[libvirt] [PATCH] qemu: match controller index for LIVE+CONFIG when doing hotplug

[Martin Kletzander]

On Sat, Jun 25, 2016 at 03:42:38PM +0200, Tomasz Flendrich wrote:
>
>> On 24 Jun 2016, at 13:25, Martin Kletzander <mkletzan at redhat.com> wrote:
>>> And what about the current bad behavior when you do this?
>>>
>>>  virsh attach interface f24 --type network --source default --live
>>>  virsh attach interface f24 --type network --source default --live
>>> --config
>>>
>>
>> This can be separated into two different issues.  If you do
>> attach-interface, we generate an XML without address, so you should be
>> able to do the above and have 2 more interfaces live, the second one
>> would be identical to the only one added to config.
>
>What if we guaranteed that adding a device with both “—live —config” options
>at once would always generate the same address? It could even leave some
>holes (unassigned addresses) in one of {config, live}, but it doesn’t bother us,
>does it? It would make the ABI stable.
>If finding such address would be impossible, the user would be informed that
>he/she can try adding the device separately using two calls without ABI stability.
>This solution means that there are less surprises for the user.
>Is there any reason it can’t be done, apart from complicating the code?
>

That's what we were talking about and that's what we need to do =)
There is no reason it can't be done.

>Besides, how often do people run —live without —config? Perhaps we should
>figure out what the most common use case is, make it work flawlessly
>and have some undesired behavior in other cases as a compromise.
>

It's hard to guess.  However when concentrating on the guarantee of ABI
stability, it's pretty clear how it should behave from the user's POV.

 - when both live and config are used, the devices plugged there must be
   identical, i.e. anything generated must be the same, all addresses, etc.

 - when you can't plug identical devices to both config and live
   definitions, just error out.  Of course the more descriptive error
   message there is, the better.

>Have a nice day,

U2

>Tomasz

Martin
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