Re: [Xenomai] Xenomai 3: kill() to non-Xenomai PIDs

[Philippe Gerum <rpm@xenomai.org>]

On 10/16/2015 06:03 PM, Jan Kiszka wrote:
> On 2015-10-16 18:00, Philippe Gerum wrote:
>> On 10/16/2015 05:57 PM, Jan Kiszka wrote:
>>> On 2015-10-16 17:31, Philippe Gerum wrote:
>>>> On 10/16/2015 05:28 PM, Jan Kiszka wrote:
>>>>> On 2015-10-16 17:22, Philippe Gerum wrote:
>>>>>> On 10/16/2015 04:56 PM, Jan Kiszka wrote:
>>>>>>> On 2015-10-16 16:49, Jan Kiszka wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> kill() is currently handled by libcobalt such that PIDs <= 0 are
>>>>>>>> forwarded to Linux and PIDs > 0 are considered to target only Xenomai
>>>>>>>> threads. But what if the user wants to address a regular Linux task from
>>>>>>>> within a Xenomai application? Shouldn't we retry kill via the Linux path
>>>>>>>> if Xenomai's syscall reports ESRCH?
>>>>>>>>
>>>>>>>
>>>>>>> IOW:
>>>>>>>
>>>>>>> diff --git a/lib/cobalt/signal.c b/lib/cobalt/signal.c
>>>>>>> index aac4059..7e03301 100644
>>>>>>> --- a/lib/cobalt/signal.c
>>>>>>> +++ b/lib/cobalt/signal.c
>>>>>>> @@ -99,6 +99,10 @@ COBALT_IMPL(int, kill, (pid_t pid, int sig))
>>>>>>>  
>>>>>>>  	ret = XENOMAI_SYSCALL2(sc_cobalt_kill, pid, sig);
>>>>>>>  	if (ret) {
>>>>>>> +		/* Retry with regular kill is no RT target was found. */
>>>>>>> +		if (ret == -ESRCH)
>>>>>>> +			return __STD(kill(pid, sig));
>>>>>>> +
>>>>>>>  		errno = -ret;
>>>>>>>  		return -1;
>>>>>>>  	}
>>>>>>>
>>>>>>> Jan
>>>>>>>
>>>>>>
>>>>>> This may break code that sends signal 0 to detect whether a rt thread
>>>>>> exists (like copperplate does), which is the reason for the lack of
>>>>>> forwarding IIRC. (ret == -ESRCH && sig) would be required to forward
>>>>>> without breaking such assumption.
>>>>>
>>>>> That still breaks POSIX (what if the user wants to test for a non-rt
>>>>> thread, like this is possible under regular Linux?). Can't copperplate
>>>>> be changed to bypass the wrapper?
>>>>>
>>>>
>>>> Probably, yes.
>>>>
>>>
>>> Looking at cluster_probe, I wonder if there is actually a problem.
>>> Doesn't that code also run over mercury? Then kill(pid, 0) also targets
>>> the whole system, not just a set of Xenomai applications.
>>
>> Over mercury, the whole system is the rt domain.
>>
>>  Or do we need
>>> to ensure that the caller is not migrated to Linux needlessly under
>>> cobalt? IOW: can that probing happen under RT constraints?
>>>
>>
>> It does with clusters. In general, no restriction on the calling domain
>> should exist for this low level interface.
> 
> Ok, will handle that path cobalt-specific then.
> 
>>
>>> The same applies for me to the other users of the kill-based probing
>>> pattern (copperplate/heapobj-pshared.c and copperplate/regd/fs-common.c).
> 
> But these are fine, no?
> 

Yes, don't care for mode switches there.


-- 
Philippe.