Expose rbd-pool-name

In some situations an existing rbd pool may already be populated
with images that are in use. This is the case when migrating
from the old topology where cinder had a direct relation to
ceph-mon.

Change-Id: I93eb801ca4a166f862d5d86711d9476c61851344

config.yaml

@@ -34,3 +34,8 @@ options:
     type: boolean
     description: |
       Optionally restrict Ceph key permissions to access pools as required.
+  rbd-pool-name:
+    default:
+    type: string
+    description: |
+      Optionally specify an existing rbd pool that cinder should map to.

hooks/cinder_contexts.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 from charmhelpers.core.hookenv import (
+    config,
     service_name,
     is_relation_made,
     leader_get,
@@ -51,9 +52,13 @@ class CephSubordinateContext(OSContextGenerator):
         else:
             volume_driver = 'cinder.volume.driver.RBDDriver'
 
+        if config('rbd-pool-name'):
+            pool_name = config('rbd-pool-name')
+        else:
+            pool_name = service
         section = {service: [('volume_backend_name', service),
                              ('volume_driver', volume_driver),
-                             ('rbd_pool', service),
+                             ('rbd_pool', pool_name),
                              ('rbd_user', service),
                              ('rbd_secret_uuid', leader_get('secret-uuid')),
                              ('rbd_ceph_conf', ceph_config_file())]}

unit_tests/test_cinder_contexts.py

@@ -19,6 +19,7 @@ from test_utils import (
 )
 
 TO_PATCH = [
+    'config',
     'is_relation_made',
     'service_name',
     'get_os_codename_package',
@@ -30,6 +31,7 @@ class TestCinderContext(CharmTestCase):
 
     def setUp(self):
         super(TestCinderContext, self).setUp(contexts, TO_PATCH)
+        self.config.side_effect = self.test_config.get
         self.leader_get.return_value = 'libvirt-uuid'
         self.maxDiff = None
 
@@ -111,3 +113,29 @@ class TestCinderContext(CharmTestCase):
                     }
                 }
             }})
+
+    def test_ceph_explicit_pool_name(self):
+        self.test_config.set('rbd-pool-name', 'special_pool')
+        self.is_relation_made.return_value = True
+        self.get_os_codename_package.return_value = "mitaka"
+        service = 'mycinder'
+        self.service_name.return_value = service
+        self.assertEqual(
+            contexts.CephSubordinateContext()(),
+            {"cinder": {
+                "/etc/cinder/cinder.conf": {
+                    "sections": {
+                        service: [
+                            ('volume_backend_name', service),
+                            ('volume_driver',
+                             'cinder.volume.drivers.rbd.RBDDriver'),
+                            ('rbd_pool', 'special_pool'),
+                            ('rbd_user', service),
+                            ('rbd_secret_uuid', 'libvirt-uuid'),
+                            ('rbd_ceph_conf',
+                             '/var/lib/charm/mycinder/ceph.conf'),
+                            ('report_discard_supported', True)
+                        ]
+                    }
+                }
+            }})