[vbox-dev] Linux guest: two framebuffer devices? Is it possible?

Michael Thayer michael.thayer at oracle.com
Tue Sep 6 09:13:07 GMT 2016

Hello Jan,

I think you asked about this on IRC yesterday.  The first file that you 
mention is part of the Linux drm driver (the rest is the other files in 
that folder).  I wrote the driver, based on in-kernel ones, but I am not 
an expert in the kernel drm subsystem, and in particular I only use the 
basic kernel fbdev translation functions to provide the framebuffer 
driver.  You would probably be better asking on the dri-devel list<1> 
about what to change to get one fbdev device per head.  You might be in 
luck and there might be a simple solution.



<1> https://lists.freedesktop.org/mailman/listinfo/dri-devel

On 05.09.2016 17:42, Jan Petrouš wrote:
> Hi,
> as VirtualBox supports dual head config I was trying to start two
> framebuffers on it.
> But unsucessfull.
> The main constraint is that guest Linux is very tiny and has no
> X-Windows inside.
> The application requires only the framebuffer devices.
> I did many hours googling to find solution but I found only solution for
> xwin environment.
> Is it even possible to enable two FB devices on dualhead configuration?
> If the answer is NO, can you show me where I should start to look inside
> the sources?
> I found the VB Additions subversion repo where are at least two video
> drivers:
> 1,
> http://www.virtualbox.org/svn/vbox/trunk/src/VBox/Additions/linux/drm/vbox_fb.c
> 2,
> http://www.virtualbox.org/svn/vbox/trunk/src/VBox/Additions/x11/vboxvideo/vboxvideo.c
> I guess that the driver for my non-x11 environment is the first one. Is
> it true?
> I'm rather linux video driver noob, but I would like to get some good
> start point
> where I can at least try to start with.
> BR.
> /Jan
> PS: Installed Fedora Server 24 Minimal config, so kernel is 4.6.7
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