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

Gregory Haskins
2009-07-07T13:31:20Z

[-- Attachment #1: Type: text/plain, Size: 2240 bytes --]

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

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 266 bytes --]