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

[Alexander Graf]

On 24.11.2009, at 20:30, Anthony Liguori wrote:

> 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?

So you want me to implement char muxing and a bootloader within a week? :)

Alex