Re: [patch 05/11] syslets: core code

[Davide Libenzi <davidel@xmailserver.org>]

On Wed, 14 Feb 2007, Ingo Molnar wrote:

> yeah, that's another key thing. I do plan to provide a sys_upcall() 
> syscall as well which calls a 5-parameter user-space function with a 
> special stack. (it's like a lightweight signal/event handler, without 
> any of the signal handler legacies and overhead - it's like a reverse 
> system call - a "user call". Obviously pure userspace would never use 
> sys_upcall(), unless as an act of sheer masochism.)

That is exactly what I described as clets. Instead of having complex jump 
and condition interpreters on the kernel (on top of new syscalls to 
modify/increment userspace variables), you just code it in C and you pass 
the clet pointer to the kernel.
The upcall will setup a frame, execute the clet (where jump/conditions and 
userspace variable changes happen in machine code - gcc is pretty good in 
taking care of that for us) on its return, come back through a 
sys_async_return, and go back to userspace.




- Davide


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