Re: [Xenomai-help] How to use Xenomai libraries with "normal" (non Xenomai) linux processes ?

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

roderik.wildenburg@domain.hid wrote:
> Sorry for the delayed answer, but I am fighting with an other Xenomai
> problem too (PPC switchtest FPU problem, you probably heard about
> it).
> 
>>> I don´t understand this. Isn´t this a contradiction to your
>> answer in
>>> 2.) ? I thought sched_setscheduler does not work for Xenomai
>>> tasks and in our testcase we could see that scheduling policy
>>> isn´t set as expected (to SCHED_FIFO).
>> Currently the posix skin library does, in init.c: 
>> parm.sched_priority = 0; err =
>> __wrap_pthread_setschedparam(pthread_self(), SCHED_OTHER, &parm);
>> 
>> We could replace this with: err =
>> pthread_getschedparam(pthread_self(), &policy, &parm); if (err) ...
>>  err = __wrap_pthread_setschedparam(pthread_self(), policy, &parm);
>> 
>> 
>> But sched_setscheduler could be called after that, so this is racy.
>> 
> 
> Please correct me if I am wrong: In your replacement
> pthread_getschedparam would read scheduling parameters which should
> have been set with sched_setscheduler before(!) your replacement gets
> active. Is this possible at all ? Wouldn´t I have to call
> sched_setscheduler (in "sysup") before I fork? And if calling after
> the fork it realy would be racy. So this isn´t a very feasible
> solution, isn´t it? Changing the scheduling paramters of a running
> Xenoami task probably isn´t possible (probably there is nothing to
> recognize the change ?)?

You can also call sched_setscheduler after fork but before exec. In case
you want to do that, here is the (untested) patch, to let the xenomai
posix skin use this priority.

Index: src/skins/posix/init.c
===================================================================
--- src/skins/posix/init.c	(revision 4572)
+++ src/skins/posix/init.c	(working copy)
@@ -48,7 +48,7 @@ static __attribute__ ((constructor))
 void __init_posix_interface(void)
 {
 	struct sched_param parm;
-	int muxid, err;
+	int muxid, err, policy;

 	muxid =
 	    xeno_bind_skin(PSE51_SKIN_MAGIC, "POSIX", "xeno_posix");
@@ -74,9 +74,14 @@ void __init_posix_interface(void)
 		exit(EXIT_FAILURE);
 	}

-	parm.sched_priority = 0;
-	err = __wrap_pthread_setschedparam(pthread_self(), SCHED_OTHER,
-					   &parm);
+	err = __real_pthread_getschedparam(pthread_self(), &policy, &parm);
+	if (err) {
+		fprintf(stderr, "Xenomai Posix skin init: "
+			"pthread_getschedparam: %s\n", strerror(err));
+		exit(EXIT_FAILURE);
+	}
+
+	err = __wrap_pthread_setschedparam(pthread_self(), policy, &parm);
 	if (err) {
 		fprintf(stderr, "Xenomai Posix skin init: "
 			"pthread_setschedparam: %s\n", strerror(err));


-- 
                                                 Gilles.