my patches went in, ultimately, and my focus was since shifted elsewhere. I just tried this by *manually* adding some extra data to a bitmap by hand.
qemu-img create -f qcow2 foo.qcow2 64m qemu-img bitmap --add foo.qcow2 mybitmap This creates a bitmap extension header like this (starting at 0x1f8) 000001f0 00 00 00 00 00 00 00 00 23 85 28 75 00 00 00 18 |........#.(u....| 00000200 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 20 |............... | 00000210 00 00 00 00 00 05 00 00 |........ | And a bitmap table that looks like this: 00050000 00 00 00 00 00 04 00 00 00 00 00 01 00 00 00 02 |................| 00050010 01 10 00 08 00 00 00 00 6d 79 62 69 74 6d 61 70 |........mybitmap| I modified the bitmap table to add eight bytes of bad data: 00050000 00 00 00 00 00 04 00 00 00 00 00 01 00 00 00 02 |................| 00050010 01 10 00 08 00 00 00 08 62 61 64 64 61 74 61 21 |........baddata!| 00050020 6d 79 62 69 74 6d 61 70 |mybitmap| And modified the header accordingly to add eight bytes to the table (0x20f := 0x28): 000001f0 00 00 00 00 00 00 00 00 23 85 28 75 00 00 00 18 |........#.(u....| 00000200 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 28 |...............(| 00000210 00 00 00 00 00 05 00 00 |........ | And in these cases, QEMU refuses to load or work with the image even slightly, rendering you unable to remove it: > ./qemu-img bitmap --remove foo.qcow2 mybitmap qemu-img: Could not open 'foo.qcow2': Bitmap extra data is not supported So, it's still an open issue. -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1808928 Title: Bitmap Extra data is not supported Status in QEMU: Incomplete Bug description: i am using dirty bitmaps and drive-backup. It works as aspected. Lately, i encounter a disastrous error. There is not any information about that situation. I cannot reach/open/attach/info or anything with a qcow2 file. virsh version Compiled against library: libvirt 4.10.0 Using library: libvirt 4.10.0 Using API: QEMU 4.10.0 Running hypervisor: QEMU 2.12.0 "qemu-img: Could not open '/var/lib/libvirt/images/test.qcow2': Bitmap extra data is not supported" what is that mean? what should i do? i cannot remove bitmap. i cannot open image or query. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1808928/+subscriptions