[libvirt] Offline manipulation of Dirty Bitmaps by qemu-img

This has come up in the past, and I believe we discussed this at KVM Forum, too: There have been requests from oVirt (via Nir Soffer) to add some offline bitmap manipulation functionality. In the past, our stance has generally been "Use QEMU without an accelerator, and use QMP to manipulate the images." We like this for a few reasons: 1. It keeps bitmap management code tightly centralized 2. It allows for the full suite of bitmap manipulations in either offline or online mode with one tool 3. We wouldn't have to write new code. 4. Or design new CLIs and duplicate our existing work. 5. Or write even more tests. However, tools like oVirt may or may not be fully equipped to launch QEMU in this context, and there is always a desire for qemu-img to be able to "do more", so existing management suites could extend functionality more easily. (Or so I am imagining.) I am still leaning heavily against adding any more CLI commands or options to qemu-img right now. Even if we do add some of the fundamental ones like "add" or "remove", it seems only a matter of time before we have to add "clear", "merge", etc. Is this just a race to code duplication? On the other hand, one of the other suggestions is to have qemu-img check --repair optionally delete corrupted bitmaps. I kind of like this idea: it's a buyer beware operation that might make management layers unhappy, but then again ... repair is always something that could make things worse. Plus, if you manage to corrupt bitmaps badly enough that they can't even be parsed, you might need a heavyweight repair operation. Nir, do you think that'd be sufficient for your needs for now, or would you still like to see more granular offline management? --js