Re: [Qemu-block] [Qemu-devel] Meeting notes on -blockdev, dynamic backend reconfiguration

[Markus Armbruster]

Fam Zheng <address@hidden> writes:

> On Wed, 12/07 10:48, Kevin Wolf wrote:
>> > If so I think there is no race to worry about, mirror-filter should go
>> > away only after a QMP command.
>> 
>> Currently, a mirror job goes away whenever it is done. This is not
>> directly tied to a QMP command.
>
> Ah right, block-job-complete is only "start to complete" and the job goes away
> at some later point. I thought this is "the" QMP command but it is not.
>
>> 
>> Of course, in the new job API we want an explicit job-delete, so in
>> that case it wouldn't happen, but we need to keep the old case for
>> compatibility.
>
> Another possibility is to add a placeholder node in the right location first
> then fill in the actual throttling node once created. QMP owns the placeholder
> node so it won't suddenly vanish when mirror job goes away.

I'm not sure I understand this idea.  Could you explain it in a bit more
detail, perhaps even with a bit of ASCII art?