01.10.2019 17:10, John Snow wrote: > > > On 10/1/19 10:00 AM, Vladimir Sementsov-Ogievskiy wrote: >>> Otherwise: I have a lot of cloudy ideas on how to solve this, but >>> ultimately what we want is to be able to find the "addressable" name for >>> the node the bitmap is attached to, which would be the name of the first >>> ancestor node that isn't a filter. (OR, the name of the block-backend >>> above that node.) >> Not the name of ancestor node, it will break mapping: it must be name of the >> node itself or name of parent (may be through several filters) block-backend >> > > Ah, you are right of course -- because block-backends are the only > "nodes" for which we actually descend the graph and add the bitmap to > its child. > > So the real back-resolution mechanism is: > > - Find the first non-filter ancestor, A > - if A is not a block-backend, we must use our node-local name. > - if A's name is empty, we must use our node-local name. > - If the name we have chosen is not id_wellformed, we have no > migration-stable addressable name for this bitmap and the migration must > fail! > > > For resolving bitmap addresses via QMP (node, name) pairs; the > resolution method would be this: > > - if the node-name N is a block-backend, descend the tree until we find > the first non-filter node V. > - if the node-name N is a BlockDriverState, use this node directly. >
Looks good for me. I also think if on destination we have both block-backend with name N and block-node with name N and the latter is not (filtered) child of the former, we should fail migration of at least that bitmap. (Hope, nobody reuse block-backend names as node-names in practice.. (should we restrict it explicitly ?)) > > (I don't have the time to investigate the code snippet right now; my > attention is being pulled to a different project. sorry!) > So, you are not working on this? Then I'll make patches. -- Best regards, Vladimir
