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

[Michael Thayer]

Hello Jan,

Only generic advice for debugging kernel modules I'm afraid: for a start 
set up a serial console (or use VirtualBox logging to the host<1>) and 
put log statements in the paths which are getting triggered to 
understand what is happening and where things hang; and/or use ftrace to 
see what is getting called.

Regards,

Michael

<1> https://www.virtualbox.org/wiki/VBoxLogging

On 14.09.2016 12:06, Jan Petrouš wrote:
> Hi Michael.
>
>> On 6 September 2016 at 11:13, Michael Thayer
> <michael.thayer at oracle.com <mailto:michael.thayer at oracle.com>> wrote:
>> >
>> > 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.
>> >
>>
>
> I just get some patches which adds to the linux vboxvideo.ko support for
> multiframebuffer (one framebuffer per display).
> But I have some very strange trouble with it.
>
> When started, only the first framebuffer is working (and so only one
> graphical display is enabled).
> Then I enable second FB by entering "fbset -ifb /dev/fb1 -accel 1".
> An that moment, I get the virtual machine freezed. Now if I try to send
> [ENTER] or any other key,
> I don't see cursor or any ather activities on the command line (on guest
> Linux system).
>
> The strangeness is that if I click on close button of guest console
> window (so the popup menu starts
> with option of save, shutdown or power-off), the windows title changed
> to "paused" and only now I can see
> the previously entered keys showed on guest console. It looks like
> console lock is released when
> popup windows started and again acquired if I cancel popup.
>
> It looks like the guest console (fbcon?) gets freezed (so locked) by
> some initialization task inside
> the modified vboxvideo driver.
>
> Configuration:
>
> Host system: Fedora 24 desktop with kernel 4.6.7, but my colleague tries
> that on Windows 7, the issue is the same,
> so I guess it is host system independetend issue
> Guest: I tried two distros, both have installed minimal packages and no Xwin
> Guest1: Fedora 24 desktop, kernel 4.6.7
> Guest2: Arch latest, kernel 4.7.2
>
> Do you have any idea how to debug such console freeze?
>
> /Jan
>
>> Yes, I was asking on irc, but I think I fallen in lunch mode there, so
> only silence :)
>> That is why I asked here again.
>>
>> Anyway, thanks for the hints! I definitely will have a try with drm.
>>
>> But it's good that the author of driver is reachable.
>> So more questions can come later ;)
>>
>> CU
>> /Jan
>>
>>
>> > Regards,
>> >
>> > Michael
>> >
>> > <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
>> >>
>> >>
>> >> _______________________________________________
>> >> vbox-dev mailing list
>> >> vbox-dev at virtualbox.org <mailto:vbox-dev at virtualbox.org>
>> >> https://www.virtualbox.org/mailman/listinfo/vbox-dev
>> >>
>> >
>> > --
>> > Michael Thayer | VirtualBox engineer
>> > ORACLE Deutschland B.V. & Co. KG | Werkstr. 24 | D-71384 Weinstadt
>> >
>> > ORACLE Deutschland B.V. & Co. KG
>> > Hauptverwaltung: Riesstraße 25, D-80992 München
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>> >
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> Handelsregister der Handelskammer Midden-Nederland, Nr. 30143697
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-- 
Michael Thayer | VirtualBox engineer
ORACLE Deutschland B.V. & Co. KG | Werkstr. 24 | D-71384 Weinstadt

ORACLE Deutschland B.V. & Co. KG
Hauptverwaltung: Riesstraße 25, D-80992 München
Registergericht: Amtsgericht München, HRA 95603

Komplementärin: ORACLE Deutschland Verwaltung B.V.
Hertogswetering 163/167, 3543 AS Utrecht, Niederlande Handelsregister 
der Handelskammer Midden-Nederland, Nr. 30143697
Geschäftsführer: Alexander van der Ven, Jan Schultheiss, Val Maher