Re: [Xenomai-help] Analogy cmd_write example explanation

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

Jan Kiszka wrote:
> Philippe Gerum wrote:
>> On Thu, 2010-04-01 at 23:54 +0200, Jan Kiszka wrote:
>>> Philippe Gerum wrote:
>>>> The bottom line for me, is that T_PRIMARY, as a user-space visible
>>>> "feature" should be dropped at some point, and never ever considered as
>>>> a way to fix the RTDM syscall issue anymore. I don't mind saving an
>>>> extra-context switch even in what I think should be _rare_ cases, but
>>>> this has to be done in a way that does not introduce the same kind of
>>>> misunderstanding the eager mode switching allowed by rt_task_set_mode()
>>>> did in the past.
>>>>
>>>> Really, I'm convinced that an awful lot of people are currently running
>>>> under-performing at best, or even broken applications today, because of
>>>> that, thing.
>>> We are not discussing T_PRIMARY here. We are discussing something like
>>> an "rtdm_is_rt_capable()" addition for those _few_ RTDM drivers that
>>> actually want to provide Ianus-like services.
>>>
>> Yes, we do discuss of T_PRIMARY in between the lines.
>>
> 
> You can take it away, and the rtdm_is_rt_capable-approach would still
> work, but that without affecting existing designs.

Ok. I almost regret I launched this troll. We have discussed some time
with Philippe, and I agree with him that drivers which this change
really broke were already broken. The only side-effect is the double
switch issue, which, per-se is not that much a trouble in real-world
applications. So what I propose is a special RTDM driver flag that would
somehow fix the issue for the switchtest driver, and would only be used
by that driver and not exported in the rtdm headers, and of course not
documented.

-- 
					    Gilles.