Re: [Xenomai-help] how to build a Xenomai posix library ?

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

roderik.wildenburg@domain.hid wrote:
>> -----Ursprüngliche Nachricht-----
>> Von: Gilles Chanteperdrix [mailto:gilles.chanteperdrix@xenomai.org] 
>> Gesendet: Donnerstag, 16. Oktober 2008 11:48
>> An: Wildenburg, Roderik RAEK3 MRA
>> Cc: xenomai@xenomai.org
>> Betreff: Re: [Xenomai-help] how to build a Xenomai posix library ?
>>
>> roderik.wildenburg@domain.hid wrote:
>>> I did so and called, within the library, every 
>> posix_rt-function with
>>> the prefix __wrap_ : e.g. __wrap_shm_open then I compiled my
>>> application, which does not use any Xenomai-function, and linked it
>>> with pthread_rt an rt (-lpthread_rt -lrt) and my new Xenomai-library
>>> (linking without any wrapping defined). Linking and 
>> compiling did not
>>> produce any error. But, when I call a function in my library, which
>>> in turn calls __wrap_shm_open, then shm_open fails. When I link my
>>> application with wrapping (as provided by the XENO_CONFIG-script)
>>> then everything is fine. Do you have an explanation for 
>> this behavior
>>> or even better a solution ?
>> __wrap_shm_open only works if you have the CONFIG_XENO_OPT_POSIX_SHM
>> option enabled. Is it enabled?
> 
> yes it is : 
> CONFIG_XENO_OPT_POSIX_SHM=y
> otherwise, I think, my application linked with wrappings defined wouldn´t work ? But it does.
> 
>> Note that xenomai posix skin shm support
>> is mainly useful for sharing memory between kernel and 
>> user-space. 
> O.k., I just want to share SHM between applications. What SHM construct should I use instead ?
> 
>> If it is enabled, then please tell us what is the value of errno when
>> __wrap_shm_open fails.
>>
> 
> shm_open fails. errno=2
> shm_open fails : : No such file or directory
> 
> I don´t know what this should mean ??

Well, it means that the shared memory does not exist.

> I call shm_open in the following way :
> #define LOGSHMNAME   "/var/logshm"
> oflags=O_RDWR;
> *shmfd = shm_open(LOGSHMNAME, oflags, 0);

a shm name should contain one slash at the beginning and no other slash,
for best portability.
If you want to create a shared memory, you should pass the O_CREAT flag.

This is all documented here:

http://www.xenomai.org/documentation/trunk/html/api/group__posix__shm.html#gf765a0fa9152fbf874436c966f3af7ba

-- 
                                                 Gilles.