Re: updating Xen public headers

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On 12/07/11 11:23, Manuel Bouyer wrote:
> 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 ?

The idea is the same as behind the disk and network drivers how to 
detect if and how many disks/vifs are available.

> > 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.

Ok.

Christoph