On 04/22/2013 03:42 PM, Jan Kiszka wrote:
> On 2013-04-22 13:37, Gilles Chanteperdrix wrote:
>> 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
>
> That's not what I suggested. I was questioning the value of _not_ doing
> mlockall automatically during init, thus reducing user duties. That
> would reduce the need to think about XENO_NOSHADOW or not as a normal user.
Currently, when the posix skin library start, it does:
mlockall
shadow main thread
munlockall
Now, the munlockall is certainly an issue when dlopening
What I propose instead is to do:
if (!getenv("XENO_NOSHADOW")) {
mlockall
shadow main thread
}
That will avoid the problem with calling munlockall, and if people who
currently use --enable-dlopen-skins really want to avoid shadowing the
main thread (which I doubt), they can set the environment variable
XENO_NOSHADOW.
--
Gilles.
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