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Date: Thu, 19 May 2011 08:23:42 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [RFC] Memory API
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To: Jan Kiszka <jan.kiszka@web.de>
Cc: Peter Maydell <peter.maydell@linaro.org>, Avi Kivity <avi@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

On 05/19/2011 01:31 AM, Jan Kiszka wrote:
> On 2011-05-18 21:10, Anthony Liguori wrote:
>> On 05/18/2011 10:30 AM, Jan Kiszka wrote:
>> static void i440fx_io_intercept(void *opaque, uint64_t addr, uint32_t
>> value, int size, MemRegion *next)
>> {
>>      I440FX *s = opaque;
>>
>>      if (range_overlaps(addr, size, PAM_REGION)) {
>>          ...
>>      } else {
>>          dispatch_io(next, addr, value, size);
>>      }
>> }
>>
>> There's no need for an explicit intercept mechanism if you make multiple
>> levels have their own dispatch tables and register progressively larger
>> regions.  In fact....
>
> Actually, things are a bit more complicated: This layer has to properly
> adopt the coalescing properties of underlying regions or we cause
> performance regressions to VGA emulation. That means it has to register
> dispatching slots of the corresponding size and set the coalescing flag
> accordingly. And it likely need to adjust them as the regions below change.

As I mentioned in another thread, I don't think we want to "design" 
coalescing into the API.  Coalescing is something that breaks through 
abstractions layers and is really just a hack.

Regards,

Anthony Liguori

> IOW, I don't think we get away with that simple approach above but still
> require to track mapping via a PhysMemClient. But we should be able to
> avoid filtering by adding overlapping regions with higher prio.
>
> Jan
>