KVM able to write graphical VM output to non-X host framebuffer?

Vedexent · 2014-02-26 22:26:33

I'm wondering if this is possible, even if it needs patches and custom building.

What I'd like to do, is install an extremely "bare bones" Arch install on my laptop - specifically I don't even want the overhead of X-Windows.

I'd like to run multiple KVM virtual machines, and some of the VMs might have an X Windowing environment - or I might even run a Windows 7 VM as well.

I'll like KVM to write the graphical output of the VM directly to the host's framebuffer, much in the same way that I can do with mplayer.

I'll also like to be able to "hot-key" and swap which of the running VMs' output is written to the framebuffer.

Has anyone done anything like this? Is this even possible to do?

Thanks,

edit: grammar

Last edited by Vedexent (2014-02-26 22:28:24)

andy123 · 2014-02-27 07:53:03

You could try running a spice or vnc client on directfb.

spice-gtk3 from [community] runs fine on wayland/weston, if that's not too much overhead for you.

Vedexent · 2014-02-27 12:20:05

andy123 wrote:

You could try running a spice or vnc client on directfb.
spice-gtk3 from [community] runs fine on wayland/weston, if that's not too much overhead for you.

That's a good suggestion, thank you.

I haven't tried it yet, but it looks like DirectVNC (found here: http://freecode.com/projects/directvnc) outputs to the framebuffer.

That's probably a much more stable solution than patching KVM to use the framebuffer.

I'll give it a shot, and post back here if it works.

Last edited by Vedexent (2014-02-27 12:20:33)

Vedexent · 2014-02-27 23:01:04

OK - the theory seems sound.

However there's no AUR package for DirectVNC, but there is one for fbvnc, so I installed that.

I launched TMux off the login, fired up a KVM image with the Slitaz live CD, with output to vnc (no virtual networking or bridging, just using the host interface)

Popping over to a new Tmux window, I was able to to connect to the laptop's IP with fbvnc and display the Slitaz graphical boot screen, all without host XWindows - so the idea seems promising.

Some wrinkles yet - and I'm not sure if they're from KVM, Slitaz, from fbvnc - at least not yet.

* The fbvnc framebuffer size is way too small, up in the top-left corner of the display
* There is no mouse support
* Attaching a plugin mouse and doing usb device pass-through to the VM still doesn't seem to result in mouse support.

Firing up my XWindows sesision (with dwm), and I can get full screen and mouse support in the VM.

I'll try and full install of a minimal desktop Linux (Slacko Puppy?) and see if that works any better "out of the box".

So ... any ideas on how to fine tune the fbkvm window size (which doesn't have man pages, and for which I cannot find any documentation) and/or resolve the mouse support problem?

andy123 · 2014-02-28 18:05:59

You could always create a package for DirectVNC, it's not that much work.

Depending on how much you want this, you might have to read the fbvnc source code, it's only 740 lines C code

Something else occured to me. The normal qemu gui is SDL, which might run on directfb (see here).

Using usb forwarding with a mouse sounds like it should work, no idea why it doesn't, how about qemu debugging output or something? I don't know how the linux usb drivers work, but it might be possible, that something like the HID driver "claims" the device and makes it unforwardable.

Arch Linux

#1 2014-02-26 22:26:33

KVM able to write graphical VM output to non-X host framebuffer?

#2 2014-02-27 07:53:03

Re: KVM able to write graphical VM output to non-X host framebuffer?

#3 2014-02-27 12:20:05

Re: KVM able to write graphical VM output to non-X host framebuffer?

#4 2014-02-27 23:01:04

Re: KVM able to write graphical VM output to non-X host framebuffer?

#5 2014-02-28 18:05:59

Re: KVM able to write graphical VM output to non-X host framebuffer?

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