Thank you Max. Can confirm your patch fixes my issue (qemu-img check ...)
Not sure about those other code paths. I don't use internal snapshots and I'm not sure under which circumstances qcow2_free_any_clusters() gets exercised. Just for good measure, with patch applied I created another >4GB compressed image then booted it a few times and all seems fine. -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1850000 Title: 4.1.0 bogus QCOW2 corruption reported after compress Status in QEMU: New Bug description: 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. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1850000/+subscriptions
