linux-kernel - Re: [patch 05/11] syslets: core code

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Date:	Wed, 14 Feb 2007 17:01:04 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Alan <alan@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 05/11] syslets: core code

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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