[Xenomai] [PATCH] psos: add interface to configure region 0

Philippe Gerum rpm at xenomai.org
Sat Dec 3 18:12:40 CET 2016

On 12/01/2016 09:08 PM, Ronny Meeus wrote:
> On Thu, Dec 1, 2016 at 6:44 PM, Philippe Gerum <rpm at xenomai.org> wrote:
>> On 11/30/2016 10:42 AM, Ronny Meeus wrote:
>>> In the pSOS interface region 0 can be used by applications to allocate
>>> memory from. It contains 'system' memory and is created by default during
>>> system init. Region 0 is currently not supported by the xenomai psos skin.
>>> This patch adds functionality to configure a 'pseudo 0' region that will
>>> be used if applications allocate memory from region 0.
>>> To enable this, following code needs to be added to the early application
>>> init code to configure region 0 (before applications use rn_getseg(0,...)).
>>> unsigned long rnid,rsize;
>>> unsigned long rn_0_size = 128000;
>>> unsigned long unit_size = 128;
>>> rn_create("_RN0",malloc(rn_0_size),rn_0_size, unit_size, 0, &rnid, &rsize);
>>> set_pseudo_rn0_id(rnid);
>>> diff --git a/include/psos/psos.h b/include/psos/psos.h
>>> --- a/include/psos/psos.h
>>> +++ b/include/psos/psos.h
>>> @@ -253,6 +253,8 @@ u_long q_vbroadcast(u_long qid,
>>>                   u_long msglen,
>>>                   u_long *count_r);
>>> +void set_pseudo_rn0_id(unsigned long id);
>>> +
>> I'm fine with the reason to add support for RN#0, not with the way you
>> do it. The proper logic would rather be:
>> - define proper tunable psos_rn0_size representing the size of RN#0,
>> defaulting to 0 bytes
>> - create RN#0 from psos_init() if psos_rn0_size is non-zero
>> That would address several issues:
>> - eliminate the quite ugly remapping from 0 to some pseudo rnid
>> - keep the tunable bits in the emulator core (this stuff is no
>> application's business in the Xenomai model).
>> - allow pulling memory from RN#0 from static C++ ctors and other library
>> init code which may run before the application entry point is reached.
>> i.e:
>> http://xenomai.org/2015/05/application-setup-and-init/#Initialization_sequence
>> The application would only have to call
>> set_config_tunable(psos_rn0_size, <size>) from a setup() handler, as
>> documented here (likewise for the unit size):
>> http://xenomai.org/2015/05/application-setup-and-init/#Overriding_factory_default_values_of_tunables
> Philippe
> disadvantage I see is that the memory allocation is not under control
> of the application.
> But we can live with it.

Since the application can fully decide whether RN#0 gets instantiated,
and how large it should be, I really don't see any restriction on memory
management using the proper tunables would introduce.

RN#0 is special, it should be addressable from early code, which is out
of the application's scope and knowledge. So in this case, the Xenomai
libs know better.

> I will add implement the tunables mechanism and provide a new patch later.
> Can I add it to the file psos/tunable.h added in the other patch I
> provided earlier?

Yes, that would make sense.

> See mail "[PATCH v2] psos.h: remove dependency on tunables.h"
> in other words, do you accept that change?

Yes, that looks ok.


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