Re: libxl: hotplug scripts and backend_domid != 0

[Marek Marczykowski <marmarek@invisiblethingslab.com>]

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On 10.04.2013 13:22, Roger Pau Monné wrote:
> On 10/04/13 13:14, Ian Campbell wrote:
>> On Thu, 2013-04-04 at 16:45 +0100, Marek Marczykowski wrote:
>>> Hi,
>>>
>>> Currently when using backend outside of dom0 (for at least one device) libxl
>>> force udev call method of hotplug scripts for entire system.
>>
>> Roger, do you remember why? Was it just because this change was
>> relatively late in the 4.2 cycle and we were being conservative?
>>
>>>  Maybe this can be
>>> changed to:
>>> a) if backend_domid==0, proceed according to run_hotplug_scipts
>>> b) if backend_domid!=0, ignore run_hotplug_scipts and always use udev
>>> ?
>>>
>>> Does it sound sensible?
>>
>> It does, although we are now relatively late in the 4.3 cycle so I'm not
>> sure it would be appropriate. George?
>>
>> I think Roger is intending to implement a new scheme for driver domains
>> etc in 4.4, which may make this particular issue disappear anyway.
> 
> Since run_hotplug_scripts is a global variable, not per-device, changing
> it when backend_domid != 0 for a certain device might cause trouble to
> other devices, or guests launched concurrently. Also udev scripts check
> run_hotplug_scripts in xenstore, so changing it while there are guests
> being created or destroyed might also cause trouble.

So this is the reason why I don't want to change it's value, but ignore for
non-dom0 backends (for which it wouldn't change anything anyway).

-- 
Best Regards / Pozdrawiam,
Marek Marczykowski
Invisible Things Lab


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