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    From
    SubjectRe: SVGA kernel chipset drivers.
    Date
    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)
    ^flag

    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. <jon@gte.esi.us.es, http://www.esi.us.es/~jon>


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