hypervisor: 0.956
risc-v: 0.947
virtual: 0.934
device: 0.917
vnc: 0.861
performance: 0.815
ppc: 0.803
PID: 0.760
files: 0.751
kernel: 0.747
architecture: 0.746
VMM: 0.745
register: 0.738
network: 0.724
graphic: 0.711
socket: 0.666
boot: 0.615
debug: 0.588
i386: 0.574
assembly: 0.573
arm: 0.555
peripherals: 0.555
x86: 0.528
KVM: 0.527
semantic: 0.518
permissions: 0.516
user-level: 0.487
TCG: 0.455
mistranslation: 0.273

qemu-img cannot repair a qcow2 in an LV because size is mis-detected when qcow2 is on an LV
Description of problem:
This is RHEV with Tb's of VMs which need to be repaired due to a datacenter-wide (the real datacenter) power outage.

Each of these VMs are on individual LVs but qemu-img check fails to perform repairs:


```
ERROR cluster 24481205 refcount=0 reference=1
ERROR cluster 24481206 refcount=0 reference=1
Rebuilding refcount structure
ERROR writing refblock: No space left on device <============
qemu-img: Check failed: No space left on device
```

Running qemu-img check or info on the LV (/dev/dm-*) works well but repairs cannot be completed:

```
# qemu-img info /dev/cdd4e215-8c6b-4877-b2be-fdba383e7eb0/fb32333b-2334-4e10-8c42-02bc97e826cc
image: /dev/cdd4e215-8c6b-4877-b2be-fdba383e7eb0/fb32333b-2334-4e10-8c42-02bc97e826cc
file format: qcow2
virtual size: 1.5 TiB (1649267441664 bytes)
disk size: 0 B <================================
cluster_size: 65536
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: true
    refcount bits: 16
    corrupt: false
    extended l2: false
```
Steps to reproduce:
1. Have a damaged VM with its qcow2 in an LV
2. run 'qemu-img check <device>' verify that it properly detects the blocks which need fixing.
3. run 'qemu-img check -r all <device>', it exits with 'no space left on device´ after a few seconds.
Additional information:
https://bugzilla.redhat.com/show_bug.cgi?id=1519071


Here is one example: