Re: [Xenomai-help] enable/disable all interrupts from user space

[Philippe Gerum <rpm@xenomai.org>]

On Fri, 2006-10-27 at 15:32 +0200, Jan Kiszka wrote:
> Jeff Weber wrote:
> > How do I enable/disable all interrupts (Linux and Xenomai) from user space?  
> > (native skin preferred)
> 
> For x86:
> 
> iopl(3);
> __asm__ __volatile__("cli/sti");
> 

Gasp...

> Ugly hack, typical a sign that something should be moved somewhere
> else... (there are a few exceptions, though)
> 
> We once had some discussion if we shouldn't export domain stalling
> features to user-space in order to support things like X-servers that
> currently come with such code, toasting any RT kernel. May come one day,
> but this will be primarily for legacy non-RT code.

Providing "cli" emulation to X-Servers would only make sense in order to
stall the Linux domain; controlling the interrupt shield dynamically
using the T_SHIELD bit would allow that already. If I understand
correctly, we are talking about stalling the Xenomai domain too, and
this is a completely different story. The day we would provide such
"feature" as an official API, we would trigger tons of misuses of this
hack, a bit like we have now with the T_PRIMARY bit, a number of people
sprinkle over their code to control the task exec mode, which is most of
the time utterly sub-optimal, and automatically handled by the nucleus
already. IOW, I'm not convinced at all that adding such API would be the
right thing to do.

For the time being, it should be possible to write a simple kernel
module using either the native or RTDM API from kernel space, which
would handle such requests from user-space. For instance, one could use
rt_task_notify() from user-space to signal a helper task in a kernel
module that carries out the job, depending on the signal received. The
same goes for a trivial RTDM driver only implementing the ioctl()
support for the same purpose.

> 
> Jan
> 
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-- 
Philippe.