In plain to drbd conversion, rename LVs back on failure

Currently, if converting an instance from plain to drbd fails after
renaming the original LVs, the instance is left in an inconsistent
state. This commit tries to undo the renaming if a failure occurs
on assembling a DRBD device, e.g., when device minor numbers are
exhausted. (Issue 229)

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Thomas Thrainer <thomasth@google.com>

lib/cmdlib.py

@@ -14008,11 +14008,22 @@ class LUInstanceSetParams(LogicalUnit):
     feedback_fn("Initializing DRBD devices...")
     # all child devices are in place, we can now create the DRBD devices
-    for disk in anno_disks:
-      for (node, excl_stor) in [(pnode, p_excl_stor), (snode, s_excl_stor)]:
-        f_create = node == pnode
-        _CreateSingleBlockDev(self, node, instance, disk, info, f_create,
-                              excl_stor)
+    try:
+      for disk in anno_disks:
+        for (node, excl_stor) in [(pnode, p_excl_stor), (snode, s_excl_stor)]:
+          f_create = node == pnode
+          _CreateSingleBlockDev(self, node, instance, disk, info, f_create,
+                                excl_stor)
+    except errors.GenericError, e:
+      feedback_fn("Initializing of DRBD devices failed;"
+                  " renaming back original volumes...")
+      for disk in new_disks:
+        self.cfg.SetDiskID(disk, pnode)
+      rename_back_list = [(n.children[0], o.logical_id)
+                          for (n, o) in zip(new_disks, instance.disks)]
+      result = self.rpc.call_blockdev_rename(pnode, rename_back_list)
+      result.Raise("Failed to rename LVs back after error %s" % str(e))
+      raise
     # at this point, the instance has been modified
     instance.disk_template = constants.DT_DRBD8