Comment 1 for bug 1808928

Hi, bitmap extensions have a field that allows us to attach extra/arbitrary data to them. It is not currently used by QEMU. If this field is set, it means something corrupted your qcow2.

Please make a backup of your qcow2 file first (because attempting to repair a broken qcow2 can sometimes make it worse), and then please try running qemu-img check to try and diagnose the image.

What happened to cause the "disastrous error", do you recall?