xenapi: attach root disk during rescue before boot

Fixes bug 1037729

The xenapi driver attaches the root disk after the rescue instance has
booted. However, hotplugging block devices is only supported on images
that use PV drivers. Attaching the disk before the rescue instance boots
will allow rescue to work on instances that don't use PV drivers.

Change-Id: I187762e4f1ea921d81afd40fcbde0b93d7d3cbc1

1 files changed, 15 insertions, 7 deletions

diff --git a/nova/virt/xenapi/vmops.py b/nova/virt/xenapi/vmops.py
index 10cca68f4..3a0c8e4d1 100644
--- a/nova/virt/xenapi/vmops.py
+++ b/nova/virt/xenapi/vmops.py
@@ -303,6 +303,18 @@ class VMOps(object):
             undo_mgr.undo_with(undo_create_vm)
             return vm_ref
 
+        if rescue:
+            # NOTE(johannes): Attach root disk to rescue VM now, before
+            # booting the VM, since we can't hotplug block devices
+            # on non-PV guests
+            @step
+            def attach_root_disk_step(undo_mgr, vm_ref):
+                orig_vm_ref = vm_utils.lookup(self._session, instance['name'])
+                vdi_ref = self._find_root_vdi_ref(orig_vm_ref)
+
+                vm_utils.create_vbd(self._session, vm_ref, vdi_ref,
+                                    DEVICE_RESCUE, bootable=False)
+
         @step
         def prepare_security_group_filters_step(undo_mgr):
             try:
@@ -345,6 +357,9 @@ class VMOps(object):
             vm_ref = create_vm_step(undo_mgr, vdis, kernel_file, ramdisk_file)
             prepare_security_group_filters_step(undo_mgr)
 
+            if rescue:
+                attach_root_disk_step(undo_mgr, vm_ref)
+
             boot_instance_step(undo_mgr, vm_ref)
 
             apply_security_group_filters_step(undo_mgr)
@@ -1054,13 +1069,6 @@ class VMOps(object):
         self._acquire_bootlock(vm_ref)
         self.spawn(context, instance, image_meta, [], rescue_password,
                    network_info, name_label=rescue_name_label, rescue=True)
-        rescue_vm_ref = vm_utils.lookup(self._session, rescue_name_label)
-        vdi_ref = self._find_root_vdi_ref(vm_ref)
-
-        rescue_vbd_ref = vm_utils.create_vbd(self._session, rescue_vm_ref,
-                                             vdi_ref, DEVICE_RESCUE,
-                                             bootable=False)
-        self._session.call_xenapi('VBD.plug', rescue_vbd_ref)
 
     def unrescue(self, instance):
         """Unrescue the specified instance.