Re: [Xenomai-help] Problem with tcb.handle and taskDesc.td_tid

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

Matthieu Connaulte wrote:
> On Tue, 26 Aug 2008 16:37:27 +0200, Gilles Chanteperdrix
> <gilles.chanteperdrix@xenomai.org> wrote:
>> Matthieu wrote:
>>> On Tue, 26 Aug 2008 14:55:19 +0200, Gilles Chanteperdrix
>>> <gilles.chanteperdrix@xenomai.org> wrote:
>>>> Gilles Chanteperdrix wrote:
>>>>> Matthieu wrote:
>>>>>> Hi
>>>>>>
>>>>>> I would like to understand the coherence between the task identifier
>> of
>>>> the
>>>>>> task control block and the task id given by taskDesk (function
>>>>>> taskInfoGet()). In fact, I init a task with taskInit, I get the tid
>>>> using
>>>>>> tid=tcb.handle. The use of taskInfoGet(tid, taskDesc) gives me a
>>>>>> taskDesk.td_tid different from the tid.
>>>>>>
>>>>>> I want to test if the task is suspended using taskIsSuspended(tid) or
>>>>>> taskIsSuspended(taskDesc.td_tid), but both get me  a 3d0001 errno
>> (code
>>>>>> error of WIND_OBJ_ERR_BASE S_objLib_OBJ_ID_ERROR). The PID given by
>>>>>> /proc/xenomai/stat also has no connection. Idem with a ps -AfL
>>>>>>
>>>>>> Thank you in advance for your explanations
>>>>> You are not supposed to use the internal fields of the structures. A
>>>>> valid id is one returned by the taskIdSelf(), taskNameToId(),
>>>>> taskIdDefault(). I can not find a service which returns the task Id
>> for
>>>>> a given TCB. Is it what you are looking for ?
>>>> By the way, if you could call taskInfoGet, you already have a valid
>> task
>>>> id...
>>>>
>>> But using taskNameToId, taskSuspend(tid) makes the same error and so is
>>> taskInfoGet().
>> Ok. So, we have a bug and these functions do not work as expected.
>>
>> In the sources, I saw that taskInfoGet seems to be a
>>> reentrant routine (see ksrc/skins/vxworks/syscall.c where a taskInfoGet
>> is
>>> call in the taskInfoGet routine)
>> If by reentrant you mean recursive, no, not at all, taskInfoGet is not
>> recursive. You see, the interface between user-space and kernel-space is
>> not a simple function call, it is a system call, that is the way the
>> whole Linux kernel works. The difference between Linux and Xenomai is
>> that Xenomai APIs are symetric between kernel-space and user-space. So,
>> the function implementing a kernel-space service is used to implement
>> the system call used by the user-space service of the same name.
>>
>> What you see in ksrc/skins/vxworks/syscall.c is that the function
>> __wind_task_info_get, which is the handler of the vxworks skin
>> __vxworks_taskinfo_get system call, calls the kernel-space taskInfoGet
>> function, so there is no recursion.
>> in src/skins/vxworks/taskInfo.c, you will see that the taskInfoGet
>> function emits the _vxworks_taskinfo_get system call.
>>
>> --
> 
> Reading that I'm not supposed to use the internal fields of the structures,
> and using taskInfoGet, I have some doubts about what I'm doing : I get a
> taskDesc structure and I modify its field td_entry to set the function
> pointer of the routine (FUNCPTR). I'm not really sure this going to works.
> On WINDRIVER, I were able to directly modify the field WIND_TCB->entry.
> What do you thing about this ?

What do YOU think ?

-- 
					    Gilles.