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SubjectRe: SVGA kernel chipset drivers.
Linus Torvalds said:
> The server does a fork(), and the child does all the graphics stuff,
> exactly so that the parent can't be impacted by a buggy (or malicious)
> graphics program.
> Essentially, this already sets up the protection domains. The server is
> protected, yet the fork() inheritance is able to give the graphics
> program all the resources it needs, and nothing more.
> > simple: a kernel trap is currently the cheapest protection domain switch
> We don't need to switch protection domains more than once. We just need
> to set up the frame buffer, put it into graphics mode, and then the
> graphics program can just use it directly. This is all assuming the card
> has a sane frame buffer and doesn't need more than the map (and perhaps
> some IO port access, but that is also set up by the startup stuff).
> I mean, you've all been trying to say that all graphics cards have frame
> buffers, so why aren't you happy now that I gave you a protected
> frame-buffer without a line of kernel code? What more do you want?

Such a daemon already exists, it is called Xfree86.

As of Xfree86 3.1.2B you can use the call

XF86DGAGetVideo(display, screen, &addr, &width, &bank, &ram);

returns a pointer to the video ram (addr) the width of a scan line (width)
the size of a bank (bank) and the total ram size (ram). You don't even need
a linear frame buffer, as

XF86DGASetVidPage(display, screen, page) a

Allows you to do video ram paging (no very optimal as you always have read and
write mapped at the same address).

XF86DGADirectVideo(display, screen, XF86DGADirectGraphics)

Gives you write access to the display. You can even add XF86DGADirectMouse
and XF86DGADirectKeyb to the flags and get raw mouse mickeys and key repeats.

Jon. <,>

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