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

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Date:	Tue, 07 Jul 2009 08:56:43 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Davide Libenzi <davidel@...ilserver.org>
Subject: Re: [KVM PATCH v9 2/2] KVM: add iosignalfd support

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


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