[Qemu-devel] Re: [PATCH] Add VirtIO Frame Buffer Support

[Alexander Graf]

On 03.11.2009, at 08:43, Avi Kivity wrote:

> On 11/03/2009 08:39 AM, Alexander Graf wrote:
> > On 03.11.2009, at 07:34, Avi Kivity wrote:
> >
> > > On 11/03/2009 08:27 AM, Alexander Graf wrote:
> > > > > How does it work today?
> > > >
> > > > You boot into a TERM=dumb line based emulation on 3270 (worst  
> > > > thing haunting people's nightmares ever), trying to get out of  
> > > > that mode as quickly as possible and off into SSH / VNC.
> > >
> > > Despite the coolness factor, IMO a few minutes during install time  
> > > do not justify a new hardware model and a new driver.
> >
> > It's more than just coolness factor. There are use cases out there (www.susestudio.com 
> > ) that don't want to rely on the guest exporting a VNC server to  
> > the outside just to access graphics.
>
> Instead you rely on the guest using virtio-fb. Since we have to make  
> guest modifications, why not go for the simpler ones?

Ok, imagine this was not this unloved S390 odd architecture but X86.  
The only output choices you have are:

1) virtio-console
2) VNC / SSH over network
3) virtio-fb

Now you want to configure a server, probably using yast and all those  
nice graphical utilities, but still enable a firewall so people  
outside don't intrude your machine. Well, you managed to configure the  
firewall by luck to allow VNC, but now you reconfigured it and  
something broke - but VNC was your only chance to access the machine.  
Oops...

> > You also want to see boot messages, have a console login screen,
>
> virtio-console does that, except for the penguins.  Better, since  
> you can scroll back.

It doesn't do graphics. Ever used yast in text mode?

> > be able to debug things without switching between virtio-console  
> > and vnc, etc. etc.
>
> Render virtio-console on your vnc session.  We do that already, no?  
> (well, the host's vnc session, not the guest's).

Yes, we do that. Still doesn't buy you graphics.

> > The hardware model isn't exactly new either. It's just the next  
> > logical step to a full PV machine using virtio. If the virtio-fb  
> > stuff turns out to be really fast and reliable, I could even  
> > imagine it being the default target for kvm on ppc as well, as we  
> > can't switch resolutions on the fly there atm.
>
> We could with vmware-vga.

The vmware-port stuff is pretty much tied onto X86. I don't think  
modifying EAX is that easy on PPC ;-).

> > > Why?  the guest will typically have networking when it's set up,  
> > > so it should have network access during install.  You can easily  
> > > use slirp redirection and the built-in dhcp server to set this up  
> > > with relatively few hassles.
> >
> > That's how I use it right now. It's no fun.
>
> The toolstack should hide the unfun parts.

You can't hide guest configuration. We as a distribution control the  
kernel. We don't control the user's configuration as that's by design  
the user's choice. The only thing we can do is give users meaningful  
choices to choose from - and having graphics available is definitely  
one of them.

Seriously, try to ask someone internally to get access to an S390. I  
think you'll understand my motivations a lot better after having used  
it for a bit.

Alex