Re: portability layer?

[Hollis Blanchard <hollis-yUx37fBWTUITNcAmw9vGhQ@public.gmane.org>]

On Wed, 2007-03-28 at 17:48 +0200, Avi Kivity wrote:
> Hollis Blanchard wrote:
> > On Tue, 2007-03-27 at 08:57 +0200, Avi Kivity wrote:
> >>
> >> I don't think we should be aiming at full source portability.  
> >> Virtualization is inherently nonportable, and as it is mostly done in 
> >> hardware, software gets to do the quirky stuff that the hardware people 
> >> couldn't bother with :)  instead we should be aiming at code reuse.
> >>     
> >
> > I'm not sure I see the distinction you're making. Operating systems
> > could also be considered "inherently nonportable", yet Linux and the
> > BSDs support an enormous range of platforms. If you're saying that we
> > shouldn't try to run x86 MMU code on a PowerPC then I can't agree
> > more. :)
> 
> No, I'm saying that some #ifdeffery in both libkvm and the ioctl 
> interface is unavoidable.

If by #ifdeffery you mean having per-architecture definitions of
structures like kvm_regs, absolutely. If you mean literal #ifdefs in the
middle a header file, I believe that can and should be avoided.

> Right now this is handled by qemu, which means our higher level tools 
> are _already_ nonportable.

Yes, but not *all* the higher level tools are. At some point you have a
common interface, and at this point I think I've answered my own
question: the qemu monitor connection is the portable interface.

That means everything layered above qemu, such as libvirt and thus
virt-manager, should work on all architectures +/- without changes.
Lower-level software, such as GDB, would need per-architecture support.

> [I have a feeling we're talking a little past each other, probably due 
> to me not knowing ppc at any level of detail.  No doubt things will 
> become clearer when the code arrives]

I don't have any code for you, but you will be the first to know when I
do. :) Right now I'm just trying to make sure we don't accidentally
paint ourselves into a corner with a stable ABI.

-Hollis


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