Import check for xen features.

MFC after:	1 month

sys/xen/features.c

@@ -0,0 +1,24 @@
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <machine/xen/xen-os.h>
+#include <machine/xen/hypervisor.h>
+#include <machine/xen/features.h>
+
+uint8_t xen_features[XENFEAT_NR_SUBMAPS * 32] /* __read_mostly */;
+
+void
+setup_xen_features(void)
+{
+        xen_feature_info_t fi;
+        int i, j;
+
+        for (i = 0; i < XENFEAT_NR_SUBMAPS; i++) {
+                fi.submap_idx = i;
+                if (HYPERVISOR_xen_version(XENVER_get_features, &fi) < 0)
+                        break;
+                for (j = 0; j < 32; j++)
+                        xen_features[i*32 + j] = !!(fi.submap & 1<<j);
+        }
+}