Re: [Xenomai-help] RTDM mmap alternative

[Rodrigo Rosenfeld Rosas <lbocseg@domain.hid>]

Em Quinta 09 Fevereiro 2006 14:53, Jan Kiszka escreveu:

> ...
>>> But I think we still need a cleanup on RTDM device closure to avoid
>>> access to the mapped physical buffers after that point. I wonder how
>>> this is done in standard drivers, will have to look at some of them.
>>
>> Sorry, I can't help here, since the user munmap don't pass through the
>> driver... :( I don't know if it is even done by the drivers. The mmap man
>> page states:
>>
>> "The  munmap()  system  call deletes the mappings for the specified
>> address range, and causes further references to addresses within the range
>> to generate invalid memory references.  The region is  also automatically
>> unmapped when the process is terminated.  On the other hand, closing the
>> file descriptor does not unmap the region."
>>
>> So, the mmap will be undone when the program finishes, I think.
>
>Indeed, this is also what I quickly verified in practice. E.g., if you
>do not munmap the region I provided in my test driver, the user-space
>tool will still be able to access the physical memory behind it.

Even if the application was closed and then rerun using a stored address? It 
would not conform to documentations in this case... I think you're talking 
about just closing the file descriptor with rtdm_dev_close, right?

>In that case, the user kmalloc'ing (or whatever) that region again after a
>kfree would access memory that is probably used in a totally different way
>meanwhile. Dangerous!

But, anyway it would be a user error. Not a driver issue... But I agree that 
it would be great to undone the mapping on closing the file descriptor, 
although it would not be compatible with normal mmap behaviour.

>If it is just RAM, you may track the releases (register vma_fops) and
>call kfree only when the last user finished. But when it's physical
>device memory, you may want to have access earlier. Thus we need
>"enforced" munmap on rt_dev_close, maintained by the individual driver.
>Therefore, I will introduce also rtdm_munmap() or so.

It would be nice to be able to call rtdm_munmap. :)

Rodrigo.

	

	
		
_______________________________________________________ 
Yahoo! doce lar. Faça do Yahoo! sua homepage. 
http://br.yahoo.com/homepageset.html