Detect shared storage; handle base cleanup better.

If base image storage is shared, we need to care about remote
instances when we clean up. This patch "learns" which storage is
shared, and then decides what base images are in use anywhere
on the set of compute nodes which share that base storage.

This is complicated because shared instance storage doesn't have
to be per-cluster. It could for example be per rack. We need to
handle that properly.

This should resolve bug 1078594.

Change-Id: I36d0d6e965b114bb68c8f7b7fd43f8e96b2dd8f5

1 files changed, 17 insertions, 1 deletions

diff --git a/nova/compute/manager.py b/nova/compute/manager.py
index 7484a9252..acadd6f61 100644
--- a/nova/compute/manager.py
+++ b/nova/compute/manager.py
@@ -73,6 +73,7 @@ from nova import quota
 from nova.scheduler import rpcapi as scheduler_rpcapi
 from nova import utils
 from nova.virt import driver
+from nova.virt import storage_users
 from nova.virt import virtapi
 from nova import volume
 
@@ -3247,4 +3248,19 @@ class ComputeManager(manager.SchedulerDependentManager):
             return
 
         all_instances = self.db.instance_get_all(context)
-        self.driver.manage_image_cache(context, all_instances)
+
+        # Determine what other nodes use this storage
+        storage_users.register_storage_use(CONF.instances_path, CONF.host)
+        nodes = storage_users.get_storage_users(CONF.instances_path)
+
+        # Filter all_instances to only include those nodes which share this
+        # storage path.
+        # TODO(mikal): this should be further refactored so that the cache
+        # cleanup code doesn't know what those instances are, just a remote
+        # count, and then this logic should be pushed up the stack.
+        filtered_instances = []
+        for instance in all_instances:
+            if instance['host'] in nodes:
+                filtered_instances.append(instance)
+
+        self.driver.manage_image_cache(context, filtered_instances)