xen: Add XEN_DISABLED mode and make it default

Also set XEN_ATTACH mode in xen_init() to reflect the truth; not that
anyone ever cared before. It was *only* ever checked in xen_init_pv()
before.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

accel/xen/xen-all.c

@@ -171,6 +171,8 @@ static int xen_init(MachineState *ms)
      * opt out of system RAM being allocated by generic code
      */
     mc->default_ram_id = NULL;
+
+    xen_mode = XEN_ATTACH;
     return 0;
 }
 

include/hw/xen/xen.h

@@ -22,8 +22,9 @@
 
 /* xen-machine.c */
 enum xen_mode {
-    XEN_EMULATE = 0,  // xen emulation, using xenner (default)
-    XEN_ATTACH        // attach to xen domain created by libxl
+    XEN_DISABLED = 0, /* xen support disabled (default) */
+    XEN_ATTACH,       /* attach to xen domain created by libxl */
+    XEN_EMULATE,      /* emulate Xen within QEMU */
 };
 
 extern uint32_t xen_domid;

softmmu/globals.c

@@ -63,5 +63,5 @@ QemuUUID qemu_uuid;
 bool qemu_uuid_set;
 
 uint32_t xen_domid;
-enum xen_mode xen_mode = XEN_EMULATE;
+enum xen_mode xen_mode = XEN_DISABLED;
 bool xen_domid_restrict;