Re: [Xenomai] shared memory compatibility - advice sought

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

On 04/11/2013 02:42 AM, Gilles Chanteperdrix wrote:

> Let us talk concretely. If I assume you want to share the same piece of
> memory in all the cases (which I originally did not). You would have a
> common kernel module able to allocate a piece of memory and associate it
> with an identifier (a string, ala shm_open/sem_open, for instance).
> 
> Then an rtdm module, with an ioctl allowing to retrieve that piece of
> memory or allocate it given the id, and if called from user-space use
> rtdm_mmap_to_user to put it in the process adress-space, if called from
> kernel-space, return the memory directly. The same RTDM code can be
> compiled both for RTAI and Xenomai and covers 4 cases. And RTDM drivers
> can be called as well from kernel space as from user-space, if I
> remember correctly.
> 
> Then another linux module, with an ioctl and an mmap call allowing to
> retrieve the same piece of memory with the same ID and map it in the
> process user-space.


That is still way too complicated. The only thing you need is a plain
Linux character device driver, with an ioctl and mmap method allowing to
map so kernel memory in user-space, and a kernel-space API giving access
to the kernel memory.

The kernel API would be used in the module initialization/cleanup
routines of your kernel mode applications. The user API would be used by
the non real-time part initialization of user applications in any mode.

As a starting point, you can have a look at the "linux device drivers"
book examples.

-- 
                                                                Gilles.