Re: libxl: hotplug scripts and backend_domid != 0

["Roger Pau Monné" <roger.pau@citrix.com>]

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.