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Re: updating Xen public headers

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.



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