Re: [Xen-devel] [PATCH v2 2/7] libxl: add new hotplug interface support to hotplug script callers [and 1 more messages]

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On 18/04/13 19:23, Ian Jackson wrote:
> Ian Jackson writes ("Re: [Xen-devel] [PATCH v2 2/7] libxl: add new hotplug 
> interface support to hotplug script callers"):
>> Roger Pau Monne writes ("[Xen-devel] [PATCH v2 2/7] libxl: add new hotplug 
>> interface support to hotplug script callers"):
> ...
>>> +PREPARE
>>> +-------
>>> +
>>> +This is the first operation that the hotplug script will be requested to
>>> +execute. This operation is executed before the disk is connected, to
>>> +give the hotplug script the chance to offload some work from the "add"
>>> +operation, that is performed later.
>>
>> But in fact in your implementation this is only called right before
>> add, isn't it ?
>>
>> Also, IIRC part of the point of this new interface is that for target
>> devices which can't be accessed simultaneously from different hosts,
>> during migration you'd be able to do costly setup during the initial
>> part of the migration and merely "activate" the devices later.
>>
>> Am I missing something ?
> 
> This question needs to be answered by the documentation, I think.
> 
> What are the guarantees that the hotplug scripts rely on ?
> 
> AFAICT what happens after your series is applied is that we always
> call prepare just before add, and unprepare just after remove (if I
> may neglect local attach for now).  So I don't see why these new
> functions are necessary to your new scripts.

Do you mean that both prepare and add are called after the domain on the
sender side is paused?

Disks are prepared on "initiate_domain_create", which is the first
function that gets called on domain creation, on the other hand they are
added much later.


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