On 04/22/2013 09:11 AM, Jan Kiszka wrote:
> On 2013-04-20 17:30, Gilles Chanteperdrix wrote:
>> On 04/20/2013 05:27 PM, Jan Kiszka wrote:
>>
>>> On 2013-04-20 17:21, Gilles Chanteperdrix wrote:
>>>> On 04/20/2013 05:18 PM, Jan Kiszka wrote:
>>>>
>>>>> On 2013-04-20 17:14, Gilles Chanteperdrix wrote:
>>>>>> On 04/20/2013 10:19 AM, Jan Kiszka wrote:
>>>>>>
>>>>>>> On 2013-04-20 08:04, Michael Haberler wrote:
>>>>>>>>
>>>>>>>> Am 19.04.2013 um 21:06 schrieb Gilles Chanteperdrix
>>>>>>>> <[email protected]>:
>>>>>>>>
>>>>>>>>> On 04/19/2013 01:46 PM, Leopold Palomo-Avellaneda wrote:
>>>>>>>>>
>>>>>>>>>> [1]
>>>>>>>>>> http://lists.mech.kuleuven.be/pipermail/orocos-users/2013-April/006986.html
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>> that link does not tell us why you need this option. And that would be
>>>>>>>>> the most important information.
>>>>>>>>
>>>>>>>> with the linuxcnc package build I need to turn on
>>>>>>>> --enable-dlopen-skins as well to get Python modules to work properly
>>>>>>>
>>>>>>> OK, it looks like we should try harder to detect dlopen scenarios during
>>>>>>> runtime to avoid build-time switches. This is likely Xenomai 3 material:
>>>>>>>
>>>>>>> - We need to disable TLS optimizations by default (no big deal).
>>>>>>>
>>>>>>> - In the POSIX skin constructor, we need to read out the mlockall
>>>>>>> state, lock everything if necessary, and restore the state
>>>>>>> accordingly afterward. The Nucleus may help us here if there is no
>>>>>>> adequate libc service (ABI change -> Xenomai 3).
>>>>>>>
>>>>>>> - IIRC, the problem with unconditional auto-shadowing back then were
>>>>>>> the improper scheduling parameters that POSIX used to apply. That
>>>>>>> was fixed a while back. So if we simple re-apply the current
>>>>>>> parameters, it should cause no harm in a dlopen scenario. But I need
>>>>>>> to check this again at work against our scenario.
>>>>>>
>>>>>>
>>>>>> You do not like the idea of an environment variable allowing to disable
>>>>>> the automatic shadowing?
>>>>>
>>>>> Not as a long-term solution as it is user-unfriendly. But it can be an
>>>>> option worth considering for 2.6.
>>>>
>>>>
>>>> Apparently -forge is already doing it. The advantage of this solution is
>>>> that the same binary serves well several usages, if we intend to provide
>>>> packages as generic as possible, this seems like the way to go. Several
>>>> of the changes I made in the last few weeks go in the same direction.
>>>
>>> I'm not sure if there is added value for the controlling auto-shadowing
>>> in general. But for the case it is in conflict with dlopen, the solution
>>> I'm proposing is clearly superior as it removes those conflicts
>>> automatically.
>>>
>>> Of course, an environment variable control can exist in parallel if
>>> there is a need beyond the dlopen conflict resolution.
>>
>>
>> The difference with what you propose is that you propose a syscall to
>> get the mlockall state. Another solution would be not to call munlockall
>> after the main thread shadowing, this looks less complicated and does
>> not require ABI changes.
>
> Yes, that's an option as well. But then we should apply this
> consistently, invoking mlockall from all skin init functions
> unconditionally. The nucleus depends on this anyway. Not sure if such
> change would be fine for 2.6 - you decide.
What we could do is:
- if XENO_NOSHADOW is set, shadow the main thread, and call mlockall
- if it is not set, do not shadow the main thread or call
mlockall/munlockall
--
Gilles.
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