Comment 5 for bug 1846427

I just quickly retested with today's master (commit 69b81893bc28feb678188fbcdce52eff1609bdad) and the automated reproducer. With the attached revert patch applied the loadvm/sleep 10/savevm/quit loop ran 50 times without problem. As soon as I removed the patch, recompiled and replaced the qemu binary with the unpatched, newly compiled one it took another two runs of the loop to produce this output:

QEMU 4.1.50 monitor - type 'help' for more information
(qemu) loadvm foo
(qemu) c
(qemu) stop
(qemu) savevm foo
(qemu) quit
QEMU 4.1.50 monitor - type 'help' for more information
(qemu) loadvm foo
(qemu) c
(qemu) stop
(qemu) savevm foo
Error: Error while deleting snapshot on device 'd': Failed to free the cluster and L1 table: Invalid argument
(qemu) quit
QEMU 4.1.50 monitor - type 'help' for more information
(qemu) loadvm foo
Error: Device 'd' does not have the requested snapshot 'foo'
(qemu) c
(qemu) qcow2_free_clusters failed: Invalid argument
qcow2_free_clusters failed: Invalid argument
qcow2_free_clusters failed: Invalid argument
qcow2_free_clusters failed: Invalid argument
qcow2_free_clusters failed: Invalid argument
qcow2_free_clusters failed: Invalid argument
^Cqemu-system-x86_64: terminating on signal 2

qemu-img check then reports:

48857 errors were found on the image.
Data may be corrupted, or further writes to the image may corrupt it.

115210 leaked clusters were found on the image.
This means waste of disk space, but no harm to data.
259259/327680 = 79.12% allocated, 2.51% fragmented, 0.00% compressed clusters
Image end offset: 17942052864

$ qemu-img check debian.qcow2 2>&1 | grep OFLAG_COPIED | wc -l
17592
$ qemu-img check debian.qcow2 2>&1 | grep ERROR | wc -l
48857
$ qemu-img check debian.qcow2 2>&1 | grep Leaked | wc -l
115210