Re: [Xenomai-help] Deprecated kernel system calls in xenomai-head and new application development paradigm

[Philippe Gerum <rpm@xenomai.org>]

On Wed, 2009-09-02 at 15:04 +0300, Rus V. Brushkoff wrote:
> On Wed, 2 Sep 2009, Philippe Gerum wrote:
> 
> :> :> :> Can you show this paradigm on pipe.c exmaple from Xenomai docs ?
> :> :> :We are talking about drivers, then just design your driver as you would
> :> :> :design a Linux driver.
> :> :> :For instance, you would implement the "write" method of the driver to
> :> :> :pass data between the user-space task and the driver.
> :> :>  This is RT driver not simply Linux driver. The previous rt_pipe_read() 
> :> :> call was running in RT task context. Now it is not clear how this can be 
> :> :> achieved with new RTDM driver model in kernel space.
> :> :The write method of an RTDM driver can run in rt context too. If the
> :> :task which issues the call to "write" is a Xenomai user-space task
> :> :running in primary mode.
> :>  Please note - I do not have any Xenomai user-space tasks running - only 
> :> normal user space programs. The Xenomai-2.4 allows developing of RT driver 
> :> in kernel space - leaving untouchable user space processes. If such new 
> :> paradigm need to write the intermediate user-space RT task proxy - than 
> :> it is wrong. Simply because its adds unneeded complexity to developing RT 
> :> kernel hardware drivers.
> :The pipe support is indeed one of a kind, since it shares semantics
> :between RT and non-RT endpoints, and it should be possible to open the
> :non-RT side from programs which were _not_ linked against any Xenomai
> :library. E.g. cat /dev/rtp22 should get any data sent from a RT endpoint
> :bound to the same pseudo-device.
> 
>  Yes, this is one of the issues - most of non-rt apps need to be relinked 
> with Xenomai and later supported, that can be impossible in the most 
> cases.
> 
> :We will solve this issue by having a RTDM-based driver, implementing the
> :services of the current RT_PIPE support, eventually taping into the
> :nucleus core. A kernel-space RTDM driver will be able to send/recv data
> :via the standard inter-driver RTDM interface - this is what your device
> :driver should do. A user-space RT application will have access to a
> :socket-type service access point for sending/receiving packets;
> :semantics close to the AF_UNIX protocol family should be used there. A
> :non-RT application will still be able to open its endpoint via the usual
> :open(2) interface, i.e. such as cat /dev/rtpX works as before.
> :
> :This work is scheduled for Xenomai v3; v2.5.x still provides the
> :kernel-based APIs available in earlier releases, and as such it is a bit
> :early for changing your code. This is also why there is no migration
> :cookbook from v2 -> v3 yet.
> :The "deprecated" messages are an early warning so that people notice
> :that things will change in the next major release, and that it may be a
> :good idea to reconsider any decision to build _applications_ in
> :kernel-space; you can still disable those messages via the
> :CONFIG_XENO_OPT_NOWARN_DEPRECATED switch if they get on your nerves.
> 
>  I think that marking some feature as deprecated need to be done _after_ 
> the ready up new solution exists, including examples in Xenomai docs. Now 
> Xenomai users are facing with problem that has no solution yet.
> 

Please read on again the last couple of mails, neither you or anything
else has problems with 2.5 compared to 2.4, because the interfaces are
still there. Maybe you should read the help text provided with the
option I mentioned, as well:

===
	Starting with Xenomai 3, the skins will not export their
	interface to kernel modules anymore, at the notable exception
	of the RTDM device driver API, which by essence must be used
	from kernel space for writing real-time device
	drivers.

	Warnings will be emitted at build time when kernel code
	invokes thread/task creation services from Xenomai skins to
	remind you that application code should run in user-space
	context instead.

	The reason for this is fully explained in the project Roadmap
	document (see What Will Change With Xenomai 3):
	http://www.xenomai.org/index.php/Xenomai:Roadmap

	You may switch those warnings off by enabling this option, but
	nevertheless, you have been WARNED.


> 
> 		Rus
-- 
Philippe.