[vbox-dev] win 95/98 guest additions ?

Michael Thayer michael.thayer at oracle.com
Mon Sep 12 13:21:31 PDT 2011

Hello Huihong,

CC-ing the list again in case this is useful for someone else (I assume 
it was just an oversight on your part though).

On 09/12/2011 10:00 PM, Huihong Luo wrote:
> When the guest window resizes, I guess the guest drvier must be
> notified, and then the guest changes the video mode? Does this mean that
> arbitrary video modes are supported?
> from BIOS view, there should be only certain number of video modes are
> supported.

When the video mode changes the notification goes through the VMMDev 
event notification mechanism which I described in a previous e-mail [1]. 
  The notification is VMMDEV_EVENT_DISPLAY_CHANGE_REQUEST - see the 
recently-added documentation near VMMDevReq_GetDisplayChangeRequest2 in 
include/VBox/VMMDev.h.  In the X.Org/X11 Additions (I think the Windows 
Additions do things similarly) a user-space client listens for these 
events and sends notifications to the drivers.  Using 
VBoxVideoSetModeRegisters() or the HGSMI APIs we can set any video mode 
(see also VBoxVideoAnyWidthAllowed() for completeness), not just those 
offered by the BIOS.



[1] http://vbox.innotek.de/pipermail/vbox-dev/2011-September/004524.html

> --- On *Mon, 9/12/11, Michael Thayer /<michael.thayer at oracle.com>/* wrote:
>     From: Michael Thayer <michael.thayer at oracle.com>
>     Subject: Re: [vbox-dev] win 95/98 guest additions ?
>     To: "Huihong Luo" <huisinro at yahoo.com>
>     Cc: vbox-dev at virtualbox.org
>     Date: Monday, September 12, 2011, 12:37 PM
>     Hello Huihong,
>     On 09/12/2011 06:30 PM, Huihong Luo wrote:
>      > We are exploring the possibility of implementing this old stuff. In
>      > particular, the mouse and graphics drivers.
>      > Seems mouse integration shouldn't be that difficult. However, for
>     video
>      > cards, it will take quite some time.
>      > I have a question, does
>      > C:\virtualbox-dev\vbox\include\VBox\Hardware\VBoxVideoVBE.h
>     contains all
>      > the video card's registry information? In other words, do these
>      > constants sufficient to develop the display driver? 95/98 uses
>     totally
>      > different driver model, and needs to implment in real mode using
>      > assembly code.
>      > So wanted to know what is the minimum requirement?
>     See the files in src/VBox/Additions/common/VBoxVideo for a first
>     approximation. Those were my first attempt at sharing video driver code
>     between Linux and Windows. For a minimal driver, the functions
>     VBoxVideoGetVRAMSize() and VBoxVideoSetModeRegisters() in
>     Modesetting.cpp which can be used without any of the rest. Those
>     functions are so basic they ought to be re-usable in 16bit code, or let
>     me know if that can be achieved with trivial changes. If you wish to go
>     further, HGSMIBase.cpp contains APIs for setting up the buffers used for
>     communicating with the graphics device (sending commands and receiving
>     replies and notifications) and for doing the actual communication.
>     Modesetting.cpp uses them to set multi-monitor graphics modes (and the
>     older APIs I mentioned for single-monitor mode-setting). VBVABase.cpp
>     contains dirty rectangle notification code, particularly for
>     accelerating remote display.
>     Feel free to send API documentation patches! I wrote the existing
>     documentation as I was getting to grips with the API (which was win32
>     only, and I am a Linux developer...) so it is a bit unclear. See
>     src/VBox/Additions/x11/vboxvideo/vbva.c for am example of how to set up
>     the graphics card. pointer.c and setmode.c in that directory build on
>     top of that.
>     Hope that helps a bit.
ORACLE Deutschland B.V. & Co. KG   Michael Thayer
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