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

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2015-10-16 17:34, Gilles Chanteperdrix wrote:
> On Fri, Oct 16, 2015 at 05:28:07PM +0200, 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?
> 
> If I have understood the "xenomai 3" philosophy, is not an
> application which wants to use the standard call supposed to use the
> __STD prefix, or not use the wrapping at all ?

That's also a theoretical option, but should only be used if we can't
fix the limitation otherwise. The more exceptions we define, the less
portable we become for POSIX/Linux applications.

Jan

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