Re: [Xenomai] [Xenomai-git] Jan Kiszka : lib/cobalt: Rework minimum stack size enforcement

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

On Tue, Apr 21, 2015 at 06:12:15PM +0200, Jan Kiszka wrote:
> On 2015-04-21 18:06, Gilles Chanteperdrix wrote:
> > On Tue, Apr 21, 2015 at 06:04:42PM +0200, Jan Kiszka wrote:
> >> On 2015-04-21 17:27, Gilles Chanteperdrix wrote:
> >>> On Tue, Apr 21, 2015 at 05:22:34PM +0200, git repository hosting wrote:
> >>>> +COBALT_IMPL(int, pthread_attr_setstack, (pthread_attr_t *attr, void *stackaddr,
> >>>> +					 size_t stacksize))
> >>>> +{
> >>>> +	if (stacksize < COBALT_STACKSIZE_MIN)
> >>>> +		return -EINVAL;
> >>>> +	return __STD(pthread_attr_setstack)(attr, stackaddr, stacksize);
> >>>> +}
> >>>
> >>> As I said, there is no reason for Xenomai to enforce a task size
> >>> larger than PTHREAD_STACK_MIN. This breaks POSIX compliance, and is
> >>> useless.
> >>
> >> Then we should not use printf & Co. from any trampoline function, e.g.
> >> vxworks/taskLib.c:task_trampoline. I only tried with a local skin, but I
> >> bet the issue is reproducible with that one.
> >>
> >> For that reason, I went down the conservative path.
> > 
> > The path you took breaks compatibility with POSIX. On a compliant
> > system, pthread_attr_setstacksize(attr, PTHREAD_STACK_MIN) is not
> > supposed to return an error.
> 
> That is true. We have to pick from one evil: fail non-compliant here or
> crash later.

The point is: you do not know if it will crash later, you can assume
that the user calling pthread_attr_setstack knows what he is doing.
Any user calling this interface should. We are doing real-time in C,
not making an API for tutorials in ADA, or C++, let us try not to
prevent the user from doing what he wants.

For pthread_attr_setstacksize, you can round to the larger size and
remain POSIX compliant.

-- 
					    Gilles.