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4.1.0 bogus QCOW2 corruption reported after compress
Creating a compressed image then running `qemu-img check <..>.qcow2' on said image seems to report bogus corruption in some (but not all) cases:
Step 1.
# qemu-img info win7-base.qcow2
image: win7-base.qcow2
file format: qcow2
virtual size: 20 GiB (21474836480 bytes)
disk size: 12.2 GiB
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: true
refcount bits: 16
corrupt: false
# qemu-img check win7-base.qcow2
No errors were found on the image.
327680/327680 = 100.00% allocated, 0.00% fragmented, 0.00% compressed clusters
Image end offset: 21478375424
Step 2.
# qemu-img convert -f qcow2 -O qcow2 -c win7-base.qcow2 test1-z.qcow2
Step 3.
# qemu-img info test1-z.qcow2
image: test1-z.qcow2
file format: qcow2
virtual size: 20 GiB (21474836480 bytes)
disk size: 5.78 GiB
cluster_size: 65536
Format specific information:
compat: 1.1
lazy refcounts: false
refcount bits: 16
corrupt: false
# qemu-img check test1-z.qcow2
ERROR cluster 1191 refcount=1 reference=2
ERROR cluster 1194 refcount=1 reference=4
ERROR cluster 1195 refcount=1 reference=7
ERROR cluster 1196 refcount=1 reference=7
ERROR cluster 1197 refcount=1 reference=6
ERROR cluster 1198 refcount=1 reference=4
ERROR cluster 1199 refcount=1 reference=4
ERROR cluster 1200 refcount=1 reference=5
ERROR cluster 1201 refcount=1 reference=3
<...> snip many errors
Leaked cluster 94847 refcount=3 reference=0
Leaked cluster 94848 refcount=3 reference=0
Leaked cluster 94849 refcount=11 reference=0
Leaked cluster 94850 refcount=14 reference=0
20503 errors were found on the image.
Data may be corrupted, or further writes to the image may corrupt it.
20503 leaked clusters were found on the image.
This means waste of disk space, but no harm to data.
197000/327680 = 60.12% allocated, 89.32% fragmented, 88.50% compressed clusters
Image end offset: 6216220672
The resultant image seems to work fine in a VM when used as a backing file.
Interestingly, if I substitute a qemu-img binary from qemu-4.0 then no errors are reported.
# /tmp/qemu-img check test1-z.qcow2
No errors were found on the image.
197000/327680 = 60.12% allocated, 89.32% fragmented, 88.50% compressed clusters
Image end offset: 6216220672
Is the image corrupted or not? I'm guessing not.
Just in case it matters, this is ext4 fs on rotational disk. Latest Arch Linux but self compiled 4.1.0 with recent QCOW2 corruption fixes added.
I haven't tried latest trunk but might do so if time permits.
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