From: Andreas Beck <becka@rz.uni-duesseldorf.de>
  To  : ggi-develop@eskimo.com
  Date: Sun, 16 May 1999 19:17:42 +0200

Re: Using Directbuffer write pointer in kernel

> > I am just trying to improve my tool application for a video card with GGI
> > DirectBuffer:
> > I would like to pass the DirectBuffer->write address to a kernel module,
> > which then writes it to my PCI video card, which in its turn writes the
> > digitized video signal to my graphics card (Complicated sentence, I know
> > ;) ).

> > I suspect this has something to do with userspace->kernel space
> > conversion, but I have no clue about these things  - is there any
> > possibility to realize this conversion, either in the user space program
> > or in the kernel module ?

This is usually impossible without quite some hacking. 
The kernel driver _could_ in theory find out the mapping or you could
read /proc/self/maps in userspace, which will allow you to find the physical
address from the logical adress ranges in the output.

I also assume that you know, that telling some DMA device to put it's data
at some physical address is something only root should be able to do.

IMHO it would be better to make the kernel modules talk to each other as
Marcus suggested. Making the video addon card a KGI subsystem would probably 
be the most straightforward way to do it.

CU, ANdy

-- 
= Andreas Beck                    |  Email :  <andreas.beck@ggi-project.org> =