Re: virtio & hypercall interface?

[Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Dor Laor wrote:
> Avi Kivity wrote:
>> Anthony Liguori wrote:
>>  
>>> Dor Laor wrote:
>>>      
>>>>> Hi all,
>>>>>
>>>>>     I've finally started looking at Dor's git tree, and it struck me
>>>>>                   
>>>> that
>>>>            
>>>>> it conflicts with Anthony's hypercall patches.  FWIW I like Anthony's
>>>>> patching thing, and don't really care about arg order.  It'd be 
>>>>> nice if
>>>>> we could pull in the same direction tho 8)
>>>>>
>>>>> Thanks,
>>>>> Rusty.
>>>>>                   
>>>> Good news you're looking at my tree, since the forum I didn't do much
>>>> since I had to catch up some gazlion other tasks, never the less
>>>> starting on Sunday I'm back again.
>>>>
>>>> Actually, I wanted to rebase my hypercalls over Anhtony's too (except
>>>> for allowing userspace handling).
>>>>           
>>> I thought we discussed just providing a signaling message to 
>>> userspace for virtio?  It's not strictly necessary to expose 
>>> hypercalls to userspace in order to implement a virtio backend in 
>>> userspace.
>>>
>>>       
>>
>> Yes, that's what I'd like to see too.  Signal a channel.
>>
>>   
> First, I though that this 
> http://www.mail-archive.com/kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org/msg06230.html
> was your latest opinion.
> Second, regardless of the channel signal notification, there are still 
> real necessities for userspace hypercall handling:
> 1. For virtio drivers there is also registration hypercall for passing 
> the shared memory pfns.
>    Sure there are other possibilities, but why limit ourselves?

Can you elaborate here?  Using a PCI discover mechanism, you've got your 
memory already.  Not point in reinventing PCI with hypercalls.

>
> 2. For other purposes such as a balloon driver, a deflate/inflate 
> hypercalls are needed.
>    Although for x86 mmio/pio can be used but this is not compatible 
> with other architectures.

Isn't a balloon driver just another virtio device?  Rather, it might be 
interesting to build a simple RPC mechanism on top of virtio and do 
things like balloon on top of that.

Regards,

Anthony Liguori

> Regards & thanks for the patch resend,
> Dor


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