From: Justin Mason (jm at domain netnoteinc.com)
Date: Thu 23 Sep 1999 - 11:18:03 IST
"John P . Looney" said:
> On Thu, Sep 23, 1999 at 10:47:24AM +0100, Jakma, Paul mentioned:
> > > Well, that's an exaggeration. Some of the video drivers are in the
> > > kernel. The Linux Kernel has /dev/fb as well as the recent DRI
> > > (Direct Rendering Interface) stuff, for 3D acceleration for
> > > X/Mesa/GLX.
>
> > but fb is nothing more than a safe way of exporting the graphics
> > hardware to userspace. all the fancy stuff still has to be done in
> > userspace. eg the matrox fb driver knows how to get the card into
> > fancy text modes and how to get back to them. Accel still has to be
> > done by userspace mmap'ing /dev/fbx and tweaking the right bits of
> > memory.
>
> Do you think that NT has all the rendering stuff in ring0 too ? No it
> doesn't - it has a little more than Linux does these days. There isn't
> much there, but what there is, apparently speeds stuff up a lot. Of
> course, Linux doesn't have multiple rings - it's in or out, so it has a
> small bit in the kernel, most of the stuff in userspace, which is a
> small difference..
I thought NT had its GDI subsystem in ring 0 -- and I also thought that
GDI handled a lot of drawing primitives?
If this is the case then surely it's a bit more than /dev/fb is exporting.
(vague recollection: isn't this how a recent MS Java bug was able to cause
blue-screens from an applet, by passing way-out-of-range values to a
low-level java.awt.Graphics drawing function?)
I could be way wrong as I've done no research into this, it's all just off
the top o' my head...
--j.
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