Re: updating Xen public headers

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Wed, Dec 07, 2011 at 11:13:57AM +0100, Christoph Egger wrote:
> >OK, looks fine. But we have to be carefull, when we'll start using
> >these features, that a dom0/domU with them can still work with a domU/dom0
> >that doesn't have them
> 
> The USB and SCSI IO interfaces need to be implemented in a frontend and
> backend PV driver. The interaction with Xen is as minimal as with
> the disk and network PV driver.

I guess a backend publish its features in the xenstore and a frontend
can check this ?

> 
> Hypercalls unknown to a xen kernel return ENOSYS. That means there are
> three ways to handle the backward compatibility:
> 
> - at compile time by introducing #ifdef XEN4 ... #endif
> - at runtime by checking the hypercall return value
> - at runtime query the xen version we are on and enable/disable
>   corresponding features.

3) is my prefered, 2 is acceptable too. We really want to avoid the
#ifdef XEN4 ... #endif if we can.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--