From f6e5fe187ea947fd7d4624a4f456dd7e11c35c7d Mon Sep 17 00:00:00 2001
From: David Hill <dhill@redhat.com>
Date: Thu, 22 Oct 2020 18:56:19 -0400
Subject: [PATCH] Do not fail when depth is greater than rbd_max_clone_depth

Removed a sanity check in the code that raised an exception
if the clone depth of a volume to be cloned exceeded the
rbd_max_clone_depth config value.  A consequence of this
check was that if an operator lowered the value, volumes
whose clone depth was greater than the new value (as would
be allowed by the previous, higher setting) could no longer
be cloned.

Change-Id: I8c445058a25c2eca2fda91bdeb6befedae34ccf2
Closes-bug: #1901241
(cherry picked from commit 8d8d242c3924037e6774a681efabce4893a26646)
(cherry picked from commit 23a821b2a4bbb5696bc27044a455fc7837641111)
---
 cinder/volume/drivers/rbd.py                         | 12 ++++--------
 releasenotes/notes/bug-1901241-361b1b361bfa5152.yaml |  8 ++++++++
 2 files changed, 12 insertions(+), 8 deletions(-)
 create mode 100644 releasenotes/notes/bug-1901241-361b1b361bfa5152.yaml

diff --git a/cinder/volume/drivers/rbd.py b/cinder/volume/drivers/rbd.py
index eadcdea1a0d..f062692b480 100644
--- a/cinder/volume/drivers/rbd.py
+++ b/cinder/volume/drivers/rbd.py
@@ -83,7 +83,9 @@ RBD_OPTS = [
                default=5,
                help='Maximum number of nested volume clones that are '
                     'taken before a flatten occurs. Set to 0 to disable '
-                    'cloning.'),
+                    'cloning. Note: lowering this value will not affect '
+                    'existing volumes whose clone depth exceeds the new '
+                    'value.'),
     cfg.IntOpt('rbd_store_chunk_size', default=4,
                help='Volumes will be chunked into objects of this size '
                     '(in megabytes).'),
@@ -640,12 +642,6 @@ class RBDDriver(driver.CloneableImageVD, driver.MigrateVD,
         if not parent:
             return depth
 
-        # If clone depth was reached, flatten should have occurred so if it has
-        # been exceeded then something has gone wrong.
-        if depth > self.configuration.rbd_max_clone_depth:
-            raise Exception(_("clone depth exceeds limit of %s") %
-                            (self.configuration.rbd_max_clone_depth))
-
         return self._get_clone_depth(client, parent, depth + 1)
 
     def _extend_if_required(self, volume, src_vref):
@@ -715,7 +711,7 @@ class RBDDriver(driver.CloneableImageVD, driver.MigrateVD,
             depth = self._get_clone_depth(client, src_name)
             # If dest volume is a clone and rbd_max_clone_depth reached,
             # flatten the dest after cloning. Zero rbd_max_clone_depth means
-            # infinite is allowed.
+            # volumes are always flattened.
             if depth >= self.configuration.rbd_max_clone_depth:
                 LOG.info("maximum clone depth (%d) has been reached - "
                          "flattening dest volume",
diff --git a/releasenotes/notes/bug-1901241-361b1b361bfa5152.yaml b/releasenotes/notes/bug-1901241-361b1b361bfa5152.yaml
new file mode 100644
index 00000000000..7609cfe9dfc
--- /dev/null
+++ b/releasenotes/notes/bug-1901241-361b1b361bfa5152.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    RBD driver `bug #1901241
+    <https://bugs.launchpad.net/cinder/+bug/1901241>`_:
+    Fixed an issue where decreasing the ``rbd_max_clone_depth`` configuration
+    option would prevent volumes that had already exceeded that depth from
+    being cloned.