Compute: Handle reshaped provider trees

This is the compute side "plumbing" for the referenced blueprint,
implementing changes in the compute manager, resource tracker, and virt
driver interface.

- The `startup` parameter (indicating compute service startup vs.
  periodic task) is percolated from the compute manager's
  update_available_resource all the way down the call stack to the
  resource tracker's _update method, where it is used to determine
  whether to allow the virt driver's update_provider_tree to indicate
  that a reshape is required.
- The update_provider_tree method gets a new `allocations` parameter.
  When None, the method should raise ReshapeNeeded (see below) if
  inventories need to be moved, whereupon the resource tracker will
  populate the `allocations` parameter and reinvoke update_provider_tree
  with it.
- A new ReshapeNeeded exception is introduced. It is used as a signal by
  the virt driver that inventories need to be moved. It should *only* be
  raised by the virt driver a) on startup, and b) when the `allocations`
  parameter is None.
- The compute manager's _update_available_resource_for_node gets special
  exception handling clauses for ReshapeNeeded and ReshapeFailed, both
  of which blow up the compute service on startup. (On periodic, where
  this should "never" happen, they just make the logs red. We may later
  want to disable the compute service or similar to make this unusual
  catastrophic event more noticeable.)

Change-Id: Ic062446e5c620c89aec3065b34bcdc6bf5966275
blueprint: reshape-provider-tree

1 files changed, 5 insertions, 0 deletions

diff --git a/nova/exception.py b/nova/exception.py
index e262100210..a9c9c4bbd6 100644
--- a/nova/exception.py
+++ b/nova/exception.py
@@ -2383,3 +2383,8 @@ class ConsumerAllocationRetrievalFailed(NovaException):
 class ReshapeFailed(NovaException):
     msg_fmt = _("Resource provider inventory and allocation data migration "
                 "failed: %(error)s")
+
+
+class ReshapeNeeded(NovaException):
+    msg_fmt = _("Virt driver indicates that provider inventories need to be "
+                "moved.")