On 2018-04-25 15:42, Alberto Garcia wrote: > On Wed 25 Apr 2018 03:06:34 PM CEST, Max Reitz wrote: >>>>>>>>> One other way is to have a more generic replace-node command >>>>>>>>> which would call bdrv_replace_node(), but I don't know if we >>>>>>>>> want to expose that and I don't have any other use case for it >>>>>>>>> at the moment. >>>>>>>> >>>>>>>> I think we do want to expose that. As far as I'm informed, for >>>>>>>> graph manipulation we want a command that can replace nodes >>>>>>>> (including replacing nothing by a new node or replacing an >>>>>>>> existing node by nothing, if the parent supports that). >>>>>>> >>>>>>> Was there any discussion about this in the mailing list? >>>>>>> (proposed name for this function, features, etc.) >>>>>> >>>>>> Well, there is x-blockdev-change. But we probably want to expose >>>>>> bdrv_reopen() in the long run. >>>>> >>>>> Exposing bdrv_reopen() itself shouldn't be too much work (it takes >>>>> just two node names, or am I missing something?). >>> >>> I just realized that I meant "Exposing bdrv_replace_node()" here. >>> >>>> So from my perspective... If you think it's easy, why don't you try >>>> it and then we'll see? *cough* >>> >>> I'm doing it :-) >>> >>>>> There's still the question of how to update the backing file string >>>>> (on the overlay). stream and commit do it automatically, but if we do >>>>> bdrv_reopen() or the aforementioned modification to blockdev-mirror >>> >>> bdrv_replace_node() again >> >> But the question stands whether we need simple node replacement when >> we want bdrv_reopen() anyway. In addition, we don't need just >> replacement, we also need addition and removal (e.g. for backing files >> or quorum children) -- and especially in the case of quorum, that is >> going to be a pain (mostly naming the children). >> >> With bdrv_reopen(), we can just require the user to respecify all >> children, so we don't run into the issue of how to name things at >> least. > > So in this example, if you want to replace [B] with [E] you would reopen > [C] specifying the new backing file? > > [A] <- [B] <- [C] <- [D] > > [E]
You can just use child node name references like in blockdev-add. Max
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