[Xenomai] Reworking file descriptors

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

Hi Jan,

I have starting reworking the posix skin on forge to use the cobalt
registry instead of the ad-hoc registry it currently uses. The next step
for that work is to convert the file descriptors, offering a unified
access with select to posix skin message queues and rtdm drivers, and
working correctly with fork().

I have a clear idea on how I would do it for the posix message queues
only. Just as I did for the semaphores, I would implement a hash table,
where the file descriptor structures are indexed by the user-space file
descriptor (obtained with open(/dev/null) for instance, so that xenomai
file descriptors follow the posix specification, and use the smallest
available descriptor), and the mm structure.

However, RTDM allows opening file descriptors in kernel-space, so it
would break my implementation, because we can use NULL or &init_mm as
the mm key, but what would we use as the file descriptor index?

Any idea is welcome.
Regards.

-- 
                                                                Gilles.