Comment 14 for bug 1746630

Verfied versions:
libvirt-2.0.0-6.el7.x86_64
qemu-kvm-rhev-2.6.0-22.el7.x86_64

Steps:
1. Prepare a NFS storage, mount the NFS storage
then start a guest which image located in the NFS storage.

# virsh list --all
 Id Name State
----------------------------------------------------
 11 vm1 running

# virsh domblklist vm1
Target Source
------------------------------------------------
hdc -
vda /tmp/zp/beaker/r73q2-1.img

check the guest is working well

2. disconnect the NFS server
# iptables -A OUTPUT -d $IP -p tcp --dport 2049 -j DROP

3. In termial 1, check IO throttlling using blkdeviotune

# virsh blkdeviotune vm1 vda
...... It will hange for a few minutes here

4. In the terminal 2, check domstats for the running guest using domstas
It also needs few minutes to get a return. But it won't hang forever.

# virsh domstats
Domain: 'vm1'
  state.state=1
  state.reason=1
  cpu.time=30014234910
  cpu.user=1760000000
  cpu.system=8750000000
  balloon.current=1048576
  balloon.maximum=1048576
  vcpu.current=1
  vcpu.maximum=8
  vcpu.0.state=1
  vcpu.0.time=26690000000
  vcpu.0.wait=0
  net.count=0
  block.count=2
  block.0.name=hdc
  block.1.name=vda
  block.1.path=/tmp/zp/beaker/r73q2-1.img

check terminal 1 agian, blkdeviotune also has a return.

# virsh blkdeviotune vm1 vda
total_bytes_sec: 0
read_bytes_sec : 0
write_bytes_sec: 0
total_iops_sec : 0
read_iops_sec : 0
write_iops_sec : 0
total_bytes_sec_max: 0
read_bytes_sec_max: 0
write_bytes_sec_max: 0
total_iops_sec_max: 0
read_iops_sec_max: 0
write_iops_sec_max: 0
size_iops_sec : 0

5. check virsh list, it also won't hang.
# virsh list
 Id Name State
----------------------------------------------------
 11 vm1 running

As above, domstats can get a return, it won't hang and it won't block other commands. From libvirt, it has been fixed.