libxl: hotplug scripts and backend_domid != 0

libxl: hotplug scripts and backend_domid != 0

[Marek Marczykowski]

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Hi,

Currently when using backend outside of dom0 (for at least one device) libxl
force udev call method of hotplug scripts for entire system. 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? If so, I can provide patches.

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


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Re: libxl: hotplug scripts and backend_domid != 0

[Ian Campbell]

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.

>  If so, I can provide patches.

Re: libxl: hotplug scripts and backend_domid != 0

[Roger Pau Monné]

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.

Re: libxl: hotplug scripts and backend_domid != 0

[Marek Marczykowski]

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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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