Re: [Qemu-devel] [RFC] Memory API

[Anthony Liguori]

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