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Re: updating Xen public headers

On 12/07/11 10:56, Manuel Bouyer wrote:
On Tue, Dec 06, 2011 at 12:22:06PM +0100, Christoph Egger wrote:
New interfaces for PV drivers:

- Xen transcedent memory

PCI IO improvements for PV domU:

- PCI MSI support
- PCI Express AER support

New features:

- xen honors flags to be placed into guest kernel available
   pte bits if enabled (for grant table)
- support for 128 vcpus
   (old interface is still present and supports up to 32 vcpus)
- PCI passthrough: new hypercalls to support SR-IOV
- new hypercall for physical cpu hotplugging
- new hypercall for physical page offlining
- fixes to compile with clang
- machine check recovery mechanism

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.

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.


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