Re: [Xenomai-core] user and kernel space

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

On 12/31/2011 12:18 PM, Jan-Erik Lange wrote:
> 
> Hello,
> 
> I have a question concerning user space and kernel space. I'm dealing
> with the native API and I read, that this API provides the same
> funtkions for both kernel and user space.
> 
> When looking at the sourcecode of buffer.h for example, there I find
> a section called public interface. When looking at the function
> rt_buffer_create(); for example, how does the Implementation von this
> function in userspace differs to the implementation for this function
> kernel space? Or is it the same implementation for user and kernel
> space.

For most services such as buffer services, user functions emit system
calls which implementation in kernel-space use the corresponding kernel
service.

There are some exceptions such as mutexes implementation where we try
hard to avoid system calls and so provide both a user-space
implementation and a kernel-space implementation.

Another exception is the __xn_rdtsc() function, which relies on most
platforms on the same mechanism in user and kernel-space to access the
machine high resolution counter, and so has an identical implementation.


-- 
                                                                Gilles.