Override disk labels and introduce 'OS_SCRIPT'

* The call to update the metadata is moved inside the
  'RunOsScriptsVirtualized' but before 'TemporaryDisks' because this
  call updates the instance configuration in the metadata daemon, and
  we want this configuration to be available when the helper VM
  starts, but we don't want it to contain information about the
  temporary disks.

* The other call to update the metadata is extracted from the 'else'
  branch to the top-level of the function because we want to update
  metadata independently of whether the instance has an OS.

* Disk paths must be overridden when running the instance inside a
  safe virtualized environment because, from the host perserspective,
  a disk path that looks like

    /srv/ganeti/file-storage/<instance>/e0105543-0979-4896-95c1-d2c477fafa9b.file.disk0

  should be presented to the instance as

    /dev/xvda (Xen)
    /dev/vda  (KVM)

  Therefore, we must pass the correct '/dev/*' disk paths to the safe
  virtualized environment when creating the environment file.  To
  achieve this, extend backend and RPC for export OS to allow disk
  paths to be overridden.

* The environment variable 'OS_SCRIPT' is introduce to tell the init
  script that runs inside the virtualized environment which OS script
  to run.  In this patch, the OS script to run is 'create_untrusted',
  but in the future it can be overridden for import, export, and
  rename.
Signed-off-by: Jose A. Lopes <jabolopes@google.com>
Reviewed-by: Hrvoje Ribicic <riba@google.com>

lib/cmdlib/instance.py

@@ -1513,7 +1513,41 @@ class LUInstanceCreate(LogicalUnit):
           result.Warn("Failed to run rename script for %s on node %s" %
                       (self.op.instance_name, self.pnode.name), self.LogWarning)
 
-  def UpdateInstanceOsInstallPackage(self, feedback_fn, instance):
+  def GetOsInstallPackageEnvironment(self, instance, script):
+    """Returns the OS scripts environment for the helper VM
+
+    @type instance: L{objects.Instance}
+    @param instance: instance for which the OS scripts are run
+
+    @type script: string
+    @param script: script to run (e.g.,
+                   constants.OS_SCRIPT_CREATE_UNTRUSTED)
+
+    @rtype: dict of string to string
+    @return: OS scripts environment for the helper VM
+
+    """
+    env = {"OS_SCRIPT": script}
+
+    # We pass only the instance's disks, not the helper VM's disks.
+    if instance.hypervisor == constants.HT_KVM:
+      prefix = "/dev/vd"
+    elif instance.hypervisor in [constants.HT_XEN_PVM, constants.HT_XEN_HVM]:
+      prefix = "/dev/xvd"
+    else:
+      raise errors.OpExecError("Cannot run OS scripts in a virtualized"
+                               " environment for hypervisor '%s'"
+                               % instance.hypervisor)
+
+    num_disks = len(self.cfg.GetInstanceDisks(instance.uuid))
+
+    for idx, disk_label in enumerate(utils.GetDiskLabels(prefix, num_disks + 1,
+                                                         start=1)):
+      env["DISK_%d_PATH" % idx] = disk_label
+
+    return env
+
+  def UpdateInstanceOsInstallPackage(self, feedback_fn, instance, override_env):
     """Updates the OS parameter 'os-install-package' for an instance.
 
     The OS install package is an archive containing an OS definition
@@ -1531,12 +1565,17 @@ class LUInstanceCreate(LogicalUnit):
     @param instance: instance for which the OS parameter
                      'os-install-package' is updated
 
+    @type override_env: dict of string to string
+    @param override_env: if supplied, it overrides the environment of
+                         the export OS scripts archive
+
     """
     if "os-install-package" in instance.osparams:
       feedback_fn("Using OS install package '%s'" %
                   instance.osparams["os-install-package"])
     else:
-      result = self.rpc.call_os_export(instance.primary_node, instance)
+      result = self.rpc.call_os_export(instance.primary_node, instance,
+                                       override_env)
       result.Raise("Could not export OS '%s'" % instance.os)
       instance.osparams["os-install-package"] = result.payload
 
@@ -1567,6 +1606,14 @@ class LUInstanceCreate(LogicalUnit):
 
     disk_size = DetermineImageSize(self, install_image, instance.primary_node)
 
+    env = self.GetOsInstallPackageEnvironment(
+      instance,
+      constants.OS_SCRIPT_CREATE_UNTRUSTED)
+    self.UpdateInstanceOsInstallPackage(feedback_fn, instance, env)
+    UpdateMetadata(feedback_fn, self.rpc, instance,
+                   osparams_private=self.op.osparams_private,
+                   osparams_secret=self.op.osparams_secret)
+
     with TemporaryDisk(self,
                        instance,
                        [(constants.DT_PLAIN, constants.DISK_RDWR, disk_size)],
@@ -1749,20 +1796,18 @@ class LUInstanceCreate(LogicalUnit):
       elif trusted:
         self.RunOsScripts(feedback_fn, iobj)
       else:
-        self.UpdateInstanceOsInstallPackage(feedback_fn, iobj)
-        UpdateMetadata(feedback_fn, self.rpc, iobj,
-                       osparams_private=self.op.osparams_private,
-                       osparams_secret=self.op.osparams_secret)
         self.RunOsScriptsVirtualized(feedback_fn, iobj)
         # Instance is modified by 'RunOsScriptsVirtualized',
         # therefore, it must be retrieved once again from the
         # configuration, otherwise there will be a config object
         # version mismatch.
         iobj = self.cfg.GetInstanceInfo(iobj.uuid)
-    else:
-      UpdateMetadata(feedback_fn, self.rpc, iobj,
-                     osparams_private=self.op.osparams_private,
-                     osparams_secret=self.op.osparams_secret)
+
+    # Update instance metadata so that it can be reached from the
+    # metadata service.
+    UpdateMetadata(feedback_fn, self.rpc, iobj,
+                   osparams_private=self.op.osparams_private,
+                   osparams_secret=self.op.osparams_secret)
 
     assert not self.owned_locks(locking.LEVEL_NODE_RES)