Re: [KVM PATCH v9 2/2] KVM: add iosignalfd support

[Gregory Haskins]

Michael S. Tsirkin wrote:
> On Tue, Jul 07, 2009 at 08:56:43AM -0400, Gregory Haskins wrote:
>   
>> Michael S. Tsirkin wrote:
>>     
>>> On Tue, Jul 07, 2009 at 03:27:49PM +0300, Avi Kivity wrote:
>>>   
>>>       
>>>> On 07/07/2009 03:22 PM, Michael S. Tsirkin wrote:
>>>>     
>>>>         
>>>>> On Tue, Jul 07, 2009 at 02:53:18PM +0300, Avi Kivity wrote:
>>>>>    
>>>>>       
>>>>>           
>>>>>>>> +		/* address-range must be precise for a hit */
>>>>>>>>
>>>>>>>>          
>>>>>>>>             
>>>>>>>>                 
>>>>>>> So there's apparently no way to specify that
>>>>>>> you want 1,2, or 4 byte writes at address X?
>>>>>>>
>>>>>>>        
>>>>>>>           
>>>>>>>               
>>>>>> Why would you want that?
>>>>>>      
>>>>>>         
>>>>>>             
>>>>> Donnu. Why would anyone want to catch 8 byte writes at all?
>>>>>    
>>>>>       
>>>>>           
>>>> One of the natural write sizes.
>>>>
>>>>     
>>>>         
>>>>> Seriously, why add artificial limitations?
>>>>> IMO, addr=0,len=1 and addr=0,len=2 should not conflict.
>>>>>
>>>>>    
>>>>>       
>>>>>           
>>>> They should not conflict, but a two byte write need not hit a one byte  
>>>> registration.
>>>>     
>>>>         
>>> Yes. That's exactly what I'm saying. I think it should be possible to
>>> create 2 fds:
>>>
>>> addr = 0
>>> len = 1
>>> addr = 0
>>> len = 2
>>> and at most one will ever trigger.
>>>
>>> But current code will not let you create the second one.
>>>
>>>   
>>>       
>> Note that this was by design to keep the code simple since we don't have
>> a (known) use case for overlap.  At the very least, you have to address
>> how data subsets are handled.  But do we really need that functionality?
>>
>> -Greg
>>
>>     
>
> Hey, forget about overlap. Overlap does not exist as a concept.  You now
> spend a lot of effort to detect it. Kill all that code, and just do
> this on assignment:
>
> list_for_each(...)
> 	if (rhs->add == lhs->addr && rhs->len == lhs->len &&
> 	    (rhs->wildcard || lhs->wildcard || rhs->data == lhs->data))
> 		return -EEXIST;
>
>   
I like it.  Will do for v10.

Thanks Michael,
-Greg

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