Config for cephfs volume path prefix

The cloud administrator needs to use the cephfs volume path prefix to
layout multiple cephfs driver backends. When cephfs has multiple
data pools, manila can configure `cephfs_volume_path_prefix` to store
volume data in different cephfs directories of a ceph filesystem [1]
for the different cephfs driver backends. Out of band of manila, the
admin can set the pool layouts of these cephfs directories to store
the volume data in different data pools of the ceph filesystem. This
is helpful for planning different data storage to different ceph OSDs.

[1] https://github.com/ceph/ceph/commit/d1a21b07ede#diff-8625369b924524f064e083e735bd34beR267

Change-Id: I19e3dd55f1fded339cb17222b3333c0c0f8835e9
Implements: blueprint cephfs-driver-configurable

manila/share/drivers/cephfs/driver.py

@@ -57,6 +57,10 @@ cephfs_opts = [
                default="manila",
                help="The name of the ceph auth identity to use."
                ),
+    cfg.StrOpt('cephfs_volume_path_prefix',
+               default="/volumes",
+               help="The prefix of the cephfs volume path."
+               ),
     cfg.BoolOpt('cephfs_enable_snapshots',
                 default=False,
                 help="Whether to enable snapshots in this driver."
@@ -180,8 +184,10 @@ class CephFSDriver(driver.ExecuteMixin, driver.GaneshaMixin,
         conf_path = self.configuration.safe_get('cephfs_conf_path')
         cluster_name = self.configuration.safe_get('cephfs_cluster_name')
         auth_id = self.configuration.safe_get('cephfs_auth_id')
+        volume_prefix = self.configuration.safe_get(
+            'cephfs_volume_path_prefix')
         self._volume_client = ceph_volume_client.CephFSVolumeClient(
-            auth_id, conf_path, cluster_name)
+            auth_id, conf_path, cluster_name, volume_prefix=volume_prefix)
         LOG.info("[%(be)s}] Ceph client found, connecting...",
                  {"be": self.backend_name})
         if auth_id != CEPH_DEFAULT_AUTH_ID:

releasenotes/notes/config-for-cephfs-volume-prefix-67f2513f603cb614.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - cephfs volume path prefix is now configurable in order to
+    enable support for multiple cephfs back ends.