[vbox-dev] grabbing text mode output

Klaus Espenlaub Klaus.Espenlaub at Sun.COM
Mon Oct 13 10:16:17 GMT 2008

Lonnie Princehouse wrote:
> Hello,
> I'm using VBox to help develop a research OS.  VBox is great tool for 
> this, and it's significantly sped up my development cycle -- so many 
> thanks to everyone responsible :) 
> My current situation is that I have no working disk or network driver 
> for the client OS, but I need to get debugging info somehow. It runs in 
> text mode, so I want to hack the VirtualBox-OSE graphics emulator to 
> dump text-mode output into a file on the (Linux) host.

This is the reason why developers are sorry that serial ports are 
disappearing at a fast rate. The traditional way of getting output to 
another system when developing an OS was using serial lines. They're 
slow, but reliable. And they're bidirectional. You just need ~15 lines 
of code (no matter what programming language) to get something written 
to the serial port if you have IO port access.

The serial port support in VirtualBox should be usable for this purpose. 
It has a few known issues, but they shouldn't matter much in this 
context. If you use them in combination with "socat" on the host you can 
achieve pretty much anything you might need - including redirection via 
the network.

> I've poked around in vbox/src/VBox/Devices/Graphics; it's not 
> immediately obvious where the display text is stored, but I think I can 
> figure that out.  I have two questions for the gurus before I try this-
> 1.Is this crazy?

Somewhat yes. But no less crazy than some parts of VirtualBox, so go 
ahead if you like that idea.

> 2. I'll need the Intel PRO/1000 MT emulation eventually, which appears 
> to only be available for the non-OSE VirtualBox.  Assuming I can get my 
> hacked graphics emulation working, is there any way I can use it with 
> Sun's VirtualBox, or any way to use the Intel PRO/1000 MT emulation with 
> VirtualBox-OSE?

There's no legal way of using the Intel PRO/1000 MT in the context of 
VirtualBox OSE. However if you manage to make your change a PDM plugin 
you might be able to combine both your hack and VirtualBox PUEL.


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