Am 10.09.2010 17:53, schrieb Anthony Liguori: > On 09/10/2010 10:18 AM, Kevin Wolf wrote: >> Am 10.09.2010 17:02, schrieb Anthony Liguori: >> >>> What makes us future proof is having a good feature support. qcow2 >>> doesn't have this. We have a good way at making purely informational >>> changes and also making changes that break the format. Those features >>> are independent so they can be backported in a compatible way too. >>> >> I might have agreed that it's useful to be able to backport them >> independently if we had had lots of such features added in the past. But >> we haven't. >> > > I think part of why we haven't had them is that the mechanisms aren't > very flexible. > > A good example of where feature support would be very nice is for > changing the way snapshots metadata is recorded in qcow2. > > It would be nice to be able to represent snapshots with a uuid. If you > added new metadata that had uuid based snapshots that were hierarchical > and added a feature bit, it would have some nice properties. > > Since most images don't have snapshots, the common case would be a qcow2 > that was fully backwards compatible. You would also get a graceful > failure for using a new image with an old QEMU.
Well, snapshots have an ID today (which is different from their name). Nobody stops you from putting a UUID there. Fully backwards compatible, no feature flag needed. I think Miguel was planning to actually do this. Kevin
