linux-kernel - Re: Userspace I/O driver core

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Date:	Thu, 14 Dec 2006 10:00:08 -0800
From:	Greg KH <greg@...ah.com>
To:	Avi Kivity <avi@...o.co.il>
Cc:	Hans-J?rgen Koch <hjk@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: Userspace I/O driver core

On Thu, Dec 14, 2006 at 12:48:55PM +0200, Avi Kivity wrote:
> [why trim the cc?]
> 
> Hans-J?rgen Koch wrote:
> >Am Donnerstag, 14. Dezember 2006 10:44 schrieb Avi Kivity:
> >
> >  
> >>I understand one still has to write a kernel driver to shut up the irq.  
> >>How about writing a small bytecode interpreter to make event than 
> >>unnecessary?
> >>
> >>The userspace driver would register a couple of bytecode programs: 
> >>is_interrupt_pending() and disable_interrupt(), which the uio framework 
> >>would call when the interrupt fires.
> >>
> >>The bytecode could reuse net/core/filter.c, with the packet replaced by 
> >>the mmio or ioregion, or use something new.
> >>
> >>    
> >
> >I think this would be overkill. The kernel module you have to write
> >is _really_ very simple. And it has to be written only once, so even
> >a manufacturer who employs no experienced kernel developers can
> >easily outsource that task.
> >
> >  
> 
> It has to be written once, but compiled for every kernel version and 
> $arch out there (for out of tree drivers), or it has to wait for the 
> next kernel release and distro sync (for in-tree drivers).

No, just get the tiny driver into the main kernel tree, like all other
drivers are required to do.

> If we make userspace drivers possible, it makes sense that the entire 
> driver be in userspace, not just 98.7% of it.

If you see a way to do this that is race-free, I know a lot of people
would be glad to see such a patch.

But until then, no, we are not making any such claims of 100% userspace
driver for hardware such as pci devices and other things that this uio
core works with.

thanks,

greg k-h
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