Re: [Qemu-devel] [PATCH 10/13] Implement early printk in virtio-console

[Anthony Liguori]

Alexander Graf wrote:
> On 24.11.2009, at 20:25, Anthony Liguori wrote:
>
>   
> > Alexander Graf wrote:
> >     
> > > On 24.11.2009, at 19:55, Anthony Liguori wrote:
> > >
> > >  
> > >       
> > > > Alexander Graf wrote:
> > > >    
> > > >         
> > > > > On our S390x Virtio machine we don't have anywhere to display early printks
> > > > > on, because we don't know about VGA or serial ports.
> > > > >
> > > > > So instead we just forward everything to the virtio console that we created
> > > > > anyways.
> > > > >       
> > > > >           
> > > > What is this used for?
> > > >    
> > > >         
> > > This is used for console output before virtio is initialized. I didn't invent 
> > > it - that's the way it's implemented in the s390 kernels today.
> > >  
> > >       
> > I don't see any code that calls this function.  Am I missing something obvious?
> >     
>
> It gets called from target-s390x/kvm.c using a special hypercall instruction.
>   

Oh, that's bad :-)

That should really be it's own character device.  We don't really have a 
way to connect two character devices like that.  Maybe muxing?

Regards,

Anthony Liguori
> Alex