Re: [Xen-devel] VIRTIO - compatibility with different virtualization solutions

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Feb 25, 2014 at 11:03:24AM +1030, Rusty Russell wrote:
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> writes:
> > On Fri, Feb 21, 2014 at 10:05:06AM +0000, Wei Liu wrote:
> >> On Thu, Feb 20, 2014 at 06:50:59PM -0800, Anthony Liguori wrote:
> >> > The standard should say, "physical address"
> >
> > This conversation is heading towards - implementation needs it - hence lets
> > make the design have it. Which I am OK with - but if we are going that
> > route we might as well call this thing 'my-pony-number' because I think
> > each hypervisor will have a different view of it.
> >
> > Some of them might use a physical address with some flag bits on it.
> > Some might use just physical address.
> >
> > And some might want an 32-bit value that has no correlation to to physical
> > nor virtual addresses.
> 
> True, but if the standard doesn't define what it is, it's not a standard
> worth anything.  Xen is special because it's already requiring guest
> changes; it's a platform in itself and so can be different from
> everything else.  But it still needs to be defined.
> 
> At the moment, anything but guest-phys would not be compliant.  That's a
> Good Thing if we simply don't know the best answer for Xen; we'll adjust
> the standard when we do.

I think Daniel's suggestion of a 'handle' should cover it, no?

Or are you saying that the 'handle' should actually say what it is
for every platform on which VirtIO will run?

For Xen it would be whatever the DMA API gives back as 'dma_addr_t'.
Which would require the VirtIO drivers to use the DMA (or PCI) APIs.


> 
> Cheers,
> Rusty.
> 

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