Description of problem:

virtlock doesn't work well with images which have backing file

Version-Release number of selected component (if applicable):

libvirt-1.2.8-16.el7.x86_64

How reproducible:

100%

Steps to Reproduce:

1. Enable virtlock

# grep -E -v "^#|^$" /etc/libvirt/qemu.conf
lock_manager = "lockd"
# grep -E -v "^#|^$" /etc/libvirt/qemu-lockd.conf
auto_disk_leases = 1
require_lease_for_disks = 1
file_lockspace_dir = "/var/lib/libvirt/lockd/files"

# systemctl restart virtlockd.service
# systemctl restart libvirtd.service

# ll /var/lib/libvirt/lockd/files
total 0


2. Prepare two image, one is using another one as backing file
# qemu-img create -f qcow2 /var/lib/libvirt/images/rh7.img 1G
Formatting '/var/lib/libvirt/images/rh7.img', fmt=qcow2 size=1073741824 encryption=off cluster_size=65536 lazy_refcounts=off

# qemu-img create -f qcow2 /var/lib/libvirt/images/rh7.s1 -b /var/lib/libvirt/images/rh7.img -o backing_fmt=qcow2
Formatting '/var/lib/libvirt/images/rh7.s1', fmt=qcow2 size=1073741824 backing_file='/var/lib/libvirt/images/rh7.img' backing_fmt='qcow2' encryption=off cluster_size=65536 lazy_refcounts=off

3. Prepare two guest use the image created in step2 as source file
# virsh domblklist rh7
Target Source
------------------------------------------------
vda /var/lib/libvirt/images/rh7.img

# virsh domblklist r7
Target Source
------------------------------------------------
vda /var/lib/libvirt/images/rh7.s1

4. Try to boot up two guest

# virsh start rh7
Domain rh7 started

# virsh start r7
Domain r7 started

# ll /var/lib/libvirt/lockd/files
total 0
-rw-------. 1 root root 0 Feb 13 13:44 79c8f5f8e3b82d8ea4bc28e8c8bdcb3a4ce4b2d6fe86feb0fe4e82188f5a9092
-rw-------. 1 root root 0 Feb 13 13:44 cb17138f2c90610971067166bec89c92184bdcf2c3a2201e72ddd946fc9f3af7


Actual results:

as above

Expected results:

Guest r7 shouldn't boot up with rh7.s1 since its backing file rh7.img is using by another guest.
This is the scenario we also try to prevent


Additional info: