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

06.12.2019 1:37, John Snow wrote: > 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. I think, all guys, who don't want to use Qemu directly for image manipulations, should hope for Kevin's "[RFC PATCH 00/18] Add qemu-storage-daemon", which is the correct solution of their problem. Still, I'm not one of these guys. > > (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. > Improving "check" is a correct thing, because it's done inside qcow2 driver itself. We just don't have corresponding qmp command or command line option for Qemu to use this thing (or I missed it).