xen: report hypervisor version

Various versions of the hypervisor have differences in what ABIs and features they support. Print some details into the boot log to help with remote debugging.

---
arch/x86/xen/enlighten.c | 8 ++++++--

1 file changed, 6 insertions(+), 2 deletions(-)

===================================================================

@@ -168,10 +168,14 @@ void xen_vcpu_restore(void)
 

static void __init xen_banner(void)
{
+ unsigned version = HYPERVISOR_xen_version(XENVER_version, NULL);
+ struct xen_extraversion extra;
+ HYPERVISOR_xen_version(XENVER_extraversion, &extra);
+

	printk(KERN_INFO "Booting paravirtualized kernel on %s\n",
	       pv_info.name);

- printk(KERN_INFO "Hypervisor signature: %s%s\n",
- xen_start_info->magic,
+ printk(KERN_INFO "Xen version: %d.%d%s%s\n",
+ version >> 16, version & 0xffff, extra.extraversion,

	       xen_feature(XENFEAT_mmu_pt_update_preserve_ad) ? " (preserve-AD)" : "");
}

applied to tip/x86/xen, thanks Jeremy.

Ingo