[Xenomai] rtdm driver open_rt/nrt handler question

[Xenomai] rtdm driver open_rt/nrt handler question

[JK.Behnke]

   Xenomai 2.6.3 documentation states, that the usage of open_rt handlers
   is deprecated
   as this feature will be removed in the future.
   As a consequence one cannot use rtdm_mutex_lock inside an nrt_open
   handler
   to synchronize multiple callers, as this will result in a
   (!xnpod_unblockable_p()) assertion.
   So using a spinlock would be the only solution in that situation.
   Is that true?

   By the way, if an rtdm driver only supports RTDM_EXCLUSIVE mode, is
   there
   a need to synchronize concurrent calls to rt_dev_open on this device at
   all?
   I guess not, because the second caller will be refused.
   Is that also true?

   Thanks for your help
   Jochen

Re: [Xenomai] rtdm driver open_rt/nrt handler question

[Gilles Chanteperdrix]

On Thu, Nov 26, 2015 at 10:00:16AM +0100, JK.Behnke@web.de wrote:
>    Xenomai 2.6.3 documentation states, that the usage of open_rt handlers
>    is deprecated
>    as this feature will be removed in the future.

Xenomai 2.6.3 is very old now. It is not even the latest release in
the 2.6 branch. open_rt has been removed from Xenomai 3.

>    As a consequence one cannot use rtdm_mutex_lock inside an nrt_open
>    handler
>    to synchronize multiple callers, as this will result in a
>    (!xnpod_unblockable_p()) assertion.
>    So using a spinlock would be the only solution in that situation.
>    Is that true?

No, the caller is a Linux task, or a Xenomai task running in
secondary mode. As such, any Linux service can be used, such as
mutex or semaphores (the Linux ones).

> 
>    By the way, if an rtdm driver only supports RTDM_EXCLUSIVE mode, is
>    there
>    a need to synchronize concurrent calls to rt_dev_open on this device at
>    all?
>    I guess not, because the second caller will be refused.
>    Is that also true?

Yes.

-- 
					    Gilles.
https://click-hack.org

Re: [Xenomai] rtdm driver open_rt/nrt handler question

[JK.Behnke]

> On Thu, Nov 26, 2015 at 10:00:16AM +0100, JK.Behnke@web.de wrote:
> > Xenomai 2.6.3 documentation states, that the usage of open_rt handlers
> > is deprecated
> > as this feature will be removed in the future.
>
> Xenomai 2.6.3 is very old now. It is not even the latest release in
> the 2.6 branch. open_rt has been removed from Xenomai 3.
>
> > As a consequence one cannot use rtdm_mutex_lock inside an nrt_open
> > handler
> > to synchronize multiple callers, as this will result in a
> > (!xnpod_unblockable_p()) assertion.
> > So using a spinlock would be the only solution in that situation.
> > Is that true?
>
> No, the caller is a Linux task, or a Xenomai task running in
> secondary mode. As such, any Linux service can be used, such as
> mutex or semaphores (the Linux ones).
Yes, I agree.
Using a xenomai spinlock would of course also result in a
xenomai assertion, hence I'm left with the linux synchronization
services.
Same goes for init_module/cleanup_module handlers, as these can
only be called by Linux tasks.

>
> >
> > By the way, if an rtdm driver only supports RTDM_EXCLUSIVE mode, is
> > there
> > a need to synchronize concurrent calls to rt_dev_open on this device at
> > all?
> > I guess not, because the second caller will be refused.
> > Is that also true?
>
> Yes.
OK.

Gilles, thanks again for responding that fast.
I really appreciate it.
Regards
Jochen