On 10/24/20 4:59 AM, Vladimir Sementsov-Ogievskiy wrote: > 23.10.2020 21:36, Eric Blake wrote: >> Preserve the tri-state encoding in the low bits, as that still remains >> a valuable way to utilize qemu-img map with x-dirty-bitmap for >> accessing quick information without needing a third-party NBD client. > > Hmm.. that doesn't sound as a good reason for redundant information in > the protocol. Previously good reason was additional effort needed to > implement sever part, but you've implemented it. And if we export depth > anyway, it seems better to hack a bit nbd_client_co_block_status to > convert extent.flags appropriately if metadata context is > "qemu:allocation-depth" (to keep x-dirty-bitmap working), than have a > workaround at the protocol layer.
I'm happy to respin this to expose JUST a depth rather than redundant information, but time is short if we want it in 5.2 (as soft freeze is this week). I'll see what I can get to today; I'll rearrange the series to put multiple bitmap exports first (as that appears ready), while saving 'qemu-nbd -A' until we're happy with the qemu:allocation-depth semantics. After all, once we release something, we've committed to that user interface. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org