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

  • To: Anthony Liguori <aliguori@xxxxxxxxxx>
  • From: Jon Smirl <jonsmirl@xxxxxxxxx>
  • Date: Mon, 5 Dec 2005 21:35:00 -0500
  • Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 06 Dec 2005 02:35:32 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

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.

I'm not exactly sure how Redhat install boots, but when it first comes
up it has to be using VGA mode or vesafb since it doesn't know what
video hardware the box has. (What does it do if there is no video card
installed? serial line?) After a couple of questions in VGA mode it
quickly starts an X server and goes graphical.

On a server box with only a serial line and no video hardware, the
install has to stay in text mode using terminal emulation.

The problem is when the distro wants to start the X sever and go into
graphics mode. That isn't going to work very well with the Xen model.
You have three choices:
1) Treat it like a server and use the virtual serial line with
terminal emulation
2) virtual VGA - Let it start the xserver and run the xserver on the
virtual VGA device.
3) or create a new install mode where the installer starts a network
device, waits for an ssh connect, and then run a remote X based

The third mode would be best for Xen but I don't believe an
distribution works that way currently. #3 is a minor change to
existing installers. One problem I see is knowing what address to ssh
into. The address could be sent to the serial console as part of the
boot process. If you want to get fancy implement a new terminal escape
sequence that could be sent down the serial line which will trigger
the ssh connect and run the graphical installer.

Jon Smirl

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