum migration downtime -- bug 561935

[Alex Jia]

Hi Daniel,
I have simulated a slow network by linux bridge on source host machine,
but I found that I hardly connected guest by serial or vnc, it is pretty 
slow, I can't run other big application in the guest, so I change my idea, 
as long as I have a slow link, whether the network is in source or target 
machine, finally, I created slow network on target machine, the attachment 
is a shell script about the network creation process.

Using 'tc' to throttle network traffic on the target host 
# tc qdisc show
qdisc tbf 8004: dev eth0 root refcnt 2 rate 128000bit burst 128Kb lat 50.0ms 
qdisc pfifo_fast 0: dev eth1 root refcnt 2 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1


WRT big apps, I use stress tool to consume guest memory(current size is 4G), 
cmd line argument as following:
stress --cpu 2 --io 2 --vm 50 --vm-bytes 128M --timeout 480s

And then running migration, and open another terminal set maximum migration 
downtime 60000 milliseconds, the following error information is raised by
libvirt:

1.open one terminal run migrate
# virsh migrate rhel6 qemu+ssh://10.66.70.152/system
root at 10.66.70.152's password: 

2.open another terminal set maximum migration downtime
# virsh migrate-setmaxdowntime --domain rhel6 --downtime 60000
error: Requested operation is not valid: domain is not being migrated

In fact, step 1 will never be finished.

BTW, the guest can be successfully migrated if I don't use the above environment 
configuration.


Best Regards,
Alex
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