答复: [Xen-devel] [RFC] Xen Virtual Framebuffer

[苗枫 <miaofeng@xxxxxxxxxxxxxxxx>]

I think this topic must be subject to Para-Virtualized Guest Linux (or some
other os), for unmodified guest os on a VTx box, do you have any suggestion
for graphic acceleration?

And, what if we adjust the qemu-dm to accommodate both Para-dom and VTx-dom?

 

Miao Feng

Star SoftComm(China) Ltd


-----邮件原件-----
发件人: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] 代表 Jon Smirl
发送时间: 2005年12月6日 11:13
收件人: Anthony Liguori
抄送: xen-devel; Antonino A. Daplas
主题: Re: [Xen-devel] [RFC] Xen Virtual Framebuffer

On 12/5/05, Anthony Liguori <aliguori@xxxxxxxxxx> wrote:
> Jon Smirl wrote:
>
> >After thinking about this for a while, wouldn't Xen be better off with
> >a virtual VGA device instead of a virtual fbdev? The virtual VGA
> >device will work for other operating systems as well as Linux.
> >Implementing a VESA BIOS may be better than emulating VGA.
> >http://www.vesa.org/public/VBE/vbecore3.pdf
> >
> >
> This is how Qemu does it so it's what we do for VT.  The VMI spec
> (VMware paravirtual spec) assumes that you'll be doing device emulation
> and calls for an emulated PCI bus.  Xen achieves really good performance
> though by avoiding device emulation.  Native speed device emulation is
> an active area of research though so this might not always be the case :-)
>
> We don't currently do that in Xen though so it would be a considerable
> amount of work to emulate a PCI bus and a VGA device (not to mention an
> emu86 to be able to run the BIOS).

VGA devices don't live on the PCI bus, they are ISA legacy devices at
fixed IO ports/RAM address. But VESA is a better solution than the VGA
device.

Does Xen supply a BIOS into the virtual machine? If so, just implement
the VESA entry points. Most of the Xen-based VESA entry points will do
nothing, but they can't return the not-implemented error. This is very
similar to what you are doing with a virtual fbdev, but the VESA
scheme will work for Windows too. Linux already has a vesafb driver
that will use the entry points you provide.

However, I am assuming that Windows/Linux will fallback to using VESA
calls if they don't find a physical VGA device. There isn't a simple
way to test this since every video card that implements VESA also
implements VGA. If you want to get errors from Linux while it is still
in real mode you need to implement the BIOS INT 10 interface.

--
Jon Smirl
jonsmirl@xxxxxxxxx

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