Re: [Qemu-devel] [Qemu-block] [PATCH v5 3/4] qmp: add monitor command to add/remove a child

[Max Reitz <mreitz@redhat.com>]

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On 08.10.2015 10:29, Alberto Garcia wrote:
> On Thu 08 Oct 2015 08:15:25 AM CEST, Markus Armbruster wrote:
>>> For the second point, you should also consider how useful this
>>> feature is to management tools. Just being able to remove and attach
>>> children from a quorum node seems very useful on its own. I don't see
>>> why we should wait for having support for other block drivers; also,
>>> for most block drivers there is no meaningful way of adding or
>>> removing children as nicely as that is possible for quorum.
>>
>> Okay, this is an argument I might be able to buy.
> 
> Note that if we want to make this interface stable there's one use case
> missing: there's currently no way to change the vote threshold.

Besides what Kevin said: If you add a new function, that would be
independent from these two functions. If want to add it as an optional
parameter to blockdev-add-child so the change is done atomically, that
wouldn't be an incompatible interface change either.

Max

> This is maybe not so important for the COLO use case, but for the
> general case of adding and removing children from a quorum node having
> the possibility to change the threshold makes a lot of sense.
> 
> That would probably require a its own API ('quorum-set-threshold' or
> something like that) so I don't think it has an effect on these
> child-add and child-del commands, but I wanted to mention it here anyway
> in case someone sees something that I'm overlooking.
> 
> Berto
> 



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