[hopem,r=gnuoy] Add support for configuring rbd client cache.

Closes-Bug: 1412856

charm-helpers-hooks.yaml

@@ -1,4 +1,4 @@
-branch: lp:charm-helpers
+branch:  lp:~hopem/charm-helpers/add-rbd-cache-config-support
 destination: hooks/charmhelpers
 include:
     - core

config.yaml

@@ -225,6 +225,14 @@ options:
     description: |
       RBD pool to use with Nova libvirt RBDImageBackend. Only required when you
       have libvirt-image-backend set to 'rbd'.
+  rbd-client-cache:
+    type: string
+    default:
+    description: |
+      Enable/disable rbd client cache. Leaving this value unset will result in
+      default Ceph rbd client settings being used (rbd cache is enabled by
+      default for Ceph >= Giant). Supported values here are "enabled" or
+      "disabled".
   ceph-osd-replication-count:
     type: int
     default: 3

hooks/charmhelpers/contrib/openstack/templates/ceph.conf

@@ -13,3 +13,9 @@ log to syslog = {{ use_syslog }}
 err to syslog = {{ use_syslog }}
 clog to syslog = {{ use_syslog }}
 
+[client]
+{% if rbd_client_cache_settings -%}
+{% for key, value in rbd_client_cache_settings.iteritems() -%}
+{{ key }} = {{ value }}
+{% endfor -%}
+{%- endif %}

hooks/nova_compute_context.py

@@ -1,5 +1,7 @@
 import uuid
+import os
 import platform
+
 from charmhelpers.contrib.openstack import context
 from charmhelpers.core.host import service_running, service_start
 from charmhelpers.fetch import apt_install, filter_installed_packages
@@ -181,6 +183,23 @@ class NovaComputeCephContext(context.CephContext):
         elif config('libvirt-image-backend') == 'lvm':
             ctxt['libvirt_images_type'] = 'lvm'
 
+        rbd_cache = config('rbd-client-cache') or ""
+        if rbd_cache.lower() == "enabled":
+            # We use write-though only to be safe for migration
+            ctxt['rbd_client_cache_settings'] = \
+                {'rbd cache': 'true',
+                 'rbd cache size': '64 MiB',
+                 'rbd cache max dirty': '0 MiB',
+                 'rbd cache writethrough until flush': 'true',
+                 'admin socket': '/var/run/ceph/rbd-client-$pid.asok'}
+
+            asok_path = '/var/run/ceph/'
+            if not os.path.isdir(asok_path):
+                os.mkdir(asok_path)
+
+        elif rbd_cache.lower() == "disabled":
+            ctxt['rbd_client_cache_settings'] = {'rbd cache': 'false'}
+
         return ctxt