Re: [Xenomai-help] RTDM mmap alternative

[Jan Kiszka <jan.kiszka@domain.hid>]

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Rodrigo Rosenfeld Rosas wrote:
>> ...
>> I tested it (after figuring out what to do at all, and how to get it
>> working then...) with a simple demo that returns a shared kernel memory
>> block, mapped into user-space via an RTDM-IOCTL. I think you should
>> easily (now really!) adapt it to your needs. Please check if this
>> functions meets your requirements and works for more than one scenario.
>> If so, I will add it to official RTDM.
>>
>>
>> @all: I would be curious to hear any comment on my /dev/zero-trick to
>> invoke mmap in kernel-space. Is this an ugly hack or may it be worth
>> considering to apply on /dev/rtheap as well - to overcome the need for
>> this device (and related user errors...)?
> 
> Jan, actually I didn't like the /dev/zero hack. If someone else is 
> using /dev/zero it will result in a problem... I think it would be better to 

Why? It isn't an exclusive device. And I'm only invoking open/close on
the original instance (which even have no handlers associated, see
drivers/char/mem.c), mmap gets overloaded.

> reserve a separate file descriptor for mmaping. Maybe in a separate module 
> like xeno_mmap that only register a, say, /dev/xenommap or /dev/xenomai/mmap. 
> I think it would be a better approach. Or maybe something like 
> 
> void *rtdm_mmap_to_user(void *buffer, size_t length, char *dev_to_use)
> 
> Just some ideas...

Maybe I'm overseeing something: Did you face real problems with my approach?

Jan


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