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

From: Anthony Liguori <anthony@codemonkey.ws>
To: Alexander Graf <agraf@suse.de>
Cc: Carsten Otte <cotte@de.ibm.com>,
	qemu-devel@nongnu.org, Aurelien Jarno <aurelien@aurel32.net>
Subject: Re: [Qemu-devel] [PATCH 10/13] Implement early printk in virtio-console
Date: Tue, 24 Nov 2009 13:30:08 -0600	[thread overview]
Message-ID: <4B0C3440.7080406@codemonkey.ws> (raw)
In-Reply-To: <158A814D-A4BB-4F3C-BFC6-8470FB559A1F@suse.de>

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